JP2006237553A - Semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device such as an IGBT with a high rate of yield, an excellent on-voltage to turn-off loss tradeoff and an excellent on-voltage to breakdown voltage tradeoff using the low-cost manufacturing process. <P>SOLUTION: An oxide film 21 is selectively formed on an n<SP>-</SP>-single crystal silicon substrate 29. A gate polysilicon 22 is formed on this oxide film 21. The surface of the gate polysilicon 22 is covered with a gate oxide film 23, and the surface of the gate oxide film 23 is covered with a cathode film 24 subject to n-type doping with a density higher than that of the n<SP>-</SP>drift layer. On this cathode film 24, a portion in contact with the n<SP>-</SP>-single crystal silicon substrate 29 is formed as a high-density n<SP>+</SP>buffer region 25, a p-base region 27 is formed next to this buffer region and an n<SP>+</SP>source region 26 is further formed next to this base region. An interlayer insulating film 28 is selectively formed on the cathode film 24, and an emitter electrode 30 is formed on this insulating film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a power semiconductor device constituting an IGBT (insulated gate bipolar transistor) and a manufacturing method thereof.

  With regard to IGBTs, performance has been improved by many improvements so far. Here, the performance of the IGBT is as a switch that keeps the voltage and shuts off the current completely when it is off, while flowing the current with the smallest possible voltage drop, that is, the smallest on-resistance when it is on. It's about performance. In the present specification, in view of the essence of the operation of the IGBT, the collector is denoted as “anode” and the emitter is denoted as “cathode”. Below, the characteristic etc. of IGBT are demonstrated.

(About IGBT performance trade-off)
There is a trade-off relationship (the so-called trade-off relationship) between the maximum voltage that can be held by the IGBT, that is, the withstand voltage level and the voltage drop at the time of ON, and the higher the withstand voltage IGBT, the higher the ON voltage. Ultimately, the limit value of this trade-off relationship is determined by the physical properties of silicon. In order to improve this trade-off to the limit, it is necessary to devise on the design side, such as preventing local electric field concentration when holding the voltage.

  As another important index representing the performance of the IGBT, there is a trade-off relationship between on-voltage and switching loss (particularly, turn-off loss). Since the IGBT is a switching device, it operates from on to off or off to on. At the moment of this switching operation, a large loss per hour occurs. In general, an IGBT having a lower on-voltage has a slower turn-off loss, and therefore has a larger turn-off loss. By improving the trade-off relationship as described above, the performance of the IGBT can be improved. Note that the dependency of the turn-on loss on the on-voltage is small. The turn-on loss greatly depends on the characteristics of the freewheeling diode used in combination with the IGBT.

(Improvement of raid-off)
In order to optimize the trade-off relationship between the on-voltage and the turn-off loss (hereinafter referred to as the on-voltage-turn-off loss relationship), it is effective to optimize the internal excess carrier distribution when the IGBT is on. . In order to lower the on-voltage, the resistance value of the drift layer may be decreased by increasing the excess carrier amount. However, at the time of turn-off, it is necessary to sweep all the excess carriers out of the device or to disappear by electron-hole recombination. Therefore, when the excess carrier amount is increased, the turn-off loss increases. Therefore, in order to optimize this trade-off relationship, the turn-off loss may be minimized with the same on-voltage.

  To achieve the optimal trade-off, the ratio of the carrier concentration on the anode side and the cathode side should be about 1: 5 by lowering the carrier concentration on the anode side and increasing the carrier concentration on the cathode side. Good. Furthermore, the average carrier concentration in the drift layer may be increased by keeping the carrier lifetime of the drift layer as large as possible.

  When the IGBT is turned off, the depletion layer extends from the pn junction on the cathode side into the drift layer and progresses toward the anode layer on the back surface. At that time, holes out of excess carriers in the drift layer are extracted from the end of the depletion layer by the electric field. In this way, an electron excess state occurs, and surplus electrons pass through the neutral region and are injected into the p-type anode layer. Then, since the anode side pn junction is slightly forward-biased, holes are reversely injected according to the injected electrons. The reversely injected holes merge with the holes extracted by the electric field described above and enter the depletion layer.

  Since carriers (here, holes) that are charge carriers pass through the electric field region and escape to the cathode side, the electric field works on the carriers. The work that the carriers receive from the electric field eventually becomes lattice vibration due to collision with a crystal lattice such as silicon, and is dissipated as heat. This dissipating energy becomes a turn-off loss. By the way, the energy dissipated by the carriers extracted before the depletion layer is fully extended is smaller than the energy dissipated by the carriers extracted when the depletion layer is fully extended. This is because if the depletion layer is not fully extended, the potential difference when carriers pass through the depletion layer is small, so that the work received from the electric field of the depletion layer is small.

  From a micro perspective, it looks like the above. From a macro viewpoint of the terminal voltage of the device, the product of the voltage and current (the current that flows before the anode-cathode voltage finishes rising, that is, the current that flows while the voltage rises) This means that the contribution to the loss expressed by (voltage × current) is small. From the above, the carrier distribution biased to the cathode side due to the IE effect described later turns off more than the carrier distribution of anode side bias under the condition that the proportion of carriers extracted at a low voltage is large and the on-voltage is the same. It can be seen that the loss is small.

  In order to lower the carrier concentration on the anode side, the total impurity amount in the anode layer may be lowered. This is not particularly difficult. However, in an IGBT having a low rated breakdown voltage such as 600 V, it is necessary to handle a wafer having a thickness of about 100 μm or thinner during the manufacturing process in order to reduce the total impurity amount of the anode layer. There are difficulties in production technology. On the other hand, the mechanism for increasing the carrier concentration on the cathode side is called the IE effect.

  As a cathode structure having a large IE effect, a HiGT structure in which a high-concentration n layer is inserted so as to surround a p base of a planar structure has been proposed (see, for example, Patent Document 1 and Patent Document 2). Further, in the trench gate structure, a CSTBT structure in which an n layer having a higher concentration than the drift layer is inserted in a mesa between adjacent trenches, an IEGT (Injection Enhancement Gate Transistor) structure, and the like have been proposed (for example, patents). Reference 3 and Non-Patent Document 1). In general, the IE effect in the trench type is larger than the IE effect in the planar type.

(IE effect)
The essence of the IE effect has been discussed and reported (for example, see Non-Patent Document 2). An IGBT equivalent circuit that is often drawn is a combination of a MOSFET (insulated gate field effect transistor having a metal-oxide-semiconductor structure) and a bipolar transistor. However, considering the actual device operation, it is considered that the combination of MOSFET 1, pnp bipolar transistor 2 and pin diode 3 is equivalent to the equivalent circuit shown in FIG.

FIG. 2 is a cross-sectional view showing a configuration of a main part of the planar IGBT. In FIG. 2, reference numeral 4 denotes a pnp bipolar transistor region (hereinafter referred to as a pnp-BJT region), and reference numeral 5 denotes a pin diode region. In FIG. 2, the solid arrow indicates the flow of the electron current, and the dotted arrow indicates the flow of the hole current. In this specification and the accompanying drawings, it means that electrons or holes are majority carriers in layers and regions with n or p, respectively. In addition, the n ⁺ or p ⁺ region (including the layer) means a higher impurity concentration than the n or p region (including the layer) not marked with “+”. Further, the n ⁺⁺ region (including the layer) means a higher impurity concentration than the n ⁺ region (including the layer).

As shown in FIG. 2, electrons from n ⁺⁺ region 6 of the surface of the MOS portion, an n ⁺ inversion layer 8 on the surface of the p layer 7 surrounding the n ⁺⁺ region 6, n ^- of the surface of the drift layer 9 It flows toward the p anode layer 11 on the back surface via the n ⁺ electron storage layer 10. A part of this electron current becomes a base current of the pnp-BJT region 4. In the pnp-BJT region 4, holes that have flowed from the p anode layer 11 by diffusion or drift only flow into the p layer 7, and the pn junction is slightly reverse-biased. Accordingly, the concentration of minority carriers in the n ⁻ drift layer 9 near the pn junction, that is, the hole concentration, is extremely low.

On the other hand, the n cathode of the pin diode region 5 is the n ⁺ electron storage layer 10 on the surface of the n ⁻ drift layer 9. Since the n ⁺ / n ⁻ junction is slightly forward-biased, electrons are injected into the n ⁻ drift layer 9. At high current, the electron concentration is much higher than the doping concentration of the n ⁻ drift layer 9 (high injection state). In order to satisfy the charge neutrality condition, holes having the same concentration as the electrons also exist. Therefore, the concentration of minority carriers in the n ⁻ drift layer 9 near the n ⁺ / n ⁻ junction, that is, the hole concentration, is extremely high.

In the IGBT, it is important to reduce the pnp-BJT region and increase the pin diode region in order to realize an optimum carrier distribution with cathode side bias. It is also very important to increase the n ⁺ / n ⁻ forward bias amount to promote electron injection. In the structure having the IE effect proposed so far, the ratio of the pin diode region is increased, and at the same time, the increase of n ⁺ / n ⁻ forward bias is realized.

By the way, in the planar structure, when the ratio of the p base in the cell pitch is reduced, the on-voltage is reduced. This has the effect of increasing the forward bias of the n ⁺ / n ⁻ junction by increasing the lateral current density near the surface and increasing the voltage drop in addition to increasing the ratio of the pin diode region. It is considered large. The reason why the forward bias of the n ⁺ / n ⁻ junction becomes large is that the n ⁺ layer has a low resistance, so its potential is equal to the cathode potential, but since the n ⁻ layer has a high resistance, its potential is increased by a large current. Because it lifts.

Similarly, the IE effect can be enhanced by reducing the ratio of the pnp-BJT region in the trench structure. In order to reduce the ratio of the pnp-BJT region, for example, the p base region may be set in a floating state in some mesa portions. The IE effect can also be increased by deepening the trench and separating the bottom of the trench from the pn junction. Further, the IE effect is increased by reducing the width of the mesa portion. In any case, it is considered that the density of the hole current flowing through the mesa portion increases, and the n ⁺ / n ⁻ forward bias due to the voltage drop increases.

Here, assuming that the doping concentration of the drift layer is Nd and the forward bias applied to the n ⁺ / n ⁻ junction is Vn, the electron concentration n on the n ⁻ layer side of the n ⁺ / n ⁻ junction is expressed by the following equation. . However, k is a Boltzmann constant and T is an absolute temperature.
n = Nd ^* exp (Vn / kT)

As is clear from the above equation, the electron concentration n on the cathode side increases exponentially according to the forward bias applied to the n ⁺ / n ⁻ junction. As means for increasing the forward bias amount, there is one that uses a voltage drop due to a large current as described above. Further, as described in Patent Documents 1 to 3, the forward bias amount can be increased by increasing the n ⁺ concentration. However, since the HiGT structure described in Patent Document 1 is a planar structure, if the concentration of the n ⁺ buffer layer on the surface side is too high, the forward breakdown voltage is greatly reduced.

On the other hand, in the CSTBT structure described in Patent Document 3, the n ⁺ buffer layer on the surface side is sandwiched between trench gate oxide films and continues to the polysilicon potential via the gate oxide film. Therefore, when holding forward voltage, that is, in blocking mode, the n ⁺ buffer layer on the surface side is depleted not only from the pn junction but also from the boundary with the trench gate oxide film on both sides, so it is completely depleted with low forward bias. Turn into. Therefore, the electric field inside the n ⁺ buffer layer on the surface side is relaxed despite the high concentration. Even if the forward bias is further increased, a local peak electric field is unlikely to appear due to the relaxation of the electric field at the mesa between the trenches.

This drifts a parallel pn structure in which vertical layered n-type regions and vertical layered p-type regions with increased impurity concentration are alternately joined instead of a uniform and single drift type drift layer. This is also in accordance with the principle of the superjunction MOSFET provided in the part. As described above, the CSTBT structure has a characteristic that the forward breakdown voltage is hardly lowered while enhancing the IE effect. Since the n ⁺ buffer layer on the surface side creates a diffusion potential with the n ⁻ drift layer and becomes a potential barrier for holes, the hole concentration in the drift layer increases.

