JP6950396B2 - Silicon Carbide Semiconductor Substrate and Method for Manufacturing Silicon Carbide Semiconductor Device Using It - Google Patents

Description

The present invention relates to a silicon carbide (hereinafter referred to as SiC) semiconductor substrate having an alignment mark used for mask alignment and a method for manufacturing a SiC semiconductor device using the same.

Conventionally, Patent Document 1 has proposed a technique for recognizing an alignment mark used when manufacturing a SiC semiconductor device with high accuracy.

When a SiC semiconductor device is manufactured using a SiC semiconductor substrate, a high-quality epitaxial layer can be grown. Therefore, an off-cut substrate that is off-cut in the <11-20> direction with respect to the (0001) plane. Is used as a SiC semiconductor substrate. Then, on such a SiC semiconductor substrate, an alignment mark is formed, and a predetermined manufacturing process such as growing an epitaxial layer or heat-treating is performed. Subsequently, the position of the alignment mark is specified by the reading device, and the transfer mask is placed on the SiC semiconductor substrate based on the alignment mark. Then, the SiC semiconductor device is manufactured by performing a predetermined manufacturing process such as a photolithography step on the transfer mask.

At this time, as the alignment mark, for example, a trench having a square opening in which two opposing sides are parallel to the off direction and the other two opposing sides are perpendicular to the off direction can be used.

However, when a trench having a square opening is used as an alignment mark, a facet surface is formed on the downstream side of the trench in the off direction, and the alignment mark cannot be recognized with high accuracy due to the influence of this facet surface. As a result, mask misalignment or the like occurs, and the SiC semiconductor device cannot be manufactured with high accuracy.

Therefore, in Patent Document 1, it is proposed to use a polygonal trench in which the shape of the opening is line-symmetrical with respect to the off direction and has an apex at a portion located on the most downstream side in the off direction as an alignment mark. Has been done. Specifically, the opening is a regular hexagon, and the trench in which one corner of the regular hexagon is located on the most downstream side in the off direction is used as an alignment mark.

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

Japanese Unexamined Patent Publication No. 2011-100928

However, simply arranging one corner of the polygonal opening on the most downstream side in the off direction is still affected by facets, and it is not sufficient to improve the accuracy of alignment mark recognition. understood.

In view of the above points, it is an object of the present invention to provide a SiC semiconductor substrate capable of recognizing alignment marks with high accuracy and a method for manufacturing a SiC semiconductor device using the SiC semiconductor substrate.

In order to achieve the above object, the SiC semiconductor substrate according to claim 1 has a main surface having an off angle on the (0001) plane, and is a silicon carbide single crystal having an off direction of <11-20>. The opening is composed of polygons on the main surface, and the corners of the polygon are located at the most downstream position in the off direction of the openings, and the most of the polygons in the off direction. A trench (12) in which the angle (θ1a, θ1b) formed by each of the two sides (12c, 12d) forming the corner portion located on the downstream side and the straight line (L) along the off direction is 22 ° or less. Is formed.

In this way, when the trench having the above-mentioned shape is formed as the alignment mark, even if the epitaxial layer is formed on the SiC semiconductor substrate, the facet surface is hardly formed in the trench formed in the epitaxial layer. can. Therefore, when the alignment mark is read by the reading device, it can be read with high accuracy without being affected by the facet surface.

The method for manufacturing a SiC semiconductor device according to claim 7 is composed of a silicon carbide single crystal having a main surface having an off angle on the (0001) plane and having an off direction of <11-20>. The silicon carbide semiconductor substrate (10) is prepared, and the opening is formed of a polygon on the main surface, and the corner of the polygon is located at the most downstream position in the off direction of the opening. The angle (θ1a, θ1b) formed by each of the two sides (12c, 12d) forming the corner portion of the polygon that is located on the most downstream side in the off direction and the straight line (L) along the off direction. It is composed of silicon carbide having a first trench (12) having a temperature of 22 ° or less and a second trench (14) on the main surface that inherits the shape of the first trench formed on the main surface. Includes growing the epitaxial layer (13), reading the second trench as an alignment mark, aligning with reference to the alignment mark, and placing a mask on the epitaxial layer. There is.

