Semiconductor substrate and method for manufacturing the same

Abstract

To improve the reliability of a semiconductor substrate.SOLUTION: A method for manufacturing a semiconductor substrate comprises: (a) a step of preparing a substrate having a front surface, a rear surface positioned on the opposite side of the front surface, a first inclined part joined to the front surface and a second inclined part joined to the rear surface; (b) a step of forming an epitaxial layer on the front surface and the first inclined part; (c) a step of polishing the rear surface after the step (b); and (d) a step of grinding the first inclined part after the step (c).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a semiconductor substrate and a manufacturing technique thereof, and more particularly to a semiconductor substrate having an inclined portion at an edge thereof and a technique that is effective when applied to the manufacturing technique thereof. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2020-11853 (Patent Document 1) describes a technology that can suppress the occurrence of cracks, chips, and the like during the process of recycling a silicon carbide epitaxial substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-11853 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, the edge of a substrate is prone to cracking or chipping during processing of the substrate, so a sloped portion called a "beveling portion" is formed on the edge of the substrate to prevent cracking or chipping at the edge of the substrate.

[0005] In this regard, the present inventors have found that merely forming a "beveling portion" is not sufficient in terms of reducing the occurrence of defects in semiconductor devices formed on a substrate. Therefore, further ingenuity is desired in order to reduce defects in semiconductor devices. [Means for solving the problem]

[0006] In one embodiment, the substrate comprises a first major surface, a second major surface opposite to the first major surface, a first inclined portion connected to the first major surface, and a second inclined portion connected to the second major surface, wherein the surface roughness of the first inclined portion is smaller than the surface roughness of the second inclined portion.

[0007] A method for manufacturing a substrate in one embodiment includes the steps of: (a) preparing a substrate having a first main surface, a second main surface opposite 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) polishing the second main surface after step (b); and (d) polishing the first inclined portion after step (c). Effect of the Invention

[0008] According to one embodiment, a substrate that reduces defects in semiconductor devices can be provided. [Brief description of the drawings]

[0009] [Figure 1] 3A to 3C are diagrams illustrating a manufacturing process of a recycled substrate in an embodiment. [Diagram 2] 2 is a diagram showing the manufacturing process of the recycled substrate following FIG. 1. [Diagram 3] 3 is a diagram showing the manufacturing process of the recycled substrate following FIG. 2. [Figure 4] 4 is a diagram showing the manufacturing process of the recycled substrate following FIG. 3. [Diagram 5] 5 is a diagram showing the manufacturing process of the recycled substrate following FIG. 4. [Figure 6] FIG. 2 is a diagram showing the structure of a recycled substrate. [Figure 7] 13 is a graph showing the relationship between the inclination angle of the inclined portion and the thickness of the recycled substrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In all the drawings for explaining the embodiments, the same members are generally designated by the same reference numerals, and the repeated explanations thereof will be omitted. In addition, hatching may be applied even to plan views in order to make the drawings easier to understand.

[0011] <Wide band gap semiconductor materials> For example, inverter circuits are used as circuits for controlling motors included in automobiles, home appliances, etc. Power semiconductor elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors) are used in these inverter circuits.

[0012] Such power semiconductor elements are required to have, for example, low on-resistance and low switching loss in addition to high voltage resistance. The current mainstream of power semiconductor elements is a field effect transistor formed on a semiconductor substrate whose main component is silicon, but this power semiconductor element is approaching its theoretical performance limit.

[0013] In this regard, semiconductor elements including field effect transistors formed on a semiconductor substrate whose main component is a semiconductor material having a band gap larger than that of silicon (hereinafter referred to as wide band gap power semiconductor elements) have attracted attention.

[0014] This is because a large band gap means that the material has high dielectric breakdown strength, making it easier to achieve high withstand voltage.

[0015] Furthermore, if the semiconductor material itself has a high dielectric breakdown strength, the withstand voltage can be ensured even if the drift layer that maintains the withstand voltage is made thin. Therefore, for example, the on-resistance of the power semiconductor element can be reduced by making the drift layer thinner and increasing the impurity concentration.

[0016] In other words, wide band gap power semiconductor elements are superior in that they can achieve both improved breakdown voltage and reduced on-resistance, which are in a trade-off relationship with each other. Therefore, wide band gap power semiconductor elements are expected to be semiconductor elements that can achieve high performance.

