JP5476746B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device including a free-wheeling diode for power conversion and a power conversion device using the semiconductor device.

  As one of power energy conversion means, a power conversion device such as an inverter is generally used. Power converters can be used for power semiconductor devices such as switching elements such as metal oxide semiconductor (MOS) field effect transistors (FETs) and insulated gate bipolar transistors (IGBTs) and free-wheeling diodes. It consists of a combination. Since power converters are required to have high efficiency and stable operation, the semiconductor device that is a component of them requires low loss and stable operation that is unlikely to cause malfunctions in both the switching element and the freewheeling diode. It is done.

  There are two main losses caused by the operation of the freewheeling diode. One is a conduction loss caused by a voltage drop in the diode when conducting by a forward bias, and the other is a reverse recovery loss caused by a reverse recovery operation when transitioning from a conduction state to a cutoff state by a reverse bias. is there. Reverse recovery loss occurs when excess carriers accumulated in the free-wheeling diode element in the conducting state transiently flow as reverse recovery current in the extinction process when transitioning to the shut-off state To do. Therefore, the reverse recovery loss depends on the amount of excess carriers immediately before the reverse recovery operation and the extinction speed of excess carriers at the time of reverse recovery operation.

  As a conventional technique for reducing the amount of excess carriers in order to reduce reverse recovery loss, a unipolar Schottky barrier diode formed of a semiconductor material made of silicon carbide has been proposed (see, for example, Patent Document 1). .

  A Schottky barrier diode has a large amount of excess carriers compared to a pn junction diode that accumulates minority carriers when conducting, because current flows only by majority carriers when conducting by forward bias. As a result, reverse recovery loss occurs. Reduced.

  However, when a Schottky barrier diode with unipolar operation is used as a freewheeling diode, it is found that there is a problem unique to unipolar operation that current and voltage are likely to vibrate during reverse recovery operation, and no countermeasure has been established. It was. This current / voltage oscillation phenomenon causes an element destruction due to a surge voltage, an increase in loss during an oscillation operation, a malfunction of a peripheral circuit, and the like, and is thus an impediment to stable operation.

  The vibration phenomenon itself is an interaction between a parasitic inductance Ls generated in a circuit of a power converter such as an inverter incorporating a freewheeling diode and a reverse recovery current Ir cutoff speed (dIr / dt) during the reverse recovery operation of the freewheeling diode. It is generally known that a surge voltage Vs is generated by this, and is generated from this.

  Therefore, in order to reduce the vibration phenomenon, conventionally used silicon pn junction diodes are used for heavy metal diffusion using gold (Au) or platinum (Pt), electron beam irradiation using electron beams, protons, etc. By controlling the lifetime of minority carriers, which are the main components of excess carriers, by means such as ion irradiation, the reverse recovery time Ir is reduced and the reverse recovery time t is optimized by limiting the reverse recovery current Ir. Efforts have been made to mitigate the current interruption speed (dI / dt) during operation and suppress the vibration phenomenon (see, for example, Non-Patent Document 1).

  On the other hand, in a Schottky barrier diode that performs unipolar operation, the reverse recovery current Ir component is composed of majority carriers, so the reverse recovery current Ir due to excess carriers is greatly reduced, but reverse recovery due to resistance limitation of the reverse recovery current Ir. Since the time t can hardly be controlled, a vibration phenomenon is likely to occur in the current / voltage, and the vibration is not easily attenuated. There are two main reasons.

  One is that the operating mechanism for the oscillation phenomenon of the drift region holding the breakdown voltage inside the element is different from that of the pn junction diode in order to achieve both the conduction loss when conducting as the freewheeling diode and the breakdown voltage when shutting off.

  In general, a pn junction diode has a conductivity modulation effect of a drift region by minority carrier injection during forward bias conduction. Therefore, in order to ensure a breakdown voltage while reducing conduction loss as much as possible, the drift region has a small thickness and an impurity concentration. Form low. Therefore, the magnitude of the resistance in the drift region of the pn junction diode is greatly different between when conducting and when the conductivity modulation just before breaking is released. For this reason, the pn junction diode operates in the reverse recovery operation state so that the resistance inside the element increases, and thus a mechanism for limiting the resistance of the reverse recovery current Ir acts on the pn junction diode itself.

  On the other hand, since the Schottky barrier diode flows almost exclusively by majority carriers when conducting, the resistance according to the thickness of the drift region and the impurity concentration inside the device does not change both when conducting and immediately before shutting off. That is, the Schottky barrier diode itself does not have a mechanism for limiting the resistance of the reverse recovery current Ir like a pn junction diode. For this reason, the Schottky barrier diode easily generates a vibration phenomenon in current and voltage even during reverse recovery, and the vibration is not easily attenuated. In other words, the Schottky barrier diode has a mechanism that suppresses the loss during conduction and the vibration phenomenon because it becomes difficult to function as a damping function for the vibration phenomenon if the resistance is reduced to reduce the conduction loss. There is a trade-off relationship.

  Furthermore, another reason is that, in the Schottky barrier diode, the excess carriers that increase from the cutoff state to the conduction state are composed only of majority carriers that fill the depletion region formed in the drift region in the cutoff state. It is a point. That is, the reverse recovery current cutoff speed (dI / dt) of the Schottky barrier diode almost depends only on the formation speed of the depletion region, and since there are almost no minority carriers, a lifetime control method such as a pn junction diode is used. It cannot be used as it is. For this reason, in the Schottky barrier diode, there is a trade-off relationship between the reduction of the transient loss due to the improvement of the switching speed and the suppression of the vibration phenomenon.

  In this way, when a unipolar Schottky barrier diode is used as a free-wheeling diode, in principle, a vibration phenomenon is likely to occur in the current / voltage during reverse recovery operation, compared with the case where a general pn junction diode is used. There was a problem unique to unipolar operation in which attenuation did not subside.

Japanese National Patent Publication No. 11-510000

Shinohara Shinichi et al., “High-speed soft recovery diode with controlled lifetime profile”, IEICE Technical Report, 1995, Vol. 192, p. 1-6

  An object of the present invention is to solve the problems of the prior art as described above, and current and voltage generated during reverse recovery operation while suppressing loss during conduction of the freewheeling diode and loss during transient operation. It is an object to provide a power semiconductor device capable of easily suppressing the vibration phenomenon.

  The present invention includes a free-wheeling diode that performs an operation equivalent to a unipolar operation, and a semiconductor circuit that includes a capacitor and a resistor connected in series and is connected in parallel to the free-wheeling diode. A semiconductor circuit includes a semiconductor substrate or a resistance region that functions as at least a part of a resistor, a capacitance reduction prevention region provided in contact with the semiconductor substrate or the resistance region, and a capacitor dielectric film that functions as at least a part of a capacitor. Prepare. The capacitance reduction prevention region alleviates the extension of the depletion layer into the semiconductor substrate or resistance region when a reverse bias voltage is applied to the freewheeling diode.

  According to the present invention, by forming a semiconductor device including a semiconductor snubber that is connected in parallel with a unipolar operation or an operation equivalent to a unipolar operation and that includes a semiconductor snubber having at least a capacitor and a resistor, The current / voltage oscillation phenomenon that occurs during the reverse recovery operation can be easily suppressed while suppressing the loss during the transient operation.

1 is a circuit diagram showing a first embodiment of the present invention. FIG. 2 is a mounting diagram for realizing the circuit diagram of FIG. 1 according to the first embodiment of the present invention. It is sectional drawing of the semiconductor chip used for FIG. 2 of the 1st Embodiment of this invention. It is sectional drawing of another semiconductor chip used for FIG. 2 of the 1st Embodiment of this invention. It is another circuit diagram corresponding to FIG. 1 of the 1st Embodiment of this invention. It is a circuit diagram of the power converter device using the circuit of FIG. 1 of the 1st Embodiment of this invention. It is a circuit diagram of another power converter device using the circuit of Drawing 1 of a 1st embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another circuit diagram of the 1st Embodiment of this invention. It is another mounting figure which implement | achieves the circuit diagram of FIG. 1 of the 1st Embodiment of this invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is another sectional view corresponding to FIG. 3 of the first embodiment of the present invention. It is a calculation result of the vibration phenomenon with respect to the capacitor capacity of the first embodiment of the present invention. It is a special drawing which shows the optimal value of the capacitor capacity ratio of the 1st Embodiment of this invention. It is a circuit diagram which shows the 2nd Embodiment of this invention. FIG. 24 is a mounting diagram for realizing the circuit diagram of FIG. 23 according to the second embodiment of the present invention. It is sectional drawing of the semiconductor chip used for FIG. 24 of the 2nd Embodiment of this invention. It is a circuit diagram of another power converter device using the circuit of Drawing 23 of a 2nd embodiment of the present invention. It is sectional drawing of the semiconductor chip used for FIG. 24 of the 3rd Embodiment of this invention. FIG. 26 is another cross-sectional view corresponding to FIG. 25 of the third embodiment of the present invention. FIG. 26 is another cross-sectional view corresponding to FIG. 25 of the third embodiment of the present invention. FIG. 26 is another cross-sectional view corresponding to FIG. 25 of the third embodiment of the present invention. It is another sectional view corresponding to FIG. 27 of the third embodiment of the present invention. FIG. 7 is a mounting diagram for realizing the circuit diagram of FIG. 1 according to a fourth embodiment of the present invention. It is sectional drawing of the semiconductor chip used for FIG. 32 of the 4th Embodiment of this invention. It is another sectional view corresponding to FIG. 33 of the fourth embodiment of the present invention. It is another sectional view corresponding to FIG. 33 of the fourth embodiment of the present invention. It is another sectional view corresponding to FIG. 33 of the fourth embodiment of the present invention. It is another sectional view corresponding to FIG. 33 of the fourth embodiment of the present invention. It is another sectional view corresponding to FIG. 33 of the fourth embodiment of the present invention. FIG. 10 is a mounting diagram for realizing the circuit diagram of FIG. 1 according to the fifth embodiment of the present invention. It is sectional drawing of the semiconductor chip used for FIG. 39 of the 5th Embodiment of this invention. FIG. 41 is another cross-sectional view corresponding to FIG. 40 of the fifth embodiment of the present invention. FIG. 41 is another cross-sectional view corresponding to FIG. 40 of the fifth embodiment of the present invention. FIG. 41 is another cross-sectional view corresponding to FIG. 40 of the fifth embodiment of the present invention.

  Next, first to fifth embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The first to fifth embodiments described below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is The material, shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the scope of the claims.

(First embodiment)
The semiconductor device according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram for explaining a first embodiment of the present invention, FIG. 2 is a mounting diagram of a semiconductor chip (semiconductor circuit) embodied as an example of the circuit diagram of FIG. 1, and FIGS. FIG. 3 is an example of a cross-sectional structure diagram of each semiconductor chip used in the mounting diagram.

  As shown in FIG. 1, the semiconductor device according to the first embodiment of the present invention includes a freewheeling diode 100 that operates in a unipolar operation or equivalent to a unipolar operation, a capacitor 210, and a resistor 220, and has a snubber function. Thus, the semiconductor snubber 200 formed of a semiconductor chip is provided. Both the free-wheeling diode 100 and the semiconductor snubber 200 are connected in parallel so as to be connected to the anode terminal 300 and the cathode terminal 400.

  In FIG. 1, the semiconductor snubber 200 is configured such that the capacitor 210 is connected to the anode terminal 300 side and the resistor 220 is connected to the cathode terminal 400 side. However, as shown in FIG. A resistor 220 may be connected to the terminal 300 side, and a capacitor 210 may be connected to the cathode terminal 400 side. Moreover, as long as the capacitor 210 and the resistor 220 are connected at least in series, the capacitor 210 and the resistor 220 may be divided into a plurality of portions, or may be formed alternately, for example.

  Although details will be described later, even in the case of a pn junction diode structure, for example, by controlling the lifetime of minority carriers that are the main components of excess carriers injected from the p-type region during conduction, it is equivalent to unipolar operation. Thus, the bipolar diode having the characteristics equivalent to the unipolar operation is also included in the unipolar operation diode described in the present invention.

In the first embodiment of the present invention, as an example, a case where the free wheel diode 100 and the semiconductor snubber 200 are formed as separate semiconductor chips will be described.

  As a configuration of the semiconductor snubber 200, for example, a case of a so-called RC snubber configuration in which a capacitor 210 and a resistor 220 are connected in series will be described. Further, the semiconductor snubber 200 will be described in the case of a so-called vertical semiconductor chip in which, for example, silicon (Si) is used as a semiconductor base material and electrodes are formed so that the anode terminal 300 and the cathode terminal 400 face each other. .

  As the freewheeling diode 100, for example, a case of a Schottky barrier diode using silicon carbide (SiC) as a semiconductor substrate material will be described. In the first embodiment of the present invention, a so-called vertical Schottky barrier diode in which electrodes are formed so that the anode terminal 300 and the cathode terminal 400 face each other will be described as an example of the Schottky barrier diode.

  FIG. 2 is a mounting diagram of a semiconductor device including the free wheeling diode 100 and the semiconductor snubber 200 shown in FIG. The free-wheeling diode 100 is, for example, a silicon carbide Schottky barrier diode, and the semiconductor snubber 200 is, for example, a silicon semiconductor RC snubber.

  In FIG. 2, as an example of a semiconductor package, for example, copper (Cu) or aluminum (Al) is formed on an insulating substrate 500 having an insulating property formed of, for example, a ceramic plate and having a function as a support. A case where a ceramic substrate on which an anode side metal film 310 and a cathode side metal film 410 made of a metal material are formed will be described.

  On the cathode side metal film 410, the cathode terminals 400 of the respective semiconductor chips of the reflux diode 100 and the semiconductor snubber 200 are arranged so as to be in contact with each other through a bonding material such as solder or brazing material. The anode terminals 300 of the semiconductor chips of the free-wheeling diode 100 and the semiconductor snubber 200 are both connected to the anode-side metal film 310 via metal wirings 320 and 330 such as aluminum wires and aluminum ribbons.

  Next, FIG. 3 and FIG. 4 show an example of a cross-sectional structure diagram of a semiconductor chip that constitutes the free wheel diode 100 and the semiconductor snubber 200, respectively.

As shown in FIG. 3, in the free-wheeling diode 100, for example, an n ⁻ type drift region 2 is formed on an n ⁺ type substrate region (semiconductor substrate) 1 having a polytype of silicon carbide (SiC) of 4H type. It consists of a substrate material. As the substrate region 1, for example, a general low resistance substrate having a resistivity of several meters to several tens of mΩcm and a thickness of several tens to several hundreds of μm can be used. Of course, the resistivity and thickness may be out of the above ranges depending on the element structure and the required breakdown voltage. However, in general, the smaller the resistivity and the thickness, the more the loss during conduction can be reduced. As the drift region 2, for example, an n-type impurity density of 10 ¹⁵ to 10 ¹⁸ cm ⁻³ and a thickness of 0.1 μm to several tens of μm can be used. It should be noted that the impurity density and thickness of the drift region 2 may of course be out of the above range depending on the element structure and required breakdown voltage. In the first embodiment of the present invention, for example, a case where an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class is used will be described.

  In the first embodiment of the present invention, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 1 and the drift region 2 will be described. However, the magnitude of the resistivity does not depend on the above example. However, a substrate formed of only the substrate region 1 may be used, or a multilayer substrate may be used. In the first embodiment of the present invention, the breakdown voltage is 600 V class as an example, but the breakdown voltage class is not limited. In the first embodiment of the present invention, the case where the substrate material is formed of a silicon carbide material is described. However, the substrate material may be formed of other semiconductor materials such as silicon.

  The upper electrode (surface electrode) 3 is in contact with the main surface of the drift region 2 facing the bonding surface with the substrate region 1, and further the lower electrode (back surface) is opposed to the upper electrode 3 and in contact with the substrate region 1. Electrode) 4 is formed. The upper electrode 3 includes a single-layer or multi-layer metal material including at least a metal material that forms a Schottky barrier with the drift region 2. For example, titanium (Ti) is used as the metal material that forms the Schottky barrier. A material such as nickel (Ni), molybdenum (Mo), gold (Au), or platinum (Pt) can be used. Further, the upper electrode 3 is connected to an external electrode as the anode terminal 300, and the outermost surface is made of a metal such as aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), or the like. A multilayer structure may be used by using a material. On the other hand, the lower electrode 4 includes an electrode material that is in ohmic contact with the substrate region 1. Examples of the electrode material to be ohmic-connected include nickel silicide and titanium material, and the lower electrode 4 is connected to an external electrode as a cathode terminal 400. 3 functions as a diode having the upper electrode 3 as an anode electrode and the lower electrode 4 as a cathode electrode.

Next, FIG. 4 is an example of a cross-sectional structure diagram of the semiconductor snubber 200. In FIG. 4, for example, in the surface layer portion of a substrate region (semiconductor substrate) 11 that is an n ⁻ type of silicon, an n ⁺ type having the same conductivity type as that of the substrate region 11 and having an impurity density equal to or higher than that of the substrate region 11 A capacitance reduction prevention region 1001 is formed, and a capacitor dielectric film 12 made of a dielectric material such as a silicon oxide film is formed on the capacitance reduction prevention region 1001. In the first embodiment of the present invention, the substrate region 11 functions as a resistor R, and the capacitor dielectric film 12 functions as a part of the capacitor C (capacitor insulating film). That is, the substrate region 11 can determine the resistivity and thickness of the substrate according to the required resistance value. For example, the substrate region 11 has a resistivity of several mΩcm to several hundreds Ωcm and a thickness of about several tens to several hundreds μm. Can be used. In the first embodiment of the present invention, a case where, for example, a resistor having a resistivity of 100 Ωcm and a thickness of 300 μm is used so as to be at least larger than the resistance value included in the freewheeling diode 100 will be described. In the first embodiment of the present invention, the substrate region 11 is illustrated as being formed with a single resistivity, but may have a plurality of resistivity.

In addition, the capacity reduction prevention region 1001 formed in the surface layer portion of the substrate region 11 is a depletion layer to the substrate region 11 when a reverse bias voltage is applied so that the free-wheeling diodes 100 connected in parallel are cut off. It functions as a region to ease the expansion of That is, if the impurity density is equal to or higher than that of the substrate region 11, the impurity density can be determined according to the impurity density (that is, resistivity) of the substrate region 11. The effect is great. In the first embodiment of the present invention, the case where the impurity density of the capacity reduction prevention region 1001 is 1 × 10 ¹⁹ cm ⁻³ (about 10 mΩcm in terms of resistivity) will be described.

  Further, the thickness and area of the capacitor dielectric film 12 can be determined according to the required breakdown voltage and the required capacitance of the capacitor C. The withstand voltage is preferably higher than that of the free-wheeling diode 100 in order to prevent the capacitor dielectric film 12 from being broken. The capacitance of the capacitor C can be selected in the range of about 1/100 to about 100 times the capacitor capacity of the depletion layer generated when the freewheeling diode 100 is in the cutoff state (when a high voltage is applied). When a sufficient snubber function is exhibited, an increase in loss is suppressed as much as possible, and a necessary chip area is taken into consideration, a range of about one-tenth to about ten times is desirable as shown in the calculation results described later.

In the first embodiment of the present invention, for example, the thickness is set to 1 μm so that the breakdown voltage is higher than that of the freewheeling diode 100, and the capacitance of the capacitor C is approximately the same as the depletion capacity formed when the freewheeling diode 100 is cut off. This will be described in the case of using the above. The capacitor dielectric film 12 may be any material other than the silicon oxide film, as long as it is a dielectric material having a predetermined withstand voltage and functioning as the capacitor C. It is even better if the product value is greater than that of the silicon oxide film. When such a material is used, a necessary capacitance can be obtained with a small area while maintaining the dielectric strength of the capacitor dielectric film 12. For example, as a physical property value of a general silicon oxide film, when a dielectric breakdown electric field is 1 × 10 ⁹ V / m and a relative dielectric constant is 3.9, a unit area is 1 cm when the thickness of the silicon oxide film is 1 μm. ^The capacitance per ² is about 3.4 nF. On the other hand, when silicon nitride (Si ₃ N ₄ ) is used instead of the silicon oxide film, the thickness is 1 μm when the dielectric breakdown electric field is 1 × 10 ⁹ V / m and the relative dielectric constant is 7.5. Therefore, the equivalent breakdown voltage can be secured. At this time, the capacitance per 1 cm ² of unit area when Si ₃ N ₄ is used is about 6.6 nF. As described above, the use of Si ₃ N ₄ increases the capacitance by about twice, and a larger capacitance can be obtained while maintaining the withstand voltage of the capacitor dielectric film. Accordingly, the area efficiency can be improved and the wafer cost can be reduced. This effect can be compared by the product of the dielectric breakdown electric field and the relative dielectric constant of the dielectric material, and the value of the silicon oxide film and the value of Si ₃ N ₄ are approximately doubled. Further, if the capacitor dielectric film is made of a ferroelectric material such as barium titanate (BaTiO ₃ ), the value is about 13 times that of the silicon oxide film, and the area can be reduced. In addition, the capacitor dielectric film is not limited to a single dielectric material, and may be a laminate of a plurality of dielectric materials. For example, in the ONO structure sandwiching _Si 3 _{N 4} in silicon oxide film, a leakage current the _Si 3 _{N 4} can be minimized by the silicon oxide film.

