A method for distinguishing the silicon side and carbon side of a silicon carbide wafer

Abstract

This application discloses a method for distinguishing the silicon and carbon surfaces of a silicon carbide wafer, belonging to the field of silicon carbide material technology. The method includes the following steps: (1) immersing the silicon carbide wafer in a sulfuric acid or hydrochloric acid solution, followed by cleaning to obtain the wafer to be tested; (2) detecting and comparing the sulfur (S) or chloride (Cl) content on the first and second surfaces of the wafer to be tested, wherein the surface with higher S or Cl content is the carbon surface, and the surface with lower S or Cl content is the silicon surface. This method is applicable to conductive and semi-insulating silicon carbide wafers after cutting, grinding, or polishing, and has advantages such as not being limited by wafer size, being non-destructive to the material, having a simple technical method, a wide range of applications, and high reliability.

Description

Technical Field

[0001] This application relates to a method for distinguishing the silicon surface and carbon surface of a silicon carbide wafer, belonging to the field of silicon carbide material technology. Background Technology

[0002] Currently, there are various methods to distinguish the polar faces of silicon carbide single crystals. Commonly used methods include: edge marking, laser marking, etching, wettability difference, roughness difference, contact potential difference, and X-ray diffraction intensity difference. Among these, edge marking and laser marking are commonly used in industry.

[0003] The positioning edge marking method distinguishes between silicon and carbon surfaces by machining markings on the edge of the ingot. Currently, the common approach is to machine two straight surfaces of different sizes on the ingot, called the primary reference surface and the secondary reference surface, and identify the silicon or carbon surface by their relative positions. However, this method reduces the effective usable area of ​​the substrate due to grinding. As the size of industrial silicon carbide substrates gradually increases, the impact of machining the positioning edge on the usable area gradually increases. For commercial 6-inch substrates, the secondary reference edge is no longer machined; for 8-inch substrates, notches are machined instead. Therefore, for such large-size substrates, laser marking is used to distinguish the silicon and carbon surfaces on the carbon surface. However, laser marking also carries significant risks. If an error occurs in the laser marking and cannot be effectively identified, it can have a significant impact on subsequent wafer processing and epitaxy.

[0004] Atomic force microscopy is used to test the surface of silicon carbide wafers after chemical polishing (CMP). The surface roughness value determines the silicon carbide surface. Although this method does not add any process and does not damage the wafer, it can only be used for wafers after chemical polishing, so its scope of application is narrow.

[0005] Chinese Patent 202010504153.5 discloses a method for determining the polarity of a single crystal using differences in wettability (contact angle). This method utilizes the significant property differences between the carbon and silicon polarities of silicon carbide. A water droplet or other liquid droplet is placed on the surface of the material to be identified, and the contact angle of the droplet is measured. The difference in droplet morphology indicates the property difference between the two polarities: a larger contact angle corresponds to the carbon polarity, and a smaller contact angle corresponds to the silicon polarity. While this method is simple to operate, for silicon carbide surfaces with high surface roughness, the three-phase contact lines encounter resistance during spreading. In this case, the apparent contact angle formed by the droplet on the solid surface is no longer a constant value but fluctuates within a certain range. Measuring only one contact angle value for such solid surfaces cannot fully describe the wetting behavior of the silicon and carbon surfaces. Although this method is a non-destructive analytical characterization method, it has high requirements for the surface processing quality of the silicon carbide wafer, large errors, and low reliability.

[0006] Chinese Patent 202210186965.9 distinguishes between silicon and carbon surfaces by the difference in X-ray diffraction intensity between the silicon and carbon surfaces of conductive silicon carbide wafers and by the unique black core in the growth of conductive silicon carbide crystals. Since semi-insulating substrates do not have crystal nuclei (black cores), this method is not applicable to semi-insulating silicon carbide wafers.