[0017] Examples of semiconductor materials having a band gap larger than that of silicon include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond, etc. The following description focuses on silicon carbide.

[0018] A single crystal made of silicon carbide (hereinafter referred to as silicon carbide single crystal) is manufactured by using, for example, a sublimation method or a gas phase method. The sublimation method is 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. Alternatively, for example, a solution method can be used. The solution method is a method of manufacturing a silicon carbide single crystal by bringing a seed crystal attached to the tip of a shaft into contact with a solution containing carbon and silicon contained in a crucible, thereby growing a silicon carbide single crystal on the seed crystal while pulling up the shaft.

[0019] The produced silicon carbide single crystal is taken out as an ingot, and the ingot is sliced ​​to obtain a silicon carbide substrate. A power semiconductor element is formed on the silicon carbide substrate thus obtained.

[0020] Here, when forming a power semiconductor element, it is necessary to form a drift layer to function as an element. For this reason, an epitaxial layer that functions as the drift layer is formed on the silicon carbide substrate. That is, a silicon carbide substrate on which an epitaxial layer is formed is used to form a power semiconductor element.

[0021] <Consideration of improvements> For example, in a substrate, a sloped portion called a "beveling portion" is formed to suppress the occurrence of cracks or chips at the edge of the substrate.

[0022] In the following, a silicon carbide substrate will be described as an example of the substrate.

[0023] As described above, an epitaxial layer may be formed on the surface of a silicon carbide substrate. At this time, an inclined portion called a "beveling portion" that is 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 that is connected to the surface. The inclined portion is formed by, for example, a polishing technique, but the surface roughness of the inclined portion is high. For this reason, the epitaxial layer formed on the inclined portion is likely to be defective. This point will be described below.

[0024] 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, the high-temperature atmosphere not only acts to form a film, but also acts as an etching action called "thermal etching." As a result, in an inclined portion with rough surface roughness, the surface unevenness is further increased by "thermal etching," and defects are likely to occur starting from these unevenness. In other words, defects are likely to occur in the epitaxial layer formed on the inclined portion with rough surface roughness, and the defect density of the epitaxial layer formed on the surface of the silicon carbide substrate may increase starting from these defects.

[0025] Furthermore, in the case of a silicon carbide substrate, epitaxial growth is performed by step-flow growth in the <11-20> direction, which may result in the epitaxial layer being formed non-uniformly and irregularly shaped on the inclined portion, which may lead to defects.

[0026] For the above reasons, the propagation of defects occurring at the inclined portion may increase the defect density in the epitaxial layer formed on the surface of the silicon carbide substrate, which may result in defects in the epitaxial layer. That is, the presence of the inclined portion with a rough surface may cause defects in the epitaxial layer formed on the surface of the silicon carbide substrate.

[0027] That is, a defect occurring in the inclined portion may extend to an epitaxial layer formed on a surface (main surface) of the silicon carbide substrate. In this case, if a defect extending to the epitaxial layer exists in a semiconductor device, for example, a power semiconductor element having an epitaxial layer as a drift layer, the device becomes defective.

[0028] <The Benefits of Recycled Substrates> As described above, there are cases where the defect density in the epitaxial layer does not meet a predetermined standard. That is, defects may occur in the epitaxial layer formed on the silicon carbide substrate. In this regard, when the epitaxial layer formed on the silicon carbide substrate is defective even though there is no problem with the silicon carbide substrate, it is not appropriate from the viewpoint of effective utilization of resources to discard the entire silicon carbide substrate on which the defective epitaxial layer is formed.

[0029] Therefore, it has been considered to reuse the silicon carbide substrate remaining after removing the defective epitaxial layer formed on the silicon carbide substrate. That is, an attempt to reuse the silicon carbide substrate by removing the defective epitaxial layer formed on the silicon carbide substrate and then forming a new epitaxial layer on the silicon carbide substrate again has been considered. According to this attempt, since a silicon carbide substrate without any problems can be reused as a reclaimed substrate (reclaim substrate), not only can resources be effectively utilized, but also the manufacturing costs of semiconductor devices and power semiconductor devices manufactured by reusing the silicon carbide substrate can be reduced. Therefore, from the viewpoint of effective utilization of resources and reduction in manufacturing costs of semiconductor devices and power semiconductor devices, it is useful to reuse the silicon carbide substrate.

