JP2015211114A - Semiconductor substrate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a semiconductor substrate manufacturing method which enables manufacturing of a semiconductor substrate with high yield.SOLUTION: A semiconductor substrate manufacturing method comprises: a step of diffusing phosphorous in a semiconductor substrate with a surface layer composed of silicon; a step (S101) of perform wet etching by a hydrofluoric acid-containing solution; a step (S103) of forming an oxide film by a wet oxidation treatment of the semiconductor substrate; a step (S104) of removing the oxide film by a hydrofluoric acid-containing solution; a step (S105) of performing rinse treatment on a surface of the semiconductor substrate; and a step (S106) of drying and dehydrating the surface of the semiconductor substrate after the step of the rinse treatment.

Description

  The present invention relates to a method for manufacturing a semiconductor substrate.

There is a thermal diffusion process for forming a pn junction in a manufacturing process of a semiconductor device using a silicon substrate, for example, a solar battery cell. For example, when phosphorus diffusion is performed on a p-type silicon substrate, the following method is used. A phosphorus glass film is formed on the surface of a p-type silicon substrate by heating in the presence of phosphorous oxychloride (POCl ₃ ) vapor, and this p-type silicon substrate is put into a thermal oxidation furnace, and phosphorus from the phosphorus glass into silicon A phosphorus diffusion layer that becomes an n-type silicon layer is formed on the surface of the p-type silicon substrate by thermal diffusion. At that time, phosphorous glass containing glass as a main component is formed on the surface of the phosphorous diffusion layer, and if phosphorous glass remains, cell conversion efficiency is lowered, so that phosphorous glass is removed. A cleaning process is required.

In general, a cleaning process for removing phosphorus glass is performed by first performing phosphorus by wet etching using a solution containing HF such as hydrofluoric acid (HF) or mixed acid (HF / HNO ₃ / H ₂ SO ₄ ). It consists of removing glass, rinsing with pure water, and draining and drying the silicon substrate. In particular, draining / drying processing in solar cells may be performed by high-temperature air blow (about 50 ° C. to 200 ° C.) from the top, bottom, left, and right directions to the cell instead of spin drying or IPA drying to reduce tact and cost is there.

  In such draining / drying treatment, there is a problem that water remains easily, and a watermark is easily generated in a portion where the water remains. When the watermark is generated, the surface of the silicon substrate may become cloudy and the appearance may be deteriorated, resulting in a decrease in yield, or film peeling or film quality deterioration may be caused in a subsequent film forming process.

  In order to solve these problems, for example, Patent Document 1 discloses a technique of performing a wet etching process again with a solution containing HF after a general cleaning process.

JP-A-5-29292

  However, in the conventional cleaning method, a watermark may be generated when draining / drying is performed. Further, in Patent Document 1, it is said that the watermark can be removed by performing the second HF process again, but the watermark generated by the draining / drying process is the second HF. It turned out that it cannot necessarily remove by the wet etching by the solution containing this. Moreover, after performing the wet etching process with the solution containing HF for the second time, a draining / drying process is required, and a new watermark may be generated at that time, resulting in a decrease in yield.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a semiconductor substrate cleaning method capable of improving the quality of a semiconductor device and producing a semiconductor substrate with a high yield.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a semiconductor substrate according to the present invention includes removing phosphorous glass by a wet etching process using a solution containing hydrofluoric acid, then performing a wet oxidation process, The oxide film is removed by wet etching with a solution containing.

  According to the present invention, a wet oxidation process is performed after the phosphorus glass removal process, and the oxide film is removed to prevent the generation of watermarks, thereby preventing an improvement in quality of semiconductor devices and a decrease in yield due to poor appearance. There is an effect that can be.

FIG. 1 is a flowchart for explaining a phosphorus glass removing step in the method of manufacturing a semiconductor substrate according to the first embodiment. 2A to 2D are process cross-sectional views for explaining a semiconductor substrate manufacturing process according to the first embodiment. FIG. 3 is an electron micrograph of the surface of the semiconductor substrate obtained in the manufacturing process of the semiconductor substrate according to the first embodiment. FIG. 4 is a flowchart for explaining a phosphorus glass removing step in the method of manufacturing a semiconductor substrate according to the third embodiment. FIG. 5 is a process sectional view for explaining the process for manufacturing the semiconductor substrate according to the third embodiment. 6A to 6B are process cross-sectional views for explaining a semiconductor substrate manufacturing process according to the third embodiment. FIG. 7 is a flowchart for explaining the phosphorus glass removing step in the method of manufacturing the semiconductor substrate of the comparative example. 8A to 8D are process cross-sectional views for explaining a manufacturing process of a semiconductor substrate of a comparative example. FIGS. 9A and 9B are electron micrographs of the surface of the semiconductor substrate for explaining the manufacturing process of the semiconductor substrate.

