阅读说明：本技术 碳化硅半导体装置及其制造方法 (Silicon carbide semiconductor device and method for manufacturing same ) 是由 登尾正人 加藤武宽 山下侑佑 于 2020-05-22 设计创作，主要内容包括：通过用外延层构成源极区域(4),减小基极区域(3)的厚度的不均,抑制阈值Vt的不均。此外,关于栅极沟槽(6)的侧面,在单元部(RC)的外侧,与单元部内的源极区域中的与基极区域相接的由外延层构成的部分相比,相对于衬底(1)的主表面的法线方向倾斜。由此,使得栅极绝缘膜(7)即使在单元部内成为厚度较薄的薄膜部,在单元部的外部也成为厚度较厚的厚膜部。(By forming the source region (4) with an epitaxial layer, variation in the thickness of the base region (3) is reduced, and variation in the threshold value Vt is suppressed. The side surfaces of the gate trench (6) are inclined with respect to the normal direction of the main surface of the substrate (1) outside the cell section (RC) compared with the portion of the source region in the cell section, which is formed of an epitaxial layer and is in contact with the base region. Thus, even if the gate insulating film (7) is a thin film portion having a small thickness in the cell portion, it is a thick film portion having a large thickness outside the cell portion.)

1. A silicon carbide semiconductor device comprising an inverted vertical semiconductor element having a trench gate structure in a cell portion (RC),

the disclosed device is provided with:

a substrate (1) having a main surface and made of silicon carbide of the 1 st or 2 nd conductivity type;

drift layers (2, 2a) formed on the main surface side of the substrate and composed of silicon carbide of the 1 st conductivity type having an impurity concentration lower than that of the substrate;

a base region (3) formed on the drift layer and made of silicon carbide of the 2 nd conductivity type;

a source region (4) of the 1 st conductivity type formed on the base region in the cell portion, having an impurity concentration higher than that of the drift layer, and at least a portion in contact with the base region being formed of an epitaxial layer of silicon carbide;

the trench gate structure is formed in a gate trench (6), has a gate insulating film (7) formed on an inner wall surface of the gate trench, and a gate electrode (8) formed on the gate insulating film, and the gate trench (6) is formed deeper than the base region from a surface of the source region, has a linear portion whose length direction is one direction, and is formed from the cell portion to an outer side of the cell portion;

an interlayer insulating film (10) in which a contact hole connected to the source region is formed on the source region and the trench gate structure;

a 1 st electrode (9) formed on the interlayer insulating film and electrically connected to the source region through the contact hole; and

a 2 nd electrode (11) electrically connected to the back surface side of the substrate;

the side surfaces of the gate trench are inclined with respect to the normal direction of the main surface of the substrate outside the cell portion, compared to the portion of the source region in the cell portion, the portion being formed of the epitaxial layer and contacting the base region.

2. The silicon carbide semiconductor device according to claim 1,

the side surface of the gate trench on the inlet side of the gate trench on the outer side of the cell portion is formed of an ion-implanted layer (31), and the side surface of the gate trench is inclined with respect to the normal direction of the main surface of the substrate in the ion-implanted layer portion.

3. The silicon carbide semiconductor device according to claim 2,

and a gate pad (8b) for the gate electrode outside the cell unit, wherein the side surface of the gate trench on the inlet side of the gate trench is formed of the ion-implanted layer at the position where the gate pad is provided.

4. The silicon carbide semiconductor device according to claim 2 or 3,

the ion-implanted layer is formed of a 2 nd conductivity type layer.

5. The silicon carbide semiconductor device according to claim 4,

an outer peripheral portion (RO) surrounding the cell portion;

an extraction pad (33) formed on the interlayer insulating film, the extraction pad being provided with the ion implantation layer formed of a 2 nd conductivity type layer and the interlayer insulating film formed on the ion implantation layer on the base region;

the ion implantation layer is electrically connected to the extraction pad through a contact hole formed in the interlayer insulating film.

6. The silicon carbide semiconductor device according to claim 5,

the outer peripheral portion has a protective ring portion (RG) surrounding the outer periphery of the cell portion and a connection portion (RJ) located between the cell portion and the protective ring portion, and the protective ring portion has a recessed portion (20) recessed from the drift layer as compared with the cell portion, thereby forming an island-shaped boss portion (RM) protruding from the cell portion and the connection portion as compared with the protective ring portion in the thickness direction of the substrate;

the ion-implanted layer is formed at the outer edge of the connecting portion, and the ion-implanted layer, the base region, and the drift layer are formed in this order at the boundary position between the boss portion and the recess portion.

7. The silicon carbide semiconductor device according to claim 6,

the ion implantation layer is formed over the entire region of the connection portion.

8. A method for manufacturing a silicon carbide semiconductor device having an inverted vertical semiconductor element of a trench gate structure in a cell portion (RC),

the method comprises the following steps:

preparing a substrate (1) having a main surface and made of silicon carbide of the 1 st or 2 nd conductivity type;

forming a drift layer (2, 2a) made of silicon carbide of the 1 st conductivity type having an impurity concentration lower than that of the substrate on the substrate;

forming a base region (3) made of silicon carbide of the 2 nd conductivity type on the drift layer;

forming a source region (4) of a 1 st conductivity type silicon carbide having a higher impurity concentration of the 1 st conductivity type than the drift layer on the base region by epitaxial growth;

forming a trench gate structure by forming a gate trench (6) on the inner wall surface of the gate trench, forming a gate insulating film (7) on the inner wall surface of the gate trench, and forming a gate electrode (8) on the gate insulating film, wherein the gate trench (6) is formed deeper than the base region from the surface of the source region, has a linear portion whose length direction is one direction, and extends from the cell portion to the outside of the cell portion;

forming an interlayer insulating film (10) having a contact hole connected to the source region on the source region and the trench gate structure;

forming a 1 st electrode (9) electrically connected to the source region via the contact hole; and

forming a 2 nd electrode (11) on the back surface side of the substrate;

in the step of forming the trench gate structure, a side surface of the gate trench is inclined with respect to a normal direction of a main surface of the substrate outside the cell portion, as compared with a portion of the source region in the cell portion, the portion being formed by the epitaxial growth and contacting the base region.

