JP2014232799A - Method of manufacturing silicon carbide semiconductor substrate - Google Patents

Abstract

A method for manufacturing a silicon carbide semiconductor substrate having good surface properties is provided.
A step (S10) of preparing a silicon carbide substrate 1 and a step (S20) of forming a silicon carbide semiconductor layer 2 using a source gas on the silicon carbide substrate 1 are provided. In the step of forming silicon carbide semiconductor layer 2 (S20), the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.0 or more and 1.2 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. It is as follows.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor substrate, and more particularly to a method for manufacturing a silicon carbide semiconductor substrate having good surface flatness and few defects.

  In recent years, the use of silicon carbide (SiC) as a material constituting a semiconductor device has been promoted in order to enable a semiconductor device to have a high breakdown voltage and low loss. Silicon carbide is a wide band gap semiconductor having a larger band gap than silicon that has been widely used as a material constituting a semiconductor device. Therefore, by adopting silicon carbide as a material constituting the semiconductor device, it is possible to achieve a high breakdown voltage and a low on-resistance of the semiconductor device. In addition, a semiconductor device that employs silicon carbide as a material has an advantage that a decrease in characteristics when used in a high temperature environment is small as compared with a semiconductor device that employs silicon as a material.

  Since silicon carbide has a very low impurity diffusion coefficient, it is difficult to dope impurities by a thermal diffusion process. As a method for forming an active region in a silicon carbide material, there are a method in which ions are implanted into an epitaxial growth layer and an epitaxial growth method in which an impurity is added by a dopant gas (see, for example, Patent Document 1).

Generally, when growing an n-type epitaxial layer on a silicon carbide substrate, nitrogen (N ₂ ) gas is used as a dopant gas. The growth temperature at this time is generally about 1400 ° C. or higher and 1700 ° C. or lower.

  At this time, there is a correlation between the ratio of the number of carbon (C) atoms to the number of silicon (Si) atoms in the source gas used during epitaxial growth (C / Si ratio) and the surface roughness of the resulting epitaxial substrate. It is known that there is.

JP 2002-280573 A

  Specifically, when the C / Si ratio is high, the surface of the epitaxial substrate becomes rough. For example, when the C / Si ratio is 1.9, the surface roughness Rms is as large as about 2.4 nm.

  On the other hand, it is known that when the C / Si ratio is low, Si droplets are generated on the surface of the epitaxial substrate.

  The present invention has been made to solve the above-described problems. A main object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor substrate having good surface properties.

  A method for manufacturing a silicon carbide semiconductor substrate of the present invention includes a step of preparing a silicon carbide substrate and a step of forming a silicon carbide semiconductor layer on a silicon carbide substrate using a source gas, thereby forming a silicon carbide semiconductor layer In the step, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.05 or more and 1.25 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. or less.

  According to the present invention, a silicon carbide semiconductor substrate having a good surface property can be obtained.

It is sectional drawing of the silicon carbide semiconductor substrate of this Embodiment. It is a flowchart of the manufacturing method of the silicon carbide semiconductor substrate of this Embodiment. It is the schematic of the vapor phase epitaxial growth apparatus used for the manufacturing method of the silicon carbide semiconductor substrate of this Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

  The method for manufacturing a silicon carbide semiconductor substrate according to the present embodiment is a method for manufacturing a silicon carbide semiconductor substrate by stacking a plurality of silicon carbide epitaxial layers having different impurity concentrations on a silicon carbide substrate. First, silicon carbide semiconductor substrate 10 according to the present embodiment will be described with reference to FIG. Silicon carbide semiconductor substrate 10 according to the present embodiment includes a silicon carbide substrate 1 and a silicon carbide semiconductor layer 2 formed on silicon carbide substrate 1.

  Silicon carbide substrate 1 is made of, for example, single crystal silicon carbide. Single crystal silicon carbide has, for example, a hexagonal crystal structure. Silicon carbide substrate 1 includes a main surface 1A.

