A cleaning method for removing a suction pen mark on a surface of a silicon carbide substrate and a silicon carbide substrate

Abstract

The application discloses a cleaning method for removing a suction pen mark on a surface of a silicon carbide substrate and the silicon carbide substrate, and belongs to the technical field of silicon carbide detection. The cleaning method comprises the following steps: (1) using a mixed solution of ammonia and hydrogen peroxide to clean the surface of the substrate, so as to pre-oxidize the surface of the substrate; (2) using ozone water to clean the pre-oxidized substrate, so as to obtain a substrate containing an oxidation layer; and (3) using an acidic cleaning solution with a pH value of 2.0-3.5 to clean the substrate containing the oxidation layer, and then performing water washing and blowing dry, so as to obtain a cleaned silicon carbide substrate. The method can change the Zeta potential of the oxidation layer on the surface of the substrate, so that the surface potential of the substrate is not lower than 0 mV, thereby reducing the adsorption of positively charged particles on the suction pen, achieving the technical effect of completely removing the suction pen mark, and improving the quality of the silicon carbide substrate.

Description

Technical Field

[0001] This application relates to a cleaning method for removing pen marks from the surface of a silicon carbide substrate and a silicon carbide substrate, belonging to the field of silicon carbide detection technology. Background Technology

[0002] After cleaning, existing silicon carbide substrates are typically inspected visually or with testing devices to detect impurities or elemental content on the substrate surface. To minimize damage during inspection, a suction pen is used to contact the substrate surface, regardless of whether visual inspection or testing is employed. However, the cleaned substrate surface carries a negatively charged oxide layer. Since most abrasive particles are positively charged, they easily attract positively charged abrasive particles from the outside environment. During inspection, the suction pen picks up positively charged abrasive particles (such as SiO2 and Al2O3 particles) from the substrate surface. When inspecting the next substrate, these positively charged particles on the suction pen easily adhere to the silicon carbide substrate surface, resulting in visible suction pen marks on the inspected substrate surface. This affects the product's appearance and reduces the surface quality of the silicon carbide substrate. However, skipping the inspection process would result in defective products reaching customers, leading to return disputes.

[0003] Currently, to reduce suction pen marks, two methods are used: first, the suction pen is cleaned every 12 hours; second, a pressure regulating valve is installed between the suction pen and the negative pressure suction line to adjust the vacuum pressure of the suction pen to -70Kpa to -60Kpa. While these methods of periodically cleaning the suction pen and adjusting the suction force can reduce suction pen marks to some extent, neither can completely remove them. Summary of the Invention

[0004] To address the aforementioned issues, a cleaning method for removing pen marks from the surface of a silicon carbide substrate and a silicon carbide substrate are provided. This method first oxidizes the substrate surface using a mixture of ammonia, hydrogen peroxide, and ozone water. Then, an acidic cleaning solution with a pH of 2.0-3.5 is used to clean the substrate surface containing the oxide layer. This alters the zeta potential of the oxide layer on the substrate surface, causing the substrate surface to carry a positive charge or have a potential of 0mV. This reduces the adsorption of positively charged particles from the pen, achieving the technical effect of completely removing the pen marks, thereby improving the aesthetic appearance and surface quality of the silicon carbide substrate.

[0005] According to one aspect of this application, a cleaning method for removing pen marks from the surface of a silicon carbide substrate is provided, comprising the following steps:

[0006] (1) The surface of the substrate is cleaned with a mixture of ammonia and hydrogen peroxide to pre-oxidize the substrate surface;

[0007] (2) The pre-oxidized substrate was cleaned with ozone water to obtain a substrate containing an oxide layer;

[0008] (3) The substrate containing the oxide layer is cleaned with an acidic cleaning solution with a pH of 2.0-3.5, and then washed with water and dried to obtain a cleaned silicon carbide substrate.

