Static elimination device and epitaxial wafer minority carrier lifetime measurement pretreatment method

Abstract

The invention provides a static electricity elimination device and an epitaxial wafer minority carrier lifetime measurement pretreatment method, and relates to the technical field of treatment before epitaxial wafer minority carrier lifetime measurement, the static electricity elimination device comprises an air ionization assembly and a circulating ion wind drainage assembly, the air ionization assembly is used for ionizing air to generate positive and negative charges; the circulating ion wind drainage assembly is used for draining ionized air at one end of the interior of the air ionization assembly and blowing the air into the circulating ion wind drainage assembly again. Through primary cleaning and secondary cleaning, dangling bonds can be effectively removed, the risk of subsequent process failure caused by surface pollution of the epitaxial wafer is reduced, the quality and performance of the epitaxial wafer are improved while the service life of minority carriers is guaranteed, static electricity on the surface of the sheet-shaped component is eliminated through positive and negative charges generated in the static electricity elimination chamber, and the performance of the sheet-shaped component is improved. Meanwhile, unpaired electrons on dangling bonds are eliminated, the influence on the service life of minority carriers can be reduced, and the service life of the minority carriers is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of processing before measuring the lifetime of minority carriers of epitaxial wafers, and in particular to a static elimination device and a processing method before measuring the lifetime of minority carriers of epitaxial wafers. Background Art

[0002] Minority carrier lifetime (MCL), as one of the basic parameters for measuring the performance of semiconductor devices, is particularly important for the quality assessment of silicon carbide (SiC) materials. The length of minority carrier lifetime directly affects the efficiency and reliability of the device, especially under extreme working conditions such as high pressure and high temperature. Therefore, it is necessary to measure the minority carrier lifetime of the epitaxial wafer. Before the measurement, the epitaxial wafer is cleaned with a hydrofluoric acid solution, and then subjected to spin drying and chemical passivation treatment in sequence after cleaning. After the treatment is completed, the minority carrier lifetime of the epitaxial wafer is measured using a measuring device. The minority carrier lifetime can be obtained by detecting the trend of microwave detection conductivity over time using the microwave photoconductivity attenuation method (μ-PCD), but the existing pre-treatment method will affect the minority carrier lifetime (calculation formula: ∑(X-μ) / n), and the deviation of the impact on the minority carrier lifetime is 20us-25us. The existing pre-treatment method for measuring the minority carrier lifetime of the epitaxial wafer is not conducive to improving the minority carrier lifetime. Summary of the invention

[0003] The object of the present invention is to provide a method for pre-measuring the minority carrier lifetime of an epitaxial wafer which is beneficial to improving the minority carrier lifetime.

[0004] On the one hand, to achieve the above-mentioned purpose, the present invention provides a static electricity elimination device, including an air ionization component and a circulating ion wind drainage component. The air ionization component is used to ionize air to generate positive and negative charges. The generated positive and negative charges can combine with static electricity or unpaired electrons on dangling bonds to achieve the purpose of eliminating static electricity and some dangling bonds; the circulating ion wind drainage component is used to drain the ionized air at one end of the interior of the air ionization component and blow it back into the interior of the circulating ion wind drainage component. Specifically, the circulating ion wind drainage component drains the air close to the positive and negative charge generation site to the site far away from the positive and negative charge generation site, and can adjust the spatial distribution of positive and negative charges, which is beneficial to improving the static electricity removal efficiency.

[0005] As a further solution of the present invention: the air ionization component includes a first electrode, a second electrode and a static elimination chamber, the first electrode and the second electrode are fixed to the inner wall of the static elimination chamber, and the distance between the discharge ends of the first electrode and the second electrode is no more than 1 mm, the voltage loaded on the discharge ends of the first electrode and the second electrode is no less than 300 volts, when the first electrode and the second electrode are powered on, a voltage of no less than 3 kilovolts / cm is generated at the discharge ends of the first electrode and the second electrode, so that the air between the first electrode and the second electrode is ionized, positive and negative charges are generated, and the static elimination chamber and the connecting space are eliminated. Static electricity, when a sheet component whose static electricity is to be eliminated is placed in a space connected to a static electricity elimination chamber, the power of the first electrode and the second electrode is turned on, so that the first electrode and the second electrode discharge and break down the air in their discharge area, causing the air to generate positive and negative charges. After the air with positive and negative charges comes into contact with the surface of the sheet component, the positive charge in the air can neutralize the negative charge on the surface of the sheet component, and at the same time, the negative charge in the air can neutralize the positive charge on the surface of the sheet component, thereby eliminating the static electricity on the surface of the sheet component. In the process of eliminating static electricity, the unpaired positive and negative charges on the hanging bonds on the surface of the sheet component can be eliminated synchronously.

