JP2019056725A - Method for manufacturing semiconductor device using silicon carbide semiconductor substrate - Google Patents

Abstract

To provide a method for manufacturing an SiC semiconductor device capable of reading out a trench formed on an epitaxial layer with high accuracy without increasing and complicating a manufacturing process.SOLUTION: A method for manufacturing an SiC semiconductor device includes: preparing a silicon carbide semiconductor substrate 10 formed of carbide silicon monocrystal having a main surface where an off angle is provided on (0001) plane and an off direction of <11>; forming a first trench 12 on the main surface; and growing an epitaxial layer formed of silicon carbide having a second trench taking over the shape of the first trench 12 formed on the main surface, on the main surface, where formation of the first trench 12 includes forming the plurality of first trenches 12 having a rectangular opening and having a longitudinal direction parallel to the off direction, in a direction perpendicular to the off direction.SELECTED DRAWING: Figure 1B

Description

  The present invention 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 produce an SiC semiconductor device by forming an epitaxial layer on a SiC semiconductor substrate and performing a predetermined semiconductor manufacturing process. Specifically, when a SiC semiconductor device is manufactured using a SiC semiconductor substrate, a high-quality epitaxial layer can be grown, so that it is off-cut in the <11-20> direction with respect to the (0001) plane. The off-cut substrate thus used is used as the SiC semiconductor substrate.

  Then, a trench serving as an alignment mark is formed on such a SiC semiconductor substrate, an impurity region having a planar pattern is formed by ion implantation or the like, and then an epitaxial layer is grown or heat-treated. A predetermined manufacturing process is performed. Subsequently, the position of the alignment mark is specified by the reading device, and a predetermined semiconductor manufacturing process using resist patterning or the like is continuously performed based on the alignment mark.

  However, when an 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 an epitaxial layer is grown on a SiC semiconductor substrate, it may grow so as to form a (0001) facet surface on the downstream side in the off direction of the trench. In this case, there is a problem that the position of the alignment mark cannot be specified with high precision due to the influence of the facet surface, and pattern displacement occurs before and after the 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 surface is formed on the downstream side in the off direction of the trench, a new trench is formed with respect to the facet surface. Is disclosed.

  According to this, the new trench is formed on the (0001) facet plane. For this reason, even if an epitaxial layer is further grown on the SiC semiconductor substrate or heat treatment is performed, it is possible to suppress the formation of a facet surface on the downstream side in the off direction of the new trench. it can. Therefore, by reading the new trench as an alignment mark by the reading device, 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 them, and means “the side on which the tip of the vector obtained by projecting the normal vector of the growth plane onto the (0001) plane is facing”.

JP 2007-280978 A

  However, in the manufacturing method described in Patent Document 1, a new trench must be formed on the facet surface, which increases the number of manufacturing steps and complicates the problem.

  An object of the present invention is to provide a method of manufacturing a SiC semiconductor device that can read a trench formed in an epitaxial layer with high accuracy without increasing or complicating the manufacturing process. .

  According to a first aspect of the present invention for achieving the above object, there is provided a method of manufacturing a SiC semiconductor device, comprising forming an epitaxial layer (13) on a main surface of a SiC semiconductor substrate (10), wherein the method is off-off to the (0001) plane. Providing a SiC semiconductor substrate made of SiC single crystal having a main surface provided with corners and having an off direction of <11-20>; and a first trench (12, 21) on the main surface. Forming an epitaxial layer made of SiC having a second trench (14, 22) taking over the shape of the first trench formed on the main surface, and forming a second layer on the main surface; By reading the trench and performing a predetermined process, and forming the first trench, the first trench whose opening is rectangular and whose longitudinal direction is parallel to the off direction is turned on. It is multiply formed along a direction perpendicular to the direction.

