A method of polishing an epitaxial substrate

Abstract

This application relates to the field of semiconductor material preparation technology and discloses a polishing method for epitaxial substrates, specifically including the following steps: S1, sampling and detecting the C concentration, N concentration, and density of BMDs of a certain size in the epitaxial substrate; S2, determining the pH value of the corresponding polishing solution based on the C concentration, N concentration, and the size and density of the BMDs; S3, determining the polishing process parameters of the epitaxial substrate based on the C and N concentrations, including the polishing pressure and rotation speed; S4, performing rough polishing, fine polishing, and high-precision polishing on the epitaxial substrate according to the determined polishing process parameters, and cleaning the epitaxial substrate after polishing to obtain the polished epitaxial substrate. Using this polishing method to polish epitaxial substrates with increased BMD density ensures the gettering effect within the epitaxial substrate while also improving the polishing effect, making this polishing method more applicable to epitaxial substrate polishing.

Description

Technical Field

[0001] This application belongs to the field of semiconductor material preparation technology, specifically relating to a polishing method for epitaxial substrates. Background Technology

[0002] Oxygen deposits are the most important micro-defects in Czochralski silicon single crystals, namely bulk micro-defects (BMDs), which have a significant impact on the properties of single-crystal silicon wafers and the yield of device wafers. Oxygen deposits of suitable size can help improve the mechanical properties of silicon wafers and thus suppress warping in high-temperature processes. In addition, oxygen deposits and their induced defects in the silicon wafer can act as gettering points to effectively adsorb metal contaminants on the silicon wafer surface, i.e., internal gettering. Controlling and utilizing oxygen deposits in device fabrication processes is a core issue in silicon wafer defect engineering. Typically, a clean region free of crystal defects and metal impurities is formed in the near-surface region of the silicon wafer, while forming high-density BMDs in the bulk can improve the yield.

[0003] In epitaxial growth, to grow an epitaxial layer with higher cleanliness, the internal gettering effect of the epitaxial substrate can be improved by increasing the BMD density of the epitaxial substrate. Currently, the BMD density of the epitaxial substrate can be improved by doping C and N elements during crystal growth.

[0004] When the BMD density of an epitaxial substrate is increased, if traditional polishing methods are used, the etching rate and polishing effect of the polishing solution on the epitaxial substrate will change due to the changes in C and N concentrations and the increase in BMD density. This can lead to problems such as over-etching and polishing, resulting in an epitaxial substrate that may not meet the requirements after polishing. Therefore, it is necessary to develop a polishing method suitable for epitaxial substrates with increased BMD density. Summary of the Invention

[0005] The purpose of this application is to provide a polishing method suitable for epitaxial substrates with increased BMD density, so as to improve the polishing effect of epitaxial substrates.

[0006] To achieve the above objectives, the basic solution of this application provides a polishing method for epitaxial substrates, which involves sampling and testing each batch of epitaxial substrates, determining the pH value of the polishing solution for the corresponding batch of epitaxial substrates based on the C concentration, N concentration, and the size and density of the BMD (Body Material Deposits), and determining the polishing process parameters for the corresponding batch of epitaxial substrates based on the C concentration and N concentration to improve the polishing effect. The method specifically includes the following steps.

[0007] S1. Sample each batch of epitaxial substrates and test the C concentration, N concentration, and density of BMD of a certain size in the sample.

[0008] S2. Determine the pH value of the polishing solution used for the corresponding batch of epitaxial substrates based on the C concentration, N concentration, and the size and density of the BMD.

[0009] S3. Determine the polishing process parameters for the corresponding batch of epitaxial substrates based on the C and N concentrations, including the polishing pressure and rotation speed.

[0010] S4. According to the determined polishing process parameters, perform rough polishing, fine polishing and high-precision polishing on the corresponding batch of epitaxial substrates. After polishing, clean the substrate to obtain the polished epitaxial substrate.

[0011] The principle and beneficial effects of this basic scheme are as follows: Before polishing the epitaxial substrate, the C and N concentrations of the sample and the density of BMD of a certain size are sampled and tested. Then, based on the C and N concentrations of the sample and the size and density of the BMD, the pH value of the polishing solution used for this batch of epitaxial substrates is determined. Based on the C and N concentrations, the polishing process parameters for the corresponding batch of epitaxial substrates are determined, including the polishing pressure and rotation speed. Then, the determined polishing process is used to polish the epitaxial substrate. Using the polishing method of this scheme to polish epitaxial substrates with increased BMD density can solve the problem of poor polishing effect caused by traditional polishing methods. While ensuring the getter effect within the epitaxial substrate, it can also improve the polishing effect of the epitaxial substrate. This polishing method has stronger applicability to epitaxial substrate polishing.

