JP2020181966A - Manufacturing method of silicon carbide substrate and silicon carbide substrate - Google Patents

Abstract

To provide a manufacturing method of a silicon carbide substrate capable of suppressing excessive grinding of an epitaxial layer to improve the yield of a silicon carbide semiconductor device and a silicon carbide substrate.SOLUTION: On a front side of an epitaxial substrate 10, a recess different from a trench 22 is provided, a carbon nitride film 41 is formed in the recess, and a trench is embedded by a p-type epitaxial layer 24. Next, the p-type epitaxial layer 24 is ground. In the grinding, when a grinding position reaches the carbon nitride film 41, the progress speed of grinding decreases so that it is possible to prevent the p-type epitaxial layer 24 from being excessively ground.SELECTED DRAWING: Figure 18

Description

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

Conventionally, a superjunction (SJ: Super Junction) 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 a substrate (hereinafter referred to as a lateral direction) as a parallel pn layer. Semiconductor devices having a structure are known. In the manufacture of a semiconductor device having a superjunction structure using silicon carbide (SiC) as a semiconductor material, a multi-stage epitaxial method or a trench-embedded epitaxial method is used for forming a parallel pn layer.

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

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 superbonded structure having a parallel pn layer. The epitaxial substrate 10 is a silicon carbide substrate formed by growing an n-type epitaxial layer 21 as a drift layer on an n ⁺ type starting substrate 1. The p-type epitaxial layer 24 is embedded in the trench 22 by forming a trench 22 in the n-type epitaxial layer 21 and growing the p-type epitaxial layer 24 on the front surface of the epitaxial substrate 10.

At this time, since columnar silicon carbide is deposited on the mesatop (between the trenches 22) of the front surface of the epitaxial substrate 10, the front surface side of the epitaxial substrate 10 becomes severely uneven. Therefore, grinding is performed from the front surface side of the p-type epitaxial layer 24 to remove unnecessary portions of the p-type epitaxial layer 24, and the front surface of the epitaxial substrate 10 is flattened. The unnecessary portion of the p-type epitaxial layer 24 is, for example, a portion of the p-type epitaxial layer 24 above the front surface of the epitaxial substrate 10 including a columnar deposition portion.

JP-A-2018-19069

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

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

Therefore, if the deposition state of unnecessary portions 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 do. When the p-type epitaxial layer 24 is ground significantly beyond the height position 13, the parallel pn layer becomes too thin, and the silicon carbide semiconductor device manufactured from the epitaxial substrate 10 has characteristics such as element withstand voltage and on-resistance. Has different characteristics from the design. Therefore, the yield in the manufacture of the silicon carbide semiconductor device is lowered. The withstand voltage is the limit voltage at which the element does not malfunction or break.

The present invention is a method for manufacturing a silicon carbide substrate and a silicon carbide substrate, which can suppress excessive grinding of the epitaxial layer and improve the yield of the silicon carbide semiconductor device in order to solve the above-mentioned problems caused by the prior art. The purpose is to provide.

In order to solve the above-mentioned problems and achieve the object of the present invention, the method for producing a silicon carbide substrate according to the present invention is to use a first conductive type semiconductor substrate made of silicon carbide, a first conductive type region and a second conductive 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 from a part of the one main surface of the semiconductor substrate toward a thickness direction orthogonal to the main surface of the semiconductor substrate, and after the first step, hardness of the semiconductor substrate is higher than that of the semiconductor substrate. The second step of forming a hard material film having a high hardness in the recess is performed. In addition, a third step of forming a trench 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 is performed. Further, after the third step, by growing a second conductive type epitaxial layer to be the second conductive type region on the one main surface of the semiconductor substrate, the inside of the trench is filled with the second conductive type epitaxial. The fourth step of embedding with a layer and forming the parallel pn layer is performed. Further, after the second step and the fourth step, the second conductive 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. Perform the fifth step.

Further, in the method for manufacturing a silicon carbide substrate according to the present invention, in the second step of the above-described invention, 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 that.

Further, in the method for manufacturing a silicon carbide substrate according to the present invention, in the above-described invention, 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 formed. It is characterized in that the recess is formed in a portion of the one main surface different from the portion in which 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 above-described invention, the semiconductor substrate has a plurality of portions along a direction perpendicular to the thickness direction, and two of the plurality of portions are adjacent to each other. A gap is provided between the two portions, and in the second step, the recess is formed in the portion of the one main surface of the semiconductor substrate that surrounds the plurality of portions and the gap portion. It is characterized by forming.

Further, the method for manufacturing a silicon carbide substrate according to the present invention includes, in the above-described invention, a seventh step of dicing the element structure into chips after the sixth step, and the seventh step. The gap is a gap on the dicing line.

