Method for eliminating time-dependent haze formed on silicon carbide, and high-stability silicon carbide substrate

Abstract

The present application belongs to the technical field of silicon carbide materials. Disclosed are a method for eliminating time-dependent haze formed on silicon carbide, and a high-stability silicon carbide substrate. The method comprises the following steps: (1) fixing silicon carbide in a vacuum box; and (2) vacuumizing the vacuum box to eliminate time-dependent haze on the silicon carbide. In the present application, time-dependent haze on a surface of silicon carbide is effectively eliminated by means of vacuumization, a silicon carbide substrate on which time-dependent haze has not grown can also be prevented from the generation of time-dependent haze, and time-dependent haze does not grow on the treated silicon carbide substrate even when the silicon carbide substrate is placed in a humid environment for a long time, thereby reducing the rework cost of a large number of finished silicon carbide substrate products.

Description

A method for eliminating silicon carbide time fog and a high-stability silicon carbide substrate

[0001] This application claims priority to a Chinese patent application filed with the Patent Office of China on January 5, 2024, with application number 202410027719.8 and invention name “A method for eliminating silicon carbide time fog and a high-stability silicon carbide substrate”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of silicon carbide materials, and in particular to a method for eliminating silicon carbide time fog and a high-stability silicon carbide substrate. Background Art

[0003] With the gradual development of the third-generation semiconductor industry, the requirements for the surface cleanliness of silicon carbide substrates are becoming increasingly higher. People use RCA cleaning processes and brush technology to remove chemical reagent residues on the surface of silicon carbide. However, despite this, metal ion residues in the cleaning solution and higher air molecules in the hundred-level space still cause SiC wafer contamination problems. For example, after the SiC substrate has been stored in a packaging and transport box for a period of time, an increase in local light scattering (LLS) may be observed during surface inspection. This is due to particle aggregation caused by surface chemical processes. This phenomenon is called time-dependent haze (TDH), hereinafter referred to as "time haze". The causes of TDH are different, such as organic additives in packaging materials, chemicals used for wafer cleaning, increased humidity or ionic contaminants.

[0004] Temporal fog on the silicon carbide surface can lead to extensive rework of finished substrates, recalls of wafers, and serious customer complaints, resulting in significant losses in production and shipping costs. Severe fog particles transferred to downstream epitaxy plants can significantly increase the number of fatal defects in the epitaxial layer. With the rapid development of integrated circuits, chip line widths have reached deep submicron levels, and even tiny defects on the silicon carbide wafer surface can easily become trapping centers for metal impurities. Heavy metal ions, in particular, can combine with electrons and holes in the silicon carbide single crystal, severely reducing the minority carrier lifetime, increasing leakage current, and causing PN junction breakdown, rendering the entire device useless.

[0005] In the past, people have done a lot of research on silicon wafer time fog. et al. reported that, through simulated pollutant experiments, NH₄SO₄ was the primary factor in the formation of time fog. They also noted that high humidity and N,N-dimethylacetamide can promote the formation of time fog. Other studies have also demonstrated that strict control of reactant concentrations on the silicon wafer surface, temperature, and humidity in the interstage environment can inhibit and eliminate time fog, or that using hot water during wafer cleaning can reduce its formation.

[0006] However, silicon carbide substrates are polar, and the surface wettability of both sides of carbon silicon is different from that of silicon wafers. After traditional RCA cleaning, chemical residues still remain on the surface. In addition, due to the lower surface wettability of the carbon surface, time fog is very likely to form. Therefore, the method for eliminating time fog on silicon wafers is not applicable to silicon carbide substrates. Currently, there is a lack of an effective method to eliminate or prevent silicon carbide time fog.

[0007] Summary of the Invention

[0008] In order to solve the above problems, a method for eliminating time fog on silicon carbide is provided. The method effectively eliminates the time fog on the surface of silicon carbide by vacuuming. The treated silicon carbide substrate will not regenerate time fog even if placed in a humid environment for a long time, thereby reducing the rework cost of a large number of silicon carbide substrate finished products.