[0012] Optionally, the size of the BMD is 40-130 nm, and the density α of the BMD is in the range of 1×10⁻⁶. 8 —2×10 10 pcs / cm 3 .

[0013] Optionally, in S1, the concentration of C is B C The range is 4×10 10 —3×10 14 atoms / cm 3 N concentration B N The range value is 2×10 11 —1×10 16 atoms / cm 3 .

[0014] The polishing method described in this application is more suitable for epitaxial substrates with C and N concentration ranges.

[0015] Optionally, when the concentration of C is B C The range is 4×10 10 atoms / cm 3 ≤B C <6×10 11 atoms / cm 3 N concentration B N The range is 2×10 11atoms / cm 3 ≤B N <8×10 12 atoms / cm 3 And the density a of BMD ranges from 1×10 8 pcs / cm 3 ≤a<7×10 8 pcs / cm 3 When the pH of the polishing solution is 11 < pH ≤ 12; when the concentration of C is B C The range is 6×10 11 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 8×10 12 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 And the density 'a' of BMD ranges from 7 × 10⁻⁶. 8 pcs / cm 3 ≤a≤8×10 9 pcs / cm 3 When the pH of the polishing solution is 9 < pH ≤ 11; when the concentration of C is B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 The density α of BMD ranges from 8 × 10⁻⁶. 9 pcs / cm 3 <a≤2×10 10 pcs / cm 3 At that time, the pH value of the polishing solution was 8 < pH ≤ 9.

[0016] When the C and N concentrations are relatively high, the density of BMD is also relatively high, making the epitaxial substrate more susceptible to etching. In this case, using an alkaline polishing solution with a relatively low pH value (8 < pH ≤ 9) can prevent the epitaxial substrate from being over-etched due to excessively fast etching within the same time period. Conversely, when the C and N concentrations are relatively low, the density of BMD is also relatively low. In this case, using an alkaline polishing solution with a relatively high pH value (11 < pH ≤ 12) can increase the etching rate of the polishing solution on the epitaxial substrate, preventing the epitaxial substrate from being etched too slowly and resulting in insufficient etching depth within the same time period.

[0017] Optionally, in S3, when the concentration of C is B C The range is 4×10 10 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 2×10 11 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 At that time, the polishing pressure F ranges from 25 < F ≤ 45 kPa, and the rotation speed n ranges from 30 < n ≤ 50 rpm; when the concentration of C is B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 At that time, the polishing pressure F ranges from 45 to 55 kPa, and the rotation speed n ranges from 50 to 60 rpm.

[0018] When the C and N concentrations are relatively high, the hardness of the epitaxial substrate will increase. Therefore, a relatively high polishing pressure and rotation speed are required during polishing to ensure the effectiveness of the polishing process. When the C and N concentrations are relatively low, the hardness of the epitaxial substrate will decrease. Therefore, a relatively low polishing pressure and rotation speed are required during polishing.

[0019] Optionally, in step S4, the polishing fluid flow rate is 3-13 L / min during coarse polishing, 1-6 L / min during fine polishing, and 0.5-4 L / min during high-precision polishing.

[0020] Optionally, in step S2, the polishing fluid comprises abrasive, organic alkali, pH adjuster, oxidant, surfactant, chelating agent, and deionized water, with the following weight percentages: abrasive 5%-30%, organic alkali 1%-3%, pH adjuster 3%-15%, oxidant 0.01%-5%, surfactant 0.1%-1.0%, chelating agent 0.01%-1%, and the balance being deionized water.

[0021] In the method of this application, after polishing is completed, the total thickness deviation (TTV) and local flatness (SFQR) of the epitaxial substrate are detected. When the total thickness deviation (TTV) of the epitaxial substrate after polishing is less than 0.1 μm and the local flatness (SFQR) is less than 50 nm, it indicates that the polishing effect is excellent. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the process of this application. Detailed Implementation

[0023] The following detailed description illustrates the specific implementation method:

[0024] A polishing method for epitaxial substrates involves sampling and testing each batch of epitaxial substrates. The pH value of the polishing solution for each batch is determined based on the C and N concentrations of the samples, as well as the size and density of the BMD (biological matrix matte). Polishing process parameters for each batch are determined based on the C and N concentrations to improve the polishing effect. Figure 1 Specifically, it includes the following steps.