[0030] <Considerations on recycled substrates> However, in the case of a reclaimed substrate, as in the case of a new substrate (bare substrate: virgin substrate) before reclaiming, if the surface roughness of the inclined portion called the "beveling portion" is rough, defects are likely to occur in the epitaxial layer, as explained in the above-mentioned "Consideration of Improvements". In other words, even if a reclaimed substrate is obtained by removing a defective epitaxial layer formed on a new substrate, if the surface roughness of the inclined portion formed on the reclaimed substrate is rough, defects are likely to occur in the epitaxial layer formed again on the reclaimed substrate. In other words, even if a reclaimed substrate is obtained, if the structure is such that defects are likely to occur in the epitaxial layer formed again on the reclaimed substrate, there is no point in using the reclaimed substrate. Therefore, when manufacturing a reclaimed substrate, it is desirable to devise a method for making it difficult for defects to occur in the epitaxial layer formed again on the reclaimed substrate.

[0031] For example, a "beveling portion" is also formed on a new substrate. Therefore, even when an epitaxial layer is formed on a new substrate, "thermal etching" occurs in the "beveling portion" with a rough surface. However, a recycled substrate is exposed to high temperatures more frequently than a new substrate, and the degree of unevenness caused by "thermal etching" is greater. Therefore, when an epitaxial layer is formed on a recycled substrate, defects in the epitaxial layer are more likely to occur than when an epitaxial layer is formed on a new substrate. For this reason, it is desirable to suppress defects in the epitaxial layer, particularly in recycled substrates.

[0032] Furthermore, when an epitaxial layer is formed on the front surface of a new substrate, the rear surface of the new substrate is placed on, for example, a susceptor. At this time, if the epitaxial growth atmosphere gets around on the rear surface of the new substrate, a convex portion may be formed, or a concave portion may be formed on the rear surface of the new substrate due to "thermal etching" acting on a small gap between the susceptor and the rear surface of the new substrate. As a result, unevenness may be formed on the rear surface of the new substrate.

[0033] When a reclaimed substrate is manufactured from such a new substrate, the back surface of the reclaimed substrate is uneven. In this state, when the back surface of the reclaimed substrate is placed on a susceptor in order to grow an epitaxial layer again on the front surface of the reclaimed substrate, the posture of the reclaimed substrate becomes unstable when the epitaxial layer is grown due to a decrease in flatness of the back surface. As a result, the quality of the epitaxial layer may be degraded. Furthermore, there is an increased possibility that the reclaimed substrate may come off the susceptor. Therefore, when manufacturing a reclaimed substrate, it is desirable to devise a way to improve the flatness of the back surface of the reclaimed substrate.

[0034] In view of this, in the present embodiment, a special effort is made to obtain a highly reliable recycled substrate. The technical concept of this special effort in the present embodiment will be described below.

[0035] <Method of manufacturing recycled substrate in embodiment> First, as shown in Fig. 1, a new substrate 100 made of, for example, a silicon carbide substrate is prepared. This new substrate 100 has a front surface 1 which is a first main surface, and a back surface 2 which is a second main surface located opposite to the first main surface. Then, 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 rougher than the surface roughness of the front surface 1. Similarly, the surface roughness of the inclined portion 4 is rougher than the surface roughness of the back surface 2.

[0036] 2, for example, by using an epitaxial growth method, an epitaxial layer 10 made of silicon carbide is formed on the surface 1 and the inclined portion 3 of the new substrate 100. At this time, the epitaxial growth is performed by step-flow growth in the <11-20> direction. Therefore, the epitaxial layer 10 is formed non-uniformly and indefinitely on the inclined portion 3, and as a result, a convex shape 10A may be formed on the inclined portion 3.

[0037] Also, as shown in FIG. 2, the epitaxial layer 10 may be formed so as to wrap around the rear surface 2 of the new substrate 100, and an attachment 10B consisting of the epitaxial layer 10 attached to the rear surface 2 of the new substrate 100 may be formed.

