WO2019059102A1

WO2019059102A1 - Method for producing semiconductor device using silicon carbide semiconductor substrate

Info

Publication number: WO2019059102A1
Application number: PCT/JP2018/034054
Authority: WO
Inventors: 愛子梶; 周平箕谷; 治人市川; 竹内　有一; 渡辺　行彦; 成岡　英樹
Original assignee: 株式会社デンソー
Priority date: 2017-09-19
Filing date: 2018-09-13
Publication date: 2019-03-28
Also published as: JP2019056725A

Abstract

In the present invention, a silicon carbide semiconductor substrate (10) that is formed of silicon carbide monocrystals having a main surface in which an off-angle is disposed at the (0001) plane and having an off-direction of <11-20> is prepared; first trenches (12) are formed in the main surface; and an epitaxial layer, which is constituted of silicon carbide and has second trenches that follow the shape of the first trenches (12) formed in the main surface, is grown on the main surface. Moreover, for the first trench (12) formation, a plurality of the first trenches (12) having a longitudinal direction parallel to the off-direction and having rectangular openings, are formed perpendicular to the off-direction.

Description

Method of manufacturing semiconductor device using silicon carbide semiconductor substrate

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2017-179509 filed on Sep. 19, 2017, the contents of which are incorporated herein by reference.

The present disclosure relates to a method of manufacturing a SiC semiconductor device configured using a silicon carbide (hereinafter referred to as SiC) semiconductor substrate on which alignment marks are formed.

Conventionally, it has been proposed to form an epitaxial layer on a SiC semiconductor substrate and perform a predetermined semiconductor manufacturing process to manufacture a SiC semiconductor device. Specifically, in the case of manufacturing a SiC semiconductor device using a SiC semiconductor substrate, a high quality epitaxial layer can be grown, so the offcut in the <11-20> direction with respect to the (0001) plane The off-cut substrate thus obtained is used as a SiC semiconductor substrate.

Then, in the case of manufacturing a SiC semiconductor device, a trench serving as an alignment mark is formed on such a SiC semiconductor substrate, and an impurity region having a planar pattern is formed by ion implantation or the like. Thereafter, when manufacturing a SiC semiconductor device, a predetermined manufacturing process such as growing an epitaxial layer or heat treatment is performed. Subsequently, when manufacturing the SiC semiconductor device, the position of the alignment mark is specified by the reader, and a predetermined semiconductor manufacturing process using resist patterning or the like is subsequently performed based on the alignment mark.

However, when the epitaxial layer is grown on the SiC semiconductor substrate in which the trench is formed, the epitaxial layer may not grow (that is, deposit) along the wall surface on the downstream side in the off direction of the trench. . That is, when the epitaxial layer is grown on the SiC semiconductor substrate, the epitaxial layer may be grown on the downstream side in the off direction of the trench so as to form a facet of the (0001) plane. In this case, the position of the alignment mark can not be specified with high precision due to the influence of the facets, and pattern deviation may occur before and after formation of the epitaxial layer.

Therefore, for example, in Patent Document 1, when an epitaxial layer is grown on a SiC semiconductor substrate and a facet is formed on the downstream side in the off direction of the trench, a new trench is formed on the facet. It has been disclosed to form

According to this, the new trench is formed in the facet of the (0001) plane. Therefore, even if the epitaxial layer is further grown on the SiC semiconductor substrate or heat treatment is performed, formation of a facet on the downstream side in the off direction of the new trench can be suppressed. it can. Therefore, by reading the new trench as the alignment mark by the reader, it is possible to suppress the occurrence of positional deviation when specifying the position of the alignment mark.

The off direction means "a direction parallel to a vector obtained by projecting the normal vector of the growth surface onto the (0001) plane". The downstream side in the off direction defines one of the sides, and means "the side where the tip of the vector obtained by projecting the normal vector of the growth surface onto the (0001) plane is facing".

JP 2007-280978 A

However, in the manufacturing method described in Patent Document 1, since a new trench needs to be formed on the facet, the manufacturing process is increased and complicated.

An object of the present disclosure is to provide a method of manufacturing a SiC semiconductor device capable of accurately reading a trench formed in an epitaxial layer without increasing or complicating a manufacturing process.

