Semiconductor substrate and method for manufacturing same

Abstract

The technical problem to be solved by the present invention is to improve the reliability of a semiconductor substrate. [Solution] A method for manufacturing a semiconductor substrate includes: (a) a step for preparing a substrate having a front surface, a back surface on the opposite side of the front surface, a first inclined portion continuous with the front surface, and a second inclined portion continuous with the back surface; (b) forming an epitaxial layer on the front surface and the first inclined portion; (c) a step for polishing the back surface after step (b); and (d) after the step (c), grinding the first inclined portion.

Description

Technical Field

[0001] The present invention relates to a semiconductor substrate and a manufacturing technology thereof, and, for example, to a technology that is effective when applied to a semiconductor substrate having an inclined portion at an end portion and a manufacturing technology thereof. Background Art

[0002] Japanese Patent Application Laid-Open No. 2020-11853 (Patent Document 1) describes a technique capable of suppressing the generation of cracks, chips, and the like during the process of regenerating a silicon carbide epitaxial substrate.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-11853 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] For example, cracks or chips are easily generated at the end of the substrate during the processing of the substrate. Therefore, by forming an inclined portion called a "bevel portion" at the end of the substrate, the generation of cracks or chips at the end of the substrate is suppressed.

[0008] In this regard, the inventors of the present invention have found that, from the viewpoint of reducing the occurrence of defects in semiconductor devices formed on a substrate, merely forming a "bevel portion" is not enough. Therefore, further research is desired to reduce the occurrence of defects in semiconductor devices.

[0009] Technical solutions for solving technical problems

[0010] A substrate of one embodiment includes: a first main surface; a second main surface located on the opposite side of the first main surface; a first inclined portion connected to the first main surface; and a second inclined portion connected to the second main surface. Here, the surface roughness of the first inclined portion is smaller than the surface roughness of the second inclined portion.

[0011] A method for manufacturing a substrate in one embodiment includes: (a) a process of preparing a substrate having a first main surface, a second main surface located on the opposite side of the first main surface, a first inclined portion connected to the first main surface, and a second inclined portion connected to the second main surface; (b) a process of forming an epitaxial layer on the first main surface and the first inclined portion; (c) a process of grinding the second main surface after process (b); and (d) a process of grinding the first inclined portion after process (c).

[0012] Effects of the Invention

[0013] According to one embodiment, a substrate capable of reducing defects in semiconductor devices can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing the manufacturing process of the regenerated substrate according to the embodiment.

[0015] Figure 2 It means succession Figure 1 A diagram showing subsequent steps of manufacturing a regenerated substrate.

[0016] Figure 3 It means succession Figure 2 A diagram showing subsequent steps of manufacturing a regenerated substrate.

[0017] Figure 4 It means succession Figure 3 A diagram showing subsequent steps of manufacturing a regenerated substrate.

[0018] Figure 5 It means succession Figure 4 A diagram showing subsequent steps of manufacturing a regenerated substrate.

[0019] Figure 6 It is a diagram showing the structure of a regenerated substrate.

[0020] Figure 7 This is a graph showing the relationship between the inclination angle of the inclined portion and the thickness of the reproduced substrate.

[0021] Description of Reference Numerals

[0022] 1: front side; 2: back side; 3: inclined portion; 4: inclined portion; 10: epitaxial layer; 10A: convex shape; 10B: attachment; 20: concave portion; 30: grinding device; 40: grinding device; 50A: grinding device; 50B: grinding device; 100: new substrate; 100A: regenerated substrate. DETAILED DESCRIPTION

[0023] In all the drawings for describing the embodiments, the same reference numerals are used for the same components in principle, and their repeated descriptions are omitted. In addition, in order to make the drawings easier to understand, hatching may be used even in top views.

[0024] <Wide Bandgap Semiconductor Materials>

[0025] For example, an inverter circuit is used as a circuit for controlling a motor included in an automobile or home appliance, etc. In the inverter circuit, a power semiconductor element represented by a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) is used.

[0026] Such power semiconductor elements require, for example, low on-resistance or low switching loss in addition to high withstand voltage. Here, the current mainstream of power semiconductor elements is a field effect transistor formed on a semiconductor substrate mainly composed of silicon, but this power semiconductor element is close to the theoretical performance limit.