9. The method for manufacturing a silicon carbide semiconductor device according to claim 8,

includes a step of forming an ion-implanted layer (31) by performing ion implantation outside the cell unit after the source region is formed;

in the step of forming the trench gate structure, the side surfaces of the gate trench are formed by the ion-implanted layer at both ends in the longitudinal direction of the gate trench, and a portion of the side surfaces of the gate trench formed by the ion-implanted layer is inclined with respect to a normal direction of the main surface of the substrate by performing heat treatment after the gate trench is formed.

10. The method for manufacturing a silicon carbide semiconductor device according to claim 9,

in the step of forming the trench gate structure, a gate pad (8b) of the gate electrode is formed outside the cell unit, and the side surface of the gate trench on the inlet side of the gate trench is formed by the ion-implanted layer at a position where the gate pad is provided.

11. The method for manufacturing a silicon carbide semiconductor device according to claim 9 or 10,

in the step of forming the trench gate structure, the gate insulating film is formed by performing thermal oxidation which is the heat treatment.

12. The method for manufacturing a silicon carbide semiconductor device according to any one of claims 9 to 11,

in the step of forming the ion-implanted layer, the ion-implanted layer is formed by ion-implanting a 2 nd conductivity type impurity, and the ion-implanted layer is made to be a 2 nd conductivity type layer.

13. The method for manufacturing a silicon carbide semiconductor device according to claim 12,

in the step of forming the ion-implanted layer, the ion-implanted layer is also formed on an outer peripheral portion (RO) surrounding an outer periphery of the cell portion;

in the step of forming the interlayer insulating film, forming the interlayer insulating film also on the ion-implanted layer, and forming a contact hole connected to the ion-implanted layer;

the method includes a step of forming an extraction pad (33) electrically connected to the ion implantation layer through the contact hole on the interlayer insulating film after the step of forming the interlayer insulating film.

14. The method for manufacturing a silicon carbide semiconductor device according to claim 13,

a step of forming a protective ring portion (RG) surrounding the outer periphery of the cell portion on the outer periphery, and forming a connection portion (RJ) located between the cell portion and the protective ring portion;

the step of forming the protective ring portion and the connecting portion is a step of: forming a recess (20) recessed from the drift layer at a position corresponding to the protective ring portion after the step of forming the ion-implanted layer, thereby forming the protective ring portion, and forming an island-shaped boss portion (RM) protruding from the protective ring portion at an inner side portion of the protective ring portion in a thickness direction of the substrate, the connection portion being formed on an outer periphery of the cell portion in the boss portion;

in the step of forming the ion-implanted layer, the ion-implanted layer is also formed at the outer edge portion of the connecting portion, and the ion-implanted layer, the base region, and the drift layer are formed in this order at the boundary position between the boss portion and the recess portion.

Technical Field

The present invention relates to a SiC semiconductor device having a vertical semiconductor element having a trench gate structure made of silicon carbide (hereinafter referred to as SiC) and a method for manufacturing the same.

Background

Conventionally, as a structure for increasing a channel density to flow a large current, there is an SiC semiconductor device having a trench gate structure. The SiC semiconductor device comprises a p-type base (base) region and an n-type drift layer sequentially formed on an n-type drift layer⁺Source region of type n⁺A trench gate structure is formed on the surface of the source region so as to penetrate the p-type base region and reach the n-type drift layer. Specifically, after a p-type base region is epitaxially grown on an n-type drift layer, an n-type impurity is ion-implanted into the p-type base region to invert a part of the p-type base region into an n-type, thereby forming an n-type base region⁺A source region of the type (see, for example, patent document 1).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2016/063644 handbook

Disclosure of Invention

However, regarding the film thickness unevenness at the time of epitaxial growth, the film thickness unevenness increases as the grown film thickness becomes thicker, but the variation in the range of ion implantation is not so large. Therefore, the film thickness unevenness of the p-type base region after ion implantation corresponds to the film thickness of epitaxial growth. Thereby, n is formed in the p-type base region by ion implantation⁺In the case of a type source region, n⁺The source region has a small thickness variation, and the p-type base region forming the channel region has a large thickness variation. Thus, there is a problem that unevenness of the threshold Vt is generated.

Thus, the present inventors have studied not only for the p-type base region but also for n⁺The source region is also formed by epitaxial growth. Thus, the thickness unevenness is respectively assigned to the p-type base region and n⁺Type source regionTherefore, the thickness variation of the p-type base region can be reduced, and the variation of the threshold value Vt can be suppressed. In addition, n is formed by epitaxial growth⁺In the case of the source region, the side surface of the trench gate structure can be made to face n⁺The surface of the source region is substantially vertically erected.

However, in the case of such a configuration, the following cases were confirmed: at the corner portion on the trench entrance side, the gate insulating film becomes thin, and when a large electric field is applied, the gate insulating film is broken at the thinned portion, and the gate life is reduced.

In the trench gate structure, a gate pad (liner) for drawing a gate electrode to the outside of the gate trench is provided at least at one of both ends in the longitudinal direction, and the gate pad is also formed on a thinned portion of the gate insulating film. Therefore, it is conceivable that a large electric field acts on a portion of the gate insulating film including the gate pad, and the gate insulating film is broken.

An object of the present invention is to provide a SiC semiconductor device having a structure capable of suppressing variation in threshold value Vt and suppressing reduction in gate life, and a method for manufacturing the same.