[0006] As a further solution of the present invention: the lower end of the static elimination chamber is connected to an elimination channel, the bottom of the elimination channel is connected to an elimination tube, a second valve is installed at the opening of the elimination tube, the elimination channel is adapted to the sheet component through the bottom opening of the elimination tube, and the sheet component to be eliminated from static electricity is adapted and placed at the opening of the elimination tube, and the second valve is opened, so that the airflow with positive and negative charges in the static elimination chamber can contact the surface of the sheet component, and the positive and negative charges generated in the static elimination chamber can eliminate the static electricity on the surface of the sheet component, and at the same time, the unpaired electrons on the dangling bonds can be eliminated, thereby reducing the impact on the minority carrier lifetime, improving the minority carrier lifetime, and reducing the detection deviation of the minority carrier lifetime.

[0007] As a further solution of the present invention: the top of the elimination channel is connected to the static elimination chamber, and the inner walls of the static elimination chamber and the elimination channel are coated with anti-static coatings to reduce the generation of static electricity. The opening area of ​​the elimination channel is 50 to 70 times the maximum cross-sectional area of ​​the epitaxial wafer, ensuring that a sufficient amount of airflow can be drawn to the surface of the elimination tube through the elimination channel to eliminate static electricity on at least one side of the epitaxial wafer surface. The elimination tube is a hollow cylindrical pipe, and the outer contour shape of the lower opening of the elimination tube is similar to the shape of the epitaxial wafer, which can adapt to the placement of the epitaxial wafer at the opening of the elimination tube. On the one hand, by adopting an elimination tube that adapts to the epitaxial wafer, the gap between the epitaxial wafer and the elimination tube can be reduced, and the exchange of gas between the static elimination chamber and the external environment can be reduced, which is beneficial to ensuring the cleanliness of the gas in the static elimination chamber.

[0008] As a further solution of the present invention: the circulating ion wind drainage component includes a drainage tube and a drainage pump, the drainage tube is airtightly connected to the drainage pump, the input end of the drainage pump is electrically connected to an external power supply, the drainage tube is connected to the top and bottom of the static elimination chamber, the air inlet and air outlet of the drainage pump are respectively connected to the middle part of the drainage tube, the drainage pump can drain the airflow from one end of the drainage tube through the static elimination chamber to the other end of the drainage tube, and a barometer is installed throughout the surface of the drainage tube. The barometer can continuously detect the air pressure in the drainage tube, which is convenient for observing the air pressure changes caused by the ionized air in the static elimination chamber, and for adjusting the air pressure values ​​in the static elimination chamber and the drainage tube, so that after being ionized, the airflow with positive and negative charges can be always drained to the place where static elimination is required.

[0009] As a further solution of the present invention: an air pressure regulating structure is connected through the surface of the drainage tube, and the air pressure regulating structure includes a pressurized airbag and a first valve installed at the connection between the pressurized airbag and the drainage tube. The first valve is used to control the on and off of the airflow inside the drainage tube, and can cooperate with the shutdown operation of the drainage pump to cut off the airflow flowing in the drainage tube, which is beneficial to adjust the air pressure value in the static elimination chamber. When the barometer detects that the air pressure in the drainage tube is lower than the preset expected value, the first valve opens, the pressurized airbag discharges the internal air into the drainage tube, and the drainage pump is started to pass the air in the drainage tube into the static elimination chamber to adjust the air pressure in the static elimination chamber. The drainage tube includes a first pipeline connected to one end of the static elimination chamber and a second pipeline connected to the other end of the static elimination chamber. The drainage pump is connected to the connection between the first pipeline and the second pipeline. The first pipeline and the second pipeline are both hollow arc tubes, which can be used as drainage channels to drain airflows with positive and negative charges and adjust the spatial distribution of airflows with positive and negative charges.

[0010] In a second aspect, the present invention further provides a method for pre-processing an epitaxial wafer minority carrier lifetime measurement, wherein the static electricity is eliminated by using the static electricity elimination device as described in the above scheme, and the method comprises the steps of:

[0011] Eliminate dangling bonds;

[0012] Eliminate static electricity;

[0013] Chemical passivation.

