JP2002100784A - Schottky barrier diode and semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diode, etc., which will not change the structure of its Schottky interface. SOLUTION: This Schottky barrier diode has an anode electrode, having unevenness on one surface, a p-type semiconductor layer which is jointed with a 1st region on the other surface of the anode electrode, an n-type semiconductor layer which is jointed with a 2nd region on the other surface of the anode electrode, and a cathode electrode and a projection part of the anode electrode is positioned above the p-type semiconductor layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a diode electrode structure.

[0002]

2. Description of the Related Art Conventionally, Pi mainly composed of silicon (Si) is used.
The N diode is a free-wheeling diode (FWDi (Free Whe
eling Diode)). The freewheeling diode FWDi is a circuit such as an inverter having an inductance component in a load that circulates or dissipates current energy stored in the load inductance when a power device connected to the circuit is turned off (open). It is a diode incorporated in the circuit for the purpose of protecting the whole, and is also called a commutation diode. Also used for bypass circuits in switching circuits and the like. The reason why the PiN diode is used as the freewheeling diode FWDi is that the PiN diode is a bipolar diode, and when a large current is applied with a forward bias, the voltage drop can be reduced by conductivity modulation. However, when a PiN diode is used, carriers remaining in the PiN diode due to conductivity modulation flow from the forward bias state to the circuit as a reverse recovery current in the process of sharply changing from the forward bias state to the reverse bias state. This is because, in a PiN diode containing Si as a main material, the remaining carriers have a long lifetime, so that many residual carriers are present.

On the other hand, a Schottky barrier diode (SBD) mainly composed of Si is replaced with a freewheel diode (FWD).
When used as i), there is no problem that a large reverse recovery current flows in the circuit. This is because the Schottky barrier diode (SBD) is a unipolar diode and has almost no carriers due to conductivity modulation.
The Schottky barrier diode (SBD) is a diode in which a metal and a semiconductor are joined together, and is a diode having a rectifying property using a potential barrier (Schottky barrier) at a Schottky interface which is a junction point. is there.

[0004]

However, when such a Schottky barrier diode (SBD) is used, a new problem arises next. First, the configuration of the Schottky barrier diode will be briefly described. FIG. 4 is a sectional view of a conventional Schottky barrier diode 40. The Schottky barrier diode 40 includes a flat first anode electrode 41 connected to an external conductor (not shown), a second anode electrode 43 adjacent to the first anode electrode 41,
Si, which is a semiconductor layer bonded to the second anode electrode 43,
It includes an n-type epitaxial layer 44 of (silicon), an n-type Si substrate 46, and a cathode electrode 47 connected to an external conductor (not shown). This Schottky barrier diode 4
At 0, a p-type semiconductor layer 45 is further formed below the second anode electrode 43. This is a so-called junction barrier control Schottky structure (JBS (Junction Barrier contr.
olled Schottky structure).

A problem of the Schottky barrier diode (SBD) 40 containing Si as a main material is that the electric field strength causing dielectric breakdown is low. This means that it is difficult to increase the breakdown voltage. High breakdown voltage Schottky barrier diode (SBD) with no reverse recovery current flowing in the circuit
Is produced, a large resistance is generated at the time of energization. Therefore, the withstand voltage is limited to about 200 V in a practical range.

[0006] Further, the conventional Schottky barrier diode (SBD) cannot exhibit desired electrical characteristics, so that it is difficult to mount it on a semiconductor module that can be used for a circuit. This is because the Schottky electrode interface 48, which is a path when current flows in the forward direction, cannot obtain the originally expected electrical characteristics. For example, considering a case where dust or the like adheres to an external conductor (not shown) connected to the first anode electrode 41 and has irregularities, the first anode electrode 41 is flat,
When connected to the external conductor, the convex portion of the first anode electrode 41 locally applies a strong pressure to the Schottky interface 48, thereby deteriorating the electrical characteristics of the Schottky electrode interface 48. Considering the case where the external conductor is wire-bonded to the first anode electrode 41 by ultrasonic waves, ultrasonic waves are directly transmitted to the Schottky interface 48 and the structure of the Schottky interface 48 changes, so that the electrical characteristics of the Schottky interface 48 change. May be.