An SiC semiconductor device according to an aspect of the present invention includes: a substrate having a main surface and made of silicon carbide of the 1 st or 2 nd conductivity type; a drift layer formed on the main surface side of the substrate and made of silicon carbide of the 1 st conductivity type having an impurity concentration lower than that of the substrate; a base region formed on the drift layer and made of silicon carbide of the 2 nd conductivity type; a source region of the 1 st conductivity type formed on the base region in the cell portion, having an impurity concentration higher than that of the drift layer, and at least a portion in contact with the base region being formed of an epitaxial layer of silicon carbide; a trench gate structure formed in a gate trench having a gate insulating film formed on an inner wall surface of the gate trench and a gate electrode formed on the gate insulating film, the gate trench being formed deeper than the base region from a surface of the source region, having a linear portion whose length direction is one direction, and being formed from the cell portion to an outer side of the cell portion; an interlayer insulating film having a contact hole connected to the source region formed on the source region and the trench gate structure; a 1 st electrode formed on the interlayer insulating film and electrically connected to the source region via the contact hole; and a 2 nd electrode electrically connected to the back surface side of the substrate. The side surfaces of the gate trench are inclined with respect to the normal direction of the main surface of the substrate, outside the cell portion, compared to the portion of the source region in the cell portion, which is formed of the epitaxial layer and contacts the base region.

In this way, since at least the portion of the source region in contact with the base region is formed of the epitaxial growth layer, variation in the thickness of the base region can be reduced, and variation in the threshold Vt can be suppressed. The side surfaces of the gate trench are inclined with respect to the normal direction of the main surface of the substrate outside the cell portion, compared to the portion of the source region in the cell portion, which is formed of the epitaxial layer and contacts the base region. Therefore, even if the gate insulating film is a thin film portion having a small thickness in the cell portion, the gate insulating film can be a thick film portion having a large thickness outside the cell portion. Therefore, it is possible to suppress the gate insulating film from being broken due to a large electric field acting on both end positions in the longitudinal direction of the trench gate structure, and to suppress a decrease in the life of the gate insulating film.

A method for manufacturing a SiC semiconductor device according to another aspect of the present invention includes: preparing a substrate having a main surface and made of silicon carbide of the 1 st or 2 nd conductivity type; forming a drift layer composed of silicon carbide of the 1 st conductivity type having an impurity concentration lower than that of the substrate over the substrate; forming a base region composed of silicon carbide of a 2 nd conductivity type over the drift layer; forming a source region of silicon carbide of the 1 st conductivity type having a higher impurity concentration of the 1 st conductivity type than the drift layer by epitaxial growth on the base region; forming a trench gate structure by forming a gate insulating film on an inner wall surface of a gate trench, which is deeper than a base region from a surface of a source region, has a linear portion whose length direction is one direction, and reaches an outer side of a cell portion from the cell portion, and forming a gate electrode on the gate insulating film after the gate trench is formed; forming an interlayer insulating film having a contact hole connected to the source region over the source region and the trench gate structure; forming a 1 st electrode electrically connected to the source region via the contact hole; a2 nd electrode is formed on the back surface side of the substrate. In the step of forming the trench gate structure, the side surface of the gate trench is inclined with respect to the normal direction of the main surface of the substrate outside the cell portion as compared with a portion of the source region in the cell portion, which portion is formed by the epitaxial layer and contacts the base region.

By forming the source region by epitaxial growth on the base region in this manner, variation in the thickness of the base region can be reduced, and variation in the threshold Vt can be suppressed. In addition, when forming the trench gate structure, the side surface of the gate trench is inclined with respect to the normal direction of the main surface of the substrate outside the cell portion as compared with the portion of the source region in the cell portion, which is formed by the epitaxial layer and is in contact with the base region. Therefore, even if the gate insulating film is a thin film portion having a small thickness in the cell portion, the gate insulating film can be a thick film portion having a large thickness outside the cell portion. Therefore, it is possible to suppress the gate insulating film from being broken due to a large electric field acting on both end positions in the longitudinal direction of the trench gate structure, and to suppress a decrease in the life of the gate insulating film.

The parenthesized reference numerals given to the respective components and the like are used to show an example of the correspondence between the components and the like and the specific components and the like described in the embodiments described later.

Drawings

Fig. 1 is a diagram schematically showing the top surface layout of an SiC semiconductor device according to embodiment 1.

Fig. 2 is a sectional view II-II of fig. 1.

Fig. 3 is a cross-sectional perspective view of the portion above the interlayer insulating film in the cross section III-III of fig. 1.

Fig. 4 is a cross-sectional view IV-IV of fig. 1.

Fig. 5 is a cross-sectional view V-V of fig. 1.

Fig. 6A is a cross-sectional view showing a manufacturing process of the SiC semiconductor device according to embodiment 1.

Fig. 6B is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6A.

Fig. 6C is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6B.

Fig. 6D is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6C.

Fig. 6E is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6D.

Fig. 6F is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6E.

Fig. 6G is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6F.

Fig. 6H is a cross-sectional view showing a manufacturing process of the SiC semiconductor device next to fig. 6G.

Fig. 7 is a diagram schematically showing the upper surface layout of the top end portion of the trench gate structure of the SiC semiconductor device according to embodiment 2.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent portions are given the same reference numerals and described.

(embodiment 1)

Embodiment 1 will be explained. Here, a SiC semiconductor device in which an inversion MOSFET is formed as a vertical semiconductor element having a trench gate structure will be described as an example.

The SiC semiconductor device shown in fig. 1 includes a cell portion in which a MOSFET having a trench gate structure is formed, and an outer peripheral portion RO surrounding the cell portion RC. The outer peripheral portion RO includes a protection ring portion RG and a connection portion RJ arranged between the cell portion RC and the protection ring portion RG on the inner side of the protection ring portion RG. Fig. 1 is not a cross-sectional view, but is partially shaded for ease of viewing the drawing.

As shown in FIG. 2, the SiC semiconductor device uses n made of SiC⁺A type substrate 1 is formed. At n⁺N composed of SiC is epitaxially grown in this order on the main surface of type substrate 1^－A type impurity layer 2, an n-type current spreading layer 2a, a p-type base region 3 and n⁺And a source region 4.

n⁺Type substrate 1, for example, having n-type impurity concentration of 1.0X 10¹⁹/cm³The surface is a (0001) Si surface. n is^－The n-type impurity concentration of the impurity layer 2 is 0.5 to 2.0 x 10¹⁶/cm³. With respect to the n-type current spreading layer 2a, the n-type impurity concentration ratio n^－The type impurity layer 2 is high, that is, low resistance, and current is dispersed and flows to a larger range, thereby playing a role in reducing the resistance of the JFET. For example, the n-type current spreading layer 2a is set to 8 × 10, for example¹⁶/cm³The thickness was 0.5. mu.m. For convenience, n is used here^－Different layers such as the n-type current spreading layer 2a and the type impurity layer 2 are explained, but both of them constitute a drift layer.