Another explanation is that electrons are injected from the n ⁺ layer because a forward bias is applied between the n ⁺ buffer layer and the n ⁻ layer on the surface side. That is, in the n ⁺ / n ⁻ junction, if the n ⁺ layer has a high concentration, the electron injection efficiency is improved. Therefore, the ratio of the electron current injected into the n ⁻ layer with respect to the hole current entering the n ⁺ layer. Becomes larger. In order for holes to diffuse and flow as minority carriers in the n ⁺ layer, the n ⁺ / n ⁻ junction needs to be forward biased. The higher the n ⁺ layer concentration, the smaller the hole concentration as a minority carrier in the thermal equilibrium state. When the forward bias amount is large, the electron current flowing into the n ⁻ layer increases, so that the electron concentration increases. This second description is physically a paraphrase of the first description.

JP 2003-347549 A Japanese translation of PCT publication No. 2002-532885 JP-A-8-316479 Eye. I. Omura, 3 others, “Carrier injection enhancement effect of high voltage MOS devices -Device physics and design concept-”, ISPSD ' 97, p. 217-220 Florin Udrea, 1 other, "A unified analytical model for the carrier dynamics in Trench Insulated Gate Bipolar Transistors (TIGBT)" ISPSD '95, p. 190-195

  As described above, even in the conventional IGBT, a carrier distribution concentrated on the cathode side due to the IE effect is realized. However, in order to optimize the trade-off between on-voltage and turn-off loss, it is necessary to further increase the carrier concentration on the cathode side in the on-state. That is, the IE effect is still insufficient in the conventional IGBT. Even though a trench gate structure such as a CSTBT structure or an IEGT structure has improved trade-off characteristics, there is still room for improvement in characteristics by further miniaturization.

  However, the manufacturing process of the trench structure is long and complicated compared to the manufacturing process of the planar structure. Therefore, the yield rate of trench type devices is lower than that of planar type devices. Therefore, the product cost of the trench type device is high. Nevertheless, if further miniaturization is performed in order to improve the characteristics, the manufacturing cost will be further increased. In the trench gate structure, the electric field tends to concentrate on the bottom of the trench and the avalanche breakdown is likely to occur, so that the trade-off between on-voltage and withstand voltage tends to deteriorate. Further, structurally, when the gate is set to a negative potential with respect to the cathode, there is a problem that the electric field strength at the bottom of the trench is increased and the breakdown voltage is further deteriorated.

  An object of the present invention is to provide a semiconductor device having an IE effect larger than that of the prior art, that is, a semiconductor device in which the on-voltage-turnoff loss trade-off is optimized, in order to solve the above-described problems caused by the prior art. It is another object of the present invention to provide a semiconductor device that does not cause a deterioration in the on-voltage-breakdown voltage trade-off by preventing local electric field concentration during voltage holding. Furthermore, it aims at providing the manufacturing method of the semiconductor device which can manufacture the semiconductor device which has such a characteristic by the low-cost manufacturing process which is not extremely fine at high yield rate.

In order to solve the above-mentioned problems and achieve the object, as a result of examining a structure that facilitates electron injection from the surface, that is, a structure having a large IE effect, a structure having the following characteristics is effective. I understood it. First, a high-concentration n ⁺ buffer layer is inserted between the p base layer and the drift layer on the surface side. However, in order to prevent the electric field intensity from becoming excessively large during forward biasing, a structure that reduces the electric field is employed. Second, the area ratio of pnp-BJT is made as small as possible. However, it should be noted that if the effective peripheral length of the channel becomes too small, the on-voltage drop in the channel portion becomes large. Third, the current path until holes flow into the p base layer is narrowed and lengthened. With such a structure, the trade-off between on-voltage and turn-off loss can be improved.

  In order to realize the above-described structure, a semiconductor device according to a first aspect of the present invention includes a first insulating film that selectively covers a first main surface of a first conductivity type single crystal semiconductor substrate, and the first insulation. A polycrystalline semiconductor region provided on the film; a second insulating film surrounding the polycrystalline semiconductor region; and a first first electrode contacting the single crystal semiconductor substrate at a window portion of the first insulating film. A first conductivity type semiconductor region; a second first conductivity type semiconductor region provided on the second insulation film outside the window portion of the first insulation film; and the first first conductivity type. A first second conductivity type semiconductor region provided on the second insulating film between the semiconductor region and the second first conductivity type semiconductor region; and the second first conductivity type semiconductor region. And a first electrode that contacts both the first second-conductivity-type semiconductor region, the first electrode, and the first electrode A third insulating film provided between the first first conductivity type semiconductor region, a second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate, And a second electrode in contact with the second second conductivity type semiconductor region.

  According to a second aspect of the present invention, there is provided the semiconductor device according to the first aspect, wherein the first first conductivity type semiconductor region is doped to a first conductivity type having a higher concentration than the single crystal semiconductor substrate. It is characterized by being.

  According to a third aspect of the present invention, there is provided a semiconductor device according to the first or second aspect of the present invention, wherein the single crystal semiconductor substrate is located between the single crystal semiconductor substrate and the second second conductivity type semiconductor region. A third impurity type semiconductor region having a high impurity concentration is provided.

  A semiconductor device according to a fourth aspect of the present invention is the semiconductor device according to any one of the first to third aspects, wherein the first first-conductivity-type semiconductor region, the second first-conductivity-type semiconductor region, and the The semiconductor film made of the first second conductivity type semiconductor region is entirely made of polycrystalline silicon.

  A semiconductor device according to a fifth aspect of the present invention is the semiconductor device according to any one of the first to third aspects, wherein the first first-conductivity-type semiconductor region, the second first-conductivity-type semiconductor region, and the A part or all of the semiconductor film formed of the first second conductivity type semiconductor region is made of single crystal silicon.

  According to a sixth aspect of the present invention, there is provided a semiconductor device including: a first insulating film that selectively covers a first main surface of a first conductivity type single crystal semiconductor substrate; and a window portion of the first insulating film. A first first-conductivity-type semiconductor region in contact with the single-crystal semiconductor substrate; and a first second-conductivity-type semiconductor provided on the first insulation film outside the window of the first insulation film A region, a second first conductivity type semiconductor region provided in the first second conductivity type semiconductor region, the first first conductivity type semiconductor region, and the second first conductivity type semiconductor region And a second insulating film covering the first second conductivity type semiconductor region, a polycrystalline semiconductor region provided on the second insulation film, the second first conductivity type semiconductor region, and the A first electrode contacting both of the first second conductivity type semiconductor regions, the first electrode, and the polycrystal; A third insulating film provided between the conductor region, a second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate, and the second second A second electrode in contact with the conductive semiconductor region is provided.

  A semiconductor device according to a seventh aspect of the present invention is the semiconductor device according to the sixth aspect, wherein the first first conductivity type semiconductor region is doped to a first conductivity type having a higher concentration than the single crystal semiconductor substrate. It is characterized by being.

  A semiconductor device according to an eighth aspect of the present invention is the semiconductor device according to the sixth or seventh aspect, wherein the semiconductor device is located between the single crystal semiconductor substrate and the second second-conductivity-type semiconductor region more than the single crystal semiconductor substrate. A third impurity type semiconductor region having a high impurity concentration is provided.

  A semiconductor device according to a ninth aspect of the present invention is the semiconductor device according to any one of the sixth to eighth aspects, wherein the first first-conductivity-type semiconductor region, the second first-conductivity-type semiconductor region, and the The semiconductor film made of the first second conductivity type semiconductor region is entirely made of polycrystalline silicon.

  A semiconductor device according to a tenth aspect of the present invention is the semiconductor device according to any one of the sixth to eighth aspects, wherein the first first-conductivity-type semiconductor region, the second first-conductivity-type semiconductor region, and the A part or all of the semiconductor film formed of the first second conductivity type semiconductor region is made of single crystal silicon.

  The semiconductor device according to an eleventh aspect of the present invention is a semiconductor device comprising: a first insulating film selectively embedded below a first main surface of a first conductivity type single crystal semiconductor substrate; and the first insulating film; A first second conductivity type semiconductor region provided between the first main surface, a first conductivity type semiconductor region provided in the first second conductivity type semiconductor region, and the first A second insulating film that covers a portion of the main surface of the first insulating film on the region where the first insulating film is not buried, a polycrystalline semiconductor region provided on the second insulating film, and the first A first electrode that contacts both the conductive semiconductor region and the first second conductive semiconductor region; a third insulating film provided between the first electrode and the polycrystalline semiconductor region; , A second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate, and the second second Characterized in that it comprises a second electrode in contact with the conductive type semiconductor region.

  A semiconductor device according to a twelfth aspect of the present invention is the semiconductor device according to the eleventh aspect, wherein a higher impurity than the single crystal semiconductor substrate is provided between the single crystal semiconductor substrate and the second second conductivity type semiconductor region. A second conductive type semiconductor region having a second concentration is provided.

  According to a thirteenth aspect of the present invention, there is provided a semiconductor device manufacturing method comprising: a first step of sequentially forming a first insulating film and a polycrystalline semiconductor film on a first main surface of a first conductivity type single crystal semiconductor substrate; And a second step of removing a part of the polycrystalline semiconductor film to form a window, and a second insulating film covering an exposed part of the polycrystalline semiconductor film, and then forming the window in the window A third step of exposing a portion of the single crystal semiconductor substrate; and laminating a first conductivity type semiconductor film on the portion of the single crystal semiconductor substrate exposed at the window and the second insulating film. A fourth step, forming a first second conductivity type semiconductor region adjacent to the first first conductivity type semiconductor region in contact with the single crystal semiconductor substrate of the first conductivity type semiconductor film; The first first conductivity type semiconductor region sandwiching the first second conductivity type semiconductor region A fifth step of forming a second first conductivity type semiconductor region on the opposite side; the first first conductivity type semiconductor region; the first second conductivity type semiconductor region; and the second first conductivity type. A third insulating film is laminated on the type semiconductor region, a contact hole is opened in the third insulating film, and the second first conductive type semiconductor region and the first second conductive type semiconductor region are formed. A sixth step of exposing a part of the second conductive type semiconductor region and a second conductive type semiconductor region on the third insulating film via the contact hole; And forming a second second-conductivity-type semiconductor region along the ground surface by grinding the second main surface of the single crystal semiconductor substrate after forming the first electrode in contact with the portion. And an eighth step of forming a second electrode in contact with the second second conductivity type semiconductor region Characterized in that it contains.

  According to a fourteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the thirteenth aspect of the present invention, wherein the first conductive semiconductor film in the fourth step is higher in concentration than the single crystal semiconductor substrate. It is characterized by doping to one conductivity type.

  According to a fifteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the thirteenth or fourteenth aspect, wherein after the second main surface of the single crystal semiconductor substrate is ground in the seventh step, the grinding is performed. A third first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is formed deeper than the second second conductivity type semiconductor region along the plane.

  According to a sixteenth aspect of the present invention, in the semiconductor device manufacturing method according to any one of the thirteenth to fifteenth aspects, the first conductive semiconductor film is formed of polycrystalline silicon.

  According to a seventeenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the thirteenth to fifteenth aspects, wherein a part or all of the first conductivity type semiconductor film is formed of single crystal silicon. It is characterized by.

  According to a eighteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising: a first step of forming a first insulating film on a first main surface of a first conductive type single crystal semiconductor substrate; A second step of removing a part of the insulating film to form a window; and a first conductive type semiconductor film on the exposed portion of the first insulating film and the single crystal semiconductor substrate in the window. A third step of stacking layers, a fourth step of sequentially forming a second insulating film and a polycrystalline semiconductor film on the first conductive type semiconductor film, and removing a portion of the polycrystalline semiconductor film. Leaving the polycrystalline semiconductor film in a portion of the first conductive semiconductor film over the first first conductive semiconductor region in contact with the single crystal semiconductor substrate; Forming a first second conductivity type semiconductor region between the first insulating film and the first main surface; and A fifth step of forming a second first-conductivity-type semiconductor region in the first second-conductivity-type semiconductor region; a third insulating film is stacked on the polycrystalline semiconductor film; A contact hole is opened in the insulating film to expose the second first conductive semiconductor region and a part of the first second conductive semiconductor region, and the contact hole is formed on the third insulating film. A sixth step of forming a first electrode in contact with the second first conductivity type semiconductor region and a part of the first second conductivity type semiconductor region via a first step; A second step of grinding a second main surface and forming a second second conductivity type semiconductor region along the ground surface; and a second electrode in contact with the second second conductivity type semiconductor region. It includes an eighth step of forming.