Further, the method for manufacturing a silicon carbide substrate according to the present invention is to form the hard material film which is in contact with the bottom surface of the recess and whose film thickness is thinner than the depth of the recess in the second step of the invention described above. It is a feature.

Further, the method for producing 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 above-described invention.

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

Further, the silicon carbide substrate according to the present invention is a first conductive type semiconductor substrate made of silicon carbide, in which a first conductive type region and a second conductive type region are parallel to one main surface of the semiconductor substrate. A silicon carbide substrate having parallel pn layers arranged alternately and repeatedly, and the semiconductor substrate is the semiconductor substrate from a portion of the one main surface of the semiconductor substrate that is different from the portion on which the element structure is formed. It is characterized by having a recess in a direction orthogonal to the main surface of the semiconductor and having a hard material film having a hardness higher than that of the semiconductor substrate in the recess.

According to the invention described above, in the grinding of the second conductive type epitaxial layer after the trench is embedded by the second conductive type epitaxial layer, when the grinding position reaches the hard material film, the progress speed of grinding is reduced by the hard material film. 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 the silicon carbide semiconductor device.

FIG. 1 is a flowchart showing an example of a method for manufacturing a silicon carbide substrate according to an embodiment. FIG. 2 is a cross-sectional view (No. 1) showing an example of each state during the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 3 is a cross-sectional view (No. 2) showing an example of each state during the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 4 is a cross-sectional view (No. 3) showing an example of each state during the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 5 is a cross-sectional view (No. 4) showing an example of each state during the manufacturing 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 the manufacturing 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 the manufacturing 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 the manufacturing 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 the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 10 is a cross-sectional view (No. 9) showing an example of each state during the manufacturing 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 the manufacturing 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 the manufacturing 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 the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 14 is a cross-sectional view (No. 13) showing an example of each state during the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 15 is a cross-sectional view (No. 14) showing an example of each state during the manufacturing 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 the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 17 is a cross-sectional view (No. 16) showing an example of each state during the manufacturing 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 the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 19 is a cross-sectional view (No. 18) showing an example of each state during the manufacturing 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 the manufacturing 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 the manufacturing of the silicon carbide substrate according to the embodiment. FIG. 22 is a diagram showing an example of a metal mask used for sputtering the silicon dioxide film according to the embodiment. FIG. 23 is a diagram showing an example of a metal mask used for sputtering the carbon nitride film according to the embodiment. FIG. 24 is a diagram showing an example of the epitaxial substrate according to the embodiment. FIG. 25 is a flowchart 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 the silicon dioxide film according to the embodiment. FIG. 27 is a diagram showing another example of a 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 superbonded structure having a parallel pn layer.

Hereinafter, a method for manufacturing a silicon carbide substrate and a preferred embodiment of the silicon carbide substrate according to the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the accompanying drawings, it means that the electrons or holes are a large number of carriers in the layers and regions marked with n or p, respectively. Further, + and-attached to n and p mean that the impurity concentration is higher and the impurity concentration is lower than that of the layer or region to which it is not attached, respectively. In the following description of the embodiment and the accompanying drawings, the same reference numerals are given to the same configurations, and duplicate description will be omitted. In this specification, in the notation of the Miller index, "-" means a bar attached to the index immediately after that, and "-" is added before the index to represent a negative index.

(Embodiment)
Regarding the method for manufacturing a silicon carbide (SiC) substrate according to the embodiment, the drift layer has an n-type (first conductive type) region and a p-type (second conductive type) region parallel to the front surface of the substrate. A case of manufacturing a silicon carbide semiconductor device having a super junction (SJ) structure having parallel pn layers arranged alternately and repeatedly in the direction will be described as an example.

FIG. 1 is a flowchart 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) in which an n-type epitaxial layer is deposited on the front surface of the n ⁺ type starting substrate is produced. Next, a recess is formed in a part 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, in the n-type epitaxial layer formed in step S1, a plurality of trenches are formed in the portion 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, the p-type epitaxial layer is embedded in the plurality of trenches of the n-type epitaxial layer by growing the p-type epitaxial layer on the front surface of the epitaxial substrate (step S5 (fourth step)). As a result, it is possible to form a parallel pn layer in which the n-type region and the p-type region are alternately and repeatedly arranged in the direction parallel to the main surface of the n ⁺ type starting substrate in the n-type epitaxial layer to be the drift layer. ..

Next, the p-type epitaxial layer formed in step S5 is ground from the side of the p-type epitaxial layer opposite to the side of the n ⁺ type starting substrate (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 (8th step)). Next, the front surface of the epitaxial substrate is polished (step S8).