[0007] Chinese patent 202210936141.9 describes a method for distinguishing between silicon and carbon surfaces by measuring the contact potential difference between the two surfaces of a conductive silicon carbide wafer and a conductive probe tip using SKPFM. While this method is non-destructive, it only applies to conductive silicon carbide wafers and is not suitable for semi-insulating silicon carbide wafers. Summary of the Invention

[0008] To address the aforementioned issues, a method for distinguishing the silicon and carbon surfaces of silicon carbide wafers is provided. This method is applicable to conductive and semi-insulating silicon carbide wafers after dicing, grinding, or polishing, and has advantages such as being unrestricted by wafer size, being non-destructive to materials, having a simple technical method, being widely applicable, and having high reliability.

[0009] This application provides a method for distinguishing the silicon surface and the carbon surface of a silicon carbide wafer, comprising the following steps:

[0010] (1) Immerse the silicon carbide wafer in sulfuric acid or hydrochloric acid solution, and then clean it to obtain the wafer to be tested;

[0011] (2) Detect and compare the content of S or Cl elements on the first and second surfaces of the wafer under test, wherein the surface with high content of S or Cl elements is the carbon surface and the surface with low content of S or Cl elements is the silicon surface.

[0012] This application found that immersing silicon carbide wafers in sulfuric acid or hydrochloric acid solutions in the early stages can leave sulfur (S) or chloride (Cl) residues on the silicon and carbon surfaces of the wafers. Due to the different polarities of the silicon and C surfaces, the residual amounts of S or Cl are different during the immersion process. After the same immersion and cleaning process, the content of S or Cl on the two surfaces of the wafer under test is different. Furthermore, it was verified that the surface with a higher content of S or Cl is the carbon surface, while the surface with a lower content of S or Cl is the silicon surface.

[0013] This method discovers the difference in residual S or Cl elements caused by the different polarities of the silicon and carbon surfaces of a wafer, and uses this characteristic to distinguish between the silicon and carbon surfaces of a wafer. It is not limited by the conductivity and processing quality of the wafer, and can be used to detect silicon carbide wafers. It has a wider range of applications, higher reliability, and higher testing accuracy.

[0014] The sulfuric acid and hydrochloric acid soaking used in step (1) can also remove metal or metal oxide impurities from the wafer surface, reducing the impact of impurities. In addition, sulfuric acid or hydrochloric acid is also used for cleaning in other processing and production of silicon carbide wafers. Using the above two solutions to distinguish the silicon side and carbon side of the wafer will not affect the properties of the wafer itself or subsequent processing and production.

[0015] Optionally, the cleaning in step (1) involves rinsing with deionized water for at least 30 seconds and then ultrasonically cleaning the silicon carbide wafer in deionized water for 3-5 minutes to ensure that its surface is completely clean.

[0016] Optionally, in step (1), the concentration of sulfuric acid in the sulfuric acid solution is 2-70 wt%.

[0017] Optionally, in step (1), the concentration of hydrochloric acid in the hydrochloric acid solution is 2-70 wt%.

[0018] The above concentration can remove impurities from the wafer surface and keep the residual amount of S or Cl elements within a reasonable range, thereby increasing the difference of S or Cl elements on the silicon and carbon surfaces, making it easier to quickly distinguish between the silicon and carbon surfaces. At the same time, it can also facilitate operation and reduce pollution and post-processing difficulties.

[0019] Optionally, the soaking time in step (1) shall not be less than 1 minute and the soaking temperature shall be 20-30℃.

[0020] The soaking time and temperature, combined with the concentration of sulfuric acid or hydrochloric acid, can improve the impurity removal rate, enhance the difference in S or Cl elements between the silicon and carbon surfaces, and prevent sulfuric acid or hydrochloric acid from corroding the wafer, thus achieving non-destructive testing.

[0021] Optionally, the content of S or Cl on the first and second surfaces can be detected using a secondary ion mass spectrometer (SIMS) or a total reflectance fluorescence spectrometer (TXRF).

[0022] The aforementioned instruments can directly detect the content of S and Cl elements on the first and second surfaces. Among them, TXRF has the advantages of low detection limit (detectable at pg, ng / ml level and above), high accuracy, availability of internal standard method, simplicity and speed, non-destructive analysis, and simultaneous multi-element analysis. However, this instrument is mainly used for the compositional analysis of micro-area surfaces, and the cost is high for testing large areas. SIMS is also suitable for the compositional analysis and depth profiling of micro-area surfaces, and has high detection sensitivity. However, this instrument is a destructive analysis and the equipment is expensive, resulting in high testing costs.

