JP2007184434A - Semiconductor device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device capable of contriving the improvement of the reproducibility of processes and the reduction of on-state resistance and a field value in a gate insulating film at a withstanding voltage. <P>SOLUTION: The semiconductor device has an n-type SiC drift layer 5; p-type SiC base regions 7 selectively formed on the n-type SiC drift layer 5; an n-type depression region 9 formed on the n-type SiC drift layer 5; n-type SiC source regions 11 formed on the surface layer of the p-type SiC base regions 7; and a gate insulating film 13 and a gate electrode 15 which are formed across upper parts of n-type SiC source regions 11, the p-type SiC base regions 7, and the n-type depression region 9. In this case, the n-type depression region 9 is formed so as to have doping density higher than that of the n-type SiC drift layer 5 while the depression region 9 is formed so as to have uniform density with respect to the longitudinal direction and the lower layer side (9c) is formed so as to have density higher than those of the upper layers side (9a, 9b) with respect to the up-and-down direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device, and more particularly to reduction of on-resistance, improvement of electric field distribution, and improvement of process reproducibility of a SiC power device.

  Improvements in the characteristics of power devices are expected from the viewpoint of energy saving, and field-effect transistors (FETs) with metal / oxide / semiconductor (MOS) structures using SiC are promising as next-generation high voltage and low loss switching elements. Is being viewed.

  As a method for reducing the on-resistance in order to reduce the steady loss of the device, a method is proposed in which the doping concentration of the n-type depletion region sandwiched between the p-type base regions is not increased as the doping concentration of the drift layer, but is increased. Has been.

  However, when the concentration of the n-type depletion region is increased, if the concentration of the entire n-type depletion region is increased, there is a concern that the breakdown voltage is lowered. Therefore, only the portion close to the p-type base region in the n-type depletion region is used. A method for increasing the concentration has also been proposed (prior art: Patent Document 1).

JP 2005-5578 A

  In general, in order to reduce the on-resistance of a MOSFET using SiC, it is effective to increase the doping concentration of the n-type depletion region and reduce the element size to increase the number of elements per unit area.

  However, when the element size is miniaturized, the length of the n-type depletion region is also miniaturized. Therefore, in the above prior art, in the ion implantation step, the n-type depletion region is close to the p-type base region. The formation of an implantation mask used for doping only a portion with a high concentration requires finer dimensional accuracy, and has a drawback that process reproducibility is not good.

  In addition, if the doping concentration or the length of the doped region cannot be controlled to a desired value, there is a disadvantage that an on-resistance increases, a breakdown voltage decreases, and an electric field value in the gate insulating film increases.

  Furthermore, the details of the high concentration of the depletion region that can reduce the on-resistance and ensure the breakdown voltage when the element dimensions such as the channel length and the depletion region length are miniaturized to about 0.5-1 μm are known. Not.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device capable of improving process reproducibility, reducing on-resistance, and reducing an electric field value in a gate insulating film at a withstand voltage, and a method for manufacturing the same.

  In order to solve the above problem, the invention according to claim 1 is a first conductivity type drift layer, a second conductivity type base region selectively formed on the first conductivity type drift layer, and the first conductivity type. A first conductivity type depletion region formed on the one conductivity type drift layer so as to be in contact with a side surface of the second conductivity type base region; and a surface layer of the second conductivity type base region on the second conductivity type base region. A first conductivity type source region formed so as to be surrounded, and gate insulation formed over the first conductivity type source region, the second conductivity type base region, and the first conductivity type depletion region And a gate electrode formed on the gate insulating film, wherein the first conductivity type depletion region is formed at a doping concentration higher than a doping concentration of the first conductivity type drift layer, So For respect and the vertical direction are formed at a uniform concentration transverse are those who lower side than the upper side is formed at a high concentration.

  According to the first aspect of the present invention, the first conductivity type depletion region is formed at a doping concentration higher than the doping concentration of the first conductivity type drift layer, and from the upper layer side in the vertical direction. Since the lower layer side is formed at a higher concentration, the electric field value in the gate insulating film at the on-resistance and the breakdown voltage can be reduced.

  In addition, since the first conductive type depletion region is formed in a uniform concentration in the lateral direction, the element fabrication process does not require finer dimensional accuracy as in the prior art, and the process reproducibility can be improved. .

<Embodiment 1>
The semiconductor device according to this embodiment is configured such that the basic cross-sectional structure of FIG. 1 has a continuous cross-sectional structure folded back in the horizontal direction.