  Embodiments of a method for manufacturing a semiconductor substrate according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment 1 FIG.
As an example of the method for manufacturing a semiconductor substrate of the present invention, FIG. 1 is a flowchart for explaining a phosphorus glass removing step in the method for manufacturing a semiconductor substrate according to the first embodiment, and steps shown in FIGS. A cross-sectional view is shown. In the present embodiment, a silicon substrate 1 is used as a semiconductor substrate. The semiconductor substrate manufacturing method according to the present embodiment is formed on the surface of a silicon substrate 1 that is implemented after a thermal diffusion process for forming a phosphorus diffusion layer 2 on a silicon substrate 1 such as a p-type single crystal silicon substrate as a semiconductor substrate. This relates to the removal process of the phosphorous glass 3. As a method for forming the phosphorus diffusion layer 2, the silicon substrate 1 is put into a thermal oxidation furnace and heated in the presence of phosphorus oxychloride (POCl ₃ ) or phosphorus hydride (PH ₃ ) to thermally diffuse the silicon. A thermal diffusion process for forming the phosphorus diffusion layer 2 on the surface layer of the substrate 1 or a thermal diffusion process for forming the phosphorus diffusion layer 2 by forming a phosphorus glass 3 on the surface of the silicon substrate 1 by CVD and thermally diffusing it. is there. In any of these methods, phosphorous glass 3 is formed on the surface after the thermal diffusion treatment, and a step of removing the phosphorous glass 3 is required, and wet etching treatment is performed.

  As shown in FIG. 1, the method of manufacturing a semiconductor substrate according to the present embodiment includes, after this wet etching process (S101), prior to draining and drying (S106), wet oxidation (S103) and wet etching process (S104). Is to implement. By adding a wet oxidation process (S103) process and a wet etching process (S104) process for removing the oxide film, the phosphorous silicide segregated on the semiconductor substrate surface is removed by the wet etching process (S101). Remove watermarks caused by surface roughness. In addition, the wet oxidation treatment in this embodiment means that an oxide film is formed by being immersed in ozone-oxidized water, hydrogen peroxide water, or pure water at 60 to 100 ° C. In the wet etching process (S101) and the wet etching (S104) for removing the oxide film, rinsing processes (S102) and (S105) using pure water are performed.

Prior to detailed description of the semiconductor substrate manufacturing method according to the present embodiment, a conventional manufacturing method will be described as a comparative example. FIG. 7 is a flowchart of the phosphorus glass removal process of the comparative example. FIG. 8 is a sectional view showing the state of the substrate surface when each treatment is performed. First, at the start of the phosphorus glass removing step, as shown in FIG. 8A, the phosphorus glass 3 is formed on the silicon substrate 1, and the phosphorus diffusion layer 2 is formed on the surface portion in the silicon substrate 1. Is formed. On the other hand, as shown in FIG. 8B, wet etching is performed using a solution containing HF such as hydrofluoric acid (HF) or mixed acid (HF / HNO ₃ / H ₂ SO ₄ ) (S001). As shown in FIG. 8B, the phosphorus glass 3 is removed. Next, rinsing with pure water is performed (S002). Next, blow high-temperature air to the silicon substrate 1 (not spin drying or IPA drying to reduce tact time and cost, but blow high-temperature air (about 50 ° C to 200 ° C) from the top, bottom, left, and right to the cell. Draining / drying treatment is performed (S006). At this time, when the remaining water 4 on the silicon substrate 1 is generated as shown in FIG. 8C, the watermark 5 is formed on the silicon substrate 1 as shown in FIG. 8D.