[0009] According to one aspect of the present application, a method for eliminating silicon carbide time fog is provided, comprising the following steps:

[0010] (1) Place silicon carbide in a vacuum box and fix it;

[0011] (2) The vacuum box is evacuated to eliminate the time fog on the silicon carbide.

[0012] The traditional RCA cleaning method for cleaning silicon carbide can only suppress the growth of time fog for a short period of time, but cannot eliminate any chemical residues. Residual chemicals will still cause the growth of time fog in a high-humidity environment. This application places silicon carbide in a vacuum environment. By vacuuming, the van der Waals force between the substance on the surface of silicon carbide and the silicon carbide substrate can be completely destroyed, and the particles on the surface of silicon carbide can be removed. After the treatment is completed, it can also accelerate the desorption of particles. Compared with wet chemical removal, it can achieve the effect of completely eliminating time fog without any chemical residues.

[0013] Optionally, in step (2), the vacuum pressure is -50 kPa to -150 kPa, and the vacuum time is at least 12 hours.

[0014] Optionally, in step (2), the pressure is first evacuated to -50 kPa to -70 kPa, treated for 0.5-1 h, then evacuated to -80 kPa to -85 kPa, treated for 0.5-1 h, and finally evacuated to -90 kPa to -150 kPa, treated for at least 10 h.

[0015] The pressure and time of the vacuuming can ensure that the van der Waals force between the particles and the silicon carbide substrate is destroyed, and the contaminants are removed by relying on the momentum transfer of the vacuuming. The step-by-step pressure increase method used in this scheme can gradually break down the van der Waals force between the particles and the silicon carbide, further increasing the total amount of particle removal and improving the elimination efficiency of the method.

[0016] Optionally, in step (2), nitrogen is introduced into the vacuum box while evacuating the vacuum box, and the flow rate of the nitrogen is 30-40 LPM.

[0017] Nitrogen is replenished while the vacuum is being drawn, so the airflow in the vacuum box will circulate continuously. In this process, the particles loaded on the surface of the silicon carbide can be taken away by the nitrogen, which not only improves the removal efficiency of the time mist, but also prevents the particles from being re-adsorbed on the silicon carbide substrate and prevents the particles from contaminating the surface of the silicon carbide substrate.

[0018] Nitrogen is an inert gas. Using nitrogen in this treatment process can improve the operational safety of the method and protect silicon carbide by avoiding the reintroduction of new impurities. The flow rate of the nitrogen can ensure that the removed particles are taken away while avoiding damage to the silicon carbide.

[0019] Optionally, the elimination rate of time fog on silicon carbide in step (2) is greater than 95%.

[0020] The method in the present application can be used to process silicon carbide that has not generated time fog. The purpose of processing silicon carbide that has not generated time fog is mainly to prevent the generation of time fog. This method of processing silicon carbide that has not generated time fog can eliminate particulate matter and chemical residual ions on the surface of silicon carbide, reduce the impurity and ion concentration on the surface of silicon carbide, and thus inhibit the generation of time fog.

[0021] Optionally, the silicon carbide substrate in step (1) is a silicon carbide substrate covered with time fog, and the silicon carbide covered with time fog is obtained by placing the polished and cleaned silicon carbide in an environment with a temperature of 20-40°C and a humidity of 10-60% for at least 3 days.

[0022] The silicon carbide substrate that is already covered with time fog is treated by vacuuming, which can completely remove the particles that cause the time fog. It will not grow again during the subsequent storage process. Moreover, as the storage time increases, the particles on the silicon carbide surface will gradually decrease until they disappear completely.

[0023] According to another aspect of the present application, a high-stability silicon carbide substrate is provided, characterized in that the silicon carbide substrate is a silicon carbide substrate that has been stored for at least three months, and the particle density of time fog on the surface of the silicon carbide substrate is less than 10 / cm 2 .