  According to a nineteenth aspect of the present invention, in the semiconductor device manufacturing method according to the eighteenth aspect, in the third step, the first conductivity type semiconductor film is formed at a concentration higher than that of the single crystal semiconductor substrate. It is characterized by doping to one conductivity type.

  According to a twentieth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the twentieth aspect of the invention, wherein the second main surface of the single crystal semiconductor substrate is ground after the second step in the seventh step. A third first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is formed deeper than the second second conductivity type semiconductor region along the plane.

  According to a twenty-first aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the eighteenth to twentieth aspects, wherein the first conductive type semiconductor film is formed of polycrystalline silicon.

  A method of manufacturing a semiconductor device according to a twenty-second aspect of the invention is the method according to any one of the eighteenth to twentieth aspects, wherein a part or all of the first conductivity type semiconductor film is formed of single crystal silicon. It is characterized by.

  According to a twenty-third aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the twenty-second aspect, wherein the first conductive type semiconductor film is formed by an epitaxial growth method.

  According to a twenty-fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising: a first step of selectively burying a first insulating film below a first main surface of a first conductivity type single crystal semiconductor substrate; A second insulating film and a polycrystalline semiconductor film are sequentially formed on the first main surface, a part of the polycrystalline semiconductor film and the second insulating film is removed, and the first insulating film is embedded. A second step of leaving the polycrystalline semiconductor film and the second insulating film in a portion above the unexposed region, and a first second between the first insulating film and the first main surface. A third step of forming a conductive semiconductor region and further forming a first conductive semiconductor region in the first second conductive semiconductor region; and a third insulating film on the polycrystalline semiconductor film. The first insulating semiconductor layer and the first second conductive layer are stacked, and a contact hole is opened in the third insulating film. A fourth step of exposing a part of the semiconductor region, and one of the first conductive type semiconductor region and the first second conductive type semiconductor region on the third insulating film via the contact hole. A fifth step of forming a second second-conductivity-type semiconductor region along the ground surface by grinding the second main surface of the single crystal semiconductor substrate after forming the first electrode in contact with the portion And a sixth step of forming a second electrode in contact with the second second conductivity type semiconductor region.

  According to a 25th aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the 24th aspect of the present invention, wherein the second main surface of the single crystal semiconductor substrate is ground on the ground surface in the fifth step. A second conductive semiconductor region having a higher impurity concentration than that of the single crystal semiconductor substrate is formed deeper than the second conductive semiconductor region.

  According to a twenty-sixth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the twenty-fourth or twenty-fifth aspect, wherein the first insulating film is formed on the single crystal semiconductor substrate in the first step. It is characterized in that oxygen ions are selectively implanted.

  According to a twenty-seventh aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the twenty-sixth aspect, wherein in the first step, oxygen ions are implanted into the single crystal semiconductor substrate and then annealed at a temperature of 1000 ° C. or higher. Thus, the first insulating film is formed.

  A semiconductor device according to a twenty-eighth aspect of the present invention is the semiconductor device according to any one of the first to tenth aspects, wherein the first insulating film in the window portion of the first insulating film of the single crystal semiconductor substrate. The second conductivity type diffusion layer is provided independently for each cell in a portion where the first conductivity type semiconductor region is in contact.

  A semiconductor device according to a twenty-ninth aspect of the invention is the semiconductor device according to the twenty-eighth aspect, wherein the applied voltage at the time of blocking forward voltage is a voltage within a range in which no avalanche breakdown occurs in any part of the element. The second conductivity type diffusion layer is completely depleted.

  A semiconductor device according to a thirtieth aspect of the present invention is the semiconductor device according to the twenty-eighth or thirty-ninth aspect, wherein the first first in the window portion of the first insulating film in the second conductivity type diffusion layer. A first conductivity type diffusion layer is provided in a portion where the conductivity type semiconductor region is in contact.

  In the semiconductor device according to a thirty-first aspect, in the invention according to the thirty-third aspect, the applied voltage at the time of blocking forward voltage is a voltage within a range in which no avalanche breakdown occurs in any part of the element. In some cases, the first conductivity type diffusion layer is completely depleted.

  According to a thirty-second aspect of the present invention, in the semiconductor device according to the thirty-first aspect, the first conductivity type diffusion layer extends below the polycrystalline semiconductor region.

  According to a thirty-third aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the thirteenth to seventeenth aspects, wherein the polycrystal is provided between the second step and the third step. Ions are implanted from the window of the semiconductor film, and the second conductivity type diffusion layer is independently formed for each cell in a self-aligned manner with the portion of the single crystal semiconductor substrate in contact with the first first conductivity type semiconductor region. It further has the process of forming, It is characterized by the above-mentioned.

  According to a thirty-fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the eighteenth to twenty-third aspects, wherein the first step is performed between the second step and the third step. The second conductivity type diffusion layer is made independent for each cell in a self-aligned manner in the portion of the single crystal semiconductor substrate in contact with the first first conductivity type semiconductor region. And a step of forming the structure.

  According to a thirty-fifth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the thirty-third or thirty-fourth aspect, wherein the second conductive type diffusion layer is formed when the second conductive type diffusion layer is formed. A first conductivity type diffusion layer is formed in a portion where the first first conductivity type semiconductor region is in contact.

  According to the semiconductor device of the present invention, since the carrier distribution in the drift layer made of the first conductivity type single crystal semiconductor substrate becomes the surface deviated type, the trade-off between the on-voltage and the turn-off loss is optimized. On the other hand, by suppressing the local peak of the electric field strength in the cathode region, local avalanche breakdown is less likely to occur, and sufficient withstand voltage can be secured, so the on-voltage-withstand voltage trade-off deteriorates. Can be prevented. In addition, according to the method of manufacturing a semiconductor device according to the present invention, the cathode region is separated from the drift layer (first conductivity type single crystal semiconductor substrate) by the first insulating film. It does not directly contribute to the drift region characteristics. Therefore, even if the source region is not made smaller than before, the trade-off characteristics are unchanged.

  According to the semiconductor device and the method for manufacturing the same according to the present invention, using a low-cost manufacturing process, with a high yield rate, an on-voltage-turn-off loss tradeoff and an on-voltage-withstand voltage tradeoff are very good. There is an effect that a semiconductor device can be obtained.

  Exemplary embodiments of a semiconductor device and a method for manufacturing the same according to the present invention will be explained below in detail with reference to the accompanying drawings. In the following description, the first conductivity type is assumed to be n-type and the second conductivity type is assumed to be p-type. However, the present invention also holds in the opposite case. Moreover, in the following description and all attached drawings, the same code | symbol is attached | subjected to the same structure and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
FIG. 3 is a cross-sectional view showing the configuration of the IGBT according to the first embodiment. As shown in FIG. 3, for example, an oxide film (first insulating film) 21 is selectively formed on the first main surface of an n ⁻ single crystal silicon substrate 29 to be a drift layer. On the oxide film 21, polysilicon (hereinafter referred to as gate polysilicon) 22 serving as a gate electrode is deposited. The surface of the gate polysilicon 22 is covered with a gate oxide film (second insulating film) 23.

The surface of the gate oxide film 23 and the portion of the n ⁻ single crystal silicon substrate 29 not covered with the oxide film 21 are n-type doped cathodes with a higher concentration than the drift layer (n ⁻ single crystal silicon substrate 29). Covered with a membrane 24. The cathode film 24 may be made of, for example, polysilicon, or may be made of n-type single crystal silicon that is epitaxially grown from a portion of the n ⁻ single crystal silicon substrate 29 that is not covered with the oxide film 21. A portion of the cathode film 24 that contacts the n ⁻ single crystal silicon substrate 29 becomes an n ⁺ buffer region (first first conductivity type semiconductor region) 25.

A portion of the cathode film 24 adjacent to the n ⁺ buffer region 25 and in contact with the gate oxide film 23 is a p base region (first second conductivity type semiconductor region) selectively doped to a high concentration p type. 27 is provided. An extremely high-concentration n ⁺ source region (second first conductivity type semiconductor region) 26 is formed in a portion of the p base region 27 away from the n ⁺ buffer region 25. On the cathode film 24, an interlayer insulating film (third insulating film) 28 made of an oxide film such as BPSG is selectively formed.

An aluminum layer to be an emitter electrode (first electrode) 30 is formed on the interlayer insulating film 28, the n ⁺ source region 26 and the p base region 27. Emitter electrode 30 is in contact with part or all of n ⁺ source region 26 and is in contact with part of p base region 27. A p ⁺ anode layer (second second conductivity type semiconductor region) 31 is formed on the second main surface of the n ⁻ single crystal silicon substrate 29. On the surface of the p ⁺ anode layer 31, an aluminum layer serving as an anode electrode (second electrode) 32 is formed. Although not particularly shown, an n ⁺ buffer layer (third first conductivity type semiconductor) having a higher impurity concentration than the drift layer (n ⁻ single crystal silicon substrate 29) is provided between the drift layer and the p ⁺ anode layer 31. Area) may be provided.

Here, the reason why the n ⁻ drift layer that holds the withstand voltage during blocking and flows current when conducting is formed of the n ⁻ single crystal silicon substrate 29 is as follows. That is, the drift layer is one-dimensional and does not have a complicated structure. Therefore, the physical characteristics are the parts that influence the characteristics of the device itself, and it is necessary to keep the physical constants (carrier mobility and carrier life) at the maximum values. Therefore, it is essential to use a single crystal. On the other hand, regarding the cathode and the anode, the physical constants of the materials constituting the cathode and the anode are not the most important, and the structure is more important. The IGBT according to the present embodiment is characterized in that the cathode region is structurally separated from the drift layer, and is effective in improving the IE effect.

  Next, the operation and effect of the first embodiment will be described. Here, it is assumed that the cathode film 24 is made of polysilicon.

(Regarding steady ON state)
When a positive potential is applied to the gate electrode (gate polysilicon 22) with respect to the emitter, the region of the p base region 27 in the vicinity of the interface with the gate oxide film 23 is inverted to n-type, thereby forming a channel. When a forward bias is applied between the collector and the emitter, electrons flow into the drift layer (n ⁻ single crystal silicon substrate 29) via the channel and the electron storage layer (n ⁺ buffer region 25), and the back surface (second It reaches the p ⁺ anode layer 31 on the main surface). As a result, the pn junction on the back surface, that is, the junction between the p ⁺ anode layer 31 and the drift layer is forward-biased, so that holes are injected from the p ⁺ anode layer 31 into the drift layer.

The injected holes enter the n ⁺ buffer region 25 when they come to the surface (first main surface) of the drift layer. Some of holes entering the n ⁺ buffer region 25 disappears recombine with electrons in the n ⁺ buffer region 25 within. The remaining holes pass through the n ⁺ buffer region 25 and flow into the p base region 27. Since the hole current flows through the narrow and long polysilicon region (cathode film 24), a voltage drop occurs. Therefore, the n ⁺ / n ⁻ junction composed of the n ⁺ buffer region 25 which is an electron storage layer and the n ⁻ drift layer is forward-biased. As a result, electrons are injected to increase the electron concentration on the cathode side, and accordingly, holes of the same concentration are accumulated to satisfy the charge neutrality condition.

Since holes are injected into the n ⁺ buffer region 25, the n ⁺ / n ⁻ junction is also forward-biased, and electrons are injected. The polysilicon region (cathode film 24) and the n ⁻ single crystal silicon substrate 29 are separated from each other by the oxide film 21 in most parts. Therefore, the pnp-BJT region is a small part of the entire device, and the majority is the pin diode region. In addition, the channel can be formed using a sufficient area, and the channel peripheral length can be increased freely. However, if the peripheral length is too large, the transfer characteristic becomes too high, the current limit at the time of short-circuiting increases, and the short-circuit withstand capability decreases, so it is necessary to determine the peripheral length in consideration of this point.