In addition, in the p-type base region 3, the p-type impurity concentration is, for example, 2.0 × 10 at the portion where the channel region is formed¹⁷/cm³About 300nm thick. With respect to n⁺A source region 4 of type having an impurity concentration ratio n^－The type impurity layer 2 is high, and the n-type impurity concentration in the surface layer portion is, for example, 2.5X 10¹⁸～1.0×10¹⁹/cm³The thickness is about 0.5 μm.

At cell portion RC, at n⁺A p-type base region 3 and n are left on the surface side of the type substrate 1⁺A source region 4 of type RJ, n at the connection part⁺The source region 4 becomes an ion implantation layer 31 described later. In addition, the protective ring portion RG is formed so as to connect these n⁺Recess 20 is formed so as to penetrate through source region 4, ion-implanted layer 31, and p-type base region 3 and reach n-type current spreading layer 2 a.

In addition, in the cell portion RC, n is increased⁺The p-type deep layer 5 is formed so as to penetrate the source region 4 and the p-type base region 3 and reach the n-type current spreading layer 2 a. The p-type impurity concentration of the p-type deep layer 5 is higher than that of the p-type base region 3. Specifically, the p-type deep layer 5 is provided in a stripe-shaped trench 5a, and is formed of a p-type epitaxial film formed by epitaxial growth, and the trench 5a is disposed in the n-type current spreading layer 2a at equal intervals and is disposed apart from each other without crossing points. The trench 5a has a width of 1 μm or less and a depth of an aspect ratio of 2 or more, for example.

For example, the p-type impurity concentration of each p-type deep layer 5 is, for example, 1.0 × 10¹⁷～1.0×10¹⁹cm³The width is about 0.7 μm and the depth is about 2.0. mu.m. The deepest bottom of each p-type deep layer 5 is positioned at a position corresponding to the n-type current spreading layers 2a and n^－The boundary position of the type impurity layer 2 is the same or closer to the p-type base region 3 than this position. That is, p-type deep layer 5 and n-type current spreading layer 2a have the same depth, or n-type current spreading layer 2a is formed to a deeper position than p-type deep layer 5. The p-type deep layer 5 is formed from one end of the cell portion RC to the other end as shown in fig. 1. The p-type deep layer 5 extends in the same direction as the trench gate structure described later as the longitudinal direction, and is connected to a p-type connection layer 30 described later, which extends from both ends of the trench gate structure further to the outside of the cell portion RC.

Furthermore, to connect the p-type base region 3 and n⁺The source region 4 is connected to n^－In the mode of impurity layer 2, for example, gate trench 6 having a width of 0.8 μm and a depth of 1.0 μm is formed. The gate trench 6 is formed not only in the cell portion RC but also protruding from the cell portion RC to the connection portion RJ. The p-type base regions 3 and n are arranged so as to be in contact with the side surfaces of the gate trench 6⁺Source region 4 and ion implantation layer 31. More specifically, in the cell portion RC, the side surface on the inlet side of the gate trench 6 is defined by n⁺The source region 4 is formed with an ion implantation layer 31 on the side surface on the entrance side of the gate trench 6 at the connection portion RJ. The gate trench 6 is formed in a layout having a straight portion in which the horizontal direction on the paper surface of fig. 2 is the width direction, the vertical direction on the paper surface is the length direction, and the vertical direction on the paper surface is the depth direction. As shown in fig. 1, the gate trench 6 is formed only by a linear portion in the cell portion RC, but is also formed only by a linear portion in the connection portion RJ in the present embodiment. The gate trenches 6 are arranged so as to be sandwiched between the p-type deep layers 5, and are arranged in parallel at equal intervals in a stripe shape.

Furthermore, in the present embodiment, as shown in fig. 2, 3, and 5, the side surfaces of the gate trench 6 are provided in the cell portion RC and the connection portion RJAre different in shape. Specifically, in the cell portion RC, the side surface of the gate trench 6 is opposed to n⁺The main surface of the substrate 1 is vertical, and in the connecting portion RJ, the side surface of the gate trench 6 on the trench entrance side is wider than the bottom side, and n is the same as n⁺The normal direction of the main surface of type substrate 1 is inclined. As shown in fig. 4, the gate trench 6 has a top end portion with a trench entrance side opposite to n, similarly to the shape of the side face of the connection portion RJ⁺The normal direction of the main surface of type substrate 1 is inclined. Hereinafter, the inclined portions of the side surfaces and the top end portions of the gate trenches 6 are referred to as inclined portions.

When the part of the p-type base region 3 located on the side of the gate trench 6 is operated as a vertical MOSFET, n⁺Type source region 4 and n^－In a channel region continuous between impurity layers 2, a gate insulating film 7 is formed on an inner wall surface of gate trench 6 including the channel region. The gate insulating film 7 is formed of a thermally oxidized film. A gate electrode 8 made of doped polysilicon is formed on the surface of the gate insulating film 7, and the gate trench 6 is completely filled with the gate insulating film 7 and the gate electrode 8. Thereby, a trench gate structure is formed.

The gate insulating film 7 is formed on the entire inner wall surface of the gate trench 6, but the thickness varies depending on the location. Specifically, n is formed on the side surface of the gate trench 6, which is the portion located in the cell portion RC⁺Source region 4 of type with side surface opposite to n⁺In a portion of type substrate 1 where the main surface is vertical, gate insulating film 7 is thinned at the corner of the trench entrance. Hereinafter, the gate insulating film 7 thinned in this portion is referred to as a thin portion 7 a. In the gate trench 6, the portion of the connection portion RJ located outside the cell portion RC, that is, the portion having the ion implantation layer 31, which will be described later, formed on the side surface and the inclined portion on the side surface is thicker than the thin film portion 7a in the thickness of the gate insulating film 7. Hereinafter, the gate insulating film 7 in this portion is referred to as a thick film portion 7 b.