In this way, when the first trench having the above-mentioned shape is formed as the alignment mark, even if the epitaxial layer is formed on the SiC semiconductor substrate, the facet surface is almost formed in the second trench formed in the epitaxial layer. It can be prevented from being formed. Therefore, when the alignment mark is read by the reading device, it can be read with high accuracy without being affected by the facet surface, and by performing the alignment based on the alignment mark, the mask is placed on the epitaxial layer with high accuracy. It becomes possible.

The reference numerals in parentheses of the above means indicate an example of the correspondence with the specific means described in the embodiment described later.

It is sectional drawing which showed the manufacturing process of the SiC semiconductor device which concerns on 1st Embodiment. It is sectional drawing which showed the manufacturing process of the SiC semiconductor device which follows FIG. 1A. It is sectional drawing which showed the manufacturing process of the SiC semiconductor device which follows FIG. 1B. It is sectional drawing which showed the manufacturing process of the SiC semiconductor device which follows FIG. 1C. It is a schematic diagram which showed the shape of the opening of the trench used as the alignment mark formed on the SiC semiconductor substrate. It is a schematic diagram which showed the state near the alignment mark when the epitaxial layer was formed on the SiC semiconductor substrate. FIG. 3A is a cross-sectional view taken along the line IIIB-IIIB in FIG. 3A. It is a chart which showed the value of the length X, the distance Y, the tan θ, and the angle θ for each sample used in an experiment. It is a top view which showed the trench shape when the angle θ = 90 °. It is a top view which showed the trench shape when the angle θ = 50 °. It is a top view which showed the trench shape when the angle θ = 40 °. It is a top view which showed the trench shape when the angle θ = 34 °. It is a top view which showed the trench shape when the angle θ = 22 °. It is a top view which showed the trench shape when the angle θ = 16 °. It is a top view which showed the trench shape when the angle θ = 13 °. It is a figure which shows the result of having investigated the relationship between the depth of a trench and the film thickness of an epitaxial layer, and whether or not an alignment mark can be recognized. It is a figure which shows the result of having investigated the relationship between the dimension in the off-vertical direction of a trench and the film thickness of an epitaxial layer, and the recognitionability of an alignment mark. As a comparative example, it is a top view when a plurality of strip-shaped trenches are arranged side by side to form an alignment mark. It is a figure which showed the shape of the trench formed when the epitaxial layer was formed on the SiC semiconductor substrate of FIG. 8A. It is a top view of the alignment mark formed on the SiC semiconductor substrate which concerns on 2nd Embodiment.

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

(First Embodiment)
A SiC semiconductor substrate to which one embodiment of the present invention is applied and a method for manufacturing a SiC semiconductor device using the SiC semiconductor substrate will be described with reference to the drawings.

First, as shown in FIG. 1A, for example, a 4H type SiC single crystal having 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>. The SiC semiconductor substrate 10 configured by the above is prepared. In the SiC semiconductor substrate 10, the region where the alignment mark is formed is referred to as the alignment mark forming region R1, and the region where the device such as the semiconductor element is formed is referred to as the device forming region R2.

After that, as shown in FIG. 1B, a mask material 11 such as a resist is arranged on the main surface of the SiC semiconductor substrate 10 to open a region of the mask material 11 corresponding to a region to be formed by a trench. Then, in a state where the SiC semiconductor substrate 10 is covered with the mask material 11, for example, anisotropic dry etching such as RIE (Reactive Ion Etching) is performed to form a trench 12 serving as an alignment mark in the alignment mark forming region R1. Specifically, in this embodiment, the trench 12 described below is formed.

Specifically, as shown in FIG. 2, in the present embodiment, the upper surface shape of the opening is line-symmetrical with respect to the off direction and is on the main surface in the direction perpendicular to the off direction (hereinafter, off). A polygonal trench 12 that is line-symmetrical with respect to the vertical direction) is formed. More specifically, the opening of the trench 12 is connected to two opposite sides 12a and 12b along the off direction and both ends of the sides 12a and 12b, respectively, and is a set arranged line-symmetrically with respect to the off direction. It has two sides 12c and 12d and another set of two sides 12e and 12f. In the case of the present embodiment, the angle formed by the two sides 12c and 12d located on the downstream side in the off direction of the trench 12 and the angle formed by the two sides 12e and 12f located on the upstream side are the same angle. As θ1, both angles θ1 are acute angles.