Silicon carbide semiconductor layer 2 is formed on main surface 1 </ b> A of silicon carbide substrate 1. Silicon carbide semiconductor layer 2 has an n conductivity type, for example. Silicon carbide semiconductor layer 2 has a thickness of, for example, 12 μm. The n-type impurity concentration in silicon carbide semiconductor layer 2 is, for example, about 7.0 × 10 ¹⁵ cm ⁻³ . Silicon carbide semiconductor layer 2 includes main surface 2 </ b> A, and main surface 2 </ b> A serves as the main surface of silicon carbide semiconductor substrate 10.

  Next, with reference to FIGS. 1 and 2, a method for manufacturing the silicon carbide semiconductor substrate of the present embodiment for manufacturing the silicon carbide semiconductor substrate will be described. The method for manufacturing a silicon carbide semiconductor substrate according to the present embodiment includes a step of preparing a silicon carbide substrate (S10), a step of forming a silicon carbide semiconductor layer on the silicon carbide substrate using a source gas (S20), Is provided.

  First, in step (S10), silicon carbide substrate 1 is prepared. Silicon carbide substrate 1 is made of single crystal silicon carbide. Silicon carbide substrate 1 has, for example, a disk shape with a thickness of 350 μm.

  Next, in step (S20), silicon carbide semiconductor layer 2 is formed on silicon carbide substrate 1 prepared in the previous step (S10) using a vapor phase epitaxial growth apparatus. With reference to FIG. 3, in this Embodiment, CVD (Chemical Vapor Deposition) apparatus 100 is used as a vapor phase epitaxial growth apparatus. In the CVD apparatus 100, the substrate holder 11 is surrounded by an induction heating coil 12, a quartz tube 13, a heat insulating material 14, and a heating element 15. Specifically, the heating element 15 has a hollow structure and forms a reaction chamber therein. Substrate holder 11 is provided inside heating element 15 and is formed, for example, such that main surface 1A thereof is flush with the reaction chamber surface when silicon carbide substrate 1 is placed. The heat insulating material 14 is disposed so as to surround the outer periphery of the heating element 15. The quartz tube 13 is disposed so as to surround the outer peripheral side of the heat insulating material 14. The induction heating coil 12 includes a plurality of coil members and is provided, for example, so as to wind the outer peripheral side of the quartz tube 13. When a high frequency current is passed through the induction heating coil 12 as a high frequency coil, the heating element 15 is induction heated by electromagnetic induction. Thereby, silicon carbide substrate 1 and the raw material gas supplied to silicon carbide substrate 1 can be heated to a predetermined temperature.

First, silicon carbide substrate 1 is arranged on substrate holder 11 provided in CVD apparatus 100. Next, a carrier gas containing hydrogen (H ₂ ) and a raw material gas containing monosilane (SiH ₄ ), propane (C ₃ H ₈ ), ammonia (NH ₃ ), and the like, through the pipe 16 in the CVD apparatus 100 Is introduced. At this time, any gas is introduced into the reaction chamber so as to be sufficiently thermally decomposed when supplied onto main surface 1A of silicon carbide substrate 1. Each gas may be mixed before being introduced into the reaction chamber of the CVD apparatus 100 or may be mixed in the reaction chamber of the CVD apparatus 100.

The silicon carbide substrate 1 disposed on the substrate holder 11 is an epitaxially grown film in which nitrogen (N) atoms are doped on the main surface 1A by receiving the supply of the carrier gas and the source gas while being heated. Silicon semiconductor layer 2 is formed. Specifically, silicon carbide semiconductor layer 2 is formed under conditions of a growth temperature of 1500 ° C. to 1700 ° C. and a pressure of 8 × 10 ³ Pa to 12 × 10 ³ Pa. At this time, the n-type impurity concentration in the silicon carbide semiconductor layer 2 is set to about 1 × 10 ¹⁸ cm ⁻³ by adjusting the flow rate of the NH ₃ gas. Silicon carbide semiconductor layer 2 has a thickness of about 10 μm.