It is an object of the present invention to provide a diode in which the structure of the Schottky interface 48 does not change. As a result, the diode can obtain the intended electrical characteristics. It is a further object of the present invention to provide a diode and a semiconductor module which have a high breakdown electric field strength and do not allow a reverse recovery current to flow through a circuit.

[0008]

According to the present invention, there is provided a Schottky barrier diode comprising: an anode electrode having an irregular surface on one surface; and a p-type semiconductor joined to a first region on the other surface of the anode electrode. A Schottky barrier diode comprising a layer, an n-type semiconductor layer joined to a second region on the other surface of the anode electrode, and a cathode electrode, wherein the convex portion of the anode electrode is A Schottky barrier diode arranged to be located above a semiconductor layer, thereby achieving the above object.

When the upper portion of the convex portion of the anode electrode is flat, the size of the upper portion of the flat convex portion may be smaller than the size of the p-type semiconductor layer.

[0010] The n-type semiconductor layer may be formed using silicon carbide SiC as a main material.

A semiconductor module according to the present invention is a semiconductor module comprising a switching element for switching a circuit, and a return diode for protecting the circuit from a current flowing through the circuit when the switching element is switched, wherein the return diode Is a Schottky barrier diode according to claim 3, thereby achieving the above object.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 and 2 of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 shows a Schottky barrier diode (SBD) 10 of the present invention and external conductors 12-1 and 12-2 connected to the Schottky barrier diode (SBD) 10 by pressure welding. It is sectional drawing. The Schottky barrier diode (SBD) 10 is a diode in which a metal and a semiconductor are joined.

The feature of the Schottky barrier diode (SBD) 10 according to the present embodiment is that irregularities are provided in the thickness of the anode electrode 1 connected to the external conductor 12-1, and the projection 2 of the anode electrode 1 is a p-type semiconductor. That is, the layer 5 is arranged so that the concave portion corresponds to the n-type epitaxial layer 4 which is an n-type semiconductor layer (in a vertical relationship). Here, the unevenness is a state of the surface relatively determined from the state of undulation in the height direction of the surroundings, for example, as a reference value with the median of the highest position and the lowest position in a certain region as a reference value, The higher part can be defined as a convex part, and the part lower than the reference value can be defined as a concave part. With this arrangement, even if the outer conductor 12-1 has irregularities, the convex portions do not apply strong pressure to the Schottky interface 8, and therefore, the Schottky barrier diode (SB)
D) The original electrical characteristics of 10 can be obtained.

The Schottky barrier diode (SBD) 10 according to the present invention will be described in detail. The Schottky barrier diode (SBD) 10 includes at least a first anode electrode 1, a second anode electrode 3, an n-type epitaxial layer 4, a p-type semiconductor layer 5, and an n-type semiconductor substrate 6.
And a cathode electrode 7.

To explain each component, the first anode electrode 1 is composed of a Schottky barrier diode (SBD) 1
This is an electrode for ensuring the connection between 0 and the external conductor 12-1. The first anode electrode 1 is connected to the external conductor 12-1 on one side, and is connected to the second anode electrode 3 on the other side. The first anode electrode 1 is an external conductor 1
The thickness of the side connected to 2-1 is provided with irregularities. The convex portion 2 of the anode electrode 1 is connected to the outer conductor 12-1.
Used to secure electrical connection with According to FIG. 1, the convex portion 2 and the concave portion of the unevenness provided on the first anode electrode 1 are both described as having a right-angled contour, but are not necessarily limited to a right angle. The shape is not limited as long as it is uneven.

Next, the second anode electrode 3 is a flat plate-like electrode, one surface of which is joined to the first anode electrode 1, and the other surface of which is the n-type epitaxial layer 4 and the p-type semiconductor layer. 5 is joined. The other surface can be divided into a region that joins with the n-type epitaxial layer 4 and a region that joins with the p-type semiconductor layer 5. In the present embodiment, the term “anode electrode” simply refers to both the first anode electrode 1 and the second anode electrode 3. The second anode 3 may be omitted, and the other side of the first anode 1 may be joined to the n-type epitaxial layer 4 and the p-type semiconductor layer 5.