[0038] 2, when the epitaxial layer 10 is formed, the back surface 2 of the new substrate 100 is placed on a susceptor. At this time, a small gap may be formed between the back surface of the new substrate 100 and the susceptor, and a high-temperature atmosphere may enter this small gap, causing "thermal etching" to proceed. As a result, a recess 20 caused by "thermal etching" may be formed on the back surface 2 of the new substrate 100.

[0039] In this manner, the epitaxial layer 10 can be formed on the surface 1 of the new substrate 100. Here, due to the occurrence 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 surface 1 may exceed a threshold value (prescribed value). In this case, a defective epitaxial layer 10 is formed on the surface 1 of the new substrate 100. Therefore, in this case, in the new substrate 100 on which the defective epitaxial layer 10 is formed, the defective epitaxial layer 10 is removed, and a regenerated substrate is manufactured from the new substrate 100. The manufacturing process of the regenerated substrate will be described below.

[0040] 3, for example, a polishing apparatus 30 is used to polish the rear surface 2 of the new substrate 100. This removes the deposits 10B adhering to the rear surface 2 of the new substrate 100, and flattens the recesses 20 formed on the rear surface 2. As a result, according to the present embodiment, the flatness of the rear surface 2 of the new substrate 100 is improved.

[0041] Next, as shown in Fig. 4, for example, a grinding device 40 using a grindstone is used to remove the epitaxial layer 10 formed on the inclined portion 3 and grind the surface of the inclined portion 3. As a result, according to this 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 this 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).

[0042] Here, the surface roughness referred to in this specification means "Ra". "Ra" is a height-direction parameter called "arithmetic mean roughness". "Ra" is obtained by extracting a portion of the roughness curve measured by a roughness meter over a reference length and expressing the unevenness of that section as an average value. Since "Ra" uses an average value, it is less susceptible to the influence of a single protruding scratch, and has the advantage of providing stable results in evaluating surface roughness.

[0043] Furthermore, additional polishing is performed on the surface of the inclined portion 3, whose surface roughness is less than 200 nm. That is, after grinding with a grinding device 40 using a grindstone in the previous step, further polishing is performed (edge ​​polishing). In this case, the inclined portion 3 is polished so that the surface roughness of the inclined portion 3 becomes less than 1 nm (Ra<1 nm). This further improves the flatness of the surface of the inclined portion 3.

[0044] 5, for example, a polishing apparatus 50A is used to remove defective epitaxial layer 10 formed on front surface 1 of new substrate 100. At this time, a polishing apparatus 50B may be used to polish back surface 2 of new substrate 100 as well.

[0045] In this manner, a reclaimed substrate 100A can be reclaimed from new substrate 100. Thereafter, a new epitaxial layer is formed on surface 1 of the reclaimed substrate 100A. In this manner, even if a defective epitaxial layer 10 is formed on surface 1 of new substrate 100, the defective epitaxial layer 10 can be removed to produce a reclaimed substrate 100A.

[0046] <Production Method Features in the Embodiments> Next, features of the manufacturing method in this embodiment will be described.

[0047] The first characteristic point of the manufacturing method is that, as shown in Figs. 2 and 3, the rear surface 2 of the new substrate 100 is polished by, for example, a polishing device 30. This makes it possible to remove, for example, the deposit 10B shown in Fig. 2, and to flatten the recess 20 formed on the rear surface 2. As a result, according to the first characteristic point of the manufacturing method, the flatness of the rear surface 2 of the new substrate 100 can be improved. This means that the flatness of the rear surface 2 can be improved in the reclaimed substrate 100A finally shown in Fig. 5. In other words, according to the first characteristic point of the manufacturing method, the flatness of the rear surface 2 of the reclaimed substrate 100A can be improved. As a result, when an epitaxial layer is formed again on the reclaimed substrate 100A, the rear surface 2 of the reclaimed substrate 100A is placed on a susceptor, and according to the present embodiment, the flatness of the rear surface 2 is improved.

[0048] A second characteristic of the manufacturing method is that, for example, as shown in Fig. 4, epitaxial layer 10 formed on the surface of inclined portion 3 is removed by grinding device 40, and the surface of inclined portion 3 is also ground. This makes it possible to reduce the surface roughness of inclined portion 3 in reclaimed substrate 100A. This makes it possible to suppress the formation of surface irregularities caused by "thermal etching" when a new epitaxial layer is formed on surface 1 of reclaimed substrate 100A.