  In this step (S20), the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.0 or more and 1.2 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. or less. This is because when the C / Si ratio is lower than 1.0, N can be sufficiently added to the epitaxial layer as an active species, while the number of triangular defects on the main surface 2A of the silicon carbide semiconductor layer 2 This is because of the increase.

Further, when a source gas having a C / Si ratio of 1.3 or more is used, the surface roughness of main surface 2A of silicon carbide semiconductor layer 2 to be formed increases. The ratio of the number of Si atoms to the number of H atoms (Si / H ratio) is 0.0002 or more and 0.0006 or less. The ratio of the number of molecules of ammonia to the number of molecules of hydrogen (NH ₃ / H ₂ ratio) is 2.0 × 10 ⁻⁸ or more and 1.0 × 10 ⁻⁶ or less.

  In the method for manufacturing the silicon carbide semiconductor substrate of the present embodiment, what is particularly important is the C / Si ratio of the source gas used in the step (S20). The inventors of the present invention determined the correlation between the triangular defect density and the surface roughness with the C / Si ratio within the range of 1.0 to 1.9. As a result, it was found that the triangular defect density and the surface roughness on the obtained silicon carbide semiconductor layer have different tendencies with respect to the C / Si ratio. Specifically, it was found that the triangular defect density can be reduced by using a source gas having a high C / Si ratio. On the other hand, it was found that the surface roughness can be reduced more when the raw material gas having a low C / Si ratio is used than when the raw material gas having a high C / Si ratio is used. Furthermore, it has been found that by using a source gas having a C / Si ratio of about 1.05 or more and 1.25 or less, each of the triangular defect density and the surface roughness can be brought to a level having no practical problem. That is, it was found that the silicon carbide semiconductor layer 2 having good surface morphology and few triangular defects can be produced.

  As described above, according to the method for manufacturing a silicon carbide semiconductor device according to the present embodiment, the flatness of the main surface is improved by using the source gas having a C / Si ratio of 1.05 or more in the step (S20). A silicon carbide semiconductor substrate that is high and has few triangular defects can be obtained. Further, since the triangular defect density can be reduced, a silicon carbide semiconductor substrate having a small total number of defects can be obtained.

Next, examples of the present invention will be described.
1. Evaluation sample (i) Example sample 1
First, a silicon carbide substrate having an outer diameter of 3 inches and a thickness of 350 μm was prepared.

Next, a silicon carbide epitaxial layer was grown on the main surface of the silicon carbide substrate using a CVD apparatus, and a silicon carbide semiconductor layer having an impurity concentration of 7.0 × 10 ¹⁵ cm ⁻³ was formed to a thickness of 13 μm. At this time, a carrier gas containing H ₂ and a source gas containing SiH ₄ , C ₃ H ₈ and NH ₃ were introduced into the reaction chamber of the CVD apparatus under the condition that the C / Si ratio was 1.1. The flow rate of H ₂ was 120 slm, the flow rate of SiH ₄ was 46 sccm, the flow rate of C ₃ H ₈ was 29 sccm, and the flow rate of NH ₃ was 5 sccm. The pressure in the growth chamber was 1 × 10 ⁴ Pa and the growth temperature was 1580 ° C.

(Ii) Example sample 2
First, a silicon carbide substrate having an outer diameter of 4 inches and a thickness of 350 μm was prepared. The sample basically had the same configuration as that of Example Sample 1 and was manufactured under the same conditions. However, it differs from Example Sample 1 in that the source gas used to form the silicon carbide semiconductor layer was used under the condition that the C / Si ratio was 1.0.

(Iii) Example Sample 3
First, a silicon carbide substrate having an outer diameter of 6 inches and a thickness of 350 μm was prepared. The sample basically had the same configuration as that of Example Sample 1 and was manufactured under the same conditions. However, it differs from Example Sample 1 in that the source gas used for forming the silicon carbide semiconductor layer is under the condition that the C / Si ratio is 1.2.