  1 includes an n-type low-resistance SiC substrate (semiconductor substrate) 3, an n-type SiC drift layer (first conductivity type drift layer) 5 formed on the n-type low-resistance SiC substrate 3, P-type SiC base region (second conductivity type base region) 7 selectively formed on n-type SiC drift layer 5 and formed so as to be in contact with the side surface of p-type SiC base region 7 on n-type SiC drift layer 5 N-type depletion region (first conductivity type depletion region) 9 and n-type SiC source region (first conductivity type) formed so as to be surrounded by p-type SiC base region 7 in the surface layer of p-type SiC base region 7 Type source region) 11, gate insulating film 13 formed over n type SiC source region 11, p type SiC base region 7, and n type depletion region, and gate insulating film 13. Get A source electrode 17 formed over the p-type SiC base region 7 and the n-type SiC source region 11, and a drain electrode 19 formed on the lower surface of the n-type low-resistance SiC substrate 3. .

The n-type SiC drift layer 5 is for maintaining a withstand voltage, and is formed with a doping concentration of, for example, 1 × 10 ¹⁵ -3 × 10 ¹⁶ / cm ³ and a layer thickness of, for example, 3-15 μm. .

  The p-type SiC base region 7 includes a lower portion 7 a of the n-type SiC source region 11, a lower portion 7 b of the n-type SiC source electrode 17, and a lower portion 7 c of the n-type SiC gate electrode 15. Become.

The source region lower portion 7a is formed with a p-type doping concentration of, for example, 5 × 10 ¹⁷ −2 × 10 ¹⁸ / cm ³ and has a layer thickness of, for example, about 0.7-1 μm.

The source electrode lower portion (p-type contact region) 7b is formed at a p-type concentration (for example, 5 × 10 ¹⁸ −1 × 10 ²⁰ / cm ³ ) higher than the p-type doping concentration of the source region lower portion 7; For example, the layer thickness is about 0.7-1 μm.

The gate electrode lower portion 7c is desirably formed in a self-aligned manner when the lateral width (channel length) W1 is about 1 μm or less, and the p-type doping concentration (for example, 5 × 10 ^{17) of the} source region lower portion 7a. −2 × 10 ¹⁸ / cm ³ ) and a p-type concentration lower than, for example, 0.7 to 1 μm or slightly thinner.

  Of the gate electrode lower portion 7c, a portion having the same depth as the n-type SiC source region 11 (hereinafter referred to as a shallow depth portion 7c-1) (that is, a portion including the channel region), and an n-type SiC source region The portion having a depth deeper than 11 (hereinafter, the depth portion 7c-2) (that is, the portion including the junction surface with the n-type SiC drift layer 5) may have a different doping concentration. Here, as an example, The shallow depth portion 7c-1 is formed to have a lower p-type concentration than the deep depth portion 7c-2. By doing so, the current drive capability of the MOS channel can be improved.

The n-type SiC source region 11 is formed with an n-type doping concentration of a somewhat high concentration (for example, 1 × 10 ¹⁹ −3 × 10 ¹⁹ / cm ³ ) so that an electrode having a low contact resistance can be formed. The layer thickness is about 2-0.4 μm.

The lateral width (depression region length) W2 of the n-type depletion region 9 is formed to be about 0.5 μm, for example. The n-type depletion region 9 is formed at a doping concentration higher than the doping concentration of the n-type SiC drift layer 5 and is formed at a uniform concentration in the lateral direction and in the vertical direction. The lower layer side (here lower layer 9c) is formed at a higher concentration than the upper layer side (here upper layer 9a and middle layer 9b). Here, the upper layer side (here, upper layer 9a and middle layer 9b) of n-type depletion region 9 is formed to a doping concentration of 3 × 10 ¹⁵ -9 × 10 ¹⁶ / cm ³ , for example. The lower layer side (here, the lower layer 9c) is formed at a doping concentration of, for example, 9 × 10 ¹⁵ −3 × 10 ¹⁷ / cm ³ .

  In this way, by forming the n-type depletion region 9 at a doping concentration higher than the doping concentration of the n-type SiC drift layer 5, the electric field value in the gate insulating film at the on-resistance and breakdown voltage as the element can be reduced. . The n-type depletion region 9 is formed with a uniform concentration in the lateral direction and in the vertical direction on the lower layer side (here lower layer 9c) than the upper layer side (here upper layer 9a and middle layer 9b). Is formed at a high concentration, it is possible to effectively reduce the electric field value in the gate insulating film at the on-resistance and breakdown voltage as the element.

