JP7283211B2 - Silicon carbide substrate manufacturing method and silicon carbide substrate - Google Patents

Description

The present invention relates to a silicon carbide substrate manufacturing method and a silicon carbide substrate.

Conventionally, the drift layer is a parallel pn layer in which an n-type region and a p-type region are alternately and repeatedly arranged in a direction parallel to the main surface of the substrate (hereinafter referred to as a lateral direction). Semiconductor devices having structures are known. 2. Description of the Related Art In manufacturing a semiconductor device having a superjunction structure using silicon carbide (SiC) as a semiconductor material, a multi-stage epitaxial (multi-epitaxial) method or a trench filling epitaxial method is used to form parallel pn layers.

For example, in the manufacture of a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a superjunction structure using silicon carbide as a semiconductor material, the trench is buried by epitaxial growth after the formation of the trench, and the upper surface of the epitaxial layer is A method for grinding a p-type semiconductor layer grown on a substrate has been proposed (see, for example, Patent Document 1 (paragraph 0133, FIGS. 3, 7, 8, etc.) below).

FIG. 29 is a cross-sectional view showing an example of a state in the middle of manufacturing a conventional silicon carbide substrate having a superjunction structure with parallel pn layers. Epitaxial substrate 10 is a silicon carbide substrate formed by growing an n-type epitaxial layer 21 to be a drift layer on n ⁺ -type starting substrate 1 . A trench 22 is formed in the n-type epitaxial layer 21 and a p-type epitaxial layer 24 is grown on the front surface of the epitaxial substrate 10 to fill the trench 22 with the p-type epitaxial layer 24 .

At this time, since columnar silicon carbide is deposited on the mesa top (between trenches 22) on the front surface of epitaxial substrate 10, the front surface side of epitaxial substrate 10 becomes highly uneven. Therefore, the p-type epitaxial layer 24 is ground from the front surface side to remove unnecessary portions of the p-type epitaxial layer 24 to flatten the front surface of the epitaxial substrate 10 . The unnecessary portion of the p-type epitaxial layer 24 is, for example, the portion of the p-type epitaxial layer 24 above the front surface of the epitaxial substrate 10, including the columnar deposited portion.

JP 2018-19069 A

However, in the conventional technology described above, it is difficult to suppress excessive grinding of p-type epitaxial layer 24, and there is a problem that the yield of silicon carbide semiconductor devices is low.

For example, in order to reliably remove an unnecessary portion of the p-type epitaxial layer 24 by grinding, the grinding is performed with the height position 13 slightly lower than the front surface of the epitaxial substrate 10 as the target. However, the amount by which the p-type epitaxial layer 24 is actually ground is controlled by, for example, the grinding execution time obtained by experiment or the like.

Therefore, if the deposition condition of the unnecessary portion of the p-type epitaxial layer 24 (for example, the shape of each column of silicon carbide) changes, the grinding of the p-type epitaxial layer 24 ends when the grinding position reaches the height position 13. It is difficult to When the p-type epitaxial layer 24 is ground far beyond the height position 13, the parallel pn layer becomes too thin, resulting in characteristics such as element breakdown voltage and on-resistance in the silicon carbide semiconductor device manufactured from the epitaxial substrate 10. becomes a characteristic different from the design. Therefore, the yield in manufacturing silicon carbide semiconductor devices is reduced. The withstand voltage is the limit voltage at which the element does not malfunction or break down.

In order to solve the above-described problems of the prior art, the present invention provides a method for manufacturing a silicon carbide substrate and a silicon carbide substrate capable of suppressing excessive grinding of an epitaxial layer and improving the yield of silicon carbide semiconductor devices. intended to provide

In order to solve the above-described problems and achieve the object of the present invention, a method for manufacturing a silicon carbide substrate according to the present invention provides a first conductivity type semiconductor substrate made of silicon carbide, a first conductivity type region and a second conductivity type region. A method for manufacturing a silicon carbide substrate having parallel pn layers in which mold regions are alternately and repeatedly arranged in a direction parallel to one main surface of the semiconductor substrate, and has the following features. First, a first step of forming a recess extending from a portion of the one main surface of the semiconductor substrate in a thickness direction orthogonal to the main surface of the semiconductor substrate; a second step of forming a hard material film with a high .DELTA. Further, a third step of forming a trench extending in the thickness direction from a portion of the one main surface of the semiconductor substrate different from the portion where the recess is formed is performed. Further, after the third step, a second conductivity type epitaxial layer is grown on the one main surface of the semiconductor substrate to form the second conductivity type epitaxial layer inside the trench. A fourth step of forming the parallel pn layer by embedding a layer is performed. Further, after the second step and the fourth step, the second conductivity type epitaxial layer is ground until it reaches at least the hard material film, and the parallel pn layer is exposed on the one main surface of the semiconductor substrate. A fifth step is performed.

Further, in the method for manufacturing a silicon carbide substrate according to the present invention, in the second step of the invention described above, the recess is formed in a portion of the one main surface of the semiconductor substrate along the outer circumference of the semiconductor substrate. It is characterized by

Further, in the method of manufacturing a silicon carbide substrate according to the present invention, in the invention described above, after the fifth step, a sixth step of forming an element structure on the semiconductor substrate is performed, and in the second step, the semiconductor substrate is The depression is formed in a portion of the one main surface of the step different from the portion where the element structure is formed in the sixth step.

Further, in the method for manufacturing a silicon carbide substrate according to the present invention, in the invention described above, the semiconductor substrate has a plurality of portions along a direction perpendicular to the thickness direction, and among the plurality of portions, two adjacent portions are formed. A gap is provided between the two portions, and in the second step, the depression is formed in the portion surrounding the plurality of portions and the portion of the gap in the one main surface of the semiconductor substrate. characterized by forming

In addition, the method for manufacturing a silicon carbide substrate according to the present invention is the method according to the above-described invention, including a seventh step of performing dicing for singulating the element structure into chips after the sixth step; 3, wherein the gap is a gap on the dicing line.

Further, in the method for manufacturing a silicon carbide substrate according to the present invention, in the second step of the invention described above, the hard material film is formed in contact with the bottom surface of the recess and has a thickness smaller than the depth of the recess. Characterized by

Further, the method for manufacturing a silicon carbide substrate according to the present invention is characterized in that the hard material film having a Knoop hardness of 3000 or more is formed in the second step of the invention described above.