In addition, in n⁺On the surfaces of the source region 4 and the p-type deep layer 5 and on the gate electrode 8, a source electrode 9 corresponding to the 1 st electrode is formed with an interlayer insulating film 10 interposed therebetween. The source electrode 9 is made of various metals, for example, Ni/AL. And areAnd, at least n-type SiC, specifically n, of the plurality of metals⁺The portion in contact with type source region 4 is composed of a metal capable of ohmic contact with n-type SiC. At least a portion of the plurality of metals that is in contact with p-type SiC, specifically, p-type deep layer 5, is made of a metal that can make ohmic contact with p-type SiC. In addition, these source electrodes 9 are electrically insulated by being formed on the interlayer insulating film 10. And the source electrode 9 and n are connected via a contact hole formed in the interlayer insulating film 10⁺The source region 4 and the deep p-type layer 5 are in electrical contact.

Further, in n⁺N is formed on the back surface of the substrate 1⁺And a drain electrode 11 electrically connected to the type substrate 1 and corresponding to the 2 nd electrode. With this structure, a MOSFET having an n-channel inversion type trench gate structure is formed. The unit section RC is configured by arranging a plurality of such MOSFETs.

On the other hand, in guard ring portion RG, as described above, concave portion 20 is formed so as to penetrate ion-implanted layer 31 and p-type base region 3, which will be described later, and reach n-type current spreading layer 2 a. Therefore, at a position away from the cell portion RC, the ion-implanted layer 31 and the p-type base region 3 are removed, and the n-type current spreading layer 2a is exposed. And, at n⁺In the thickness direction of the type substrate 1, the cell portion RC and the connecting portion RJ inside the recess 20 form a boss portion RM protruding in an island shape. The side surface of the recess 20, that is, the boundary position between the boss portion RM and the recess 20, the corner of the boss portion RM is inclined. In addition, although the gate insulating film 7 is formed and the interlayer insulating film 10 is formed thereon in the recess 20, a residue 8a of polysilicon for forming the gate electrode 8 may remain at a boundary position between the recess 20 and the boss portion RM.

Further, a plurality of p-type guard rings 21 are provided in a surface layer portion of the n-type current spreading layer 2a located below the recess 20 so as to surround the cell portion RC. In the present embodiment, the p-type guard ring 21 is a quadrangle with rounded four corners, but may be formed of another frame shape such as a circle. The p-type guard ring 21 is disposed in the trench 21a formed in the n-type current spreading layer 2a, and is formed of an epitaxially grown p-type epitaxial film. The trench 21a has a width of 1 μm or less and a depth with an aspect ratio of 2 or more, for example.

The structure of each portion constituting the p-type guard ring 21 is the same as that of the p-type deep layer 5 described above. The upper surface of the p-type guard ring 21 is shaped like a frame surrounding the cell portion RC and the connection portion RJ, and is different from the p-type deep layer 5 formed linearly in this respect, and the other is the same. That is, p-type guard ring 21 has the same width and the same thickness, that is, the same depth as p-type deep layer 5. The interval between the p-type guard rings 21 may be equal, but the interval between the p-type guard rings 21 is narrower on the cell RC side and larger on the outer peripheral side so that the equipotential lines are directed further on the outer peripheral side by alleviating the electric field concentration on the inner peripheral side, that is, the cell RC side.

Although not shown, a protection ring portion RG having an outer peripheral voltage-resistant structure surrounding the cell portion RC is configured by providing an EQR structure on the outer periphery of the p-type guard ring 21 as needed.

Further, a portion from the cell portion RC to the protection ring portion RG is defined as a connection portion RJ, and n is a number n of the connection portion RJ^－The surface layer portion of the impurity layer 2 is formed with a plurality of p-type connecting layers 30. In the case of the present embodiment, as shown by the broken line hatching in fig. 1, the connection portion RJ is formed so as to surround the cell portion RC and at the outer periphery of the cell portion RC, and a plurality of rectangular p-type guard rings 21 having a rounded quadrangle are formed so as to surround the outer side of the connection portion RJ. The p-type connection layers 30 are arranged in parallel with the p-type deep layers 5 formed in the cell portion RC, and in the present embodiment, are arranged at intervals equal to the intervals between the adjacent p-type deep layers 5. Further, p-type connection layer 30 is provided so as to extend from p-type deep layer 5 at a position separated by a distance from cell portion RC to p-type guard ring 21, so that the distance from the tip of p-type connection layer 30 to p-type guard ring 21 is shortened.

Each p-type connection layer 30 is disposed in such a manner that n is⁺The source region 4 and the base region 3 reach n^－The trench 30a of the type impurity layer 2 is formed of an epitaxially grown p-type epitaxial film. Between the cell portion RC and the protection ring portion RG in the longitudinal direction of the p-type deep layer 5 and the top of the p-type deep layer 5And are connected end to form a p-type connection layer 30. The trench 30a has a width of 1 μm or less and an aspect ratio of 2 or more. The p-type connecting layer 30 is in contact with the p-type base region 3 so as to be fixed at the source potential.

Each portion constituting p-type connecting layer 30 has the same configuration as p-type deep layer 5 and p-type guard ring 21 described above, and differs from p-type guard ring 21 formed in a frame shape in that the upper surface of p-type connecting layer 30 has a linear shape, and the other portions are the same. That is, p-type connection layer 30 has the same width, the same thickness, and the same depth as p-type deep layer 5 and p-type guard ring 21. The interval between the p-type continuous layers 30 is equal to the interval between the p-type deep layers 5 in the cell portion RC in the present embodiment, but may be different.