[0027] In this regard, semiconductor devices including field effect transistors formed on a semiconductor substrate mainly composed of a semiconductor material having a larger bandgap than silicon (hereinafter referred to as wide bandgap power semiconductor devices) have attracted attention.

[0028] This is because a large band gap means a high dielectric breakdown strength, and thus a high withstand voltage can be easily achieved.

[0029] Furthermore, if the semiconductor material itself has a high dielectric breakdown strength, the withstand voltage can be ensured even if the drift layer is thinned to maintain the withstand voltage. Therefore, for example, by thinning the drift layer and increasing the impurity concentration, the on-resistance of the power semiconductor element can be reduced.

[0030] That is, the wide bandgap power semiconductor element is excellent in that it is possible to achieve both improvement in withstand voltage and reduction in on-resistance, which are in a trade-off relationship. Therefore, the wide bandgap power semiconductor element is expected to be a semiconductor element capable of achieving high performance.

[0031] Examples of semiconductor materials having a larger band gap than silicon include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond, etc. Hereinafter, the description will focus on silicon carbide.

[0032] A single crystal composed of silicon carbide (hereinafter referred to as a silicon carbide single crystal) is manufactured, for example, by using a sublimation method or a gas phase method. The sublimation method refers to a method of manufacturing a silicon carbide single crystal by sublimating a powder raw material of silicon carbide at a high temperature of about 2400°C and then reprecipitating it. In addition, for example, a solution method can also be used. The solution method refers to a method in which a seed crystal mounted on the front end of a shaft is brought into contact with a solution containing carbon and silicon contained in a crucible, while a silicon carbide single crystal is grown in the seed crystal and the shaft is lifted, thereby manufacturing a silicon carbide single crystal.

[0033] The manufactured silicon carbide single crystal is taken out as an ingot. Then, the ingot is sliced ​​to obtain a silicon carbide substrate. A power semiconductor element is formed on the silicon carbide substrate thus obtained.

[0034] Here, when forming a power semiconductor element, it is necessary to form a drift layer for functioning as an element. Therefore, an epitaxial layer functioning as a drift layer is formed on a silicon carbide substrate. That is, in order to form a power semiconductor element, a silicon carbide substrate with an epitaxial layer formed thereon is used.

[0035] <Discussion on improvement>

[0036] For example, by forming an inclined portion called a "bevel portion" in the substrate, the occurrence of cracks or chips at the end of the substrate is suppressed.

[0037] Hereinafter, a silicon carbide substrate will be described as an example of a substrate.

[0038] As described above, an epitaxial layer is sometimes formed on the surface of a silicon carbide substrate. At this time, an inclined portion called a "bevel portion" connected to the surface is formed at the end of the silicon carbide substrate, and the epitaxial layer is formed not only on the surface of the silicon carbide substrate, but also on the inclined portion connected to the surface. The inclined portion is formed, for example, by a grinding technique, but the surface roughness of the inclined portion becomes larger. Therefore, the epitaxial layer formed on the inclined portion is prone to be defective. This point is explained below.

[0039] For example, when an epitaxial layer is grown by an epitaxial growth method (e.g., CVD (Chemical Vapor Deposition) film formation), the silicon carbide substrate is exposed to a high-temperature atmosphere of about 2000°C. In this case, due to the high-temperature atmosphere, not only a film-forming effect is exerted, but also an etching effect called "thermal etching" is exerted. As a result, in the inclined portion with large surface roughness, the surface unevenness becomes further increased due to "thermal etching", and defects are likely to occur starting from the unevenness. That is, defects are likely to occur in the epitaxial layer formed on the inclined portion with large surface roughness, and sometimes the defect density of the epitaxial layer formed on the surface of the silicon carbide substrate starting from the defect becomes high.

[0040] In addition, in a silicon carbide substrate, epitaxial growth is performed by step flow growth in the <11-20> direction. Therefore, in the inclined portion, since the epitaxial layer is formed unevenly and irregularly, defects may be easily generated.

[0041] Therefore, due to the propagation of defects generated in the inclined portion, the defect density of the epitaxial layer formed on the surface of the silicon carbide substrate becomes high, and as a result, the epitaxial layer may be defective. In other words, due to the presence of the inclined portion with large surface roughness, the epitaxial layer formed on the surface of the silicon carbide substrate may be defective.