Further, the method for manufacturing a silicon carbide substrate according to the present invention is characterized by including an eighth step of removing the hard material film after the fifth step in the above-described invention.

Further, a silicon carbide substrate according to the present invention includes a first conductivity type semiconductor substrate made of silicon carbide, a first conductivity type region and a second conductivity type region extending in a direction parallel to one main surface of the semiconductor substrate. A silicon carbide substrate provided with parallel pn layers alternately and repeatedly arranged, wherein the semiconductor substrate extends from a portion of the one main surface of the semiconductor substrate different from a portion where an element structure is formed. and a hard material film having a hardness higher than that of the semiconductor substrate is provided in the recess.

According to the invention described above, in grinding the second conductivity type epitaxial layer after filling the trench with the second conductivity type epitaxial layer, when the grinding position reaches the hard material film, the hard material film slows down the progress of grinding. be able to.

According to the method for manufacturing a silicon carbide substrate and the silicon carbide substrate according to the present invention, it is possible to suppress excessive grinding of the epitaxial layer and improve the yield of silicon carbide semiconductor devices.

FIG. 1 is a flow chart showing an example of a method for manufacturing a silicon carbide substrate according to an embodiment. FIG. 2 is a cross-sectional view (part 1) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 3 is a cross-sectional view (part 2) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 4 is a cross-sectional view (part 3) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 5 is a cross-sectional view (part 4) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 6 is a cross-sectional view (No. 5) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 7 is a cross-sectional view (No. 6) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 8 is a cross-sectional view (No. 7) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 9 is a cross-sectional view (No. 8) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 10 is a cross-sectional view (part 9) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 11 is a cross-sectional view (No. 10) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 12 is a cross-sectional view (No. 11) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 13 is a cross-sectional view (No. 12) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 14 is a cross-sectional view (part 13) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 15 is a cross-sectional view (part 14) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 16 is a cross-sectional view (No. 15) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 17 is a cross-sectional view (part 16) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 18 is a cross-sectional view (No. 17) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 19 is a cross-sectional view (part 18) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 20 is a cross-sectional view (No. 19) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 21 is a cross-sectional view (No. 20) showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. FIG. 22 is a diagram showing an example of a metal mask used for sputtering a silicon dioxide film according to the embodiment. FIG. 23 is a diagram showing an example of a metal mask used for sputtering a carbon nitride film according to the embodiment. FIG. 24 is a diagram illustrating an example of an epitaxial substrate according to the embodiment; FIG. 25 is a flow chart showing another example of the method for manufacturing the silicon carbide substrate according to the embodiment. FIG. 26 is a diagram showing another example of a metal mask used for sputtering a silicon dioxide film according to the embodiment; FIG. 27 is a diagram showing another example of the metal mask used for sputtering the carbon nitride film according to the embodiment. FIG. 28 is a diagram showing another example of the epitaxial substrate according to the embodiment; FIG. 29 is a cross-sectional view showing an example of a state in the middle of manufacturing a conventional silicon carbide substrate having a superjunction structure with parallel pn layers.

Preferred embodiments of a silicon carbide substrate manufacturing method and a silicon carbide substrate according to the present invention will be described below in detail with reference to the accompanying drawings. In this specification and the accompanying drawings, layers and regions prefixed with n or p mean that electrons or holes are majority carriers, respectively. Also, + and - attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region not attached, respectively. In the following description of the embodiments and accompanying drawings, the same configurations are denoted by the same reference numerals, and overlapping descriptions are omitted. In this specification, in the notation of the Miller index, "-" means a bar attached to the index immediately after it, and adding "-" before the index indicates a negative index.

(Embodiment)
In the method for manufacturing a silicon carbide (SiC) substrate according to the embodiment, the drift layer is formed such that the n-type (first conductivity type) region and the p-type (second conductivity type) region are parallel to the front surface of the substrate. A case of manufacturing a silicon carbide semiconductor device having a super junction (SJ: Super Junction) structure in which parallel pn layers are alternately arranged in a direction will be described as an example.

FIG. 1 is a flow chart showing an example of a method for manufacturing a silicon carbide substrate according to an embodiment. As shown in FIG. 1, first, an n-type epitaxial layer is grown on the front surface of an n ⁺ -type starting substrate made of silicon carbide (step S1). As a result, an epitaxial substrate (silicon carbide substrate) is produced by depositing an n-type epitaxial layer on the front surface of the n ⁺ -type starting substrate. Next, a recess is formed in a portion of the n-type epitaxial layer formed in step S1 (step S2 (first step)). Next, a carbon nitride film (hard material film) is formed in the recess formed in step S2 (step S3 (second step)).

Next, a plurality of trenches are formed in portions of the n-type epitaxial layer formed in step S1 where the carbon nitride film is not formed in step S3 (step S4 (third step)). The plurality of trenches are arranged in a direction parallel to the main surface of the n ⁺ -type starting substrate.

Next, by growing a p-type epitaxial layer on the front surface of the epitaxial substrate, the plurality of trenches of the n-type epitaxial layer are filled with the p-type epitaxial layer (step S5 (fourth step)). As a result, a parallel pn layer in which n-type regions and p-type regions are alternately and repeatedly arranged in a direction parallel to the main surface of the n ⁺ -type starting substrate can be formed in the n-type epitaxial layer serving as the drift layer. .

Next, the p-type epitaxial layer formed in step S5 is ground from the side opposite to the n ⁺ -type starting substrate side of the p-type epitaxial layer (step S6 (fifth step)). This grinding is performed at least until the carbon nitride film is reached. Next, the carbon nitride film formed in step S3 is removed (step S7 (eighth step)). Next, the front surface of the epitaxial substrate is polished (step S8).

Next, a predetermined element structure is formed by a general method on the epitaxial substrate whose front surface has been polished in step S8 (step S9 (sixth step)). A stepper (reduction projection exposure apparatus), for example, can be used to form the device structure. After that, the epitaxial substrate is diced (cut) into individual chips (seventh step), thereby manufacturing a silicon carbide semiconductor device having a superjunction structure.

The silicon carbide semiconductor device is, for example, an SJ-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an SJ-PN diode.

2 to 21 are cross-sectional views showing an example of each state during manufacture of the silicon carbide substrate according to the embodiment. Each step shown in FIG. 1 will be specifically described with reference to FIGS. 2 to 21. FIG.