(For forward blocking state)
Next, the operation in the blocking mode in which the gate potential is the same or negative compared to the emitter potential and a forward bias is applied between the collector and the emitter will be described. A depletion layer spreads from the pn junction composed of the p base region 27 and the n ⁺ buffer region 25, and a depletion layer also spreads from the gate oxide film 23. This is because the n ⁺ buffer region 25 is positively biased while the gate electrode is below the emitter potential. Since the n ⁺ buffer region 25 is only the thickness of the polysilicon serving as the cathode film 24, it is completely depleted with a slight forward bias. If the total impurity amount in the n ⁺ buffer region 25 is set to a certain value or less, the maximum electric field strength in the n ⁺ buffer region 25 can be suppressed.

As the forward bias is further increased, the depletion layer extends into the n ⁻ drift layer. Most of the applied forward bias is carried by the n ⁻ drift layer. Since the local peak of the electric field intensity in the cathode region can be suppressed, local avalanche breakdown hardly occurs. Therefore, a sufficient breakdown voltage can be ensured. As a result, the on-voltage-withstand voltage trade-off does not deteriorate. This is a great advantage compared to conventional planar type or trench type IGBTs. In the conventional planar type or trench type IGBT, it is difficult to avoid local electric field concentration.

(About trade-off characteristics)
Polysilicon is inferior in terms of mobility and carrier life compared to single crystal silicon. However, by annealing at a high temperature of 1000 ° C. or higher, the mobility and carrier life of polysilicon are restored to a considerable extent. A technique for restoring mobility while controlling the crystal grain size by laser annealing has also been developed. If such a technique is used, it is considered that characteristic variations such as threshold values and transfer characteristics can be reduced.

FIG. 4 shows potential sharing in the ON state of the IGBT having the configuration shown in FIG. As shown in FIG. 4, the on-voltage of the IGBT includes a voltage drop in the n ⁺ source region 26 (indicated by an arrow 41) and a voltage drop in the channel region (p base region 27) (indicated by an arrow 42). And a voltage drop in the n ⁺ buffer region 25 (indicated by an arrow 43), and a forward bias (indicated by an arrow 44) between the n ⁺ buffer region 25 and the n ⁻ drift layer (n ⁻ single crystal silicon substrate 29). ), A voltage drop in the n ⁻ drift layer (indicated by an arrow 45), and a voltage drop between the n ⁻ drift layer and the p ⁺ anode layer 31 (indicated by an arrow 46).

In the n ⁺ source region 26, since the doping concentration is very high, the resistance is low even if the mobility is low, so there is almost no voltage drop. In this embodiment, since the peripheral length of the channel region (p base region 27) can be set relatively freely, the voltage drop can be reduced by increasing the peripheral length so as to compensate for the mobility degradation. It can be set to the same level as a conventional IGBT. In the n ⁺ buffer region 25, since the polysilicon has a low mobility, the voltage drop slightly increases, but the contribution to the total on-voltage is small as shown in a later simulation. Conversely, the voltage drop in the n ⁺ buffer region 25 causes the potential of the n ⁻ drift layer to rise with respect to the emitter potential. On the other hand, the electron accumulation layer on the surface of the n ⁺ buffer region 25 has a very high electron concentration (˜1 × 10 ¹⁹ cm ⁻³ ) and a low electric resistance, so that the voltage drop is small.

For this reason, the junction composed of the n ⁺ electron storage layer and the n ⁻ drift layer is more forward-biased, so that electrons are easily injected. That is, when a voltage drop occurs in the n ⁺ buffer region 25, the carrier distribution in the n ⁻ drift layer becomes a surface-biased type. This optimizes the on-voltage-turnoff loss tradeoff. This means that the voltage drop in the n ⁻ drift layer, which occupies most of the on-voltage sharing, particularly in the high voltage IGBT, is minimized for a certain turn-off loss.

(Latch-up tolerance)
When the carrier lifetime and mobility in the n ⁺ buffer region 25 are low, the diffusion length of holes that are minority carriers is shortened, and the recombination of carriers in the n ⁺ buffer region 25 is increased. As a result, the hole current flowing through the p base region 27 and flowing into the emitter electrode 30 is reduced. For this reason, the hole current contributing to latch-up is reduced, and the latch-up resistance is improved.

Here, if not dare to restore the properties of polysilicon, n ⁺ hole diffusion length in the buffer area 25 is much shorter than the length of the n ⁺ buffer region 25. Accordingly, since most of the holes disappear due to recombination in the n ⁺ buffer region 25, the hole current reaching the p base region 27 becomes zero. In this case, a latch-up free IGBT, that is, a latch-up free IGBT is realized. This is essentially different in operation from conventional IGBTs. In this case, since the p base region 27 does not operate as a collector of the BJT, an equivalent circuit model of a conventional IGBT combining a MOSFET and a BJT is not established. When such an IGBT is represented by an equivalent circuit, a circuit combining a MOSFET and a pin diode is obtained.

(About micro processes)
The above-described IGBT structure has a design advantage that extreme miniaturization is unnecessary. The cathode region is electrically separated from the drift layer by the oxide film 21 and is connected to the drift layer only at a portion where the oxide film 21 is not present, that is, at a window portion of the oxide film 21. Therefore, the design dimensions of the cathode region do not directly contribute to the drift layer characteristics. This is symmetric to the conventional planar type or trench type IGBT. In the conventional IGBT, all of the cathode region is directly connected to the drift layer, and the design dimensions are directly related to the characteristics. Therefore, in the present embodiment, the trade-off characteristics are unchanged even if the n ⁺ source region 26 is not particularly miniaturized.

Embodiment 2. FIG.
FIG. 5 is a cross-sectional view showing the configuration of the IGBT according to the second embodiment. As shown in FIG. 5, the second embodiment is different from the first embodiment in that first, the surface of the oxide film 21 to be the first insulating film, and the oxide film of the n ⁻ single crystal silicon substrate 29. The portion not covered with 21 is covered with the cathode film 24. Second, the gate oxide film 23 is formed on the surface of the cathode film 24, and the gate polysilicon 22 is provided on the gate oxide film 23. Third, an interlayer insulating film 28 is provided on the gate polysilicon 22, and the gate polysilicon 22 is insulated from the emitter electrode 30 by the interlayer insulating film 28. Fourth, the emitter electrode 30 is in contact with the n ⁺ source region 26 and the p base region 27 through a contact hole that penetrates the interlayer insulating film 28 and the gate oxide film 23.

In the cathode film 24, the n ⁺ buffer region 25 is a portion in contact with the n ⁻ single crystal silicon substrate 29, and the p base region 27 is provided on the oxide film 21 outside the window portion of the oxide film 21. Yes. N ⁺ source region 26 is provided in a surface region inside p base region 27. Other configurations are the same as those in the first embodiment. As in the first embodiment, a high impurity concentration n ⁺ buffer layer serving as the third first conductivity type semiconductor region may be provided between the drift layer and the p ⁺ anode layer 31. Further, since the operation and effect of the second embodiment are the same as those of the first embodiment, the description thereof is omitted.

In the second embodiment, when the gate electrode (gate polysilicon 22) is set to a positive potential with respect to the cathode, electrons are induced in a region of the p base region 27 in the vicinity of the interface with the gate oxide film 23, thereby forming a channel. Is done. Electrons enter the n ⁺ buffer region 25 through this channel. Since an extremely high concentration electron storage layer is formed on the surface of the n ⁺ buffer region 25, most of the electron current flows through the electron storage layer. Then, when electrons enter the drift layer (n ⁻ single crystal silicon substrate 29), they are injected into the p ⁺ anode layer 31 on the back surface due to electric field drift. The electrons injected into the p ⁺ anode layer 31 move to the anode electrode 32 by diffusion.

Since the junction between the n ⁻ drift layer and the p ⁺ anode layer 31 is forward-biased, holes are injected from the anode, move in the n ⁻ drift layer due to electric field drift, and enter the n ⁺ buffer region 25. Since most of the holes have a short diffusion length, they recombine with electrons in the n ⁺ buffer region 25 and the electron storage layer of the n ⁺ buffer region 25 and disappear. Since the junction composed of the electron storage layer and the n ⁻ drift layer is forward-biased, electron injection from the electron storage layer is promoted (IE effect). For this reason, the carrier concentration on the cathode side is increased, and the trade-off between on-voltage and switching loss is improved.

Embodiment 3 FIG.
6 to 13 are cross-sectional views for explaining the manufacturing method of the third embodiment. Although not particularly limited, in the third embodiment, a case will be described in which a non-punch through type IGBT having a rated voltage of 600 V to which the structure of the second embodiment is applied is manufactured. First, as the n ⁻ single crystal silicon substrate 29, for example, an n-type FZ silicon substrate of 30 Ωcm is prepared. Then, thermal oxidation is performed to grow an oxide film 21 having a thickness of, for example, 0.1 μm on the mirror polished surface of the substrate (FIG. 6). Next, patterning and etching are performed to remove a part of the oxide film 21 (FIG. 7).

Next, on the exposed portions of the oxide film 21 and the n ⁻ single crystal silicon substrate 29 in the window portion of the oxide film 21, for example, polysilicon doped in the n-type at a concentration of 1 × 10 ¹⁶ cm ⁻³ is used. Deposit to a thickness of 0.25 μm. This polysilicon is a cathode film 24, which later becomes a source region, a channel region, and a buffer region (FIG. 8). Next, thermal oxidation is performed to oxidize the surface of the cathode film 24 to form a gate oxide film 23 having a thickness of 0.1 μm, for example. At that time, since the film thickness of polysilicon is reduced by, for example, 0.05 μm, the thickness of the cathode film 24 becomes, for example, 0.2 μm.

Next, on the gate oxide film 23, a gate polysilicon 22 to be a gate electrode is deposited to a thickness of 0.5 μm, for example. Then, for example, heat treatment is performed at 900 ° C. in a POCl ₃ atmosphere to dope the gate polysilicon 22 to a high concentration n-type (FIG. 9). Next, patterning and etching are performed to remove a part of the gate polysilicon 22. Using the remaining gate polysilicon 22 as a mask, boron having a dose of, for example, 5 × 10 ¹⁴ cm ⁻² and arsenic having a dose of, for example, 1 × 10 ¹⁵ cm ⁻² are ion-implanted into the cathode film 24. Then, for example, driving is performed at 1150 ° C. for 2 hours in a nitrogen atmosphere to form a p base region 27 and an n ⁺ source region 26 which become channel regions (FIG. 10).

Next, BPSG having a thickness of, for example, 1 μm is deposited as the interlayer insulating film 28, and patterning and etching are performed to form a contact hole that penetrates the interlayer insulating film 28 and the gate oxide film 23. Next, a metal such as aluminum is sputtered on the interlayer insulating film 28 to a thickness of 5 μm, for example. Then, patterning and etching of a metal such as aluminum is performed to form the emitter electrode 30 (FIG. 11). Next, the back surface of the n ⁻ single crystal silicon substrate 29 is ground to a wafer thickness of, for example, 100 μm. Thereafter, boron having a dose of, for example, 1 × 10 ¹⁴ cm ⁻² is ion-implanted into the ground surface. Then, for example, annealing is performed at 380 ° C. for 1 hour to form the p ⁺ anode layer 31 (FIG. 12).

Next, a metal such as aluminum is deposited on the surface of the p ⁺ anode layer 31 to form the anode electrode 32 (FIG. 13). It should be noted that n-type impurities such as phosphorus may be ion-implanted into the ground surface of the back surface of the n ⁻ single crystal silicon substrate 29 before annealing. That way, by annealing, with p ⁺ anode layer 31, n ^- n ⁺ buffer layer is formed between the drift layer and the p ⁺ anode layer 31. Finally, the wafer is diced to complete the chip.

