A cleaning process for cadmium zinc telluride wafers

Abstract

The application belongs to the field of semiconductor substrate manufacturing, and discloses a cleaning process of a cadmium zinc telluride wafer. The process comprises the following steps: placing the polished and waxed wafer in an alkaline solution for soaking treatment; placing the wafer in S1 cleaning solution for cleaning treatment, wherein the S1 cleaning solution is a mixture of hydrogen peroxide, nitric acid and water; placing the wafer in S2 cleaning solution for cleaning treatment, wherein the S2 cleaning solution is a mixture of hydrogen peroxide and ammonium hydroxide; placing the wafer in S3 cleaning solution for cleaning treatment, wherein the S3 cleaning solution is a mixture of hydrochloric acid, hydrofluoric acid and water; placing the wafer in S4 cleaning solution for cleaning treatment, wherein the S4 cleaning solution is a mixture of phosphoric acid and / or sulfurous acid and water; placing the wafer in an organic solution for cleaning treatment; and drying. The cleaning process can improve the yield of products and reduce production costs.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor substrate manufacturing and relates to a cleaning process for cadmium zinc telluride wafers. Background Technology

[0002] Currently, with the development and use of cadmium zinc telluride detectors, it has become possible to obtain high-performance photons through efficient detectors. With the continuous improvement of high-quality CdZnTe semiconductor crystal preparation technology, a deeper understanding of the carrier collection process, and the rapid development of low-noise microelectronics, CdZnTe detectors will surely be applied in a wider range of fields.

[0003] In the production process of cadmium zinc telluride (CZT) wafer substrates, processes such as dicing and grinding require the extensive use of various adhesives, abrasives, coolants, polishing waxes, and polishing slurries, inevitably leading to various forms of contamination on the wafers. Therefore, cleaning the CZT wafers is crucial. The surface quality of the cleaned CZT wafers directly affects the quality of the epitaxial layer, and consequently, the performance of CZT-based devices. Besides ensuring the substrate material's performance quality meets customer requirements, the surface quality of the wafer substrate must also meet customer usage requirements and be compatible with the customer's MOCVD process.

[0004] The existing cleaning process has the following problems: after cleaning, it will corrode the wafer surface, resulting in more particles and excessive roughness on the wafer surface. It will also form a thick oxide film on the wafer surface. At the same time, uncontrollable white fog defects will be generated on the wafer surface, causing the surface impurity content to exceed the standard and fail to meet the requirements, resulting in low overall yield and high production cost. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the present invention aims to provide a cleaning process for cadmium zinc telluride wafers with high yield and low production cost. This cleaning process ensures the cleanliness of the wafer surface without damaging the roughness after polishing, reduces the thickness of the oxide layer after cleaning, avoids the formation of white haze defects on the wafer surface, and effectively controls the surface impurity content.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A cleaning process for cadmium zinc telluride wafers includes the following steps: (1) The polished and dewaxed wafers are immersed in an alkaline solution, wherein the alkaline solution is at least one of tetramethylammonium hydroxide solution, sodium hydroxide solution, and potassium hydroxide solution; (2) The wafer processed in step (1) is placed in S1 cleaning solution for cleaning treatment, wherein S1 cleaning solution is a mixture of hydrogen peroxide, nitric acid and water; (3) The wafer processed in step (2) is placed in S2 cleaning solution for cleaning treatment, wherein the S2 cleaning solution is a mixture of hydrogen peroxide and ammonium hydroxide; (4) The wafer processed in step (3) is placed in S3 cleaning solution for cleaning treatment. The S3 cleaning solution is a mixture of hydrochloric acid, hydrofluoric acid and water. (5) The wafer processed in step (4) is placed in S4 cleaning solution for cleaning, wherein S4 cleaning solution is a mixture of phosphoric acid and / or sulfurous acid and water; (6) The wafer processed in step (5) is placed in an organic solution for cleaning; (7) Dry the wafer after step (6).

