A cleaning method for ultra-thin germanium single crystal polishing wafer

Abstract

The invention discloses a cleaning method for an ultra-thin germanium single crystal polished wafer, comprising the following steps: 1) rinsing with high-purity water, drying, peeling off a UV film on the back, and inserting the wafer into a slot of a plug with the polished surface facing a U-head of the plug; 2) immersing the wafer in a 3%-40% alkali solution for 2-5 minutes, rinsing with deionized water for 3-5 minutes, and then drying the wafer in a spin dryer; 3) immersing the wafer in a tetramethylammonium hydroxide aqueous solution for 30-120 seconds, and then rinsing with pure water for 30-90 seconds; 4) immersing the wafer in a corrosive solution with a temperature below 6°C for 120-300 seconds, and then rinsing with pure water for 30-90 seconds, drying the wafer, and filling the wafer with nitrogen after checking that the surface quality is qualified. The present invention can effectively remove abrasive particles, damaged oxide layers, and polishing residual solutions on the surface of the polishing wafer. Through cleaning with three solutions, a high-quality cleaned surface of a germanium single crystal polishing wafer can be obtained, with almost no surface particles larger than 0.3 microns. After cleaning, the surface is clean and bright, and the surface is uniform and fine, with a roughness of less than 0.2 nanometers. The method is simple to operate and easy to achieve mass production.

Description

Technical Field

[0001] The invention relates to a cleaning method for an ultra-thin germanium single crystal polishing sheet, and belongs to the technical field of processing ultra-thin germanium single crystal polishing sheets. Background Art

[0002] Germanium is a benchmark material in semiconductor research. Future growth in demand for germanium products in the solar cell sector is primarily driven by two key factors: the rapid development of the aerospace and satellite markets, and the rapid growth of the terrestrial photovoltaic industry. Ultra-thin germanium wafers are attracting significant attention from numerous domestic and international institutions in the aerospace sector.

[0003] Ultra-thin germanium single crystal polished wafers have good mechanical properties and thermal conductivity and are mainly used in high-efficiency batteries. Multi-junction compound batteries can be made by epitaxially growing other semiconductor materials on germanium single crystal substrates. Since the production of multi-junction batteries requires multiple layers of semiconductor materials, heterogeneous structures are easily generated during the production process. Therefore, the surface quality requirements of ultra-thin germanium single crystal polished wafers are extremely high. In the current solar cell production process, the cleaning methods mainly use hot acid, cold acid washing and other methods. After the ultra-thin germanium single crystal polished wafers are cleaned by this method, there are problems such as excessive surface particulate matter, white fog, white spots, and opacity on the surface, and instability of downstream epitaxial wafers, which in turn affect the battery conversion rate. Summary of the Invention

[0004] The present invention provides a method for cleaning an ultra-thin germanium single crystal polishing wafer. The method is not only simple to operate, but also uses a simple, easily available, and low-cost etching solution. Furthermore, a high-quality cleaned surface of the germanium polishing wafer can be obtained, with almost no particles larger than 0.3 microns, a clean and translucent surface, and uniform and fine texture, with a roughness of less than 0.2 nanometers.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] A method for cleaning an ultrathin germanium single crystal polishing wafer, wherein the ultrathin germanium single crystal polishing wafer is polished by a method of attaching a UV film, and the cleaning method includes the following steps in sequence:

[0007] (1) Rinse the ultra-thin germanium single crystal polished sheet with high-purity water, dry it, and irradiate it under ultraviolet light. Remove the UV film on the back of the ultra-thin germanium single crystal polished sheet and insert it into the slot of the plug with the polished surface facing the U-head of the plug.