Embodiment 4 FIG.
14 to 21 are cross-sectional views for explaining the manufacturing method of the fourth embodiment. Although not particularly limited, in the fourth embodiment, a case of manufacturing a field stop type IBGT having a rated 1200 V breakdown voltage to which the structure of the first embodiment is applied will be described. However, in the fourth embodiment, an n ⁺ buffer layer 33 having a higher impurity concentration than the drift layer is formed as a field stop layer between the drift layer (n ⁻ single crystal silicon substrate 29) and the p ⁺ anode layer 31. Is done.

First, as the n ⁻ single crystal silicon substrate 29, for example, an n-type FZ silicon substrate of 80 Ωcm is prepared. Then, thermal oxidation is performed to grow an oxide film 21 having a thickness of, for example, 0.1 μm on the mirror polished surface of the substrate. Subsequently, a gate polysilicon 22 is deposited on the oxide film 21 to a thickness of 0.5 μm, for example. Then, for example, heat treatment is performed at 900 ° C. in a POCl ₃ atmosphere to dope the gate polysilicon 22 to a high concentration n-type (FIG. 14).

Next, patterning and etching are performed to remove a part of the gate polysilicon 22 (FIG. 15). Next, thermal oxidation is performed to oxidize the surface of the gate polysilicon 22 to form a gate oxide film 23 having a thickness of, for example, 0.1 μm. Subsequently, patterning and etching are performed to remove portions of the gate oxide film 23 and the oxide film 21 where the gate polysilicon 22 is not present (FIG. 16). Next, on the exposed portions of the gate oxide film 23 and the n ⁻ single crystal silicon substrate 29, polysilicon doped in an n-type at a concentration of 1 × 10 ¹⁶ cm ⁻³ is deposited to a thickness of, for example, 0.25 μm. (FIG. 17). This polysilicon is the cathode film 24 and later becomes a source region, a channel region, and a buffer region.

Next, using the patterned resist as a mask, boron having a dose of, for example, 5 × 10 ¹⁴ cm ⁻² and arsenic having a dose of, for example, 1 × 10 ¹⁵ cm ⁻² are ion-implanted into the cathode film 24. Then, after the resist is ashed, for example, driving is performed at 1150 ° C. for 2 hours in a nitrogen atmosphere to form the p base region 27 and the n ⁺ source region 26 that become the channel region. At that time, the crystal grain size of polysilicon (cathode film 24) is increased, and the mobility is recovered (FIG. 18).

Next, BPSG having a thickness of 1 μm, for example, is deposited as the interlayer insulating film 28, and patterning and etching are performed to form a contact hole penetrating the interlayer insulating film 28 (FIG. 19). Next, a metal such as aluminum is sputtered on the interlayer insulating film 28 to a thickness of 5 μm, for example. Then, patterning and etching of a metal such as aluminum is performed to form the emitter electrode 30. Next, the back surface of the n ⁻ single crystal silicon substrate 29 is ground to a wafer thickness of, for example, 140 μm.

Thereafter, phosphorus having a dose of, for example, 2 × 10 ¹² cm ⁻² and boron having a dose of, for example, 5 × 10 ¹⁴ cm ⁻² are ion-implanted into the ground surface. Then, for example, annealing is performed at 450 ° C. for 5 hours to form the n ⁺ buffer layer 33 and the p ⁺ anode layer 31. The n ⁺ buffer layer 33 is formed at a position deeper than the p ⁺ anode layer 31 (FIG. 20). Next, a metal such as aluminum, titanium, nickel and gold is deposited on the surface of the p ⁺ anode layer 31 to form the anode electrode 32 (FIG. 21). Finally, the wafer is diced to complete the chip.

FIG. 22 shows the output characteristics of a field stop IGBT with a rated voltage of 1200 V manufactured according to the fourth embodiment (referred to as an example) and a conventional field stop IGBT with a rated voltage of 1200 V (referred to as a conventional example). FIG. As shown in FIG. 22, the on-voltage of the example was 1.4 V at a temperature of 125 ° C. and a current density of 100 A / cm ² . On the other hand, the on-voltage of the conventional example was 2.2V. Accordingly, it was confirmed that the on-voltage was lower in the example.

  FIG. 23 shows the on-voltage sharing in the steady-on state of the field-stop IGBT with a rated voltage of 1200 V manufactured according to the fourth embodiment. FIG. 23 shows the magnitude of the bias shared by each region of the device when a voltage of 2 V is applied between the collector and the emitter. Looking at the overall diagram (the diagram on the left side of FIG. 23), on the surface side where the carrier concentration is high (the upper side in the diagram), the electrical resistance is low, so the interval between equipotential lines is wide. On the other hand, since the electrical resistance is high on the back surface side (lower side in the figure) where the carrier concentration is low, the interval between equipotential lines is narrow.

Further, when the enlarged view of the cathode region in FIG. 23 (the diagram on the right side of FIG. 23) is seen, in the cathode region on the surface (polysilicon region of the cathode film 24), the carrier mobility is 1/3 or less of single crystal silicon. Despite being, it can be seen that the equipotential line spacing is wide, that is, the resistance is low. This is because most of the current flows through the electron storage layer. The lifetime of electrons and holes is 500 ps. The hole diffusion length in the polysilicon is about 0.5 μm. Therefore, many of the holes that have entered the cathode region disappear due to recombination within the n ⁺ buffer region 25. In addition, since the hole current in the p base region 27 is extremely small, there is no voltage drop in the p base region seen in the conventional IGBT. Accordingly, since the junction between the n ⁺ source region 26 and the p base region 27 is not forward-biased, the thyristor operation due to latch-up does not occur. That is, since it is latch-up free, it is expected that the short-circuit tolerance and the reverse bias safe operation area are improved.

However, when the hole lifetime of the cathode region is too short, n ⁺ becomes the hole current density in the buffer area 25 is low, n ⁺ voltage drop in the buffer area 25 within decreases. In this case, since the forward bias amount of the junction between the electron storage layer and the n ⁻ drift layer is reduced, electron injection from the cathode region is reduced. Therefore, the IE effect is improved by generating a voltage drop in the n ⁺ buffer region 25 by securing a certain hole current. As a result, the voltage drop in the n ⁺ buffer region 25 is canceled by optimizing the carrier distribution in the n ⁻ drift layer.

  FIG. 24 shows a longitudinal direction in the ON state of a field stop type IGBT with a rated voltage of 1200 V manufactured according to the fourth embodiment (referred to as an example) and a conventional field stop type IGBT with a rated voltage of 1200 V withstand voltage (referred to as a conventional example). It is a characteristic view which shows excess carrier distribution. As shown in FIG. 24, in the example, the cathode side carrier concentration was about 5 times higher than the anode side carrier concentration, and it was confirmed that the distribution was ideal. FIG. 25 shows the on-state voltage of the field-stop type IGBT with a rated voltage of 1200 V manufactured according to the fourth embodiment (example) and the conventional field-stop type IGBT with a rated voltage of 1200 V (referred to as a conventional example). It is a characteristic view which shows the trade-off of turn-off loss. As shown in FIG. 25, it was confirmed that the trade-off of the example was greatly improved as compared with the conventional example.

  FIG. 26 is a diagram showing an electric field distribution in a blocking mode of a field stop IGBT (with an example) having a rated voltage of 1200 V manufactured according to the fourth embodiment. FIG. 27 is a diagram showing an electric field distribution in a blocking mode of a conventional field stop type IGBT (conventional example) having a rated withstand voltage of 1200V. From both figures, it was confirmed that the withstand voltage of the example at a current of 1 mA was 1420V, which was improved from the withstand voltage (1370V) of the conventional IGBT. In the blocking mode of the embodiment, the electric field is averaged, and a numerical value close to the one-dimensional ideal withstand voltage is obtained. For this reason, even if the wafer is made thinner, a breakdown voltage comparable to that of the conventional example can be obtained. Of course, the on-voltage of the embodiment is reduced. This means that the on-voltage-withstand voltage trade-off of the embodiment is excellent.

FIG. 28 is an enlarged view showing the electric field distribution in the blocking mode of the field-stop type IGBT with a rated 1200 V breakdown voltage manufactured according to the fourth embodiment. FIG. 28 shows that the maximum electric field is present in the vicinity of the boundary surface between polysilicon (cathode film 24) and single crystal silicon (n ⁻ single crystal silicon substrate 29).

Embodiment 5. FIG.
29 to 33 are cross-sectional views for explaining the manufacturing method of the fifth embodiment. Although not particularly limited, in the fifth embodiment, a case where a reverse blocking type IBGT having a rated withstand voltage of 600 V to which the structure of the first embodiment is applied will be described. However, in FIGS. 29 to 33, only the active portion is shown, and the separation layer region is not shown. Also, the process for forming the separation layer region is not shown.

First, as the n ⁻ single crystal silicon substrate 29, for example, an n-type FZ silicon substrate of 30 Ωcm is prepared. Then, in order to form the separation layer region, thermal oxidation is performed, and an oxide film having a thickness of 1.6 μm, for example, is grown on the mirror polished surface of the substrate. Subsequently, patterning and etching are performed to remove a part of the oxide film. Next, a boron source is applied, and driving is performed at 1300 ° C. for 90 hours in an oxygen atmosphere to form a separation layer region.

Next, thermal oxidation is performed to grow an oxide film 21 having a thickness of, for example, 0.1 μm. Subsequently, a gate polysilicon 22 is deposited on the oxide film 21 to a thickness of 0.5 μm, for example. Then, for example, heat treatment is performed at 900 ° C. in a POCl ₃ atmosphere, and the gate polysilicon 22 is doped to a high concentration n-type. Next, patterning and etching are performed to remove a part of the gate polysilicon 22. Next, thermal oxidation is performed to oxidize the surface of the gate polysilicon 22 to form a gate oxide film 23 having a thickness of, for example, 0.1 μm. Subsequently, patterning and etching are performed to remove portions of the gate oxide film 23 and the oxide film 21 where the gate polysilicon 22 is not present (see FIGS. 14, 15 and 16).

Next, a single crystal silicon layer containing phosphorus having a concentration of, for example, 1 × 10 ¹⁶ cm ^{−3 is} grown from the opening of the n ⁻ single crystal silicon substrate 29 by an epitaxial method. The epitaxial growth layer first grows upward from the opening of the n ⁻ single crystal silicon substrate 29 and does not grow on the gate oxide film 23. When the epitaxial growth layer grows up to the height of the upper surface of the gate oxide film 23, the epitaxial growth layer continues to grow upward and laterally. Eventually, the epitaxial growth layers grown from the adjacent openings of the n ⁻ single crystal silicon substrate 29 come into contact with each other, and the upper surface of the gate oxide film 23 is completely covered with the epitaxial growth layer. This epitaxially grown single crystal silicon layer is a cathode film 24, which later becomes a source region, a channel region, and a buffer region (FIG. 29).

Next, boron having a dose of 1.5 × 10 ¹⁴ cm ⁻² is ion-implanted into the cathode film 24, for example. Subsequently, arsenic having a dose of, for example, 1 × 10 ¹⁵ cm ⁻² is ion-implanted into the cathode film 24 using the patterned resist as a mask. Then, after the resist is incinerated, for example, driving is performed at 1150 ° C. for 2 hours in a nitrogen atmosphere to form a p base region 27 and an n ⁺ source region 26 which become channel regions (FIG. 30). Next, BPSG having a thickness of 1 μm, for example, is deposited as the interlayer insulating film 28, and patterning and etching are performed to form a contact hole penetrating the interlayer insulating film 28 (FIG. 31).

Next, a metal such as aluminum is sputtered on the interlayer insulating film 28 to a thickness of 5 μm, for example. Then, patterning and etching of a metal such as aluminum is performed to form the emitter electrode 30. Next, the back surface of the n ⁻ single crystal silicon substrate 29 is ground to a wafer thickness of, for example, 100 μm. Thereafter, boron having a dose of, for example, 1 × 10 ¹⁴ cm ⁻² is ion-implanted into the ground surface. Then, for example, annealing is performed at 380 ° C. for 1 hour to form the p ⁺ anode layer 31 (FIG. 32). Next, a metal such as aluminum, titanium, nickel and gold is deposited on the surface of the p ⁺ anode layer 31 to form the anode electrode 32 (FIG. 33). Finally, the wafer is diced to complete the chip.