[0014] As a further scheme of the present invention: the method for eliminating dangling bonds includes primary cleaning and secondary cleaning, the primary cleaning includes primary immersion and primary drying, the secondary cleaning includes secondary immersion and secondary drying, the primary cleaning is used to remove organic compounds and metal impurities attached to the surface of the epitaxial wafer, and by reducing the organic compounds and metal impurities, the dangling bonds on the surface of the epitaxial wafer can be reduced, the secondary cleaning is used to remove alkali metal particles, heavy metal ions and oxide layers on the surface of the epitaxial wafer, and reduce the generation of dangling bonds, and by further removing the alkali metal particles, heavy metal ions and oxide layers on the surface of the epitaxial wafer, the cleanliness of the surface of the epitaxial wafer can be maintained, and the existence of dangling bonds can be further reduced.

[0015] As a further scheme of the present invention: the one-time immersion includes immersing the epitaxial wafer in a No. 1 solution for cleaning, the cleaning time is 50 seconds to 100 seconds, the No. 1 solution is composed of ammonia water, hydrogen peroxide and pure water, the volume ratio of ammonia water, hydrogen peroxide and pure water is ammonia water: hydrogen peroxide: pure water = 1:1:5-8, after cleaning, the epitaxial wafer is rinsed with deionized water, the rinsing time is 50 seconds to 100 seconds, until the No. 1 solution attached to the surface of the epitaxial wafer is washed away, and the one-time immersion is completed, after the one-time immersion is completed, the epitaxial wafer is dried once, the drying temperature is 40°C-65°C, and the drying time is 50 seconds to 100 seconds, until there is no liquid attached to the surface of the epitaxial wafer.

[0016] As a further solution of the present invention: the secondary immersion includes immersing the epitaxial wafer after the primary cleaning in a second solution for cleaning, the cleaning time is 25 seconds to 50 seconds, the second solution is composed of hydrochloric acid, hydrogen peroxide and pure water, the volume ratio of hydrochloric acid, hydrogen peroxide and pure water is hydrochloric acid: hydrogen peroxide: pure water = 1:1:5-9, after cleaning, the epitaxial wafer is rinsed again with deionized water, the rinsing time is 25 seconds to 50 seconds.

[0017] As a further solution of the present invention: the secondary cleaning also includes immersing the epitaxial wafer that has been immersed for the second time with a hydrofluoric acid solution, the immersion time is 50 seconds to 100 seconds, and rinsing the epitaxial wafer with deionized water after the immersion cleaning, the rinsing time is 50 seconds to 100 seconds, and the rinsed epitaxial wafer is secondary dried, the secondary drying temperature is 45°C-65°C, the secondary drying time is 50 seconds to 100 seconds, until there is no liquid attached to the surface of the epitaxial wafer.

[0018] As a further solution of the present invention: the dilution ratio of the hydrofluoric acid solution is 1:10-20, and the epitaxial wafer is soaked and cleaned with the diluted hydrofluoric acid solution to remove the oxide layer naturally formed on the surface of the epitaxial wafer and the oxide layer formed during the cleaning process. Through one cleaning and two cleanings, dangling bonds can be effectively removed, greatly reducing the risk of subsequent process failure due to surface contamination of the epitaxial wafer, and effectively improving the quality and performance of the epitaxial wafer.

[0019] As a further solution of the present invention: the method for eliminating static electricity includes ionizing air to generate positive and negative charges, and neutralizing the static electricity on the surface of the epitaxial wafer and the unpaired electrons on the surface of dangling bonds through the positive and negative charges, thereby reducing the impact of the pre-treatment process on the minority carrier lifetime, which is beneficial to improving the minority carrier lifetime.

[0020] As a further solution of the present invention: the primary drying and the secondary drying both include spin drying and / or oven drying.

[0021] As a further solution of the present invention: the chemical passivation method includes passivation layer deposition, heat treatment and local field oxidation (LFO) process. After the epitaxial wafer is cleaned once and twice, a passivation layer is deposited. Commonly used passivation materials include silicon oxide or silicon nitride. Silicon oxide or silicon nitride is deposited on the epitaxial wafer by chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD). After the passivation layer is deposited, a heat treatment process is performed to make the passivation layer and the epitaxial wafer surface better interact and bond, thereby improving the passivation effect. Finally, local field oxidation (LFO) is performed. The local field oxidation (LFO) method includes forming a local oxide layer on the device surface to effectively control the surface electric field and reduce surface recombination.