Next, a predetermined element structure is formed on the epitaxial substrate whose front surface has been polished in step S8 by a general method (step S9 (sixth step)). For example, a stepper (reduced projection type exposure apparatus) can be used to form the element structure. After that, a silicon carbide semiconductor device having a superbonded structure can be manufactured by dicing (cutting) the epitaxial substrate and dicing the pieces into individual chips (7th step).

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

2 to 21 are cross-sectional views showing an example of each state during the manufacturing 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.

Step S1 shown in FIG. 1 will be described. First, the 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 crystal (4H-SiC) structure. The front surface of the n ⁺ type starting substrate 1 can be, for example, a (0001) surface (so-called Si surface) or a (000-1) surface (so-called C surface). Further, the n ⁺ type starting substrate 1 can be, for example, a substrate having a diameter of 3 inches. Next, the n ⁺ type starting substrate 1 is cleaned by, for example, organic cleaning and RCA cleaning.

Next, as shown in FIG. 2, an n-type epitaxial layer 21 made of silicon carbide in which an n-type impurity such as nitrogen (N) is introduced into the front surface of the n ⁺ type starting substrate 1 at a predetermined doping concentration. Epitaxially grow. 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 in which the n-type epitaxial layer 21 is deposited on the front surface of the n ⁺ type starting substrate 1 is produced, and step S1 shown in FIG. 1 is completed. In the silicon carbide semiconductor device using the epitaxial substrate 10, the n ⁺ type starting substrate 1 becomes an n ⁺ type drain layer, and the n-type epitaxial layer 21 becomes an n-type drift layer.

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

Next, as shown in FIG. 4, the silicon dioxide film 31 is applied to the portion of the front surface of the epitaxial substrate 10 that is not masked by the metal mask 30 by sputtering using silicon dioxide (SiO ₂ ) as the sputtering target. Accumulate. Sputtering for depositing the silicon dioxide film 31 is, for example, a gas obtained by adding 20% oxygen (O ₂ ) to argon (Ar) in a gas having an atmospheric pressure of 1 Pa and a room temperature (for example, about 25 ° C.). It can be carried out. The film thickness of the silicon dioxide film 31 can be, for example, about 1 μm. Next, the epitaxial substrate 10 on which the silicon dioxide film 31 is formed is cleaned by, for example, organic cleaning and RCA cleaning.

Next, as shown in FIG. 5, the metal mask 30 is removed from the front surface of the epitaxial substrate 10. Next, as shown in FIG. 6, the portion of the front surface of the epitaxial substrate 10 that is not masked by the silicon dioxide film 31 is etched, for example, by dry etching. As a result, the recess 11 is formed in the portion of the front surface of the epitaxial substrate 10 that is not masked by the silicon dioxide film 31. The depth of the recess 11, that is, the depth D1 for etching can be, for example, about 1 μm. As a result, the recess 11 is formed, and step S2 is completed.

Step S3 shown in FIG. 1 will be described. First, next, as shown in FIG. 7, a metal mask 40 is installed on the front surface of the silicon dioxide film 31. The metal mask 40 has a shape that masks a portion of the front surface of the epitaxial substrate 10 other than at least a part of the portion where the recess 11 is formed. A carbon nitride film 41 described later 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, for example, FIGS. 23 and 27).

Next, as shown in FIG. 8, carbon nitride (C _1-X) is applied to a portion of the front surface of the epitaxial substrate 10 that is not masked by the metal mask 40 by sputtering using carbon (C) as a sputtering target. a film of N _X) is deposited. X is an integer. As a result, a carbon nitride film 41 made of carbon nitride, which is a hard material having a hardness (for example, Knoop hardness) higher than that of silicon carbide on which the n-type epitaxial layer 21 is grown, is formed in the recess 11.

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

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

Next, the metal mask 40 is removed as shown in FIG. Next, as shown in FIG. 10, the silicon dioxide film 31 is removed with dilute hydrofluoric acid (HF) or the like. As a result, the carbon nitride film 41 is formed in the recess 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, for example, organic cleaning and RCA cleaning. 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 on which the silicon dioxide film 51 is formed is cleaned by, for example, organic cleaning and RCA cleaning.

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

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 (the length in the lateral direction of FIG. 13) can be, for example, about 2.5 μm. The distance between the adjacent openings of the resist film 32 can be, for example, about 2.5 μm.