Step S1 shown in FIG. 1 will be described. First, an n ⁺ -type starting substrate 1 made of silicon carbide shown in FIG. 2 is prepared. The crystal structure of the n ⁺ -type starting substrate 1 can be, for example, a four-layer periodic hexagonal (4H—SiC) structure. The front surface of the n ⁺ -type starting substrate 1 can be, for example, the (0001) plane (so-called Si plane) or the (000-1) plane (so-called C plane). Also, the n ⁺ -type starting substrate 1 can be a substrate with a diameter of 3 inches, for example. The n ⁺ -type starting substrate 1 is then cleaned, for example by organic cleaning and RCA cleaning.

Next, as shown in FIG. 2, an n ^- type epitaxial layer 21 made of silicon carbide into which an n-type impurity such as nitrogen (N) is introduced at a predetermined doping concentration is formed on the front surface of the n + -type starting substrate 1. is epitaxially grown. The film thickness (thickness) of the n-type epitaxial layer 21 formed at this time can be, for example, about 30 μm. As described above, the epitaxial substrate 10 having the n-type epitaxial layer 21 deposited on the front surface of the n ⁺ -type starting substrate 1 is manufactured, and the step S1 shown in FIG. 1 is completed. In a silicon carbide semiconductor device using epitaxial substrate 10, n ⁺ -type starting substrate 1 serves as an n ⁺ -type drain layer, and n-type epitaxial layer 21 serves as an n-type drift layer.

Step S2 shown in FIG. 1 will be described. First, the epitaxial substrate 10 is cleaned by organic cleaning and RCA cleaning, for example. Next, as shown in FIG. 3, a metal mask 30 is placed on the n-type epitaxial layer 21 . The metal mask 30 has a shape that partially masks the front surface of the epitaxial substrate 10 . A recess 11 described later is formed in a portion of the n-type epitaxial layer 21 masked by the metal mask 30 , and a carbon nitride film 41 described later is formed in at least part of the recess 11 . The process of forming the recess 11 and the carbon nitride film 41 will be described later (see FIGS. 6 and 8, for example). Also, the shape of the metal mask 30 will be described later (see FIGS. 22 and 26, for example).

Next, as shown in FIG. 4, a silicon dioxide film 31 is formed on a portion of the front surface of the epitaxial substrate 10 not masked by the metal mask 30 by sputtering using silicon dioxide (SiO ₂ ) as a sputtering target. deposit. Sputtering for depositing the silicon dioxide film 31 is performed, for example, in a gas containing 20% oxygen (O ₂ ) in argon (Ar) at a pressure of 1 Pa and room temperature (for example, about 25° C.). It can be carried out. Also, the film thickness of the silicon dioxide film 31 can be set to, for example, about 1 μm. Next, the epitaxial substrate 10 with the silicon dioxide film 31 formed thereon is cleaned, for example, by organic cleaning and RCA cleaning.

Next, the metal mask 30 is removed from the front surface of the epitaxial substrate 10 as shown in FIG. Next, as shown in FIG. 6, the portion of the front surface of the epitaxial substrate 10 not masked by the silicon dioxide film 31 is etched by dry etching, for example. As a result, recesses 11 are formed in portions of the front surface of epitaxial substrate 10 that are not masked by silicon dioxide film 31 . The depth of the depression 11, that is, the etching depth D1 can be, for example, about 1 μm. As a result, the depression 11 is formed, and step S2 is completed.

Step S3 shown in FIG. 1 will be described. First, as shown in FIG. 7, a metal mask 40 is placed on the front surface of the silicon dioxide film 31 . The metal mask 40 has a shape that masks the front surface of the epitaxial substrate 10 other than at least part of the recess 11 formed therein. A later-described carbon nitride film 41 is formed on a portion of the epitaxial substrate 10 that is not masked by the metal mask 40 (see FIG. 8). The shape of the metal mask 40 will be described later (see FIGS. 23 and 27, for example).

Next, as shown in FIG. 8, carbon nitride (C _{1-x Nx} ) film is deposited. X is an integer. As a result, a carbon nitride film 41 made of carbon nitride, which is a hard material having higher hardness (for example, Knoop hardness) than silicon carbide on which the n-type epitaxial layer 21 is grown, is formed in the depression 11 .

Sputtering for forming the carbon nitride film 41 can be performed, for example, in nitrogen gas at room temperature under a pressure of 1 Pa while applying a negative bias of -200 V to the epitaxial substrate 10 . By performing the sputtering while applying a negative bias in this manner, the carbon nitride film 41 having a higher hardness can be formed. Also, instead of nitrogen gas, a gas obtained by adding 50% nitrogen gas to argon may be used.

The carbon nitride film 41 is formed, for example, in contact with the bottom surface of the recess 11 so that the film thickness (D2) is thinner than the depth of the recess 11 (D1 shown in FIG. 6). That is, the carbon nitride film 41 is formed such that the height of the front surface of the carbon nitride film 41 (the distance from the back surface of the n ⁺ -type starting substrate 1) is the same as the recess 11 formed in the front surface of the epitaxial substrate 10. It is formed so that it is lower than the height of the part where it is not installed. For example, when the depth of the depression 11 is about 1 μm as described above, the thickness of the carbon nitride film 41 can be about 0.7 μm, for example. In this case, the height of the front surface of carbon nitride film 41 is about 0.3 μm lower than the height of the portion of epitaxial substrate 10 where recess 11 is not formed.

Next, as shown in FIG. 9, the metal mask 40 is removed. Next, as shown in FIG. 10, the silicon dioxide film 31 is removed with dilute hydrofluoric acid (HF) or the like. Thus, the carbon nitride film 41 is formed in the depression 11 on the front surface of the epitaxial substrate 10, and step S3 shown in FIG. 1 is completed.

Step S4 shown in FIG. 1 will be described. First, the epitaxial substrate 10 is cleaned by organic cleaning and RCA cleaning, for example. Next, as shown in FIG. 11, a silicon dioxide film 51 is deposited on the front surface of the epitaxial substrate 10 by plasma CVD (Chemical Vapor Deposition). The thickness of the silicon dioxide film 51 can be, for example, about 5 μm. Next, the epitaxial substrate 10 with the silicon dioxide film 51 formed thereon is cleaned, for example, by organic cleaning and RCA cleaning.

Next, as shown in FIG. 12, a photoresist 61 is applied to the front surface of the silicon dioxide film 51 . Next, as shown in FIG. 13, a resist film 32 is formed by exposing and developing the photoresist 61 by photolithography. The resist film 32 is a resist having openings corresponding to portions where trenches 22 (see FIG. 16, for example) to be described later are formed.