[0024] The particle density of time fog on the current silicon carbide substrate increases with the extension of storage time. Generally, the particle density of time fog on the surface of silicon carbide substrates stored for more than three months is greater than 2000 particles / cm 2 The silicon carbide substrate of the present application can still maintain a particle density of time fog on its surface of less than 10 / cm when stored for more than three months. 2 , improving the production quality and processing efficiency of the downstream epitaxial layer.

[0025] Optionally, the particle size of the time mist on the surface of the silicon carbide substrate is no more than 300 nm.

[0026] Optionally, a ratio of particle density of the time fog on the C surface and the Si surface of the silicon carbide substrate is (1.3-1.5):1.

[0027] Optionally, the silicon carbide substrate includes a central area and an edge area, the edge area is an area within 3 mm from the edge of the silicon carbide substrate, the central area is an area surrounded by the edge area, and the particle density of the time fog in the central area is less than that in the edge area.

[0028] Optionally, the metal ion concentration on the surface of the silicon carbide substrate is ≤1×10 11 atoms / cm 2 .

[0029] The above metals include Na, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb.

[0030] Optionally, the concentration of S element on the surface of the silicon carbide is ≤1×10 12 atoms / cm 2 .

[0031] Optionally, the number of particles on the surface of the silicon carbide substrate is ≤180.

[0032] Optionally, the number of particles on the surface of the silicon carbide substrate is ≤150.

[0033] Optionally, the number of particles on the surface of the silicon carbide substrate is ≤140.

[0034] Optionally, the curvature of the silicon carbide substrate is ≤20 μm, the total thickness deviation is ≤5 μm, and the local thickness deviation within a 10 mm*10 mm test range is ≤2 μm.

[0035] Optionally, the silicon carbide substrate has a C-surface roughness Ra of 0.1-0.15 nm and a Si-surface roughness Ra of 0.07-0.08 nm.

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

[0037] 1. The method for eliminating silicon carbide time fog disclosed in the present application can completely eliminate and suppress the generation of time fog on the surface of silicon carbide, reduce the rework cost of a large number of silicon carbide substrate finished products, reduce the increase in the number of fatal defects in the downstream silicon carbide epitaxial layer caused by unclean substrate wafers, reduce the risk of epitaxial furnace contamination, and improve the processing efficiency of the downstream silicon carbide industry chain.

[0038] 2. The method of eliminating silicon carbide time fog in the present application obtains a silicon carbide substrate with higher surface cleanliness, effectively eliminates the fog particles on the silicon carbide surface and no longer grows even if placed in a long-term humid environment, which facilitates the subsequent processing of the silicon carbide substrate, reduces the defects of epitaxial growth, and improves product processing quality.

[0039] 3. The method of eliminating silicon carbide time fog in the present application is to remove particles carried by van der Waals forces on the surface of silicon carbide under vacuum force. After the silicon carbide substrate is treated by this method, no generation of time fog is observed after being placed for more than three months.

[0040] 4. The method of eliminating silicon carbide time fog in the present application uses a long-term vacuum extraction method to eliminate stripe fog while reducing the residual moisture in the wafer, extending the storage time of the substrate, improving processing efficiency, and reducing rework costs.

[0041] 5. After the silicon carbide substrate is treated by the method of eliminating silicon carbide time fog of this application, the number of particles on its surface is greatly reduced. Even if there are particles that have not been eliminated, the chemical interaction force between the particles and silicon carbide has been greatly weakened due to the vacuum effect, and the particles will be further completely eliminated as time goes by.

[0042] 6. The silicon carbide substrate of the present application has high stability and can maintain a clean surface even after being placed for a long time, thereby reducing the generation of surface particles and improving the production quality of downstream products.

[0043] 7. The substrate can only be used for the production of downstream products after being cut. The area of ​​the central region of the silicon carbide substrate of this application accounts for a large proportion. Since the quality of the central region is higher, the available area of ​​the substrate is increased, and a larger number of qualified products can be obtained, thereby improving the utilization rate of the silicon carbide substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present application. For those skilled in the art, other drawings can be obtained based on these drawings without inventive work. In the drawings:

[0045] FIG1 is a diagram of the SCN scattering channels of the Si surface of silicon carbide before vacuum treatment in Example 1 of the present application.