[0025] S1. Sample each batch of epitaxial substrates and test the C concentration, N concentration, and density of BMD of a certain size in the samples. C The range is 4×10 10 —3×10 14 atoms / cm 3 N concentration B N The range value is 2×10 11 —1×10 16 atoms / cm 3 The size of the BMD ranges from 40 to 130 nm, and the density value of the BMD ranges from 1 × 10⁻⁶. 8 —2×10 10 pcs / cm 3 During sampling, the first epitaxial substrate from each batch is selected as the sample.

[0026] S2. Determine the pH value of the polishing solution used for the corresponding batch of epitaxial substrates based on the C concentration, N concentration, and the size and density of the BMD.

[0027] When C concentration B C The range is 4×10 10 atoms / cm 3 ≤B C <6×10 11 atoms / cm 3 N concentration B N The range is 2×10 11 atoms / cm 3 ≤B N <8×10 12 atoms / cm 3 And the density a of BMD ranges from 1×10 8 pcs / cm 3 ≤a<7×10 8 pcs / cm 3 When the pH of the polishing solution is 11 < pH ≤ 12; when the concentration of C is B C The range is 6×10 11 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 8×10 12 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 And the density 'a' of BMD ranges from 7 × 10⁻⁶. 8 pcs / cm 3 ≤a≤8×10 9 pcs / cm 3 When the pH of the polishing solution is 9 < pH ≤ 11; when the concentration of C is B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 The density α of BMD ranges from 8 × 10⁻⁶. 9 pcs / cm 3 <a≤2×10 10 pcs / cm 3 At that time, the pH value of the polishing solution was 8 < pH ≤ 9.

[0028] The polishing fluid contains abrasives, organic alkalis, pH adjusters, oxidants, surfactants, chelating agents, and deionized water. The weight percentages of each component are as follows: abrasives 5%-30%, organic alkalis 1%-3%, pH adjusters 3%-15%, oxidants 0.01%-5%, surfactants 0.1%-1.0%, chelating agents 0.01%-1%, and the balance is deionized water.

[0029] S3. Determine the polishing process parameters for the corresponding batch of epitaxial substrates based on the C and N concentrations, including the polishing pressure and rotation speed.

[0030] When C concentration B C The range is 4×10 10 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 2×10 11 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 At that time, the polishing pressure F ranges from 25 < F ≤ 45 kPa, and the rotation speed n ranges from 30 < n ≤ 50 rpm.

[0031] When C concentration B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 At that time, the polishing pressure F ranges from 45 to 55 kPa, and the rotation speed n ranges from 50 to 60 rpm.

[0032] S4. According to the determined polishing process parameters, perform rough polishing, fine polishing and high-precision polishing on the corresponding batch of epitaxial substrates. After polishing, clean the substrate to obtain the polished epitaxial substrate. The flow rate of the polishing slurry during rough polishing is 3-13 L / min, the flow rate of the polishing slurry during fine polishing is 1-6 L / min, and the flow rate of the polishing slurry during high-precision polishing is 0.5-4 L / min.

[0033] Example 1

[0034] The first epitaxial substrate from a certain batch was selected as sample 1. This sample was tested, and the C concentration was found to be 6.25 × 10⁻⁶. 10 atoms / cm 3 The nitrogen concentration was 2.32 × 10⁻⁶. 11 atoms / cm 3 The density of BMD in the 40-130nm range is 6.78×10⁻⁶. 8 pcs / cm 3 Based on the C and N concentrations of the sample, as well as the size and density of the BMD, the pH value of the polishing solution used for polishing this batch of epitaxial substrates was determined to be 11 < pH ≤ 12. Based on the C and N concentrations of the sample, the polishing pressure F for polishing this batch of epitaxial substrates was determined to be in the range of 25 < F ≤ 45 kPa, and the rotation speed n was determined to be in the range of 30 < n ≤ 50 rpm.

[0035] In this embodiment, when performing chemical mechanical polishing on the batch of epitaxial substrates, the pH value of the polishing solution was selected as 12, the polishing pressure was selected as 30 kPa, the rotation speed was selected as 35 rpm, and the polishing temperature was 25-35℃. After the epitaxial substrates were polished, polished epitaxial substrates were obtained. The total thickness deviation (TTV) and local flatness (SFQR) values ​​of any 3 epitaxial substrates in the batch were randomly selected for inspection.