The openings of the resist film 32 are arranged, for example, in a striped layout (not shown) extending in a direction parallel to the front surface of the epitaxial substrate 10 when viewed from the front surface side of the epitaxial substrate 10 . The width of the opening of the resist film 32 (horizontal length in FIG. 13) can be set to, for example, about 2.5 μm. The interval between adjacent openings of the resist film 32 can be set to, for example, about 2.5 μm.

Next, as shown in FIG. 14, the portions of the silicon dioxide film 51 that are not masked by the resist film 32 are dry-etched. Next, as shown in FIG. 15, the resist film 32 is removed.

Next, as shown in FIG. 16, the portions of the n-type epitaxial layer 21 that are not masked by the silicon dioxide film 51 are dry-etched. The depth of dry etching at this time can be, for example, about 25 μm. A trench 22 is thereby formed in the n-type epitaxial layer 21 . The trenches 22 are, for example, a plurality of trenches having an interval of about 2.5 μm, a width of about 2.5 μm, and a depth of about 25 μm. Next, as shown in FIG. 17, the silicon dioxide film 51 is removed with dilute hydrofluoric acid or the like. Thus, trenches 22 are formed in n-type epitaxial layer 21, and step S4 shown in FIG. 1 is completed.

Step S5 shown in FIG. 1 will be described. First, the epitaxial substrate 10 is cleaned by organic cleaning and RCA cleaning, for example. Next, as shown in FIG. 18, the p-type epitaxial layer 24 is grown on the front surface of the epitaxial substrate 10 using CVD to fill the trenches 22 with the p-type epitaxial layer 24 .

The CVD in step S5 can be performed using gases containing, for example, hydrochloric acid (HCl), silane (SiH ₄ ), propane (C ₃ H ₈ ), and trimethylaluminum (TMA) as raw materials. Further, the CVD in step S5 can be performed while etching silicon carbide in the vicinity of the opening of the trench 22 and the mesa top using, for example, HCl. The mesa top is, for example, the portion between the trenches 22 on the front surface of the epitaxial substrate 10 .

By CVD in step S5, as shown in FIG. 18, columnar silicon carbide is deposited on the mesa top of the front surface of epitaxial substrate 10, so that the front surface side of epitaxial substrate 10 becomes highly uneven. . In addition, in the CVD of step S5, the silicon carbide on the carbon nitride film 41 does not grow epitaxially and becomes the silicon carbide polycrystalline film 12, and the appearance of the film is different from that of the embedded portion of the trench 22. FIG. As described above, the trench 22 of the n-type epitaxial layer 21 is filled with the p-type epitaxial layer, and step S5 shown in FIG. 1 is completed.

Step S6 shown in FIG. 1 will be described. A height position 13 shown in FIG. 18 is the target position for grinding in step S6 of FIG. back side) is determined. Therefore, by grinding up to the height position 13, the p-type epitaxial layer 24 other than the portion embedded in the trench 22 can be reliably removed. However, when the accuracy of the front surface of epitaxial substrate 10 and the accuracy of grinding are high, height position 13 may be determined to be the same height as the front surface of epitaxial substrate 10 .

The etching depth (D1 shown in FIG. 6) for forming the recess 11 and the thickness for depositing the carbon nitride film (D2 shown in FIG. 8) for forming the carbon nitride film 41 is formed such that the height of the front surface of the carbon nitride film 41 coincides with the height position 13 . For example, assume that the height position 13 is determined to be about 0.3 μm lower than the height of the portion of the front surface of the epitaxial substrate 10 shown in FIG. 18 where the trench 22 is not formed.

In this case, as described above, the depth of the recess 11 (D1 shown in FIG. 6) is set to, for example, about 1 μm, and the thickness of the carbon nitride film 41 (D2 shown in FIG. 8) is set to, for example, about 0.7 μm. . Thereby, the height of the front surface of the carbon nitride film 41 matches the height position 13 . Therefore, the epitaxial substrate 10 can be ground from the front surface to the height position 13 by performing the grinding in step S6 until the carbon nitride film 41 is reached. The depth of the depression 11 at this time is about 0.7 μm by grinding. Also, in this case, if the trench 22 having a depth of about 25 μm is formed in step S4 as described above, the depth of the trench 22 immediately after step S6 is about 24.7 μm, for example.

The grinding in step S6 will be specifically described. As shown in FIG. 19, the p-type epitaxial layer 24 is ground from the opposite side of the p-type epitaxial layer 24 to the n ⁺ -type starting substrate side (upper side in FIG. 19) using, for example, a grinding device 14 . The grindstone 14 a of the grinding device 14 is in contact with the n-type epitaxial layer 21 and has friction with the n-type epitaxial layer 21 . The grindstone 14a is smaller than the wafer formed by the epitaxial substrate 10, for example. Then, for example, while the grindstone 14a moves on the front surface of the epitaxial substrate 10, it is rotated by a rotation axis perpendicular to the main surface of the epitaxial substrate 10, thereby coming into contact with the grindstone 14a of the n-type epitaxial layer 21. The part where there is is ground.

The n-type epitaxial layer 21 is ground until, for example, the silicon carbide polycrystalline film 12 is scraped away to expose the carbon nitride film 41 on the front surface of the epitaxial substrate 10, that is, the grindstone 14a of the grinding device 14 grinds the carbon nitride film 41. is reached. In the example shown in FIG. 19, grinding is performed until the grindstone 14a of the grinding device 14 reaches the height position 13 shown in FIG. However, the grinding of n-type epitaxial layer 21 may be continued until part of carbon nitride film 41 on the front surface side is further scraped off.

The amount of grinding of the n-type epitaxial layer 21 is controlled by, for example, the time of grinding by the grinding device 14 (hereinafter referred to as grinding time). For example, a grinding time for just reaching the carbon nitride film 41 or a grinding time for scraping off a part of the front surface side of the carbon nitride film 41 is derived by experiment, and only the derived grinding time is used when the epitaxial substrate 10 is manufactured. Grinding by the grinding device 14 is performed.

At this time, due to errors in the epitaxial substrate 10 due to the above-described steps up to grinding by the grinding device 14 and errors in grinding by the grinding device 14, the grindstone 14a may advance further to the back side of the epitaxial substrate 10 than expected. .