[0049] As a result, by implementing the second characteristic feature of the manufacturing method, it is possible to suppress the occurrence of defects due to the rough surface of the inclined portion 3. In other words, the second characteristic feature of the manufacturing method makes it difficult for defects to occur in the new epitaxial layer formed on the inclined portion 3, and it is possible to reduce the defect density of the epitaxial layer formed on the surface 1 of the reclaimed substrate 100A. In other words, by implementing the second characteristic feature of the manufacturing method in this embodiment, it is possible to improve the quality of the epitaxial layer formed on the surface 1 of the reclaimed substrate 100A.

[0050] Furthermore, when a new epitaxial layer is formed on the surface 1 of the reclaimed substrate 100A, the suppression of 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, as shown in Fig. 5, when a defective epitaxial layer 10 formed on the surface 1 is removed by a polishing device 50A, the generation of scratches caused by the adhesion of foreign matter to the surface 1 can be suppressed.

[0051] As a result of the above, the defect rate of the epitaxial layer newly formed on the front surface 1 of the reclaimed substrate 100A can be reduced, and as a result, the manufacturing cost of the power semiconductor element can be reduced.

[0052] Therefore, the first characteristic feature of the manufacturing method suppresses cracks and chips in the reclaimed substrate 100A, and the second characteristic feature of the manufacturing method reduces the defect density in the epitaxial layer, thereby improving the reliability of the reclaimed substrate 100A according to the present embodiment.

[0053] <Structure of Recycled Substrate in the Embodiment> Next, the structure of the reclaimed substrate produced by the above-mentioned production method will be described.

[0054] FIG. 6 is a diagram showing the structure of the regenerated substrate 100A.

[0055] In FIG. 6, 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. In this case, in the regenerated substrate 100A in this embodiment, the surface roughness of the inclined portion 3 is smaller than the surface roughness of the inclined portion 4. This is because, for example, as shown in FIG. 4, 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 additional polishing (edge ​​polishing) is performed on the surface of the inclined portion 3 whose surface roughness is less than 200 nm, the surface roughness of the inclined portion 3 becomes less than 1 nm. Then, as shown in FIG. 6, when the angle between the front surface 1 and the inclined portion 3 is an inclination angle θ1 and the angle between the back surface 2 and the inclined portion 4 is an inclination angle θ2, it is desirable that the inclination angle θ1 is smaller than the inclination angle θ2.

[0056] The above-mentioned inclination angle θ1 is desirably equal to or less than 45°, because if the inclination angle θ1 is greater than 45°, the function of preventing cracking or chipping of the recycled substrate 100A by the inclined portion 3, which is the "beveling portion," decreases.

[0057] On the other hand, it is desirable that the inclination angle θ1 is equal to or greater than the value expressed by the following formula.

[0058] θ1≧0.04t+0.3 t indicates the thickness (μm) of regenerated substrate 100A. Note that Fig. 7 shows the above-mentioned formula showing the relationship between the inclination angle (°) of inclined portion 3 and the thickness (μm) of regenerated substrate 100A.

[0059] When the reclaimed substrate 100A has the inclination angle shown by the above formula, it satisfies the "SEMI standard." That is, the present inventor has newly discovered that when the inclination angle θ1 of the inclined portion 3 has a value that satisfies the above formula, the inclined portion 3 of the reclaimed substrate 100A complies with the "SEMI standard." Therefore, in this embodiment, by grinding or polishing the inclined portion 3 so that it has the inclination angle θ1 that satisfies the above formula, a reclaimed substrate 100A having the inclination angle θ1 that complies with the "SEMI standard" can be obtained.

[0060] <Scope of application of the technical ideas in the embodiment> The technical idea of ​​the present embodiment is effective when applied to a manufacturing technique for the reclaimed substrate 100A. However, the technical idea of ​​the present embodiment is not limited to this, and can also be applied to a manufacturing technique for the new substrate 100, for example.

[0061] For example, the surface roughness of the inclined portion 3 in the new substrate 100 is usually rough, and the presence of the inclined portion 3 with rough surface roughness may increase the probability that the epitaxial layer formed on the surface of the new substrate 100 will be defective.