  According to this, since the opening has a rectangular shape and a plurality of first trenches whose longitudinal direction is parallel to the off direction are formed along the direction orthogonal to the off direction, The length in the direction orthogonal to the direction is shortened. For this reason, when growing an epitaxial layer, it can suppress that a facet surface is formed in the downstream of the OFF direction in each 1st trench. Therefore, the second trench can be read with high accuracy. Moreover, since it is not necessary to form a new trench, the manufacturing process is not increased or complicated.

  In addition, the code | symbol in the bracket | parenthesis in the said and the claim shows the correspondence of the term described in the claim, and the concrete thing etc. which illustrate the said term described in embodiment mentioned later. .

It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 1st Embodiment. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 1st Embodiment following FIG. 1A. FIG. 1D is a cross-sectional view showing a manufacturing step of the SiC semiconductor device in the first 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 an experimental result which shows the relationship between the width | variety of a trench and the depth of a trench in the case of growing an epitaxial layer by 1.4 micrometers, and the readability. It is an experimental result which shows the relationship between the width | variety of a trench and the depth of a trench in the case of growing an epitaxial layer 2.1 micrometers, and the readability. It is sectional drawing which shows the manufacturing process of the SiC semiconductor device in 2nd Embodiment, and is sectional drawing of an alignment mark formation area. 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. FIG. 5D is a cross-sectional view showing a manufacturing step of the SiC semiconductor device according to the second embodiment following FIG. 5C. It is a top view which shows the planar shape and arrangement | positioning of a trench used as a mark for alignment inspection. It is a top view of the pattern for a test | inspection in FIG. 5D.

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

(First embodiment)
The manufacturing method of the SiC semiconductor device in 1st Embodiment is demonstrated referring drawings.

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

  Next, as shown in FIG. 1B, a mask material 11 such as a resist is disposed on the main surface of the SiC semiconductor substrate 10, and a region corresponding to the trench formation scheduled region in the mask material 11 is opened. Then, with the SiC semiconductor substrate 10 covered with the mask material 11, for example, anisotropic dry etching such as RIE (that is, reactive ion etching) is performed to form a trench 12 serving as an alignment mark in the alignment mark formation region R 1. To 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 a rectangular opening and a longitudinal direction parallel to the off direction are formed along a direction orthogonal to the off direction. A more detailed shape of the trench 12 will be described later.

  Subsequently, as shown in FIG. 1C, an epitaxial layer 13 made of SiC is grown on the SiC semiconductor substrate 10 by, for example, a CVD (ie, Chemical Vapor Deposition) method. Thereby, the shape of SiC semiconductor substrate 10 used as a foundation is also inherited on the surface of epitaxial layer 13. Then, a trench 14 is formed at a position corresponding to the trench 12 on the surface of the epitaxial layer 13, and this 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 surface can be formed on the downstream side of the trench 14 in the off direction, but the facet surface is formed depending on the length of the trench 14 in the direction orthogonal to the off direction. That is, the shorter the length in the direction orthogonal to the off direction, the harder the facet surface is formed. Therefore, as in the present embodiment, the 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.

  Note that, if the growth rate of the epitaxial layer 13 is too high, defects such as 3C-SiC defects may be generated. For this reason, in the present embodiment, the epitaxial layer 13 is grown under conditions where the growth rate is 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 reading device, a plurality of laser beams are irradiated onto the SiC semiconductor substrate 10 on which the epitaxial layer 13 is formed while scanning the reading device, and reflected by the SiC semiconductor substrate 10 with the reading device. Information contained in the laser beam is analyzed. Thereby, the formation position of the trench 14 can be 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 reading device, and is compared with the portion where the alignment mark is not formed. As the distance increases, the strength decreases. For this reason, for example, the position of the alignment mark can be specified by causing the reading device to read intensity signals of a plurality of reflected laser beams. In addition, the intensity signal read by the reading device can be converted into a signal that shows a peak when the intensity signal changes, and the position of the alignment mark can be specified based on the converted signal.