[0009] Since silicon carbide substrates are not easily oxidized, the pre-oxidation of the substrate surface with a mixture of ammonia and hydrogen peroxide in step (1) can improve the oxidation degree of the silicon carbide substrate. Combined with ozone oxidation in step (2) to form a uniform oxide layer, this oxide layer can protect the silicon carbide substrate. In step (3), the acidic cleaning solution with a pH of 2.0-3.5 cleans the substrate containing the oxide layer. First, it can change the potential of the oxide layer, making the surface potential of the silicon carbide substrate between 0mV and 30mV, thereby reducing the adsorption of positively charged particles on the suction pen, so as to completely remove the suction pen marks. Second, it can reduce the metal ions on the surface of the silicon carbide substrate, further improving the surface cleanliness of the substrate and the product quality. If the pH of the acidic cleaning solution is too high, the substrate surface will carry a negative charge, and it will still be easy to produce suction pen marks. If the pH is too low and the acidity is too strong, it will etch too much SiO2 oxide layer on the substrate surface, causing an increase in surface roughness and reducing the surface quality of the substrate.

[0010] Preferably, the pH of the acidic cleaning solution is 2.0-3.0.

[0011] Optionally, the volume ratio of ammonia to hydrogen peroxide in the mixture in step (1) is 1:(1-1.5), and the concentration of hydrogen peroxide in the hydrogen peroxide is 30%.

[0012] In the mixture, hydrogen peroxide plays the main oxidation role, while ammonia plays the auxiliary oxidation role. The combination of the two can achieve uniform pre-oxidation and improve the density and uniformity of the pre-oxidized layer. If the amount of hydrogen peroxide is too small, the pre-oxidation effect will decrease. If the amount of hydrogen peroxide is too large, the pre-oxidation rate will increase, and the density and uniformity of the pre-oxidized layer will decrease.

[0013] Optionally, the cleaning time in step (1) is 10-15 minutes, preferably 10 minutes.

[0014] The cleaning time, combined with the ratio of ammonia and hydrogen peroxide in the mixture, can improve the pre-oxidation effect on silicon carbide substrates and help reduce the roughness of the substrate surface. If the cleaning time is too long, the roughness of the substrate surface will increase and the product quality will decrease. If the cleaning time is too short, the pre-oxidation effect will decrease, which is not conducive to the formation of a dense and uniform oxide layer.

[0015] Optionally, the concentration of ozone in the ozone water in step (2) is 50-70 ppm, and the cleaning time is 30-60 s;

[0016] Preferably, the ozone concentration in the ozone water in step (2) is 60 ppm, and the cleaning time is 45 s.

[0017] The ozone concentration and cleaning time mentioned above are all to ensure the formation of a dense and uniform oxide layer, and to further reduce the roughness of the substrate surface. If the ozone concentration is too high or the cleaning time is too long, the roughness of the substrate surface will also increase, resulting in a decrease in product quality. If the ozone concentration is too low or the time is too short, the oxide layer will be uneven, which will lead to a decrease in product quality and will not be conducive to the formation of a substrate with a positive surface potential.

[0018] Optionally, the acidic cleaning solution in step (3) comprises concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of (3-5.5):5.

[0019] The ratio of this acidic cleaning solution ensures that the pH of the solution is between 2.0 and 3.5, thereby improving the cleaning efficiency of the silicon carbide substrate. If there is too much concentrated hydrochloric acid, the etching depth of the surface oxide layer will be too large. If there is too little concentrated hydrochloric acid, the potential of the substrate surface will be too low, making it easy to adsorb metal ions and affecting the cleaning effect.

[0020] Optionally, the cleaning time in step (3) is 5-20 minutes, preferably 10 minutes.

[0021] This cleaning time ensures that metal ions and impurities on the substrate surface are thoroughly cleaned. It also changes the potential of the silicon carbide substrate surface to ensure that the potential is not lower than 0mV. If the cleaning time is too short, the surface charge will be uneven and impurities will not be easily removed. If the cleaning time is too long, it will corrode the wafer surface, causing abnormal roughness and reducing the surface quality of the substrate.

[0022] Optionally, step (3) involves drying with an inert gas.

[0023] Optionally, the zeta potential on the surface of the cleaned silicon carbide substrate is 0mV-30mV.

[0024] Preferably, the zeta potential on the surface of the cleaned silicon carbide substrate is 5mV-15mV, more preferably 5mV-10mV.