According to one aspect of the present disclosure, in a method of manufacturing a SiC semiconductor device, it is a SiC single crystal having a main surface provided with an off angle in the (0001) plane and having an off direction of <11-20>. Providing a structured SiC semiconductor substrate, forming a first trench in the main surface, and SiC having a second trench on the main surface that inherits the shape of the first trench formed in the main surface And growing the epitaxial layer formed in the second trench and performing predetermined processing by reading the second trench, and forming the first trench, the opening is rectangular and the longitudinal direction is off. A plurality of first trenches parallel to the direction are formed along the direction orthogonal to the off direction.

According to this, since the openings are rectangular and a plurality of first trenches having a longitudinal direction parallel to the off direction are formed along the direction orthogonal to the off direction, the first trenches are turned off. The length in the direction orthogonal to the direction becomes short. Therefore, when the epitaxial layer is grown, formation of facets can be suppressed on the downstream side in the off direction of each first trench. Therefore, the second trench can be read with high accuracy. In addition, since it is not necessary to form a new trench, the manufacturing process is not increased or complicated.

The reference numerals in parentheses attached to each component, etc., shows an example of a relationship of the specific component such as described in the following embodiments and their components, and the like.

FIG. 7 is a cross-sectional view showing the manufacturing process of the SiC semiconductor device in the first embodiment. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 1st Embodiment following FIG. 1A. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 1st Embodiment following FIG. 1B. It is a top view which shows the planar shape and arrangement | positioning of the trench formed in the SiC semiconductor substrate. It is a figure which shows the experimental result about the relationship between the width | variety of the trench in the case of making an epitaxial layer 1.4 micrometers grow, and the depth of a trench, and the readability or not. It is a figure which shows the experimental result about the relationship between the width | variety of the trench in the case of making an epitaxial layer 2.1 micrometers grow, and the depth of a trench, and the decision | availability of reading. FIG. 16 is a cross sectional view showing a manufacturing step of the SiC semiconductor device in the second embodiment, and a cross sectional view of an alignment mark formation region. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 2nd Embodiment following FIG. 5A. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 2nd Embodiment following FIG. 5B. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 2nd Embodiment following FIG. 5C. It is a top view which shows the planar shape and arrangement of a trench used as a mark for alignment inspection. It is a top view of the test pattern vicinity in FIG. 5D.

Hereinafter, embodiments of the present disclosure will be described based on the drawings. In the following embodiments, parts that are the same as or equivalent to each other will be described with the same reference numerals.

First Embodiment
A method of manufacturing the SiC semiconductor device in the first embodiment will be described with reference to the drawings.

First, as shown in FIG. 1A, for example, a 4H-type SiC single crystal in which the main surface forms an angle with the (0001) Si plane, that is, the off angle is 4 ° and the off direction is <11-20>. The SiC semiconductor substrate 10 configured by the above is prepared. In the following, of the SiC semiconductor substrate 10, a region for forming an alignment mark is referred to as an alignment mark formation region R1, and a region for forming a device such as a semiconductor element is referred to as a device formation region R2.

Next, as shown in FIG. 1B, a mask material 11 such as a resist is disposed on the main surface of SiC semiconductor substrate 10, and a region corresponding to a trench formation planned region of mask material 11 is opened. Then, while the SiC semiconductor substrate 10 is covered with the mask material 11, anisotropic dry etching such as RIE (that is, Reactive Ion Etching) is performed to form a trench 12 to be an alignment mark in the alignment mark formation region R1. Do. In the present embodiment, the trench 12 corresponds to a first trench and a first main trench.

Specifically, as shown in FIG. 2, a plurality of trenches 12 having rectangular openings and whose longitudinal direction is parallel to the off direction are formed along the direction orthogonal to the off direction. The more detailed shape of the trench 12 will be described later.

Subsequently, as shown in FIG. 1C, an epitaxial layer 13 composed of SiC is grown on the SiC semiconductor substrate 10 by, for example, a CVD (that is, Chemical Vapor Deposition) method. Thereby, the shape of the SiC semiconductor substrate 10 to be the base is taken over to the surface of the epitaxial layer 13. Therefore, on the surface of epitaxial layer 13, trench 14 is formed at a position corresponding to trench 12. Then, the trench 14 becomes a new alignment mark. In the present embodiment, the trench 14 corresponds to a second trench and a second main trench.