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

Next, as shown in FIG. 16, the portion of the n-type epitaxial layer 21 that is not masked by the silicon dioxide film 51 is dry-etched. The depth of dry etching at this time can be, for example, about 25 μm. As a result, the trench 22 is formed in the n-type epitaxial layer 21. The trench 22 is, for example, a plurality of trenches having an interval of about 2.5 μm, a width of each 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. As a result, the trench 22 is formed in the 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, for example, organic cleaning and RCA cleaning. Next, as shown in FIG. 18, the p-type epitaxial layer 24 is embedded in the trench 22 by growing the p-type epitaxial layer 24 on the front surface of the epitaxial substrate 10 using CVD.

CVD of step S5, for example, hydrochloric acid (HCl), silane (SiH _4), it is possible to perform a gas containing propane (C ₃ H ₈₎ and trimethyl aluminum (TMA) as a starting material. Further, the CVD in step S5 can be performed while etching the silicon carbide near the opening of the trench 22 and the mesatop using, for example, HCl. The mesatop is, for example, a portion of the front surface of the epitaxial substrate 10 between the trenches 22.

As shown in FIG. 18, the CVD of step S5 causes columnar silicon carbide to be deposited on the mesatop of the front surface of the epitaxial substrate 10, so that the front surface side of the epitaxial substrate 10 becomes extremely uneven. .. Further, in the CVD of step S5, the silicon carbide on the carbon nitride film 41 does not epitaxially grow and becomes a silicon carbide polycrystalline film 12, and the appearance of the film is different from that of the embedded portion of the trench 22. As described above, the p-type epitaxial layer is embedded in the trench 22 of the n-type epitaxial layer 21, and step S5 shown in FIG. 1 is completed.

Step S6 shown in FIG. 1 will be described. The height position 13 shown in FIG. 18 is the target position for grinding in step S6 of FIG. 1, and is slightly lower than the portion of the front surface of the epitaxial substrate 10 where the trench 22 is not formed (of the epitaxial substrate 10). Determined (on the back side). Therefore, by grinding to the height position 13, the portion of the p-type epitaxial layer 24 other than the portion embedded in the trench 22 can be reliably removed. However, if the accuracy of the front surface of the epitaxial substrate 10 and the accuracy of grinding are high, the height position 13 may be determined to be the same height as the front surface of the epitaxial substrate 10.

The depth at which etching is performed when the above-mentioned recess 11 is formed (D1 shown in FIG. 6), and the thickness at which the carbon nitride film is deposited when the carbon nitride film 41 is formed (D2 shown in FIG. 8). Is formed so that the height of the front surface of the carbon nitride film 41 coincides with the height position 13. For example, it is assumed 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 in which 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. .. As a result, the height of the front surface of the carbon nitride film 41 coincides with the height position 13. Therefore, by performing the grinding in step S6 until the carbon nitride film 41 is reached, the epitaxial substrate 10 can be ground from the front surface to the height position 13. The depth of the recess 11 at this time is about 0.7 μm by grinding. Further, in this case, for example, assuming that 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, for example, about 24.7 μm.

The grinding in step S6 will be specifically described. As shown in FIG. 19, for example, a grinding device 14 is used to grind the p-type epitaxial layer 24 from the side of the p-type epitaxial layer 24 opposite to the side of the n ⁺ type starting substrate (upper side of FIG. 19). The grindstone 14a 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, for example, the epitaxial substrate 10. Then, for example, the grindstone 14a moves on the front surface of the epitaxial substrate 10 and rotates on a rotation axis orthogonal to the main surface of the epitaxial substrate 10, so that the grindstone 14a comes into contact with the grindstone 14a of the n-type epitaxial layer 21. The part is ground.

Grinding of the n-type epitaxial layer 21 is performed until, for example, the silicon carbide polycrystalline film 12 is scraped off and the carbon nitride film 41 is exposed on the front surface of the epitaxial substrate 10, that is, the grindstone 14a of the grinding device 14 is the carbon nitride film 41. It is done until it reaches. 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. 18, that is, just reaches the carbon nitride film 41. However, the n-type epitaxial layer 21 may be further ground until a part of the carbon nitride film 41 on the front surface side is scraped off.

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

At this time, the grindstone 14a may advance to the back surface side of the epitaxial substrate 10 more than expected due to the error of the epitaxial substrate 10 in each of the above steps up to the grinding by the grinding device 14 and the error of grinding by the grinding apparatus 14. ..

Even in such a case, since the hardness of the carbon nitride film 41 is higher than the hardness of the n-type epitaxial layer 21 as described above, after the grindstone 14a reaches the carbon nitride film 41, the advancing speed of the grindstone 14a is adjusted to the carbon nitride film. It can be lowered by 41. Therefore, as compared with the case where the carbon nitride film 41 is not provided, it is possible to suppress excessive scraping of the front surface side of the epitaxial substrate 10 due to each error.