Further, on the main surface, the angle θ1a of the angle formed by the straight line L and the side 12c along the off direction and the angle θ1b formed by the straight line L and the side 12d are 10 ° ≦ θ1a and θ1b ≦ 22 °. It is set in the range. Therefore, the angle θ1, that is, the sum of the angle θ1a and the angle θ1b is set in the range of 20 ° ≦ θ1 ≦ 44 °. In FIG. 2, the angle formed by the side 12a and the side 12c is described as θ1a, and the angle formed by the side 12b and the side 12d is described as θ1b. However, since the sides 12a and 12b and the straight line L are both parallel straight lines along the off direction, the angle θ1a formed by the side 12a and the side 12c is the same as the angle formed by the straight line L and the side 12c. , The angle θ1b formed by the side 12b and the side 12d agrees with the angle formed by the straight line L and the side 12d.

Here, the dimensions of the trench 12 are basically arbitrary, and may be set to such a dimension that the alignment arc cannot be recognized by the thickness of the film formed on the SiC semiconductor substrate 10. In the present embodiment, as shown in FIG. 2, on the straight line L along the off direction, the lengths when the two opposing sides 12c and 12d are projected are X, and the two opposite straight lines L along the off direction. The distance Y to the sides 12a and 12b is set, the length X is set to 5 μm, and the distance Y is set to 2 μm. That is, in the present embodiment, while the trench 12 constituting the alignment mark has a hexagonal shape, the trench 12 has a longitudinal direction in the off direction, and two of the hexagons are formed at both ends in the longitudinal direction. The corners are arranged.

Subsequently, as shown in FIG. 1C, the epitaxial layer 13 made of SiC is grown on the SiC semiconductor substrate 10 by, for example, a CVD (Chemical Vapor Deposition) method. As a result, the shape of the underlying SiC semiconductor substrate 10 is inherited on the surface of the epitaxial layer 13, and the trench 14 is formed at a position corresponding to the trench 12 on the surface of the epitaxial layer 13, which serves as a new alignment mark. Become. Then, alignment is performed with reference to the alignment mark, a mask is placed on the epitaxial layer 13, and a predetermined manufacturing process such as ion implantation or etching is performed on the device formation region R2.

FIG. 3A is a partially enlarged view of the alignment mark forming region R1 after the epitaxial layer 13 is grown on the SiC semiconductor substrate 10, and FIG. 3B is a cross-sectional view of the alignment mark IIIB-IIIB shown in FIG. 3A. In this way, when the epitaxial layer 13 is grown on the SiC semiconductor substrate 10, the length of the portion of the trench 12 downstream in the off direction, which is located on the most downstream side in the off direction, in the off direction and perpendicular to the off direction. Dependent facets may be formed.

However, in the present embodiment, as described above, the trench 12 has a hexagonal shape in which the off direction is the longitudinal direction. Then, with respect to the corners of the trench 12 located downstream in the off direction of both ends in the longitudinal direction, the angles θ1a and θ1b formed with respect to the two sides 12c and 12d and the straight line L along the off direction are 10 ° ≦. It is set in the range of θ1a and θ1b ≦ 22 °. As a result, the facet surface can be prevented from being formed on the epitaxial layer 13 formed on the SiC semiconductor substrate 10. The trench 14 serving as the alignment mark has a size substantially the same as that of the trench 12, although the size of the trench 12 is reduced by the film thickness of the epitaxial layer 13. That is, as shown in FIG. 3A, the openings of the trench 14 are connected to two opposite sides 14a and 14b along the off direction and both ends of the sides 14a and 14b, and are arranged line-symmetrically with respect to the off direction. It has a set of two sides 14c and 14d and another set of two sides 14e and 14f.

Here, as described above, the reason why the angles θ1a and θ1b are set in the range of 10 ° ≦ θ1a and θ1b ≦ 22 ° will be described with reference to the experimental results.