Even in such a case, the hardness of the carbon nitride film 41 is higher than that of the n-type epitaxial layer 21 as described above. 41 can be lowered. Therefore, as compared with the case where the carbon nitride film 41 is not provided, excessive grinding of the front surface side of the epitaxial substrate 10 due to each error can be suppressed.

Alternatively, the amount of grinding of the n-type epitaxial layer 21 may be controlled by stopping the detection by the grinding device 14 when a decrease in the traveling speed of the grindstone 14a is detected instead of the grinding time described above. As a result, detection by the grinding device 14 is stopped when the grindstone 14a reaches the carbon nitride film 41, and excessive grinding of the front surface side of the epitaxial substrate 10 can be suppressed.

Detection of a decrease in the advancing speed of the grindstone 14a is performed, for example, by a detector that detects changes in the stress on grinding of the grinding device 14, a detector of the advancing speed of the grindstone 14a using an image obtained by photographing the grinding device 14, Alternatively, it can be carried out by visual inspection of the production manager. Even when these detection methods are used to control the amount of grinding of the n-type epitaxial layer 21, there are cases where the grindstone 14a advances further toward the back side of the epitaxial substrate 10 than expected due to errors in detection by these detection methods. be.

Even in such a case, after the grindstone 14a reaches the carbon nitride film 41, the advancing speed of the grindstone 14a can be reduced by the carbon nitride film 41, as in the case where the grinding amount is controlled by the grinding time. Therefore, as compared with the case where the carbon nitride film 41 is not provided, excessive grinding of the front surface side of the epitaxial substrate 10 due to each error can be suppressed. As described above, the p-type epitaxial layer 24 is ground, and step S6 shown in FIG. 1 is completed.

Step S7 shown in FIG. 1 will be described. As shown in FIG. 20, the carbon nitride film 41 formed in the depression 11 of the n-type epitaxial layer 21 is removed by dry etching or ashing. The removal of the carbon nitride film 41 by ashing can be performed, for example, by oxygen plasma generated by plasmatizing oxygen (O ₂ ) gas at an atmospheric pressure of 5 Pa. As shown in FIG. Thus, the carbon nitride film 41 is removed, and step S7 shown in FIG. 1 is completed.

Step S8 shown in FIG. 1 will be described. Using a polishing apparatus and silicon carbide slurry, epitaxial substrate 10 is polished from the front surface side, as shown in FIG. Chemical mechanical polishing (CMP), for example, can be used for the polishing in step S8. By polishing, the center line average roughness Ra (defined in JISB0601) is set to 1 μm or less, and the filtered center line waviness Wca (defined in JISB0610) is set to 10 μm or less.

As described above, when the depth of the depression 11 is set to about 0.7 μm by the grinding in step S6, the polishing in step S8 is performed to reduce the thickness of the portion of the n-type epitaxial layer 21 where the depression 11 is not formed, for example. This can be done until the thickness is reduced by about 0.7 μm. As a result, the recesses 11 formed in the n-type epitaxial layer 21 are eliminated, and the epitaxial substrate 10 having a flat and smooth superjunction structure can be manufactured. In the manufactured epitaxial substrate 10, parallel pn layers in which n-type regions and p-type regions are alternately and repeatedly arranged are exposed on the front surface.

By making the front surface of the epitaxial substrate 10 flat and smooth, it is possible to prevent the formation of the device structure described later from being hindered. This epitaxial substrate 10 has a superjunction structure with a depth of about 23.7 μm, for example. As described above, the front surface of epitaxial substrate 10 is polished, and step S8 shown in FIG. 1 is completed.

Epitaxial substrate 10 having a superjunction structure can be manufactured by the steps shown in FIGS. A device structure is formed on manufactured epitaxial substrate 10 using a stepper or the like, and epitaxial substrate 10 having the device structure formed thereon is diced, thereby manufacturing a silicon carbide semiconductor device having a superjunction structure.

As described above, in the manufacturing method according to the embodiment, the carbon nitride film 41 is formed in the depression 11 formed on the front surface of the epitaxial substrate 10 . As a result, excessive grinding of the front surface of the epitaxial substrate 10 can be suppressed when removing the excess portion of the p-type epitaxial layer 24 deposited to fill the trenches 22 by grinding. Therefore, the aforementioned parallel pn layer is prevented from becoming too thin, and the characteristics such as element breakdown voltage and on-resistance in silicon carbide semiconductor devices such as SJ-MOSFETs and SJ-PN diodes manufactured from the epitaxial substrate 10 are maintained as designed. can be Therefore, it is possible to improve the yield in manufacturing the silicon carbide semiconductor device.

FIG. 22 is a diagram showing an example of a metal mask used for sputtering a silicon dioxide film according to the embodiment. 22 shows the upper surface (the surface opposite to n-type epitaxial layer 21) of metal mask 30 placed on the front surface of epitaxial substrate 10 in the step shown in FIG. 3 of step S2 in FIG. ing. As shown in FIG. 22 , the metal mask 30 has a circular outer shape and has an annular portion 221 and a mask portion 222 .

The annular portion 221 is an annular portion along the outer circumference of the metal mask 30 . The annular portion 221 is provided with four screw holes 221a arranged at regular intervals along the annular shape. The screw holes 221a are provided so as to correspond to the positions of four screw holes provided in a substrate holder (not shown), which is a tray on which the epitaxial substrate 10 is placed.

The mask portion 222 is connected to the annular portion 221 and provided so as to mask the portion forming the recess 11 described above. In the example shown in FIG. 22, four mask portions 222 are provided at equal intervals so as to be inscribed in the ring portion 221 . A portion of the metal mask 30 surrounded by the ring portion 221 and the mask portion 222 forms an opening 223 . 3, one of the mask portions 222 of the metal mask 30 is illustrated.

In the process shown in FIG. 3, the epitaxial substrate 10 is covered with a metal mask 30 while the epitaxial substrate 10 is placed on a substrate holder. By screwing the metal mask 30 to the substrate holder using the screw holes 221a, the metal mask 30 can be fixed to the substrate holder on which the epitaxial substrate 10 is placed.

In the process shown in FIG. 4, the silicon dioxide film 31 is formed on the portion of the front surface of the epitaxial substrate 10 corresponding to the opening 223 by performing sputtering with the metal mask 30 fixed to the substrate holder. is formed. As a result, in the step shown in FIG. 6, recesses 11 are formed in portions of n-type epitaxial layer 21 corresponding to annular portion 221 and mask portion 222 .