Alternatively, the grinding amount of the n-type epitaxial layer 21 may be controlled by stopping the detection by the grinding apparatus 14 when a decrease in the traveling speed of the grindstone 14a is detected instead of the above-mentioned grinding time. As a result, the detection by the grinding apparatus 14 can be stopped when the grindstone 14a reaches the carbon nitride film 41, and it is possible to prevent the front surface side of the epitaxial substrate 10 from being excessively scraped.

To detect a decrease in the traveling speed of the grindstone 14a, for example, a detector that detects a change in stress with respect to grinding of the grinding device 14, a detector that detects the traveling speed of the grindstone 14a using an image obtained by photographing the grinding device 14. Alternatively, it can be performed visually by the manufacturing manager. Even when the grinding amount of the n-type epitaxial layer 21 is controlled by using these detection methods, the grindstone 14a may advance to the back surface side of the epitaxial substrate 10 more than expected due to the detection error by these detection methods. is there.

Even in such a case, after the grindstone 14a reaches the carbon nitride film 41, the traveling 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, it is possible to suppress excessive scraping of the front surface side of the epitaxial substrate 10 due to each error. As a result, 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 recess 11 of the n-type epitaxial layer 21 is removed by dry etcher or ashing. The carbon nitride film 41 can be removed by ashing, for example, by using oxygen plasma obtained by plasmaizing oxygen (O ₂ ) gas at an atmospheric pressure of 5 Pa. As a result, 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. As shown in FIG. 21, the epitaxial substrate 10 is polished from the front surface side using a polishing device and a slurry (slurry) for silicon carbide. For the polishing in step S8, for example, chemical mechanical polishing (CMP) can be used. By polishing, the center line average roughness Ra (specified in JISB0601) is set to 1 μm or less, and the wave center line swell Wca (specified in JISB0610) is set to 10 μm or less.

As described above, when the depth of the recess 11 is set to about 0.7 μm in the grinding of step S6, in the polishing of step S8, for example, the thickness of the portion of the n-type epitaxial layer 21 in which the recess 11 is not formed is, for example. It can be done until it becomes thin by about 0.7 μm. As a result, the recess 11 formed in the n-type epitaxial layer 21 is eliminated, and the epitaxial substrate 10 having a superbonded structure having a flat and smooth front surface 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 element structure described later from being hindered. The epitaxial substrate 10 has, for example, a superbonded structure having a depth of about 23.7 μm. As a result, the front surface of the epitaxial substrate 10 is polished, and step S8 shown in FIG. 1 is completed.

The epitaxial substrate 10 having a superbonded structure can be manufactured by each of the steps shown in FIGS. 2 to 21. A silicon carbide semiconductor device having a superjunction structure can be manufactured by forming an element structure on the manufactured epitaxial substrate 10 by using a stepper or the like and dicing the epitaxial substrate 10 on which the element structure is formed.

As described above, in the manufacturing method according to the embodiment, the carbon nitride film 41 is formed in the recess 11 formed on the front surface of the epitaxial substrate 10. As a result, when the excess portion of the p-type epitaxial layer 24 deposited by embedding the trench 22 is removed by grinding, excessive scraping of the front surface of the epitaxial substrate 10 can be suppressed. Therefore, the above-mentioned parallel pn layer is suppressed from becoming too thin, and the characteristics such as element withstand voltage and on-resistance in the silicon carbide semiconductor device such as SJ-MOSFET and SJ-PN diode manufactured from the epitaxial substrate 10 are as designed. Can be. Therefore, it is possible to improve the yield in the manufacture of the silicon carbide semiconductor device.

FIG. 22 is a diagram showing an example of a metal mask used for sputtering the silicon dioxide film according to the embodiment. FIG. 22 shows the upper surface (the surface opposite to the n-type epitaxial layer 21) of the metal mask 30 installed on the front surface of the epitaxial substrate 10 in the step shown in FIG. 3 in step S2 of 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 ring portion 221 is a ring-shaped portion along the outer circumference of the metal mask 30. The annular portion 221 is provided with four screw holes 221a arranged at equal intervals along the annular shape. The screw holes 221a are provided so as to correspond to the positions of four screw holes provided in the substrate holder (not shown), which is a tray on which the epitaxial substrate 10 is placed.

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

In the step shown in FIG. 3, the epitaxial substrate 10 is placed on the substrate holder, and the metal mask 30 is put on the epitaxial substrate 10. Then, 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, by performing sputtering with the metal mask 30 fixed to the substrate holder, the silicon dioxide film 31 is formed on the front surface of the epitaxial substrate 10 corresponding to the opening 223. Is formed. As a result, in the step shown in FIG. 6, a recess 11 is formed in the portion of the n-type epitaxial layer 21 corresponding to the annular portion 221 and the mask portion 222.