[0025] Optionally, the silicon carbide substrate includes conductive silicon carbide and semi-insulating silicon carbide.

[0026] According to another aspect of this application, a silicon carbide substrate is provided, which is obtained by cleaning using any of the cleaning methods described above.

[0027] The beneficial effects of this application include, but are not limited to:

[0028] 1. The cleaning method of this application makes the surface of the silicon carbide substrate positively charged after cleaning, thereby reducing the adsorption of positively charged particles on the suction pen, so as to achieve the technical effect of completely removing the suction pen mark and improving the quality of the silicon carbide substrate after inspection.

[0029] 2. The cleaning method according to this application reduces the cleaning frequency of the suction pen, improves the efficiency of visual or device inspection of silicon carbide substrates, thereby improving the processing and production efficiency of silicon carbide substrate products and facilitating large-scale industrial application.

[0030] 3. The silicon carbide substrate obtained by the cleaning method of this application has high quality, thereby reducing the number of defects in the epitaxial wafers prepared using the silicon carbide substrate. Attached Figure Description

[0031] 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:

[0032] Figure 1 This is a visual observation of the silicon carbide substrate involved in Embodiment 1 of this application after it has been adsorbed by a suction pen.

[0033] Figure 2 This is a visual observation of the silicon carbide substrate involved in Comparative Example 4 of this application after it has been adsorbed by a suction pen. Detailed Implementation

[0034] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0035] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application were all purchased commercially.

[0036] Unless otherwise specified, the methods used in the embodiments and comparative examples of this application are conventional methods in the prior art.

[0037] Example 1

[0038] This embodiment relates to a cleaning method for removing pen marks from the surface of a silicon carbide substrate, comprising the following steps:

[0039] (1) The surface of the silicon carbide substrate was cleaned for 10 minutes with a mixture of ammonia and hydrogen peroxide (30% hydrogen peroxide concentration) in a volume ratio of 1:1 to pre-oxidize the substrate surface.

[0040] (2) The pre-oxidized substrate was cleaned with ozone water with an ozone concentration of 60 ppm for 45 seconds to obtain a substrate containing an oxide layer.

[0041] (3) The substrate containing the oxide layer was cleaned for 10 minutes with an acidic cleaning solution of concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 5:5. The pH of the acidic cleaning solution was 2.5. After that, the substrate was washed with deionized water and dried with nitrogen to obtain the cleaned silicon carbide substrate.

[0042] Example 2

[0043] This embodiment relates to a cleaning method for removing pen marks from the surface of a silicon carbide substrate, comprising the following steps:

[0044] (1) The surface of the silicon carbide substrate was cleaned for 15 minutes with a mixture of ammonia and hydrogen peroxide (30% hydrogen peroxide concentration) in a volume ratio of 1:1.5 to pre-oxidize the substrate surface.

[0045] (2) The pre-oxidized substrate was cleaned with ozone water with an ozone concentration of 70 ppm for 30 seconds to obtain a substrate containing an oxide layer.

[0046] (3) The substrate containing the oxide layer was cleaned for 5 minutes with an acidic cleaning solution of concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 3:5.5. The pH of the acidic cleaning solution was 3.5. After that, the substrate was washed with deionized water and dried with nitrogen to obtain the cleaned silicon carbide substrate.

[0047] Example 3

[0048] This embodiment relates to a cleaning method for removing pen marks from the surface of a silicon carbide substrate, comprising the following steps:

[0049] (1) The surface of the silicon carbide substrate was cleaned for 10 min with a mixture of ammonia and hydrogen peroxide (30% hydrogen peroxide concentration) in a volume ratio of 1:1.5 to pre-oxidize the substrate surface.

[0050] (2) The pre-oxidized substrate was cleaned with ozone water with an ozone concentration of 50 ppm for 60 s to obtain a substrate containing an oxide layer.

[0051] (3) The substrate containing the oxide layer was cleaned for 20 minutes with an acidic cleaning solution of concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 3:5. The pH of the acidic cleaning solution was 2.1. After that, the substrate was washed with deionized water and dried with nitrogen to obtain the cleaned silicon carbide substrate.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that the volume ratio of ammonia and hydrogen peroxide in the mixture in step (1) is 1:0.8, while the rest is the same as in embodiment 1.