  In the first embodiment of the present invention, as will be described later, for example, when a Schottky barrier diode is used as the freewheeling diode 100, the current / voltage oscillation phenomenon that is essentially generated by the unipolar operation, Traditionally used as a snubber circuit to reduce the vibration of diodes that operate in bipolar operation, without using a method of wiring external discrete components such as film capacitors or metal clad resistors in the path through which the main current flows. By connecting the semiconductor snubber 200 having the capacitor C and the resistor R in parallel, the vibration phenomenon can be easily and effectively suppressed. Further, C = 1 / (2πfR) is generally known as a design formula that effectively exhibits the snubber function (f is the frequency of the vibration phenomenon), and in the first embodiment of the present invention, The capacitor C and the resistor R using the small-capacity semiconductor snubber 200 can be easily set so as to satisfy the equation.

  Further, an upper electrode 13 is formed so as to be in contact with the capacitor dielectric film 12, and further, a lower electrode 14 is formed so as to be opposed to the upper electrode 13 and in contact with the substrate region 11. The upper electrode 13 is formed of, for example, a metal material so as to be connected to an external electrode as the anode terminal 300, and aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver ( A single-layer or multilayer structure using a metal material such as Ag) may be used. Similarly, the lower electrode 14 is formed of, for example, a metal material so as to be connected to the external electrode as the cathode terminal 400, and aluminum (Al), copper (Cu), gold (Au), nickel ( A single-layer or multilayer structure using a metal material such as Ni) or silver (Ag) may be used. As described above, the semiconductor snubber 200 shown in FIG. 4 has a semiconductor RC snubber in which the upper electrode 13 is connected to the anode electrode of the freewheeling diode 100 shown in FIG. 3 and the lower electrode 14 is connected to the cathode electrode of the freewheeling diode 100 shown in FIG. Function as.

  Next, the operation of the first exemplary embodiment of the present invention will be described in detail.

  The semiconductor device according to the first embodiment of the present invention includes, for example, a converter as shown in FIG. 6 or an inverter as shown in FIG. In the converter, the power supply voltage (+ V) (for example, 400 V in the first embodiment of the present invention) is connected so as to be reverse-biased, and is used as passive elements A and B that circulate current. The operation mode of the semiconductor device according to the first embodiment of the present invention is changed from a cut-off state in which current is cut off to a conductive state in which current is circulated in conjunction with a switching operation of a switching element such as a MOSFET or IGBT. Operates from state to block state. In a power conversion device, a stable operation that is low loss and is unlikely to cause malfunctions is required for a passive element that circulates current as well as a switching element. In the first embodiment of the present invention, the operation will be described by taking the converter circuit of FIG. 6 as an example. In addition, the switching element D in FIG. 6 is demonstrated by the case where it is comprised, for example by IGBT.

  First, in a state where the switching element D is turned on and a current flows through the switching element D, the passive element A is in a reverse bias state and is in a cutoff state. In the freewheeling diode 100 shown in FIG. 3 (here, a Schottky barrier diode), a reverse bias voltage is applied between the anode terminal 300 and the cathode terminal 400, so that the Schottky between the upper electrode 3 and the drift region 2 is present. A depletion layer extending from the junction is generated and the cut-off state is maintained. Further, in the semiconductor snubber 200 shown in FIG. 4, as will be described later, by forming the capacitance decrease prevention region 1001, only the capacitor dielectric film 12 functioning as the capacitor C is in a state of being charged with a high voltage. And maintain the shut-off state.

  Thus, in the cut-off state, the passive element has a function similar to that of the prior art in which only the Schottky barrier diode is configured.

  Next, in conjunction with the switching element D being turned off and the switching element D shifting to the off state, the passive element A enters the forward bias state and shifts to the conductive state. The depletion layer that has spread into the drift region 2 of the free-wheeling diode 100 shown in FIG. 3 recedes, and the Schottky junction formed between the upper electrode 3 and the drift region 2 corresponds to the Schottky barrier height. When the forward bias voltage is applied, the freewheeling diode 100 becomes conductive. At this time, the current flowing through the freewheeling diode 100 is composed of only the electron current supplied from the lower electrode 4 side in the drift region 2 and performs a unipolar operation. Also, in the semiconductor snubber 200 shown in FIG. 4, similarly to the freewheeling diode 100, since the high voltage reverse bias state shifts to the low voltage forward bias state, the charge charged in the capacitor dielectric film 12 is discharged. And a transient current flows. However, in the first embodiment of the present invention, the capacitor capacitance of the capacitor dielectric film 12 is as small as the depletion capacitance formed when the free-wheeling diode 100 is cut off. The magnitude is very small compared to the forward bias current flowing through the freewheeling diodes 100 in parallel, and hardly affects the operation. The semiconductor snubber 200 is in the cut-off state after the transient current accompanying the change in the bias voltage flows, so that it shifts to the forward bias state and the steady state, and only the freewheeling diode 100 is in the conductive state. At this time, in the first embodiment of the present invention, since the free-wheeling diode 100 is composed of a Schottky barrier diode made of a silicon carbide material semiconductor substrate, compared with a pn junction diode made of a general silicon material. The resistance of the drift region 2 can be formed with a lower resistance, and the conduction loss can be reduced. As described above, the first embodiment of the present invention has an effect similar to that of the conventional technique in which the passive element is configured only by the Schottky barrier diode even in the conductive state.

  Next, as the switching element D is turned on and the switching element D shifts to the on state, the passive element A enters the reverse bias state and shifts to the cutoff state. As shown in FIG. 3, in the Schottky barrier diode, the electron current supplied from the lower electrode 4 side into the drift region 2 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the Schottky barrier height of the Schottky junction, and when the reverse bias voltage starts to be applied to the Schottky junction, the upper electrode 3 is placed in the drift region 2. The depletion layer extending from the Schottky junction spreads out and shifts to the cutoff state.

  When transitioning from the conductive state to the cut-off state, a transiently generated current is a reverse recovery current in the process in which excess carriers accumulated in the elements of the freewheeling diode disappear. The reverse recovery current flows as a transient current in the passive element A and the switching element D, and a loss (herein referred to as reverse recovery loss) occurs in each element. For this reason, it is better that the reverse recovery current generated in the freewheeling diode is as small as possible.

  In the first embodiment of the present invention, the freewheeling diode 100 is formed of a unipolar Schottky barrier diode formed of a semiconductor material made of silicon carbide, and is compared with a pn junction diode formed of general silicon. And this reverse recovery current is much smaller. That is, reverse recovery loss can be greatly reduced.

  This difference in reverse recovery loss can be explained by the difference in the shutoff / conduction mechanism between the two.

First, a pn junction diode formed of general silicon has a drift region conductivity modulation effect due to minority carrier injection during forward bias conduction. Therefore, in order to secure a breakdown voltage while minimizing conduction loss, In general, the thickness is small and the impurity concentration is low. For example, if a pn junction diode of 600V class is to be realized, the drift is relatively drifting to about 50 μm when the impurity density of the drift region is about 10 ¹⁴ cm ⁻³ due to the limitation of the feasibility of low impurity concentration. It is necessary to use a thick substrate. When conducting, due to the conductivity modulation effect of bipolar operation, the minority carriers and the majority carriers are injected into the drift region so as to have substantially the same concentration according to the magnitude of the flowing current, so that a low resistance can be obtained. For example, when a forward bias current of about several hundred A / cm ² flows, carriers are injected to such an extent that the concentration of majority carriers (electrons) and minority carriers (holes) are both 10 ¹⁷ cm ⁻³ , and they are excessive carriers. And it works.

On the other hand, since the Schottky barrier diode is composed only of electrons that are majority carriers, the amount of excess carriers generated when shifting to the cut-off state is almost completely depleted in the freewheeling diode 100. Only the amount of carriers discharged from the depletion layer is generated when the is formed. That is, for example, even when the drift region 2 having an impurity density of 10 ¹⁶ cm ⁻³ and a thickness of 5 μm in the 600 V class is depleted entirely, the carrier density is 1/10 compared to the pn junction diode. Since the thickness of the drift region in which carriers are distributed becomes 1/10, only about 1/100 excess carriers are generated in total. Thus, by forming the freewheeling diode 100 with an element that performs a unipolar operation, the reverse recovery current can be greatly reduced, and as a result, the reverse recovery loss can be greatly reduced. As described above, the effect of reducing the reverse recovery loss is the same as that of the conventional technique in which the passive element is configured only by the Schottky barrier diode.

  Furthermore, in the first embodiment of the present invention, the current during the reverse recovery operation unique to the unipolar operation that could not be solved essentially when the passive element of the prior art is constituted only by the Schottky barrier diode.・ Has a function to suppress voltage oscillation.

  This vibration phenomenon itself is caused by the mutual relationship between the parasitic inductance Ls generated in the circuit of the power converter such as an inverter incorporating the freewheeling diode and the cutoff speed (dIr / dt) of the reverse recovery current Ir during the reverse recovery operation of the freewheeling diode. It is generally known that a surge voltage Vs is generated by the action and is generated from this. This vibration phenomenon of current and voltage causes destruction of the element due to surge voltage, increase of loss during vibration operation, malfunction of peripheral circuits, etc., and it becomes a hindrance to stable operation, so suppression is required. . For this reason, in order to reduce the vibration phenomenon, it is necessary to relax the current interruption speed (dIr / dt) during the reverse recovery operation, and further to have a mechanism that quickly attenuates the oscillating current and converges the vibration. It becomes.

  However, only the conventional Schottky barrier diode that performs the unipolar operation includes the majority component of the reverse recovery current Ir, so the reverse recovery current Ir due to excess carriers is greatly reduced, but the depletion layer formation speed is almost the same. Since the determined reverse recovery time t can hardly be controlled, a vibration phenomenon is likely to occur in the current / voltage, and the vibration is not easily attenuated. There are two main reasons.

  One is that, as described above, in the Schottky barrier diode, the amount of excess carriers injected from the cut-off state to the conductive state is composed only of majority carriers that supplement the depletion region formed in the drift region at the time of cut-off. It is a point that has been. That is, the reverse recovery current cutoff speed (dI / dt) of the Schottky barrier diode almost depends only on the formation speed of the depletion region, and since there are almost no minority carriers, a lifetime control method such as a pn junction diode is used. It cannot be used as it is. For this reason, when using only a Schottky barrier diode, an attempt to improve the switching speed of the switching element and reduce the transient loss will cause a more severe vibration phenomenon, so there is a trade-off between reducing the transient loss and suppressing the vibration phenomenon. There was an off relationship.

  The other is that since the Schottky barrier diode operates with almost majority carriers only when conducting, the resistance inside the device does not change with the resistance according to the thickness of the drift region and the impurity concentration, either immediately before conduction or immediately before interruption. is there. As described above, the pn junction diode has a low resistance due to the conductivity modulation effect during conduction, but the drift region has a high resistance during the reverse recovery operation in which the conductivity modulation is canceled, and the reverse recovery current Ir is resistance limited. It has a mechanism. On the other hand, the Schottky barrier diode has a low resistance as its own resistance component both at the time of conduction and immediately before the interruption, and does not have a mechanism for limiting the resistance of the reverse recovery current Ir. Therefore, a vibration phenomenon is likely to occur in the current / voltage, and the vibration is not easily attenuated. Furthermore, by using a wide gap semiconductor such as silicon carbide as the semiconductor material, the resistance of the element itself is small, so that the conduction loss can be reduced, but the vibration phenomenon is more likely to occur. Therefore, when only the Schottky barrier diode is used, there is a trade-off relationship between the loss during conduction and the suppression mechanism of the vibration phenomenon.

  On the other hand, in the first embodiment of the present invention, a simple configuration in which the freewheeling diode 100 and the semiconductor snubber 200 are connected in parallel reduces the transient loss and the conduction loss and suppresses the vibration phenomenon. be able to. Furthermore, in the first embodiment of the present invention, when the reverse bias voltage is applied to the freewheeling diode 100, the capacitance decrease prevention region 1001 that relaxes the extension of the depletion layer to the resistance region constituting the resistor R is provided. Since it is formed, the formation of a depletion capacitance in the resistance region due to the reverse bias voltage can be suppressed. Therefore, for example, since it is possible to suppress the formation of a depletion capacitor connected in series with the capacitor C formed of the capacitor dielectric film 12 made of a dielectric, it is possible to suppress a decrease in the capacitor capacitance as the semiconductor snubber 200. . As a result, the current / voltage oscillation phenomenon that occurs during the reverse recovery operation can be more stably suppressed, and the semiconductor snubber 200 can be densified as much as the reduction in the capacitance of the capacitor can be prevented. The chip size of the snubber 200 can be reduced.

  In other words, in the first embodiment of the present invention, when the forward bias current decreases and the forward bias current becomes zero in the freewheeling diode 100, a depletion layer is formed in the drift region 2 due to the reverse bias voltage, and the excess current is excessive. A reverse recovery current composed of carriers starts to flow. Almost simultaneously with the application of the reverse bias voltage, an equivalent reverse bias voltage is applied to the capacitor C formed of the capacitor dielectric film 12 in the semiconductor snubber 200, and a corresponding transient current flows in the semiconductor snubber 200. start. The transient current flowing through the semiconductor snubber 200 is determined by the size of the capacitor C formed of the capacitor dielectric film 12 and the size of the resistance R component of the substrate region 11, and can be designed freely.

  In the first embodiment of the present invention, the capacitance lowering prevention region 1001 formed on the surface layer portion of the substrate region 11 so as to be in contact with the capacitor dielectric film 12 has a depletion layer formed on the substrate region 11. Since it functions as a mitigating region, the size of the capacitor C can be formed almost by the capacitor dielectric film 12, and the vibration phenomenon can be sufficiently suppressed.

  That is, in the state where the passive element A performs the reverse recovery operation, the reverse bias voltage is applied to the free-wheeling diode 100 and the semiconductor snubber 200. Therefore, in the semiconductor snubber 200, a high voltage is applied to the lower electrode 14 side. It becomes. At this time, excess electrons in the n-type substrate region 11 are attracted to the lower electrode 14 side. For this reason, for example, when the capacitance reduction prevention region 1001 is not formed, the depletion layer extends from the portion in contact with the capacitor dielectric film in the substrate region 11, and a depletion capacitance is also formed in the substrate region 11. In the first embodiment of the present invention, for example, a silicon substrate having a high resistivity of 100 Ωcm, that is, a low impurity density is used for the substrate region 11 so that the semiconductor snubber 200 functions sufficiently. The depletion layer is more likely to spread. In the case of a capacitance formed by a depletion layer, the capacitor capacitance decreases as the depletion layer increases, and this depletion layer capacitance is connected in series with the dielectric capacitance formed by the capacitor dielectric film 12. Therefore, the capacitor capacity as the semiconductor snubber 200 is lower than the capacitor capacity obtained by at least the dielectric capacity alone. For example, in the first embodiment of the present invention, when the depletion layer extending into the substrate region 11 extends by 10 μm, when the relative dielectric constant of silicon is 11.9, the capacitance per unit area is about 1 About 0.0μF. That is, in addition to the capacitance of about 3.4 μF when the capacitor dielectric film 12 is formed of a silicon oxide film having a thickness of 1 μm, a small capacitance is formed, and they are connected in series. For this reason, the combined capacitor capacity is about 0.8 μF, which is about 1/4 of the capacity of the capacitor dielectric film. Furthermore, the capacitor capacity decreases as the depletion layer increases.

  On the other hand, in the first embodiment of the present invention, the capacitance reduction prevention region 1001 is formed in the substrate region 11 in contact with the capacitor dielectric film 12 where the depletion layer is easily formed. The growth of the depletion layer has been greatly eased. In other words, electrons in the capacity reduction prevention region 1001 formed with a high impurity density are not easily depleted even when a high voltage is applied to the lower electrode 14 side, so that the depletion layer hardly spreads. In general, since the elongation of the depletion layer is inversely proportional to the size of the impurity density, if the impurity density is 5 orders of magnitude, the extension of the depletion layer will be 5 orders of magnitude smaller. That is, in the first embodiment of the present invention, since the depletion layer hardly extends in the substrate region 11, the semiconductor snubber 200 functions as a capacitor capacitance formed by the capacitor dielectric film 12. For this reason, it is possible to sufficiently suppress the vibration phenomenon without substantially reducing the dielectric capacitance per unit area.

  Further, even if the depletion layer is formed, if the capacitance formed by the capacitor dielectric film 12 is, for example, 10 times the capacitance, the decrease in the capacitance of the capacitor as the semiconductor snubber 200 is suppressed to about 10%. be able to. Considering that the actual manufacturing variation of the semiconductor device and the semiconductor process is about 10%, it is desirable to suppress the depletion layer to grow at least to such a degree as to be reduced.

  In any case, the suppression of the vibration phenomenon can be efficiently realized by forming the capacity decrease prevention region 1001 that relaxes the extension of the depletion layer to the substrate region 11.

  The operation of the first embodiment of the present invention has been described above. There are three effects of the semiconductor snubber 200 connected in parallel.

  First, since the semiconductor snubber 200 does not operate unless there is a voltage transient, it does not affect the switching speed of the switching element D, and the loss depending on the switching speed can be kept low as in the conventional case. is there. That is, since the cutoff speed of the forward bias current flowing through the freewheeling diode 100 can be set at a high speed, the loss accompanying the cutoff of the main current can be reduced.

  Second, when the freewheeling diode 100 enters the reverse recovery operation, the capacitor component and the resistance component of the semiconductor snubber 200 connected in parallel to the freewheeling diode 100 are operated, and the reverse recovery current cutoff speed (dIr / dt). The surge voltage itself can be reduced.

  Third, since the current flowing through the semiconductor snubber 200 is consumed by the resistance component of the substrate region 11, the energy generated by the parasitic inductance Ls can be absorbed and the vibration phenomenon can be quickly converged.

  As described above, in the present invention, while having the performance of reducing the transient loss and conduction loss of the freewheeling diode 100, the essential vibration phenomenon unique to the unipolar operation can be solved by using the semiconductor snubber 200. It has the characteristics.

    In general, the RC snubber configuration is a conventionally known circuit when viewed as a circuit, but a semiconductor snubber 200 that forms a snubber circuit on a semiconductor substrate is combined with a freewheeling diode 100 having a unipolar operation or an operation equivalent to a unipolar operation. Thus, it is possible to fulfill a sufficient function as a snubber circuit for the first time. In other words, in a pn junction diode made of silicon that has been generally used in power conversion devices such as inverters, a snubber circuit on a semiconductor chip is practically difficult due to power capacity limitation, and a film capacitor that is a discrete component This is because it is necessary to arrange a capacitor composed of the above and a resistor composed of a metal clad resistor in a path through which the main current flows inside or outside the semiconductor package of the power converter. The reason for this is that in order for the snubber circuit to function sufficiently, in order to mitigate the reverse recovery current cutoff speed (dIr / dt), the capacity must be such that a transient current equivalent to the reverse recovery current flowing in the diode flows. And a resistor having a power capacity capable of consuming the current flowing through the capacitor is required to attenuate the vibration phenomenon. As described above, in the pn junction diode, the magnitude of the reverse recovery current varies depending on the magnitude of the circulating current. In the above example, the reverse recovery current is 100 times that of the unipolar Schottky barrier diode. As the current density flowing through the diode further increases and the withstand voltage class increases, the excess carriers injected during conduction further increase and the reverse recovery current also increases. For this reason, when the capacitor is formed on the semiconductor chip, the thickness is limited by the required withstand voltage, and therefore the area needs to be simply calculated to be 100 times larger. Further, since the electric power to be consumed for the resistor R is 100 times, the volume needs to be 100 times, and as a result, the chip size is required 100 times. Therefore, the idea of forming a snubber circuit in a power conversion device with a semiconductor chip is practically difficult with the extension of the prior art.