The shape of the mask portion 222 may be determined so that the recesses 11 to be formed are easy to see so that it is easy to determine the end of polishing in step S8 shown in FIG. For example, as in the example shown in FIG. 22, by forming the shape of the opening 223 into a shape having sharp corners toward the center of the metal mask 30, the formed depression 11 also has the same shape. This makes it easier to see the dents 11 at the time of polishing in step S8, and makes it easier to polish until the dents 11 disappear as described above.

FIG. 23 is a diagram showing an example of a metal mask used for sputtering a carbon nitride film according to the embodiment. FIG. 23 shows the top surface of the metal mask 40 placed on the front surface of the silicon dioxide film 31 in the step shown in FIG. 7 of step S3 in FIG. As shown in FIG. 23, metal mask 40 has the same circular outer shape as metal mask 30 shown in FIG. A portion of the metal mask 40 excluding the screw holes 231 and the openings 232 is a mask portion.

The screw holes 231 are provided at positions corresponding to the screw holes 221a of the metal mask 30 shown in FIG. 22, that is, at positions corresponding to the four screw holes provided in the substrate holder. The openings 232 are provided at four locations corresponding to the mask portions 222 of the metal mask 30 shown in FIG. The four openings 232 are formed in positions and shapes that are symmetrical about the center of the metal mask 40 .

In the example shown in FIG. 23, each of the four openings 232 is a combination of one circle and two rectangles. However, the shape of the opening 232 is not limited to this, and if it is included in the portion corresponding to the mask portion 222 of the metal mask 30 shown in FIG. and other various shapes.

In the process shown in FIG. 7, the epitaxial substrate 10 is placed on the substrate holder and the epitaxial substrate 10 is covered with the metal mask 40 . By screwing the metal mask 40 to the substrate holder using the screw holes 231, the metal mask 40 can be fixed to the substrate holder on which the epitaxial substrate 10 is placed.

In the process shown in FIG. 8, the carbon nitride film 41 is formed on the portion of the front surface of the epitaxial substrate 10 corresponding to the opening 232 by performing the sputtering in the state where the screw is fixed as described above. . In the example using the metal mask 40 shown in FIG. 23, carbon nitride films 41 having a shape that is a combination of one circle and two rectangles are formed at four locations.

FIG. 24 is a diagram illustrating an example of an epitaxial substrate according to the embodiment; By steps S1 to S9 shown in FIG. 1, an epitaxial substrate 10 shown in FIG. 24, for example, is manufactured. A plurality of lattice-shaped element structure formation regions 241 are each region (shot) in which an element structure is formed by a stepper used for manufacturing the epitaxial substrate 10 .

The hard material formation region 242 is the position of the opening 232 of the metal mask 40 shown in FIG. 23, that is, the position where the carbon nitride film 41 is formed. As shown in the hard material formation region 242 of FIG. 24, the carbon nitride film 41 is formed in a portion near the periphery of the epitaxial substrate 10, which is different from the element structure formation region 241 where the element structure is formed. Also, the carbon nitride film 41 is formed point-symmetrically about the center of the epitaxial substrate 10 . However, carbon nitride film 41 is removed in step S7 of FIG. 1 and the process shown in FIG. Therefore, epitaxial substrate 10 shown in FIG. 24 does not include carbon nitride film 41 .

Also, the epitaxial substrate 10 may be provided with orientation flats 243 and 244 . The orientation flats 243 and 244 are linear notches for aligning the orientation of the epitaxial substrate 10 (wafer).

Epitaxial substrate 10 shown in FIG. 23 is diced along the boundary between element structure formation regions 241, and each element structure formation region 241 is separated into chips, thereby manufacturing a silicon carbide semiconductor device having a superjunction structure. can be manufactured.

FIG. 25 is a flow chart showing another example of the method for manufacturing the silicon carbide substrate according to the embodiment. Although the manufacturing method for removing the carbon nitride film 41 in step S7 has been described in FIG. 1, the manufacturing method is not limited to this. For example, if the remaining carbon nitride film 41 does not affect the formation of the device structure in subsequent steps, a manufacturing method that omits the step of removing the carbon nitride film 41 may be used as shown in FIG. It is possible.

Steps S11 to S16 shown in FIG. 25 are the same as steps S1 to S6 shown in FIG. 1, respectively. Steps S17 and S18 shown in FIG. 25 are the same as steps S8 and S9 shown in FIG. 1, respectively. That is, the manufacturing method shown in FIG. 25 is a manufacturing method in which step S7 is omitted from the manufacturing method shown in FIG. However, the polishing in step S17 shown in FIG. 25 is performed, for example, until the height of the front surface of epitaxial substrate 10 reaches the height of the front surface of carbon nitride film 41 that has not been removed.

When manufacturing an epitaxial substrate 10 having an element structure by a manufacturing method that omits the step of removing the carbon nitride film 41, for example, the metal mask 40 is removed so that the carbon nitride film 41 is not formed on the above-described dicing line. An opening 232 is formed. This can prevent the remaining carbon nitride film 41 from interfering with dicing.

Alternatively, the carbon nitride film 41 may be removed immediately before dicing, that is, after the polishing described above. This can prevent the carbon nitride film 41 from interfering with dicing.

By not removing the carbon nitride film 41 by ashing or the like, as in the example shown in FIG.

FIG. 26 is a diagram showing another example of a metal mask used for sputtering a silicon dioxide film according to the embodiment; 26, the same reference numerals are given to the same parts as those shown in FIG. 22, and the description thereof is omitted. 3 of step S2 in FIG. 1, the metal mask 30 shown in FIG. 26, for example, may be used as the metal mask 30 placed on the front surface of the epitaxial substrate 10. As shown in FIG. A metal mask 30 shown in FIG. 26 has a circular outer shape and has an annular portion 221 and mask portions 261 and 262 .

The mask portion 261 is connected to the annular portion 221, and is provided so that the portion surrounded by the annular portion 221 and the mask portion 261 corresponds to the element structure formation region 241 (see FIG. 24, for example) of the epitaxial substrate 10. It is The mask portion 262 is connected to the annular portion 221 and is elongated so as to bisect the portion surrounded by the annular portion 221 and the mask portion 261 . In addition, the mask portion 262 is provided parallel to the boundary line between the element structure forming regions 241 of the epitaxial substrate 10, that is, parallel to the dicing line.