[0054] Example 5

[0055] The difference between this embodiment and embodiment 1 is that the volume ratio of ammonia and hydrogen peroxide in the mixture in step (1) is 1:2, while the rest is the same as in embodiment 1.

[0056] Example 6

[0057] The difference between this embodiment and embodiment 1 is that the cleaning time in step (1) is 20 minutes, while the rest is the same as in embodiment 1.

[0058] Example 7

[0059] The difference between this embodiment and embodiment 1 is that the ozone concentration in step (2) is 80 ppm, while the rest is the same as in embodiment 1.

[0060] Example 8

[0061] The difference between this embodiment and embodiment 1 is that the ozone concentration in step (2) is 40 ppm, while the rest is the same as in embodiment 1.

[0062] Example 9

[0063] The difference between this embodiment and embodiment 1 is that the ozone cleaning time in step (2) is 70 seconds, while the rest is the same as in embodiment 1.

[0064] Example 10

[0065] The difference between this embodiment and embodiment 1 is that the ozone cleaning time in step (2) is 25 seconds, while the rest is the same as in embodiment 1.

[0066] Example 11

[0067] The difference between this embodiment and Embodiment 1 is that the acidic cleaning solution is sulfuric acid and hydrofluoric acid in a volume ratio of 6:5, and the pH of the acidic cleaning solution is 2.5. The rest is the same as in Embodiment 1.

[0068] Example 12

[0069] The difference between this embodiment and embodiment 1 is that the cleaning time in step (3) is 25 minutes, while the rest is the same as in embodiment 1.

[0070] Example 13

[0071] The difference between this embodiment and embodiment 1 is that the cleaning time in step (3) is 3 minutes, while the rest is the same as in embodiment 1.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that in step (1), only ammonia water is used to clean the surface of the substrate, while the rest is the same as in Example 1.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that in step (1), only hydrogen peroxide is used to clean the surface of the substrate, while the rest is the same as in Example 1.

[0076] Comparative Example 3

[0077] The difference between this comparative example and Example 1 is that step (2) is performed first, then step (1), and finally step (3). The rest is the same as Example 1.

[0078] Comparative Example 4

[0079] The difference between this comparative example and Example 1 is that in step (3), an acidic cleaning solution composed of concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 5:7 is used, and its pH is 4. The rest is the same as in Example 1.

[0080] Comparative Example 5

[0081] The difference between this comparative example and Example 1 is that in step (3), an acidic cleaning solution composed of concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 8:1 is used, and its pH is 1.5. The rest is the same as in Example 1.

[0082] Test case

[0083] The conductive silicon carbide substrate surface was cleaned using the cleaning methods described in the above embodiments and comparative examples. Subsequently, potential tests, surface roughness tests, and suction pen adsorption tests were performed on both the carbon and silicon surfaces of the silicon carbide substrate. The surface particulate matter in the adsorption area after suction pen adsorption was calculated. Five parallel experiments were conducted, and the results of the five experiments, along with the average values ​​for the carbon and silicon surfaces, were taken. The test results are shown in Table 1. The specific test methods are as follows:

[0084] 1. Potential test: The Zeta potential of the carbon and silicon surfaces of the silicon carbide substrate was tested using Anton Paar's SurPass2000. The test solution was 1 mmol KCl solution, and the test area was 1 cm * 2 cm.

[0085] 2. Surface roughness test: The roughness change of the material was characterized by atomic force microscopy using Parker equipment, with a test area of ​​10μm*10μm.

[0086] 3. Vacuum pen adsorption test: To maintain the objectivity of the test, the vacuum pen is purged with nitrogen for 30 seconds before use to remove surface dust. A vacuum pen is used to adsorb the wafer. During adsorption, the pen tip is in complete contact with the wafer surface to prevent the wafer from falling. The back of the wafer is used as the point of force, and the substrate is pulled out vertically to prevent scratches. The speed is kept stable.