  Table 1 shows that the upper layer 9a (the layer near the gate insulating film 13), the middle layer 9b and the lower layer 9c (the layer near the boundary with the n-type SiC drift layer 5) of the n-type depletion region 9 are as described above. It is a table verifying that the electric field value in the gate insulating film can be reduced most effectively when the doping concentration of the lower layer 9c is maximized.

  In Table 1, when the doping concentration of the n-type depletion region 9 is at least three times that of the n-type SiC drift layer 5, only the upper layer 9a of the n-type depletion region 9 is further tripled (thus, the drift layer 5). 9 times, and so on), when the n-type depletion region 9 middle layer 9b is further tripled, and only the lower layer 9c of the n-type depletion region 9 is tripled. In the three cases of concentration, the on-resistance and the electric field value in the gate insulating film are compared.

  In Table 1, the above comparison is made when the depth portion 7c-2 of the p-type SiC base region 7 is as high as the source region lower portion 7a and the depth portion 7c of the p-type SiC base region 7. -2 shows the result obtained when the concentration is lower than that of the lower portion 7a of the source region.

  From Table 1, in the n-type depletion region 9, when the doping concentration of the lower layer 9c is increased rather than the doping concentration of the upper layer 9a or the middle layer 9b, the electric field value in the gate insulating film at the on-resistance and breakdown voltage is effectively increased. It can be seen that the voltage can be reduced and a sufficient breakdown voltage (breakdown voltage) can be secured.

  Further, from Table 1, the n-type depletion region 9 of the n-type depletion region 9 is not limited to a portion close to the p-type SiC base region 7 in the n-type depletion region 9 as in the prior art, and the concentration of the n-type depletion region 9 is not limited to It can be seen that even when uniform in the lateral direction (lateral width W2 direction), the on-resistance can be reduced, the electric field value in the gate insulating film at the withstand voltage can be reduced, and the withstand voltage can be sufficiently secured.

  Next, a method for manufacturing this semiconductor device will be described with reference to FIGS.

  This semiconductor device includes, for example, a drift layer growth step (FIG. 2), a p-type SiC base region injection step (FIG. 3), an n-type SiC source region injection step (FIG. 4), and an n-type depletion region injection step (FIG. 5). The p-type contact region injection step (FIG. 6), the gate insulating film / gate electrode formation step (FIG. 7), the source electrode formation step (FIG. 8), and the drain electrode formation step (FIG. 9) are performed in this order. The activation heat treatment of the ion implantation species may be performed collectively immediately before the formation of the gate insulating film 13 or the gate electrode 15, or may be performed each time.

First, in the drift growth step (FIG. 2), the n-type layer (first conductivity type layer) 100 is formed on the n-type low-resistance SiC substrate (semiconductor layer) 3 by epitaxial growth while controlling the doping concentration. (Part of the n-type depletion region 9 that becomes the high-concentration lower layer 9c) (doping concentration: for example, 9 × 10 ¹⁵ -3 × 10 ¹⁷ / cm ³ ) is the portion 100b, 100c (doping concentration: For example, it is formed so as to be a high-concentration layer having a higher doping concentration than 1 × 10 ¹⁵ -3 × 10 ¹⁶ / cm ³ ), and the lower layer below the intermediate layer (high-concentration layer) 100a in the n-type layer 100 Portion 100 c is used as n-type SiC drift layer 5.

Then, in the next p-type SiC base region implantation step (FIG. 3), ions are selectively implanted into the upper layer portion (upper layer 100a and intermediate layer 100b) other than drift layer 5 in n-type layer 100 to form p-type. A SiC base region 7 is formed. More specifically, regarding the upper layer portion (upper layer 100a and intermediate layer 100b) of n-type layer 100, the portion 7ab to be the source region lower portion 7a and source electrode lower portion 7b of p-type SiC base region 7 For example, the p-type concentration of 5 × 10 ¹⁷ −2 × 10 ¹⁸ / cm ³ is collectively used, and the portion to be the deep portion 7c-2 of the p-type SiC base region 7 is set to a p-type concentration lower than that of the portion 7ab. The p-type SiC base region 7 has a lower p-type concentration than the portion to be the deep portion 7c-2. The p-type SiC base region 7 (here, 7ab, 7c) has a lower p-type concentration than the portion to be the deep portion 7c-2. -1 and 7c-2).