[0046] FIG2 is a diagram of the SCN scattering channels of the Si surface of silicon carbide after vacuum treatment in Example 1 of the present application.

[0047] FIG3 is a diagram of the SCN scattering channels of the Si surface of silicon carbide before vacuum treatment in Example 2 of the present application.

[0048] FIG4 is a diagram of the SCN scattering channels of the Si surface of silicon carbide after vacuum treatment in Example 2 of the present application.

[0049] FIG5 is an SCN scattering channel diagram of the Si surface of silicon carbide after vacuum treatment in Example 2 of the present application for 60 days. DETAILED DESCRIPTION

[0050] Embodiments of the present application provide a method for eliminating silicon carbide time fog and a high-stability silicon carbide substrate.

[0051] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0052] In the following examples and comparative examples, the characterization of time fog on silicon carbide was verified using the SCN scattering channel of the Candela8520 machine.

[0053] The cleaning steps in the following embodiments and comparative examples include SPM, HF, SC1, and SC2 processes.

[0054] Example 1

[0055] This embodiment relates to a method for eliminating silicon carbide time fog, comprising the following steps:

[0056] (1) The polished and cleaned silicon carbide was placed in an environment with a temperature of 20°C and a humidity of 60% for 3 days to obtain silicon carbide covered with time fog. The particle density of the time fog on the silicon carbide was tested. The test diagram of the time fog on the Si surface of the silicon carbide is shown in Figure 1. The missing center circle in Figure 1 is caused by the excessive number of software defects exceeding the detection limit. The silicon carbide was then placed in a vacuum chamber and fixed.

[0057] (2) The vacuum box was evacuated to a pressure of -90 kPa and the pressure was maintained for 12 h to eliminate the time fog on the silicon carbide. The treated silicon carbide was subjected to a time fog test. The test results of the Si surface are shown in Figure 2.

[0058] As shown in Figure 1, the SCN scattering channel covered with time fog has a central area of ​​about 140 cm 2 , the density of fog particles reaches 2326 / cm 2 The particle size is >300nm, as evidenced by the central synthetic channel diagram. Furthermore, the time mist particles are very evenly distributed on the wafer surface, indicating that chemical residues are distributed across the entire wafer surface after RCA cleaning. Figure 2 shows that after vacuum treatment, all surface particles on silicon carbide have disappeared, with a particle density reduced to 4 particles / cm 2 , which proves that the method of the present application can effectively and completely remove the time fog, and also proves that the interaction between the chemical residues on the surface of silicon carbide and the surface of silicon carbide is weak and can be disintegrated and removed by vacuuming.

[0059] Example 2

[0060] This embodiment relates to a method for eliminating silicon carbide time fog, comprising the following steps:

[0061] (1) The polished and cleaned silicon carbide was placed in an environment with a temperature of 40° C. and a humidity of 10% for 4 days to obtain silicon carbide covered with time fog. The particle density of the time fog on the silicon carbide was tested. The test diagram of the time fog on the Si surface of the silicon carbide is shown in FIG3 ; the silicon carbide was then placed in a vacuum chamber and fixed;

[0062] (2) The vacuum box was evacuated to a pressure of -70 kPa and the pressure was maintained for 13 h to eliminate the time fog on the silicon carbide. The treated silicon carbide was subjected to a time fog test. The test results of the Si surface are shown in Figure 4.

[0063] According to Figure 3, the SCN scattering channel of silicon carbide is on the right side of the wafer, with an area of ​​about 74cm 2 A large number of time fog particles appear, with a particle density of about 2500 / cm 2 The distribution is clustered, which may be attributed to the difficulty in cleaning the edges during the cleaning process. Figure 4 shows that after vacuum treatment, some particles on the surface of silicon carbide have been eliminated, and the density has been reduced to 770 particles / cm2 The remaining particles that were not eliminated have been significantly weakened due to the vacuum treatment, and the chemical interaction between the particles and the wafer has been further reduced over time. As shown in Figure 5, the particle density of the time fog has dropped to 8 particles / cm 2 .