By forming such p-type connecting layers 30 and setting the p-type connecting layers 30 to a predetermined interval, for example, an interval equal to or smaller than the p-type deep layer 5, it is possible to suppress excessive elevation of equipotential lines between the p-type connecting layers 30. This can suppress formation of a portion where electric field concentration occurs between p-type connected layers 30, and can suppress a decrease in withstand voltage.

Further, in the connection portion RJ, n is formed in the cell portion RC by the pair⁺The ion implantation layer 31 is formed by ion implantation in the source region 4. In the present embodiment, the entire region above p-type base region 3 is provided as ion-implanted layer 31. The conductivity type of the portion of the ion-implanted layer 31 located on the side of the gate trench 6 is arbitrary, here, by applying n after epitaxial growth⁺The source region 4 is ion-implanted with a p-type impurity to invert the conductivity type to be p-type.

As shown in fig. 3 and 4, a gate pad 8b is drawn from the gate electrode 8 at the tip of the trench gate structure extending to the connecting portion RJ. An interlayer insulating film 10 is also formed on the surfaces of the gate pad 8b and the ion-implanted layer 31, and a gate pad 32 and an extraction pad 33 for hole extraction shown in fig. 1 are formed on the interlayer insulating film 10 at a position away from the cell portion RC in the connection portion RJ. The gate pad 32 is electrically connected to the gate pad 8b via a contact hole, not shown, formed in the interlayer insulating film 10. The extraction pad 33 is also electrically connected to the p-type connection layer 30 and the ion implantation layer 31 via a contact hole, not shown, formed in the interlayer insulating film 10.

As described above, in the connecting portion RJ, inclined portions are formed on the side surfaces and the distal end portions of the gate trench 6. Specifically, the position of gate trench 6 corresponding to ion-implanted layer 31 is formed as an inclined portion, and the inclined portion is formed to a depth approximately equal to the boundary position between ion-implanted layer 31 and p-type base region 3. In the case of the present embodiment, the ion implantation layer 31 is formed in the entire region within the connection portion RJ, but the ion implantation layer 31 may be formed at least in the portion constituting the side surface and the tip portion of the gate trench 6 outside the cell portion RC. In this way, the inclined portions can be formed at all the positions overlapping with the gate pad 8b in the side surfaces and the top end of the gate trench 6.

Further, since the ion-implanted layer 31 is provided over the entire periphery of the outer edge portion of the connecting portion RJ, the outer edge portion of the boss portion RM, that is, the boundary position with the recess 20 is constituted by the ion-implanted layer 31, the p-type base region 3, and the n-type current spreading layer 2a in this order from the top as shown in fig. 2. Therefore, it is possible to prevent the ion-implanted layer 31 from being kept at n⁺N in the order from the top as in the case of the source region 4⁺An npn structure comprising source region 4, p-type base region 3, and n-type current spreading layer 2 a.

As described above, the SiC semiconductor device of the present embodiment is configured. In the SiC semiconductor device having the above-described configuration, when the MOSFET is turned on, a channel region is formed in the surface portion of p-type base region 3 located on the side surface of gate trench 6 by controlling the voltage applied to gate electrode 8. Thereby passing through n⁺Type source region 4 and n^－The impurity layer 2 allows current to flow between the source electrode 9 and the drain electrode 11.

Even when a high voltage is applied when the MOSFET is turned off, the p-type deep layer 5 formed to a position deeper than the trench gate structure suppresses the electric field from entering the bottom of the gate trench, and reduces the electric field concentration at the bottom of the gate trench. This prevents the gate insulating film 7 from being damaged.

Further, the rise of the equipotential lines is suppressed at the connecting portion RJ and directed toward the protection ring portion RG. In the protective ring portion RG, the p-type guard ring 21 terminates the equipotential lines while expanding the interval in the outer circumferential direction, and a desired withstand voltage can be obtained even in the protective ring portion RG.

In the SiC semiconductor device having such a structure, the side surface on the inlet side of the gate trench 6 constituting the trench gate structure faces n in the cell portion RC⁺The main surface of the type substrate 1 is vertically erected, but is inclined in the connecting portion RJ. Thus, even if the gate insulating film 7 is a thin film portion 7a having a small thickness in the cell portion RC, the thick film portion 7b having a large thickness can be formed in the connection portion RJ. Therefore, it is possible to suppress the gate insulating film 7 from being broken by a large electric field applied to both end positions in the longitudinal direction of the trench gate structure, and to suppress a decrease in the life of the gate insulating film 7.

Further, if holes are not extracted satisfactorily from the outer periphery of the cell portion RC at the time of avalanche breakdown of the vertical MOSFET, the tolerance of the SiC semiconductor device is lowered. Assume that the ion implantation layer 31 is not provided in the connection portion RJ, and that n is formed in the uppermost portion of the semiconductor in the same manner as the cell portion RC⁺The source region 4 forms a PN junction with the p-type base region 3, and thus cannot extract holes.

In contrast, in the present embodiment, the uppermost layer of the semiconductor is the ion-implanted layer 31 made of a p-type layer. Therefore, by electrically connecting extraction pad 33 formed on interlayer insulating film 10 to ion-implanted layer 31, holes can be extracted from p-type base region 3 through ion-implanted layer 31 via extraction pad 33. This enables holes to be extracted from the outer periphery of the cell portion RC satisfactorily at the time of avalanche breakdown of the vertical MOSFET, and thus can suppress a decrease in the tolerance of the SiC semiconductor device.

Further, in the SiC semiconductor device of the present embodiment, the boundary position between the mesa portion RM and the recess 20 is composed of the ion-implanted layer 31, the p-type base region 3, and the n-type current-spreading layer 2a in this order from the top. That is, the ion-implanted layer 31 is not kept at n⁺N in the order from the top as in the case of the source region 4⁺An npn structure comprising source region 4, p-type base region 3, and n-type current spreading layer 2 a.