Here, phosphorus glass removal was performed on 10 silicon substrates having a phosphorus concentration of 0.5 to 2 × 10 ²¹ cm ^{−3 on} the outermost surface of the phosphorus diffusion layer 2 in accordance with a flowchart of a conventional phosphorus glass removal process. . In the wet etching process of step S001 in FIG. 7, the phosphorus glass was removed by dipping in an HF solution. The number of watermarks generated after the phosphorus glass removal step was 5 (occurrence rate 50%). Here, FIG. 9A shows an electron micrograph of the surface of the silicon substrate 1 where no watermark was generated, and FIG. 9B shows the surface of the silicon substrate 1 where the watermark was generated. There was no surface roughness on the silicon substrate in which no watermark was generated, and surface roughness on the order of several nanometers was observed on the silicon substrate 1 in which the watermark 5 was generated.

In general, the surface of a silicon substrate immersed in an HF solution has water repellency and good drainage. However, a silicon substrate with a rough surface has poor drainage during draining / drying treatment, and water remains on the silicon substrate. It became easy and it became clear that it was the cause of the generation of the watermark. As a cause of the surface roughness of the silicon substrate caused by the wet etching process using the HF solution, when the phosphorus concentration on the outermost surface of the phosphorus diffusion layer 2 is 1 × 10 ²¹ cm ⁻³ or more, as shown in FIG. It has been reported that phosphorus silicide (SiP) 6 which is a compound of Si and P is segregated near the interface between the phosphorus glass 3 and the phosphorus diffusion layer 2 (phys. Stat. Sol. (B), 222 (2000), pp. 327-336). From this fact, it is considered that the surface roughness occurred on the silicon substrate after the wet etching process as shown in FIG. 6B because the phosphorus silicide 6 was dissolved in HF and the phosphorus diffusion layer 2 was hardly dissolved in HF. . The thickness of the phosphide silicide 6 is about 0.5 to 3 nm, which coincides with the surface roughness formed on the silicon substrate after the wet etching process. Further, according to this study, even on a silicon substrate having a phosphorus concentration of 0.5 × 10 ²¹ cm ⁻³ on the outermost surface of the phosphorus diffusion layer 2, surface roughness occurs in the silicon substrate after the wet etching process. When the phosphorus concentration on the outermost surface of the diffusion layer 2 is 0.5 × 10 ²¹ cm ⁻³ or more, it is considered that segregation of the phosphorus silicide 6 occurs near the interface between the phosphorus glass 3 and the phosphorus diffusion layer 2.

  In order to suppress the surface roughness of the silicon substrate 1, it is possible to reduce the etching amount of the phosphor silicide 6 by reducing the HF concentration of the HF solution or shortening the immersion time in the HF solution during the wet etching process. . However, when the HF concentration of the HF solution and the immersion time are insufficient, the water repellency of the silicon substrate surface is lowered even if the surface is not roughened, and the water breakage becomes worse during the draining / drying process. It tends to occur. Therefore, in order to suppress the generation of watermarks and prevent the yield from being deteriorated due to poor appearance, the surface roughness generated on the surface of the silicon substrate is suppressed, the wet etching process using a solution containing HF is performed at a constant concentration for a predetermined time,・ It is necessary to improve drainage during the drying process.

In the following first to third embodiments, an example in which the phosphorous concentration of the outermost surface of the phosphorous diffusion layer is 0.5 × 10 ²¹ cm ⁻³ or more over the entire surface of the silicon substrate will be described. The processing shown in this embodiment is also applied to a structure in which the phosphorus concentration on the outermost surface of the phosphorus diffusion layer is 0.5 × 10 ²¹ cm ⁻³ or more in a part of a silicon substrate called a selective emitter structure in the cell. The method is applicable. Hereinafter, the manufacturing method of the semiconductor device of each embodiment will be described in detail.

(Embodiment 1)
FIG. 1 shows a flowchart of a phosphorus glass removing process in the method for manufacturing a semiconductor substrate according to the first embodiment. 2A to 2D are sectional views showing the state of the substrate surface when each treatment in the phosphorus glass removing step according to the present embodiment is performed. First, at the start of the phosphorus glass removing process, as shown in FIG. 2A, the phosphorus glass 3 is formed on the silicon substrate 1, and the phosphorus diffusion layer 2 is formed on the surface portion in the silicon substrate 1. When the phosphorus concentration on the outermost surface of the phosphorus diffusion layer 2 is 0.5 × 10 ²¹ cm ⁻³ or more, the phosphorus silicide 6 is formed on the outermost surface of the phosphorus diffusion layer 2. In this embodiment, wet etching (S101) is performed using a solution containing HF such as hydrofluoric acid (HF) or mixed acid (HF / HNO ₃ / H ₂ SO ₄ )), as shown in FIG. Only the phosphorus glass 3 is removed. Next, rinsing with pure water is performed (S102).