[0064] Example 3

[0065] This embodiment relates to a method for eliminating silicon carbide time fog, comprising the following steps:

[0066] (1) The polished and cleaned silicon carbide was placed in an environment with a temperature of 30° C. and a humidity of 40% for 4 days to obtain silicon carbide covered with time fog, and the particle density of the time fog on the silicon carbide was tested; then the silicon carbide was placed in a vacuum chamber and fixed;

[0067] (2) The vacuum box is evacuated to a pressure of -50 kPa and maintained at pressure for 1 hour. Then, the vacuum box is evacuated to a pressure of -80 kPa and maintained at pressure for 1 hour. Finally, the vacuum box is evacuated to a pressure of -90 kPa and maintained at pressure for 10 hours. During this period, 30 LPM of nitrogen is introduced to eliminate the time fog on the silicon carbide. The treated silicon carbide is subjected to a time fog test to obtain the particle density.

[0068] Example 4

[0069] This embodiment relates to a method for eliminating silicon carbide time fog, comprising the following steps:

[0070] (1) A time fog test is performed on the silicon carbide obtained after polishing and cleaning. Since it has just been cleaned and has not been exposed to foreign substances, the time fog particle density on the surface of the silicon carbide is 0. Then the silicon carbide is placed in a vacuum box and fixed;

[0071] (2) The vacuum box was evacuated to a pressure of -70 kPa and maintained at pressure for 0.5 h. Then, the vacuum box was evacuated to a pressure of -85 kPa and maintained at pressure for 0.5 h. Finally, the vacuum box was evacuated to a pressure of -150 kPa and maintained at pressure for 10 h. During this period, 40 LPM of nitrogen was introduced. The treated silicon carbide was subjected to a time fog test. The particle density of the time fog was still 0.

[0072] Example 5

[0073] The difference between this embodiment and embodiment 1 is that in step (2), the vacuum is evacuated to a pressure of -30 kPa, and the remaining steps are the same as those in embodiment 1.

[0074] Example 6

[0075] The difference between this embodiment and embodiment 1 is that the pressure holding time in step (2) is 8 hours, and the remaining steps are the same as those in embodiment 1.

[0076] Comparative Example 1

[0077] This comparative example relates to a method for eliminating time fog on silicon carbide, wherein the silicon carbide covered with time fog obtained in step (1) of Example 1 is cleaned with pure water (60°C).

[0078] Comparative Example 2

[0079] This comparative example is silicon carbide obtained through the same polishing and cleaning steps as in Example 4, and the silicon carbide is not subjected to any treatment.

[0080] The silicon carbide substrates treated in the above-described embodiments and comparative examples were tested for time fog. The results showed that the particle density of the time fog in the central area of ​​the silicon carbide substrate was lower than that in the edge area. The edge area was the area within 3 mm from the edge of the silicon carbide substrate, and the central area was the area surrounded by the edge area. Specific test results are shown in Tables 1 and 2 below. The elimination rate in Table 1 = (particle density of time fog before vacuum treatment - particle density of time fog after vacuum treatment) / particle density of time fog before vacuum treatment * 100:

[0081] Table 1

[0082] Table 2

[0083] The silicon carbide substrates treated in the above embodiments and comparative examples were left for three months and then subjected to a time fog test. The test results are shown in Tables 3 and 4 below:

[0084] Table 3

[0085] Table 4

[0086] The data in the above table are average values ​​obtained from five tests, and the particle density of time fog refers to the average density on the C and Si surfaces of silicon carbide. The number of particles on the surface in Tables 1 and 3 is an estimate, and the values ​​used are rounded. According to the contents of Tables 1 to 4 above, it can be seen that the method for eliminating time fog in silicon carbide of the present application can eliminate time fog on silicon carbide covered with time fog, and can also prevent time fog on polished and cleaned silicon carbide. By comparing Example 4 with Comparative Example 2, it can be seen that silicon carbide that has just been polished and cleaned does not generate time fog. As the placement time of the silicon carbide substrate increases, the particle density of time fog gradually increases. After the vacuum treatment is performed in advance, the van der Waals force between the chemical substance and the surface of the silicon carbide can be destroyed, thereby preventing the generation of time fog. As the placement time of the silicon carbide substrate in Example 4 increases, the particle density of time fog only increases to 1 / cm 2 , and still meets the standards for subsequent processing of silicon carbide substrates.