  In the p-type contact region implantation step (FIG. 6), which will be described later, a portion of the portion 7ab that is to be the p-type contact region 7b (see FIG. 1) is selectively ion-implanted, and the p-type contact region is selectively formed. 7b is formed, and the p-type SiC base region 7 is finally completed.

Then, in the n-type SiC source region implantation step (FIG. 4), ions are selectively implanted into the portion to be the n-type SiC source region 11 in the surface layer of the portion 7ab of the p-type SiC base region 7, for example, 1 An n-type SiC source region 11 having a concentration of × 10 ¹⁹ -3 × 10 ¹⁹ / cm ³ is formed.

  In addition, when forming the p-type SiC base region 7 and the n-type SiC source region 11, they may be formed using different implantation masks, but a tapered structure or a two-layer structure is used as the implantation mask, and an oblique direction By using ion implantation, implantation spreading, or the like, one mask or a mask obtained by processing one mask may be formed in a self-aligned manner.

Then, in the n-type depletion region implantation step (FIG. 5), the portion 100b-1 of the upper layer 100b of the n-type layer 100 that has not been formed into the p-type SiC base region 7 is more ionized than the n-type SiC drift layer 5 by ion implantation. The upper middle layer of the n-type depletion region 9 is adjusted to a higher concentration and lower than the high-concentration lower layer 9c of the n-type depletion region 9 (for example, an n-type concentration of 3 × 10 ¹⁵ -9 × 10 ¹⁶ / cm ³ ). Mold to 9ab.

  Thus, the portion 100b-1 finished in the upper middle layer 9ab of the n-type depletion region 9 and the portion 100a of the intermediate layer (high concentration layer) 100a of the n-type layer 100 that has not been made the p-type SiC base region 7 -1 (the portion of the n-type depletion region 9 that becomes the high-concentration lower layer 9c) constitutes the n-type depletion region 9.

Then, in the p-type contact region implantation step (FIG. 6), ions are selectively implanted into the portion to be the p-type contact region of the portion 7ab of the p-type SiC base region 7, thereby 5 × 10 ¹⁸ −1 ×. A p-type contact region 7b having a p-type concentration of 10 ²⁰ / cm ³ is formed (as a result, the remainder other than the p-type contact region 7b in the portion 7ab becomes the source region lower layer 7a). Thereby, the p-type SiC base region 7 is finally completed.

  Then, in the gate insulating film / gate electrode forming step (FIG. 7), the gate insulating film 13 and the gate electrode 15 are sequentially formed on the n-type SiC source region 11, the p-type SiC base region 7 and the n-type depletion region 9. Form. At that time, the gate insulating film 13 may be formed by thermally oxidizing, nitriding, or depositing an insulating film of a silicon oxide film or a silicon oxynitride film, or a combination thereof.

  Then, in the source electrode formation step (FIG. 8), the source electrode 17 is formed over the p-type SiC base region 7 and the n-type SiC source region 11. Then, in the drain electrode formation step (FIG. 9), the drain electrode 19 is formed on the lower surface of the n-type low resistance SiC substrate 3. In this way, a semiconductor device is manufactured.

  The structure shown in FIG. 1 is manufactured by growing the n-type SiC drift layer 5 with a uniform doping concentration and performing ion implantation so that the n-type depletion region 9 has a concentration distribution in the depth direction. However, when fabricated in this manner, a relatively high concentration is implanted into a relatively deep position (the lower layer 9c of the n-type depletion region 9). There is a possibility that recovery is not possible.

  Therefore, as in the present invention, when the n-type SiC drift layer 5 is grown, only the lower layer side (here, the lower layer 9c) of the n-type depletion region 9 is higher than the upper layer side (here, the upper layer 9a and the middle layer 9b). By setting the doping concentration to a high concentration, it is not necessary to implant a relatively high concentration in the lower layer 9c (relatively deep position) of the n-type depletion region 9 when the n-type depletion region 9 is formed. In this activation heat treatment, the crystallinity can be sufficiently recovered.

  At that time, the doping on the lower layer side (here, lower layer 9c) of the n-type depletion region 9 is controlled only by drift layer growth, and on the lower layer side when ions are implanted into the upper layer side (here, upper layer 9a and middle layer 9b). The ion implantation may not be performed, or the doping on the lower layer side of the n-type depletion region 9 is performed by doping the n-type SiC drift layer 5 and the ion implantation on the upper layer side of the n-type depletion region 9. It is also possible to add the above.