The present inventors have changed the shape of the trench 14 formed in the epitaxial layer 13 when the epitaxial layer 13 is formed on the SiC semiconductor substrate 10 in which the trench 12 having a hexagonal opening is formed. We conducted an experiment to find out if it would be done. Specifically, the distance Y shown in FIG. 2 was fixed at 2 μm, and the length X was variously changed to confirm how the facet surface was formed. Further, for the angles θ1a and θ1b, the experiment was conducted with the same angles θ. FIG. 4 is a chart showing the values of the length X, the distance Y, the tan θ, and the angle θ for each sample used in the experiment. As a reference, an experiment is also conducted when the length X = 0, that is, when the trench 12 is a square. 5A to 5G are views showing the state of the epitaxial layers 13 of the samples SS1, SS3, SS5, SS7, SS9, SS11, and SS13 shown in FIG. 4 after the film formation.

As shown in FIG. 5A, when the angle θ = 90 °, a trapezoidal facet surface 15 was formed on the downstream side of the trench 14 in the off direction. Further, as shown in FIGS. 5B to 5D, when the angles θ = 50 °, 40 °, and 34 °, the facet surface 15 gradually becomes smaller, but downstream of the hexagonal trench 14 in the off direction. The facet surface 15 was formed so as to extend from the angle located on the side.

On the other hand, as shown in FIG. 5E, when the angle θ = 22 °, the facet surface 15 was hardly formed, and the trench 12 had the shape of the trench 14 formed on the SiC semiconductor substrate 10. It had almost the same shape as. Then, as shown in FIGS. 5F and 5G, the cases where the angles θ = 16 ° and 13 ° were the same as those when the angle θ = 22 °. Therefore, it can be said that if the angle θ is 22 ° or less, the facet surface 15 can be prevented from being formed. According to the experiment, the facet surface 15 is not formed at least until the angle θ is 10 °. confirmed. Therefore, in the present embodiment, the angles θ1a and θ1b are set in the range of 10 ° ≦ θ1a and θ1b ≦ 22 °, so that the above effect can be obtained.

Next, the trench 14 serving as the alignment mark is read by a reading device (not shown). For example, when reading an alignment mark with a reading device, a plurality of laser beams are applied to the SiC semiconductor substrate 10 on which the epitaxial layer 13 is formed while scanning the reading device, and the SiC semiconductor substrate 10 reflects the laser light with the reading device. The 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 reader, and is compared with the portion where the alignment mark is formed and the portion where the alignment mark is not formed. The distance becomes longer and the strength becomes weaker. Therefore, the position of the alignment mark can be specified by having the reading device read, for example, the intensity signals of a plurality of reflected laser beams. Further, the intensity signal read by the reader can be converted into a signal in which a peak appears when the intensity signal changes, and the position of the alignment mark can be specified based on the converted signal.

At this time, if the facet surface is formed in the trench 14 serving as the alignment mark, the laser beam 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, the formation of the facet surface causes a positional deviation in specifying the position in the off direction. For this reason, there is a problem that a position shift occurs when a mask such as a transfer mask is arranged on the epitaxial layer 13, and a highly accurate device cannot be manufactured. However, if the shape of the alignment mark is as in the present embodiment, the facet surface can be prevented from being formed in the trench 14, so that the alignment mark can be read with high accuracy by the reading device.

Then, by reading the formation position of the alignment mark indicated by the trench 14 in this way, the mask for forming the impurity layer by implanting ions into the epitaxial layer 13, forming the trench in the epitaxial layer 13, and the like. Alignment can be performed.

For example, after forming a mask material on the epitaxial layer 13, the mask material is patterned using a transfer mask, and the patterned mask material is used as a mask to implant an impurity layer at a desired position of the epitaxial layer 13. The forming step can be performed. At this time, when the mask material is placed on the epitaxial layer 13 on which the trench 14 is formed, the shape of the trench 14 is inherited by the mask material as well. Since the facet surface is not formed in the trench 14, the alignment mark can be read with high accuracy by the reading device by using the trench formed in the mask material as the alignment mark.

Further, even when the step of further forming the epitaxial layer on the upper layer of the epitaxial layer 13 is performed, the trench having the same shape as the trench 14 is inherited by the epitaxial layer. Even in that case, since the facet surface is hardly formed in the trench formed in the epitaxial layer formed in the upper layer, the same effect as described above can be obtained by using the trench as an alignment mark.