  Next, wet oxidation treatment (S103) is performed to oxidize the surface of the phosphorous diffusion layer 2 as shown in FIG. In the present embodiment, the wet oxidation process is a process of immersing in ozone water or hydrogen peroxide water.

  Next, an oxide film removal process is performed using a solution containing HF (S104). In the oxide film removal process in the present embodiment, the outermost surface of the phosphorus diffusion layer 2 is oxidized by the wet oxidation process to form the surface oxide layer 7, and a solution containing HF is used as shown in FIG. Since the surface oxide layer 7 can be removed simultaneously with the phosphorous silicide 6 when the wet etching process is performed, the surface roughness of the silicon substrate can be suppressed. The thickness of the surface oxide layer 7 removed by the wet etching process is preferably 0.5 to 3 nm from the surface of the phosphorus diffusion layer 2. In the case where the thickness of the surface oxide layer 7 is 0.5 nm or less, since the thickness of the phosphor silicide 6 is smaller than the segregation thickness, the effect of suppressing the surface roughness is lowered. On the other hand, when the thickness of the surface oxide layer 7 is 3 nm or more, surface roughness can be suppressed, but a desired concentration distribution of the phosphorus diffusion layer 2 cannot be obtained.

  Next, after rinsing with pure water (S105), draining and drying (S106) are performed. This draining / drying process is performed by blowing hot air to the silicon substrate 1.

Here, according to the flowchart of the phosphorus glass removing process shown in the present embodiment, the phosphorus glass is applied to 10 semiconductor substrates having a phosphorus concentration of the outermost surface of the phosphorus diffusion layer 2 of 0.5 to 2 × 10 ²¹ cm ^−3. Removal was performed. In the wet etching process (S101), the substrate is immersed in an HF solution to remove only the phosphor glass. The HF concentration and immersion time of the HF solution can be arbitrarily changed under the condition that only the phosphor glass is removed.

Next, rinse treatment (S102) and wet oxidation treatment (S103) are immersed in hydrogen peroxide water H ₂ O ₂ : H ₂ O = 1: 10 at 25 ° C. for 5 minutes, and oxide film removal treatment is immersed in an HF solution. The treatment is performed until the oxide film is removed and the surface of the silicon substrate becomes water repellent. The HF concentration and immersion time of the HF solution can be arbitrarily changed under the condition that the oxide film is removed and the surface of the silicon substrate becomes water repellent.

  Then, rinse treatment (S105) and draining / drying treatment (S106) were performed. As a result, no watermark was seen as shown in FIG. This is considered to be because the surface roughness of the silicon substrate is suppressed and the water drainage on the silicon substrate is improved, so that the watermark generation rate is 0%.

  As described above, in the present embodiment, the phosphorus diffusion layer other than the phosphorus silicide portion segregated to the outermost surface of the phosphorus diffusion layer of 0.5 to 3 nm is oxidized, and the oxide film is removed with a solution containing hydrogen fluoride. A process is added. Thereby, generation | occurrence | production of the watermark which generate | occur | produces at the time of draining / drying process can be suppressed by preventing the surface roughness of a silicon substrate and improving water drainage. In the case where the thickness of the surface oxide layer 7 is 0.5 nm or less, since the thickness of the phosphor silicide 6 is smaller than the segregation thickness, the effect of suppressing the surface roughness is lowered. On the other hand, when the thickness of the surface oxide layer 7 is 3 nm or more, surface roughness can be suppressed, but a desired concentration distribution of the phosphorus diffusion layer 2 cannot be obtained.

  In the present embodiment, an example of wet oxidation by hydrogen peroxide treatment was shown, but the same effect can be obtained by wet oxidation by ozone water treatment, and 0.5 nm to 3 nm regardless of their concentration and time. Similar effects can be obtained if an oxide film is formed.