The shape of the mask portion 222 may be determined so that the formed recess 11 has a shape that is easy to see so that the end of polishing can be easily determined in step S8 shown in FIG. For example, as in the example shown in FIG. 22, by making the shape of the opening 223 a shape having a sharp angle toward the center of the metal mask 30, the recess 11 formed has the same shape. As a result, when polishing in step S8, the dent 11 is easily visible, and as described above, it is easy to polish until the dent 11 disappears.

FIG. 23 is a diagram showing an example of a metal mask used for sputtering the carbon nitride film according to the embodiment. FIG. 23 shows the upper surface of the metal mask 40 installed on the front surface of the silicon dioxide film 31 in the step shown in FIG. 7 in step S3 of FIG. As shown in FIG. 23, the metal mask 40 has the same circular shape as the metal mask 30 shown in FIG. 22, and has a screw hole 231 and an opening 232. The portion of the metal mask 40 excluding the screw hole 231 and the opening 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 positions of the four screw holes provided in the above-mentioned substrate holder. Four openings 232 are provided in the portion corresponding to the mask portion 222 of the metal mask 30 shown in FIG. 22. Further, the four openings 232 are formed at point-symmetrical positions and shapes 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. 22, a fan shape, a circle, a square, a rectangle, a triangle, or a combination thereof. It can be in various shapes such as.

In the process shown in FIG. 7, the epitaxial substrate 10 is placed on the substrate holder and the metal mask 40 is put on the epitaxial substrate 10. Then, 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 step 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 sputtering in the state of being screwed 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 showing an example of the epitaxial substrate according to the embodiment. By steps S1 to S9 shown in FIG. 1, for example, the epitaxial substrate 10 shown in FIG. 24 is manufactured. The plurality of lattice-shaped element structure forming regions 241 are regions (shots) in which the element structure is formed by the stepper used for manufacturing the epitaxial substrate 10.

The hard material forming 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 forming region 242 of FIG. 24, the carbon nitride film 41 is formed in a portion near the outer periphery of the epitaxial substrate 10, which is different from the element structure forming region 241 in which the element structure is formed. Further, the carbon nitride film 41 is formed point-symmetrically about the center of the epitaxial substrate 10. However, the carbon nitride film 41 is removed in the steps shown in steps S7 and 20 of FIG. Therefore, the epitaxial substrate 10 shown in FIG. 24 does not include the carbon nitride film 41.

Further, the epitaxial substrate 10 may be provided with orientation flats 243 and 244. The orientation flats 243 and 244 are notches on a straight line for aligning the orientation of the epitaxial substrate 10 (wafer).

By dicing the epitaxial substrate 10 shown in FIG. 23 along the boundary between the element structure forming regions 241 and individualizing each of the element structure forming regions 241 into chips, a silicon carbide semiconductor device having a superbonded structure can be obtained. Can be manufactured.

FIG. 25 is a flowchart 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 by step S7 has been described in FIG. 1, the manufacturing method is not limited to such a manufacturing method. For example, if the carbon nitride film 41 remains but has little effect on the formation of the element structure in the subsequent process, 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. Further, 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 until, for example, the height of the front surface of the epitaxial substrate 10 reaches the height of the front surface of the carbon nitride film 41 that has not been removed.

When the epitaxial substrate 10 having an element structure is manufactured by a manufacturing method that omits the step of removing the carbon nitride film 41, for example, the metal mask 40 is used so that the carbon nitride film 41 is not formed on the above-mentioned dicing line. The opening 232 is formed. As a result, it is possible to prevent the remaining carbon nitride film 41 from hindering dicing.

Alternatively, the carbon nitride film 41 may be removed immediately before dicing, that is, after the above-mentioned polishing. As a result, it is possible to 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. 25, the manufacturing process of the epitaxial substrate 10 can be reduced and the manufacturing cost of the epitaxial substrate 10 can be suppressed.

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

The mask portion 261 is provided so as to be connected to the annular portion 221 and the portion surrounded by the annular portion 221 and the mask portion 261 is a portion corresponding to the element structure forming region 241 (for example, see FIG. 24) of the epitaxial substrate 10. Has been done. The mask portion 262 is connected to the annular portion 221 and is provided in an elongated shape so as to bisect the portion surrounded by the annular portion 221 and the mask portion 261. Further, 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 line for dicing.