Subsequently, the n-type epitaxial layer 4 is a low-concentration semiconductor layer formed mainly of, for example, Si or the like. As described above, although the Schottky barrier diode (SBD) 10 is a diode in which a metal and a semiconductor are joined, the anode electrode corresponds to “metal” and the n-type epitaxial layer 4 corresponds to “semiconductor”. The junction surface between the anode electrode and the n-type epitaxial layer 4 is called a Schottky interface 8. The n-type epitaxial layer 4 is connected to the n-type semiconductor substrate 6 on the other side.

The p-type semiconductor layer 5 is, for example, a p-type semiconductor layer mainly composed of Si. The p-type semiconductor layer 5 is formed below the second anode electrode 3, and its junction surface is also
Called Schottky interface 9. This p-type semiconductor layer 5
Is provided to prevent an increase in the electric field at the Schottky interface 8. That is, according to the p-type semiconductor layer 5,
At the time of reverse bias, the electric field intensity on the side of the n-type epitaxial layer 4 at the Schottky interface 8 can be reduced to reduce the leak current.

The n-type semiconductor substrate 6 is an n-type semiconductor substrate containing a high-concentration material, for example, Si as a main material. The n-type semiconductor substrate 6 is joined to the n-type epitaxial layer 4 on the one hand,
On the other hand, it is joined to the cathode electrode 7.

The cathode electrode 7 is an electrode for securing the connection between the Schottky barrier diode (SBD) 10 and the external conductor 12-2. The cathode electrode 7 is connected to the external conductor 12-2 on one side, and is connected to the n-type semiconductor substrate 6 on the other side.

The current flowing in the Schottky barrier diode (SBD) 10 configured as described above flows from the anode electrode to the cathode electrode 7 via the Schottky interface 8, the n-type epitaxial layer 4 and the n-type semiconductor substrate 6. Reach.

As described above, the structure in which the p-type semiconductor layer 5 is formed under the second anode electrode 3 is a junction barrier control Schottky structure (JBS).
olled Schottky structure). As mentioned in the description of the p-type semiconductor layer 5, in the JBS structure, the p-type semiconductor layer 5 is closely related to the characteristics of the Schottky barrier diode (SBD) 10 at the time of reverse bias.
On the other hand, in the Schottky barrier diode (SBD) 10 having the JBS structure, the Schottky interface 8 plays a basic role of current control. This is because a current flows through the Schottky interface 8 at the time of forward bias. Literature (Metal Sem by Rhoderick, EH And Williams, RH
iconductor Contacts, 2nd edition, Chap. 1, Oxford
As described in University Press (1988) "), the electrical properties of the Schottky barrier diode (SBD) 10 are sensitively dependent on the structure of the Schottky interface 8. Therefore, the Schottky barrier diode (SB
D) In the case where an electrode is connected to 10, for example, care must be taken not to change the structure of the Schottky interface 8.

Therefore, the convex portion 2 of the first anode electrode 1
Are positioned above p-type semiconductor layer 5 (in a direction perpendicular to the electrode surface of first anode electrode 1). In other words, the concave portion of the first anode electrode 1 is located above the Schottky interface 8 of the n-type epitaxial layer 4 (external conductor 12-1).
Side). At this time, the upper part of the convex part 2 of the anode electrode is flat, the width of the convex part 2 of the first anode electrode 1 is Wa, and the width of the p-type semiconductor layer 5 is Wp.
Then, Wa ≦ Wp. As long as this condition is met,
This is because the structure of the Schottky interface 8 is not affected even when pressure due to dust or the like is applied to the convex portion 2. When the upper portion of the convex portion 2 is not flat, a predetermined reference value is obtained as described above, a portion higher than the reference value is defined as a convex portion, a portion lower than the reference value is defined as a concave portion, and the like. The width of the portion 2 and the width of the p-type semiconductor layer 5 may be determined. FIG.
Is a cross-sectional view, so the word "width" means "size"
Can be paraphrased. Therefore, it can be said that the size of the convex portion 2 of the first anode electrode 1 is equal to or smaller than the size of the p-type semiconductor layer 5.