[0062] In this regard, when the technical idea of ​​this embodiment is applied to new substrate 100, the surface roughness of inclined portion 3 of new substrate 100 can be reduced. This reduces the probability that the epitaxial layer formed on the surface of new substrate 100 will be defective. In other words, by applying the technical idea of ​​this embodiment to new substrate 100, the quality of the epitaxial layer formed on the surface of new substrate 100 can be improved.

[0063] In this way, the technical idea of ​​this embodiment is a useful technical idea in that it can be widely applied not only to the manufacturing technique for reclaimed substrate 100A but also to the manufacturing technique for new substrate 100.

[0064] <The Essence of Technical Ideas> The essence of the technical idea of ​​this embodiment is that the surface roughness of the inclined portion connected to the main surface of the semiconductor substrate (the surface on which the epitaxial layer is formed) is small.

[0065] This reduces defects in the epitaxial layer formed on the inclined portion, thereby reducing defects extending to the epitaxial layer formed on the main surface, thereby improving the quality of the epitaxial layer on the main surface that functions as the drift layer.

[0066] However, simply saying that the surface roughness of the inclined portion is small makes it difficult to quantitatively grasp the difference because there is nothing to compare it to. Therefore, in order to clearly indicate the comparison and express the essence of the technical idea, for example, in a semiconductor substrate having a first main surface, a second main surface located opposite 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 can be expressed as being smaller than the surface roughness of the second inclined portion.

[0067] In this regard, in general technology, the surface roughness of the first inclined portion and the surface roughness of the second inclined portion are approximately the same. In contrast, if the surface roughness of the first inclined portion is smaller than that of the second inclined portion, it is considered that the effect of the technical idea of ​​this embodiment can be obtained even if the degree of difference is small. In this regard, if the degree of difference is small, it may be considered that the surface roughness of the first inclined portion is within the same range as the surface roughness of the second inclined portion.

[0068] 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 how much smaller the surface roughness of the first inclined portion must be than that of the second inclined portion for it to be said that "the surface roughness of the first inclined portion is smaller than that of the second inclined portion" while taking into consideration variations due to individual differences and the measurement accuracy of the measuring device. Thus, in this 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 can be said that "the surface roughness of the first inclined portion is smaller than that of the second inclined portion" beyond the substantially same range.

[0069] From a different perspective, the essence of the technical idea of ​​the present embodiment described above can be expressed by expressing the surface roughness of the inclined portion as an absolute numerical range without using a comparison object (see appendix). In this case, regardless of the surface roughness of the comparison object, if the surface roughness of the inclined portion is within the absolute numerical range, it can be said to be within the scope of the technical idea.

[0070] (Appendix 1) a main surface on which an epitaxial layer can be formed; an inclined portion connected to the main surface; A semiconductor substrate comprising: The surface roughness of the inclined portion is less than 200 nm.

[0071] (Appendix 2) 2. The semiconductor substrate according to claim 1, The surface roughness of the inclined portion is less than 1 nm.

[0072] The invention made by the inventor has been specifically described above based on the embodiment thereof. However, it goes without saying that the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0073] 1 surface 2 Back side 3 Slope 4 Slope 10 Epitaxial layer 10A Convex shape 10B Adhesion 20 Recess 30 Polishing equipment 40 Grinding Equipment 50A polishing equipment 50B Polishing equipment 100 new boards 100A Remanufactured Board

Claims

1. A first major surface; A second main surface located opposite the first main surface; A first inclined portion connected to the first main surface; A second inclined portion connected to the second main surface; A semiconductor substrate comprising: A semiconductor substrate, wherein the surface roughness of the first inclined portion is smaller than the surface roughness of the second inclined portion.

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

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

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

5. 5. The semiconductor substrate according to claim 4, The thickness of the semiconductor substrate is t (μm), When the value of the first tilt angle is θ (°), θ≧0.04t+0.3 The following relationship holds.

6. 2. The semiconductor substrate according to claim 1, The semiconductor substrate has an epitaxial layer formed on the first major surface.

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

8. (a) preparing a substrate having a first main surface, a second main surface located opposite to 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 major surface and on the first inclined portion; (c) after the step (b), polishing the second main surface; (d) after the step (c), grinding the first inclined portion; A method for manufacturing a semiconductor substrate comprising the steps of:

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

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

11. 9. The method for manufacturing a semiconductor substrate according to claim 8, (f) after the step (d), polishing the first inclined portion.

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

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