[0007] The cleaning process of the present invention creatively introduces S1 cleaning solution, S2 cleaning solution, S3 cleaning solution and S4 cleaning solution to clean zinc cadmium telluride wafers: Step (1) uses an alkaline solution, such as tetramethylammonium hydroxide, to remove organic matter and metal ions; Step (2) sets a cleaning solution with strong oxidizing acid, which has a good removal effect on most metal elements; Step (3) sets an oxidizing and weakly alkaline cleaning agent, which can effectively remove small particulate organic matter; In Step (4), the cleaning agent mixes hydrochloric acid and hydrofluoric acid together, which reduces the corrosiveness of hydrofluoric acid, while ensuring the removal efficiency of silicon dioxide; In Step (5), the cleaning agent can effectively remove silicon dioxide from the wafer surface; In Steps (6) and (7), the wafer is cleaned and dried.

[0008] Furthermore, in step (1), the soaking temperature is 20~30℃; the soaking time is 20~40s; and the pH value of the alkaline solution is ≥12.5.

[0009] Further, in step (2), the volume ratio of hydrogen peroxide, nitric acid and water in the S1 cleaning solution is 1:1~2:2~8; the cleaning temperature is 5~10℃; the cleaning time is 20~60s; the mass concentration of hydrogen peroxide used for preparation is ≥30.0% and the mass concentration of nitric acid used for preparation is ≥69.0%.

[0010] Further preferably, the mass concentration of hydrogen peroxide used for preparation is 30.0~32.0%, and the mass concentration of nitric acid used for preparation is 69.0~72.0%.

[0011] Further, in step (3), the volume ratio of hydrogen peroxide to ammonium hydroxide in the S2 cleaning solution is 1:1~10; the cleaning time is 30~60s; the mass concentration of hydrogen peroxide used for preparation is ≥30.0% and the mass concentration of ammonium hydroxide used for preparation is ≥28%.

[0012] Further preferably, the mass concentration of hydrogen peroxide used for preparation is 30.0~32.0%, and the mass concentration of ammonium hydroxide used for preparation is 28~30.0%.

[0013] Further, in step (4), the volume ratio of hydrochloric acid, hydrofluoric acid and water in the S3 cleaning solution is 3~7:1~10:40~50, and the cleaning time is 30~60s; the mass concentration of hydrochloric acid used for preparation is ≥36.0%, and the mass concentration of hydrofluoric acid used for preparation is ≥48.8%.

[0014] Further preferably, the mass concentration of the hydrochloric acid used for preparation is 36.0~38.0%, and the mass concentration of the hydrofluoric acid used for preparation is 48.8~49.2%.

[0015] Further, in step (5), the volume ratio of phosphoric acid to water in the S4 cleaning solution is 1:1~10, and the cleaning time is 30~60s; the mass concentration of phosphoric acid used for preparation is ≥85.0%.

[0016] Further, in step (6), the organic solution is an isopropanol solution. More preferably, step (6) specifically involves: placing the wafer in the isopropanol solution and rinsing it twice, with each rinse lasting 30-60 seconds.

[0017] Further, the drying process in step (7) specifically involves placing the wafer into a drying chamber and drying it for 30 to 220 seconds.

[0018] Furthermore, in steps (2), (3), and (4), the cleaning temperature is below 25°C.

[0019] Furthermore, in steps (1) to (6), a water rinsing process is set between adjacent steps. The rinsing process is as follows: the wafer is placed in a water rinsing tank for rinsing, and the rinsing time is 30 to 60 seconds.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The cleaning process of the present invention, by introducing cleaning solutions S1, S2, S3 and S4, can effectively remove metal compound ions, organic particles, heavy metals and inorganic impurities from the surface of the zinc zinc cadmium wafer substrate, ensuring the cleanliness of the wafer surface. At the same time, the cleaning process does not damage the roughness of the wafer after polishing, can reduce the oxide layer thickness, control the surface haze, and effectively control the surface impurity content. It achieves optimization and improvement of the substrate surface quality, meeting the customer's purpose.

[0021] (2) The cleaning process of the present invention can significantly improve the product yield and greatly reduce production costs. Detailed Implementation

[0022] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments in the specification, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0024] The component concentrations used in the various embodiments and comparative examples of this invention are as follows: Hydrogen peroxide, with a mass concentration of 30.0%; Nitric acid, with a mass concentration of 69.0%; Ammonium hydroxide, with a mass concentration of 28%; Hydrochloric acid, with a mass concentration of 36.0%; Hydrofluoric acid, with a mass concentration of 48.8%; Phosphoric acid, with a mass concentration of 85.0%; Tetramethylammonium hydroxide solution, pH 12.5.