[0023] While the detection accuracy is high when using the aforementioned detection instruments, they are only suitable for component testing in microscopic areas. If it is necessary to detect larger areas of the wafer, it will increase the detection time and cost, and the equipment is expensive.

[0024] Optionally, in step (2), the content of S or Cl on the first and second surfaces is extracted and detected using an extraction solution:

[0025] An extraction solution is coated onto the first and second surfaces of the wafer to be tested, and after standing, the extraction solution is collected to obtain the first test solution and the second test solution, respectively.

[0026] The first test solution and the second test solution are tested. The content of S or Cl elements in the first test solution represents the content of S or Cl elements on the first surface, and the content of S or Cl elements in the second test solution represents the content of S or Cl elements on the second surface.

[0027] The same extraction solution is used to extract S or Cl elements from the first and second surfaces respectively to obtain the first test solution and the second test solution. Then, by detecting the content of S or Cl elements in the first and second test solutions, the difference in the content of S or Cl elements in the first and second surfaces can be obtained, thereby quickly distinguishing the carbon surface and silicon surface of the wafer.

[0028] The method of extraction and detection using an extraction solution is an indirect detection method. This method is simple, can shorten the detection time, has a low detection limit, can achieve omnidirectional extraction of wafers, and has a smaller error in comparing the differences in S or Cl content on silicon or carbon surfaces.

[0029] Optionally, the solute in the extract includes hydrofluoric acid, and the solvent is ultrapure water.

[0030] During the settling process, the above-mentioned extract can destroy the surface oxide layer of the wafer, thereby attracting the residual S or Cl elements on the wafer surface into the extract, so that the S or Cl element content in the first test solution and the second test solution can respectively represent the S or Cl element content of the first surface and the second surface.

[0031] Those skilled in the art will understand that during the settling process of the above-mentioned extractant, although the extractant extracts S or Cl elements from the wafer surface, it does not extract all the S or Cl elements remaining on the wafer surface. Rather, under the same extraction conditions, the difference in the content of S or Cl elements on the first surface and the second surface is the same as the difference in the content of S or Cl elements in the first test solution and the second test solution, so that the first test solution and the second test solution are representative.

[0032] Optionally, the solute in the extract may also include hydrogen peroxide, which promotes oxidation of the substrate surface, and hydrofluoric acid promotes the destruction of the oxide layer. The interaction between these two substances makes it easier to extract residual sulfur or chloride elements.

[0033] Optionally, the volume fraction of hydrofluoric acid in the extract is 1%-10%, and the volume fraction of hydrogen peroxide in the extract is 1%-10%. These concentrations can increase the dissolution rate of the oxide layer on the wafer surface, improve detection efficiency, and will not damage the wafer.

[0034] Optionally, the settling time in step S2 is not less than 15 seconds. This settling time ensures that the extraction solution effectively extracts from the first and second surfaces of the wafer, and the difference in S or Cl elements in the first and second test solutions can be observed within the settling time.

[0035] Optionally, an inductively coupled plasma mass spectrometer is used to detect the content of S or Cl elements in the first and second test solutions.

[0036] The beneficial effects of this application include, but are not limited to:

[0037] 1. The method for distinguishing the silicon surface and carbon surface of silicon carbide wafers according to this application can be applied to conductive and semi-insulating silicon carbide wafers after cutting, grinding or polishing, and is not limited by wafer size and thickness, which facilitates large-scale industrial application.

[0038] 2. The method for distinguishing the silicon surface and carbon surface of a silicon carbide wafer according to this application has the advantages of not being limited by wafer size, being non-destructive to materials, having a simple technical method, a wide range of applications, and high reliability. Therefore, it has wider applicability and higher reliability and testing accuracy. Attached Figure Description

[0039] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0040] Figure 1 This is a graph showing the ratio of S or Cl elements in the carbon and silicon surfaces of the conductive silicon carbide wafer involved in Test Example 2 of this application after immersion in sulfuric acid or hydrochloric acid.