As will be described later, since the gate insulating film 7 and the gate electrode 8 are formed after the recess 20 and the gate trench 6 are formed, the same trench gate structure is formed not only in the gate trench 6 but also in the recess 20. Therefore, the polysilicon remaining in the recess 20 and serving as the material of the gate electrode 8 is removed later. However, as shown in fig. 2, a residue 8a of polycrystalline silicon may remain at the boundary position between the recess 20 and the boss portion RM.

In the case of such a structure, if the boundary portion between the mesa portion RM and the recess 20 has an npn structure, an inversion channel is formed in the p-type base region 3 when the potential of the residue 8a, which becomes a floating potential, increases due to external charges or the like. Therefore, it is possible to generate the AND⁺The source electrode 9 and the like electrically connected to the source type region 4 have a problem of leakage current.

However, since the ion-implanted layer 31 composed of a p-type layer is provided as in the present embodiment, an npn structure can be made not to be formed, and therefore, even if the residue 8a is present, the flow of leakage current can be suppressed.

Next, a method for manufacturing the SiC semiconductor device of the present embodiment will be described with reference to fig. 6A to 6H.

[ procedure shown in FIG. 6A ]

First, n is prepared⁺The type substrate 1 serves as a semiconductor substrate. And, at the n⁺Epitaxially growing n composed of SiC on the main surface of type substrate 1^－And a type impurity layer 2.

[ procedure shown in FIG. 6B ]

Then, at n^－On the type impurity layer 2, an n-type current spreading layer 2a, a p-type base region 3 and n are epitaxially grown in this order⁺And a source region 4. Thus, n is formed by epitaxial growth⁺A source region 4 of type, so that p-type base regions 3 and n are aligned⁺Since the source regions 4 are distributed with variations in thickness, variations in thickness of the p-type base regions 3 can be reduced, and variations in thickness can be reducedUnevenness in threshold value Vt is suppressed.

And, at n⁺After a mask, not shown, is disposed on source region 4, a planned formation region of ion-implanted layer 31 in the mask is opened. Then, by ion-implanting a p-type impurity such as aluminum using this mask, the ion-implanted layer 31 is formed. At this time, damage such as distortion occurs in the crystal structure of the ion-implanted portion.

[ procedure shown in FIG. 6C ]

Then, at n⁺A mask, not shown, is disposed on the surfaces of source region 4 and ion implantation layer 31, and the planned formation regions of p-type deep layer 5, p-type guard ring 21, and p-type connection layer 30 in the mask are opened. Then, trenches 5a, 21a, and 30a are formed by anisotropic etching such as rie (reactive Ion etching) using a mask.

[ procedure shown in FIG. 6D ]

After the mask is removed and the p-type layer is formed, the p-type layer is etched back to be formed at a ratio of n⁺The upper portion of the surface of the source region 4 is removed to form a p-type deep layer 5, a p-type guard ring 21, and a p-type connection layer 30.

At this time, the trenches 5a, 21a, and 30a are formed to have the same width by embedding the p-type layer in the trenches 5a, 21a, and 30a by buried epitaxial growth, and therefore, the occurrence of shape irregularities or irregularities on the surface of the p-type layer can be suppressed. Therefore, the p-type layer can be reliably embedded in the trenches 5a, 21a, and 30a, and the surface of the p-type layer can be formed into a flat shape with less unevenness.

As described above, ion-implanted layer 31 is formed in the step shown in fig. 6B, but ion-implanted layer 31 may be formed after p-type deep layer 5, p-type guard ring 21, and p-type connecting layer 30 are formed. This can suppress excessive etching of the ion-implanted layer 31 which is damaged by high temperature during epitaxial growth or by etching back.

[ procedure shown in FIG. 6E ]

At n⁺After forming a mask (not shown) on the source region 4, etc., the gate trench 6 in the mask is formedThe region is open. Next, the gate trench 6 is formed by anisotropic etching such as RIE using a mask.

Further, after the mask is removed, the mask not shown is formed again, and the planned formation region of the recess 20 in the mask is opened. Next, the concave portion 20 is formed by anisotropic etching such as RIE using a mask. Thereby, n is set at the position where the concave portion 20 is formed⁺Type source region 4 and p-type base region 3 penetrate and n-type current spreading layer 2a is exposed, and a plurality of p-type guard rings 21 are arranged from the surface of n-type current spreading layer 2 a.

Here, the gate trench 6 and the recess 20 are formed by different processes using different masks, but may be formed simultaneously using the same mask.

[ procedure shown in FIG. 6F ]

Removing the mask, thermally oxidizing to form a gate insulating film 7, and forming n on the inner wall surface of the gate trench 6 with the gate insulating film 7⁺The surface of the source region 4 is covered. At this time, n which is not damaged by ion implantation⁺Type source region 4 is thermally oxidized to the same extent as p type base region 3, and ion implantation layer 31 having been damaged is more easily thermally oxidized than p type base region 3. Therefore, in the cell portion RC, the entrance side of the gate trench 6 is opposite to n⁺The main surface of the substrate 1 is substantially vertically erected, and the entrance side of the gate trench 6 is an inclined portion at the connection portion RJ. Therefore, at the corner on the inlet side of the gate trench 6, the gate insulating film 7 becomes a thin film portion 7a which is thinned in the cell portion RC and a thick film portion 7b which is thicker in the connection portion RJ.

Here, the entrance side of the gate trench 6 in the connection portion RJ is inclined by thermal oxidation, but this shape can be obtained by heat treatment. For example, even if sacrificial oxidation or the like is performed, the ion implantation layer 31 in the connection portion RJ and n in the cell portion RC are caused⁺Since the oxidation of the source region 4 is promoted as compared with that of the source region, the entrance side of the gate trench 6 in the connecting portion RJ is an inclined portion. Thus, the gate insulating film 7 is formed without thermal oxidationIn the case of (3), the gate insulating film 7 may be formed by, for example, cvd (chemical vapor deposition), so that the thin film portion 7a becomes thinner in the cell portion RC and the thick film portion 7b becomes thicker in the connecting portion RJ.

Then, after depositing polysilicon doped with a p-type impurity or an n-type impurity, the polysilicon is etched back so as to remain at least in the gate trench 6, thereby forming the gate electrode 8. Thereby, a trench gate structure is formed.