  In the first embodiment of the present invention, it is noted that the transient current flowing through the freewheeling diode 100 is a transient current consisting only of carriers generated when a depletion layer is formed in the drift region 2 at most. Is formed by a small-capacity semiconductor snubber 200, which is different from the prior art. Furthermore, with the configuration of the first embodiment of the present invention, it is possible to obtain new effects not found in the prior art in suppressing the performance and vibration phenomenon of reducing transient loss and conduction loss.

  First, once a semiconductor snubber 200 having a predetermined capacitor capacity and resistance value is connected in parallel to the freewheeling diode 100 that performs unipolar operation, the snubber function becomes effective in the entire current range and temperature range in which the freewheeling diode operates. Is to work. As described above, the reverse recovery current of the Schottky barrier diode is composed only of excess carriers generated when the depletion layer is generated by the reverse bias voltage, and thus depends on the magnitude of the current flowing during the reflux operation. This is because an almost constant reverse recovery current flows every time. For the same reason, the reverse recovery current flows almost without being affected by the temperature of the freewheeling diode. For this reason, it is possible to reduce the transient loss and suppress the vibration phenomenon in the entire current range and temperature range. These are effects that cannot be obtained in combination with a general pn junction diode.

  The other is that the snubber circuit is formed of the semiconductor snubber 200 as shown in FIG. 2, so that it can be mounted with a low inductance in the immediate vicinity of the freewheeling diode 100, further reducing the transient loss and suppressing the vibration phenomenon. Is a point. This is because, as the parasitic inductance generated when the snubber circuit is connected in parallel to the freewheeling diode 100 is smaller, the transient current flowing through the snubber circuit is more likely to flow, and the cutoff speed (dIr / dt) of the reverse recovery current flowing through the freewheeling diode is reduced. This is because the back electromotive force generated by the parasitic inductance superimposed on the voltage applied to the capacitor in the snubber circuit is small, and the switching time can be shortened in the withstand voltage range of the capacitor. Therefore, in the first embodiment of the present invention, the parasitic inductance is reduced as compared with the case of a snubber circuit using a capacitor composed of a film capacitor or the like, which is a conventional discrete component, and a resistor composed of a metal clad resistor or the like. By reducing it, the switching time can be shortened and the transient loss can be reduced, and the reverse recovery current cutoff speed (dIr / dt) can be moderated and the vibration phenomenon can be suppressed.

  In addition, mounting the snubber circuit in the immediate vicinity of the freewheeling diode 100 also reduces unnecessary noise emission. For example, in the case of a snubber circuit using a capacitor C made of a conventional discrete component such as a film capacitor and a resistor R made of a metal clad resistor, the oscillating current generated by the freewheeling diode 100 passes through these components, and the freewheeling diode 100 Take the path back to. At that time, the oscillating current is suppressed by the resistor R, but the surface formed by this current path so far works as a kind of loop antenna and radiates noise. When the snubber circuit is formed by the semiconductor snubber 200, the surface formed by the current path of the oscillating current is much smaller than when discrete components are used because it is mounted in the immediate vicinity of the freewheeling diode 100. , Noise emission due to oscillating current is reduced. Thereby, it is possible to prevent malfunction of the control circuit and the like due to noise.

  Furthermore, in the first embodiment of the present invention, since the snubber circuit is formed of the semiconductor snubber 200, the power conversion device can be configured using the same mounting process as that of the freewheeling diode 100. In addition, the vibration phenomenon can be easily suppressed, and the required volume can be greatly reduced as compared with the conventional snubber circuit.

  Further, since the resistance component of the semiconductor snubber 200 can be formed of a semiconductor substrate and directly mounted on a semiconductor package as shown in FIG. 2, high heat dissipation can be obtained. Therefore, it is possible to design a resistor with a higher density than an external resistor. That is, the resistance to destruction is high and further downsizing can be realized.

  Further, as exemplified in the first embodiment of the present invention, for example, by configuring the freewheeling diode 100 with a Schottky barrier diode made of silicon carbide, the effects of the present invention can be maximized. . That is, in order to obtain a predetermined breakdown voltage, as the depletion layer thickness can be reduced by the wide band gap, the resistance of the freewheeling diode 100 itself can be reduced and the low conduction loss can be reduced. This is because (dIr / dt) becomes high and vibration energy is not consumed, and therefore, the vibration phenomenon has a more remarkable property. For example, when a Schottky barrier diode made of silicon is used as the freewheeling diode 100, a certain level of effect can be obtained as an effect of the present invention. Compared to the diode itself, which has a large resistance component, vibration energy is easily consumed and attenuated by the diode itself. From this, when the free-wheeling diode 100 is formed of a wide band gap semiconductor such as silicon carbide, both reduction of conduction loss and reduction of vibration phenomenon can be achieved more remarkably.

  In the first embodiment of the present invention, the case where the semiconductor material of the free-wheeling diode 100 is silicon carbide is described. However, the same effect can be obtained by using a wide gap semiconductor such as gallium nitride or diamond. Can be obtained.

  4 also has a function of adjusting the resistance value of the resistance R of the semiconductor snubber 200, so that the effect of suppressing the vibration phenomenon of the semiconductor snubber 200 can be easily and maximized. Is possible. For example, the resistance R is configured to be substantially determined by the resistance value of the substrate region 11, but when the resistance value is changed or adjusted, it is possible to cope with it by changing the area, thickness, and impurity density (specific resistance). However, the area depends on the area necessary for the capacitor capacitance C, the thickness is required to be machined when changing its own thickness, and can be set only within a range where mechanical strength can be obtained. As for the impurity density, it is not easy to finely adjust or change the resistance because the conditions need to be determined when the substrate region 11 is created, that is, when the semiconductor wafer is created. However, in the first embodiment of the present invention, when forming the capacitance decrease prevention region 1001, the value of the resistance R can be easily adjusted by adjusting the thickness and area of the capacitance decrease prevention region 1001. it can. That is, the capacity reduction prevention region 1001 in FIG. 4 is formed, for example, by introducing phosphorus or arsenic that becomes an n-type impurity into the surface layer portion of the substrate region 11 by ion implantation, and activating and diffusing the impurity by thermal diffusion. In this case, the thickness of the capacity decrease prevention region 1001 can be controlled by changing the thermal diffusion conditions. When the thickness of the capacitance reduction prevention region 1001 is reduced, the resistance region (substrate region) 11 is increased. Therefore, the value of the resistance R is increased, and when the thickness of the capacitance reduction prevention region 1001 is increased, the resistance region (substrate region). Since the thickness of 11 becomes smaller, the value of the resistance R becomes smaller.

  Further, as shown in FIGS. 8 and 9, the resistance R can also be adjusted by changing the area (the width in the cross-sectional structures of FIGS. 8 and 9) in which the capacitance decrease prevention region 1001 is formed. 8 and 9 show an example of the semiconductor snubber 200 around the chip end portion of the chip structure of the semiconductor snubber 200 shown in FIG. FIG. 8 shows a case where the capacity reduction prevention region 1001 is formed so that the end comes to a position substantially equal to the end of the upper electrode 13. That is, in the semiconductor snubber 200 in FIG. 8, the case where the area of the capacitance lowering prevention region 1001 is equivalent to that of the upper electrode serving as the capacitor capacitance C is shown. In the drawing, the portion indicated by a broken line indicates the spread of electrons flowing in the substrate region 11 with a 45 degree approximation when a reverse bias voltage is applied.

  On the other hand, in the semiconductor snubber 200 in FIG. 9, the case where the area of the capacitance lowering prevention region 1001 is formed larger than the upper electrode serving as the capacitor capacitance C is shown. In FIG. 9, since electrons easily move in the lateral direction in the capacity reduction prevention region 1001 formed of high impurities, the range of electron flow indicated by broken lines in the drawing is wider than that in FIG. Will flow. That is, the resistance can be made lower than that in FIG. As described above, the capacitance reduction prevention region 1001 not only prevents the reduction of the capacitor C but also facilitates the adjustment of the resistance R, is easy to manufacture, and has a feature that the vibration phenomenon can be further alleviated.

  The basic operation of the semiconductor snubber 200 according to the first embodiment of the present invention has been described above with reference to FIGS. 4, 8, and 9. FIGS. 10 and 11 illustrate the substrate region 11 in contact with the lower electrode 14. Even in the surface layer portion, it is more preferable to form the capacity decrease prevention region 1002. 4 is a cross-sectional view corresponding to FIG. 8, and FIG. 11 is a cross-sectional view corresponding to FIG. Since the substrate region 11 having a small impurity density and a large specific resistance is connected to the lower electrode 14 as it is, a Schottky connection is formed. Therefore, although the influence is smaller than the upper electrode 13 side, the substrate region 11 formed on the lower electrode 14 side. This is because the capacity of the is not stable. Therefore, by forming the capacity reduction prevention region 1002 having a high impurity concentration and making ohmic contact with the lower electrode 14, it is possible to prevent unnecessary capacitance from being formed in the substrate region 11 on the lower electrode 14 side.

  As described above, in FIGS. 4 and 8 to 11, the case where the substrate region 11 is formed in the n-type has been described. However, as illustrated in FIGS. 12 to 14, the substrate region 11 may be formed in the p-type. 12 corresponds to FIG. 4, FIG. 13 corresponds to FIG. 10, and FIG. 14 corresponds to FIG. When the substrate region 11 is p-type, as shown in FIG. 12, when a reverse bias voltage is applied to the freewheeling diode, a depletion layer easily spreads in the surface layer portion of the substrate region 11 on the lower electrode 14 side. The capacity reduction prevention region 1003 is preferably formed so as to be in contact with the lower electrode 14 and to be in ohmic contact. That is, in a state where a high voltage is applied to the lower electrode 14, excess holes in the p-type substrate region 11 are attracted to the upper electrode 13 side. This is because the depletion layer extends in the substrate region 11 on the lower electrode 14 side. In FIG. 12, since the capacitance reduction prevention region 1003 is formed, the capacitance of the capacitor is unlikely to decrease even when a reverse bias voltage is applied. Further, in FIG. 13, the depletion capacity formation on the upper electrode 13 side is prevented by the capacity lowering prevention region 1004, and in FIG. 14, the resistance R on the upper electrode 13 side by the capacity lowering prevention region 1004 as in FIG. 11. Can be adjusted easily.

  As described above, the basic operation has been described based on FIGS. 1 to 4 as an example of the first embodiment of the present invention. However, the semiconductor snubber 200 is not limited to the simple RC snubber circuit shown in FIG. For example, as shown in FIG. 15, the diode 230 may be connected to the resistor 220 in parallel. This is because the semiconductor snubber 200 configured to have at least the capacitor C and the resistor R can obtain the same effect as described above.

  In addition to the semiconductor package using the ceramic substrate of FIG. 2 shown as an example of the mounting form, for example, as shown in FIG. 16, a metal base 420 is used as a support base and a cathode terminal, and an anode terminal 340 and a mold resin are used. A so-called mold package type mounting form consisting of 510 may be used, or another mounting form may be used. In the first embodiment of the present invention, the case where each of the free-wheeling diode 100 and the semiconductor snubber 200 is one chip is shown, but one or both of them may be composed of a plurality of chips. 2 and 16 show an example in which only the lower electrodes 4 and 14 on the cathode terminal side are mounted by solder or the like, and the metal wirings 320 and 330 are wired on the anode terminal side. It is good also as a system which mounts both surfaces of a terminal with solder. Since the cooling performance is improved by mounting both surfaces with solder or the like, the heat dissipating property of the reflux diode 100 and the heat dissipating property of the resistor 210 of the semiconductor snubber 200 are increased.

  Further, in describing the first embodiment of the present invention, the basic operation has been described with reference to FIG. 4 as an example of the structure of the semiconductor snubber 200. As shown in FIGS. Of course, the resistor R may be formed in another configuration.

FIG. 17 shows a case where the main component of the resistance R including the substrate region 11 shown in FIG. 17, instead of the substrate region 11 used in FIG. 4, a low-resistance substrate region 16 formed of an n ⁺ -type low-resistance substrate is formed, and the main component of the resistor R is formed on the capacitor dielectric film 12, for example. The resistor region 17 is made of n-type polycrystalline silicon. An advantage of the resistance region 17 made of polycrystalline silicon is that the resistance value can be freely changed by changing the thickness and impurity concentration. That is, since the semiconductor snubber 200 can be formed using any substrate when selecting the substrate region as the support base, it is possible to increase the degree of freedom of feasibility.

  Also in FIG. 18, the n-type high-concentration capacity reduction prevention region 1005 is on the upper electrode 13 side so that the depletion layer does not spread in the resistance region 17 when a reverse bias voltage is applied to the freewheeling diode 100. Is formed. By forming in this way, it is possible to prevent the capacitor C from being lowered even when the resistance region 17 is used. The resistance region 17 may be made of any material other than polycrystalline silicon. However, the resistance region 17 may be made of a material having a higher dielectric breakdown field than that of silicon. There is an effect of facilitating further. For example, when 100 V is applied as a surge voltage across the freewheeling diode 100 during reverse recovery, a transient current flows through the capacitor C in the semiconductor snubber 200. Is applied. At this time, a breakdown voltage greater than or equal to the breakdown voltage determined by the breakdown field and thickness corresponding to the material is required for the resistance region. In order to give a breakdown voltage of 100 V, in the case of silicon, since the dielectric breakdown electric field is about 0.3 MV / cm, a thickness of about 3 μm is required. If polysilicon carbide having a higher breakdown electric field than silicon is used, the breakdown electric field is about 3.6 MV / cm, so that the thickness can be reduced to about 1/10. Therefore, it is possible to shorten the deposition time when the resistance region is manufactured, and to facilitate the process. Further, since silicon carbide has a thermal conductivity approximately three times better than silicon, there is an effect of improving the heat dissipation of the resistance region 17.

  FIG. 18 shows a case where the substrate region 11 described in FIG. 4 and the resistor region 17 described in FIG. 17 are connected in series as the main component of the resistor R. Also in FIG. 18, the formation of the depletion layer can be suppressed by forming the capacitance lowering prevention region 1001 in the substrate region 11 and forming the capacitance lowering prevention region 1005 in the resistance region 17.

  17 and 18 have been described with respect to the case where the resistance region 17 is formed of n-type polycrystalline silicon. However, when the resistance region 17 is formed of p-type polycrystalline silicon, as shown in FIGS. 19 and 20. In addition, a p-type high-concentration capacity reduction prevention region 1006 may be formed in the resistance region 17 on the capacitor dielectric film 12 side.

  As described above, the main component of the resistor R may be configured in any region as long as it is formed so as to be connected in series with the component of the capacitor C.

  21 and 22 are circuit simulators as an example of the relationship between the suppression effect of the vibration phenomenon and the increase in loss due to the transient current flowing in the capacitor capacitance C depending on the size of the capacitor capacitance C used in the snubber circuit. It is the result calculated using. The vibration reduction of the snubber circuit can be calculated by a simple circuit composed of the parasitic inductance Ls in the circuit, the capacitor capacity component C0 of the freewheeling diode, and the capacitor capacity C of the snubber circuit connected in parallel to the freewheeling diode and the resistor R. For example, in this calculation, the parasitic inductance in the effect circuit is fixed to Ls = 99 nH and the resistance R = 40Ω, and the decay time of the vibration phenomenon and the transient loss generated in the snubber circuit are increased depending on the magnitude of C / C0. The change of was verified. Note that the capacitor capacitance C0 of the freewheeling diode is set to 150 pF, for example. First, as C / C0 increases, the decay time of the vibration phenomenon decreases. The axis on the left side of FIG. 22 represents the time until the voltage or current oscillation is attenuated to 1/10 in the absence of the snubber circuit, and when the snubber circuit is added, the vibration is equivalent to that in the absence of the snubber circuit. The vibration phenomenon convergence time ratio t / t0 when the time until is t is shown. From FIG. 21, the damping effect of the vibration phenomenon becomes remarkable from the value of C / C0 around 0.1. On the other hand, the value of the convergence time ratio of the vibration phenomenon tends to be saturated when C / C0 exceeds 10. Further, as shown on the right axis of FIG. 22, the capacitor capacitance C formed in the snubber circuit generates a loss E due to a transient current proportional to the size of the capacitor capacitance C during transient operation. Is preferably as small as possible. Note that E0 is a loss caused by a transient current flowing through the freewheeling diode.

  Therefore, the size of the capacitor capacitance C of the snubber circuit used in the first embodiment of the present invention is 1/10 times or more and 10 times the size of the capacitance of the capacitor component in the cutoff state of the freewheeling diode 100. By selecting the capacitance within the following range, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the examples described in the first embodiment.

(Second Embodiment)
A semiconductor device according to the second embodiment of the present invention will be described with reference to FIGS. 23 to 25, 3, and 4. In the second embodiment of the present invention, the description of the same operation as that of the first embodiment is omitted, and different features will be described in detail.

  FIG. 23 is a circuit diagram for explaining a second embodiment of the present invention corresponding to FIG. 1, FIG. 24 is a semiconductor chip mounting diagram embodied as an example of the circuit diagram of FIG. 23 corresponding to FIG. 3 and 4 are examples of cross-sectional structural diagrams of the semiconductor chip used in the mounting diagram of FIG.

  As shown in FIG. 23, the semiconductor device according to the second embodiment of the present invention includes a free-wheeling diode 100 that performs the unipolar operation or the unipolar operation described in the first embodiment, and at least a capacitor 210. In addition to the semiconductor snubber 200 configured to include the resistor 220, the switching element 600 is a semiconductor device connected in parallel so as to be connected to the emitter terminal 301 and the collector terminal 401, respectively.

  In the second embodiment of the present invention, as an example, a case where the free wheel diode 100, the semiconductor snubber 200, and the switching element 600 are formed as separate semiconductor chips will be described. The configuration of the semiconductor snubber 200 and the configuration of the freewheeling diode 100 will be described, for example, when the same configuration as that of the first embodiment is used. As for the switching element 600, for example, a case where an IGBT using silicon as a semiconductor substrate material is used will be described. In the second embodiment of the present invention, a so-called vertical IGBT in which electrodes are formed so that the emitter terminal 301 and the collector terminal 401 face each other will be described as an example.

  FIG. 24 shows a specific example of a semiconductor device including the freewheeling diode 100 (for example, silicon carbide Schottky barrier diode) and the semiconductor snubber 200 (for example, silicon semiconductor RC snubber) and the switching element 600 (for example, silicon IGBT) shown in FIG. It is the mounting diagram which showed the apparatus.

  In FIG. 24, a case where a ceramic substrate is used as an example of a semiconductor package as in FIG. 2 will be described. On the cathode side metal film 410, the collector terminal 401 side of each of the semiconductor chips of the reflux diode 100, the semiconductor snubber 200, and the switching element 600 is disposed so as to be in contact with each other through a bonding material such as solder or brazing material. . Then, the emitter terminal 301 side of each semiconductor chip of the freewheeling diode 100, the semiconductor snubber 200, and the switching element 600 are all anode-side metal films 310 via metal wirings 320, 330, 350 such as aluminum wires and aluminum ribbons, for example. It is the composition connected to. Furthermore, in the second embodiment of the present invention, the gate terminal of the switching element 600 is connected to the gate-side metal film 700 via the metal wiring 710.

  The cross-sectional structures of the semiconductor chips constituting the switching element 600, the freewheeling diode 100, and the semiconductor snubber 200 are shown in the cross-sectional structure diagrams of FIGS. 25, 3, and 4, respectively.

As shown in FIG. 25, the switching element 600 shows the structure of a general IGBT as an example. For example, a case where a substrate material in which an n ⁻ type drift region 23 is formed on a p ⁺ type substrate region 21 made of silicon via an n type buffer region 22 will be described. As the substrate region 21, for example, a substrate having a resistivity of several meters to several tens of mΩcm and a thickness of several to several hundreds μm can be used. As the drift region 23, for example, an n-type impurity density of 10 ¹³ to 10 ¹⁶ cm ⁻³ and a thickness of several tens to several hundred μm can be used. Of course, the resistivity, impurity density, and thickness may be out of the above ranges depending on the element structure and the required breakdown voltage.However, in general, the smaller the resistivity and thickness, the lower the conduction loss. It is desirable to make it smaller. In the second embodiment of the present invention, for example, an impurity density of 10 ¹⁴ cm ⁻³ , a thickness of 50 μm, and a breakdown voltage of 600 V class will be described. The buffer region 22 is formed to prevent punch-through with the substrate region 21 when a high electric field is applied to the drift region 23. In the second embodiment of the present invention, the case where the substrate region 21 is used as a support base material is described as an example, but the buffer region 22 and the drift region 23 may be used as a support base material. The buffer region 22 may be omitted as long as the substrate region 21 and the drift region 23 do not punch through.