[0041] Figure 2 This is a graph showing the ratio of S or Cl elements in the carbon and silicon surfaces of the semi-insulating silicon carbide wafer involved in Test Example 2 of this application after it has been soaked in sulfuric acid or hydrochloric acid. Detailed Implementation

[0042] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0043] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0044] Example 1

[0045] This embodiment relates to a method for distinguishing the silicon side and the carbon side of a silicon carbide wafer, including the following steps:

[0046] (1) The conductive silicon carbide wafer was placed in a 2wt% sulfuric acid solution and immersed at 30°C for 1 min. Then it was rinsed with deionized water for 30 s and ultrasonically cleaned in deionized water for 3 min to obtain the wafer to be tested.

[0047] (2) The S element content on the first and second surfaces of the wafer under test is detected and compared by TXRF. The surface with high S element content is the carbon surface, and the surface with low S element content is the silicon surface.

[0048] Example 2

[0049] This embodiment relates to a method for distinguishing the silicon side and the carbon side of a silicon carbide wafer, including the following steps:

[0050] (1) The semi-insulating silicon carbide wafer was placed in a 70wt% sulfuric acid solution and immersed at 20°C for 2 min. Then it was rinsed with deionized water for 40 s and ultrasonically cleaned in deionized water for 5 min to obtain the wafer to be tested.

[0051] (2) SIMS is used to detect and compare the S content on the first and second surfaces of the wafer under test. The surface with high S content is the carbon surface, and the surface with low S content is the silicon surface.

[0052] Example 3

[0053] This embodiment relates to a method for distinguishing the silicon side and the carbon side of a silicon carbide wafer, including the following steps:

[0054] (1) Place the semi-insulating silicon carbide wafer in a 2wt% hydrochloric acid solution and immerse it at 30°C for 1 min. Then rinse it with deionized water for 30 s and place the silicon carbide wafer in deionized water for ultrasonic cleaning for 3 min to obtain the wafer to be tested.

[0055] (2) The first and second surfaces of the wafer to be tested are coated with the extraction solution respectively. After standing, the extraction solution is collected to obtain the first test solution and the second test solution respectively. The extraction solution is hydrofluoric acid solution and the solvent is ultrapure water. The volume fraction of hydrofluoric acid in the extraction solution is 8%.

[0056] Inductively coupled plasma mass spectrometry was used to detect the first and second test solutions. The Cl content in the first test solution represents the Cl content on the first surface, and the Cl content in the second test solution represents the Cl content on the second surface. The surface with a high Cl content is the carbon surface, and the surface with a low Cl content is the silicon surface.

[0057] Example 4

[0058] The difference between this embodiment and Embodiment 3 is that the silicon carbide wafer is placed in a 70wt% hydrochloric acid solution, while the remaining steps are the same as in Embodiment 3.

[0059] Example 5

[0060] The difference between this embodiment and Example 3 is that the extract is a solution of hydrofluoric acid and hydrogen peroxide, and the solvent is ultrapure water. The volume fraction of hydrofluoric acid in this extract is 1%, and the volume fraction of hydrogen peroxide is 10%. The remaining steps are the same as in Example 3.

[0061] Example 6

[0062] The difference between this embodiment and Example 3 is that the extract is a solution of hydrofluoric acid and hydrogen peroxide, and the solvent is ultrapure water. The volume fraction of hydrofluoric acid in this extract is 10%, and the volume fraction of hydrogen peroxide is 1%. The remaining steps are the same as in Example 3.