  At this time, if a facet surface is formed in the trench 14 serving as an alignment mark, the laser light is scattered on the facet surface, and the alignment mark cannot be read with high accuracy by the reading device. Specifically, when specifying the position of the alignment mark, a positional deviation occurs in specifying the position in the off direction due to the formation of the facet surface. For this reason, there is a problem that a positional deviation occurs when a mask such as a transfer mask is arranged on the epitaxial layer 13 and high-precision device manufacturing cannot be performed.

  However, in the present embodiment, the trench 12 has a rectangular shape whose short side is the direction in which the opening is orthogonal to the off direction. For this reason, it is suppressed that a facet surface is formed in the trench 14. Accordingly, the alignment mark can be read with high accuracy by the reading device.

  Then, by reading the formation position of the alignment mark formed in the trench 14 in this way, a mask for performing an impurity layer forming step by ion implantation into the epitaxial layer 13, a trench formation in the epitaxial layer 13, or the like. Can be aligned.

  Next, the detailed shape of each trench 12 of this embodiment is demonstrated, referring FIG. 3 and FIG. As shown in FIGS. 3 and 4, the readable range is different between the case where the epitaxial layer 13 is grown by 1.4 μm and the case where the epitaxial layer 13 is grown by 2.1 μm, and the film of the epitaxial layer 13 is different. The thicker the thickness, the narrower the readable range. 3 and 4, the hatched portion, that is, the portion surrounded by the straight lines L <b> 1 to L <b> 5 is the shape of the trench 12 that can read the trench 14 with high accuracy.

  For this reason, it is preferable that the shape of the trench 14 is defined in consideration of the film thickness of the epitaxial layer 13 to be grown, and the trench 14 is formed so as to satisfy all the following mathematical expressions 1 to 5. Hereinafter, the length in the direction perpendicular to the longitudinal direction of the trench 12 and along the surface direction of the SiC semiconductor substrate 10 is also referred to as the width w of the trench 12, and the depth of the trench 12 is the depth of the trench 12. Also called d. Further, when the trench 14 cannot be read with high accuracy, the trench 14 can be read with high accuracy due to the presence of a plurality of intensity change peaks (that is, facets) in the intensity signal read by the reading device. The case where it cannot be performed or the case where the intensity change itself cannot be clearly read is included.

  First, if the width w of the trench 12 is too narrow, when the epitaxial layer 13 is grown, the trench 12 is easily buried and the trench 14 is not formed in the epitaxial layer 13. That is, the alignment mark cannot be read by the reading device. For example, FIG. 3 shows that the trench 14 may be accurately read when the width w is about 1.3 μm or more. FIG. 4 shows that the trench 14 may be accurately read when the width w is less than about 1.95 μm. For this reason, the trench 12 is formed so as to satisfy the following expression, where t is the thickness of the epitaxial layer 13 to be grown.

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

  Further, if the trench 12 has a slightly larger width w but a shallow depth d, the trench 12 is easily buried when the epitaxial layer 13 is grown, and the trench 14 is not formed in the epitaxial layer 13. That is, the alignment mark cannot be read by the reading device. FIG. 3 shows that the trench 14 may be accurately read if d ≧ −0.56w + 1.18. FIG. 4 shows that the trench 14 may be accurately read when d ≧ −0.86w + 1.76. For this reason, the trench 12 is formed so that the width w and the depth d satisfy the following expression based on the film thickness t of the epitaxial layer 13 to be grown.

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

  Furthermore, if the depth d of the trench 12 is too shallow, when the epitaxial layer 13 is grown, the trench 12 is easily buried and the trench 14 is not formed in the epitaxial layer 13. That is, the alignment mark cannot be read by the reading device. FIG. 3 shows that the trench 14 may be accurately read if d ≧ 0.2. FIG. 4 shows that if d ≧ 0.29, the trench 14 may be read accurately. For this reason, the trench 12 is formed so that the depth d satisfies the following formula based on the film thickness t of the epitaxial layer 13 to be grown.