[0025] Example 1 This embodiment discloses a cleaning process for cadmium zinc telluride wafers, including the following steps: (1) Select 20 pieces of zinc cadmium telluride wafers that have been polished and waxed using the waxing process, and soak them in an aqueous solution of tetramethylammonium hydroxide with a pH of 12.5 and a temperature of 25°C for 30 seconds; immediately rinse them in a water tank for 40 seconds.

[0026] (2) The wafer processed in step (1) is placed in S1 cleaning solution for cleaning treatment, and then placed in a rinsing tank for rinsing. The rinsing time is 30s. The S1 cleaning solution is a mixture of hydrogen peroxide, nitric acid and water. The volume ratio of hydrogen peroxide, nitric acid and water in the S1 cleaning solution is 1:1:8. The cleaning treatment temperature is 8℃. The cleaning treatment time is 40s.

[0027] (3) The wafer after step (2) is placed in S2 cleaning solution for cleaning treatment, and then placed in a rinsing tank for rinsing. The rinsing time is 30s. The volume ratio of hydrogen peroxide and ammonium hydroxide in the S2 cleaning solution is 1:1. The cleaning treatment time is 60s. The cleaning treatment temperature is 25℃.

[0028] (4) The wafer after step (3) is placed in S3 cleaning solution for cleaning treatment, and then placed in a rinsing tank for rinsing. The rinsing time is 30s. The volume ratio of hydrochloric acid, hydrofluoric acid and water in the S3 cleaning solution is 7:3:40. The cleaning treatment time is 30s. The cleaning treatment temperature is 25℃.

[0029] (5) The wafer after step (4) is placed in S4 cleaning solution for cleaning treatment, and then placed in a rinsing tank for rinsing. The rinsing time is 30s, the volume ratio of phosphoric acid and water in S4 cleaning solution is 1:1, the cleaning treatment time is 30~60s, and the cleaning treatment temperature is 25℃.

[0030] (6) The wafer treated in step (5) is rinsed twice in isopropanol solution, the first rinse time is 30s and the second rinse time is 60s; (7) The wafers processed in step (6) are dried with hot nitrogen at 60°C. After the dried wafers pass inspection, they can be packaged and shipped.

[0031] Comparative Example 1 This comparative example discloses a cleaning process for cadmium zinc telluride wafers, including the following steps: (1) Select 10 pieces of zinc cadmium telluride wafers that have been polished and waxed using a waxing process. Use a cleaning fixture to take one piece of zinc cadmium telluride wafer at a time and clamp it. Soak it in sulfuric acid at 65°C for 5 seconds.

[0032] (2) Soak the wafer after soaking in step (1) in sulfuric acid at 25°C for 3 seconds; then put it in a water bowl and rinse the water bowl with a water gun at the same time to keep the water overflowing, and clean for 45 seconds.

[0033] (3) The wafer after step (2) is placed in S1 cleaning solution for cleaning. The volume ratio of hydrogen peroxide, nitric acid and water in S1 cleaning solution is 1:2:3; the cleaning temperature is 4℃; the cleaning time is 60s. During the cleaning process, the wafer is rotated continuously to make the wafer surface evenly coated with liquid. Then it is rinsed with a water gun for 45s.

[0034] (4) The wafer after step (3) is placed in S2 cleaning solution for cleaning. The volume ratio of hydrogen peroxide to ammonium hydroxide in S2 cleaning solution is 3:7. The cleaning time is 30s and the cleaning temperature is room temperature. Then, it is rinsed with a water gun for 45s.

[0035] (5) The wafer processed in step (4) is placed in S3 cleaning solution for cleaning. The volume ratio of hydrochloric acid, hydrofluoric acid and water in S3 cleaning solution is 3:1:40. The cleaning time is 45s. The cleaning temperature is room temperature.

[0036] (6) Place the cleaned wafer from step (5) into the overflow tank and simultaneously rinse the overflow tank with a water gun to keep the water overflowing. Cleaning time: 30s.

[0037] (7) Soak in hydrogen peroxide at room temperature for 30 seconds, then rinse with a water gun for 45 seconds.

[0038] (8) After each wafer is cleaned and dried, it is placed in a cassette that has been dried with nitrogen and stored until it passes inspection. Then it can be packaged and shipped.

[0039] Examples 2-5 To verify the cleaning effect, Examples 2-5 were consistent with Example 1.