(Iv) Comparative sample 1
A silicon carbide substrate having an outer diameter of 3 inches and a thickness of 350 μm was prepared. The silicon carbide semiconductor layer was basically formed under the same conditions as in Example Sample 1 described above. However, it differs from the said Example sample 1 by the point which used the conditions from which C / Si ratio becomes 0.8 about the source gas used for formation of a silicon carbide semiconductor layer.

(V) Comparative sample 2
A silicon carbide substrate having an outer diameter of 3 inches and a thickness of 350 μm was prepared. The silicon carbide semiconductor layer was basically formed under the same conditions as in Example Sample 1 described above. However, it differs from the said Example sample 1 by the point which used the conditions from which C / Si ratio becomes 1.3 about the source gas used for formation of a silicon carbide semiconductor layer.

(Vi) Comparative sample 3
A silicon carbide substrate having an outer diameter of 4 inches and a thickness of 350 μm was prepared. The silicon carbide semiconductor layer was basically formed under the same conditions as in Example Sample 1 described above. However, the source gas used for forming the silicon carbide semiconductor layer is different from the above-described example sample in that the condition that the C / Si ratio is 1.5 is used.

(Vii) Comparative sample 4
A silicon carbide substrate having an outer diameter of 3 inches and a thickness of 350 μm was prepared. The sample basically had the same configuration as that of Example Sample 1 and was manufactured under the same conditions. However, it differs from Example Sample 1 in that the source gas used for forming the silicon carbide semiconductor layer is under the condition that the C / Si ratio is 1.9.

  In this manner, five types of silicon carbide semiconductor substrates manufactured using source gases having different C / Si ratios were manufactured.

2. Experiment Using the atomic force microscope (AFM, Nanoscope IIIa manufactured by Digital Instruments) for the five types of silicon carbide semiconductor substrates obtained as described above, the surface roughness Rq at the center of the measurement area of 10 μm square was determined. It was measured. Furthermore, the number of triangular defects on each main surface (excluding a region 2 mm from the outer peripheral edge) was measured using an optical microscope (Olympus MX51). The density of triangular defects was calculated by dividing the number of measured triangular defects by the area of the main surface of the silicon carbide semiconductor substrate.

3. Results The measurement results are shown in Table 1.

As shown in Table 1, the surface roughness of the main surface of the silicon carbide semiconductor substrate of Example Sample 1 manufactured with a C / Si ratio of 1.1 was as small as 0.30 nm, and the density of triangular defects was 1 It was as low as .9 pieces / cm ² and was good. Further, the surface roughness of the main surface of the silicon carbide semiconductor substrate of Example Sample 3 manufactured with a C / Si ratio of 1.2 was as small as 0.45 nm, and the triangular defect density was as extremely high as 0.3 pieces / cm ^2. Low and good. Although the surface roughness of the main surface of the silicon carbide semiconductor substrate of Example Sample 2 produced with a C / Si ratio of 1.0 is as small as 0.24 nm, the triangular defect density is 3.0 compared to Example Sample 1. Although it was as high as pieces / cm ² , it was within the allowable range. On the other hand, the triangular defect density on the main surface of the silicon carbide semiconductor substrate of Comparative Example Sample 1 manufactured with a C / Si ratio of 0.8 was as high as 25.3 / cm. The surface roughness is [* Delete measurement results if not required]. Although the triangular defect density on the main surface of the silicon carbide semiconductor substrate of Comparative Example Sample 2 produced with a C / Si ratio of 1.3 was as low as 1.8 / cm, the surface roughness was as large as 2.69 nm. . Although the triangular defect density on the main surface of the silicon carbide semiconductor substrate of Comparative Example Sample 3 produced with a C / Si ratio of 1.5 was as low as 1.5 pieces / cm, the surface roughness was as large as 2.55 nm. . The triangular defect density on the main surface of the silicon carbide semiconductor substrate of Comparative Example Sample 4 produced with a C / Si ratio of 1.9 was as low as 0.3 / cm, but the surface roughness was as large as 1.92 nm. .