  The reverse blocking type IBGT manufactured according to the fifth embodiment is excellent in the on-voltage-turn-off loss trade-off characteristic. Further, according to the reverse blocking type IBGT manufactured according to the fifth embodiment, the reverse leakage current in the reverse bias application mode peculiar to the reverse blocking type IBGT is reduced as compared with the conventional reverse blocking type IBGT. In the reverse blocking IGBT, when an electron current generated at the pn junction on the back surface side is injected into the p base region on the front surface side, the electron current becomes a base current of a pnp structure. Therefore, a large hole current is injected from the p base region on the surface side due to the amplification effect.

One of the major factors determining the magnitude of the hole current with respect to the electron current, that is, the amplification factor of the grounded emitter, is the impurity amount ratio between the p base region and the n-type drift layer. When the value of this ratio is large, the emitter injection efficiency increases and the amplification factor increases. In the conventional reverse blocking type IBGT with a rated withstand voltage of 600 V, the impurity amount of the n-type drift layer is about 1.5 × 10 ¹² cm ⁻² . On the other hand, since the impurity amount of the p base region is about 1.5 × 10 ¹⁴ cm ⁻² , the impurity amount ratio between the p base region and the n-type drift layer is 100 times.

On the other hand, in the reverse blocking type IBGT with a rated voltage of 600 V manufactured according to the fifth embodiment, the impurity amount ratio between the p base region and the n type drift layer is about 30 times. In the fifth embodiment, the impurity amount of the p base region 27 is 1.5 × 10 ¹⁴ cm ⁻² which is the same as that of the conventional reverse blocking type IBGT, but the high concentration n ⁺ buffer region 25 is provided. This is because the n-type total impurity amount increases to about 5 × 10 ¹² cm ⁻² .

  As described above, since the impurity amount ratio between the p base region and the n-type drift layer is lower than the conventional one, the emitter injection efficiency is reduced to 1/3 or less of the conventional one. For this reason, since the amplification factor is lowered, the reverse leakage current is reduced to 1/3 or less of the conventional one. Further, the reverse avalanche breakdown voltage is improved by reducing the amplification factor of the pnp structure.

Embodiment 6 FIG.
34 to 41 are cross-sectional views for explaining the manufacturing method of the sixth embodiment. In the sixth embodiment, a field stop type IBGT having a rated withstand voltage of 600 V to which the structure of the second embodiment is applied will be described. However, in the sixth embodiment, an n ⁺ buffer layer 33 having a higher impurity concentration than the drift layer is formed as a field stop layer between the drift layer (n ⁻ single crystal silicon substrate 29) and the p ⁺ anode layer 31. Is done. The oxide film 21 serving as the first insulating film is formed at a predetermined depth from the surface (first main surface) of the n ⁻ single crystal silicon substrate 29, and the oxide film 21 and the n ⁻ single crystal are formed. An n ⁺ source region 26 and a p base region 27 are formed between the surface of the silicon substrate 29.

First, as the n ⁻ single crystal silicon substrate 29, for example, an n-type FZ silicon substrate of 30 Ωcm is prepared. Then, thermal oxidation is performed to grow an oxide film 34 having a thickness of, for example, 1 μm on the mirror polished surface of the substrate (FIG. 34). Next, patterning and etching are performed to remove a part of the oxide film 34. With the remaining oxide film 34 as a mask, oxygen with a dose of 1 × 10 ¹⁵ cm ⁻² is ion-implanted into the n ⁻ single crystal silicon substrate 29 at an acceleration voltage of 100 keV, for example (FIG. 35). In FIG. 35, a hatched region indicated by reference numeral 35 is an oxygen ion implantation region.

  Next, annealing is performed at 1300 ° C. to recover crystal defects. As a result, as shown in FIG. 36, an oxide film 21 having a thickness of, for example, 0.1 μm is selectively formed under a single crystal silicon having a thickness of, for example, 0.3 μm. This single crystal silicon layer having a thickness of 0.3 μm corresponds to the cathode film 24 in the first to fifth embodiments. After removing the oxide film 34 used as a mask, thermal oxidation is performed to oxidize the substrate surface to form a gate oxide film 23 having a thickness of, for example, 0.1 μm. At this time, since the single crystal silicon layer corresponding to the cathode film 24 is reduced by, for example, 0.05 μm, the thickness of the single crystal silicon layer is, for example, 0.25 μm.

Next, a gate polysilicon 22 is deposited on the gate oxide film 23 to a thickness of 0.5 μm, for example. Then, for example, heat treatment is performed at 900 ° C. in a POCl ₃ atmosphere, and the gate polysilicon 22 is doped to a high concentration n-type (FIG. 36). Next, patterning and etching are performed to remove part of the gate polysilicon 22 and the gate oxide film 23 (FIG. 37). Using the remaining gate polysilicon 22 as a mask, a single crystal silicon layer corresponding to the cathode film 24 is formed with boron having a dose of, for example, 5 × 10 ¹⁴ cm ⁻² and arsenic having a dose of, for example, 1 × 10 ¹⁵ cm ^−2. Ion implantation. Then, for example, driving is performed at 1150 ° C. for 2 hours in a nitrogen atmosphere to form a p base region 27 and an n ⁺ source region 26 which become channel regions (FIG. 38).

Next, BPSG having a thickness of, for example, 1 μm is deposited as the interlayer insulating film 28, and patterning and etching are performed to form a contact hole penetrating the interlayer insulating film 28 (FIG. 39). Next, a metal such as aluminum is sputtered on the interlayer insulating film 28 to a thickness of 5 μm, for example. Then, patterning and etching of a metal such as aluminum is performed to form the emitter electrode 30. Next, the back surface of the n ⁻ single crystal silicon substrate 29 is ground to a wafer thickness of, for example, 100 μm.

Thereafter, phosphorus having a dose of, for example, 2 × 10 ¹² cm ⁻² and boron having a dose of, for example, 5 × 10 ¹⁴ cm ⁻² are ion-implanted into the ground surface. Then, for example, annealing is performed at 1000 ° C. for 5 hours to form the n ⁺ buffer layer 33 and the p ⁺ anode layer 31. The n ⁺ buffer layer 33 is formed at a position deeper than the p ⁺ anode layer 31 (FIG. 40). Next, a metal such as aluminum, titanium, nickel and gold is deposited on the surface of the p ⁺ anode layer 31 to form the anode electrode 32 (FIG. 41). Finally, the wafer is diced to complete the chip. According to the IGBT manufactured according to the sixth embodiment, an effect that there is little characteristic variation and an effect that there is little leakage current are obtained.

Embodiment 7 FIG.
FIG. 42 is a cross-sectional view showing the configuration of the IGBT according to the seventh embodiment. As shown in FIG. 42, the seventh embodiment differs from the first embodiment in that a p diffusion layer 41 is provided in a portion of the n ⁻ single crystal silicon substrate 29 in contact with the n ⁺ buffer region 25. The n ⁺ diffusion layer 42 is provided in a portion of the p diffusion layer 41 that is in contact with the n ⁺ buffer region 25.

The n ⁺ diffusion layer 42 extends under the gate polysilicon 22. That is, when this device is viewed from the emitter electrode 30 side, the edge of the n ⁺ diffusion layer 42 overlaps the gate polysilicon 22. The p diffusion layer 41 is provided independently for each cell so as to surround the n ⁺ diffusion layer 42 and not to contact the p diffusion layer 41 (not shown in the drawing) of an adjacent cell. Other configurations are the same as those in the first embodiment.

The p diffusion layer 41 and the n ⁺ diffusion layer 42 are completely depleted when the applied voltage at blocking forward voltage is a voltage within a range where no avalanche breakdown occurs in any part of the element. Next, the operation and effect of the seventh embodiment will be described. In the seventh embodiment, the following operations and effects are obtained in addition to the operations and effects of the first embodiment.

(Regarding steady ON state)
When the gate potential is made positive compared to the emitter potential and a forward bias is applied between the collector and the emitter to turn on the forward direction, electrons are transferred from the emitter electrode 30 through the channel formed in the p base region 27 to the n ⁺ buffer. Flow into region 25. Since the p diffusion layer 41 and the n ⁺ diffusion layer 42 in the seventh embodiment as described above is provided, electrons flow from the n ⁺ buffer region 25 into the n ⁺ diffusion layer 42.

Then, electrons, over a channel surface of the p diffusion layer 41 can be inverted to n-type drift layer ^- flow into (n single-crystal silicon substrate 29), p ⁺ anode of the back surface (second main surface) Layer 31 is reached. As a result, the pn junction on the back surface, that is, the junction between the p ⁺ anode layer 31 and the drift layer is forward-biased, so that holes are injected from the p ⁺ anode layer 31 into the drift layer.

The injected holes are injected into the n ⁺ diffusion layer 42 via the p diffusion layer 41. As a result, the pn junction between the n ⁺ diffusion layer 42 and the p diffusion layer 41 is forward-biased, so that electrons are injected from the n ⁺ diffusion layer 42 into the p diffusion layer 41 and the thyristor operation is started. At this point, the role of the channel on the surface of the p diffusion layer 41 ends. That is, the channel on the surface of the p diffusion layer 41 is for turning on the thyristor. Once the thyristor operation is started, the p diffusion layer 41 is in a high injection state in which the carrier concentration is higher than the original doping concentration, so that the p diffusion layer 41 hardly affects the device characteristics.

(Forward blocking state and turn-off state)
When the forward bias is increased even after the n ⁺ buffer region 25 is completely depleted in the forward blocking mode, the depletion layer becomes a pn between the p diffusion layer 41 and the drift layer (n ⁻ single crystal silicon substrate 29). It begins to grow from the joint. At this time, most of the applied forward bias is carried by the n ⁻ drift layer. Since the distance between the adjacent p diffusion layers 41 is short, the depletion layer is easily pinched off. As a result, the portion having the curvature of the pn junction is eliminated, so that the electric field can be prevented from being concentrated on the portion having the curvature of the conventional pn junction.

In the conventional planar IGBT, when the collector region of the BJT is enlarged, the IE effect is impaired. In order not to impair the IE effect, it is necessary to design a wide distance between the p diffusion layers 41. On the other hand, in the seventh embodiment, the p diffusion layer 41 provided in the portion where the n ⁺ buffer region 25 is in contact with the n ⁻ single crystal silicon substrate 29 is not a BJT collector region. Even if it is provided, the IE effect does not change. Therefore, the withstand voltage is greatly improved as compared with the conventional planar IGBT, and the trade-off between on-voltage and turn-off loss is improved.

The important point in the forward blocking mode is that the n ⁺ buffer region 25 functioning as the cathode when the thyristor is in the on state is completely depleted. This prevents thyristor operation at turn-off. That is, when the n ⁺ buffer region 25, the n ⁺ diffusion layer 42, the p diffusion layer 41, and the n ⁻ drift layer (n ⁻ single crystal silicon substrate 29) are depleted, the original conductivity type of these regions and layers is reduced. Whether it is p-type or n-type does not affect the device characteristics.

  In this way, the problem that the controllable current peculiar to the MOS type thyristor element is low is solved. At the time of turn-off, not the channel on the surface of the p diffusion layer 41 but the channel in the p base region 27 disappears, whereby the supply of current is cut off and the turn-off operation is started.

43 and 44 are diagrams showing a doping distribution of a field stop IGBT having a rated withstand voltage of 1200 V to which the configuration of the seventh embodiment is applied and a corresponding electric field distribution in the blocking mode. As is apparent from these drawings, the electric field strength becomes maximum at the junction between the p diffusion layer 41 and the n ⁻ drift layer (n ⁻ single crystal silicon substrate 29), and the first main surface is formed in the p diffusion layer 41. It gets weaker as you get closer to. Therefore, the electric field strength in the cathode region is reduced, and avalanche breakdown is unlikely to occur in the cathode region. When there is a concern about a decrease in breakdown voltage due to the crystallinity of the cathode film 24, the electric field in the cathode film 24 is greatly relaxed by the configuration of the seventh embodiment, so that an ideal single crystal plane junction breakdown voltage is obtained. be able to.