At this time, a facet may be formed on the downstream side of the trench 14 in the off direction, but the facet is formed depending on the length of the trench 14 in the direction orthogonal to the off direction. That is, as the length in the direction orthogonal to the off direction is shorter, the facets are less likely to be formed. Therefore, formation of the facets can be suppressed by forming the trench 12 so that the opening has a rectangular shape and the longitudinal direction is parallel to the off direction as in the present embodiment.

In the epitaxial layer 13, if the growth rate is too fast, defects such as 3C-SiC defects may be generated. For this reason, in the present embodiment, the epitaxial layer 13 is grown under the conditions of a growth rate of 2 μm / h or less.

Thereafter, the trench 14 serving as an alignment mark is read by a reader (not shown), and a predetermined manufacturing process such as ion implantation or etching is performed on the device formation region R2.

For example, when reading an alignment mark with a reader, the laser diode is irradiated with a plurality of laser beams while scanning the reader, and the SiC semiconductor substrate 10 on which the epitaxial layer 13 is formed is reflected. Analyze the information contained in the received laser light. Thereby, the formation position of the trench 14 is specified.

Specifically, the intensity of the laser beam reflected by the epitaxial layer 13 depends on the distance between the light source and the epitaxial layer 13 in the reader, and is compared with the portion where the alignment mark is not formed. Distance becomes longer and the strength becomes weaker. Therefore, the position of the alignment mark can be specified by reading the intensity signals of the plurality of reflected laser beams, for example. In addition, since the intensity of the laser light depends on the distance between the light source and the epitaxial layer 13, the reading device converts the read intensity signal into a signal that causes a peak to appear when the intensity signal changes, for example. The position of the alignment mark can also be identified based on the signal.

At this time, if a facet is formed in the trench 14 to be an alignment mark, the laser light is scattered on the facet and the reading of the alignment mark by the reader can not be performed with high accuracy. Specifically, when the position of the alignment mark is specified, positional deviation may occur in specifying the position in the off direction because the facets are formed. For this reason, when disposing a mask such as a transfer mask on the epitaxial layer 13, positional deviation occurs, which may cause problems such as failure to perform high-precision device manufacture.

However, in the present embodiment, the trench 12 has a rectangular shape whose short side is a direction in which the opening is orthogonal to the off direction. Thus, the formation of facets in the trench 14 is suppressed. Therefore, the reading of the alignment mark by the reader can be performed with high accuracy.

Then, by reading the formation position of the alignment mark formed in trench 14 in this manner, the process of forming the impurity layer by ion implantation into epitaxial layer 13 and the mask alignment in forming trench etc. It can be done to the accuracy.

Next, the detailed shape of each trench 12 of the present embodiment will be described with reference to FIGS. 3 and 4. As shown in FIGS. 3 and 4, the readable range is different between the case where the epitaxial layer 13 is grown to 1.4 μm and the case where the epitaxial layer 13 is grown to 2.1 μm, and the film of the epitaxial layer 13 is different. The thicker the thickness, the narrower the readable range. In FIGS. 3 and 4, hatched portions, that is, portions surrounded by straight lines L1 to L5 each have a shape of trench 12 in which trench 14 can be read with high accuracy.

Therefore, it is preferable that the shape of the trench 12 be defined in consideration of the film thickness of the epitaxial layer 13 to be grown, and the trench 12 is formed so as to satisfy all of the following mathematical expressions 1 to 5. Hereinafter, the length in the direction perpendicular to the longitudinal direction of trench 12 and along the surface direction of SiC semiconductor substrate 10 is also referred to as width w of trench 12, and the depth of trench 12 is the depth of trench 12. It is also called d. In FIG. 2, the width W of the trench 12 is in the vertical direction in the drawing. In addition, when the trench 14 can not be read with high accuracy, the trench 14 can be read with high accuracy by the presence of a plurality of intensity change peaks (that is, facets) in the intensity signal read by the reader. Cases that can not be included are included. Furthermore, when the trench 14 can not be read with high accuracy, the case where the intensity change itself can not be read clearly may be included.