[0008] (2) Immerse the card containing the ultra-thin germanium single crystal polishing wafer in an alkaline solution with a mass concentration of 3%-40% for 2-5 minutes, then rinse with deionized water for 3-5 minutes to remove abrasive particles and damaged oxide layers on the wafer surface. Then place it in a spin dryer to dry;

[0009] (3) Place the dried germanium single crystal polished wafer on a wafer clamp, immerse it in a tetramethylammonium hydroxide aqueous solution and wash it for 30-120 seconds, then rinse it with pure water for 30-90 seconds;

[0010] (4) The polished germanium single crystal wafer is then placed in an etching solution with a temperature below 6° C. and soaked for 120-300 seconds, and then rinsed with pure water for 30-90 seconds, wherein the etching solution is a mixture of water, hydrogen peroxide, and ammonia water in a volume ratio of (7-9):1:(1-3);

[0011] (5) Shake dry the polished germanium single crystal wafer, check the surface quality and fill it with nitrogen for packaging.

[0012] As common sense, one end of the card is an H head and the other end is a U head, with a total of 25 slots from the H head to the U head.

[0013] Ultra-thin in this application refers to a wafer with a thickness of less than 200 microns.

[0014] The above-mentioned 3%-40% alkali solution has a certain corrosive effect on the surface oxide layer of the ultra-thin germanium single crystal polishing wafer. In the 3%-40% alkali solution, the abrasive silica particles on the surface of the germanium single crystal polishing wafer will dissolve in the solution, and the damaged oxide layer can be peeled off, thereby removing the particle defects and damaged oxide layer defects on the surface of the germanium polishing wafer. Some of the residual potion defects from polishing are also peeled off, thereby obtaining a relatively intact germanium polishing surface. The residual particles of the germanium wafer are then effectively removed by immersing it in a tetramethylammonium hydroxide aqueous solution. Finally, it is further immersed in a special weak corrosive solution to obtain a wafer with a clean, translucent, uniform and delicate surface. After the customer buys it, it is "clean-free" and "ready to use" out of the box.

[0015] In the above step (4), the amount of corrosion is very small, calculated in mg, which can ensure cleanliness, reduce losses and ensure quality.

[0016] To improve the cleaning effect, in step (1), at least one slot is left empty between two adjacent ultra-thin germanium single crystal polished wafers. A cartridge with 25 slots can be filled with 8-13 ultra-thin germanium single crystal polished wafers. This ensures that each wafer is fully soaked in each step.

[0017] In order to balance cost and cleaning quality, in the above step (2), the alkali solution is at least one of an ammonia solution, a sodium hydroxide solution or a potassium hydroxide solution.

[0018] In order to take into account both the cleaning effect and the product quality, in step (3), the mass concentration of the tetramethylammonium hydroxide aqueous solution is 15-35%.

[0019] In order to balance the cleaning effect and product quality, in step (4), the mass concentration of hydrogen peroxide is 28-32%, and the mass concentration of ammonia is 26-30%. Preferably, in step (4), the mass concentration of hydrogen peroxide is 30%, and the mass concentration of ammonia is 28%. More preferably, in step (4), the etching solution is a mixture of water, hydrogen peroxide, and ammonia in a volume ratio of 8:1:2.

[0020] The technologies not mentioned in this invention are all referred to the prior art.

[0021] The cleaning method of the ultra-thin germanium single crystal polishing wafer of the present invention can effectively remove abrasive particles, damaged oxide layers, and polishing residual solutions on the surface of the polishing wafer. Through cleaning with three solutions, a high-quality cleaned surface of the germanium single crystal polishing wafer can be obtained, and the surface particles with a surface size greater than 0.3 microns are almost absent. After cleaning, the surface is clean and translucent, the surface is uniform and fine, and the roughness is less than 0.2 nanometers, fully meeting the "no cleaning" level for immediate use out of the box. The method is simple to operate, has a simple solution composition, is low in cost, and is easy to promote and mass-produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the effect diagram of the wafer after cleaning in Example 1 measured under candela (particle size tester, model: CS20):

[0023] Figure 2 This is a picture of the wafer after cleaning in Example 1 scanned under caemeral (atomic force microscope: model: Park FX40);

[0024] Figure 3 This is a picture of the wafer scanned under a microscope after cleaning in Example 1. DETAILED DESCRIPTION

[0025] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0026] In each step, if the temperature is not mentioned, the operation is carried out at room temperature, which is 15-25°C.