A p-type well region 24 is formed in the surface layer portion in the drift region 23, and an n ⁺ -type emitter region 25 is formed in the surface layer portion in the well region 24. A gate electrode 27 made of, for example, n-type polycrystalline silicon is provided via a gate insulating film 26 made of, for example, a silicon oxide film so as to be in contact with the surface layer portions of the drift region 23, the well region 24, and the emitter region 25. Has been. Further, an emitter electrode 28 made of, for example, an aluminum material is formed so as to be in contact with the emitter region 25 and the well region 24. An interlayer insulating film 29 made of, for example, a silicon oxide film is formed between the emitter electrode 28 and the gate electrode 27 so as not to contact each other. A collector electrode 30 is formed so as to be in ohmic contact with the substrate region 21. As described above, the IGBT used in this description has a so-called planar type in which the gate electrode 27 is formed on a plane with respect to the semiconductor substrate.

  The configuration of the free wheeling diode (here Schottky barrier diode) 100 shown as an example in FIG. 3 is the same as that described in the first embodiment.

  However, although the basic configuration of the semiconductor snubber 200 shown in FIG. 4 is the same as that of the first embodiment, the switching element 600 newly connected in parallel is used in order to effectively exhibit the snubber function. It is desirable to set the capacitor C in consideration of the above and the resistance R by the substrate region 11. However, as will be described later, when the reverse recovery current flows through the freewheeling diode 100, the parallel switching element 600 is always in the cut-off state, so the setting of the capacitor C and the resistance R of the semiconductor snubber 200 is the first implementation. As in the case described in the above embodiment, it is possible to cope with the setting according to the depletion capacity when the free wheel diode 100 and the switching element are cut off. That is, the substrate region 11 can have the resistivity and thickness of the substrate depending on the required resistance value, for example, the resistivity is several mΩcm to several hundreds Ωcm, and the thickness is about several tens to several hundreds μm. Can be handled by using. Further, the capacitance of the capacitor C can be dealt with by changing the thickness and area of the capacitor dielectric film 12 so as to obtain the required capacitance while satisfying the required withstand voltage at a minimum. In the second embodiment of the present invention, about 1/100 to 100 times the sum of the depletion capacities charged when the free-wheeling diode 100 and the switching element 600 are cut off (when a high voltage is applied), respectively. It can be selected in the range of about, but it exhibits a sufficient snubber function, suppresses the increase of loss as much as possible, and considering the necessary chip area, as shown in the calculation results described later, about 1/10 The range of about 10 times is desirable. In the second embodiment of the present invention, for example, the thickness is 1 μm so as to be higher than the breakdown voltage of the freewheeling diode 100 and the switching element 600, and the capacitance of the capacitor C is when the freewheeling diode 100 and the switching element 600 are cut off. A description will be given of the case where the same depletion capacity formed is used.

  Also in the second embodiment of the present invention in which the switching elements 600 are connected in parallel, as will be described later, for example, when a Schottky barrier diode is used as the freewheeling diode 100, a current that is essentially generated by unipolar operation.・ Uses a method of wiring external discrete components such as film capacitors and metal clad resistors in the main current flow path, which is conventionally used as a snubber circuit to reduce the vibration of bipolar diodes against voltage oscillation phenomena. In addition, the semiconductor snubber 200 having a small capacity and a small size capacitor C and a resistor R are connected in parallel, so that the vibration phenomenon can be easily and effectively suppressed. Further, C = 1 / (2πfR) is generally known as a design formula that effectively exhibits the snubber function (f is the frequency of the vibration phenomenon), and in the second embodiment of the present invention, The capacitor C and the resistor R using the small-capacity semiconductor snubber 200 can be easily set so as to satisfy the equation.

  Next, the operation of the second exemplary embodiment of the present invention will be described in detail.

  The configuration of the semiconductor device described in the second embodiment of the present invention is a so-called inverter for moving a three-phase AC motor as shown in FIG. It can be used for such a power conversion device as a so-called H-bridge. For example, in the inverter shown in FIG. 7, the switching element E1 and the passive element B1 that are connected in parallel to form the upper arm with respect to the power supply voltage (+ V) (for example, 400 V in the second embodiment of the present invention) The switching element E4 and the passive element B4 connected in parallel forming the lower arm are connected in series so as to be reverse-biased. Furthermore, the parallel-connected switching element E2 and passive element B2 that form the upper arm, and the parallel-connected switching element E5 and passive element B5 that form the lower arm are connected in series to form the upper arm. The switching element E3 and the passive element B3, and the switching element E6 and the passive element B6 connected in parallel to form the lower arm are connected in series. In this way, the three phases are connected to form a three-phase inverter. The operation mode of the semiconductor device according to the second embodiment of the present invention is such that when either the upper arm or the lower arm switching element performs the switching operation, the switching element and the passive element of the arm not performing the switching operation are interlocked. Then, it operates from a cut-off state where current is cut off to a conductive state where current is circulated, and from a conductive state to a cut-off state. Here, the operation of the semiconductor device will be described using the operation of one of the three phases in FIG. 7, and the switching elements E4, E5, E6 of the lower arm perform the switching operation as an example. A case where the arm switching elements E1, E2, E3 and the passive elements B1, B2, B3 perform a reflux operation will be described.

  First, when the switching elements E4, E5, and E6 are turned on and the current flows through the switching elements E4, E5, and E6, the switching elements E1, E2, and E3 of the upper arm and the passive elements B1, B2, and B3 are reversed. Biased and cut off.

  First, in the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 in the conductive state of the lower arm, the freewheeling diode 100 and the semiconductor snubber 200 maintain the cutoff state. That is, the Schottky barrier diode shown in FIG. 3 that is the freewheeling diode 100 is applied with a reverse bias voltage although the voltage applied to both ends thereof is as low as the ON voltage of the switching elements E4, E5, and E6. It is. Further, in the semiconductor snubber 200 shown in FIG. 4, since the capacitor dielectric film 12 functioning as the capacitor C operates only when the voltage changes, the voltage about the ON voltage of the switching elements E4, E5, E6 is in a steady state. In the applied state, it becomes a cut-off state.

  On the other hand, the switching elements E1, E2, E3 and the passive elements B1, B2, B3 on the upper arm are also maintained in the cut-off state because a reverse bias voltage of about the power supply voltage is applied. That is, with respect to the IGBT which is the switching element 600 shown in FIG. 25, since a reverse bias voltage is applied between the emitter terminal 301 and the collector terminal 401, the drift region 23 extends from the pn junction with the well region 24. This is because a depletion layer is formed and the blocking state is maintained. In the Schottky barrier diode, which is the freewheeling diode 100 shown in FIG. 3, a reverse bias voltage is applied between the upper electrode 3 and the lower electrode 4, so that the Schottky junction with the upper electrode 3 is in the drift region 2. A depletion layer extending from the portion is generated and the cut-off state is maintained. Also in the semiconductor snubber 200 shown in FIG. 4, the capacitor dielectric film 12 functioning as the capacitor C is charged with a high voltage, and the cut-off state is maintained.

  As described above, when the switching elements E4, E5, and E6 of the lower arm are in the conductive state, the upper and lower arms have the same function as that of the prior art in which the passive element is configured only by the Schottky barrier diode.

  Next, a case where the switching elements E4, E5, and E6 of the lower arm are turned off to shift to the cutoff state will be described.

  For example, in a motor inverter circuit (L load circuit) as shown in FIG. 7, when the switching elements E4, E5, E6 are turned off, the phases of voltage rise and current interruption are shifted, so that the current during conduction is substantially maintained. In this state, first, the voltage rise of the switching elements E4, E5, E6 occurs.

  First, for the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 that turn off the lower arm, the voltage of the switching elements E4, E5, and E6 is the same for both the free wheel diode 100 and the semiconductor snubber 200. As the voltage rises, the reverse bias voltage changes from a low reverse bias voltage of about the ON voltage to a high reverse bias voltage of the power supply voltage, and therefore a transient current corresponding to the speed of the voltage change flows. That is, in the free-wheeling diode 100 shown in FIG. 3, when a depletion layer spreads from the upper electrode 3 side in the drift region 2 as the voltage rises, electrons flow as a transient current to the lower electrode 4 side. In the semiconductor snubber 200 shown, a transient current flows because the capacitor dielectric film 12 acting as a capacitor capacity is charged according to the applied voltage. At this time, the transient voltage rise generated between the collectors / emitters of the switching elements E4, E5, and E6 is mitigated by the charging action of the capacitor capacitance of the capacitor dielectric film 12 of the semiconductor snubber 200, and the parasitic inductance included in the circuit It is possible to suppress the occurrence of a surge voltage due to. In other words, in the second embodiment of the present invention, the switching element 600 is also connected in parallel, thereby causing element destruction, malfunction to other peripheral circuits, etc. even when the switching element 600 itself is turned off. Surge voltage can be reduced and more stable operation can be realized.

  Then, after the voltage of the switching element 600 rises, the current is cut off at a predetermined speed. At this time, in the IGBT described as an example in the second embodiment of the present invention, the current interruption speed is limited and a loss occurs due to the influence of the hole current injected from the substrate region 21 at the time of conduction. The phenomenon hardly occurs and as a result contributes to stable operation. Then, after the current of the switching element 600 is cut off, the switching elements E4, E5, E6 and the passive elements B4, B5, B6 of the lower arm are in a steady off state and maintain the cut-off state.

  On the other hand, the passive elements B1, B2, and B3 connected in parallel with the switching elements E1, E2, and E3 of the upper arm are in a forward bias state in conjunction with the turn-off operation of the switching elements E4, E5, and E6 of the lower arm. Transition to the conductive state. The depletion layer that has spread into the drift region 2 of the free-wheeling diode 100 shown in FIG. 3 recedes, and the Schottky junction formed between the upper electrode 3 and the drift region 2 corresponds to the Schottky barrier height. When the forward bias voltage is applied, the freewheeling diode 100 becomes conductive. At this time, the current flowing through the freewheeling diode 100 is composed of only the electron current supplied from the lower electrode 4 side in the drift region 2 and performs a unipolar operation.

  Also, in the semiconductor snubber 200 shown in FIG. 4, similarly to the freewheeling diode 100, since the high voltage reverse bias state shifts to the low voltage forward bias state, the charge charged in the capacitor dielectric film 12 is discharged. And a transient current flows. However, in the second embodiment of the present invention, the capacitor capacity of the capacitor dielectric film 12 is as small as the depletion capacity formed when the free-wheeling diode 100 and the switching element 600 are cut off. The magnitude of the flowing transient current is very small compared to the forward bias current flowing through the parallel free-wheeling diode 100, and hardly affects the operation. In addition, for the switching elements E1, E2, and E3 connected in parallel, the voltage between the collector and the emitter shifts from the reverse bias voltage state to the forward bias state, but the gate signal is controlled to maintain the off state. In addition, since the pn junction between the substrate region 21 and the buffer region 22 is in a reverse bias state, the off state is maintained. However, since the voltage state between the collector and the emitter is displaced, a transient current due to the discharge as the capacitor C accompanying the capacitance change of the depletion layer generated in the drift region 23 in the switching element 600 flows, but the semiconductor snubber 200 and Similarly, it is very small compared to the forward bias current flowing through the freewheeling diodes 100 in parallel, and hardly affects the operation. Then, the semiconductor snubber 200 and the switching element 600 are cut off because a transition is made between the forward bias state and the steady state after the transient current accompanying the change in the bias voltage flows, and only the freewheeling diode 100 is turned on.

  In the second embodiment of the present invention, since the freewheeling diode 100 is composed of a Schottky barrier diode made of a silicon carbide material semiconductor substrate, it has a drift as compared with a pn junction diode made of a general silicon material. Since the resistance of the region 2 can be formed with a low resistance, conduction loss during forward bias conduction can be reduced. Thus, even in the conductive state, the same effect as in the conventional technique in which the passive element is configured only by the Schottky barrier diode is obtained.

  Next, an operation in which the switching elements E4, E5, and E6 of the lower arm are turned on and the switching elements E4, E5, and E6 are turned on again will be described.

  For example, in a motor inverter circuit (L load circuit) as shown in FIG. 7, when the switching elements E4, E5, and E6 are turned on, the phases of current rise and voltage drop are shifted, so a relatively high voltage is applied. In this state, current starts to flow through the switching elements E4, E5, E6. For the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 that turn off the lower arm, the current flows through the switching elements E4, E5, and E6 in both the free wheel diode 100 and the semiconductor snubber 200, As the collector-emitter voltage decreases, the reverse bias voltage, which is as high as the power supply voltage, changes from the reverse bias voltage, which is as low as the on-voltage, so the transient current corresponding to the speed of the voltage change Flowing. At this time, in the free-wheeling diode 100 shown in FIG. 3, the depletion layer that has spread in the drift region 2 as the voltage decreases gradually narrows to the upper electrode 3 side, and electrons enter the drift region 2 from the lower electrode 4 side. Flows as a transient current. In the semiconductor snubber 200 shown in FIG. 4, a transient current flows because the capacitor dielectric film 12 serving as a capacitor capacitance is discharged as the applied voltage decreases.

  This transient current has a magnitude that hardly affects the turn-on current flowing through the switching elements 600 arranged in parallel. Thus, since the semiconductor snubber 200 and the freewheeling diode 100 in the lower arm transition to a steady state after the transient current flows and the current is cut off, only the switching element 600 becomes conductive.

  On the other hand, the passive elements B1, B2, B3 connected in parallel with the switching elements E1, E2, E3 of the upper arm are in a reverse bias state in conjunction with the turn-on operation of the switching elements E4, E5, E6 of the lower arm. Transition to the shut-off state. As shown in FIG. 3, in the Schottky barrier diode, the electron current supplied from the lower electrode 4 side into the drift region 2 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the Schottky barrier height of the Schottky junction, and when the reverse bias voltage starts to be applied to the Schottky junction, the upper electrode 3 is placed in the drift region 2. The depletion layer extending from the Schottky junction spreads out and shifts to the cutoff state.

  When transitioning from the conductive state to the cut-off state, a transiently generated current is a reverse recovery current in the process in which excess carriers accumulated in the elements of the freewheeling diode disappear. This reverse recovery current flows as a transient current in the passive elements B1, B2, and B3 and the lower-arm switching elements E4, E5, and E6, and a loss (herein referred to as reverse recovery loss) occurs in each element. For this reason, it is better that the reverse recovery current generated in the freewheeling diode is as small as possible.

  In the second embodiment of the present invention, the free-wheeling diode 100 is formed of a unipolar Schottky barrier diode formed of a semiconductor material made of silicon carbide, compared with a pn junction diode formed of general silicon. And this reverse recovery current is much smaller. That is, reverse recovery loss can be greatly reduced.

  Furthermore, in the second embodiment of the present invention, the current at the time of reverse recovery operation unique to the unipolar operation that cannot be essentially solved when the passive element of the prior art is composed of only the Schottky barrier diode.・ Has a function to suppress voltage oscillation. In other words, in the second embodiment of the present invention, when the forward bias current decreases and the forward bias current becomes zero in the freewheeling diode 100, a depletion layer is formed in the drift region 2 due to the reverse bias voltage. A reverse recovery current composed of carriers starts to flow. At substantially the same time as the reverse bias voltage is applied, an equivalent reverse bias voltage is also applied to the capacitor C formed of the capacitor dielectric film 12 in the switching element 600 and the semiconductor snubber 200, and the switching element 600 and the semiconductor snubber 200 The corresponding transient current begins to flow. The transient current flowing through the semiconductor snubber 200 is determined by the size of the capacitor C formed of the capacitor dielectric film 12 and the size of the resistance R component of the substrate region 11, and can be designed freely.

  In the second embodiment of the present invention, as described in the first embodiment, the capacitance lowering prevention region 1001 formed on the surface layer portion of the substrate region 11 so as to be in contact with the capacitor dielectric film 12 includes: Since it functions as a region that alleviates the formation of a depletion layer in the substrate region 11, the size of the capacitor C can be formed almost by the capacitor dielectric film 12, and a sufficient vibration phenomenon can be suppressed. Also in the second embodiment of the present invention, not only the structure shown in FIG. 4 but also the structures of FIGS. 8 to 20, 17 and 18 are shown in the first embodiment. The same operation can be obtained, and the same effect can be obtained.

  The operation of the second embodiment of the present invention has been described above. There are three effects of the semiconductor snubber 200 connected in parallel.

  First, since the semiconductor snubber 200 does not operate unless there is a voltage transient, it does not affect the switching speed of the switching elements E4, E5, and E6 of the lower arm, and the loss depending on the switching speed is the same as the conventional one. It can be kept low. That is, since the cutoff speed of the forward bias current flowing through the freewheeling diode 100 can be set at a high speed, the loss accompanying the cutoff of the main current can be reduced.

  Second, when the freewheeling diode 100 enters the reverse recovery operation, the capacitor component and the resistance component of the semiconductor snubber 200 connected in parallel to the freewheeling diode 100 are operated, and the reverse recovery current cutoff speed (dIr / dt). The surge voltage itself can be reduced.

  Third, since the current flowing through the semiconductor snubber 200 is consumed by the resistance component of the substrate region 11, the energy generated by the parasitic inductance Ls can be absorbed and the vibration phenomenon can be quickly converged.

  As described above, in the second embodiment of the present invention, the semiconductor snubber 200 is used to reduce the transient loss and conduction loss of the free-wheeling diode 100 and to reduce the inherent vibration phenomenon unique to the unipolar operation. It has the feature that it can be solved by.

In the second embodiment of the present invention, the transient current flowing through the freewheeling diode 100 and the switching element 600 is a transient current consisting only of carriers generated when a depletion layer is formed in the drift regions 2 and 23 at most. Focusing on this point, the point that the snubber circuit is formed of a small-capacity semiconductor snubber 200 is different from the prior art. Furthermore, with the configuration of the second embodiment of the present invention, it is possible to obtain new effects not found in the prior art in suppressing the performance and vibration phenomenon of reducing transient loss and conduction loss.

  One is that once a semiconductor snubber 200 having a predetermined capacitor capacity and resistance value is connected in parallel to the freewheeling diode 100 and the switching element 600 that perform unipolar operation, the snubber is operated in the entire current range and the entire temperature range in which the freewheeling diode operates. The function works effectively. As described above, the reverse recovery current generated at the time of reverse recovery of the Schottky barrier diode is composed only of excess carriers generated when a depletion layer is generated in the freewheeling diode 100 and the switching element 600 by the reverse bias voltage. This is because an almost constant reverse recovery current flows every time regardless of the magnitude of the current flowing during the reflux operation. For the same reason, the reverse recovery current flows almost without being affected by the temperature of the freewheeling diode. For this reason, it is possible to reduce the transient loss and suppress the vibration phenomenon in the entire current range and temperature range. These are effects that cannot be obtained in combination with a general pn junction diode.

  The other is that the snubber circuit is formed by the semiconductor snubber 200 as shown in FIG. 24, so that it can be mounted with low inductance in the immediate vicinity of the freewheeling diode 100 and the switching element 600, further reducing transient loss and vibration. The phenomenon can be suppressed. This is because, as the parasitic inductance generated when the snubber circuit is connected in parallel to the freewheeling diode 100 and the switching element 600 is smaller, the transient current flowing through the snubber circuit is more likely to flow, and the reverse recovery current cutoff speed (dIr / dt flowing through the freewheeling diode) ) And the back electromotive force generated by the parasitic inductance superimposed on the voltage applied to the capacitor in the snubber circuit is small, so that the switching time can be shortened in the withstand voltage range of the capacitor. Therefore, in the second embodiment of the present invention, the parasitic inductance is reduced as compared with the case of a snubber circuit using a capacitor composed of a film capacitor or the like which is a conventional discrete component and a resistor composed of a metal clad resistor or the like. By reducing it, the switching time can be shortened and the transient loss can be reduced, and the reverse recovery current cutoff speed (dIr / dt) can be moderated and the vibration phenomenon can be suppressed.