  In the manufacturing method of the present invention, the entire intermediate layer 100a of the n-type layer 100 (that is, not only the portion that becomes the lower layer 9c of the n-type depletion region 9 but also the portion that becomes the p-type SiC base region 7) Although the concentration is high, the p-type SiC base region 7 is a p-type having a relatively high concentration. Therefore, even if the entire intermediate layer 100a of the n-type layer 100 is made high in concentration, this means that the p-type SiC base region 7 is formed. Will not be affected.

  According to the semiconductor device configured as described above, the n-type depletion region 9 is formed at a doping concentration higher than the doping concentration of the n-type SiC drift layer 5, and the upper layer (for example, Since the lower layer side (for example, the lower layer 9c) is formed at a higher concentration than the upper layer 9a and middle layer 9b) side, the electric field value in the gate insulating film at the on-resistance and breakdown voltage as the element can be reduced.

  Further, since the n-type depletion region 9 is formed in a uniform concentration in the lateral direction, the finer dimensional accuracy as in the prior art is not required in the element manufacturing process, and the reproducibility of the process can be improved.

  Further, the n-type layer 100 is formed on the n-type low-resistance SiC substrate 3 by epitaxial growth so that the intermediate layer 100a becomes a higher concentration layer having a higher doping concentration than the portions 100b and 100c other than the layer, The lower layer portion 100c below the high-concentration layer 100a in the n-type layer 100 is defined as the n-type SiC drift layer 5, and the remaining upper layer portions (upper layer 100b and intermediate layer 100c) in the n-type layer 100 are selectively p. Since the type SiC base region 7 is formed and the remainder of the upper layer portion is formed into the n-type depletion region 9, the lower layer 9c of the n-type depletion region 9 can be highly concentrated without using the ion implantation method.

  In this embodiment, as shown in FIG. 10 or FIG. 11, a channel is formed so as to extend over the n-type SiC source region 11, the p-type SiC base region 7 and the n-type depletion region 9 immediately below the gate insulating film 13. A layer 23 may be provided. When the channel layer 23 is provided in this way, its conductivity type may be n-type or p-type. In order to improve the surface roughness caused by the activation heat treatment of the ion-implanted species, epitaxial growth is performed as shown in FIG. It is desirable to form the channel layer 23 so as to have a structure. If the surface roughness caused by the activation heat treatment is small, the channel layer 23 may be formed so as to have a structure as shown in FIG. 11 by selective ion implantation. Good.

  In the case where the channel layer 23 is provided in this manner, the ion implantation species activation heat treatment is performed before the formation of the gate insulating film 13 in the case where the channel layer 23 is provided so as to have the configuration shown in FIG. When the channel layer 23 is provided so as to have the configuration as in FIG. 10, it may be performed all at once before the channel layer 23 is formed, or may be performed for each ion implantation.

<Embodiment 2>
In the first embodiment, the high-concentration lower layer 9c of the n-type depletion region 9 is further interposed between the n-type SiC drift layer 5 and the p-type SiC base region 7 as shown in FIG. A part may be interposed.

  12 is a diagram when the second embodiment is applied to the semiconductor device of FIG. 1 (that is, the semiconductor device without the channel layer 23), and FIG. 13 is a diagram of the semiconductor device of FIG. 10 (that is, epitaxial growth). FIG. 14 is a diagram in the case where the second embodiment is applied to a semiconductor device in which the channel layer 23 is provided by FIG. 14, and FIG. 14 shows the semiconductor device in FIG. 11 (that is, the channel layer 23 is provided by selective ion implantation). It is a figure at the time of applying this Embodiment 2 to the semiconductor device at the time of being carried out.

  With such a configuration, the electron flow from the n-type depletion region 9 flows through the high-concentration lower layer 9c of the n-type depletion region 9 as well as directly under the n-type depletion region 9 as well as the entire n-type SiC drift layer 5. However, the on-resistance as an element can be further reduced.

  In this case, in the p-type SiC base region implantation step (FIG. 3) of the first embodiment, the p-type SiC base region 7 (part consisting of 7ab and 7c) and the n-type SiC drift layer 5 are used. The p-type SiC base region 7 may be formed so that the intermediate layer (high concentration layer) 100b of the n-type layer 100 is interposed therebetween.

  In this way, a part of the high-concentration lower layer 9c of the n-type depletion region 9 can be interposed between the n-type SiC drift layer 5 and the p-type SiC base region 7 without performing ion implantation. .