Embodiment 8 FIG.
45 to 51 are cross-sectional views for explaining the manufacturing method according to the eighth embodiment. Although not particularly limited, in the eighth embodiment, a case of manufacturing a field stop type IBGT having a rated 1200 V breakdown voltage to which the structure of the seventh embodiment is applied will be described. However, in the eighth embodiment, an n ⁺ buffer layer 33 having a higher impurity concentration than the drift layer is formed as a field stop layer between the drift layer (n ⁻ single crystal silicon substrate 29) and the p ⁺ anode layer 31. Is done.

First, in the same manner as in the fourth embodiment, a stacked structure of an n ⁻ single crystal silicon substrate 29, an oxide film 21, and an n-type gate polysilicon 22 is formed (FIG. 14). As the n ⁻ single crystal silicon substrate 29, for example, an 80 Ωcm n-type FZ silicon substrate is used. The thickness of oxide film 21 and the thickness of gate polysilicon 22 are the same as in the fourth embodiment. Next, patterning and etching are performed to remove a part of the gate polysilicon 22.

Then, self-aligning manner n and the gate polysilicon 22 as a mask ^- the single crystal silicon substrate 29, for example, 1 × 10 ¹² cm ^-2 and the boron dose of, for example, 1 × 10 ¹² cm ^-2 dose of Arsenic ions are implanted. Then, for example, driving is performed at 1150 ° C. for 2 hours in a nitrogen atmosphere to form the p diffusion layer 41 and the n ⁺ diffusion layer 42 on the first main surface side of the n ⁻ single crystal silicon substrate 29 (FIG. 45).

  Thereafter, the process up to the completion of the chip is the same as in the fourth embodiment. Accordingly, with respect to the subsequent processes, FIG. 16, FIG. 17, FIG. 18, FIG. 19, FIG. 20 and FIG. 21 in FIG. 46, FIG. 47, FIG. 48, FIG. The description which overlaps with FIG. 51 is omitted.

FIG. 52 shows the on-voltage-turn-off loss of a field stop IGBT with a rated voltage of 1200 V manufactured according to the eighth embodiment (referred to as an example) and a conventional field stop IGBT with a rated voltage of 1200 V (referred to as a conventional example). It is a characteristic view which shows the trade-off of. As shown in FIG. 52, at a temperature of 125 ° C. and a current density of 100 A / cm ² , it was confirmed that the trade-off was slightly improved in the example compared to the conventional example. Further, the withstand voltage of the conventional example is 1078 to 1370V, whereas the withstand voltage of the example is 1615V, and it was confirmed that the withstand voltage was significantly increased (about +250 to + 500V).

The electric field distribution in the blocking mode of the field stop IGBT having a rated voltage of 1200 V manufactured according to the eighth embodiment is as shown in FIG. The breakdown voltage at a current of 1 mA is 1615V. As shown in FIG. 44, the electric field strength is maximized at the junction between the p diffusion layer 41 and the n ⁻ drift layer (n ⁻ single crystal silicon substrate 29). The electric field in the vicinity of the interface between the cathode film 24 and the single crystal silicon (n ⁺ diffusion layer 42) is relaxed by the p diffusion layer 41. Therefore, when the cathode film 24 is made of polysilicon, even if a problem such as an increase in the impact ionization rate derived from the polysilicon occurs, it can be concealed. In addition, since the depletion layer between the adjacent p diffusion layers 41 is pinched off, a breakdown voltage close to the ideal breakdown voltage of the one-dimensional planar junction can be obtained.

Embodiment 9 FIG.
FIG. 53 is a cross-sectional perspective view showing a main part of the configuration of the IGBT according to the ninth embodiment. As shown in FIG. 53, the IGBT of the ninth embodiment is an element having the same cross-sectional configuration as the IGBT of the second embodiment shown in FIG. However, in the ninth embodiment, the epitaxial layer grown from the exposed portion of the window portion of the oxide film 21 of the single crystal silicon substrate 29 is used as the cathode film 24. In the ninth embodiment, when viewed from above the stripe cell, both the source region 26 and the base region 27 are formed in a stripe shape. The emitter electrode 30 is in contact with both the source region 26 and the base region 27 through a contact hole opened in the interlayer insulating film 28.

  In order to improve device characteristics, it is advantageous to reduce the cell pitch by miniaturization. Therefore, it is desirable that the width of the source region 26 is narrow. However, if mask displacement occurs in patterning when forming contact holes in the interlayer insulating film 28, the emitter electrode 30 may not contact the source region 26. In that case, since the electronic current does not flow, the IGBT is not turned on. In order to prevent this, it is necessary to increase the width of the source region 26 to such an extent that the emitter electrode 30 reliably contacts the source region 26 even if mask displacement occurs.

Embodiment 10 FIG.
FIG. 54 is a cross-sectional perspective view showing a main part of the configuration of the IGBT according to the tenth embodiment. As shown in FIG. 54, the IGBT of the tenth embodiment is similar to the IGBT of the ninth embodiment shown in FIG. 53, in which the source region 26 is formed in a comb shape when viewed from above the stripe cell. A part (tip portion of the comb tooth) extends below the emitter electrode 30 and comes into contact with the emitter electrode 30, and the base region 27 is exposed at a portion between the comb teeth and comes into contact with the emitter electrode 30. It is what you do. Although not particularly limited, the tenth embodiment is an example of a non-punch through IGBT having a rated withstand voltage of 1200V.

  In the IGBT according to the ninth embodiment, as described in the ninth embodiment, since the width of the source region 26 needs to be widened, the cell pitch cannot be sufficiently reduced. Therefore, there is a possibility that sufficiently excellent device characteristics cannot be obtained. Further, if the base region 27 in contact with the emitter electrode 30 becomes extremely narrow, the contact resistance increases and the parasitic thyristor is likely to be latched up, so that the reverse bias safe operation region (RBSOA) withstand capability and the short circuit withstand capability may be reduced. is there.

  On the other hand, in the IGBT of the tenth embodiment, by forming the source region 26 in a comb-like shape, the emitter electrode 30 reliably contacts the source region 26 when a mask shift occurs even if the cell has a fine size. . For example, according to the dimensions shown as an example in FIG. 54, even if the mask is displaced by 1 μm, the emitter electrode 30 is in reliable contact with the source region 26, thereby avoiding the on-impossibility due to the emitter electrode 30 not being in contact with the source region 26. be able to. In addition, since the emitter electrode 30 reliably contacts the p base region 27, the parasitic thyristor is less likely to latch up. That is, according to the tenth embodiment, the drawbacks of the IGBT of the ninth embodiment can be overcome.

Embodiment 11 FIG.
FIG. 55 is a cross-sectional perspective view showing a main part of the configuration of the IGBT according to the eleventh embodiment. As shown in FIG. 55, in the IGBT of the eleventh embodiment, the source region 26 is formed in a discontinuous island shape (rectangular shape) when viewed from above the stripe cell in the IGBT of the ninth embodiment shown in FIG. Then, a part of the source region 26 extends below the emitter electrode 30 and contacts the emitter electrode 30, and the emitter electrode 30 contacts the base region 27 at a portion between the islands of the source region 26. It is a thing. Although not particularly limited, the eleventh embodiment is an example of a non-punch-through IGBT having a rated withstand voltage of 1200 V. According to the eleventh embodiment, similarly to the tenth embodiment, the drawbacks of the IGBT of the ninth embodiment can be overcome.

As described above, according to the embodiment, since the carrier distribution in the drift layer made of the n ⁻ single crystal silicon substrate 29 is a surface-biased type, the trade-off between on-voltage and turn-off loss is optimized. On the other hand, by suppressing the local peak of the electric field strength in the cathode region, local avalanche breakdown is less likely to occur, and sufficient withstand voltage can be secured, so the on-voltage-withstand voltage trade-off deteriorates. Can be prevented. In addition, since the cathode region is separated from the drift layer by the oxide film 21, the design dimension of the cathode region does not directly contribute to the characteristics of the drift region. It is. Therefore, using a low-cost manufacturing process, it is possible to obtain an IGBT having a very good product ratio and a very good on-voltage-turn-off loss trade-off and on-voltage-withstand voltage trade-off.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the withstand voltage class of the IGBT, the size and concentration of each part, the dose amount, and the like are examples and can be changed.

  As described above, the semiconductor device and the manufacturing method thereof according to the present invention are useful for a power semiconductor device used for a power conversion device and the like, and are particularly suitable for an IGBT.

It is a figure which shows the equivalent circuit of IGBT. It is sectional drawing which shows the structure of the principal part of planar type IGBT. 1 is a cross-sectional view showing a configuration of an IGBT according to a first embodiment. FIG. 4 is a cross-sectional view for explaining potential sharing in the ON state of the IGBT having the configuration shown in FIG. 3. 6 is a cross-sectional view showing a configuration of an IGBT according to a second embodiment. FIG. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the third embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fourth embodiment. FIG. 10 is a characteristic diagram showing output characteristics of an IGBT manufactured according to the fourth embodiment. It is a figure which shows on-voltage sharing at the time of the steady-on state of IGBT manufactured by Embodiment 4. FIG. FIG. 10 is a characteristic diagram showing an excess carrier distribution in the on state of an IGBT manufactured according to the fourth embodiment. FIG. 10 is a characteristic diagram showing a trade-off between an on-voltage and a turn-off loss of an IGBT manufactured according to the fourth embodiment. It is a figure which shows the electric field distribution at the time of the blocking mode of IGBT manufactured by Embodiment 4. FIG. It is a figure which shows the electric field distribution at the time of blocking mode of the conventional IGBT. 6 is an enlarged view showing an electric field distribution in the blocking mode of an IGBT manufactured according to Embodiment 4. FIG. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fifth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fifth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fifth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fifth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the fifth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. 10 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 11 is a cross-sectional view for illustrating the manufacturing method according to the sixth embodiment. FIG. 10 is a cross-sectional view showing a configuration of an IGBT according to a seventh embodiment. FIG. 10 is a diagram showing an IGBT doping distribution of the seventh embodiment. FIG. 25 is a diagram showing an electric field distribution in the blocking mode of the IGBT according to the seventh embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a cross-sectional view for illustrating the manufacturing method according to the eighth embodiment. FIG. 10 is a characteristic diagram showing a trade-off between on-state voltage and turn-off loss of an IGBT manufactured according to the eighth embodiment. FIG. 25 is a cross-sectional perspective view of a relevant part showing a configuration of an IGBT according to a ninth embodiment. FIG. 38 is a main-portion cross-sectional perspective view showing the configuration of the IGBT according to the tenth embodiment. FIG. 38 is a main-portion cross-sectional perspective view showing the configuration of the IGBT according to the eleventh embodiment.