(Embodiment 2)
A method for manufacturing a semiconductor substrate according to the second embodiment will be described. In the first embodiment, an example of hydrogen peroxide water or ozone water treatment was shown during the wet oxidation process (S103). However, in the second embodiment, it is immersed in high-temperature pure water without using a chemical solution. As shown in FIG. 2C, the surface of the phosphorus diffusion layer 2 can be oxidized to form the surface oxide layer 7 as shown in FIG. Here, when the temperature of the pure water is low, the oxidation does not proceed easily in a short time and the immersion time becomes long, so the high temperature is preferable and 60 ° C to 100 ° C is more preferable. For example, the wet oxidation treatment conditions were immersed in water at 80 ° C. for 10 minutes. Here, all the same processes as in the first embodiment were performed except for the conditions of the wet oxidation process.

  According to the method of the present embodiment, after performing oxidation by immersing in high-temperature pure water, the oxide film removal treatment is performed, whereby the occurrence rate of the watermark becomes 0%. By performing the wet oxidation treatment with pure water, the amount of chemical solution used can be reduced and the manufacturing cost can be reduced.

  As described above, by immersing in pure water heated to 60 ° C. to 100 ° C., the amount of chemical solution used can be reduced in the wet oxidation step, and the manufacturing cost can be reduced. By performing the wet oxidation process and removing the oxide film formed there, it is possible to prevent the surface of the silicon substrate 1 from being roughened and to improve water drainage, thereby suppressing the generation of watermarks that occur during the draining / drying process. .

(Embodiment 3)
FIG. 4 shows a flowchart of the phosphorus glass removing step in the method of manufacturing a semiconductor substrate according to the third embodiment. 5A to 5E are process cross-sectional views illustrating the manufacturing process of the solar cell according to the present embodiment, and show the substrate surface state when each treatment in the phosphor glass removing process is performed. . First, at the start of the phosphorus glass removing process, as shown in FIG. 5A, the phosphorus glass 3 is formed on the silicon substrate 1, and the phosphorus diffusion layer 2 is formed on the surface portion in the silicon substrate 1. When the phosphorus concentration on the outermost surface of the phosphorous diffusion layer 2 is 1 × 10 ²¹ cm ⁻³ or more, the phosphorous silicide 6 is formed on the outermost surface of the phosphorous diffusion layer 2. In the third embodiment, wet etching (S201) is performed using a solution containing HF such as hydrofluoric acid (HF) or mixed acid (HF / HNO ₃ / H ₂ SO ₄ ), as shown in FIG. 5B. Only the phosphorus glass 3 is removed. Next, rinsing with pure water is performed (S202).

  Next, a wet oxidation process (S203) is performed for a short time to form a thin surface oxide layer 7 as shown in FIG. Next, an oxide film removal process using a solution containing an HF solution is performed for a short time, and the thin surface oxide layer 7 is removed as shown in FIG. The wet oxidation (S203) and the wet etching process (S204S1) are repeated a plurality of times until the thickness of the surface oxide layer 7 removed by the wet etching process reaches 0.5 to 3 nm, and finally, as shown in FIG. In addition, a surface with less unevenness can be obtained. In the first embodiment, a surface oxide layer is formed by a single wet oxidation process up to a thickness range of 0.5 to 3 nm where the phosphorous silicide 6 is segregated, and an oxide film removal process is performed with a solution containing HF, thereby surface oxidation. The layer was removed. In general, in the wet oxidation treatment, the oxidation rate is the fastest immediately after being immersed in the solution and decreases with time. By repeatedly performing the wet oxidation treatment (S203) and the wet etching (S204S1) in a short time, the surface oxide layer can be efficiently formed and removed, so that the entire treatment time can be shortened.

  Next, wet treatment is performed using a solution containing HF in order to improve the water repellency on the surface of the silicon substrate and improve water drainage (S204S1). Here, when the wet oxidation process and the oxide film removal process are repeated, the time of the last repeated oxide film removal process may be extended. Thereafter, similarly to the first embodiment, a rinsing process with pure water (S205) is performed, and high temperature air is blown to the silicon substrate to perform a draining and drying process (S206).