Two portions of the metal mask 30 shown in FIG. As a result, in the step shown in FIG. 3, the silicon dioxide film 31 is formed only on the portion corresponding to the opening 263, that is, the portion where the element structure formation region 241 is to be formed. As a result, in the step shown in FIG. 6, recesses 11 are formed in portions of n-type epitaxial layer 21 corresponding to annular portion 221 and mask portions 261 and 262 .

FIG. 27 is a diagram showing another example of the metal mask used for sputtering the carbon nitride film according to the embodiment. In FIG. 27, the same parts as those shown in FIG. 23 are given the same reference numerals, and the description thereof is omitted. When the metal mask 30 shown in FIG. 26 is used as the metal mask 30, the metal mask 40 placed on the front surface of the silicon dioxide film 31 in the step shown in FIG. 7 of step S3 in FIG. A metal mask 40 shown in FIG. 27 can be used.

A metal mask 40 shown in FIG. 27 has the same circular outer shape as the metal mask 30 shown in FIG. The annular portion 271 has the same shape as the annular portion 221 of the metal mask 30 shown in FIGS. The mask portions 272 are two mask portions corresponding to the shapes of the two openings 263 of the metal mask 30 shown in FIG.

A plurality of connection portions 273 are provided so as to fix and connect the ring portion 271 and the mask portion 272 . Moreover, the connecting portion 273 is elongated to the extent that the ring portion 271 and the mask portion 272 can be fixed and connected by maintaining the strength. In the example shown in FIG. 27, twelve connection portions 273 are provided on the metal mask 40 .

Also, the connecting portion 273 is made of the same metal material as the annular portion 271 and the mask portion 272, for example. In this case, the annular portion 271, the mask portion 272 and the connecting portion 273 may be integrally formed. However, the connection portion 273 may be made of a material different from that of the annular portion 271 and the mask portion 272 .

Twelve portions of the metal mask 40 shown in FIG. Thus, in the step shown in FIG. 8, carbon nitride film 41 is formed at 12 portions corresponding to openings 274 on the front surface of epitaxial substrate 10 .

The shape of the opening 274 may be determined so that the carbon nitride film 41 to be formed has a shape that is easy to see so that it is easy to judge the end of polishing in step S17 shown in FIG. 25, for example. For example, as in the example shown in FIG. 27, by forming the opening 274 into a shape having sharp corners toward the center of the metal mask 40, the formed carbon nitride film 41 also has the same shape. (See, for example, FIG. 28). As a result, the carbon nitride film 41 can be easily visually observed during polishing in step S17 shown in FIG.

FIG. 28 is a diagram showing another example of the epitaxial substrate according to the embodiment; 28, the same parts as those shown in FIG. 24 are denoted by the same reference numerals, and descriptions thereof are omitted. 25 is performed and the metal masks 30 and 40 shown in FIGS. 26 and 27 are used, the epitaxial substrate 10 shown in FIG. 28, for example, is produced.

Since carbon nitride film 41 is not removed in the manufacturing method shown in FIG. 25, carbon nitride film 41 remains on the front surface of epitaxial substrate 10 as shown in FIG. In this way, by not removing the carbon nitride film 41 by ashing or the like, the manufacturing steps of the epitaxial substrate 10 can be reduced, and the manufacturing cost of the epitaxial substrate 10 can be suppressed.

Moreover, by using the metal masks 30 and 40 shown in FIGS. 26 and 27, carbon nitride is deposited on the portion of the epitaxial substrate 10 shown in FIG. 28 corresponding to the opening 274 of the metal mask 40 shown in FIG. A membrane 41 is formed. Specifically, the portion of the epitaxial substrate 10 excluding the ring-shaped portion along the outer circumference, element structure forming regions 241a and 241b described later, and 12 elongated portions connecting these regions. A carbon nitride film 41 is formed on the surface.

Therefore, the carbon nitride film 41 can be formed in a wider range than the example shown in FIG. 24, for example. As a result, the traveling speed of the grindstone 14a of the grinding device 14 can be further reduced by the carbon nitride film 41 in the grinding of step S16 shown in FIG. 25, for example. Therefore, excessive grinding of the front surface side of epitaxial substrate 10 due to each error can be further suppressed.

When using the metal masks 30 and 40 shown in FIGS. 26 and 27 , the carbon nitride film 41 is also formed on the elongated portion of the epitaxial substrate 10 corresponding to the mask portion 262 of the metal mask 30 . The carbon nitride film 41 in this portion is referred to as a carbon nitride film 41a. Since the carbon nitride film 41a is formed including the vicinity of the center of the epitaxial substrate 10, for example, in the grinding in step S16 shown in FIG. can be suppressed.

When the carbon nitride film 41a is formed using the metal masks 30 and 40 shown in FIGS. 26 and 27, the element structure shown in FIG. 24 is formed so as to avoid the carbon nitride film 41a as shown in FIG. The region 241 is divided into element structure forming regions 241a and 241b. The element structure forming regions 241a and 241b are a plurality of portions provided along the direction perpendicular to the thickness direction of the epitaxial substrate 10 .

That is, a gap 241c on the dicing line is provided between the element structure forming regions 241a and 241b, and the carbon nitride film 41a (the recess 11 described above) is formed in the gap 241c. This can prevent the carbon nitride film 41a from affecting the formation of the element structure. The arrangement of the element structure forming regions 241 can be adjusted by the shot interval in the stepper for forming the element structure.

In this manner, the carbon nitride film 41 is formed not only in the vicinity of the periphery surrounding the element structure formation region 241 of the epitaxial substrate 10 but also in the gap 241c between the element structure formation regions 241a and 241b, that is, in the vicinity of the center of the epitaxial substrate 10. can be formed. Therefore, when the grinding device 14, which is smaller than the metal mask 40, is moved and ground, the tilting of the grinding device 14 and over-grinding of only the center portion of the epitaxial substrate 10 can be suppressed. The surface can be ground evenly. Also, for example, in the polishing of step S17 shown in FIG. 25, the front surface of the epitaxial substrate 10 can be uniformly polished.

Each of the above-described embodiments can be implemented in different combinations. For example, it is possible to perform the manufacturing method shown in FIG. 1 and use the metal masks 30 and 40 shown in FIGS. In this case, since the carbon nitride film 41 is removed in the manufacturing method shown in FIG. 1, for example, the epitaxial substrate 10 shown in FIG. 28 is manufactured with the carbon nitride film 41 removed.