[0063] Test Example 1

[0064] The methods described in Examples 1-6 above were used to test silicon carbide wafers with known carbon and silicon surfaces to verify the accuracy of the method. Each example used 10 different production batches of silicon carbide wafers for verification, with 5 wafers taken from each batch. The number of correctly distinguished wafers was recorded, and the accuracy rate was calculated using the following formula:

[0065] A = (Number of correctly distinguished pieces / 50) × 100. The results are shown in Table 1 below:

[0066] Table 1

[0067] Test number Accuracy (%) Example 1 100 Example 2 100 Example 3 100 Example 4 100 Example 5 100 Example 6 100

[0068] As shown in Table 1, the above method can quickly distinguish between the carbon and silicon surfaces of silicon carbide wafers, and can guarantee 100% accuracy under repeated testing, thus demonstrating higher reliability and testing precision.

[0069] Test Example 2

[0070] Using the method of this application, 4H conductive silicon carbide wafers and 4H semi-insulating silicon carbide wafers were immersed in 2wt% sulfuric acid and 2wt% hydrochloric acid solutions, respectively, and extracted using the same 8% (v / v) hydrofluoric acid extraction solution. The ratio of S and Cl elements in the extraction solution on the carbon and silicon surfaces of the silicon carbide wafers were analyzed. The detection results for the 4H conductive silicon carbide wafers are shown in […]. Figure 1 , Figure 1 The vertical axis represents the ratio of sulfur (S) or chloride (Cl) content on the carbon and silicon surfaces. The results show that, for sulfuric acid immersion using the S content testing method, the C surface contains more than twice the S content of the silicon surface; for hydrochloric acid immersion using the Cl content testing method, the C surface contains more than three times the Cl content of the silicon surface. The test results for the 4H semi-insulating silicon carbide wafer are shown below. Figure 2 , Figure 2 The vertical axis represents the ratio of sulfur (S) or chloride (Cl) on the carbon and silicon surfaces. The results show that, using sulfuric acid immersion (S content testing method) and hydrochloric acid immersion (Cl content testing method), the C surface contains more than twice the amount of S or Cl compared to the silicon surface. Based on the above... Figure 1 and Figure 2 The tests show that, in the differentiation method of this application, the content of S and Cl elements in the carbon surface and the silicon surface differs by at least 100%, so the method has a high degree of differentiation between the carbon surface and the silicon surface.

[0071] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for distinguishing the silicon surface and carbon surface of a silicon carbide wafer, characterized in that, Includes the following steps: (1) Immerse the silicon carbide wafer in sulfuric acid or hydrochloric acid solution, and then clean it to obtain the wafer to be tested. The concentration of sulfuric acid in the sulfuric acid solution is 2-70 wt%, the concentration of hydrochloric acid in the hydrochloric acid solution is 2-70 wt%, the immersion time is not less than 1 min, and the immersion temperature is 20-30℃. (2) Detect and compare the content of S or Cl elements on the first and second surfaces of the wafer to be tested, wherein the surface with high content of S or Cl elements is the carbon surface and the surface with low content of S or Cl elements is the silicon surface.

2. The method according to claim 1, characterized in that, The content of S or Cl on the first and second surfaces was detected by secondary ion mass spectrometry and total reflectance fluorescence spectrometry.

3. The method according to claim 1, characterized in that, In step (2), the content of S or Cl elements on the first and second surfaces is extracted and detected using an extraction solution: An extraction solution is coated onto the first and second surfaces of the wafer to be tested, and after standing, the extraction solution is collected to obtain the first test solution and the second test solution, respectively. The first test solution and the second test solution are tested. The content of S or Cl elements in the first test solution represents the content of S or Cl elements on the first surface, and the content of S or Cl elements in the second test solution represents the content of S or Cl elements on the second surface.

4. The method according to claim 3, characterized in that, The solute in the extract includes hydrofluoric acid, and the solvent is ultrapure water.

5. The method according to claim 4, characterized in that, The solute in the extract also includes hydrogen peroxide.

6. The method according to claim 5, characterized in that, The volume fraction of hydrofluoric acid in the extract is 1%-10%, and the volume fraction of hydrogen peroxide in the extract is 1%-10%.

7. The method according to claim 4, characterized in that, The settling time in step S2 shall not be less than 15 seconds.

8. The method according to claim 4, characterized in that, The content of S or Cl in the first and second test solutions was detected by inductively coupled plasma mass spectrometry.

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