[0036] Example 2

[0037] The first epitaxial substrate from the second batch, serial number 2, was selected as the sample. Testing of this sample revealed a C concentration of 7.14 × 10⁻⁶. 11 atoms / cm 3 The nitrogen concentration was 9.29 × 10⁻⁶. 12 atoms / cm 3 The density of BMD in the 40-130nm range is 7.11×10⁻⁶. 8 pcs / cm 3 Based on the C and N concentrations of the sample, as well as the size and density of the BMD, the pH value of the polishing solution used for polishing this batch of epitaxial substrates was determined to be 9 < pH ≤ 11. Based on the C and N concentrations of the sample, the polishing pressure F for polishing this batch of epitaxial substrates was determined to be in the range of 25 < F ≤ 45 kPa, and the rotation speed n was determined to be in the range of 30 < n ≤ 50 rpm.

[0038] In this embodiment, when performing chemical mechanical polishing on the batch of epitaxial substrates, the pH value of the polishing solution is selected as 10, the polishing pressure is selected as 40 kPa, the rotation speed is selected as 45 rpm, and the polishing temperature is 25-35℃. After the epitaxial substrates are polished, polished epitaxial substrates are obtained. The total thickness deviation (TTV) and local flatness (SFQR) values ​​of any 3 epitaxial substrates in the batch are randomly selected for inspection.

[0039] Example 3

[0040] The first epitaxial substrate from the third batch was selected as a sample. The sample was tested, and the C concentration was found to be 5.34 × 10⁻⁶. 13 atoms / cm 3 The nitrogen concentration was 2.87 × 10⁻⁶. 15 atoms / cm 3 The density of BMD in the 40-130nm range is 9.65×10⁻⁶. 9 pcs / cm 3 Based on the C and N concentrations of the sample, as well as the size and density of the BMD, the pH value of the polishing solution used for polishing this batch of epitaxial substrates was determined to be 8 < pH ≤ 9. Based on the C and N concentrations of the sample, the polishing pressure F for polishing this batch of epitaxial substrates was determined to be in the range of 45 < F ≤ 55 kPa, and the rotation speed n was determined to be in the range of 50 < n ≤ 60 rpm.

[0041] In this embodiment, when performing chemical mechanical polishing on the batch of epitaxial substrates, the pH value of the polishing solution is selected as 9, the polishing pressure is selected as 50 kPa, the rotation speed is selected as 55 rpm, and the polishing temperature is 25-35℃. After the epitaxial substrates are polished, polished epitaxial substrates are obtained. The total thickness deviation (TTV) and local flatness (SFQR) values ​​of any 3 epitaxial substrates in the batch are randomly selected for inspection.

[0042] Comparative Example

[0043] Three different batches of epitaxial substrates were selected, and the first epitaxial substrate from each batch was randomly selected as a sample, numbered 4, 5, and 6 respectively. These three samples were tested, and the C concentrations of the three samples were found to be 7.33 × 10⁻⁶. 10 atoms / cm 3 9.56×10 11 atoms / cm 3 7.36×10 13 atoms / cm 3 The nitrogen concentrations were 3.41 × 10⁻⁶. 11 atoms / cm 3 7.38×10 13 atoms / cm 3 3.74×10 15 atoms / cm 3 The densities of BMD in the 40-130nm range are 3.54 × 10⁻⁶. 8 pcs / cm 3 4.27×10 9 pcs / cm 3 1.22×10 10 pcs / cm3 .

[0044] When performing chemical mechanical polishing on the epitaxial substrate, a traditional polishing process (some parameters of the traditional polishing process used in this embodiment are as follows: the pH value of the polishing solution is 9-12, the polishing pressure is 25-40 kPa, and the rotation speed is 30-55 rpm; in this comparative example, the pH value is 10, the polishing pressure is 35 kPa, and the rotation speed is 40 rpm; the polishing temperature is 25-30℃) is used to polish the epitaxial substrate to obtain the polished epitaxial substrate; the total thickness deviation (TTV) and the local flatness (SFQR) values ​​of any two epitaxial substrates from each of the three batches are sampled and tested.

[0045] When the epitaxial substrate was polished using this method, the TTV of the epitaxial substrate obtained by sampling after polishing was less than 0.1 μm and the SFQR was less than 50 nm, indicating excellent polishing effect. In contrast, when the epitaxial substrate was polished using the traditional polishing method, the TTV value of the epitaxial substrate obtained by sampling after polishing fluctuated around 0.1 μm with relatively large fluctuations, and the SFQR value fluctuated around 50 nm with relatively large fluctuations, indicating unstable polishing effect.