[0042] That is, defects generated in the inclined portion sometimes extend to the epitaxial layer formed on the surface (main surface) of the silicon carbide substrate. In this case, in a semiconductor device, such as a power semiconductor element using the epitaxial layer as a drift layer, if there are defects extending to the epitaxial layer, it will become defective.

[0043] <Usefulness of recycled substrates>

[0044] As described above, the defect density in the epitaxial layer may not meet the prescribed standard. In other words, defects may occur in the epitaxial layer formed on the silicon carbide substrate. In this regard, although there is no problem in the silicon carbide substrate, if the epitaxial layer formed on the silicon carbide substrate is defective, it cannot be said that it is appropriate to discard the silicon carbide substrate with the defective epitaxial layer formed thereon from the viewpoint of effective use of resources.

[0045] Therefore, the reuse of the silicon carbide substrate remaining after removing the bad epitaxial layer formed on the silicon carbide substrate is explored. That is, after removing the bad epitaxial layer formed on the silicon carbide substrate, an attempt is explored to reuse the silicon carbide substrate by forming a new epitaxial layer on the silicon carbide substrate again. According to this attempt, the silicon carbide substrate without any problems can be reused as a regenerated substrate (recovered substrate), so not only can resources be used effectively, but also the manufacturing cost of semiconductor devices and power semiconductor devices manufactured by reusing the silicon carbide substrate can be reduced. Therefore, from the perspective of effective use of resources and reducing the manufacturing cost of semiconductor devices or power semiconductor devices, it is useful to reuse the silicon carbide substrate.

[0046] <Study on recycled substrates>

[0047] However, in the regenerated substrate, similarly to the new substrate before regeneration (bare substrate: virgin substrate), if the surface roughness of the inclined portion called the "bevel portion" is large, defects in the epitaxial layer are likely to occur as described in the above-mentioned "Discussion on Improvement". That is, even if a regenerated substrate is obtained by removing the defective epitaxial layer formed on the new substrate, if the surface roughness of the inclined portion formed on the regenerated substrate is large, defects are likely to occur on the epitaxial layer formed again on the regenerated substrate. That is, even if a folded corner or regenerated substrate is obtained, if the structure is likely to cause defects in the epitaxial layer formed again on the regenerated substrate, there is no point in using the regenerated substrate. Therefore, when manufacturing a regenerated substrate, it is desired to conduct research to make the epitaxial layer formed again on the regenerated substrate less likely to cause defects.

[0048] For example, a "bevel portion" is also formed in a new substrate. Therefore, even when an epitaxial layer is formed on a new substrate, "thermal etching" occurs in the "bevel portion" with a large surface roughness. However, in a regenerated substrate, the number of times it is exposed to high temperature becomes greater than that of a new substrate, so the degree of unevenness caused by "thermal etching" is aggravated. Therefore, when an epitaxial layer is formed on a regenerated substrate, it is easy to produce defects in the epitaxial layer compared to the case where the epitaxial layer is formed on a new substrate. Therefore, it is particularly desirable to suppress defects in the epitaxial layer in the regenerated substrate.

[0049] Furthermore, when an epitaxial layer is formed on the front side of the new substrate, the back side of the new substrate is placed on a susceptor, for example. At this time, if the atmosphere of epitaxial growth enters the back side of the new substrate, a convex portion may be formed, and sometimes "thermal etching" acts in a small gap between the susceptor and the back side of the new substrate to form a concave portion on the back side of the new substrate. As a result, concavities and convexities may be formed on the back side of the new substrate.

[0050] Furthermore, if a regenerated substrate is manufactured from such a new substrate, unevenness is formed on the back side of the regenerated substrate. In this state, if the back side of the regenerated substrate is placed on a base in order to grow an epitaxial layer again on the front side of the regenerated substrate, the posture of the regenerated substrate during the epitaxial layer growth becomes unstable due to the reduction in the flatness of the back side. As a result, the quality of the epitaxial layer may be reduced. Moreover, the possibility of a failure causing the regenerated substrate to detach from the base is also increased. Therefore, when manufacturing a regenerated substrate, research is also desired to improve the flatness of the back side of the regenerated substrate.