[0022] As a further solution of the present invention: the passivation method also includes a thermal oxidation method and / or a charge deposition method.

[0023] As a further solution of the present invention: after the chemical passivation step is completed, a final performance test is performed on the epitaxial wafer to ensure that the passivation effect meets the device performance requirements. The performance test is based on physical, chemical and / or electrochemical principles, and the passivation effect is evaluated by measuring the electrochemical behavior, corrosion resistance and mechanical performance parameters of the epitaxial wafer surface.

[0024] As a further solution of the present invention: the method of using the deionized water to rinse the epitaxial wafer includes rinsing the epitaxial wafer three times with cold, hot and cold water flows, the cold water flow temperature is 20°C-25°C, and the hot water flow temperature is 45°C-55°C.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention removes organic compounds and metal impurities attached to the surface of the epitaxial wafer through a primary cleaning, and removes the oxide layer naturally formed on the surface of the epitaxial wafer and the oxide layer, alkali metal particles, heavy metal ions and oxide layer formed during the cleaning process through a secondary cleaning. Through primary cleaning and secondary cleaning, dangling bonds can be effectively removed, greatly reducing the risk of subsequent process failure due to surface contamination of the epitaxial wafer, while ensuring the minority carrier lifetime, the quality and performance of the epitaxial wafer are improved.

[0027] 2. The present invention eliminates static electricity on the surface of sheet components by using positive and negative charges generated in the static elimination chamber, and can also eliminate unpaired electrons on dangling bonds, thereby reducing the impact on the minority carrier lifespan and improving the minority carrier lifespan.

[0028] 3. The present invention uses a circulating ion wind drainage component to drain the air near the positive and negative charge generation sites to sites far away from the positive and negative charge generation sites, which can adjust the spatial distribution of positive and negative charges and is beneficial to improving the static electricity removal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A partial cross-sectional view of the static eliminator of the present invention;

[0030] Figure 2 It is a step diagram of the static elimination method of the present invention;

[0031] Figure 3 is a diagram of minority carrier lifetime before the method of the present invention is adopted;

[0032] Figure 4 This is a diagram of minority carrier lifetime after adopting the method of the present invention.

[0033] In the figure: 1. first electrode; 2. second electrode; 3. static electricity elimination chamber; 4. elimination channel; 401. elimination tube; 402. second valve; 5. drainage tube; 501. first pipeline; 502. second pipeline; 6. drainage pump; 7. pressure gauge; 8. pressurized airbag; 9. first valve. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0035] like Figure 1The figure shows a partial cross-sectional view of the static elimination device of the present invention, which provides a static elimination device, including an air ionization component and a circulating ion wind drainage component. The air ionization component is used to ionize air to generate positive and negative charges. The generated positive and negative charges can combine with static electricity or unpaired electrons on dangling bonds to achieve the purpose of eliminating static electricity and some dangling bonds; the circulating ion wind drainage component is used to drain the ionized air at one end of the interior of the air ionization component and blow it back into the interior of the circulating ion wind drainage component. Specifically, the circulating ion wind drainage component drains the air close to the positive and negative charge generation site to the site far away from the positive and negative charge generation site, and can adjust the spatial distribution of positive and negative charges, which is beneficial to improving the static removal efficiency.