[0087] Examples 1-3 show that after vacuum treatment of a silicon carbide substrate covered with time fog, the density of the time fog particles is significantly reduced. Furthermore, the particles not only do not increase but actually decrease with increasing exposure time. This indicates that vacuum treatment disrupts the chemical intermolecular forces of the time fog, accelerating particle desorption and thus eliminating it. Examples 5 and 6 show that decreasing the pressure or shortening the vacuum treatment time weakens the van der Waals forces, and the density of the time fog particles does not decrease with increasing exposure time.

[0088] According to the comparison between Comparative Example 1 and Example 1, for a silicon carbide substrate covered with time fog, although pure water cleaning can eliminate the time fog to a certain extent, the time fog will regenerate as the placement time increases, and the time fog cannot be eliminated from the root.

[0089] The various embodiments in this application are described in a progressive manner. Similar portions between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from the other embodiments. In particular, the device, apparatus, and non-volatile computer storage medium embodiments are generally similar to the method embodiments, so their descriptions are relatively simple. For relevant portions, refer to the descriptions of the method embodiments.

[0090] Finally, it should be understood that the above embodiments of the present application are intended only to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the above embodiments, or replace some of the technical features therein with equivalents; and such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for eliminating silicon carbide time fog, wherein, It includes the following steps: (1) Fix the silicon carbide in a vacuum chamber; (2) Evacuate the vacuum chamber to eliminate the time fog on the silicon carbide.

2. The method according to claim 1, wherein, In step (2), the pressure for evacuation is -50 kPa to -150 kPa, and the evacuation time is at least 12 h.

3. The method according to claim 2, wherein In step (2), first evacuate to a pressure of -50 kPa to -70 kPa, process for 0.5 - 1 h, then evacuate to a pressure of -80 kPa to -85 kPa, process for 0.5 - 1 h, and finally evacuate to a pressure of -90 kPa to -150 kPa, process for at least 10 h.

4. The method according to claim 1, wherein, In step (2), nitrogen is introduced into the vacuum chamber while evacuating, and the flow rate of the nitrogen is 30 - 40 LPM.

5. The method according to claim 1, wherein In step (2), the elimination rate of the time fog on the silicon carbide is greater than 95%.

6. The method according to claim 1, wherein The silicon carbide substrate in step (1) is a silicon carbide substrate covered with time fog, and the silicon carbide after polishing and cleaning is placed in an environment with a temperature of 20 - 40 °C and a humidity of 10 - 60% for at least 3 days to obtain the silicon carbide covered with time fog.

7. A silicon carbide substrate with high stability, wherein, The silicon carbide substrate is a silicon carbide substrate that has been stored for at least three months, and the particle density of the time fog on the surface of the silicon carbide substrate is less than 10 particles / cm 2 .

8. The high-stability silicon carbide substrate according to claim 7, wherein The particle size of the time fog on the surface of the silicon carbide substrate is not greater than 300 nm.

9. The high-stability silicon carbide substrate according to claim 7, wherein, The ratio of the particle density of the time fog on the C surface and the Si surface of the silicon carbide substrate is (1.3 - 1.5):

1.

10. The high-stability silicon carbide substrate according to claim 7, wherein, The silicon carbide substrate includes a central region and an edge region. The edge region is the region within 3 mm from the edge of the silicon carbide substrate. The central region is the region surrounded by the edge region, and the particle density of the time fog in the central region is less than that in the edge region.

11. The high-stability silicon carbide substrate according to claim 7, wherein, The metal ion concentration on the surface of the silicon carbide substrate is all ≤ 1×10 11 atoms / cm 2 .

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