[0087] 4. Calculation of surface particulate matter in the adsorption area after adsorption by the suction pen: The number of particles on the carbon surface of the wafer is tested using a Lumina device, and the square area larger than 1 mm of the adsorption area by the suction pen is considered as the particles marked by the suction pen.

[0088] Table 1

[0089]

[0090]

[0091] In the suction pen adsorption test, the intuitive observation image of the silicon carbide substrate of Example 1 after being adsorbed by the suction pen is shown below. Figure 1 As shown, a visual observation of the silicon carbide substrate of Comparative Example 4 after it has been adsorbed by a suction pen is as follows: Figure 2 As shown in the figure, it can be seen that the cleaning method of this application can remove the ink pen marks.

[0092] According to Table 1 and the above test results, the positive potential on the wafer surface after acid cleaning can reduce particle adsorption. However, excessive acidity will reduce the surface roughness of the wafer and affect the number of epitaxial layer defects. At the same time, the stronger the oxidation effect of ozone, the greater the impact on the surface roughness of the wafer. Therefore, Example 1 ensures the surface roughness of the wafer while inhibiting the adsorption of abrasive particles.

[0093] Example 14

[0094] Based on Example 1, this embodiment uses acidic cleaning solutions with different pH values ​​to clean the carbon and silicon surfaces of a semi-insulating silicon carbide substrate. Potential tests, surface roughness tests, and suction pen adsorption tests are performed on the two cleaned surfaces. The surface particulate matter in the adsorption area after suction pen adsorption is calculated. When the pH is below 3.5, the silicon carbide surface exhibits a positive potential, higher than that of conductive silicon carbide, and no suction pen mark is formed; the surface particulate matter in the adsorption area is relatively small. When the pH is above 3.5, the surface exhibits a negative potential, resulting in suction pen marks and increased surface particulate matter in the adsorption area. The higher the pH, the more obvious the mark and the more surface particulate matter in the adsorption area. When the pH is below 2.0, the surface roughness of the silicon carbide substrate increases significantly.

[0095] 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 cleaning method for removing pen marks from the surface of a silicon carbide substrate, characterized in that, Includes the following steps: (1) The substrate surface is cleaned with a mixture of ammonia and hydrogen peroxide to pre-oxidize the substrate surface; (2) The pre-oxidized substrate is cleaned with ozone water to obtain a substrate containing an oxide layer, wherein the concentration of ozone in the ozone water is 50-70 ppm; (3) The substrate containing the oxide layer is cleaned with an acidic cleaning solution with a pH of 2.0-3.

5. The acidic cleaning solution includes concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of (3-5.5):

5. After washing with water and drying, the cleaned silicon carbide substrate is obtained. The zeta potential on the surface of the cleaned silicon carbide substrate is 1.8mV-30mV.

2. The cleaning method according to claim 1, characterized in that, In step (1), the volume ratio of ammonia to hydrogen peroxide in the mixture is 1:(1-1.5), and the concentration of hydrogen peroxide in the hydrogen peroxide is 30%.

3. The cleaning method according to claim 1, characterized in that, The cleaning time for step (1) is 10-15 minutes.

4. The cleaning method according to claim 3, characterized in that, The cleaning time for step (1) is 10 minutes.

5. The cleaning method according to claim 1, characterized in that, The ozone water cleaning time in step (2) is 30-60 seconds.

6. The cleaning method according to claim 5, characterized in that, In step (2), the ozone concentration in the ozone water is 60 ppm and the cleaning time is 45 s.

7. The cleaning method according to claim 1, characterized in that, The cleaning time for step (3) is 5-20 minutes.

8. The cleaning method according to claim 7, characterized in that, The cleaning time for step (3) is 10 minutes.

9. The cleaning method according to claim 1, characterized in that, Step (3) Drying is performed using inert gas.

10. The cleaning method according to claim 1, characterized in that, The silicon carbide substrate includes conductive silicon carbide and semi-insulating silicon carbide.

11. A silicon carbide substrate, characterized in that, The silicon carbide substrate is obtained by cleaning using the cleaning method described in any one of claims 1-10.

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