[0036] Preferably, the air ionization component includes a first electrode 1, a second electrode 2 and a static elimination chamber 3, wherein the first electrode 1 and the second electrode 2 are fixed to the inner wall of the static elimination chamber 3, and the distance between the discharge ends of the first electrode 1 and the second electrode 2 is 0.5 mm, and the voltage applied to the discharge ends of the first electrode 1 and the second electrode 2 is 300 volts. When the first electrode 1 and the second electrode 2 are powered on, a voltage of not less than 6 kilovolts / cm is generated at the discharge ends of the first electrode 1 and the second electrode 2, so that the air between the first electrode 1 and the second electrode 2 is ionized to generate positive and negative charges. The power supply of the first electrode 1 and the second electrode 2 is turned on, so that the first electrode 1 and the second electrode 2 are discharged and break down the air in their discharge areas, so that the air generates positive and negative charges. When the epitaxial wafer is placed at the opening at the bottom of the elimination tube 401, the second valve 402 is opened, and the drainage pump 6 is started. The drainage pump 6 can drain the air with positive and negative charges in the static elimination chamber 3 to the second pipeline 502 through the first pipeline 501, and discharge the air with positive and negative charges to the static elimination chamber 3 and the connected space near the elimination tube 401 through the second pipeline 502 to eliminate the static electricity. When the sheet component to be eliminated from static electricity is placed in the space connected to the static elimination chamber, after the air with positive and negative charges contacts the surface of the sheet component, the positive charge in the air can neutralize the negative charge on the surface of the sheet component, and at the same time, the negative charge in the air can neutralize the positive charge on the surface of the sheet component, thereby eliminating the static electricity on the surface of the sheet component. In the process of static electricity elimination, the unpaired positive and negative charges on the dangling bonds on the surface of the sheet component can be eliminated synchronously, thereby clearing the static electricity on the surface of the epitaxial wafer and the unpaired positive and negative charges on the dangling bonds.

[0037] Preferably, the sheet-like component is an epitaxial wafer.

[0038] Preferably, the lower end of the static elimination chamber 3 is connected to an elimination channel 4, the bottom of the elimination channel 4 is connected to an elimination tube 401, and a second valve 402 is installed at the opening of the elimination tube 401. The elimination channel 4 adapts the sheet component through the bottom opening of the elimination tube 401. By adapting and placing the sheet component to be eliminated at the opening of the elimination tube 401 and opening the second valve 402, the positive and negative charges in the static elimination chamber 3 can be brought into contact with the surface of the sheet component, and the positive and negative charges generated in the static elimination chamber 3 can eliminate the static electricity on the surface of the sheet component, and at the same time, the unpaired electrons on the dangling bonds can be eliminated, thereby reducing the impact on the lifetime of minority carriers.

[0039] Preferably, the top of the elimination channel 4 is connected to the static elimination chamber 3, and the inner walls of the static elimination chamber 3 and the elimination channel 4 are coated with an anti-static coating to reduce the generation of static electricity. The opening area of ​​the elimination channel 4 is 3 times the maximum cross-sectional area of ​​the epitaxial wafer, ensuring that a sufficient amount of airflow can be guided to the surface of the elimination tube 401 through the elimination channel 4 to eliminate static electricity on at least one side of the epitaxial wafer surface. The elimination tube 401 is a hollow cylindrical pipe, and the outer contour shape of the lower opening of the elimination tube 401 is similar to the shape of the epitaxial wafer, which can adapt to the placement of the epitaxial wafer at the opening of the elimination tube 401. On the one hand, by adopting the elimination tube 401 that is adapted to the epitaxial wafer, the gap between the epitaxial wafer and the elimination tube 401 can be reduced, and the exchange between the static elimination chamber 3 and the external environment gas can be reduced, which is beneficial to ensure the cleanliness of the gas in the static elimination chamber 3.

[0040] Preferably, the circulating ion wind drainage component includes a drainage tube 5 and a drainage pump 6. The drainage tube 5 is connected to the top and the bottom of the static elimination chamber 3. The air inlet and the air outlet of the drainage pump 6 are respectively connected to the middle part of the drainage tube 5. A barometer 7 is installed on the surface of the drainage tube 5. The barometer 7 can continuously detect the air pressure in the drainage tube 5, which is convenient for observing the air pressure changes caused by the ionized air in the static elimination chamber 3 and adjusting the air pressure values ​​in the static elimination chamber 3 and the drainage tube 5.

[0041] Preferably, the surface of the drainage tube 5 is connected through with an air pressure regulating structure, which includes a pressurized airbag 8 and a first valve 9 installed at the connection between the pressurized airbag 8 and the drainage tube 5. The first valve 9 is used to control the on-off of the airflow inside the drainage tube 5, and can cooperate with the shutdown operation of the drainage pump 6 to cut off the airflow flowing in the drainage tube 5, which is conducive to adjusting the air pressure value in the static elimination chamber 3. When the barometer 7 detects that the air pressure in the drainage tube 5 is lower than the preset expected value, the first valve 9 opens, the pressurized airbag 8 discharges the internal air into the drainage tube 5, starts the drainage pump 6, and passes the air in the drainage tube 5 into the static elimination chamber 3 to adjust the static elimination. The air pressure in the static elimination chamber 3, the drainage pipe 5 includes a first pipeline 501 connected to one end of the static elimination chamber 3 and a second pipeline 502 connected to the other end of the static elimination chamber 3, and the drainage pump 6 is connected to the connection between the first pipeline 501 and the second pipeline 502. The first pipeline 501 and the second pipeline 502 are both hollow arc tubes, which can be used as drainage channels to drain the airflow with positive and negative charges and adjust the spatial distribution of the airflow with positive and negative charges. The interior of the boosting airbag 8 is filled with air when the first electrode 1 and the second electrode 2 are started, so that the air pressure inside the boosting airbag 8 is at least 1.5 times to 3 times the air pressure in the static elimination chamber 3.