Note that the trench gate structure may be formed only in the gate trench 6, but since the recess 20 is formed to form the boss portion RM, the same structure is formed in the recess 20. In this portion, although the polysilicon is removed by the etch back, the residue 8a may remain at the boundary position between the boss portion RM and the recess 20.

[ procedure shown in FIG. 6G ]

An interlayer insulating film 10 made of, for example, an oxide film is formed so as to cover the surfaces of the gate electrode 8 and the gate insulating film 7. Next, after forming a mask, not shown, on the surface of the interlayer insulating film 10, a portion of the mask located between the gate electrodes 8, that is, a portion corresponding to the p-type deep layer 5 and the vicinity thereof are opened. Then, the interlayer insulating film 10 is patterned using a mask to form p-type deep layers 5, n⁺And a contact hole exposing the source region 4. In addition, in a cross section different from that of the present drawing, a contact hole is also formed to partially expose the gate electrode 8 and the ion-implanted layer 31.

[ procedure shown in FIG. 6H ]

An electrode material having a laminated structure of a plurality of metals, for example, is formed on the surface of the interlayer insulating film 10. Next, the source electrode 9 and the extraction pad 33 are formed by patterning the electrode material. Further, the gate pad 32 is also formed in a cross section different from that of the present drawing. In addition, a gate pad 8b connected to the gate electrode 8 of each cell is provided in a cross section different from that of the present drawing. The gate pad 32 and the gate electrode 8 are electrically connected by opening a contact hole in the interlayer insulating film 10 at a position where the gate pad 8b is extended. Similarly, a contact hole connected to the ion-implanted layer 31 is formed in a cross section different from that of the present drawing, and the extraction pad 33 and the ion-implanted layer 31 are electrically connected through the contact hole.

The subsequent steps are not shown, but are performed at n⁺The step of forming drain electrode 11 and the like on the back surface side of type substrate 1 completes the SiC semiconductor device of the present embodiment.

As described above, in the present embodiment, the side surface on the inlet side of the gate trench 6 constituting the trench gate structure is opposed to the n side surface in the cell portion RC⁺The main surface of the type substrate 1 is vertically erected, and is formed as an inclined portion in the connecting portion RJ. Thus, even if the gate insulating film 7 is a thin film portion 7a having a small thickness in the cell portion RC, the gate insulating film 7 can be a thick film portion 7b having a large thickness in the connection portion RJ. Therefore, the gate insulating film 7 is not broken by a large electric field applied to both end positions in the longitudinal direction of the trench gate structure, and a decrease in the life of the gate insulating film 7 can be suppressed. And, since n is formed by epitaxial growth⁺Source region 4, so that the thickness variation is distributed to p-type base regions 3 and n⁺Since source region 4 has a small variation in the thickness of p-type base region 3, variation in threshold Vt can be suppressed. This makes it possible to obtain a SiC semiconductor device having a structure in which variation in threshold Vt is suppressed and degradation in gate life is suppressed.

(other embodiments)

The present invention has been described in terms of the above embodiments, but is not limited to the embodiments, and various modifications and equivalent variations are also included. In addition, various combinations and forms, and further, other combinations and forms including only one element, more than one element, or less than one element are also within the scope and spirit of the present invention.

(1) In the above embodiments, n⁺The source region 4 is formed of only an epitaxial growth layer, but n may be formed⁺The source region 4 is formed of an epitaxial growth layer and has a region ion-implanted in a surface layer portion thereof to increase the n-type impurity concentration. In this case, n⁺Boundary between source region 4 and p-type base region 3Since the positions and the thicknesses thereof are also defined by epitaxial growth, the effect of suppressing variation in threshold Vt is obtained. Further, in the case of such a configuration, n is⁺The surface layer portion of source region 4 can be in a state where the side surface of gate trench 6 is inclined. However, since only n is paired⁺Since the surface layer portion of source region 4 is ion-implanted, the side surface of gate trench 6 is n⁺The portion of source region 4 is inclined to a deeper position than the portion of ion-implanted layer 31. And, at n⁺The side surface of gate trench 6 is opposite to n at the lower position of source region 4, i.e. the portion contacting p-type base region 3⁺The main surface of the type substrate 1 is vertically erected.

(2) In the above-described embodiments, a MOSFET having an n-channel inverted trench gate structure is described as an example of a vertical power element. However, the above embodiments merely show an example of a vertical semiconductor element having a trench gate structure, and may have another structure or conductivity type as long as a current flows between the 1 st electrode provided on the front surface side and the 2 nd electrode provided on the back surface side of the semiconductor substrate.

For example, in embodiment 1 and the like, an n-channel MOSFET in which the 1 st conductivity type is an n-type and the 2 nd conductivity type is a p-type has been described as an example, but a p-channel MOSFET in which the conductivity types of the respective components are inverted may be used. In the above description, the MOSFET is described as an example of the semiconductor element, but the present invention can be applied to an IGBT having the same structure. In the IGBT, only n is used in comparison with the above embodiments⁺The conductivity type of the type substrate 1 is changed from n-type to p-type, and other structures and manufacturing methods are the same as those of the above embodiments.

(3) In the above embodiment, the trench gate structure is formed only with the linear portion. In contrast, as shown in fig. 7, both ends of the adjacent gate trenches 6 may be connected in a semicircular shape in the connecting portion RJ outside the cell portion RC, so that the gate trenches 6 may have an oval shape when viewed from above. In this case, the entire area around the semicircular portion located at the tip of the linear portion of the gate trench 6 may be the ion-implanted layer 31, and the side surface of the gate trench 6 may be inclined.

(5) In the above embodiment, the ion implantation layer 31 is a p-type layer, but may be an n-type layer instead of a p-type layer as long as the side surface of the gate trench 6 is inclined. Further, aluminum is exemplified as a doping source for ion implantation, but an n-type impurity such as nitrogen may be used, or an inert element such as carbon, silicon, or argon which does not become an impurity may be used.