Of the metal mask 30 shown in FIG. 26, two portions surrounded by the annular portion 221 and the mask portions 261,262 are open openings 263. As a result, in the process shown in FIG. 3, the silicon dioxide film 31 is formed only in the portion corresponding to the opening 263, that is, the portion in which the device structure forming region 241 is formed. As a result, in the step shown in FIG. 6, a recess 11 is formed in the portion of the n-type epitaxial layer 21 corresponding to the annular portion 221 and the mask portion 261,262.

FIG. 27 is a diagram showing another example of a 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 designated by the same reference numerals, and the description thereof will be omitted. When the metal mask 30 shown in FIG. 26 is used as the metal mask 30, for example, as the metal mask 40 installed on the front surface of the silicon dioxide film 31 in the step shown in FIG. 7 in step S3 of FIG. The metal mask 40 shown in FIG. 27 can be used.

The metal mask 40 shown in FIG. 27 has the same circular shape as the metal mask 30 shown in FIG. 26, and has an annular portion 271, a mask portion 272, and a connecting portion 273. The annular portion 271 has the same shape as the annular portion 221 of the metal mask 30 shown in FIGS. 22 and 26. The mask portion 272 is two mask portions corresponding to the shapes of the two openings 263 of the metal mask 30 shown in FIG. 26.

A plurality of connecting portions 273 are provided so as to fix and connect the annular portion 271 and the mask portion 272. Further, the connecting portion 273 is provided in an elongated shape within a range in which the strength capable of fixing and connecting the annular portion 271 and the mask portion 272 can be maintained. In the example shown in FIG. 27, the metal mask 40 is provided with 12 connecting portions 273.

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

Of the metal mask 40 shown in FIG. 27, 12 portions surrounded by the annular portion 271, the mask portion 272, and the connecting portion 273 are open openings 274. As a result, in the process shown in FIG. 8, the carbon nitride film 41 is formed at 12 portions of the front surface of the epitaxial substrate 10 corresponding to the opening 274.

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, for example, so that it is easy to determine the end of polishing in step S17 shown in FIG. For example, as in the example shown in FIG. 27, by making the shape of the opening 274 a shape having a sharp angle toward the center of the metal mask 40, the carbon nitride film 41 formed has the same shape. (See, for example, FIG. 28). As a result, for example, when polishing in step S17 shown in FIG. 25, the carbon nitride film 41 can be easily visually recognized, and as described above, it becomes easy to polish until the carbon nitride film 41 is reached.

FIG. 28 is a diagram showing another example of the epitaxial substrate according to the embodiment. In FIG. 28, the same parts as those shown in FIG. 24 are designated by the same reference numerals, and the description thereof will be omitted. When the manufacturing methods of S11 to S17 shown in FIG. 25 are performed and the metal masks 30 and 40 shown in FIGS. 26 and 27 are used at that time, for example, the epitaxial substrate 10 shown in FIG. 28 is manufactured.

Since the carbon nitride film 41 is not removed in the manufacturing method shown in FIG. 25, the carbon nitride film 41 remains on the front surface of the epitaxial substrate 10 as shown in FIG. 28. By not removing the carbon nitride film 41 by ashing or the like in this way, the manufacturing process of the epitaxial substrate 10 can be reduced, and the manufacturing cost of the epitaxial substrate 10 can be suppressed.

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

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

Further, when the metal masks 30 and 40 shown in FIGS. 26 and 27 are used, 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 of step S16 shown in FIG. 25, the vicinity of the center of the epitaxial substrate 10, that is, the portion where the element structure is formed is excessively ground. Can be suppressed.

Further, when the carbon nitride film 41a is formed by using the metal masks 30 and 40 shown in FIGS. 26 and 27, the device structure is formed as shown in FIG. 24 so as to avoid the carbon nitride film 41a as shown in FIG. 28. The region 241 is divided into the element structure forming regions 241a and 241b and arranged. 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 a carbon nitride film 41a (the above-mentioned recess 11) is formed in the gap 241c. As a result, it is possible to prevent the carbon nitride film 41a from affecting the formation of the device structure. The arrangement of the element structure forming region 241 can be adjusted by the shot interval in the above-mentioned stepper forming the element structure.

As described above, in the epitaxial substrate 10, the carbon nitride film 41 is formed not only in the vicinity of the outer periphery surrounding the element structure forming region 241 but also in the gap 241c between the element structure forming regions 241a and 241b, that is, in the vicinity of the center of the epitaxial substrate 10. Can be formed. For this reason, especially when grinding while moving the grinding device 14 smaller than the metal mask 40, it is possible to prevent the grinding device 14 from tilting and grinding too much only in the vicinity of the center of the epitaxial substrate 10, and mainly the epitaxial substrate 10. The surface can be ground uniformly. Further, 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 also possible to perform the manufacturing method shown in FIG. 1 and use the metal masks 30 and 40 shown in FIGS. 26 and 27 at that time. 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 in a state where the carbon nitride film 41 is 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 in a state in which the carbon nitride film 41 having a shape corresponding to the opening 232 of the metal mask 40 shown in FIG. 23 remains.