  In addition, mounting the snubber circuit in the immediate vicinity of the freewheeling diode 100 also reduces unnecessary noise emission. For example, in the case of a snubber circuit using a capacitor C made of a conventional discrete component such as a film capacitor and a resistor R made of a metal clad resistor, the oscillating current generated by the freewheeling diode 100 passes through these components, and the freewheeling diode 100 Take the path back to. At that time, the oscillating current is suppressed by the resistor R, but the surface formed by this current path so far works as a kind of loop antenna and radiates noise. When the snubber circuit is formed by the semiconductor snubber 200, the surface formed by the current path of the oscillating current is much smaller than when discrete components are used because it is mounted in the immediate vicinity of the freewheeling diode 100. , Noise emission due to oscillating current is reduced. Thereby, it is possible to prevent malfunction of the control circuit and the like due to noise.

Furthermore, in the second embodiment of the present invention, the snubber circuit is formed of the semiconductor snubber 200, so that the power conversion device can be configured using the same mounting process as the free wheel diode 100 and the switching element 600. Therefore, the vibration phenomenon can be easily and easily suppressed, and the required volume can be significantly reduced as compared with the conventional snubber circuit.

  Further, as in the first embodiment of the present invention, the resistance component of the semiconductor snubber 200 can be formed of a semiconductor substrate and directly mounted on a semiconductor package as shown in FIG. Can do. Therefore, it is possible to design a resistor with a higher density than an external resistor. That is, the resistance to destruction is high and further downsizing can be realized.

  Further, as exemplified in the first embodiment, the effect of the present invention can be maximized by configuring the free wheeling diode 100 with a Schottky barrier diode made of silicon carbide. That is, in order to obtain a predetermined breakdown voltage, as the depletion layer thickness can be reduced by the wide band gap, the resistance of the freewheeling diode 100 itself can be reduced and the low conduction loss can be reduced. This is because (dIr / dt) becomes high and vibration energy is not consumed, and therefore, the vibration phenomenon has a more remarkable property. From this, when the free-wheeling diode 100 is formed of a wide band gap semiconductor such as silicon carbide, both reduction of conduction loss and reduction of vibration phenomenon can be achieved more remarkably.

In the second embodiment of the present invention, the case where the semiconductor material of the free wheel diode 100 is silicon carbide is described. However, the same effect can be obtained by using a wide gap semiconductor such as gallium nitride or diamond. Can be obtained.

Also in the second embodiment of the present invention, the configuration of the semiconductor snubber 200 has a diode 230 so as to be connected in parallel to the resistor 220 corresponding to FIG. 15 described in the first embodiment. There may be. This is because the semiconductor snubber 200 configured to have at least the capacitor C and the resistor R can obtain the same effect as described above.

As for the mounting form, as in the first embodiment, a so-called mold package type mounting form corresponding to FIG. 16 may be used, or another mounting form may be used. Further, in the second embodiment of the present invention, the case where each of the free-wheeling diode 100, the semiconductor snubber 200, and the switching element 600 is one chip is shown, but one or both are constituted by a plurality of chips. Of course it is good. In addition, as described above in the first embodiment, both the collector terminal and the emitter terminal may be mounted with solder or the like. Since the cooling performance is improved by mounting both surfaces with solder or the like, the heat dissipating property of the reflux diode 100 and the heat dissipating property of the resistor 210 of the semiconductor snubber 200 are increased.

In addition, as described with reference to FIGS. 21 and 22 in the first embodiment, the size of the capacitor capacitance C used in the snubber circuit is the value of the capacitor capacitance component of the freewheeling diode and the switching element in the cutoff state. With respect to the sum C0, the damping effect of the vibration phenomenon becomes significant when C / C0 is around 0.1, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when C / C0 exceeds 10. In addition, the capacitor capacitance C formed in the snubber circuit generates a loss E due to a transient current proportional to the size of the capacitor capacitance C during transient operation. Therefore, it is desirable that the size of the capacitor capacitance C be as small as possible.

From this, the size of the capacitor capacitance C of the snubber circuit used in the second embodiment of the present invention is 1/10 compared with the total capacitance of the capacitor components in the cutoff state of the freewheeling diode 100 and the switching element 600. By selecting the capacitance within the range of not less than 10 times and not more than 10 times, it is possible to more significantly reduce the vibration phenomenon while suppressing an increase in loss. This effect can be obtained in any of the examples described in the second embodiment.

(Third embodiment)
In the third embodiment of the present invention, in the configuration in which the free-wheeling diode 100, the semiconductor snubber 200, and the switching element 600 described in the second embodiment are connected in parallel, the free-wheeling diode 100 and the switching element 600 are each shot. The case where it comprises with elements other than a key barrier diode and IGBT is demonstrated. 27 shows an example of the freewheeling diode 100 corresponding to FIG. 3, and FIG. 28 shows an example of the switching element 600 corresponding to FIG. Also in the third embodiment of the present invention, the description of the same operation as in the first embodiment or the second embodiment is omitted, and different features will be described in detail.

As shown in FIG. 27, the free-wheeling diode 100 is made of, for example, a substrate material in which an n ⁻ type drift region 42 is formed on an n ⁺ type substrate region 41 whose polytype of silicon carbide is 4H type. . As the substrate region 41, for example, one having a resistivity of several meters to several tens of mΩcm and a thickness of several tens to several hundreds of μm can be used. As the drift region 42, for example, an n-type impurity density of 10 ¹⁵ to 10 ¹⁸ cm ⁻³ and a thickness of several to several tens of μm can be used. Of course, the resistivity, impurity density, and thickness may be out of the above ranges depending on the element structure and the required breakdown voltage.However, in general, the smaller the resistivity and thickness, the lower the conduction loss. It is desirable to make it smaller. In the third embodiment of the present invention, for example, an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class will be described. In the third embodiment of the present invention, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 41 and the drift region 42 will be described. However, the magnitude of the resistivity does not depend on the above example. A substrate formed of only the substrate region 41 may be used, or a multilayer substrate may be used. In the third embodiment of the present invention, the breakdown voltage is 600 V class as an example, but the breakdown voltage class is not limited.

A hetero semiconductor region 43 made of polycrystalline silicon having a band gap smaller than that of silicon carbide is deposited so as to be in contact with the main surface of the drift region 42 facing the bonding surface with the substrate region 41. At the junction between the drift region 42 and the hetero semiconductor region 43, a hetero junction diode is formed of a material having different band gaps between silicon carbide and polycrystalline silicon, and an energy barrier exists at the junction interface. Since the heterojunction diode can control the height of the energy barrier of the heterojunction by changing the impurity density of the hetero semiconductor region 43, an optimum barrier height can be obtained according to the required breakdown voltage. it can. Here, as an example, a description will be given of a p-type impurity density of 10 ¹⁹ cm ⁻³ and a thickness of 0.5 μm.

  In the third embodiment of the present invention, the upper electrode 44 is formed so as to be in contact with the hetero semiconductor region 43, and the lower electrode 45 is formed so as to be in contact with the substrate region 41. In order to connect the upper electrode 44 as an anode terminal 302 to an external electrode, a metal material such as aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), or the like is provided on the outermost surface. A multilayer structure may be used. On the other hand, the lower electrode 45 is made of an electrode material that is in ohmic contact with the substrate region 41. Examples of the electrode material to be ohmic-connected include nickel silicide and titanium material, and the lower electrode 45 is connected to an external electrode as a cathode terminal 402. 27 functions as a vertical diode in which the upper electrode 44 is an anode electrode and the lower electrode 45 is a cathode electrode.

On the other hand, as shown in FIG. 28, switching element 600 shows a MOSFET made of silicon carbide as an example. In FIG. 28, for example, the substrate material is made of a substrate material in which an n ⁻ type drift region 52 is formed on an n ⁺ type substrate region 51 whose polytype of silicon carbide is 4H type. As the substrate region 51, for example, a substrate having a resistivity of several meters to several tens of mΩcm and a thickness of several to several hundreds μm can be used. As the drift region 52, for example, an n-type impurity density of 10 ¹⁴ to 10 ¹⁷ cm ⁻³ and a thickness of several to several tens of μm can be used. Of course, the resistivity, impurity density, and thickness may be out of the above ranges depending on the element structure and the required breakdown voltage.However, in general, the smaller the resistivity and thickness, the lower the conduction loss. It is desirable to make it smaller. In the third embodiment of the present invention, the case where an impurity density of 2 × 10 ¹⁶ cm ⁻³ , a thickness of 5 μm and a breakdown voltage of 600 V class is used will be described. In the third embodiment of the present invention, the case where the substrate region 51 is used as a support base material is described as an example, but the drift region 52 may be used as a support base material.

A p-type well region 53 is formed in the surface layer portion of the drift region 52, and an n ⁺ -type source region 54 is formed in the surface layer portion of the well region 53. A gate electrode 56 made of, for example, n-type polycrystalline silicon is disposed through a gate insulating film 55 made of, for example, a silicon oxide film so as to be in contact with the surface layer portions of the drift region 52, the well region 53, and the source region 54. Has been. Further, a source electrode 57 made of, for example, an aluminum material is formed so as to be in contact with the source region 54 and the well region 53. An interlayer insulating film 58 made of, for example, a silicon oxide film is formed between the source electrode 57 and the gate electrode 56 so as not to contact each other. A drain electrode 59 is formed so as to be in ohmic contact with the substrate region 51. Thus, the MOSFET used in this description is a so-called planar type in which the gate electrode 56 is formed on a plane with respect to the semiconductor substrate.

  Also in the third embodiment, the free wheeling diode 100 shown in FIG. 27 and the switching element 600 shown in FIG. 28 are used in parallel with the semiconductor snubber 200 shown in FIG. 4, but the snubber function is effective. In order to achieve this, it is desirable that the capacitor C is set by the capacitor dielectric film 12 and the resistance R is set by the substrate region 11 in consideration of the capacitor capacity when the freewheeling diode 100 and the switching element 600 are cut off. Similar to the first embodiment and the second embodiment, in the third embodiment of the present invention, for example, the thickness is set to 1 μm so as to be higher than the breakdown voltage of the freewheeling diode 100 and the switching element 600, for example. The case where the capacitor C having the same capacity as the sum of the depletion capacities formed when the free-wheeling diode 100 and the switching element 600 are cut off will be described. Also in the third embodiment of the present invention, as described in the first embodiment, since the capacitance lowering prevention region 1001 is formed, the capacitance of the capacitor C is almost equal to the capacitor dielectric film 12. It is determined by the capacitor capacity.

  Next, the operation of the third embodiment of the present invention will be described in detail in correspondence with the operation of the inverter shown in FIG. 7, for example, as in the second embodiment.

  First, when the switching elements E4, E5, and E6 in FIG. 7 are turned on and a current flows through the switching elements E4, E5, and E6, the upper-arm switching elements E1, E2, and E3 and the passive elements B1, B2 , B3 is in a reverse bias state and is in a cut-off state.

  First, since the switching elements E4, E5, and E6 in the conductive state of the lower arm are composed of MOSFETs made of silicon carbide material, they are conductive with lower on-resistance than the IGBT described in the second embodiment. can do. This is because the band gap of the silicon carbide material is about three times larger than that of the silicon material and the maximum insulating electric field is about one digit larger, so that the thickness and the impurity concentration can be increased in the drift region 52. For this reason, the resistance of the drift region 52 can be lowered without the bipolar operation like the IGBT.

  In addition, in the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 in the conductive state of the lower arm, the freewheeling diode 100 and the semiconductor snubber 200 maintain the cut-off state. That is, the reverse junction voltage is applied to the heterojunction diode shown in FIG. 27, which is the freewheeling diode 100, although the voltage applied to both ends thereof is as low as the ON voltage of the switching elements E4, E5, E6. is there. Further, in the semiconductor snubber 200 shown in FIG. 4, since the capacitor dielectric film 12 functioning as the capacitor C operates only when the voltage changes, the voltage about the ON voltage of the switching elements E4, E5, E6 is in a steady state. In the applied state, it becomes a cut-off state.

  On the other hand, the switching elements E1, E2, E3 and the passive elements B1, B2, B3 on the upper arm are also maintained in the cut-off state because a reverse bias voltage of about the power supply voltage is applied. That is, in the MOSFET that is the switching element 600 shown in FIG. 28, since a reverse bias voltage is applied between the source terminal 302 and the drain terminal 402, the drift region 52 extends from the pn junction with the well region 53. This is because a depletion layer is formed and the blocking state is maintained. In the heterojunction diode, which is the freewheeling diode 100 shown in FIG. 27, a reverse bias voltage is applied between the upper electrode 44 and the lower electrode 45, so that the heterojunction between the hetero semiconductor region 43 and the drift region 42 is provided. As a result, a depletion layer extending from is formed, and the cut-off state is maintained. Also in the semiconductor snubber 200 shown in FIG. 4, the capacitor dielectric film 12 functioning as the capacitor C is charged with a high voltage, and the cut-off state is maintained.

  As described above, when the switching elements E4, E5, and E6 of the lower arm are in the conductive state, the passive elements of both the upper and lower arms have the same function as that of the conventional technique configured in the second embodiment.

  Next, a case where the switching elements E4, E5, and E6 of the lower arm are turned off to shift to the cutoff state will be described.

  For example, in a motor inverter circuit (L load circuit) as shown in FIG. 7, when the switching elements E4, E5, E6 are turned off, the phases of voltage rise and current interruption are shifted, so that the current during conduction is substantially maintained. In this state, first, the voltage rise of the switching elements E4, E5, E6 occurs.

  First, for the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 that turn off the lower arm, both the freewheeling diode 100 and the semiconductor snubber 200 increase the voltage of the switching elements E4, E5, and E6. Along with this, since the reverse bias voltage as low as the ON voltage changes from the reverse bias voltage as high as the power supply voltage, a transient current corresponding to the speed of the voltage change flows. That is, in the free-wheeling diode 100 shown in FIG. 3, when a depletion layer spreads from the hetero semiconductor region 43 side in the drift region 42 as the voltage increases, electrons flow as a transient current to the lower electrode 45 side. In the semiconductor snubber 200 shown in FIG. 2, a transient current flows because the capacitor dielectric film 12 acting as a capacitor capacitance is charged according to the applied voltage. The charging action of the capacitor capacitance of the capacitor dielectric film 12 of the semiconductor snubber 200 alleviates a transient voltage rise generated between the collectors / emitters of the switching elements E4, E5, E6, and is caused by the parasitic inductance included in the circuit. Generation of a surge voltage can be suppressed. That is, in the third embodiment of the present invention, the switching element 600 is also connected in parallel, so that even when the switching element 600 itself performs a turn-off operation, element destruction, malfunction to other peripheral circuits, and the like are caused. Surge voltage can be reduced.

  In the MOSFET made of silicon carbide cited as an example in the third embodiment of the present invention, the current is sharply interrupted after the voltage rises. Unlike the IGBT described in the second embodiment, this is a unipolar operation during conduction, so that the electron current discharged from the depletion layer due to the voltage rise depends on the extension speed of the depletion layer. This is because it is blocked. In other words, although the switching element 600 is a MOSFET made of silicon carbide, a low on-resistance can be realized when conducting, but the switching element 600 itself is easily turned off due to the fast shutoff performance of the switching element 600. Furthermore, since the resistance is smaller, there is a problem that the vibration phenomenon is hardly attenuated. However, since the semiconductor snubber 200 is formed in parallel in the third embodiment of the present invention, it is effective. The vibration phenomenon can be alleviated.

  That is, in the third embodiment of the present invention, when the current of the switching element 600 is cut off, it resonates with the parasitic inductance in the circuit and the oscillation phenomenon starts in the current and voltage, but the capacitor in the semiconductor snubber 200 An equivalent voltage is also applied to the capacitor C made of the dielectric film 12, and a corresponding transient current starts to flow. Then, the capacitor C and the resistor R alleviate the slope (dI / dt) of the current vibration and consume the energy generated by the parasitic inductance Ls by the resistance R component of the substrate region 11, so that the vibration phenomenon can be quickly converged. . Therefore, as in the third embodiment of the present invention, even when the switching element 600 is a unipolar type and has a high-speed cutoff performance, the vibration phenomenon can be suppressed. In addition, even if the switching element is made of a wide gap semiconductor having a smaller conduction loss and is difficult to attenuate for the vibration phenomenon, the vibration phenomenon can be easily attenuated without deteriorating the conduction loss. As described above, in the third embodiment of the present invention, the switching element 600 also has a configuration that can achieve both a conduction loss and a transient loss at a high level, that is, a unipolar type capable of high-speed operation and a low on-state. By combining with the configuration of a wide band gap semiconductor that can realize resistance, a higher effect can be obtained.

  Then, after the current of the switching element 600 is cut off, the switching elements E4, E5, E6 and the passive elements B4, B5, B6 of the lower arm are in a steady off state and maintain the cut-off state.

  On the other hand, the passive elements B1, B2, and B3 connected in parallel with the switching elements E1, E2, and E3 of the upper arm are in a forward bias state in conjunction with the turn-off operation of the switching elements E4, E5, and E6 of the lower arm. Transition to the conductive state. The depletion layer that has spread into the drift region 42 of the free-wheeling diode 100 shown in FIG. 27 recedes, and the heterojunction formed between the hetero semiconductor region 43 and the drift region 42 is ordered according to the height of the hetero barrier. When the bias voltage is applied, the freewheeling diode 100 becomes conductive. A heterojunction diode has a large heterobarrier against holes on the valence band side, although a forward current flows with a voltage drop determined by the sum of built-in potentials spreading from the heterojunction to the drift region 42 side and the hetero semiconductor region 43 side. The current is constituted only by the electron current supplied from the side of the lower electrode 45 in the drift region 42, and performs a unipolar operation. At this time, in the Schottky barrier diode described in the second embodiment, the Schottky barrier height is uniquely determined by the work function difference unique to the Schottky metal of the upper electrode 13, so that a predetermined breakdown voltage is obtained. While the impurity concentration and thickness of drift region 13 are limited, in the third embodiment of the present invention, the hetero barrier can be changed by controlling the impurity concentration of hetero semiconductor region 43. The resistance of the drift region 42 can be made lower. That is, loss during conduction can be further reduced.

  In the semiconductor snubber 200 shown in FIG. 4, when the freewheeling diode 100 shifts from the reverse bias state to the forward bias state, the charge charged in the capacitor dielectric film 12 is discharged as a transient current. In the third embodiment of the present invention, the capacitance of the capacitor dielectric film 12 as the capacitor C is as small as the depletion capacitance formed in the free-wheeling diode 100 and the switching element 600, and thus flows by discharge. Although the transient current flows, it has a magnitude that hardly affects the forward bias current flowing in the parallel free-wheeling diode 100. The semiconductor snubber 200 shifts to a steady state after the transient current flows, and the current is cut off. In addition, for the switching elements E1, E2, and E3 connected in parallel, the gate signal is controlled to maintain the off state, although the drain / source voltage shifts from the reverse bias voltage state to the forward bias state. In addition, although the pn junction between the well region 53 and the drift region 52 is in the forward bias state, the off-state is maintained because the built-in potential is as large as 2 to 3V. However, since the voltage state between the drain and the source is displaced, a transient current due to the discharge as the capacitor C accompanying the capacitance change of the depletion layer generated in the drift region 52 in the switching element 600 flows, but the semiconductor snubber 200 and Similarly, the magnitude is almost insignificant compared to the forward bias current flowing through the freewheeling diodes 100 in parallel. Thus, since the semiconductor snubber 200 and the switching element 600 of the upper arm transition to a steady state after the transient current flows and the current is cut off, only the freewheeling diode 100 is in a conductive state.

  Next, an operation in which the switching elements E4, E5, and E6 of the lower arm are turned on and the switching elements E4, E5, and E6 are turned on again will be described.

  For example, in a motor inverter circuit (L load circuit) as shown in FIG. 7, when the switching elements E4, E5, and E6 are turned on, the phases of current rise and voltage drop are shifted, so a relatively high voltage is applied. In this state, current starts to flow through the switching elements E4, E5, E6. For the passive elements B4, B5, and B6 connected in parallel to the switching elements E4, E5, and E6 that turn on the lower arm, the current flows through the switching elements E4, E5, and E6 in both the free wheel diode 100 and the semiconductor snubber 200, As the drain-source voltage drops, the reverse bias voltage, which is as high as the power supply voltage, changes from the reverse bias voltage, which is as low as the on-voltage, so the transient current corresponding to the speed of the voltage change Flowing. At this time, in the free-wheeling diode 100 shown in FIG. 27, the depletion layer that has spread in the drift region 42 as the voltage decreases gradually narrows to the hetero semiconductor region 43 side, and enters the drift region 42 from the lower electrode 45 side. Electrons flow as transient currents. In the semiconductor snubber 200 shown in FIG. 4, a transient current flows because the capacitor dielectric film 12 serving as a capacitor capacitance is discharged as the applied voltage decreases. This transient current has a magnitude that hardly affects the turn-on current flowing through the switching elements 600 arranged in parallel. Thus, since the semiconductor snubber 200 and the freewheeling diode 100 in the lower arm transition to a steady state after the transient current flows and the current is cut off, only the switching element 600 becomes conductive.