It is also possible to perform the manufacturing method shown in FIG. 25 and use the metal masks 30 and 40 shown in FIGS. 22 and 23 at that time. In this case, the epitaxial substrate 10 shown in FIG. 24 is manufactured with the carbon nitride film 41 having a shape corresponding to the opening 232 of the metal mask 40 shown in FIG. 23 remaining.

Although the case where the carbon nitride film 41 is used as the hard material film has been described, the hard material film is not limited to the carbon nitride film 41, and may be a film using various materials having higher hardness than the n-type epitaxial layer 21. The Knoop hardness of silicon carbide on which n-type epitaxial layer 21 is grown is, for example, about 2400 or more and 3000 or less. Therefore, the hard material film can be a film using various materials having a Knoop hardness of 3000 or more, for example.

Moreover, the hard material film is preferably a film using a material whose heat resistance temperature is equal to or higher than the epitaxial growth temperature (for example, about 1700° C.) of the p-type epitaxial layer 24 . Moreover, when the step of removing the carbon nitride film 41 is performed, the hard material film is desirably a film using various materials that can be removed by ashing or dry etching.

For example, a DLC (diamond-like carbon) film may be used as the hard material film. DLC can be formed by sputtering in the same manner as the carbon nitride film 41 . Also in this case, a DLC film with higher hardness can be formed by performing sputtering while applying a negative bias. However, the sputtering of DLC is performed, for example, in argon gas.

As described above, according to the embodiments, a recess separate from the trench is provided on the front surface side of the semiconductor substrate of the first conductivity type made of silicon carbide, and the hard material film is formed in the recess. can be formed. Thus, in grinding the second conductivity type epitaxial layer after filling the trench with the second conductivity type epitaxial layer, when the grinding position reaches the hard material film, the hard material film can slow down the progress of grinding. Therefore, excessive grinding of the second conductivity type epitaxial layer can be suppressed, and the yield of the silicon carbide semiconductor device can be improved.

The present invention can be modified in various ways, and in each of the above-described embodiments, for example, the dimensions and impurity concentration of each part are set variously according to the required specifications. In each embodiment, the first conductivity type is n-type and the second conductivity type is p-type. It holds.

As described above, the method for manufacturing a silicon carbide substrate and the silicon carbide substrate according to the present invention provide a silicon carbide semiconductor device including parallel pn layers in which first conductivity type regions and second conductivity type regions are alternately and repeatedly arranged. is useful for the production of

Reference Signs List 1 n ⁺ -type starting substrate 10 epitaxial substrate 11 recess 12 silicon carbide polycrystalline film 13 height position 14 grinding device 14a grindstone 21 n-type epitaxial layer 22 trench 24 p-type epitaxial layer 30, 40 metal mask 31, 51 silicon dioxide film 32 Resist films 41, 41a Carbon nitride film 61 Photoresist 221, 271 Annular portions 221a, 231 Screw holes 222, 261, 262, 272 Mask portions 223, 232, 263, 274 Openings 241, 241a, 241b Device structure forming region 241c Gap 242 Hard material forming region 243, 244 Orientation flat 273 Connection

Claims (9)

A first-conductivity-type semiconductor substrate made of silicon carbide and a parallel pn layer in which first-conductivity-type regions and second-conductivity-type regions are alternately and repeatedly arranged in a direction parallel to one main surface of the semiconductor substrate. A method for manufacturing a silicon carbide substrate comprising:
a first step of forming a recess extending from a portion of the one main surface of the semiconductor substrate in a thickness direction orthogonal to the main surface of the semiconductor substrate;
After the first step, a second step of forming a hard material film having a hardness higher than that of the semiconductor substrate in the recess;
a third step of forming a trench extending in the thickness direction from a portion of the one main surface of the semiconductor substrate that is different from the portion where the recess is formed;
After the third step, by growing a second conductivity type epitaxial layer to be the second conductivity type region on the one main surface of the semiconductor substrate, the inside of the trench is filled with the second conductivity type epitaxial layer. a fourth step of forming the embedded parallel pn layer;
After the second step and the fourth step, the second conductivity type epitaxial layer is ground until it reaches at least the hard material film, and the parallel pn layer is exposed on the one main surface of the semiconductor substrate. process and
A method for manufacturing a silicon carbide substrate, comprising: 2. The method of manufacturing a silicon carbide substrate according to claim 1, wherein in said second step, said recess is formed in a portion of said one main surface of said semiconductor substrate in the vicinity of an outer periphery of said semiconductor substrate. After the fifth step, including a sixth step of forming an element structure on the semiconductor substrate,
3. The recess is formed in a portion of the one main surface of the semiconductor substrate in the second step, which is different from a portion where the element structure is formed in the sixth step. 3. The method for manufacturing the silicon carbide substrate according to 1. The semiconductor substrate has a plurality of portions along a direction perpendicular to the thickness direction, and a gap is provided between two adjacent portions of the plurality of portions,
In the second step, of the one main surface of the semiconductor substrate, the recess is formed in a portion surrounding the plurality of portions and in a portion of the gap.
4. The method for manufacturing a silicon carbide substrate according to claim 3, wherein: After the sixth step, including a seventh step of performing dicing for singulating the element structure into chips,
5. The method of manufacturing a silicon carbide substrate according to claim 4, wherein said dicing is performed along said gap in said seventh step. 6. The silicon carbide according to any one of claims 1 to 5, wherein in said second step, said hard material film is formed in contact with the bottom surface of said depression and has a film thickness thinner than the depth of said depression. Substrate manufacturing method. 7. The method for manufacturing a silicon carbide substrate according to claim 1, wherein the hard material film having a Knoop hardness of 3000 or more is formed in the second step. 8. The method for manufacturing a silicon carbide substrate according to claim 1, further comprising an eighth step of removing said hard material film after said fifth step. A first-conductivity-type semiconductor substrate made of silicon carbide and a parallel pn layer in which first-conductivity-type regions and second-conductivity-type regions are alternately and repeatedly arranged in a direction parallel to one main surface of the semiconductor substrate. A silicon carbide substrate comprising:
The semiconductor substrate has a recess extending in a direction orthogonal to the main surface of the semiconductor substrate from a portion different from the portion where the element structure is formed in the one main surface of the semiconductor substrate, and has a hardness higher than that of the semiconductor substrate. A silicon carbide substrate, comprising: a hard material film having a high resistance within said recess.

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