First, when the width w of the trench 12 is too narrow, when the epitaxial layer 13 is grown, the trench 12 is easily filled and the trench 14 is not formed in the epitaxial layer 13. That is, the reading device can not read the alignment mark. For example, FIG. 3 shows that the trench 14 may be able to be read correctly if the width w is about 1.3 μm or more. It is shown in FIG. 4 that the trench 14 may be able to be read correctly if the width w is greater than about 1.95 μm. Therefore, when the film thickness of the epitaxial layer 13 to be grown is t, the trench 12 is formed to satisfy the following equation.

(Equation 1) w ((1.3 / 1.4) t = 0.93 t
The straight line L1 is w = 0.93 t.

When the epitaxial layer 13 is grown, the trench 12 is easily filled and the trench 14 is not formed in the epitaxial layer 13 if the trench 12 has a small depth d even if the width w is slightly increased. That is, the reading device can not read the alignment mark. FIG. 3 shows that it may be possible to read the trench 14 correctly if d ≧ −0.56 w + 1.18. FIG. 4 shows that it may be possible to read the trench 14 correctly if d ≧ −0.86 w + 1.76. For this reason, the trench 12 is formed such that the width w and the depth d satisfy the following equation based on the film thickness t of the epitaxial layer 13 to be grown.

(Equation 2) d ≧ (−0.41 w + 0.84) t
The straight line L2 is d = (− 0.41 w + 0.84) t.

Furthermore, when the depth d of the trench 12 is too shallow, when the epitaxial layer 13 is grown, the trench 12 is easily filled and the trench 14 is not formed in the epitaxial layer 13. That is, the reading device can not read the alignment mark. It is shown in FIG. 3 that the trench 14 may be able to be read correctly if d ≧ 0.2. It is shown in FIG. 4 that it may be possible to accurately read the trench 14 if d トレンチ 0.29. Therefore, the trench 12 is formed such that the depth d satisfies the following equation based on the thickness t of the epitaxial layer 13 to be grown.

(Equation 3) d ((0.2 / 1.4) t = 0.14 t
The straight line L3 is d = 0.14t.

In addition, even if the width w is larger than Formula 1 and the depth d is larger than Formula 3, the trench 12 may not be able to accurately read the trench 14 by the reading device. This is because the shape of the opening of the trench 14 becomes gentle depending on the shape of the trench 12 and the reader can not clearly detect the change of the intensity signal. It is shown in FIG. 3 that it may be possible to read the trench 14 correctly if d ≧ 0.67 w−1.4. It is shown in FIG. 4 that the trench 14 may be able to be read correctly if d ≧ 1.0 w−2.1. For this reason, the trench 12 is formed such that the width w and the depth d satisfy the following equation based on the film thickness t of the epitaxial layer 13 to be grown.

(Equation 4) d ((0.48 w-1.0) t
The straight line L4 is d = (0.48 w-1.0) t.

Then, when the width w is too large, the trench 12 forms a facet. That is, the reading device can not read the alignment mark with high accuracy. FIGS. 3 and 4 show that the trench 14 may be able to be read correctly if the width w is less than about 3.0 μm. Therefore, the trench 12 is formed to satisfy the following equation.

(Equation 5) w ≦ 3.0
The straight line L5 is w = 3.0.

As described above, in the present embodiment, the trench 12 is formed so as to satisfy the equations 1 to 4 based on the film thickness t of the epitaxial layer 13 while satisfying the equation 5.

As described above, in the present embodiment, a plurality of the trenches 12 whose opening is rectangular and whose longitudinal direction is parallel to the off direction are formed in the direction orthogonal to the off direction. Therefore, when the epitaxial layer 13 is grown, formation of facets on the downstream side in the off direction of each trench 12 is suppressed. Therefore, trench 14 after epitaxial layer 13 is grown can be read with high accuracy as an alignment mark. Further, in the present embodiment, since it is not necessary to form a new trench, the number of manufacturing steps is not increased or complicated.

The trench 12 has a width w of 3.0 μm or less. Thus, the formation of facets in the trench 14 is suppressed.