Further, as shown in FIG. 1D, in the device forming region R2, a groove portion 16 is formed in the epitaxial layer 13 by using a mask aligned with reference to the alignment mark, and the groove portion 16 is further formed in the epitaxial layer 17 by the epitaxial layer 17. The epitaxial layer 13 may be left only in the groove 16 after embedding. For example, the epitaxial layer 17 formed on the outside of the groove 16 is removed by a flattening step such as etch back or CMP (Chemical Mechanical Polishing). At this time, the epitaxial layer 17 is also formed in the trench 14, but the trench 14 has a larger dimension than the groove portion 16, and the epitaxial layer 17 also has the trench 18 in which the shape of the trench 14 is inherited. Therefore, even if the flattening step is performed, the epitaxial layer 17 is removed by substantially the same thickness inside and outside the trench 14. Therefore, even after the flattening step is performed, the trench 14 or the trench 18 remains, and the alignment mark can be prevented from disappearing.

In this way, it is possible to manufacture a SiC semiconductor device in which a desired semiconductor element is formed in the device forming region R2. For example, it is possible to manufacture a SiC semiconductor device in which a diode, a transistor, or the like is formed in the device forming region R2.

As described above, in the present embodiment, the upper surface shape of the opening of the trench 12 is a polygon that is line-symmetrical with respect to the off-direction and also line-symmetrically with respect to the off-vertical direction, here, a hexagon. It has a shape. Then, of the sides 12a to 12f forming the hexagonal shape of the opening of the trench 12, the angles θ1a and θ1b formed with respect to the straight line L along the off direction with respect to the sides 12c and 12d located on the downstream side in the off direction. However, θ1a and θ1b ≦ 22 °. More preferably, the angles θ1a and θ1b are set to be in the range of 10 ° ≦ θ1a and θ1b ≦ 22 °.

As a result, even if the epitaxial layer 13 is formed on the SiC semiconductor substrate 10, the facet surface can be substantially prevented from being formed in the trench 14 formed in the epitaxial layer 13. Therefore, when the alignment mark is read by the reading device, it can be read with high accuracy without being affected by the facet surface. Since the alignment mark can be read with high accuracy in this way, it is possible to suppress a positional deviation when arranging the mask, and it is possible to manufacture a device with high accuracy.

Further, with respect to the trench 12, since the angles θ1a and θ1b need only be set in the range of 10 ° ≦ θ1a and θ1b ≦ 22 °, the angle θ1a and the angle θ1b do not necessarily have to be the same value. However, when the angle θ1a and the angle θ1b are set to the same value as in the present embodiment, the epitaxial layer 13 grows symmetrically with respect to the off direction on the inner wall surface of the trench 12, and the alignment mark is off. The shape is symmetrical with respect to the direction. Therefore, when the position of the alignment mark is specified by the reading device, it is possible to prevent the position deviation from occurring in the direction perpendicular to the off direction.

Further, the trench 12 is line-symmetrical even in the off-vertical direction. Therefore, when the position of the alignment mark is specified by the reader, the reflection of the laser beam can be made symmetrical with respect to the off-vertical direction, so that the position shift in the direction parallel to the off-direction is suppressed. be able to. Therefore, since the positional deviation when specifying the position of the alignment mark can be suppressed, the alignment between the SiC semiconductor substrate 10 and the transfer mask can be further performed with high accuracy.

The depth of the trench 12 and the size of the opening are arbitrary, but if the film thickness of the epitaxial layer 13 formed on the SiC semiconductor substrate 10 is thick, the size of the opening of the trench 14 becomes small, and the reading device. It becomes difficult to read the alignment mark. Therefore, it is preferable to set the depth of the trench 14 and the size of the opening based on the film thickness of the epitaxial layer 13.

For example, when the relationship between the depth of the trench 12 and the dimension in the off-vertical direction and the film thickness of the epitaxial layer 13 and the recognition of the alignment mark were investigated, the results shown in FIGS. 6 and 7 were obtained. “O” in FIGS. 6 and 7 indicates a case where it can be recognized, and “X” indicates a case where it cannot be recognized. As shown in FIG. 6, the deeper the depth d of the trench 12, and the larger the off-vertical dimension of the trench 12, the larger the film thickness of the epitaxial layer 13 is, the more the alignment mark can be recognized. Met. Then, when an approximate straight line passing through the upper limit of the film thickness of the epitaxial layer 13 that can recognize the alignment mark corresponding to each depth of the trench 12 shown in FIG. 6 is drawn, the film thickness of the epitaxial layer 13 is x, and the trench 12 The approximate straight line is expressed by the following formula, where y is the depth of.