Such an electrode structure is realized by the following manufacturing process. First, the process up to the formation of the p-type semiconductor layer 5 is performed by using a known technique such as vapor deposition, crystal growth, ion implantation, and the like, and a detailed description thereof will be omitted. FIG. 5 shows the Schottky barrier diode (SBD) 10 (FIG. 1) in the manufacturing process. p-type semiconductor layer 5
When (FIG. 1) is formed, when forming the second anode electrode 3 (FIG. 1), an alignment marker 56 is formed outside the diode element region 54 on the Si wafer 52. The alignment marker 56 is used for aligning the shape of the p-type semiconductor layer 5 (FIG. 1) with the shape of the first anode electrode 1 (FIG. 1).

More specifically, before forming the second anode electrode 3 (FIG. 1), a photoresist is coated on the Si wafer 52 by spin coating, and the second anode electrode 3 (FIG. The mask for 1) is exposed and developed according to the shape of the p-type semiconductor layer 5 (FIG. 1). The pattern of the alignment marker 56 is applied to the mask for the second anode electrode 3 (FIG. 1). When the development is completed, a metal (for example, Al) for the second anode electrode 3 (FIG. 1) is vapor-deposited on the patterned photoresist by electron beam vapor deposition or the like.
The metal (for example, Al) for the anode electrode 1 (FIG. 1) is deposited on the metal for the second anode electrode 3 (FIG. 1). Then, by removing the photoresist with an organic solvent or the like, the second anode electrode 3 (FIG. 1) and the first portion 2 (FIG. 1) in which the convex portion 2 (FIG.
The anode electrode 1 (FIG. 1) is formed. At this time, the alignment marker 56 is also formed outside the diode element region 54. Since the relative positions of the alignment marker 56 and the shape of the p-type semiconductor layer 5 (FIG. 1) are determined,
A mask pattern for providing the first anode electrode 1 (FIG. 1) with the convex portion 2 (FIG. 1) is prepared so as to correspond to the relative position. Thereby, the pattern of the convex portion 2 (FIG. 1) of the first anode electrode 1 and the p-type semiconductor layer 5 (FIG. 1)
Can be matched with the pattern of the shape.

The photoresist is again coated on the Si wafer 52 by spin coating, and a mask for giving the convex portion 2 (FIG. 1) to the first anode electrode 1 (FIG. 1) by a microscope or the like is aligned with the alignment marker 56. Exposure and development. Then, the first anode electrode 1 is formed on the patterned photoresist by electron beam evaporation or the like.
The metal for (FIG. 1) is deposited. When the photoresist is removed, a first anode electrode 1 (FIG. 1) having a convex portion 2 (FIG. 1) is formed. The height of the convex portion 2 (FIG. 1) can be changed by changing the deposition time. When the convex portion 2 (FIG. 2) is pressed against the outer conductor 12-1 (FIG. 1), the convex portion 2 (FIG. 2) is pressed by pressure.
Is slightly deformed, but the deformation is negligible because the degree is small, and the convex portion 2 (FIG. 2) has a sufficient strength.

Referring again to FIG. 1, according to such a structure, even if dust or the like adheres to outer conductor 12-1 and irregularities occur, the structure of Schottky interface 8 can be changed when the outer conductor is connected. There is no. The reason is that the outer conductor 1 due to dust etc.
When the convex portion of 2-1 faces the concave portion of the first anode electrode 1, the convex portion of the external conductor 12-1 fits into the concave portion of the first anode electrode 1, so that the external conductor 12-
This is because the convex portion of 1 does not apply strong pressure to the Schottky interface 8. At this time, the bottom surface of the external conductor 22-1 is prevented from contacting the concave portion of the first anode electrode 1. When bonding is performed by using ultrasonic waves, the ultrasonic waves propagate through the convex portion of the first anode electrode 1, so that bonding can be performed without locally applying a strong pressure to the Schottky interface 8. On the other hand, when the convex portion of the outer conductor 12-1 comes into contact with the convex portion of the first anode electrode 1, the structure of the Schottky interface 9 does not affect the control of the current. There is no problem even if a strong pressure is applied to the Schottky interface 9 by the convex portion of. In that case, it is only necessary that at least the second anode electrode 3 and the p-type semiconductor layer 5 be electrically connected. As described above, even when Wa ≦ Wp is not satisfied, Wa and Wp
If the difference is small enough, no strong pressure is applied to the Schottky interface 8 as in the prior art, so that the Schottky barrier diode (SBD) 10 can be manufactured without changing the structure of the Schottky interface 8.