Furthermore, the trench 12 is formed so as to satisfy the above formulas (1) to (4). Therefore, it can be suppressed that the trench 14 is not formed in the epitaxial layer 13 and that the trench 14 formed in the epitaxial layer 13 can not be read correctly.

Second Embodiment
The second embodiment will be described. In the present embodiment, an alignment inspection mark is formed in the alignment mark formation region R1, and the other parts are the same as in the first embodiment, and thus the description thereof is omitted here.

In the present embodiment, as shown in FIG. 5A, in the step of forming the trench 12, first, the region corresponding to the trench formation planned region of the mask material 11 and the region corresponding to the inspection trench formation planned region are opened. Do. Then, while the SiC semiconductor substrate 10 is covered with the mask material 11, anisotropic dry etching such as RIE is performed to form the inspection trench 21 together with the trench 12 in the alignment mark formation region R1.

Specifically, as shown in FIG. 6, the inspection trench 21 has a first direction trench 21a and a second direction trench 21b. The first direction trench 21a and the second direction trench 21b are formed such that a region surrounded by the first direction trench 21a and the second direction trench 21b has a substantially shape.

More specifically, the first direction trench 21 a has the same shape as the trench 12. Further, in the present embodiment, two rows of first direction trenches 21a are formed along the direction orthogonal to the off direction. The second direction trench 21b has a rectangular shape whose longitudinal direction is the off direction, and the length in the longitudinal direction is larger than that of the first direction trench 21a. The second direction trenches 21b are formed on both end sides in the arrangement direction of the first direction trenches 21a. In the present embodiment, the first direction trench 21a corresponds to the first trench and the first sub-trench.

Next, as shown in FIG. 5B, epitaxial layer 13 made of SiC is grown on SiC semiconductor substrate 10. Thereby, on the surface of the epitaxial layer 13, the inspection trench 22 which inherits the shape of the inspection trench 21 is formed together with the trench 14. In the present embodiment, the inspection trench 22 corresponds to a second trench and a second sub-trench.

Thereafter, as shown in FIG. 5C, a film 23 for pattern formation made of an oxide film or the like is formed by a CVD method or the like. At this time, the trench 15 corresponding to the shape of the trench 14 and the inspection trench 24 corresponding to the shape of the inspection trench 22 are formed in the film 23 for pattern formation. That is, in the pattern forming film 23, the inspection trench 24 which inherits the shapes of the trench 14 and the inspection trench 22 is formed. In the present embodiment, the trench 15 corresponds to a third main trench, and the inspection trench 24 corresponds to a third sub-trench.

Subsequently, a resist 25 is formed on the pattern forming film 23 by a coating method or the like. At this time, in the resist 25, the trench 16 corresponding to the shape of the trench 15 and the inspection trench 26 corresponding to the shape of the inspection trench 24 are formed. That is, in the resist 25, the inspection trench 26 which inherits the shape of the trench 15 and the shape of the inspection trench 24 is formed. In the present embodiment, the trench 16 corresponds to a fourth main trench, and the inspection trench 26 corresponds to a fourth sub-trench.

Then, as shown in FIG. 5D, with the trench 16 as an alignment mark, the resist 25 is exposed and developed to pattern the resist 25. At this time, an inspection pattern 27 composed of a trench is simultaneously formed in the resist 25. In the present embodiment, the inspection pattern 27 is formed in the region surrounded by the inspection trench 26.

Next, the inspection pattern 27 and the inspection trench 26 are read by a reading device (not shown), and the distance between the inspection pattern 27 and the inspection trench 26 is measured to inspect the alignment accuracy. Specifically, as shown in FIG. 7, the inspection trench 26 and the inspection pattern 27 formed on the first direction trench 21a are read along the off direction, and the intervals x1 and x2 are measured. Further, the inspection trench 26 and the inspection pattern 27 formed on the second direction trench 21b are read along the direction orthogonal to the off direction, and the interval y1 and the interval y2 are measured. Then, it is determined whether or not each interval x1, x2, y1, y2 is an allowable error, and if it is an allowable error, the subsequent steps are performed using the resist 25 as a mask. On the other hand, if it is not the tolerance, for example, the resist 25 is removed and a new resist is formed again. Then, new inspection patterns are formed in consideration of the measured intervals x1, x2, y1, and y2 so that the intervals x1, x2, y1, and y2 become tolerances.