[Number 1] y = 0.263x + 0.0089
Similarly, for the film thickness of the epitaxial layer 13 in which the alignment mark can be recognized corresponding to each off-vertical dimension of the trench 12 shown in FIG. 7, an approximate straight line passing through the upper limit value is drawn to obtain the film thickness of the epitaxial layer 13. The approximate straight line is expressed by the following formula, where x and the off-vertical dimension of the trench 12 are y.

[Number 2] y = 0.8108x + 0.0494
Therefore, the depth of the trench 12 is preferably deeper than the film thickness of the epitaxial layer 13 to be grown × 0.26. The off-vertical dimension of the trench 12 is preferably larger than the film thickness of the epitaxial layer 13 to be grown × 0.8.

(Second Embodiment)
The second embodiment will be described. This embodiment has a plurality of alignment marks with respect to the first embodiment, and the other parts are the same as those of the first embodiment. Therefore, only the parts different from the first embodiment will be described.

When forming the alignment mark to be aligned in the off-vertical direction, for example, as shown in FIG. 8A, a strip-shaped trench 12 extending along the off-vertical direction is formed on the surface of the SiC semiconductor substrate 10. It is advisable to arrange multiple strips at equal intervals along the off direction. In this way, when a plurality of trenches 12 are arranged to form an alignment mark, when the reflected light of the laser beam is acquired by the scanning reader, the intensity signal of the laser beam is repeatedly generated at the position where the trench 12 is formed. Will change. Therefore, the position of the alignment mark can be more accurately specified based on the change in the intensity signal and the formation interval of the trench 12.

However, when the trench 12 is formed into a strip-shaped structure extending in the off-vertical direction when aligned in the off-direction and parallel direction, the epitaxial layer 13 is formed on the surface of the SiC semiconductor substrate 1 as shown in FIG. 8B. When the film is applied, a trapezoidal facet surface 15 is formed on the downstream side of the trench 14 in the off direction over a wide area. Therefore, it becomes impossible to specify the position of the alignment mark with high accuracy.

Therefore, as shown in FIG. 9, a plurality of trenches 12 are arranged in the off-vertical direction at equal intervals to form a broken line-shaped alignment mark, and a plurality of broken-line alignment marks are arranged in the off-direction. Then, for the trench 12 that constitutes each of the dots of the broken line alignment mark, the formation interval is shorter than the distance between the two opposite sides 12a and 12b, for example, 2 μm, and each trench 12 is set. It has the structure described in the first embodiment.

That is, as in FIG. 2, the upper surface shape of the opening of each trench 12 is a hexagonal shape that is line-symmetrical with respect to the off-direction and line-symmetrical with respect to the off-vertical direction. Further, of the sides 12a to 12f forming the hexagonal shape of the opening of the trench 12, the angles θ1a and θ1b formed with respect to the straight line L along the off direction with respect to the sides 12c and 12d located on the downstream side in the off direction. However, θ1a and θ1b ≦ 22 °. More preferably, the angles θ1a and θ1b are set to be in the range of 10 ° ≦ θ1a and θ1b ≦ 22 °.

In this way, when the epitaxial layer 13 is formed on the SiC semiconductor substrate 10, the facet surface can be prevented from being formed for each of the trenches 14. Therefore, it is possible to suppress the scattering of the laser beam emitted by the reader due to the influence of the facet surface. Further, if the formation interval of each of the trenches 12 constituting the alignment marks arranged in a broken line is shortened, when the laser beam is simultaneously irradiated to a plurality of the trenches 12 arranged in a broken line, the reflected light of the whole is reflected. The intensity signal corresponding to the average value can be read. Therefore, it is possible to specify the alignment mark in the same manner as in the case where the trench 12 is arranged in a straight line while the trench 12 is arranged in a broken line. Therefore, the alignment mark can be specified with higher accuracy.