  On the other hand, the passive elements B1, B2, B3 connected in parallel with the switching elements E1, E2, E3 of the upper arm are in a reverse bias state in conjunction with the turn-on operation of the switching elements E4, E5, E6 of the lower arm. Transition to the shut-off state. In the heterojunction diode, which is the freewheeling diode 100 shown in FIG. 27, the electron current supplied from the lower electrode 45 side into the drift region 42 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the hetero barrier height of the heterojunction portion, and when the reverse bias voltage is further applied to the heterojunction portion, the drift region 42 is heterogeneous with the hetero semiconductor region 43. A depletion layer extending from the junction is generated, and the state shifts to a cutoff state.

  Since the third embodiment of the present invention has a unipolar operation as in the Schottky barrier diode described in the first and second embodiments, it is formed of general silicon. This reverse recovery current is much smaller than the pn junction diode made. That is, reverse recovery loss can be greatly reduced.

  Furthermore, in the third embodiment of the present invention, by combining the semiconductor snubber 200 with a heterojunction diode capable of reducing conduction loss as compared with a Schottky barrier diode, both conduction loss and transient loss can be achieved at a high level. Can do. That is, in the third embodiment of the present invention, when the freewheeling diode 100 performs reverse recovery operation, a reverse bias voltage is applied in the drift region 42 and a reverse recovery current composed of excess carriers starts to flow. At substantially the same time, an equivalent reverse bias voltage is applied to the capacitor C formed of the capacitor dielectric film 12 in the switching element 600 and the semiconductor snubber 200, and a corresponding transient current starts to flow in the switching element 600 and the semiconductor snubber 200. In the third embodiment of the present invention, the size of the capacitor C is set with a capacity that is substantially equal to the transient current flowing through the freewheeling diode 100 and the switching element 600, so that the switching element of the lower arm The reverse recovery current cutoff speed (dI / dt) can be relaxed without substantially changing the switching speed of E4, E5, and E6. Furthermore, since the current flowing through the semiconductor snubber 200 is consumed by the resistance R component of the substrate region 11, energy generated by the parasitic inductance Ls can be absorbed and the vibration phenomenon can be quickly converged. In other words, even when the freewheeling diode 100 becomes a heterojunction diode and the conduction loss is reduced, as in the case where the Schottky barrier diode described in the second embodiment is used, the fundamental vibration phenomenon unique to the unipolar operation is observed in the semiconductor. The snubber 200 can solve this.

Therefore, a higher effect can be obtained by combining with a heterojunction diode capable of realizing a low on-resistance.
Also in the third embodiment of the present invention, paying attention to the fact that the transient current flowing through the freewheeling diode 100 and the switching element 600 is only the carriers generated when the depletion layer is formed in the drift regions 42 and 52 at most, The point where the snubber circuit is formed by the semiconductor snubber 200 is different from the conventional technique.

  Further, since the switching element is also a unipolar type as in the configuration of the third embodiment of the present invention, not only when the freewheeling diode 100 performs reverse recovery operation, but also when the switching element 600 is turned off, The snubber function works effectively in the entire current range and temperature range.

  As described above, the switching element 600 can obtain the same effect by using other unipolar elements as shown in FIGS. 29 and 30 in addition to the MOSFET.

FIG. 29 shows an example in which an n ⁻ type drift region 62 is formed on an n ⁺ type substrate region 61 of, for example, a silicon carbide polytype of 4H type, and the drift region 62 faces the junction surface with the substrate region 61. A hetero semiconductor region 63 made of, for example, n-type polycrystalline silicon is formed so as to be in contact with the surface. That is, the junction between the drift region 62 and the hetero semiconductor region 63 is made of a hetero junction made of materials having different band gaps between silicon carbide and polycrystalline silicon, and an energy barrier exists at the junction interface. A gate insulating film 64 made of, for example, a silicon oxide film is formed so as to be in contact with the junction surface between the hetero semiconductor region 63 and the drift region 62 together. Further, the gate electrode 65 is connected to the gate insulating film 64, the source electrode 66 is connected to the opposite surface of the hetero semiconductor region 63 facing the drift region 62, and the drain electrode 68 is connected to the substrate region 1. Is formed. An interlayer insulating film 67 made of, for example, a silicon oxide film is formed so as to insulate the gate electrode 65 and the source electrode 66 from each other.

  Next, the operation of the switching element of FIG. 29 will be described. The switching element of FIG. 29 is also used so that the source electrode 66 is grounded and a positive potential is applied to the drain electrode 68, as in the MOSFET.

  First, when the gate electrode 65 is set to a ground potential or a negative potential, for example, the cutoff state is maintained. That is, an energy barrier against conduction electrons is formed at the heterojunction interface between the hetero semiconductor region 63 and the drift region 62.

  Next, when a positive potential is applied to the gate electrode 65 so as to shift from the cut-off state to the conductive state, electrons are accumulated in the surface layer portions of the hetero semiconductor region 63 and the drift region 62 to which the gate electric field is applied via the gate insulating film 64. A layer is formed. Then, in the surface layer portion of the hetero semiconductor region 63 and the drift region 62, a potential at which free electrons can exist is present, the energy barrier extending toward the drift region 62 becomes steep, and the energy barrier thickness is reduced. As a result, the electronic current is conducted. In this case, in the switching element shown in FIG. 29, the length of the so-called channel portion that controls the conduction / cutoff of the current is about the thickness of the energy barrier formed by the hetero barrier, and is a predetermined required for holding the breakdown voltage in the MOSFET. Therefore, it is possible to conduct with a lower resistance. For this reason, as described above, the semiconductor snubber 200 can achieve both a conduction loss and a transient loss at a higher level.

  Next, in the third embodiment of the present invention, when the gate electrode 65 is set to the ground potential again in order to shift from the conductive state to the cut-off state, the heterojunction interface between the hetero semiconductor region 63 and the drift region 62 is formed. The accumulated state of conduction electrons is released, and tunneling in the energy barrier stops. Then, when the flow of conduction electrons from the hetero semiconductor region 63 to the drift region 62 stops and the conduction electrons existing in the drift region 62 flow to the substrate region 61 and are depleted, the drift region 62 side has a depletion layer from the heterojunction portion. Spreads and becomes a cut-off state.

  In the switching element of FIG. 29, for example, reverse conduction (reflux operation) in which the source electrode 66 is grounded and a negative potential is applied to the drain electrode 68 is also possible.

  For example, when the source electrode 66 and the gate electrode 65 are set to the ground potential and a predetermined positive potential is applied to the drain electrode 68, the energy barrier to the conduction electrons disappears, and conduction electrons are transferred from the drift region 62 side to the hetero semiconductor region 63 side. Flow and reverse conducting state. At this time, since there is no injection of holes and conduction is performed only with conduction electrons, loss due to reverse recovery current when shifting from the reverse conduction state to the cutoff state is small. Note that the above-described gate electrode 65 may be used as a control electrode without being grounded. 29 can be used as a unipolar freewheeling diode, for example, the freewheeling diode 100 can be shared by the switching element of FIG. That is, in the switching element shown in FIG. 29, in addition to forming the freewheeling diode 100 as a separate chip, the freewheeling diode 100 and the switching element 600 can be made into one chip, and the semiconductor package can be downsized. As a result, the parasitic inductance generated in the wiring or the like can be further reduced, so that the vibration phenomenon caused by the semiconductor snubber 200 can be further reduced. In addition, shortening the wiring length has an effect of reducing radiation noise generated from the wiring due to the oscillating current. Further, the cost is reduced by reducing the chip size, and the sum of the capacitor capacities of the freewheeling diode 100 and the switching element 600 is reduced, so that the capacitor capacity C required for the semiconductor snubber 200 can also be reduced. That is, the vibration phenomenon can be suppressed with a small size and low cost.

As described above, in FIG. 29, the example in which polycrystalline silicon is used as the material used for the hetero semiconductor region 63 has been described. However, as long as the material forms a heterojunction with silicon carbide, other materials such as single crystal silicon and amorphous silicon are used. Any material such as silicon materials, other semiconductor materials such as germanium and silicon germanium, and other polytypes of silicon carbide such as 6H and 3C may be used. In addition, as an example, n-type silicon carbide is used as the drift region 62 and p-type polycrystalline silicon is used as the hetero semiconductor region 63. However, n-type silicon carbide and p-type polycrystalline silicon are used, respectively. Any combination of p-type silicon carbide and p-type polycrystalline silicon, or p-type silicon carbide and n-type polycrystalline silicon may be used.

  Next, FIG. 30 illustrates a case where a junction FET called a junction field effect transistor (JFET) is used as a switching element.

In Figure 30, for example polytype of silicon carbide n on the substrate region 71 and n ⁺ -type 4H types ^- type drift region 72 is formed, n ⁺ -type source region 73 and p-type gate region 74 The gate region 74 is connected to the gate electrode 75, the source region 73 is connected to the source electrode 76, and the substrate region 71 is connected to the drain electrode 78. Reference numeral 77 denotes an interlayer insulating film.

  Since the JFET of FIG. 30 performs a unipolar operation like the MOSFET, it is possible to obtain the same effect as that obtained by the MOSFET. Further, in the JFET, an essential gate insulating film is unnecessary in the MOSFET, so that operation at a high temperature exceeding 200 ° C. is relatively easy from the viewpoint of ensuring reliability. From this, by using JFET, the effect which can suppress a vibration phenomenon irrespective of the use temperature range which is the characteristics of this invention can be utilized as a strength more. In high temperature applications, the semiconductor snubber 200 can also exhibit the effect while ensuring reliability, for example, the configuration using a depletion capacitor that does not use a silicon oxide film as a capacitor capacitor as shown in FIGS. .

As described above, the effect when the switching element other than the MOSFET is used for the switching element 600 has been described. However, the same effect can be obtained for the freewheeling diode 100 as long as the diode operates in a unipolar operation or a unipolar operation. Can be obtained.

  For example, even in the structure of a pn junction diode as shown in FIG. 31, excess carriers made up of fractional carriers injected from the p-type region during conduction, heavy metal diffusion using gold or platinum, and electrons using an electron beam By controlling the lifetime of minority carriers, which are the main components of excess carriers, by measures such as ion irradiation using proton irradiation and protons, it is applicable even when the operation is almost equivalent to unipolar operation. The effects described as the embodiments of the present invention can be obtained in the same way.

For example, the case where the pn junction diode shown in FIG. 31 is configured by a soft recovery diode will be described. As shown in FIG. 31, the freewheeling diode 100 is made of a substrate material in which an n ⁻ type drift region 82 is formed on an n ⁺ type substrate region 81 made of, for example, silicon. As the substrate region 81, for example, a substrate having a resistivity of several meters to several tens of mΩcm and a thickness of several tens to several hundreds of μm can be used. As the drift region 82, for example, an n-type impurity density of 10 ¹³ to 10 ¹⁷ cm ⁻³ and a thickness of several to several hundred μm can be used. In the third embodiment of the present invention, a case where an impurity density of 10 ¹⁴ cm ⁻³ , a thickness of 50 μm and a breakdown voltage of 600 V class is used will be described. In the third embodiment of the present invention, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 81 and the drift region 82 will be described. However, the magnitude of resistivity does not depend on the above example. A substrate formed of only the substrate region 81 may be used, or a multilayer substrate may be used. In the third embodiment of the present invention, the breakdown voltage is 600 V class as an example, but the breakdown voltage class is not limited.

  A p-type opposite conductivity type region 83 is formed so as to be in contact with the main surface of the drift region 82 facing the bonding surface with the substrate region 81, and the upper electrode 84 is connected to the opposite conductivity type region 83 so that the substrate electrode 81 is connected to the opposite conductivity type region 83. A lower electrode 85 is formed so as to be in contact with. Although the free wheeling diode shown in FIG. 31 is formed only by a pn junction, for example, a part may be configured to function as a Schottky diode, or may include other configurations.

  As one method for causing the pn junction diode shown in FIG. 31 to function as a soft recovery diode, for example, there is a method of controlling the lifetime of minority carriers injected into the drift region 82 during conduction. For example, by using ion irradiation or the like in the drift region 82, the minority carrier lifetime is controlled to be different between the side close to the opposite conductivity type region 83 and the side close to the substrate region 81, and the minority flowing during reverse recovery. While the transient current due to the carriers is reduced, the decrease time of the minority carriers staying on the substrate region 81 side can be relaxed, and the vibration phenomenon can be prevented from occurring in the reverse recovery operation at a large current.

  However, in a pn junction diode in which the minority carrier lifetime is controlled, the minority carrier lifetime is shortened regardless of the magnitude of the current. Therefore, when the current is small, minority carriers disappear instantaneously during reverse recovery. Therefore, the operation is almost the same as the unipolar operation. In this case, since the transient current flowing through the diode shown in FIG. 31 flows due to the movement of majority carriers when the depletion layer spreads as in the unipolar diode described with reference to FIG. 3 and the like, there is no semiconductor snubber 200 Then, a vibration phenomenon occurs. However, as in the third embodiment of the present invention, the semiconductor snubber 200 can be connected in parallel to alleviate the vibration phenomenon at low currents. That is, the vibration phenomenon can be alleviated by a combination of the soft recovery diode and the semiconductor snubber at both a large current and a small current. Here, the effect of the embodiment of the present invention has been described using a soft recovery diode as an example. However, even when a fast recovery diode whose reverse recovery characteristics are not softened at a large current is used, it is equivalent to the unipolar operation. If there is a current region in which the above operation is performed, at least an effect of suppressing a vibration phenomenon at a low current can be obtained. In addition, in a material that is less likely to recover crystals due to heat treatment than a silicon material, such as a pn junction diode made of silicon carbide, the minority carrier lifetime is originally small, for example, when a p-type region is formed by ion implantation. Also in the diode, as described above, the effect of suppressing the vibration phenomenon can be obtained. In any structure, the effect of the present invention can also be obtained when the pn junction diode is reversely recovered under the condition that at least current does not flow and minority carriers are not injected.

  Thus, if the diode has at least a part of the operation equivalent to the unipolar operation, the effect of the present invention can be obtained that the vibration phenomenon is reduced during the reverse recovery operation.

  31 has the same effect even when the switching element shown in the first embodiment is not connected in parallel. Therefore, only the free-wheeling diode 100 and the semiconductor snubber 200 are connected in parallel. Also good.

  Furthermore, in the third embodiment, the free wheel diode 100 and the switching element 600 described in the second embodiment have been described in different combinations, but any combination of the free wheel diode 100 and the switching element 600 is combined. May be. That is, for example, the freewheeling diode 100 may use the Schottky barrier diode described in the second embodiment, and the switching element 600 may be combined with the MOSFET described in the third embodiment. Further, the reflux diode 100 and the switching element 600 may be formed on the same chip.

  Further, as described with reference to FIGS. 21 and 22 in the first embodiment, the size of the capacitor capacitance C used in the snubber circuit is the capacitance of the capacitor capacitance component of the free-wheeling diode and the switching element in the cutoff state. With respect to the sum C0, the damping effect of the vibration phenomenon becomes significant when C / C0 is around 0.1, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when C / C0 exceeds 10. In addition, the capacitor capacitance C formed in the snubber circuit generates a loss E due to a transient current proportional to the size of the capacitor capacitance C during transient operation. Therefore, it is desirable that the size of the capacitor capacitance C be as small as possible.

  Therefore, the size of the capacitor capacitance C of the snubber circuit used in the third embodiment of the present invention is 1/10 times the total capacitance of the capacitor components in the cutoff state of the free-wheeling diode 100 and the switching element 600. By selecting the capacitance within the range of 10 times or less, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the examples described in the above embodiment.

(Fourth embodiment)
In the fourth embodiment of the present invention, the case where the free wheel diode 100 and the semiconductor snubber 200 are formed on one chip in the circuit diagram shown in FIG. 1 of the first embodiment will be exemplified.

  32 is a mounting diagram of the semiconductor chip corresponding to FIG. 2, and FIG. 33 is an example of a cross-sectional structure diagram of the semiconductor chip used in the mounting diagram of FIG. That is, in the cross-sectional structure diagram shown in FIG. 33, the free-wheeling diode 100 and the semiconductor snubber 200 are formed. In the fourth embodiment of the present invention, the description of the same operation as in the first embodiment is omitted, and different features will be described in detail.

  As shown in FIG. 32, on the cathode side metal film 410, the cathode terminal 400 side of the semiconductor snubber built-in reflux diode 800 is disposed so as to be in contact via a bonding material such as solder or brazing material. Then, the anode terminal 300 side of the semiconductor chip of the semiconductor snubber built-in reflux diode 800 is connected to the anode-side metal film 310 via a metal wiring 320 such as an aluminum wire or an aluminum ribbon.

  Moreover, the cross-sectional structure of the semiconductor chip constituting the semiconductor snubber built-in reflux diode 800 is shown in the cross-sectional structure diagram of FIG.

  As shown in FIG. 33, the semiconductor snubber built-in freewheeling diode 800 is composed of a part of the freewheeling diode 100 formed on the right side of the right broken line and a part of the semiconductor snubber 200 formed on the left side of the left broken line.

First, the part of the freewheeling diode 100 is made of a substrate material in which an n ⁻ type drift region 2 is formed on an n ⁺ type substrate region 1 of, for example, silicon carbide whose polytype is 4H type. As the substrate region 1, for example, one having a resistivity of several meters to several tens of mΩcm and a thickness of several tens to several hundreds of μm can be used. As the drift region 2, for example, an n-type impurity density of 10 ¹⁵ to 10 ¹⁸ cm ⁻³ and a thickness of several to several tens of μm can be used. In the fourth embodiment of the present invention, for example, an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class will be described. In the fourth embodiment of the present invention, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 1 and the drift region 2 will be described. However, the magnitude of the resistivity depends on the above example. It is possible to use a substrate formed only of the non-substrate region 1, or a multilayer substrate. In the fourth embodiment of the present invention, the breakdown voltage is 600 V class as an example, but the breakdown voltage class is not limited.

  33, the upper part of the free-wheeling diode 100 formed on the right side of the broken line on the right side is in contact with the main surface of the drift region 2 facing the junction surface with the substrate region 1, and the upper electrode 3 is further in contact with the main surface. A lower electrode 4 is formed so as to face the substrate region 1. The upper electrode 3 is made of a single-layer or multi-layer metal material including at least a metal material that forms a Schottky barrier between the upper electrode 3 and the drift region 2. For example, the metal material that forms the Schottky barrier includes titanium. (Ti), nickel (Ni), molybdenum (Mo), gold (Au), platinum (Pt), or the like can be used. Further, the upper electrode 3 is connected to an external electrode as the anode terminal 300, and the outermost surface is made of a metal such as aluminum (Al), copper (Cu), gold (Au), nickel (Ni), silver (Ag), or the like. A multilayer structure may be used by using a material. On the other hand, the lower electrode 4 is made of an electrode material that is in ohmic contact with the substrate region 1. As an example of an electrode material for ohmic connection, nickel silicide, titanium material, or the like can be cited, and the lower electrode 4 is connected to an external electrode as a cathode terminal 400. Thus, the free-wheeling diode 100 shown in FIG. 33 functions as a diode in which the upper electrode 3 is an anode electrode and the lower electrode 4 is a cathode electrode. Further, in FIG. 33, a field insulating film 5 made of, for example, a silicon oxide film is formed at the end of the joint surface between the drift region 2 and the upper electrode 3 so as to be in contact with the drift region 2 and the upper electrode 3, respectively. Yes. The field insulating film 5 is a structure that is generally used when the free-wheeling diode 100 is manufactured as a semiconductor chip, for example, to alleviate electric field concentration at the Schottky junction on the outer periphery of the chip. In the fourth embodiment of the present invention, as an example of the shape of the end portion of the field insulating film 5 shown in FIG. 33, the portion in contact with the upper electrode is perpendicular, but the end portion has an acute angle shape. Of course it is good. Further, as a configuration of the outer peripheral end portion where the field insulating film 5 is formed, for example, as shown in FIG. 34, a p-type electric field relaxation region is formed in a portion where the upper electrode 3 and the field insulating film 5 are in contact with each other in the drift region 2. 7 may be formed. Furthermore, in addition to the configuration of FIG. 34, one or more guard rings may be formed so as to surround the outer periphery of the electric field relaxation region 7.