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

  In addition, the trench 12 may not be accurately read by the reader even if the width w is larger than Equation 1 and the depth d is deeper than Equation 3. This is because, depending on the shape of the trench 12, the shape of the opening of the trench 14 becomes gentle, and the change in the intensity signal cannot be clearly detected by the reading device. FIG. 3 shows that the trench 14 may be accurately read when d ≧ 0.67w−1.4. FIG. 4 shows that the trench 14 may be accurately read when d ≧ 1.0w−2.1. For this reason, the trench 12 is formed so that the width w and the depth d satisfy the following expression based on the film thickness t of the epitaxial layer 13 to be grown.

(Equation 4) d ≧ (0.48−1.0) t
The straight line L4 is d = (0.48−1.0) t.

  When the width w of the trench 12 becomes too large, a facet surface is formed. That is, the alignment mark cannot be read with high accuracy by the reading device. FIGS. 3 and 4 show that the trench 14 may be accurately read when the width w is about 3.0 μm or less. For this reason, the trench 12 is formed to satisfy the following expression.

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

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

  As described above, in the present embodiment, a plurality of trenches 12 having a rectangular opening and a longitudinal direction parallel to the off direction are formed in a direction perpendicular to the off direction. For this reason, when the epitaxial layer 13 is grown, the facet plane is suppressed from being formed on the downstream side of each trench 12 in the off direction. Therefore, the second trench 14 after the 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 manufacturing process is not increased or complicated.

  The trench 12 has a width w of 3.0 μm or less. For this reason, it is suppressed that a facet surface is formed in the trench 14.

  Furthermore, the trench 12 is formed so as to satisfy the above mathematical expressions 1 to 4. For this reason, it can suppress that the trench 14 is not formed in the epitaxial layer 13, and it can suppress that the trench 14 formed in the epitaxial layer 13 cannot be read correctly.

(Second Embodiment)
A second embodiment will be described. In the present embodiment, alignment inspection marks are formed in the alignment formation region R1, and the others are the same as those 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 and the region corresponding to the inspection trench formation planned region in the mask material 11 are opened. To do. Then, with the SiC semiconductor substrate 10 covered with the mask material 11, for example, anisotropic dry etching such as RIE (Reactive Ion Etching) is performed to form the inspection trench 21 together with the trench 12 in the alignment mark formation region R 1. Form.

  Specifically, as shown in FIG. 6, the inspection trench 21 includes a first direction trench 21a and a second direction trench 21b. The first direction trench 21a and the second direction trench 21b are formed so that the region surrounded by the first direction trench 21a and the second direction trench 21b is substantially shaped.

  More specifically, the first direction trench 21 a has the same shape as the trench 12. In the present embodiment, the first direction trenches 21a are formed in two rows along a 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, an epitaxial layer 13 made of SiC is grown on the SiC semiconductor substrate 10. As a result, a test trench 22 that inherits the shape of the test trench 21 is formed along with the trench 14 on the surface of the epitaxial layer 13. In the present embodiment, the inspection trench 22 corresponds to a second trench and a second sub-trench.

  Thereafter, a pattern forming film 23 composed of an oxide film or the like is formed by a CVD method or the like. At this time, a trench 15 corresponding to the shape of the trench 14 and an inspection trench 24 corresponding to the shape of the inspection trench 22 are formed in the pattern forming film 23. That is, in the pattern forming film 23, the trench 15 that inherits the shape of the trench 14 and the inspection trench 24 that inherits the shape of the inspection trench 22 are 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, a trench 16 corresponding to the shape of the trench 15 and an inspection trench 26 corresponding to the shape of the inspection trench 24 are formed in the resist 25. That is, in the resist 25, a trench 16 that inherits the shape of the trench 15 and an inspection trench 26 that inherits the shape of the inspection trench 24 are 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, the resist 25 is patterned by exposing and developing the resist 25 using the trench 16 as an alignment mark. At this time, an inspection pattern 27 composed of trenches 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, each of the inspection pattern 27 and the inspection trench 26 is read by a reading device (not shown), and the alignment accuracy is inspected by measuring the interval between the inspection pattern 27 and the inspection trench 26. 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, along the direction orthogonal to the off direction, the inspection trench 26 and the inspection pattern 27 formed on the second direction trench 21b are read, and the interval y1 and the interval y2 are measured. Then, it is determined whether or not each of the intervals x1, x2, y1, and y2 is an allowable error. If it is an allowable error, the subsequent process is performed using the resist 26 as a mask. On the other hand, if it is not an allowable error, for example, the resist 25 is removed and a new resist is formed again. Then, new inspection patterns are formed in consideration of the intervals x1, x2, y1, and y2, and the intervals x1, x2, y1, and y2 are allowed to have an allowable error.