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 a film using various materials having a hardness higher than that of the n-type epitaxial layer 21 can be used. The Knoop hardness of silicon carbide for growing the n-type epitaxial layer 21 is, for example, about 2400 or more and 3000 or less. Therefore, the hard material film can be, for example, a film using various materials having a Knoop hardness of 3000 or more.

Further, the hard material film is preferably a film using a material whose heat resistant temperature is equal to or higher than the epitaxial growth temperature (for example, about 1700 ° C.) of the p-type epitaxial layer 24. When the step of removing the carbon nitride film 41 is performed, it is desirable that the hard material film is 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. The DLC can be formed by sputtering like the carbon nitride film 41. In this case as well, a DLC film having a higher hardness can be formed by performing sputtering while applying a negative bias. However, DLC sputtering is performed in, for example, argon gas.

As described above, according to the embodiment, a recess different from the trench is provided on the front surface side of the first conductive type semiconductor substrate made of silicon carbide, and a hard material film is formed in the recess. It can be formed. As a result, in the grinding of the second conductive type epitaxial layer after the trench is embedded by the second conductive type epitaxial layer, when the grinding position reaches the hard material film, the progress speed of the grinding can be reduced by the hard material film. Therefore, it is possible to suppress excessive grinding of the second conductive type epitaxial layer and improve the yield of the silicon carbide semiconductor device.

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

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

1 n ⁺ type starting substrate 10 epitaxial substrate 11 depression 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 film 41, 41a Carbon nitride film 61 Photoresist 221,27 Annulus 221a, 231 Screw hole 222, 261,262, 272 Mask part 223, 232, 263, 274 Opening 241,241a, 241b Element structure formation region 241c Gap 242 Hard material forming area 243, 244 Orientation flat 273 Connection

Claims (9)

A first conductive type semiconductor substrate made of silicon carbide is provided with a parallel pn layer in which a first conductive type region and a second conductive type region are alternately and repeatedly arranged in a direction parallel to one main surface of the semiconductor substrate. This is a method for manufacturing a silicon carbide substrate.
A first step of forming a recess from a part of the one main surface of the semiconductor substrate toward 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, and
A third step of forming a trench 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 conductive type epitaxial layer to be the second conductive type region on the one main surface of the semiconductor substrate, the inside of the trench is formed by the second conductive type epitaxial layer. The fourth step of forming the embedded parallel pn layer and
After the second step and the fourth step, the second conductive 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 producing a silicon carbide substrate, which comprises. The method for manufacturing a silicon carbide substrate according to claim 1, wherein in the second step, the recess is formed in a portion of the one main surface of the semiconductor substrate near the outer periphery of the semiconductor substrate. After the fifth step, the sixth step of forming an element structure on the semiconductor substrate is included.
Claim 1 or 2 characterized in that, in the second step, the recess is formed in a portion of the one main surface of the semiconductor substrate that is different from the portion where the element structure is formed by the sixth step. The method for manufacturing a silicon carbide substrate according to the above. 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, the recess is formed in a portion of the one main surface of the semiconductor substrate that surrounds the plurality of portions and a portion in the gap.
The method for manufacturing a silicon carbide substrate according to claim 3, wherein the silicon carbide substrate is manufactured. After the sixth step, a seventh step of dicing the element structure into chips is included.
The method for producing a silicon carbide substrate according to claim 4, wherein the dicing is performed along the gap in the seventh step. The silicon carbide according to any one of claims 1 to 5, wherein in the second step, the hard material film is formed in contact with the bottom surface of the recess and having a film thickness thinner than the depth of the recess. Substrate manufacturing method. The method for producing a silicon carbide substrate according to any one of claims 1 to 6, wherein in the second step, the hard material film having a Knoop hardness of 3000 or more is formed. The method for producing a silicon carbide substrate according to any one of claims 1 to 7, further comprising an eighth step of removing the hard material film after the fifth step. A first conductive type semiconductor substrate made of silicon carbide is provided with a parallel pn layer in which a first conductive type region and a second conductive type region are alternately and repeatedly arranged in a direction parallel to one main surface of the semiconductor substrate. Silicon carbide substrate
The semiconductor substrate has a recess in a direction orthogonal to the main surface of the semiconductor substrate from a portion of the one main surface of the semiconductor substrate that is different from the portion where the element structure is formed, and is harder than the semiconductor substrate. A silicon carbide substrate having a hard material film having a high hardness in the recess.

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