[0051] Therefore, in this embodiment, research is conducted to obtain a highly reliable regenerated substrate. The technical concept of this embodiment in which this research is conducted will be described below.

[0052] <Method for producing regenerated substrate according to embodiment>

[0053] First, if Figure 1 As shown, for example, a new substrate 100 composed of a silicon carbide substrate is prepared. The new substrate 100 has a front surface 1 as a first main surface and a back surface 2 as a second main surface located on the opposite side of the first main surface. Moreover, an inclined portion 3 connected to the front surface 1 and an inclined portion 4 connected to the back surface 2 are formed at the end of the new substrate 100. Here, for example, the surface roughness of the inclined portion 3 is greater than the surface roughness of the front surface 1. Similarly, the surface roughness of the inclined portion 4 is greater than the surface roughness of the back surface 2.

[0054] Then, if Figure 2 As shown, for example, an epitaxial layer 10 made of silicon carbide is formed on the front surface 1 and the inclined portion 3 of the new substrate 100 by using an epitaxial growth method. At this time, the epitaxial growth is performed by step flow growth in the <11-20> direction. Therefore, the epitaxial layer 10 is formed unevenly and irregularly in the inclined portion 3, and as a result, a convex shape 10A is sometimes formed in the inclined portion 3.

[0055] In addition, if Figure 2 As shown, the epitaxial layer 10 is sometimes formed so as to wrap around the back surface 2 of the new substrate 100 , and sometimes a deposit 10B consisting of the epitaxial layer 10 attached to the back surface 2 of the new substrate 100 is formed.

[0056] Moreover, if Figure 2As shown, when forming the epitaxial layer 10, the back side 2 of the new substrate 100 is placed on the susceptor. At this time, a small gap is sometimes formed between the back side of the new substrate 100 and the susceptor, and sometimes a high-temperature atmosphere enters the small gap to perform "thermal etching". As a result, a recessed portion 20 caused by "thermal etching" is sometimes formed on the back side 2 of the new substrate 100.

[0057] In this way, the epitaxial layer 10 can be formed on the front surface 1 of the new substrate 100. Here, due to the generation of defects caused by the convex shape 10A formed on the inclined portion 3, for example, the defect density of the epitaxial layer 10 formed on the front surface 1 may exceed a threshold value (predetermined value). In this case, a defective epitaxial layer 10 is formed on the front surface 1 of the new substrate 100. Therefore, in this case, the defective epitaxial layer 10 is removed from the new substrate 100 on which the defective epitaxial layer 10 is formed, and a regenerated substrate is manufactured from the new substrate 100. The manufacturing process of the regenerated substrate is described below.

[0058] like Figure 3 As shown, for example, the back side 2 of the new substrate 100 is ground by using a grinding device 30. Thus, the attached matter 10B attached to the back side 2 of the new substrate 100 is removed, and the concave portion 20 formed on the back side 2 is flattened. As a result, according to the present embodiment, the flatness of the back side 2 of the new substrate 100 is improved.

[0059] Then, if Figure 4 As shown, for example, by using a grinding device 40 with a grindstone, the epitaxial layer 10 formed on the inclined portion 3 is removed, and the surface of the inclined portion 3 is ground. Thus, according to the present embodiment, the surface roughness of the inclined portion 3 is reduced. In other words, the flatness of the surface of the inclined portion 3 is improved. Specifically, in the present embodiment, the inclined portion 3 is ground so that the surface roughness of the inclined portion 3 is less than 200 nm (Ra<200 nm).

[0060] Here, the surface roughness mentioned in this specification refers to "Ra". "Ra" refers to a parameter in the height direction called "arithmetic mean roughness". "Ra" is obtained by selecting a part of the roughness curve measured by a roughness meter according to the reference length and expressing the concave and convex state of the section with the average value. "Ra" has the advantage of being not affected by a protruding scratch and obtaining a stable result in evaluating the surface roughness because it uses the average value.

[0061] Furthermore, the surface of the inclined portion 3 having a surface roughness of less than 200 nm is additionally ground. That is, after being ground by the grinding device 40 using a grindstone in the previous stage, further grinding (edge ​​polishing) is performed. In this case, the inclined portion 3 is ground so that the surface roughness of the inclined portion 3 is less than 1 nm (Ra < 1 nm). As a result, the flatness of the surface of the inclined portion 3 is further improved.