  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 a direction perpendicular to the off direction. For this reason, when the epitaxial layer 13 is grown, the facet surface is suppressed from being formed on the downstream side in the off direction of each first-direction trench 21a. That is, when the pattern forming film 23 and the resist 25 are formed on the epitaxial layer 13, the formation of facet surfaces 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, alignment inspection regarding misalignment in the off direction can be performed with high accuracy.

(Other embodiments)
The present invention is not limited to the embodiment described above, and can be appropriately changed within the scope described in the claims.

  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, 3C type, and 15R may be used. In addition, although an example of 4 ° as the off-angle with respect to the (0001) plane has been given, other angles may be used.

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

  In addition, when indicating the orientation of a crystal, a bar (-) should be attached on a desired number, but there is a limitation on expression based on an electronic application. A bar shall be placed in front of the number.

10 SiC semiconductor substrate 12, 21 First trench 13 Epitaxial layer 14, 22 Second trench

Claims (4)

A method for 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 comprising a silicon carbide single crystal having a main surface provided with an off angle on the (0001) plane and having an off direction of <11-20>;
Forming a first trench (12, 21a) in the main surface;
Growing on the main surface the epitaxial layer composed of silicon carbide having a second trench (14, 22) that takes over the shape of the first trench formed on the main surface;
Reading the second trench and performing a predetermined process;
In forming the first trench, a plurality of the first trenches having an opening having a rectangular shape and a longitudinal direction parallel to the off direction are formed along a direction orthogonal to the off direction. Device manufacturing method.   2. The silicon carbide according to claim 1, wherein in forming the first trench, a plurality of the first trenches satisfying w ≦ 3.0 are formed when a width in a direction orthogonal to the off direction is w [μm]. A method for manufacturing a semiconductor device.   In forming the first trench, if the depth is d [μm] and the film thickness of the epitaxial layer grown by growing the epitaxial layer is t [μm], w ≧ 0.93 t, 3. The plurality of first trenches satisfying d ≧ (−0.41w + 0.84) t, d ≧ 0.14 t, and d ≧ (0.48w−1.0) t. A method for manufacturing a silicon carbide semiconductor device. In the formation of the first trench, the first main trench (12) for alignment marks and the first sub-trench (21a) for alignment inspection are respectively arranged along the direction orthogonal to the off direction as the first trench. Forming multiple,
In the growth of the epitaxial layer, the second main trench (14) taking over the shape of the first main trench and the second sub-trench (22) taking over the shape of the first sub-trench are used as the second trench. Growing said epitaxial layer comprising:
A pattern forming film (23) in which a third main trench (15) that inherits the shape of the second main trench and a third sub trench (24) that inherits the shape of the second sub trench are formed on the epitaxial layer. )
A resist (25) in which a fourth main trench (16) that inherits the shape of the third main trench and a fourth subtrench (26) that inherits the shape of the third subtrench are formed on the pattern formation film. Forming
Reading the fourth main trench as an alignment mark for the resist, and forming a predetermined pattern including an inspection pattern (27) on the resist based on the alignment mark;
The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the alignment accuracy is inspected based on an interval between the fourth sub-trench and the inspection pattern.

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