[0027] Example 1

[0028] In this example, an ultra-thin germanium single crystal wafer with a diameter of 100 mm and a thickness of 140 ± 10 μm was polished with a back-side UV film (Nisshin 224 blue film). The cleaning steps are as follows:

[0029] (1) Rinse the polished wafer with plenty of high-purity water, spin dry, and irradiate it under a 30W UV lamp for 45 seconds. Remove the UV film on the back and insert one wafer into the slot with one empty slot, with the polished surface facing the U-head of the card. Insert a total of 12 ultra-thin germanium wafers into the card with 25 slots.

[0030] (2) Prepare ammonia water with a mass concentration of 14%;

[0031] (3) Immerse the card plug containing 12 germanium single crystal polishing wafers in 14% ammonia water (replace it after continuous use for 8 hours) for 4 minutes, then rinse it with deionized water for 3 minutes to remove abrasive particles and damaged oxide layers on the surface of the germanium single crystal polishing wafers, and then place it in a spin dryer to dry;

[0032] (4) Place the dried germanium single crystal polished wafer on a wafer clamp, immerse it in a 20% tetramethylammonium hydroxide aqueous solution (replaced every 4 hours) for 60 seconds, and then rinse with pure water for 70 seconds;

[0033] (5) The polished germanium single crystal wafer is then placed in an etching solution at a temperature of 0-2°C (used continuously for 12 hours and then replaced) for 180 seconds, and then rinsed with pure water for 45 seconds. The etching solution is a mixture of water, hydrogen peroxide, and ammonia water in a volume ratio of 8:1:2, with a mass concentration of hydrogen peroxide of 30% and a mass concentration of ammonia of 28%.

[0034] (6) Dry the polished germanium single crystal wafer. The cleaning effect is as follows: Figure 1 As shown, the surface quality is checked and then packaged.

[0035] After cleaning 360 pieces continuously, the surface quality was counted and the average value was calculated. The results are as follows: Figure 1 As shown, there are 0 particles with a surface particle size greater than 0.3 microns, and no more than 8 particles with a surface particle size between 0.08 and 0.3 microns; Figure 3 As shown, after cleaning, the surface is clean and bright, and the surface is even and delicate. Figure 2 As shown, the roughness is less than 0.2 nanometers, the thickness is 140±10μm, and the yield is 100%.

[0036] Comparative Example 1

[0037] The 14% ammonia water in steps (2) and (3) was replaced with 14% sulfuric acid, and the rest was the same as in Example 1. After continuously cleaning 360 pieces, the surface quality was counted and the average value was calculated. The results were as follows: 246 pieces had a surface particle size greater than 0.3 μm, and the surface had a white fog and was not transparent.

[0038] Comparative Example 2

[0039] The 14% mass concentration of sulfuric acid in Comparative Example 1 was replaced with 14% mass concentration of hydrochloric acid, and the rest of the process was the same as in Example 1. After continuously cleaning 360 pieces, the surface quality was counted and the average value was calculated. The results were as follows: 287 pieces had a surface particle size greater than 0.3 μm, and the surface had white fog and white spots, and was not transparent.

[0040] Comparative Example 3

[0041] The 14% mass concentration of sulfuric acid in Comparative Example 1 was replaced with 14% mass concentration of citric acid, and all other conditions were the same as in Example 1. After continuously cleaning 360 pieces, the surface quality was counted and the average value was calculated. The results were as follows: the number of surface particles larger than 0.3 μm was greater than 300, the surface had white fog and white spots, and was not transparent.

[0042] Comparative Example 4

[0043] The ammonia soaking in steps (2) and (3) was omitted, and the rest was the same as in Example 1. After continuously cleaning 360 pieces, the surface quality was counted and the average value was calculated. The results were as follows: the number of surface particles larger than 0.3 μm was greater than 300, and the surface was whiny and opaque.