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

For example, in each of the above embodiments, the opening of the trench 12 has a hexagonal shape, but any other polygonal shape may be used as long as the corner portion is arranged downstream in the off direction. ..

In that case, the polygon does not have to be line-symmetrical with respect to the off-direction, but the epitaxial layer 13 grows symmetrically with respect to the off-direction on the inner wall surface of the trench 12, and the alignment mark is off. The shape is symmetrical with respect to the direction. Therefore, when the position of the alignment mark is specified by the reading device, it is possible to prevent the position deviation from occurring in the direction perpendicular to the off direction.

Similarly, the trench 12 is a polygon that is line-symmetrical with respect to the off-vertical direction, but it does not necessarily have to be line-symmetrical. However, if line symmetry is used, when the position of the alignment mark is specified by the reader, the reflection of the laser light can be made symmetrical with respect to the off vertical direction, so that the position shifts in the direction parallel to the off direction. It can be suppressed from occurring. Therefore, it is preferable that the trench 12 is a polygon that is line-symmetrical with respect to the off-vertical direction.

Further, 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. Further, although 4 ° is given as an example as the off angle with respect to the (0001) plane, other angles may be used.

10 Semiconductor substrate 11 Mask material 12, 14, 18 Trench 12a to 12f, 14a to 14f Side 13, 17 Epitaxial layer 15 Facet surface 16 Groove 17 Epitaxial layer

Claims (8)

It is composed of a silicon carbide single crystal having a main surface having an off angle on the (0001) plane and having an off direction of <11-20>.
The opening is formed of a polygon on the main surface, and the corner portion of the polygon is located at the most downstream position of the opening in the off direction, and the corner of the polygon is located in the off direction of the polygon. The angle (θ1a, θ1b) formed by each of the two sides (12 c , 12 d ) constituting the corner located on the most downstream side of the above and the straight line (L) along the off direction is set to 22 ° or less. A silicon carbide semiconductor substrate on which a vertical trench (12) is formed. The silicon carbide semiconductor substrate according to claim 1, wherein the angle is 10 ° or more. The silicon carbide semiconductor substrate according to claim 1 or 2, wherein the polygon is a hexagon whose longitudinal direction is the off direction. The silicon carbide semiconductor substrate according to claim 3, wherein the hexagon is line-symmetrical with respect to the off direction. The silicon carbide semiconductor substrate according to claim 3 or 4, wherein the hexagon is line-symmetrical with respect to the off-vertical direction, which is a direction perpendicular to the off-direction on the main surface. An epitaxial layer (13) made of silicon carbide is formed on the main surface, and the trench formed on the main surface is used as a first trench on the surface of the epitaxial layer, and the shape of the first trench is formed. The silicon carbide semiconductor substrate according to any one of claims 1 to 5, wherein a second trench (14) is formed. A silicon carbide semiconductor substrate (10) having a main surface having an off-angle on the (0001) plane and being made of a silicon carbide single crystal whose off-direction is <11-20> is prepared.
The opening is formed of a polygon on the main surface, and the corner portion of the polygon is located at the most downstream position of the opening in the off direction, and the corner of the polygon is located in the off direction of the polygon. The angle (θ1a, θ1b) formed by each of the two sides (12 c , 12 d ) constituting the corner portion located on the most downstream side of the above and the straight line (L) along the off direction is 22 ° or less. Forming the first trench (12) and
To grow an epitaxial layer (13) made of silicon carbide having a second trench (14) that inherits the shape of the first trench formed on the main surface on the main surface.
A method for manufacturing a silicon carbide semiconductor device, which comprises reading the second trench as an alignment mark, performing alignment with reference to the alignment mark, and arranging a mask on the epitaxial layer. In the silicon carbide semiconductor substrate, the region where the first trench is formed is defined as an alignment mark forming region (R1), the region where a device is formed is defined as a device forming region (R2), and the epitaxial layer is designated as the first layer.
In the device forming region, forming a groove (16) in the first layer and
Forming an epitaxial layer (17) to be a second layer on the upper layer of the first layer after forming the groove portion,
The method for manufacturing a silicon carbide semiconductor device according to claim 7, further comprising removing a portion of the second layer formed outside the groove portion by flattening.

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