Explanation of symbols

21 First insulating film (oxide film)
22 Polycrystalline semiconductor region (gate polysilicon)
23 Second insulating film (gate oxide film)
24 First conductivity type semiconductor film (cathode film)
25 1st 1st conductivity type semiconductor region (n ⁺ buffer region)
26 Second first conductivity type semiconductor region (n ⁺ source region)
27 1st 2nd conductivity type semiconductor region (p base region)
28 Third insulating film (interlayer insulating film)
29 1st conductivity type single crystal semiconductor substrate (n ^- single crystal silicon substrate)
30 First electrode (emitter electrode)
31 2nd 2nd conductivity type semiconductor region (p ⁺ anode layer)
32 Second electrode (anode electrode)
33 3rd 1st conductivity type semiconductor region (n ⁺ buffer layer)
41 Second conductivity type diffusion layer (p diffusion layer)
42 First conductivity type diffusion layer (n ⁺ diffusion layer)

Claims (35)

A first insulating film that selectively covers the first main surface of the first conductivity type single crystal semiconductor substrate;
A polycrystalline semiconductor region provided on the first insulating film;
A second insulating film surrounding the polycrystalline semiconductor region;
A first first-conductivity-type semiconductor region in contact with the single crystal semiconductor substrate at a window portion of the first insulating film;
A second first conductivity type semiconductor region provided on the second insulating film outside the window of the first insulating film;
A first second conductivity type semiconductor region provided on the second insulating film between the first first conductivity type semiconductor region and the second first conductivity type semiconductor region;
A first electrode in contact with both the second first conductivity type semiconductor region and the first second conductivity type semiconductor region;
A third insulating film provided between the first electrode and the first first conductivity type semiconductor region;
A second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate;
A second electrode in contact with the second second conductivity type semiconductor region;
A semiconductor device comprising:   2. The semiconductor device according to claim 1, wherein the first first conductivity type semiconductor region is doped to a first conductivity type having a concentration higher than that of the single crystal semiconductor substrate.   A third first conductivity type semiconductor region having a higher impurity concentration than that of the single crystal semiconductor substrate is provided between the single crystal semiconductor substrate and the second second conductivity type semiconductor region. The semiconductor device according to claim 1 or 2.   The semiconductor film comprising the first first conductivity type semiconductor region, the second first conductivity type semiconductor region, and the first second conductivity type semiconductor region is all made of polycrystalline silicon. The semiconductor device according to claim 1.   Part or all of the semiconductor film formed of the first first conductivity type semiconductor region, the second first conductivity type semiconductor region, and the first second conductivity type semiconductor region is made of single crystal silicon. The semiconductor device according to claim 1, wherein: A first insulating film that selectively covers the first main surface of the first conductivity type single crystal semiconductor substrate;
A first first-conductivity-type semiconductor region in contact with the single crystal semiconductor substrate at a window portion of the first insulating film;
A first second conductivity type semiconductor region provided on the first insulating film outside the window portion of the first insulating film;
A second first conductivity type semiconductor region provided in the first second conductivity type semiconductor region;
A second insulating film covering the first first conductivity type semiconductor region, the second first conductivity type semiconductor region, and the first second conductivity type semiconductor region;
A polycrystalline semiconductor region provided on the second insulating film;
A first electrode in contact with both the second first conductivity type semiconductor region and the first second conductivity type semiconductor region;
A third insulating film provided between the first electrode and the polycrystalline semiconductor region;
A second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate;
A second electrode in contact with the second second conductivity type semiconductor region;
A semiconductor device comprising:   The semiconductor device according to claim 6, wherein the first first conductivity type semiconductor region is doped with a first conductivity type having a higher concentration than the single crystal semiconductor substrate.   A third first conductivity type semiconductor region having a higher impurity concentration than that of the single crystal semiconductor substrate is provided between the single crystal semiconductor substrate and the second second conductivity type semiconductor region. The semiconductor device according to claim 6 or 7.   The semiconductor film comprising the first first conductivity type semiconductor region, the second first conductivity type semiconductor region, and the first second conductivity type semiconductor region is all made of polycrystalline silicon. The semiconductor device as described in any one of Claims 6-8.   Part or all of the semiconductor film formed of the first first conductivity type semiconductor region, the second first conductivity type semiconductor region, and the first second conductivity type semiconductor region is made of single crystal silicon. The semiconductor device according to claim 6, wherein: A first insulating film selectively embedded below the first main surface of the first conductivity type single crystal semiconductor substrate;
A first second conductivity type semiconductor region provided between the first insulating film and the first main surface;
A first conductivity type semiconductor region provided in the first second conductivity type semiconductor region;
A second insulating film covering a portion of the first main surface on a region where the first insulating film is not embedded;
A polycrystalline semiconductor region provided on the second insulating film;
A first electrode that contacts both the first conductive semiconductor region and the first second conductive semiconductor region;
A third insulating film provided between the first electrode and the polycrystalline semiconductor region;
A second second conductivity type semiconductor region provided along the second main surface of the single crystal semiconductor substrate;
A second electrode in contact with the second second conductivity type semiconductor region;
A semiconductor device comprising:   A second first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is provided between the single crystal semiconductor substrate and the second second conductivity type semiconductor region. The semiconductor device according to claim 11. A first step of sequentially forming a first insulating film and a polycrystalline semiconductor film on a first main surface of a first conductivity type single crystal semiconductor substrate;
A second step of removing a part of the polycrystalline semiconductor film to form a window;
A third step of exposing a part of the single crystal semiconductor substrate in the window after forming a second insulating film covering the exposed portion of the polycrystalline semiconductor film;
A fourth step of laminating a first conductivity type semiconductor film on the exposed portion of the window portion of the single crystal semiconductor substrate and the second insulating film;
A first second conductivity type semiconductor region is formed in the first conductivity type semiconductor film adjacent to the first first conductivity type semiconductor region in contact with the single crystal semiconductor substrate, and the first second conductivity type is further formed. A fifth step of forming a second first conductivity type semiconductor region on the opposite side of the first first conductivity type semiconductor region across the type semiconductor region;
A third insulating film is laminated on the first first conductive semiconductor region, the first second conductive semiconductor region, and the second first conductive semiconductor region, and the third insulating film A sixth step of opening a contact hole to expose a portion of the second first conductive semiconductor region and the first second conductive semiconductor region;
A first electrode that contacts the second first conductive semiconductor region and a part of the first second conductive semiconductor region through the contact hole is formed on the third insulating film. A seventh step of grinding a second main surface of the single crystal semiconductor substrate and forming a second second conductivity type semiconductor region along the ground surface;
An eighth step of forming a second electrode in contact with the second second conductivity type semiconductor region;
A method for manufacturing a semiconductor device, comprising:   14. The method of manufacturing a semiconductor device according to claim 13, wherein in the fourth step, the first conductive semiconductor film is doped to a first conductive type having a higher concentration than the single crystal semiconductor substrate.   In the seventh step, after the second main surface of the single crystal semiconductor substrate is ground, a third first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is formed along the ground surface. 15. The method of manufacturing a semiconductor device according to claim 13, wherein the semiconductor device is formed deeper than the second second conductivity type semiconductor region.   The method of manufacturing a semiconductor device according to claim 13, wherein the first conductive semiconductor film is formed of polycrystalline silicon.   16. The method of manufacturing a semiconductor device according to claim 13, wherein a part or all of the first conductive semiconductor film is formed of single crystal silicon. A first step of forming a first insulating film on the first main surface of the first conductivity type single crystal semiconductor substrate;
A second step of removing a part of the first insulating film to form a window;
A third step of laminating a first conductive type semiconductor film on the exposed portion of the first insulating film and the single crystal semiconductor substrate in the window;
A fourth step of sequentially forming a second insulating film and a polycrystalline semiconductor film on the first conductive type semiconductor film;
A portion of the polycrystalline semiconductor film is removed, and the polycrystalline semiconductor film is formed on a portion of the first conductive semiconductor film above the first first conductive semiconductor region in contact with the single crystal semiconductor substrate. A first second conductivity type semiconductor region is formed between the first insulating film and the first main surface of the first conductivity type semiconductor film, and the first second conductivity type is further formed. A fifth step of forming a second first conductivity type semiconductor region in the semiconductor region;
A third insulating film is stacked on the polycrystalline semiconductor film, a contact hole is opened in the third insulating film, and the second first conductivity type semiconductor region and the first second conductivity type semiconductor are formed. A part of the region is exposed, and a part of the second first conductive type semiconductor region and a part of the first second conductive type semiconductor region are contacted on the third insulating film through the contact hole. A sixth step of forming a first electrode to be performed;
A seventh step of grinding a second main surface of the single crystal semiconductor substrate and forming a second second conductivity type semiconductor region along the ground surface;
An eighth step of forming a second electrode in contact with the second second conductivity type semiconductor region;
A method for manufacturing a semiconductor device, comprising:   19. The method of manufacturing a semiconductor device according to claim 18, wherein in the third step, the first conductivity type semiconductor film is doped to a first conductivity type having a concentration higher than that of the single crystal semiconductor substrate.   In the seventh step, after the second main surface of the single crystal semiconductor substrate is ground, a third first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is formed along the ground surface. 20. The method of manufacturing a semiconductor device according to claim 18, wherein the semiconductor device is formed deeper than the second second conductivity type semiconductor region.   21. The method of manufacturing a semiconductor device according to claim 18, wherein the first conductive semiconductor film is formed of polycrystalline silicon.   21. The method of manufacturing a semiconductor device according to claim 18, wherein a part or all of the first conductive type semiconductor film is formed of single crystal silicon.   23. The method of manufacturing a semiconductor device according to claim 22, wherein the first conductivity type semiconductor film is formed by an epitaxial growth method. A first step of selectively embedding a first insulating film under the first main surface of the first conductivity type single crystal semiconductor substrate;
A second insulating film and a polycrystalline semiconductor film are sequentially formed on the first main surface, a part of the polycrystalline semiconductor film and the second insulating film is removed, and the first insulating film is A second step of leaving the polycrystalline semiconductor film and the second insulating film in a portion on a region not buried;
A first second conductivity type semiconductor region is formed between the first insulating film and the first main surface, and a first conductivity type semiconductor region is further formed in the first second conductivity type semiconductor region. A third step of forming;
A third insulating film is stacked on the polycrystalline semiconductor film, and a contact hole is opened in the third insulating film to form one of the first conductive type semiconductor region and the first second conductive type semiconductor region. A fourth step of exposing the part;
Forming a first electrode in contact with a part of the first conductive type semiconductor region and the first second conductive type semiconductor region through the contact hole on the third insulating film; A fifth step of grinding a second main surface of the single crystal semiconductor substrate and forming a second second conductivity type semiconductor region along the ground surface;
A sixth step of forming a second electrode in contact with the second second conductivity type semiconductor region;
A method for manufacturing a semiconductor device, comprising:   In the fifth step, after the second main surface of the single crystal semiconductor substrate is ground, the second first conductivity type semiconductor region having a higher impurity concentration than the single crystal semiconductor substrate is formed along the ground surface. 25. The method of manufacturing a semiconductor device according to claim 24, wherein the semiconductor device is formed deeper than the second second conductivity type semiconductor region.   26. The method of manufacturing a semiconductor device according to claim 24, wherein in the first step, oxygen ions are selectively implanted into the single crystal semiconductor substrate in order to form the first insulating film. Method.   27. The first insulating film according to claim 26, wherein, in the first step, oxygen ions are implanted into the single crystal semiconductor substrate, and then the first insulating film is formed by annealing at a temperature of 1000 ° C. or higher. A method for manufacturing a semiconductor device.   A second conductivity type diffusion layer is independently provided for each cell in a portion of the single crystal semiconductor substrate where the first first conductivity type semiconductor region is in contact with the window portion of the first insulating film. The semiconductor device according to claim 1, wherein the semiconductor device is a semiconductor device.   The second conductivity type diffusion layer is completely depleted when an applied voltage at the time of forward voltage blocking is a voltage within a range in which no avalanche breakdown occurs in any part of the element. Item 29. The semiconductor device according to Item 28.   In the second conductivity type diffusion layer, a first conductivity type diffusion layer is provided at a portion where the first first conductivity type semiconductor region is in contact with the window portion of the first insulating film. 30. The semiconductor device according to claim 28 or 29.   The first conductivity type diffusion layer is completely depleted when an applied voltage at the time of forward voltage blocking is a voltage within a range in which no avalanche breakdown occurs in any part of the element. Item 30. The semiconductor device according to Item 30.   32. The semiconductor device according to claim 31, wherein the first conductivity type diffusion layer extends below the polycrystalline semiconductor region.   A portion where the first first-conductivity-type semiconductor region is in contact with the single-crystal semiconductor substrate by performing ion implantation from the window of the polycrystalline semiconductor film between the second step and the third step. The method of manufacturing a semiconductor device according to claim 13, further comprising a step of independently forming the second conductivity type diffusion layer for each cell in a self-aligning manner.   Between the second step and the third step, ion implantation is performed from the window portion of the first insulating film so that the first first-conductivity-type semiconductor region of the single crystal semiconductor substrate is in contact 24. The method of manufacturing a semiconductor device according to claim 18, further comprising a step of independently forming a second conductivity type diffusion layer for each cell in a self-aligned manner with respect to the portion. When forming the second conductivity type diffusion layer, the first conductivity type diffusion layer is formed in a portion of the second conductivity type diffusion layer in contact with the first first conductivity type semiconductor region. 35. A method of manufacturing a semiconductor device according to claim 33 or 34.

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