[0044] Comparative Example 5

[0045] The 20% tetramethylammonium hydroxide aqueous solution soaking in step (4) was omitted, and the rest was the same as in Example 1. After continuously cleaning 360 pieces, the surface quality was counted and the average value was calculated. The results were as follows: 96 pieces had a surface particle size greater than 0.3 μm, and the surface was whiny and opaque.

[0046] Comparative Example 6

[0047] Step (5) was omitted, and the rest was the same as in Example 1. After continuously cleaning 360 wafers, the surface quality was counted and the average value was calculated. The results were as follows: 56 wafers had surface particles larger than 0.3 μm, and 35% of the wafers had whining or opaque surfaces.

[0048] Comparative Example 7

[0049] In step (5), the etching solution is a mixture of water, hydrogen peroxide and ammonia water in a volume ratio of 8:2:1, and the rest is the same as in Example 1. After continuously cleaning 360 wafers, the surface quality is counted and the average value is calculated. The results are as follows: there is white fog and white spots on the wafer surface.

[0050] Example 2

[0051] In this example, an ultra-thin germanium single crystal wafer with a diameter of 100 mm and a thickness of 140 ± 10 μm was polished with a UV film attached to the back. The cleaning steps are as follows:

[0052] (1) Rinse the polished germanium single crystal wafer with a large amount of high-purity water, dry it, and irradiate it under a 30W ultraviolet lamp for 45 seconds. Remove the UV film on the back, and insert one wafer into the slot with one empty slot in the slot with 25 slots. Insert a total of 13 ultra-thin germanium single crystal polished wafers into the slot.

[0053] (2) preparing an aqueous sodium hydroxide solution with a mass concentration of 18%;

[0054] (3) Immerse the card plug containing 13 germanium single crystal polishing wafers in 18% sodium hydroxide aqueous solution (replaced after continuous use for 8 hours) for 2 minutes, rinse with deionized water for 3 minutes to remove abrasive particles and damaged oxide layers on the wafer surface, and then place it in a spin dryer to dry;

[0055] (4) Place the dried germanium single crystal polished wafer on a wafer clamp, immerse it in a 15% tetramethylammonium hydroxide solution (replaced every 4 hours) for 90 seconds, and then rinse with pure water for 70 seconds;

[0056] (5) The polished germanium single crystal wafer is then placed in an etching solution (replaced after 12 hours of continuous use) at a temperature of 0-2°C and soaked for 150 seconds, and then rinsed with pure water for 45 seconds. The etching solution is a mixture of water, hydrogen peroxide, and ammonia water in a volume ratio of 8:1:2, with a mass concentration of hydrogen peroxide of 30% and a mass concentration of ammonia of 28%.

[0057] (6) Shake the germanium sheets dry and pack them after checking the surface quality.

[0058] After continuously cleaning 390 pieces, the surface quality was counted and the average value was calculated. The results are as follows: there were 0 particles with a surface particle size greater than 0.3 microns, and no more than 8 particles with a particle size of 0.08 to 0.3 microns. After cleaning, the surface was clean and bright, the surface was uniform and fine, the roughness was less than 0.2 nanometers, the thickness was 140±10μm, and the yield rate was 100%.

[0059] Example 3

[0060] In this example, an ultra-thin germanium single crystal wafer with a diameter of 100 mm and a thickness of 140 ± 10 μm was polished with a UV film attached to the back. The cleaning steps are as follows:

[0061] (1) Rinse the polished germanium single crystal wafer with a large amount of high-purity water, dry it, and irradiate it under a 30W ultraviolet lamp for 45 seconds. Remove the UV film on the back, and insert one wafer into the slot with one empty slot in the slot with 25 slots. Insert a total of 13 ultra-thin germanium wafers into the slot.

[0062] (2) preparing a potassium hydroxide solution with a mass concentration of 22%;

[0063] (3) Immerse the plug containing the 13-Ge single crystal polishing wafer in a 22% potassium hydroxide solution (replaced after continuous use for 8 hours) for 1.5 minutes, rinse with deionized water for 5 minutes to remove abrasive particles and damaged oxide layers on the wafer surface, and then place it in a spin dryer to dry;

[0064] (4) Place the dried germanium single crystal polished wafer on a wafer clamp, immerse it in a 15% tetramethylammonium hydroxide aqueous solution (replaced after continuous use for 4 hours) for 90 seconds, and then rinse with pure water for 60 seconds.