Here, according to the flowchart of the phosphorus glass removing process shown in the present embodiment, the phosphorus glass is applied to 10 semiconductor substrates having a phosphorus concentration of the outermost surface of the phosphorus diffusion layer 2 of 0.5 to 2 × 10 ²¹ cm ^−3. Removal was performed. As a wet oxidation treatment (S203), it was immersed in hydrogen peroxide water H ₂ O ₂ : H ₂ O = 1: 10 at 25 ° C. for 0.5 minutes, and immersed in an HF solution as an oxide film removal treatment (S204S1). The oxide layer 7 is removed. Thereafter, the etching amount is measured and compared with a reference value (0.5 to 3 nm) determined in advance (S204S2). If the etching amount is smaller than the reference value, the process returns to the wet oxidation process (S203) again. When it is determined that the etching amount has reached the reference value, the next process, the wet process (S204S3) for improving water drainage, is entered. Here, the wet oxidation process (S203), the oxide film removal process (S204S1), and the etching amount measurement and determination process (S204S2) were repeated three times. However, by setting the HF concentration in the wet process (S204S3) higher than the HF concentration in the oxide film removal process (S204S1), the time required for the surface of the silicon substrate to be water repellent can be shortened.

  Next, the substrate is immersed in an HF solution as a wet treatment (S204S3), and the treatment is performed until the surface of the silicon substrate becomes water-repellent. Thereafter, similarly to Embodiment 1, after rinsing with pure water (S205), high-temperature air was blown to the silicon substrate 1 to perform draining and drying (S206). As a result, the occurrence of watermark was 0%.

  As described above, according to the present embodiment, it is possible to efficiently form and remove the surface oxide layer by repeatedly performing wet oxidation treatment and wet etching in a short time. it can. In the wet oxidation treatment, it is considered that the oxidation rate is the fastest immediately after immersion in the solution and decreases with the passage of time.

  Needless to say, the first to third embodiments described above are particularly effective after the phosphorus glass removal step after phosphorus diffusion, particularly after the formation of a selective emitter structure that requires the formation of a high concentration phosphorus diffusion layer. For example, after forming a separate impurity-containing layer for each region, performing solid phase diffusion from each impurity-containing layer, and then removing the oxide layer containing phosphorous glass in a lump, etc. It can also be applied to a cleaning process.

  In the present embodiment, the step of forming the n-type diffusion layer by phosphorus diffusion on the surface of the p-type silicon substrate has been described, but the compound including the step of forming the n-type diffusion layer by diffusion of the back surface of the n-type silicon substrate is used. The present invention can be applied to a substrate other than a silicon substrate, such as a case where an n-type diffusion layer is formed on the surface of a silicon layer formed on the surface of a semiconductor substrate other than a silicon substrate, such as a semiconductor substrate.

  As described above, the method for manufacturing a semiconductor substrate according to the present invention is a method for cleaning a substrate surface after forming an n-type diffusion layer by phosphorus diffusion on a silicon substrate in a method for manufacturing a solar cell. It is an object of the present invention to provide a semiconductor substrate capable of forming a highly reliable solar cell with no residue.

  1 Silicon substrate, 2 Phosphorus diffusion layer, 3 Phosphorus glass, 4 Water residue, 5 Water mark, 6 Phosphorus silicide (SiP), 7 Surface oxide layer.

Claims (6)

A step of diffusing phosphorus in a semiconductor substrate whose surface layer is made of silicon;
Performing a wet etching process on the semiconductor substrate with a solution containing hydrofluoric acid;
Forming an oxide film by wet oxidation of the semiconductor substrate;
Removing the oxide film with a solution containing hydrofluoric acid;
Rinsing the surface of the semiconductor substrate;
And a step of draining and drying the surface of the semiconductor substrate after the rinsing step. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein an outermost surface concentration of the phosphorus diffusion layer of the semiconductor substrate after the step of diffusing phosphorus is 0.5 × 10 ²¹ cm ⁻³ or more.   The method of manufacturing a semiconductor substrate according to claim 1, wherein the wet oxidation step is a step of generating an oxide film having an oxide film thickness of 0.5 to 3 nm.   The method of manufacturing a semiconductor substrate according to claim 3, wherein the wet oxidation step is an oxidation step using ozone oxidation water or hydrogen peroxide water.   The method for manufacturing a semiconductor substrate according to claim 3, wherein the wet oxidation step is a step of immersing in pure water at 60 ° C. to 100 ° C. 5.   The method for manufacturing a semiconductor substrate according to claim 3, wherein the wet oxidation step and the wet etching treatment step are each performed a plurality of times.