[0062] Then, if Figure 5 As shown, for example, by using a polishing device 50A, the defective epitaxial layer 10 formed on the front surface 1 of the new substrate 100 is removed. At this time, the back surface 2 of the new substrate 100 may also be polished by using a polishing device 50B.

[0063] As described above, the regenerated substrate 100A can be regenerated from the new substrate 100. Thereafter, a new epitaxial layer is formed on the front surface 1 of the regenerated regenerated substrate 100A. Thus, even if a defective epitaxial layer 10 is formed on the front surface 1 of the new substrate 100, the defective epitaxial layer 10 can be removed to manufacture the regenerated substrate 100A.

[0064] <Production method features of the embodiment>

[0065] Next, the characteristic points of the manufacturing method of this embodiment will be described.

[0066] The first characteristic point of the method is that Figures 2 to 3 As shown, for example, the back side 2 of the new substrate 100 is ground by a grinding device 30. Thus, for example, it is possible to remove Figure 2 As a result, according to the first characteristic point in the manufacturing method, the flatness of the back side 2 of the new substrate 100 can be improved. This means that, in the end, Figure 5 In the regenerated substrate 100A shown, the flatness of the back surface 2 can be improved. That is, according to the first characteristic point in the manufacturing method, the flatness of the back surface 2 of the regenerated substrate 100A can be improved. As a result, when the epitaxial layer is formed again on the regenerated substrate 100A, the back surface 2 of the regenerated substrate 100A is arranged on the base, but according to this embodiment, the flatness of the back surface 2 is improved.

[0067] Next, the second characteristic point of the manufacturing method is that, for example, Figure 4 As shown, the epitaxial layer 10 formed on the surface of the inclined portion 3 is removed by the grinding device 40, and the surface of the inclined portion 3 is ground. As a result, in the regenerated substrate 100A, the surface roughness of the inclined portion 3 can be reduced. As a result, when a new epitaxial layer is formed on the front surface 1 of the regenerated substrate 100A, the formation of surface irregularities caused by "thermal etching" is suppressed.

[0068] As a result, by implementing the second characteristic point in the manufacturing method, the generation of defects caused by the large surface roughness of the inclined portion 3 can be suppressed. That is, according to the second characteristic point in the manufacturing method, defects are not easily generated in the new epitaxial layer formed on the inclined portion 3, and the defect density of the epitaxial layer formed on the front surface 1 of the regenerated substrate 100A can be reduced. In other words, by implementing the second characteristic point in the manufacturing method of this embodiment, the quality of the epitaxial layer formed on the front surface 1 of the regenerated substrate 100A can be improved.

[0069] In addition, when a new epitaxial layer is formed on the front surface 1 of the regenerated substrate 100A, suppressing the formation of surface irregularities caused by "thermal etching" means that the generation of foreign matter caused by the irregularities can also be suppressed. In this case, for example, Figure 5 As shown, when the defective epitaxial layer 10 formed on the front surface 1 is removed by the polishing device 50A, the generation of scratches due to adhesion of foreign matter to the front surface 1 can be suppressed.

[0070] Therefore, the defect rate of the epitaxial layer newly formed on the front surface 1 of the regenerated substrate 100A can be reduced, and as a result, the manufacturing cost of the power semiconductor element can also be reduced.

[0071] Therefore, according to the first characteristic point in the manufacturing method, cracks or chips of the regenerated substrate 100A are suppressed, and according to the second characteristic point in the manufacturing method, the defect density of the epitaxial layer is reduced. Therefore, according to this embodiment, the reliability of the regenerated substrate 100A can be improved.

[0072] <Structure of Regenerated Substrate According to Embodiment>

[0073] Next, the structure of the reproduced substrate manufactured by the above-mentioned manufacturing method will be described.

[0074] Figure 6 It is a diagram showing the structure of the regenerated substrate 100A.