[0065] (5) The polished germanium single crystal wafer is then placed in an etching solution (used continuously for 8 hours and replaced) at a temperature of 0-2°C and soaked for 180 seconds, and then rinsed with pure water for 50 seconds. The etching solution is a mixture of water, hydrogen peroxide, and ammonia water in a volume ratio of 8:1:2, with a mass concentration of hydrogen peroxide of 30% and a mass concentration of ammonia of 28%.

[0066] (6) Shake the germanium sheets dry, check the surface quality and then pack them.

[0067] After continuously cleaning 390 pieces, the surface quality was counted and the average value was calculated. The results are as follows: there were 0 particles with a surface particle size greater than 0.3 microns, and no more than 8 particles with a particle size of 0.08 to 0.3 microns. After cleaning, the surface was clean and bright, the surface was uniform and fine, the roughness was less than 0.2 nanometers, the thickness was 140±10μm, and the yield rate was 100%.

Claims

1. A method for cleaning an ultra-thin germanium single crystal polished wafer, characterized in that: The thickness of the ultra-thin germanium single crystal polishing sheet is less than 200 microns. The ultra-thin germanium single crystal polishing sheet is polished by pasting UV film. The cleaning steps include the following steps: (1) Rinse the ultra-thin germanium single crystal polished sheet with high-purity water, dry it, and irradiate it under ultraviolet light. Remove the UV film on the back of the ultra-thin germanium single crystal polished sheet and insert it into the slot of the plug with the polished surface facing the U-head of the plug. (2) Immerse the plug containing the ultra-thin germanium single crystal polished wafer in an alkaline solution with a mass concentration of 3% to 40% for 2 to 5 minutes, then rinse with deionized water for 3 to 5 minutes, and then place it in a spin dryer to dry; (3) Place the dried germanium single crystal polished wafer on a wafer clamp, immerse it in a tetramethylammonium hydroxide aqueous solution and wash it for 30-120 seconds, then rinse it with pure water for 30-90 seconds; (4) The polished germanium single crystal wafer is then placed in an etching solution with a temperature below 6° C. and soaked for 120-300 seconds, and then rinsed with pure water for 30-90 seconds, wherein the etching solution is a mixture of water, hydrogen peroxide, and ammonia water in a volume ratio of (7-9):1:(1-3); (5) Dry the polished germanium single crystal wafer, check the surface quality and fill it with nitrogen for packaging; In step (3), the mass concentration of the tetramethylammonium hydroxide aqueous solution is 15-35%; In step (4), the mass concentration of hydrogen peroxide is 28-32%, and the mass concentration of ammonia water is 26-30%; The germanium single crystal polished wafer obtained in step (5) has zero particles with a surface particle size greater than 0.3 μm, a roughness less than 0.2 nm, and a clean and bright surface.

2. The method for cleaning an ultra-thin germanium single crystal polished wafer according to claim 1, wherein: In step (1), there is at least one empty slot between two adjacent ultra-thin germanium single crystal polished wafers, and a total of 25 slots are inserted into the plug, into which 8-13 ultra-thin germanium single crystal polished wafers are inserted.

3. The cleaning method of the ultra-thin germanium single crystal polishing wafer according to claim 1 or 2, wherein: In step (2), the alkali solution is at least one of an aqueous ammonia solution, a sodium hydroxide solution or a potassium hydroxide solution.

4. The method for cleaning an ultra-thin germanium single crystal polished wafer according to claim 1 or 2, wherein: In step (4), the mass concentration of hydrogen peroxide is 30%, and the mass concentration of ammonia water is 28%.

5. The method for cleaning an ultra-thin germanium single crystal polished wafer according to claim 1 or 2, wherein: In step (4), the etching solution is prepared by mixing water, hydrogen peroxide and ammonia water in a volume ratio of 8:1:2.

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