1 is a basic cross-sectional structure diagram of a semiconductor device according to a first embodiment; FIG. 10 is a diagram for explaining a drift layer growth step in the method for manufacturing a semiconductor device according to the first embodiment. 6 is a diagram illustrating a p-type SiC base region implantation step in the method for manufacturing a semiconductor device according to the first embodiment. FIG. 6 is a diagram illustrating an n-type SiC source region implantation step in the method for manufacturing a semiconductor device according to the first embodiment. FIG. FIG. 10 is a diagram for explaining an n-type depletion region injection step in the method for manufacturing a semiconductor device according to the first embodiment. FIG. 10 is a diagram for explaining a p-type contact region injection step in the method for manufacturing a semiconductor device according to the first embodiment. 6 is a diagram illustrating a gate insulating film / gate electrode forming step in the method of manufacturing a semiconductor device according to the first embodiment. FIG. FIG. 10 is a diagram for explaining a source electrode formation step in the method for manufacturing a semiconductor device according to the first embodiment. FIG. 10 is a diagram for explaining a drain electrode formation step in the method for manufacturing a semiconductor device according to the first embodiment. 6 is a diagram for explaining a modification (modification provided with a channel layer) of the semiconductor device according to the first embodiment; FIG. It is a figure explaining the other modification (other modification provided with the channel layer) of the semiconductor device which concerns on Embodiment 1. FIG. FIG. 6 is a diagram for explaining a semiconductor device (configuration corresponding to FIG. 1) according to a second embodiment. FIG. 10 is another basic cross-sectional structure diagram for explaining the semiconductor device according to the second embodiment (configuration corresponding to FIG. 10). FIG. 10 is still another basic cross-sectional structure diagram for explaining the semiconductor device according to the second embodiment (configuration corresponding to FIG. 11).

Explanation of symbols

3 n-type low-resistance SiC substrate, 5 n-type SiC drift layer, 7 p-type SiC base region, 7a source region lower part, 7b source electrode lower part, 7c gate electrode lower part, 7c-1 gate electrode lower side Shallow part of the part, 7c-2 Deep part of the lower part of the gate electrode, 9 n-type depletion region, upper layer of 9a n-type depletion region, 9b middle layer of n-type depletion region, lower layer of 9c n-type depletion region, 11 n Type SiC source region, 13 gate insulating film, 15 gate electrode, 17 source electrode, 19 drain electrode, 23 channel layer, 100 n type layer, 100b n type layer upper layer, 100b-1 n type depletion region of upper layer 100 Part which becomes upper middle layer of layer, intermediate layer (high concentration layer) of 100a n-type layer, n-type depletion region of 100a-1 intermediate layer Areas of lower, horizontal width of W1 gate electrode lower part, the width of W2 n-type depletion region.

Claims (4)

A first conductivity type drift layer;
A second conductivity type base region selectively formed on the first conductivity type drift layer;
A first conductivity type depletion region formed on the first conductivity type drift layer so as to be in contact with a side surface of the second conductivity type base region;
A first conductivity type source region formed on the surface layer of the second conductivity type base region so as to be surrounded by the second conductivity type base region;
A gate insulating film formed over the first conductivity type source region, the second conductivity type base region, and the first conductivity type depletion region;
A gate electrode formed on the gate insulating film;
With
The first conductivity type depletion region is formed at a doping concentration higher than the doping concentration of the first conductivity type drift layer, and is formed at a uniform concentration in the lateral direction and in the vertical direction. The semiconductor device is characterized in that the lower layer side is formed at a higher concentration than the upper layer side.   The part of the high-concentration lower layer of the first conductivity type depletion region is interposed between the first conductivity type drift layer and the second conductivity type base region. Semiconductor device. On the semiconductor substrate, the first conductivity type layer is formed by epitaxial growth so that the intermediate layer becomes a high concentration layer having a higher doping concentration than the portion other than the layer, and the first conductivity type layer of the first conductivity type layer is formed. A first step in which a lower layer portion below the high concentration layer is a first conductivity type drift layer;
A second step of selectively forming a second conductivity type base region in the remaining upper layer portion of the first conductivity type layer;
A third step of forming a portion of the upper layer portion other than the second conductivity type base region into a first conductivity type depletion region;
A method for manufacturing a semiconductor device, comprising: In the second step, the second conductivity type base region is formed such that the high concentration layer is interposed between the first conductivity type drift layer and the second conductivity type base region. A method for manufacturing a semiconductor device according to claim 3.

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