[0040] Comparative Examples 2-5 To compare the cleaning effects, Comparative Examples 2-5 were kept consistent with Comparative Example 1.

[0041] The cleaned wafers from Examples 1-5 and Comparative Examples 1-5 were tested, and the results are shown in Table 1. The specific test process is as follows: Two cleaned cadmium zinc telluride wafer substrates were randomly selected from each experimental group. The number of bright spots on the cadmium zinc telluride wafer substrates was detected with a strong light, and the average value was taken for each experimental group.

[0042] Two cleaned cadmium zinc telluride wafer substrates were randomly selected from each experimental group. The thickness of the oxide layer on the cadmium zinc telluride wafer substrate was measured using an ellipsometry, and the average value was taken for each experimental group.

[0043] Two cleaned cadmium zinc telluride (CZN) wafer substrates were randomly selected from each experimental group. The silicon content on the CZN wafer substrates was tested using TOF-SIMS surface analysis, and the average value was taken for each experimental group.

[0044] The criterion for judging the yield rate is: check the surface of each wafer with a strong light to see if there are scratches, damage, chemicals, etc.

[0045] Table 1 It can be seen that the cadmium zinc telluride wafer cleaning process of this application can effectively improve the cleaning effect on the wafer surface.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A cleaning process for cadmium zinc telluride wafers, characterized in that, Includes the following steps: (1) The polished and dewaxed wafers are immersed in an alkaline solution, wherein the alkaline solution is at least one of tetramethylammonium hydroxide solution, sodium hydroxide solution, and potassium hydroxide solution; the immersion temperature is 20~30℃; the immersion time is 20~40s; and the pH value of the alkaline solution is ≥12.

5. (2) The wafer processed in step (1) is placed in cleaning solution S1 for cleaning treatment. The cleaning solution S1 is a mixture of hydrogen peroxide, nitric acid and water. The volume ratio of hydrogen peroxide, nitric acid and water in the cleaning solution S1 is 1:1~2:2~8. The cleaning treatment temperature is 5~10℃. The cleaning treatment time is 20~60s. The mass concentration of hydrogen peroxide used for preparation is ≥30.0%, and the mass concentration of nitric acid used for preparation is ≥69.0%. (3) The wafer processed in step (2) is placed in S2 cleaning solution for cleaning treatment, wherein the S2 cleaning solution is a mixture of hydrogen peroxide and ammonium hydroxide; (4) The wafer processed in step (3) is placed in S3 cleaning solution for cleaning treatment. The S3 cleaning solution is a mixture of hydrochloric acid, hydrofluoric acid and water. The volume ratio of hydrochloric acid, hydrofluoric acid and water in the S3 cleaning solution is 3~7:1~10:40~50. The cleaning treatment time is 30~60s. The mass concentration of hydrochloric acid used for preparation is ≥36.0%, and the mass concentration of hydrofluoric acid used for preparation is ≥48.8%. (5) The wafer processed in step (4) is placed in S4 cleaning solution for cleaning treatment. The S4 cleaning solution is a mixture of phosphoric acid and / or sulfurous acid and water. The volume ratio of phosphoric acid to water in the S4 cleaning solution is 1:1~10, and the cleaning treatment time is 30~60s. The mass concentration of phosphoric acid used for preparation is ≥85.0%. (6) Place the wafer treated in step (5) in isopropanol solution and rinse twice, each time for 30~60s; (7) Dry the wafer after step (6).

2. The cleaning process as described in claim 1, characterized in that, In step (3), the volume ratio of hydrogen peroxide to ammonium hydroxide in the S2 cleaning solution is 1:1~10; the cleaning time is 30~60s; the mass concentration of hydrogen peroxide used for preparation is ≥30.0% and the mass concentration of ammonium hydroxide used for preparation is ≥28%.

3. The cleaning process as described in claim 1, characterized in that, The drying process in step (7) specifically involves placing the wafer in a drying chamber for 30 to 220 seconds.

4. The cleaning process as described in claim 1, characterized in that, In steps (2), (3), and (4), the cleaning temperature is below 25°C.

5. The cleaning process as described in claim 1, characterized in that, In steps (1) to (6), a water rinsing process is set between adjacent steps. The rinsing process is as follows: the wafer is placed in a water rinsing tank for rinsing, and the rinsing time is 30 to 60 seconds.

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