[0046] The above descriptions are merely embodiments of this application. Common knowledge such as specific structures and characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of this application, and these should also be considered within the scope of protection of this application. These will not affect the implementation effect of this application or the practicality of the patent. The scope of protection claimed by this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A polishing method for an epitaxial substrate, characterized in that: Each batch of epitaxial substrates is sampled and tested. The pH value of the polishing solution for the corresponding batch of epitaxial substrates is determined based on the C and N concentrations of the samples, as well as the size and density of bulk microdefects (BMDs). The polishing process parameters for the corresponding batch of epitaxial substrates are determined based on the C and N concentrations to improve the polishing effect. The specific steps include the following: S1. Sample each batch of epitaxial substrates and test the C concentration, N concentration, and density of BMD of a certain size in the sample. S2. Determine the pH value of the polishing solution used for the corresponding batch of epitaxial substrates based on the C concentration, N concentration, and the size and density of the BMD. S3. Determine the polishing process parameters for the corresponding batch of epitaxial substrates based on the C and N concentrations, including the polishing pressure and rotation speed. S4. According to the determined polishing process parameters, perform rough polishing, fine polishing and high-precision polishing on the corresponding batch of epitaxial substrates. After polishing, clean the substrate to obtain the polished epitaxial substrate.

2. The polishing method for an epitaxial substrate according to claim 1, characterized in that: In step S1, the size of the BMD is 40-130 nm, and the density α of the BMD ranges from 1 × 10⁻⁶. 8 —2×10 10 pcs / cm 3 .

3. The polishing method for an epitaxial substrate according to claim 2, characterized in that: In S1, the concentration of C is B C The range is 4×10 10 —3×10 14 atoms / cm 3 N concentration B N The range value is 2×10 11 —1×10 16 atoms / cm 3 .

4. The polishing method for an epitaxial substrate according to claim 3, characterized in that: In S2, When C concentration B C The range is 4×10 10 atoms / cm 3 ≤B C <6×10 11 atoms / cm 3 N concentration B N The range is 2×10 11 atoms / cm 3 ≤B N <8×10 12 atoms / cm 3 And the density a of BMD ranges from 1×10 8 pcs / cm 3 ≤a<7×10 8 pcs / cm 3 At that time, the pH value of the polishing solution was 11 < pH ≤ 12; When C concentration B C The range is 6×10 11 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 8×10 12 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 And the density 'a' of BMD ranges from 7 × 10⁻⁶. 8 pcs / cm 3 ≤a≤8×10 9 pcs / cm 3 At that time, the pH value of the polishing solution was 9 < pH ≤ 11; When C concentration B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 The density α of BMD ranges from 8 × 10⁻⁶. 9 pcs / cm 3 <a≤2×10 10 pcs / cm 3 At that time, the pH value of the polishing solution was 8 < pH ≤ 9.

5. The polishing method for an epitaxial substrate according to claim 4, characterized in that: In S3, When C concentration B C The range is 4×10 10 atoms / cm 3 ≤B C ≤4×10 13 atoms / cm 3 N concentration B N The range is 2×10 11 atoms / cm 3 ≤B N ≤9×10 14 atoms / cm 3 At that time, the polishing pressure F ranges from 25 < F ≤ 45 kPa, and the rotation speed n ranges from 30 < n ≤ 50 rpm; When C concentration B C The range is 4×10 13 atoms / cm 3 <B C ≤3×10 14 atoms / cm 3 N concentration B N The range is 9×10 14 atoms / cm 3 <B N ≤1×10 16 atoms / cm 3 At that time, the polishing pressure F ranges from 45 < F ≤ 55 kPa, and the rotation speed n ranges from 50 < n ≤ 60 rpm.

6. The polishing method for an epitaxial substrate according to claim 1, characterized in that: In step S4, the flow rate of the polishing fluid during coarse polishing is 3-13 L / min, the flow rate of the polishing fluid during fine polishing is 1-6 L / min, and the flow rate of the polishing fluid during precision polishing is 0.5-4 L / min.

7. The polishing method for an epitaxial substrate according to claim 1, characterized in that: In step S2, the polishing fluid comprises abrasive, organic alkali, pH adjuster, oxidant, surfactant, chelating agent, and deionized water, with the following weight percentages: abrasive 5%-30%, organic alkali 1%-3%, pH adjuster 3%-15%, oxidant 0.01%-5%, surfactant 0.1%-1.0%, chelating agent 0.01%-1%, and the remainder being deionized water.

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