  In other words, the surface roughness of the silicon carbide semiconductor substrate was reduced when the C / Si ratio was about 1.9, compared to when the surface roughness was about 1.3 or more and 1.5 or less. It was confirmed that when the C / Si ratio is about 1.2 or less, the C / Si ratio can be further reduced as compared with the case where the C / Si ratio is about 1.9. On the other hand, it was confirmed that the triangular defect density on the main surface of the silicon carbide semiconductor substrate tends to decrease as the C / Si ratio increases.

  Here, although there is a part which overlaps with embodiment mentioned above, the characteristic structure of this invention is enumerated.

  The method for manufacturing a silicon carbide semiconductor substrate according to the present invention includes a step of preparing silicon carbide substrate 1 (S10) and a step of forming silicon carbide semiconductor layer 2 on silicon carbide substrate 1 using a source gas (S20). ). In the step of forming silicon carbide semiconductor layer 2 (S20), the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.0 or more and 1.2 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. It is as follows.

  Thus, the surface roughness of main surface 2A of silicon carbide semiconductor substrate 10 can be reduced, and the density of triangular defects on main surface 2A of silicon carbide semiconductor substrate 10 can be reduced. Further, since the triangular defect density can be reduced, a silicon carbide semiconductor substrate having a small total number of defects can be obtained.

  In the step of forming the silicon carbide semiconductor layer, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.1 or more and 1.2 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. or less. Good.

  Thereby, the surface roughness of main surface 2A of silicon carbide semiconductor substrate 10 can be reduced, and the density of triangular defects on main surface 2A of silicon carbide semiconductor substrate 10 can be reduced.

  The source gas may include propane and one selected from the group consisting of monosilane, dichlorosilane, and trichlorosilane.

  Even in this case, the surface roughness of the main surface 2A of the silicon carbide semiconductor substrate 10 can be reduced by setting the C / Si ratio of the source gas to 1.0 or more and 1.2 or less, and the carbonization is performed. Triangular defect density on main surface 2A of silicon semiconductor substrate 10 can be reduced.

  Although the embodiments and examples of the present invention have been described above, various modifications can be made to the above-described embodiments and examples. Further, the scope of the present invention is not limited to the above-described embodiments and examples. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The method for manufacturing a silicon carbide semiconductor substrate of the present invention is particularly advantageously applied to a method for manufacturing a silicon carbide semiconductor substrate that requires a silicon carbide semiconductor substrate having good surface morphology and few defects.

  DESCRIPTION OF SYMBOLS 1 Silicon carbide substrate, 1A, 2A main surface, 2 Silicon carbide semiconductor layer, 10 Silicon carbide semiconductor substrate, 11 Substrate holder, 12 Induction heating coil, 13 Quartz tube, 14 Thermal insulation, 15 Heat generating body, 16 Piping, 100 CVD apparatus.

Claims (3)

Preparing a silicon carbide substrate;
Forming a silicon carbide semiconductor layer on the silicon carbide substrate using a source gas,
In the step of forming the silicon carbide semiconductor layer, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.0 or more and 1.2 or less, and the growth temperature is 1500 ° C. or more and 1700 ° C. or less. A method for manufacturing a silicon carbide semiconductor substrate.   In the step of forming the silicon carbide semiconductor layer, the ratio C / Si of the number of carbon atoms to the number of silicon atoms in the source gas is 1.10 to 1.20, and the growth temperature is 1550 ° C. to 1700 ° C. A method for manufacturing a silicon carbide semiconductor substrate according to claim 1.   3. The method for manufacturing a silicon carbide semiconductor substrate according to claim 1, wherein the source gas includes one selected from the group consisting of monosilane, dichlorosilane, and trichlorosilane, and propane.

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