[0075] exist Figure 6 In the embodiment, the regenerated substrate 100A has a front surface 1, a back surface 2 located on the opposite side of the front surface 1, an inclined portion 3 connected to the front surface 1, and an inclined portion 4 connected to the back surface 2. At this time, in the regenerated substrate 100A of this embodiment, the surface roughness of the inclined portion 3 is smaller than the surface roughness of the inclined portion 4. The reason for this is that, for example, Figure 4 As shown in FIG. 1 , the surface of the inclined portion 3 is ground by a grinding device 40. In particular, the surface roughness of the inclined portion 3 is less than 200 nm. Furthermore, when the surface of the inclined portion 3 having a surface roughness less than 200 nm is additionally ground (edge ​​polishing), the surface roughness of the inclined portion 3 is less than 1 nm. Furthermore, as Figure 6As shown, when the angle between the front surface 1 and the inclined portion 3 is defined as the inclined angle θ1 and the angle between the rear surface 2 and the inclined portion 4 is defined as the inclined angle θ2, the inclined angle θ1 is preferably smaller than the inclined angle θ2.

[0076] The above-mentioned inclination angle θ1 is preferably 45° or less. This is because if the inclination angle θ1 is larger than 45°, the function of the inclined portion 3 as the “bevel portion” to suppress cracks or chips in the reproduced substrate 100A is reduced.

[0077] On the other hand, it is desirable that the inclination angle θ1 is equal to or larger than the value represented by the following formula.

[0078] θ1≥0.04t+0.3

[0079] t represents the thickness (μm) of the regenerated substrate 100A. Figure 7 , the above-mentioned formula showing the relationship between the inclination angle (°) of the inclined portion 3 and the thickness (μm) of the regenerated substrate 100A is shown in FIG.

[0080] In the case of having the tilt angle represented by the above formula, the regenerated substrate 100A satisfies the "SEMI standard". That is, the inventors of the present invention have newly discovered that if the tilt angle θ1 of the tilted portion 3 has a value satisfying the above formula, the tilted portion 3 of the regenerated substrate 100A complies with the "SEMI standard". Therefore, in the present embodiment, the tilted portion 3 is ground or polished to have the tilt angle θ1 satisfying the above formula, thereby obtaining the regenerated substrate 100A having the tilt angle θ1 complying with the "SEMI standard".

[0081] <Scope of application of the technical concept of the embodiment>

[0082] The technical concept of this embodiment is effectively applied to the manufacturing technology of the regenerated substrate 100A. However, the technical concept of this embodiment is not limited thereto, and can also be applied to the manufacturing technology of the new substrate 100, for example.

[0083] For example, generally, since the surface roughness of the inclined portion 3 in the new substrate 100 is large, the probability that the epitaxial layer formed on the surface of the new substrate 100 becomes defective due to the presence of the inclined portion 3 having the large surface roughness may increase.

[0084] In this regard, if the technical concept of this embodiment is applied to the new substrate 100, the surface roughness of the inclined portion 3 in the new substrate 100 can be reduced. Therefore, the probability of the epitaxial layer formed on the surface of the new substrate 100 becoming defective can be reduced. That is, by applying the technical concept of this embodiment to the new substrate 100, the quality of the epitaxial layer formed on the surface of the new substrate 100 can be improved.

[0085] As described above, the technical idea of ​​the present embodiment is useful in that it can be widely applied not only to the manufacturing technology of the regenerated substrate 100A but also to the manufacturing technology of the new substrate 100 .

[0086] <The Essence of Technological Thought>

[0087] The essence of the technical concept of the present embodiment is that the surface roughness of the inclined portion connected to the main surface (the surface where the epitaxial layer is formed) of the semiconductor substrate is small.

[0088] Thus, defects in the epitaxial layer formed on the inclined portion are reduced, resulting in defects extending to the epitaxial layer formed on the main surface being reduced, and the quality of the epitaxial layer on the main surface functioning as a drift layer can be improved.

[0089] However, if only the surface roughness of the inclined portion is small, there is no comparison object, so it is difficult to grasp quantitatively. Therefore, in order to clearly indicate the comparison object and express the essence of the technical idea, for example, it can be expressed as follows: in a semiconductor substrate having a first main surface, a second main surface located on the opposite side of the first main surface, a first inclined portion connected to the first main surface, and a second inclined portion connected to the second main surface, the surface roughness of the first inclined portion is smaller than the surface roughness of the second inclined portion.