As described above, in the Schottky barrier diode (SBD) 10 having the JBS structure, the thickness of the portion of the first anode electrode 1 corresponding to the p-type semiconductor layer 5 corresponds to the n-type epitaxial layer 4. By increasing the thickness of the Schottky barrier diode (S
Even if the BD 10 is connected to the external conductors 12-1 and 12-2, the original electrical characteristics of the Schottky barrier diode (SBD) 10 can be obtained, and the yield in the product manufacturing process can be improved. Since the above description is of the first feature relating to the structure of the Schottky barrier diode (SBD) 10, it goes without saying that the p-type semiconductor layer 5, the n-type epitaxial layer 4, and the n-type substrate 6 are made of Si. However, the above-described effects can be obtained even when the film is formed of another known material.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The feature of the second embodiment is the first embodiment.
In the Schottky barrier diode (SBD) 10 described above, the n-type epitaxial layer 4 is an n-type SiC semiconductor layer mainly composed of silicon carbide (SiC). Si
By using C, a breakdown electric field strength about 10 times that of Si can be obtained, and at the same time, by using the Schottky barrier diode (SBD) 10 having the structure described in the first embodiment, the Schottky interface 8 can be formed. It is stable and can exhibit desired electrical characteristics when mounted on a semiconductor module.

Schottky barrier diode (SBD)
An example of a semiconductor module to which No. 10 is applied will be described. FIG.
1 is a cross-sectional view of a press-contact type semiconductor module 20 on which a Schottky barrier diode (SBD) 10 is mounted. The press-contact type semiconductor module 20 includes a Schottky barrier diode (SBD) 10, a switching element 23, and external conductors 22-1 and 2 sandwiching the Schottky barrier diode (SBD) 10 and the switching element 23.
2-2 and insulating module housings 26-1 and 26-2 for fixing and integrating these components.

Schottky barrier diode (SBD)
Reference numeral 10 denotes a Schottky barrier diode according to the first embodiment, which includes not only n-type epitaxial layer 4 (FIG. 1) but also p-type epitaxial layer 4.
Semiconductor layer 5 (FIG. 1) and n-type substrate 6 (FIG. 1)
It is formed using iC as a main material. This is because it is easy to fabricate with current technology, but p
The type semiconductor layer 5 (FIG. 1) and the n-type substrate 6 (FIG. 1) may be formed of different materials.

The outer conductors 22-1 and 22-2 are pressed against the Schottky barrier diode (SBD) 10, and correspond to the outer conductors 12-1 and 12-2 (FIG. 1). The switching element 23 is, for example, an IGBT (Insu
lated Gate Bipolar Transistor) or MOSFE
T (Metal Oxide Semiconductor Field Effect Transis
tor) and the like, which is a semiconductor switching element that performs circuit switching. FIG. 2 shows one Schottky barrier diode (SBD) 10 and one switching element 23.
Are shown, but a plurality of each may be used.

The press-contact type semiconductor module 20 will be described with reference to the circuit diagram of FIG. FIG. 3 is a circuit diagram of the press-contact type semiconductor module 20. 1 and 2 are denoted by the same reference numerals. In the press contact type semiconductor module 20, a Schottky barrier diode (SB
D) 10 and the switching element 23 are connected in anti-parallel. As described with reference to FIG. 1, the current flows through the Schottky barrier diode (SBD) 10 from the first anode electrode 1 to the cathode electrode 7 on the side of the external conductor 22-1.
Flows to On the other hand, when the switching element 23 is, for example, IG
When BT is used, the electrode 24-1 is a collector electrode, and the electrode 24 is
-2 is an emitter electrode, and the electrode 24-3 is a gate electrode. Since the Schottky barrier diode (SBD) 10 and the switching element 23 are connected in anti-parallel in this manner, the Schottky barrier diode (SBD) 10 functions as a freewheel diode FWDi.