Next, the configuration of the semiconductor snubber 200 formed on the left side of the broken line in FIG. 33 will be described. The surface layer portion of the substrate region 1 has the same conductivity type as that of the substrate region 1 so as to be in contact with a predetermined region of the field insulating film 5 used for electric field relaxation at the outer peripheral end portion of the reflux diode 100. In addition, an n ⁺ -type capacity lowering prevention region 1001 having an impurity density equal to or higher than that is formed. On the field insulating film 5, a resistance region 6 made of, for example, n-type polycrystalline silicon is formed. Further, an n ⁺ -type capacitance lowering prevention region 1005 having the same conductivity type as that of the resistance region 6 and having an impurity density equal to or higher than that of the resistance region 6 is formed in the surface layer portion of the resistance region 6. Further, the upper electrode 3 is formed on the capacity decrease prevention region 1005 and has the same potential as the anode terminal 300 of the free-wheeling diode 100. That is, in the semiconductor snubber 200 according to the fourth embodiment of the present invention, the substrate region 1 and the resistor region 6 function as the resistor R, and the field insulating film 5 functions as the capacitor C. The configuration corresponds to FIG. 18 in the embodiment. The resistance region 6 can be changed in impurity concentration and thickness in accordance with the required resistance value. At this time, as shown in the first embodiment, it is possible to easily adjust by changing the thickness or area of any one of the capacity drop prevention regions 1001 and 1005. Also, the thickness and area of the field insulating film 5 can be determined according to the required breakdown voltage and the required capacitance of the capacitor C. With respect to the withstand voltage, not only as a function of the semiconductor snubber 200 but also in order to satisfy the function of relaxing the electric field of the free-wheeling diode 100, in order to prevent the field insulating film 5 from being broken, High is desirable. The capacity of the capacitor C can be selected in a range from about 1/100 to about 100 times the depletion capacity charged when the freewheeling diode 100 is in a cutoff state (when a high voltage is applied). When a sufficient snubber function is exhibited, an increase in loss is suppressed as much as possible, and a necessary chip area is taken into consideration, a range of about 1/10 to about 10 times is desirable as shown in the calculation results described later. In the fourth embodiment of the present invention, as shown in the first embodiment, by forming the capacitance lowering prevention regions 1001 and 1005, the capacitor C formed by the dielectric capacitance made of the field oxide film 5 is formed. Since the operation can be performed without reducing the size, the vibration phenomenon can be easily damped optimally.

In the fourth embodiment of the present invention, for example, the thickness is set to 1 μm so that the breakdown voltage of the freewheeling diode 100 is higher than that of the Schottky barrier diode, and the capacitance of the capacitor C is formed when the freewheeling diode 100 is cut off. An explanation will be given for the case where the same capacity as the depletion capacity is used. The field insulating film 5 may be any material other than a silicon oxide film as long as it is a dielectric material that has a predetermined breakdown voltage and functions as an electric field relaxation function and a capacitor C. It is even better if the value of the product with the dielectric constant is larger than that of the silicon oxide film. When such a material is used, a necessary capacitance can be obtained with a small area while maintaining the dielectric strength of the capacitor dielectric film 12. For example, when a dielectric breakdown electric field is 1 × 10 9 V / m and a relative dielectric constant is 3.9 as a physical property value of a general silicon oxide film, per unit area 1 cm ² when the thickness of the silicon oxide film is 1 μm. The capacitance of is about 3.4 nF. On the other hand, when Si ₃ N ₄ is used instead of the silicon oxide film, the dielectric breakdown electric field is 1 × 10 ⁹ V / m and the relative dielectric constant is 7.5. Can be secured. At this time, the capacitance per 1 cm ² of unit area when Si ₃ N ₄ is used is about 6.6 nF. As described above, the use of Si ₃ N ₄ increases the capacitance by about twice, and a larger capacitance can be obtained while maintaining the withstand voltage of the capacitor dielectric film. Accordingly, the area efficiency can be improved and the wafer cost can be reduced. This effect can be compared by the product of the dielectric breakdown electric field and the relative dielectric constant of the dielectric material, and the value of the silicon oxide film and the value of Si ₃ N ₄ are approximately doubled. Further, when the capacitor dielectric film is made of a ferroelectric material such as BaTiO ₃ , the value is about 13 times that of the silicon oxide film, and the area can be reduced. In addition, the capacitor dielectric film is not limited to a single dielectric material, and may be a laminate of a plurality of dielectric materials. For example, in the ONO structure sandwiching _Si 3 _{N 4} in silicon oxide film, a leakage current the _Si 3 _{N 4} can be minimized by the silicon oxide film.

  The resistance R of the resistance region 6 is preferably set so as to satisfy a general design formula C = 1 / (2πfR) that effectively exhibits a snubber function.

  As described above, even when the freewheeling diode 100 and the semiconductor snubber 200 are formed on one chip, the operations and effects described in the first embodiment can be obtained.

  Furthermore, in the fourth embodiment of the present invention, the free-wheeling diode 100 and the semiconductor snubber 200 share the substrate region 1 and the drift region 2 as the supporting base, and the upper electrode 3 and the lower electrode 4 are used as electrode materials. Shared. Furthermore, the field insulating film 5 that functions as the electric field relaxation function of the freewheeling diode 100 can also be shared as the function of the capacitor C. That is, since these portions can be formed by the same process, the manufacturing process can be simplified. In addition, since the mounting area (site area) can be reduced by using one chip, the semiconductor package can be reduced in size. Further, the free-wheeling diode 100 and the upper electrode 3 of the semiconductor snubber 200 serve as a common electrode, and the parasitic inductance generated in the wiring and the like is further reduced as compared with the case where the first embodiment is connected by the metal wirings 320 and 330. Therefore, the vibration phenomenon in the reflux diode 100 can be further reduced. Further, the shortening of the wiring length has an effect of further reducing radiation noise generated from the wiring due to the oscillating current. Furthermore, when the fourth embodiment of the present invention is used in an L load circuit, a new effect can be produced in which the freewheeling diode 100 and the semiconductor snubber 200 are integrated into one chip. That is, as has been described through the first to third embodiments, the semiconductor snubber 200 does not operate when the freewheeling diode 100 is cut off and conductive, and operates only during a transient state. The resistor R component generates heat to consume the depletion capacity and the transient current generated due to the capacitor capacity C of the semiconductor snubber 200. On the other hand, the freewheeling diode 100 does not generate much heat during the turn-on and turn-off transient operations due to the phase shift between the current and voltage. That is, the freewheeling diode 100 generates the most heat during steady conduction. That is, the timing of heat generation is different in a series of operations of the freewheeling diode 100, the semiconductor snubber 200, and the switching circuit. For this reason, by making the chip into one chip, for example, when the part of the freewheeling diode 100 is generating heat when conducting, the semiconductor snubber 200 part is in a cut-off state and does not generate heat. Compared to the case of the chip, it can be kept low. In other words, the conduction performance of the free-wheeling diode 100 can be improved by using one chip.

  As described above, according to the fourth embodiment of the present invention, both the effect of further suppressing the vibration phenomenon and improving the transient performance and the conduction performance can be improved, and at the same time, it can be realized in a small size and at a low cost.

  As described above, in FIG. 33 and FIG. 34, the case where the free wheel diode 100 is a Schottky barrier diode has been described. However, the heterojunction diode described in the third embodiment can be easily realized as well. FIG. 35 is a cross-sectional view corresponding to FIG.

  35, in addition to the heterojunction diode including the substrate region 41, the drift region 42, the p-type hetero semiconductor region 43, the upper electrode 44, and the lower electrode 45, the field insulating film 46 includes the drift region 42, the hetero semiconductor region 43, and the like. The drift region 42 and the hetero semiconductor region 43 are in contact with each other at the end of the junction surface. Further, a resistance region 47 made of, for example, polycrystalline silicon is formed on a predetermined region of the field insulating film 46. The upper electrode 44 is formed so as to be in contact with the resistance region 47 and has the same potential as the anode terminal 300 of the freewheeling diode 100. 35, similarly to FIG. 33, the shape of the end of the field insulating film 46 may be an acute angle shape, or a p-type electric field relaxation region may be formed as shown in FIG. One or a plurality of guard rings may be formed so as to surround the outer periphery of the electric field relaxation region.

  In addition, with respect to the operation of FIG. 35, it is possible to realize the unique effect described in the third embodiment and the effect when the chip is formed as described in the fourth embodiment of the present invention. Furthermore, the feature of FIG. 35 is that the resistance region 47 is formed of the same material as the hetero semiconductor region 43 of the free wheeling diode 100. With such a configuration, in addition to the effect of using a heterojunction diode as the freewheeling diode 100, the manufacturing process can be further simplified and realized at low cost.

  35 illustrates the case where the resistance region 47 is formed of the same p-type polycrystalline silicon as that of the hetero semiconductor region 43, so that the capacitance reduction is prevented in the resistance region 47 on the field oxide film 46 side. Region 1006 is formed. Although the positions to be formed are different, the same effects as those of the above-described configuration can be obtained.

  In addition, the freewheeling diode 100 and the semiconductor snubber 200 can be integrated into one chip with the configuration shown in FIGS.

  FIG. 36 differs from FIG. 33 in that the resistance R component of the semiconductor snubber 200 is configured by the low concentration drift region 8. The fourth embodiment of the present invention can be easily realized by forming the drift region 2 by introducing impurities and activating the impurities using, for example, a semiconductor material including the substrate region 1 and the low concentration drift region 8. The capacitance lowering prevention region 1001 is formed in the surface layer portion on the capacitor dielectric film side in the low concentration drift region 8. With such a configuration, even when the freewheeling diode 100 and the semiconductor snubber 200 are made into one chip, the semiconductor substrate can be used as a resistance component, and heat energy generated by the vibration phenomenon can be radiated through the semiconductor substrate. The resistance portion can be densified.

  FIG. 37 differs from FIG. 33 in that a pn junction diode having an operation equivalent to the unipolar operation shown in FIG. 31 is configured as the freewheeling diode 100 instead of the Schottky barrier diode. Also in the fourth embodiment of the present invention, as in FIG. 33, the one-chip configuration can be easily realized, the vibration phenomenon is further suppressed, the transient performance is improved, and the conduction performance is improved. And it can be realized at low cost.

  FIG. 38 differs from FIG. 37 in that the resistance R component of the semiconductor snubber 200 is configured by a low concentration drift region 88. The fourth embodiment of the present invention can be easily realized by forming the drift region 82 by introducing impurities and activating the impurities using, for example, a semiconductor material including a substrate region 81 and a low concentration drift region 88. With such a configuration, even when the freewheeling diode 100 and the semiconductor snubber 200 are made into one chip, the semiconductor substrate can be used as a resistance component, and heat energy generated by the vibration phenomenon can be radiated through the semiconductor substrate. The resistance portion can be densified.

  As described above, a plurality of configurations in which the freewheeling diode 100 and the semiconductor snubber 200 are made into one chip have been exemplified. However, in addition to the above examples, the combination of the freewheeling diode 100 and the semiconductor snubber 200 can be changed into one chip. Is of course good. Also, in the fourth embodiment of the present invention, the case where only the freewheeling diode 100 and the semiconductor snubber 200 corresponding to the first embodiment are connected in parallel has been exemplified, but the second embodiment In addition, the effect of the present invention can be similarly exhibited in a circuit in which the switching elements 800 as shown in the third embodiment are connected in parallel. In any case, at least the freewheeling diode 100 and the semiconductor snubber 200 are integrated into one chip, thereby further suppressing the vibration phenomenon and improving the transient performance and the conduction performance, and at the same time realizing a small size and low cost. can do.

  Further, as described with reference to FIG. 21 and FIG. 22 in the first embodiment, the size of the capacitor capacitance C used in the snubber circuit is the free-wheeling diode in the cut-off state or the capacitor of the free-wheeling diode and the switching element. The damping effect of the vibration phenomenon becomes significant when C / C0 is around 0.1 with respect to the total sum C0 of the capacitance components, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when C / C0 exceeds 10. . In addition, the capacitor capacitance C formed in the snubber circuit generates a loss E due to a transient current proportional to the size of the capacitor capacitance C during transient operation. Therefore, it is desirable that the size of the capacitor capacitance C be as small as possible.

  Therefore, the size of the capacitor capacitance C of the snubber circuit used in the fourth embodiment of the present invention is 1/10 times the total capacitance of the capacitor components in the cutoff state of the freewheeling diode 100 and the switching element 600. By selecting the capacitance within the range of 10 times or less, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the examples described in the above embodiment.

(Fifth embodiment)
In the fifth embodiment of the present invention, the case where the switching element 600 and the semiconductor snubber 200 are formed on one chip in the circuit diagram shown in FIG. 23 of the second embodiment will be exemplified.

  39 is a mounting diagram of a semiconductor chip corresponding to FIG. 24, and FIG. 40 is an example of a cross-sectional structure diagram of the semiconductor chip used in the mounting diagram of FIG. That is, in the cross-sectional structure diagram shown in FIG. 40, the switching element 600 and the semiconductor snubber 200 are formed. In the fifth embodiment of the present invention, the description of the same operation as in the second embodiment is omitted, and different features will be described in detail.

  As shown in FIG. 39, on the cathode side metal film 410, the collector terminal 401 side of the semiconductor snubber built-in switching element 900 is in contact with the cathode terminal of the reflux diode 100 through a bonding material such as solder or brazing material. Is arranged. The emitter terminal 301 side of the semiconductor chip of the semiconductor snubber built-in switching element 900 is connected to the anode side metal film 310 together with the anode terminal of the freewheeling diode 100 through a metal wiring 350 such as an aluminum wire or an aluminum ribbon. It becomes the composition.

  FIG. 40 is a cross-sectional structure diagram showing a cross-sectional structure of a semiconductor chip constituting the semiconductor snubber built-in switching element 900.

  As shown in FIG. 40, the semiconductor snubber built-in switching element 900 includes a switching element 600 formed on the right side of the right broken line and a semiconductor snubber 200 formed on the left side of the left broken line.

First, the portion of the switching element 600 shows a general IGBT configuration as an example. For example, it is made of a substrate material in which an n ⁻ type drift region 23 is formed on a p ⁺ type substrate region 21 made of silicon via an n type buffer region 22. A p-type well region 24 is formed in the surface layer portion in the drift region 23, and an n ⁺ -type emitter region 25 is formed in the surface layer portion in the well region 24. A gate electrode 27 made of, for example, n-type polycrystalline silicon is provided via a gate insulating film 26 made of, for example, a silicon oxide film so as to be in contact with the surface layer portions of the drift region 23, the well region 24, and the emitter region 25. Has been. Further, an emitter electrode 28 made of, for example, an aluminum material is formed so as to be in contact with the emitter region 25 and the well region 24. A collector electrode 30 is formed so as to be in ohmic contact with the substrate region 21. As described above, the IGBT used in this description has a so-called planar type in which the gate electrode 27 is formed on a plane with respect to the semiconductor substrate.

  Further, in FIG. 40, a field insulating film 31 made of, for example, a silicon oxide film is formed so as to be in contact with the surface layer portion of the drift region 23 or the well region 24. The field insulating film 31 is a structure that is generally used when the switching element 600 is manufactured as a semiconductor chip, for example, to alleviate electric field concentration at a pn junction on the outer periphery of the chip. In the fifth embodiment of the present invention, as an example of the shape of the end portion of the field insulating film 31, FIG. 40 shows a case where the portion in contact with the upper electrode is a right angle, but the end portion has an acute angle shape. Of course it is good. Further, as a configuration of the outer peripheral end where the field insulating film 31 is formed, one or a plurality of guard rings may be formed so as to surround the outer periphery of the well region 24.

Next, the configuration of the semiconductor snubber 200 formed on the left side of the left broken line in FIG. 40 will be described. The surface layer portion of the drift region 23 is of the same conductivity type as the drift region 23 so as to be in contact with a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral end portion of the switching element 600 and from the drift region 23. In addition, an n ⁺ -type capacity lowering prevention region 1001 having an impurity density equal to or higher than that is formed. Further, on the field insulating film 5, for example, an n-type polycrystalline silicon is used via an insulating film 32 formed when the gate insulating film 26 of the switching element 600, an interlayer insulating film (not shown), or the like is formed. A resistance region 33 is formed. Although the case where the insulating film 32 is formed is illustrated in the fifth embodiment of the present invention, it goes without saying that the resistance region 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween. good.

Further, an n ⁺ -type capacity lowering prevention region 1005 having the same conductivity type as that of the resistance region 33 and having an impurity density equal to or higher than that of the resistance region 33 is formed in the surface layer portion of the resistance region 33. Further, the upper electrode 28 is formed on the capacitance decrease prevention region 1005 and has the same potential as the emitter terminal 301 of the switching element 600. That is, in the semiconductor snubber 200 according to the fifth embodiment of the present invention, the drift region 23 and the resistance region 33 function as the resistor R, and the field insulating film 31 and the insulating film 32 function as the capacitor C. The configuration corresponds to FIG. 18 in the first embodiment. The resistance region 6 can be changed in impurity concentration and thickness in accordance with the required resistance value. At this time, as shown in the first embodiment, it is possible to easily adjust by changing the thickness or area of any one of the capacity drop prevention regions 1001 and 1005.

  Also, the thickness and area of the field insulating film 31 can be determined according to the required breakdown voltage and the required capacitance of the capacitor C. The withstand voltage is desirably higher than the withstand voltage of the switching element 600 not only as a function of the semiconductor snubber 200 but also for preventing breakdown of the field insulating film 31 for satisfying the electric field relaxation function of the switching element 600. Further, the capacity of the capacitor C is 1/100 of the depletion capacity charged when the free-wheeling diodes 100 connected in parallel with the switching elements 600 on the same chip are respectively cut off (when a high voltage is applied). Although it can be selected in the range of about 100 to 100 times, if a sufficient snubber function is exhibited, an increase in loss is suppressed as much as possible, and a necessary chip area is taken into consideration, as shown in a calculation result to be described later, it is about 10 A range of about 1 to 10 times is desirable.

  In the fifth embodiment of the present invention, as shown in the first embodiment, by forming the capacitance lowering prevention regions 1001 and 1005, the capacitor C formed by the dielectric capacitance made of the field oxide film 5 is formed. Since the operation can be performed without reducing the size, the vibration phenomenon can be easily damped optimally.

  In the fifth embodiment of the present invention, for example, the thickness is 1 μm so as to be higher than the breakdown voltage of the switching element 600, and the capacitance of the capacitor C is depleted when the switching element 600 and the free-wheeling diode 100 are disconnected. An explanation will be given of the case where the same capacity as the sum of the capacities is used. The field insulating film 31 may be any material other than a silicon oxide film as long as it has a predetermined breakdown voltage and functions as an electric field relaxation function and a capacitor C.

  The resistance R of the resistance region 33 is preferably set so as to satisfy a general design formula C = 1 / (2πfR) that effectively exhibits a snubber function.

  As described above, even when the switching element 600 and the semiconductor snubber 200 are formed on one chip, the operations and effects described in the first embodiment can be obtained.

  Furthermore, in the fifth embodiment of the present invention, the switching element 600 and the semiconductor snubber 200 share the substrate region 21, the buffer region 22, and the drift region 23 as the support base, and the emitter electrode 28 and The collector electrode 30 is shared. Further, the field insulating film 31 serving as the electric field relaxation function of the switching element 600 can also be shared as the function of the capacitor C. Furthermore, a polycrystalline silicon film serving as the gate electrode 27 of the switching element 600 can be similarly formed as the resistance region 33 as a resistance R component. Furthermore, the capacitance reduction prevention region 1001 can be formed in common with the emitter region 25 of the switching element 600, and can be formed simultaneously at the same depth, for example.

  That is, since these portions can be formed by the same process, the manufacturing process can be simplified. In addition, since the mounting area (site area) can be reduced by using one chip, the semiconductor package can be reduced in size. In addition, the switching element 600 and the emitter electrode 28 of the semiconductor snubber 200 serve as a common electrode, and the parasitic inductance generated in the wiring and the like is further reduced as compared with the case where the metal wiring 350 and 330 are connected in the second embodiment. Therefore, the vibration phenomenon at the time of reverse recovery of the reflux diode 100 connected in parallel can be further reduced. Furthermore, when the fifth embodiment of the present invention is used in an inverter circuit as shown in FIG. 7, for example, a new effect can be produced in which the switching element 600 and the semiconductor snubber 200 are integrated into one chip. In other words, as described in the second to third embodiments, when the freewheeling diode 100 performs a reverse recovery operation, the semiconductor snubber 200 has the freewheeling diode 100, The transient current generated due to the depletion capacity of the switching element 600 and the capacitor capacity C of the semiconductor snubber 200 is consumed and heat is generated by the resistance R component. On the other hand, when the freewheeling diode 100 performs a reverse recovery operation, the switching element 600 connected in parallel thereto is not in a conductive state and therefore hardly generates heat. From this, by making one chip, when the portion of the semiconductor snubber 200 is generating heat during reverse recovery, the portion of the switching element 600 is in a cut-off state and is not generating heat. Compared to the case of another chip, it can be kept low. In other words, by integrating into one chip, high integration of the resistance region 33 due to heat generation can be expected.