[0090] In this regard, in general technology, the surface roughness of the first inclined portion and the surface roughness of the second inclined portion are the same. In contrast, it is considered that as long as the surface roughness of the first inclined portion is less than the surface roughness of the second inclined portion, even if the degree of difference is small, the effect of the technical idea of ​​the present embodiment can be obtained. In this regard, when the degree of difference is small, it may be considered that the surface roughness of the first inclined portion is limited to the same range as the surface roughness of the second inclined portion.

[0091] Therefore, in order to say that the surface roughness of the first inclined portion is substantially smaller than that of the second inclined portion, it is desirable to quantitatively define the extent to which the surface roughness of the first inclined portion is smaller than that of the second inclined portion in consideration of the deviation caused by individual differences or the measurement accuracy of the measuring device. Therefore, in the present embodiment, for example, when the surface roughness of the first inclined portion is smaller than that of the second inclined portion by 100 nm or more, it is substantially beyond the range of the same extent, and it can be said that "the surface roughness of the first inclined portion is smaller than that of the second inclined portion".

[0092] In addition, even if the viewpoint is changed and the comparison object is not used, the essence of the technical idea of ​​the present embodiment described above can be expressed by expressing the surface roughness of the inclined portion in an absolute numerical range (see Supplementary Note). In this case, regardless of the surface roughness of the comparison object, as long as the surface roughness of the inclined portion falls within the absolute numerical range, it can fall within the scope of the technical idea.

[0093] (Note 1)

[0094] A semiconductor substrate comprising:

[0095] a main surface capable of forming an epitaxial layer; and

[0096] An inclined portion connected to the main surface, wherein

[0097] The surface roughness of the inclined portion is less than 200 nm.

[0098] (Note 2)

[0099] The semiconductor substrate according to Supplementary Note 1, wherein:

[0100] The surface roughness of the inclined portion is less than 1 nm.

[0101] As mentioned above, the invention proposed by the present inventors has been specifically described based on the embodiments thereof, but the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the gist thereof.

Claims

1. A semiconductor substrate, characterized in that: have: first main surface; a second main surface located on the opposite side of the first main surface; a first inclined portion connected to the first main surface; and a second inclined portion connected to the second main surface, The surface roughness of the first inclined portion is smaller than the surface roughness of the second inclined portion.

2. The semiconductor substrate according to claim 1, wherein: The surface roughness of the first inclined portion is less than 200 nm.

3. The semiconductor substrate according to claim 1, wherein: The surface roughness of the first inclined portion is less than 1 nm.

4. The semiconductor substrate according to claim 1, wherein: When the angle between the first main surface and the first inclined portion is defined as a first inclined angle, and the angle between the second main surface and the second inclined portion is defined as a second inclined angle, The first inclination angle is smaller than the second inclination angle.

5. The semiconductor substrate according to claim 4, wherein: When the thickness of the semiconductor substrate is t, the unit is μm, and the value of the first inclination angle is θ, the unit is degrees, The relationship of θ≥0.04t+0.3 holds.

6. The semiconductor substrate according to claim 1, wherein: The semiconductor substrate has an epitaxial layer formed on the first main surface.

7. The semiconductor substrate according to claim 1, wherein: The semiconductor substrate is a silicon carbide substrate.

8. A method for manufacturing a semiconductor substrate, characterized in that: include: (a) preparing a substrate having a first main surface, a second main surface located on the opposite side of the first main surface, a first inclined portion connected to the first main surface, and a second inclined portion connected to the second main surface; (b) forming an epitaxial layer on the first main surface and the first inclined portion; (c) after the step (b), a step of grinding the second main surface; and (d) After the step (c), a step of grinding the first inclined portion.

9. The method for manufacturing a semiconductor substrate according to claim 8, wherein: The method comprises the step of (e) removing the epitaxial layer formed on the first main surface after the step (d).

10. The method for manufacturing a semiconductor substrate according to claim 8, wherein: After the step (c), the surface roughness of the first inclined portion is less than 200 nm.

11. The method for manufacturing a semiconductor substrate according to claim 8, wherein: The method comprises the step of (f) grinding the first inclined portion after the step (d).

12. The method for manufacturing a semiconductor substrate according to claim 11, wherein: After the step (f), the surface roughness of the first inclined portion is less than 1 nm.

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