As described above, by forming the n-type epitaxial layer 4 (FIG. 1) mainly composed of SiC, a Schottky barrier diode (SBD) 10 having a high breakdown electric field strength and a high breakdown voltage, and Can be obtained. Also, by incorporating such a Schottky barrier diode (SBD) 10 as a freewheeling diode FWDi in a circuit, the reverse recovery current and the energy loss caused thereby can be drastically reduced. Further, when the switching element 23 is turned on (at the time of switching), the reverse recovery current is not superimposed on the current flowing through the element, so that the risk of element destruction due to overcurrent can be greatly reduced. The press-contact type semiconductor module 20 is a Schottky barrier diode (SB).
Since D) 10 is incorporated, the effect based on Embodiment 1 described above can of course also be obtained.

[0036]

According to the present invention, unevenness is provided on one surface of the anode electrode, and the convex portion is arranged on the p-type semiconductor layer and the concave portion is arranged on the n-type epitaxial layer. Thus, even if the outer conductor has irregularities, the convex portions do not apply strong pressure to the Schottky interface 8 (FIG. 1), and therefore, the Schottky interface 8 (FIG. 1)
Can obtain a Schottky barrier diode (SBD) having the intended electrical characteristics in which the structure does not change.

When the upper part of the convex portion of the anode electrode is flat, the size of the flat portion may be smaller than the size of the p-type semiconductor layer. Thereby, even when using the wire bonding by the ultrasonic wave, the ultrasonic wave is transmitted only through the convex portion of the anode electrode, so that the ultrasonic wave can be brought into contact with the Schottky interface 8 (FIG. 1) without locally applying a strong pressure. . Further, the yield in the product manufacturing process can be improved.

According to the present invention, a Schottky barrier diode (SBD) having a high breakdown electric field strength and a high breakdown voltage can be obtained by forming the n-type semiconductor layer using silicon carbide SiC as a main material. .

Further, according to the present invention, such a Schottky barrier diode (SBD) is replaced with a freewheel diode F.
By incorporating it into a circuit as WDi, the reverse recovery current and the energy loss caused thereby can be drastically reduced. In addition, the risk of element destruction from overcurrent can be greatly reduced.

[Brief description of the drawings]

FIG. 1 shows a Schottky barrier diode (S) of the present invention.
FIG. 10B is a cross-sectional view of the external conductor connected to the Schottky barrier diode (SBD) by pressure welding.

FIG. 2 is a sectional view of a press-contact type semiconductor module equipped with a Schottky barrier diode (SBD).

FIG. 3 is a circuit diagram of a press contact type semiconductor module.

FIG. 4 is a cross-sectional view of a conventional Schottky barrier diode.

FIG. 5 is a view showing a Schottky barrier diode (SBD) in a manufacturing process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st anode electrode, 2 convex part, 3 2nd anode electrode, 4n type epitaxial layer, 5p type SiC semiconductor layer, 6 n type SiC substrate, 7 cathode electrode, 8 Schottky interface, 9 Schottky interface, 10 Schottky barrier diode (SBD),
22-1 and 22-2 outer conductor

Claims (4)

[Claims] An anode electrode provided with irregularities on one surface; a p-type semiconductor layer joined to a first region on the other surface of the anode electrode; and a second electrode on the other surface of the anode electrode. A Schottky barrier diode including an n-type semiconductor layer joined to a region of the above, and a cathode electrode, wherein the projected portion of the anode electrode is arranged so as to be located on the p-type semiconductor layer. Key barrier diode. 2. The Schottky barrier according to claim 1, wherein when the upper portion of the convex portion of the anode electrode is flat, the size of the upper portion of the flat convex portion is equal to or smaller than the size of the p-type semiconductor layer. diode. 3. The Schottky barrier diode according to claim 1, wherein said n-type semiconductor layer is formed using silicon carbide SiC as a main material. 4. A semiconductor module comprising: a switching element for switching a circuit; and a return diode for protecting the circuit from a current flowing in the circuit when the switching element is switched, wherein the return diode is A semiconductor module, which is the Schottky barrier diode according to item 1.