  As described above, according to the fifth embodiment of the present invention, both the effect of further suppressing the vibration phenomenon and improving the transient performance and the conduction performance can be improved, and at the same time, it can be realized in a small size and at a low cost.

  39 and 40, the case where the switching element 600 is an IGBT has been described. However, for example, even when the various switching elements 600 described in the second embodiment and the third embodiment are integrated into one chip. It can be easily realized as well. FIGS. 41 to 43 are examples thereof.

FIG. 41 shows a case where a MOSFET is used instead of the IGBT as the switching element 600 of FIG. 41 shows a case where the MOSFET of FIG. 41 is made of, for example, a silicon carbide semiconductor substrate. For example, a substrate material in which an n ⁻ type drift region 52 is formed on an n ⁺ type substrate region 51 is used, and a p type well region 53 is formed in a surface layer portion of the drift region 52, and further in the well region 53. An n ⁺ type source region 54 is formed in the surface layer portion. A gate electrode 56 made of, for example, n-type polycrystalline silicon is disposed through a gate insulating film 55 made of, for example, a silicon oxide film so as to be in contact with the surface layer portions of the drift region 52, the well region 53, and the source region 54. Has been. Further, a source electrode 57 is formed so as to be in contact with the source region 54 and the well region 53, and a drain electrode 59 is formed so as to be in ohmic contact with the substrate region 51.
Further, in FIG. 41, a field insulating film 31 made of, for example, a silicon oxide film is formed so as to be in contact with the surface layer portion of the drift region 52 or the well region 53. The field insulating film 31 is a structure that is generally used when the switching element 600 is manufactured as a semiconductor chip, for example, to alleviate electric field concentration at a pn junction on the outer periphery of the chip. In the fifth embodiment of the present invention, as an example of the shape of the end portion of the field insulating film 31, FIG. 41 shows a case where the portion in contact with the upper electrode is a right angle, but the end portion has an acute angle shape. Of course it is good. Further, as a configuration of the outer peripheral end where the field insulating film 31 is formed, one or a plurality of guard rings may be formed so as to surround the outer periphery of the well region 53.

Next, the configuration of the semiconductor snubber 200 formed on the left side of the left broken line in FIG. 41 will be described. The surface layer of the drift region 52 has the same conductivity type as that of the drift region 52 and comes from the drift region 52 so as to be in contact with a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral end of the switching element 600. In addition, an n ⁺ -type capacity lowering prevention region 1001 having an impurity density equal to or higher than that is formed. Further, on the field insulating film 31, for example, an n-type polycrystalline silicon is used via an insulating film 32 formed when forming a gate insulating film 55, an interlayer insulating film (not shown) or the like of the switching element 600. A resistance region 33 is formed. Although the case where the insulating film 32 is formed is illustrated in the fifth embodiment of the present invention, it goes without saying that the resistance region 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween. good.

Further, an n ⁺ -type capacity lowering prevention region 1005 having the same conductivity type as that of the resistance region 33 and having an impurity density equal to or higher than that of the resistance region 33 is formed in the surface layer portion of the resistance region 33. Further, a source electrode 57 is formed on the capacitance reduction prevention region 1005 and has the same potential as the emitter terminal 302 of the switching element 600. That is, in the semiconductor snubber 200 according to the fifth embodiment of the present invention, the drift region 52 and the resistance region 33 function as the resistance R, and the field insulating film 31 and the insulating film 32 function as the capacitor C. The resistance region 33 can be changed in impurity concentration and thickness in accordance with the required resistance value. At this time, as shown in the first embodiment, it is possible to easily adjust by changing the thickness or area of any one of the capacity drop prevention regions 1001 and 1005.

  With respect to the operation of FIG. 41, it is possible to realize the unique effect described in the third embodiment and the effect obtained when the chip is formed as described in the fifth embodiment of the present invention. Furthermore, FIG. 41 is characterized in that the resistance region 33 is formed of the same material as the gate electrode 56 of the switching element 600 as in FIG. Further, the capacitance reduction prevention region 1001 can be formed in common with the source region 54 of the switching element 600, and can be formed at the same depth, for example.

  With such a configuration, in addition to the effect of using a MOSFET as the switching element 600, the manufacturing process can be further simplified and realized at low cost.

FIG. 42 shows a case where the JFET shown in FIG. 30 is used instead of the IGBT as the switching element 600 of FIG. In Figure 42, for example polytype of silicon carbide n on the substrate region 71 and n ⁺ -type 4H types ^- type drift region 72 is formed, n ⁺ -type source region 73 and p-type gate region 74 The gate region 74 is connected to the gate electrode 75, the source region 73 is connected to the source electrode 76, and the substrate region 71 is connected to the drain electrode 78.

  Further, in FIG. 42, a field insulating film 31 made of, for example, a silicon oxide film is formed so as to be in contact with the surface layer portion of the drift region 72. The field insulating film 31 has a structure that is used, for example, to alleviate electric field concentration at the heterojunction portion on the outer periphery of the chip when the switching element 600 is manufactured as a semiconductor chip. In the fifth embodiment of the present invention, FIG. 42 shows, as an example, a case where the shape of the end portion of the field insulating film 31 is a right angle, but the end portion may of course have an acute angle shape. Further, as a configuration of the outer peripheral end portion where the field insulating film 31 is formed, one or a plurality of guard rings may be formed so as to surround the outer periphery of the gate region 74.

Next, the configuration of the semiconductor snubber 200 formed on the left side of the left broken line in FIG. 42 will be described. The surface layer portion of the drift region 72 has the same conductivity type as that of the drift region 72 and has the same conductivity type as that of the drift region 72 so as to be in contact with a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral end of the switching element 600. Thus, an n ⁺ -type capacity reduction prevention region 1001 having an impurity density equal to or higher than that is formed. Further, a resistance region 33 made of n-type polycrystalline silicon is formed on the field insulating film 31 via an insulating film 32 formed when the switching element 600 or the interlayer insulating film 77 is formed. ing. Although the case where the insulating film 32 is formed is illustrated in the fifth embodiment of the present invention, it goes without saying that the resistance region 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween. good.

Further, an n ⁺ -type capacity lowering prevention region 1005 having the same conductivity type as that of the resistance region 33 and having an impurity density equal to or higher than that of the resistance region 33 is formed in the surface layer portion of the resistance region 33. A source electrode 76 is formed on the capacitance reduction prevention region 1005 and has the same potential as the emitter terminal 302 of the switching element 600. That is, in the semiconductor snubber 200 according to the fifth embodiment of the present invention, the drift region 72 and the resistance region 33 function as the resistance R, and the field insulating film 31 and the insulating film 32 function as the capacitor C. The resistance region 33 can be changed in impurity concentration and thickness in accordance with the required resistance value. At this time, as shown in the first embodiment, it is possible to easily adjust by changing the thickness or area of any one of the capacity drop prevention regions 1001 and 1005.

  In addition to the unique effects described in the third embodiment, the operation of FIG. 42 can also be formed by sharing the capacitance lowering prevention region 1001 with the source region 73 of the switching element 600 and be formed at the same time. Can do. As described above, also in the fifth embodiment of the present invention, it is possible to realize the effect when it is made into one chip, further simplify the manufacturing process, and realize it at low cost.

  FIG. 43 shows a case where a transistor for driving the heterojunction portion shown in FIG. 29 with an insulated gate electrode is used instead of using the IGBT as the switching element 600 in FIG.

For example, n ⁻ type drift region 62 is formed on substrate region 61 of silicon carbide polytype 4H type n ⁺ type, and is in contact with the main surface of drift region 62 facing the junction surface with substrate region 61. In addition, a hetero semiconductor region 63 made of, for example, n-type polycrystalline silicon is formed. A gate insulating film 64 made of, for example, a silicon oxide film is formed so as to be in contact with the junction surface between the hetero semiconductor region 63 and the drift region 62. Further, the gate electrode 65 is connected to the gate insulating film 64, the source electrode 66 is connected to the opposite surface of the hetero semiconductor region 63 facing the drift region 62, and the drain electrode 68 is connected to the substrate region 1. Is formed.

  Further, in FIG. 43, a field insulating film 31 made of, for example, a silicon oxide film is formed so as to be in contact with the surface layer portion of the drift region 62. The field insulating film 31 has a structure that is used, for example, to alleviate electric field concentration at the outer periphery of the chip when the switching element 600 is manufactured as a semiconductor chip. In the fifth embodiment of the present invention, as an example of the shape of the end portion of the field insulating film 31, FIG. 43 shows a case where the portion in contact with the upper electrode is a right angle, but the end portion has an acute angle shape. Of course it is good. Further, as a configuration of the outer peripheral end portion where the field insulating film 31 is formed, one or a plurality of guard rings may be formed so as to form a well region or the like and surround the outer periphery thereof.

Next, the configuration of the semiconductor snubber 200 formed on the left side of the broken line in FIG. 43 will be described. The surface layer of the drift region 62 is of the same conductivity type as the drift region 62 so as to be in contact with a predetermined region of the field insulating film 31 used for the electric field relaxation at the outer peripheral end of the switching element 600. In addition, an n ⁺ -type capacity lowering prevention region 1001 having an impurity density equal to or higher than that is formed. On the field insulating film 31, a resistance region 33 made of n-type polycrystalline silicon is formed. Further, an n ⁺ -type capacity lowering prevention region 1005 having the same conductivity type as that of the resistance region 33 and having an impurity density equal to or higher than that of the resistance region 33 is formed in the surface layer portion of the resistance region 33. In addition, a source electrode 66 is formed on the capacitance decrease prevention region 1005 and has the same potential as the source terminal 302 of the switching element 600. That is, in the semiconductor snubber 200 according to the fifth embodiment of the present invention, the drift region 62 and the resistance region 33 function as the resistance R, and the field insulating film 31 functions as the capacitor C. The resistance region 33 can be changed in impurity concentration and thickness in accordance with the required resistance value. At this time, as shown in the first embodiment, it is possible to easily adjust by changing the thickness or area of any one of the capacity drop prevention regions 1001 and 1005.

  With respect to the operation of FIG. 43, it is possible to realize the unique effect described in the third embodiment and the effect obtained when the chip is formed as described in the fifth embodiment of the present invention. Further, the feature of FIG. 43 is that the resistance region 33 is formed of the same material as the hetero semiconductor region 63 of the switching element 600. Further, as in the case of the switching element 600 in FIGS. 40 and 34, the resistance region 33 can be formed of the same material as the gate electrode 65 of the switching element 600.

  Furthermore, as described in the third embodiment, in the fifth embodiment of the present invention, the switching element 600 can be used as a unipolar freewheeling diode. The semiconductor device shown at 43 can be shared. That is, in the fifth embodiment of the present invention, in addition to forming the freewheeling diode 100 as a separate chip, the freewheeling diode 100, the switching element 600, and the semiconductor snubber 200 are integrated into one chip, thereby reducing the size of the semiconductor package. can do. As a result, the parasitic inductance generated in the wiring or the like can be further reduced, so that the vibration phenomenon caused by the semiconductor snubber 200 can be further reduced. Further, the shortening of the wiring length has an effect of further reducing radiation noise generated from the wiring due to the oscillating current. Further, the cost is reduced by reducing the chip size, and the sum of the capacitor capacities of the freewheeling diode 100 and the switching element 600 is reduced, so that the capacitor capacity C required for the semiconductor snubber 200 can also be reduced. That is, the vibration phenomenon can be suppressed with a small size and low cost.

  As described above, an example in which the switching element 600 and the semiconductor snubber 200 are integrated into one chip has been described. A substrate region or drift region in the semiconductor substrate may be used. Further, as the capacitor capacity component of the semiconductor snubber 200, a depletion layer may be formed at the time of reverse bias such as a pn junction or a hetero junction other than the field insulating film 31 made of, for example, a silicon oxide film. good. Further, for example, a freewheeling diode 100 may be built in the switching element 600 such as a MOSFET having a Schottky barrier diode, and the semiconductor snubber 200 may be integrated into one chip. In any configuration, the vibration phenomenon, which is a feature of the present invention, can be further suppressed, and both the transient performance and the conduction performance can be improved.

  Further, as described with reference to FIG. 21 and FIG. 22 in the first embodiment, the size of the capacitor capacitance C used in the snubber circuit is the free-wheeling diode in the cut-off state or the capacitor of the free-wheeling diode and the switching element. The damping effect of the vibration phenomenon becomes significant when C / C0 is around 0.1 with respect to the total sum C0 of the capacitance components, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when C / C0 exceeds 10. . In addition, the capacitor capacitance C formed in the snubber circuit generates a loss E due to a transient current proportional to the size of the capacitor capacitance C during transient operation. Therefore, it is desirable that the size of the capacitor capacitance C be as small as possible.

  Therefore, the size of the capacitor capacitance C of the snubber circuit used in the fifth embodiment of the present invention is 1/10 times the total capacitance of the capacitor components in the cutoff state of the free wheel diode 100 and the switching element 600. By selecting the capacitance within the range of 10 times or less, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the examples described in the above embodiment.

(Other embodiments)
As described above, the present invention has been described according to the first to fifth embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, as long as the semiconductor snubber 200 is connected in parallel with at least the freewheeling diode 100, an effect of reducing the oscillation phenomenon can be obtained even if it is not mounted on the same mounting board.

  In all the embodiments, the materials of the free wheel diode 100, the switching element 600, and the semiconductor snubber 200 have been described using silicon materials, silicon carbide materials, and the like as examples. The material may be other semiconductor materials such as silicon germane, gallium nitride and diamond. Moreover, although 4H type was demonstrated as a polytype of silicon carbide, other polytypes, such as 6H and 3C, may be sufficient. In addition, although the case where the drift region of the switching element 600 and the reflux diode 100 is n-type has been described, it may of course be configured as a p-type.

  Further, as a power conversion device to which the semiconductor device according to the first embodiment of the present invention can be applied, a DC / DC converter, a three-phase AC inverter, and the like have been described as an example. You may use for the power converter device called a bridge | bridging etc. In any case, all types of power conversion such as inverters that convert DC voltage to AC voltage, rectifiers that convert AC voltage to DC voltage, and DC / DC converters that output DC voltage by changing the voltage, etc. It can be applied to the device. And if it is a power converter device using the structure of this invention, in any area | region of a large electric current area | region and a zero electric power area | region, and also in both the low temperature and the time of high temperature, a vibration phenomenon can be reduced. For this reason, the conduction loss and the transient loss can be reduced and the density can be increased, and the vibration phenomenon can be reduced and the operation can be stably performed, so that the basic performance of the apparatus can be improved at the same time.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

A, B1, B2, B3, B4, B5, B6 ... passive elements D, E1, E2, E3, E4, E5, E6 ... switching elements 1, 11, 21, 41, 51, 61, 71, 81 ... substrate region 2, 13, 23, 42, 52, 62, 72, 82 ... drift region 3, 13, 28, 44, 84 ... upper electrode 4, 14, 45, 85 ... lower electrode 5, 31, 46 ... field insulating film ( Field oxide film)
6, 17, 33, 47 ... resistance region 7 ... electric field relaxation region 8, 88 ... low concentration drift region 12 ... capacitor dielectric film 16 ... low resistance substrate region 22 ... buffer region 24, 53 ... well region 25 ... emitter region 26 , 55, 64 ... gate insulating film 27, 56, 65, 75 ... gate electrode 28 ... emitter electrode 29, 58, 67, 77 ... interlayer insulating film 30 ... collector electrode 32 ... insulating film 43, 63 ... hetero semiconductor region 54, 73 ... Source region 57, 66, 76 ... Source electrode 59, 68, 78 ... Drain electrode 74 ... Gate region 83 ... Opposite conductivity type region 100 ... Free-wheeling diode 200 ... Semiconductor snubber (semiconductor circuit)
210 ... Capacitor 210, 220 ... Resistance 230 ... Diode 300,340 ... Anode terminal 301 ... Emitter terminal 302 ... Anode terminal (emitter terminal)
302 ... Source terminal 310 ... Anode side metal film 320, 330, 350 ... Metal wiring 400, 402 ... Cathode terminal 401 ... Collector terminal 402 ... Drain terminal 410 ... Cathode side metal film 420 ... Metal base material 500 ... Insulating substrate 510 ... Mold Resin 600 ... Switching element 700 ... Gate side metal film 710 ... Metal wiring 800 ... Switching element (reflux diode with built-in semiconductor snubber)
900 ... Switching element with built-in semiconductor snubber 1001, 1002, 1003, 1004, 1005, 1006 ... Capacity reduction prevention region

Claims (15)

A free-wheeling diode that performs unipolar operation;
Comprising at least a capacitor and a resistor, and comprising a semiconductor circuit connected in parallel to the reflux diode,
The semiconductor circuit is:
A semiconductor substrate that functions as at least part of the resistor;
A capacitor dielectric film provided on the semiconductor substrate and functioning as at least part of the capacitor;
A resistance region functioning as at least part of the resistance provided on the capacitor dielectric film;
A capacitance lowering prevention region provided in contact with the upper surface of the resistance region,
The semiconductor device according to claim 1, wherein the capacitance lowering prevention region alleviates extension of a depletion layer into the resistance region when a reverse bias voltage is applied to the freewheeling diode. A free-wheeling diode that performs unipolar operation;
Comprising at least a capacitor and a resistor, and comprising a semiconductor circuit connected in parallel to the reflux diode,
The semiconductor circuit is:
A semiconductor substrate that functions as at least part of the resistor;
A capacitor dielectric film provided on the semiconductor substrate and functioning as at least part of the capacitor;
A capacitance lowering prevention region provided on the capacitor dielectric film;
A resistance region functioning as at least a part of the resistance provided in contact with the upper surface of the capacitance reduction prevention region;
The semiconductor device according to claim 1, wherein the capacitance lowering prevention region alleviates extension of a depletion layer into the resistance region when a reverse bias voltage is applied to the freewheeling diode. 3. The semiconductor device according to claim 1, wherein the capacitance reduction prevention region has the same conductivity type as the resistance region and has a high impurity density equal to or higher than an impurity density of the resistance region. The resistance region, the semiconductor device according to claim 1, characterized in that it consists of a conductive material having a large dielectric breakdown field strength than the breakdown field strength of silicon. The semiconductor device according to claim 1 , wherein the capacitance lowering prevention region is in contact with the capacitor dielectric film. The semiconductor device according to any one of claims 1 to 5, wherein the capacitor dielectric film is a silicon oxide film. Of the surface area of the portion constituting the capacitor of the capacitor dielectric film, a semiconductor device according to any one of claims 1 to 6, the surface area of the capacitor drop prevention region is equal to or is equal to or higher . The semiconductor device according to any one of claims 1 to 7, further comprising a parallel-connected switching element to the return diode. The capacitor has a value in the range of 1/10 to 10 times the total of the capacitance of the free-wheeling diode connected in parallel, or the total of the capacitance of the free-wheeling diode and the switching element. the semiconductor device according to any one of claims 1-8, characterized. The semiconductor circuit, the semiconductor device according to any one of claims 1 to 9, characterized in that it is formed to the return diode chip to the reflux diode are formed. The semiconductor device according to claim 8 , wherein the semiconductor circuit is formed in a switching element chip in which the switching element is formed. The switching element comprises a three-terminal element having a gate electrode, a source electrode and a drain electrode;
12. The semiconductor device according to claim 11 , wherein the capacitance reduction prevention region has the same conductivity type and the same impurity density as the source region that is in ohmic contact with the source electrode. The semiconductor device according to claim 12 , wherein the capacitance reduction prevention region has the same depth as the source region. The switching element comprises a three-terminal element having a gate electrode, an emitter electrode and a collector electrode;
The semiconductor device according to claim 11 , wherein the capacitance lowering prevention region has the same conductivity type and the same impurity density as an emitter region that is in ohmic contact with the emitter electrode. 15. The semiconductor device according to claim 14 , wherein the capacitance lowering prevention region has the same depth as the emitter region.

Images