As described above, in the present embodiment, a plurality of first direction trenches 21a having a rectangular opening and a longitudinal direction parallel to the off direction are formed in the direction orthogonal to the off direction. Therefore, when the epitaxial layer 13 is grown, formation of facets is suppressed on the downstream side of the first direction trenches 21 a in the off direction. That is, when the pattern forming film 23 and the resist 25 are formed on the epitaxial layer 13, formation of facets in the

inspection trenches

24 and 26 formed on the first direction trench 21 a is suppressed. Therefore, the inspection trench 26 formed on the first direction trench 21a can be read with high accuracy, and in particular, the alignment inspection regarding positional deviation in the off direction can be performed with high accuracy.

(Other embodiments)
Although the present disclosure has been described in accordance with the embodiment, it is understood that the present disclosure is not limited to the embodiment or the structure. The present disclosure also includes various modifications and variations within the equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element, or more or less than these elements are also within the scope and the scope of the present disclosure.

For example, in each of the above embodiments, the 4H-type SiC semiconductor substrate 10 has been described as an example, but other polymorphic SiC semiconductor substrates such as 6H-type, 3C-type, 15R-type, etc. may be used. Also, although 4 ° has been exemplified as the off angle with respect to the (0001) plane, other angles may be used.

In the second embodiment, the inspection trench 21 may have only the first direction trench 21a. In this case, only one row of first direction trenches 21a may be formed in the direction orthogonal to the off direction.

In addition, when indicating the orientation of a crystal, a bar (-) should normally be added above the desired number, but since there is a limitation in expression based on the electronic application, it is desirable in the present specification to be a desired one. A bar shall be put in front of the numbers.

Claims

A method of manufacturing a silicon carbide semiconductor device comprising forming an epitaxial layer (13) on a main surface of a silicon carbide semiconductor substrate (10),
Providing the silicon carbide semiconductor substrate having the main surface of which the (0001) plane is provided with the off angle, and made of the silicon carbide single crystal whose off direction is <11-20>;
Forming a first trench (12, 21a) in the main surface;
Growing the epitaxial layer made of silicon carbide having a second trench (14, 22) which inherits the shape of the first trench formed on the main surface, on the main surface;
Reading the second trench and performing a predetermined process;
By forming the first trench, a silicon carbide semiconductor is formed along the direction orthogonal to the off direction, in which the opening is rectangular and the longitudinal direction is parallel to the off direction. Device manufacturing method.
The silicon carbide according to claim 1, wherein a plurality of first trenches are formed such that w ≦ 3.0 where w [μm] is a width in a direction orthogonal to the off direction in forming the first trenches. Semiconductor device manufacturing method.
In forming the first trench, w ≧ 0.93 t, where d [μm] is the depth and t [μm] is the film thickness of the epitaxial layer to be grown by growing the epitaxial layer. The plurality of first trenches according to claim 2, wherein d ((-0.41w + 0.84) t, d ≧ 0.14t, and d ≧ (0.48w-1.0) t are formed. Method of manufacturing a silicon carbide semiconductor device
In forming the first trench, the first main trench (12) for alignment mark and the first sub-trench (21a) for alignment inspection as the first trench are respectively arranged along the direction orthogonal to the off direction. Form multiple
In growing the epitaxial layer, as the second trench, a second main trench (14) which inherits the shape of the first main trench, and a second sub-trench (22) which inherits the shape of the first sub-trench. Growing the epitaxial layer comprising
A film for forming a pattern (23 on which the third main trench (15) taking over the shape of the second main trench and the third sub trench (24) taking over the shape of the second sub trench are formed on the epitaxial layer Form) and
A resist (25) is formed on the pattern forming film with a fourth main trench (16) taking over the shape of the third main trench and a fourth sub-trench (26) taking over the shape of the third sub-trench. To form
Reading the fourth main trench as an alignment mark, and forming a predetermined pattern including a test pattern (27) on the resist based on the alignment mark;
The method for manufacturing a silicon carbide semiconductor device according to any one of claims 1 to 3, wherein the alignment accuracy is inspected based on a distance between the fourth sub-trench and the inspection pattern.