[0042] like Figure 2 The figure shows the steps of the static elimination method of the present invention, which provides a method for pre-processing the minority carrier lifetime measurement of an epitaxial wafer, using the static elimination device of the above scheme to eliminate static electricity, and the method includes the following steps:

[0043] S1: Eliminate dangling bonds;

[0044] S2: Eliminate static electricity;

[0045] S3: Chemical passivation.

[0046] Preferably, the method for eliminating dangling bonds includes primary cleaning and secondary cleaning, the primary cleaning includes primary immersion and primary drying, and the secondary cleaning includes secondary immersion and secondary drying. The primary cleaning is used to remove organic compounds and metal impurities attached to the surface of the epitaxial wafer. By reducing the organic compounds and metal impurities, the dangling bonds on the surface of the epitaxial wafer can be reduced. The secondary cleaning is used to remove alkali metal particles, heavy metal ions and oxide layers on the surface of the epitaxial wafer. By further removing the alkali metal particles, heavy metal ions and oxide layers on the surface of the epitaxial wafer, the cleanliness of the surface of the epitaxial wafer can be maintained and the presence of dangling bonds can be further reduced.

[0047] Preferably, a leaching comprises immersing the epitaxial wafer in a No. 1 solution for cleaning, the cleaning time is 100 seconds, the No. 1 solution is composed of ammonia water, hydrogen peroxide and pure water, and the volume ratio of ammonia water, hydrogen peroxide and pure water is ammonia water: hydrogen peroxide: pure water = 1:1:8. After cleaning, the epitaxial wafer is rinsed with deionized water for 100 seconds until the No. 1 solution attached to the surface of the epitaxial wafer is washed away, and a leaching is completed. After the leaching is completed, the epitaxial wafer is dried once, the drying temperature is 65°C, and the drying time is 100 seconds, until there is no liquid attached to the surface of the epitaxial wafer. The total time for a leaching and a drying is 300 seconds, which can effectively remove organic compounds and metal impurities on the surface of the epitaxial wafer. The completion of a leaching and a drying can achieve the first cleaning of the surface of the epitaxial wafer, which can serve as a step to initially reduce dangling bonds on the surface of the epitaxial wafer.

[0048] Preferably, the secondary immersion includes immersing the epitaxial wafer after the primary cleaning in a second solution for cleaning for 50 seconds. The second solution is composed of hydrochloric acid, hydrogen peroxide and pure water. The volume ratio of hydrochloric acid, hydrogen peroxide and pure water is hydrochloric acid: hydrogen peroxide: pure water = 1:1:5. After cleaning, the epitaxial wafer is rinsed again with deionized water for 50 seconds. The total time of the secondary immersion and rinsing is 100 seconds.

[0049] Preferably, the secondary cleaning also includes immersing the epitaxial wafer that has been immersed in a hydrofluoric acid solution for 50 seconds, and rinsing the epitaxial wafer with deionized water after the immersion cleaning for 50 seconds, and secondary drying the rinsed epitaxial wafer at a temperature of 65°C for 50 seconds, until there is no liquid attached to the surface of the epitaxial wafer. The total time for completing the secondary cleaning is 250 seconds.

[0050] Preferably, the dilution ratio of the hydrofluoric acid solution is 1:20, i.e., a 5% hydrofluoric acid solution. The epitaxial wafer is cleaned by immersing it in the diluted hydrofluoric acid solution to remove the oxide layer naturally formed on the surface of the epitaxial wafer and the oxide layer formed during the cleaning process. Through one cleaning and two cleanings, dangling bonds can be effectively removed, greatly reducing the risk of subsequent process failure due to surface contamination of the epitaxial wafer, and effectively improving the quality and performance of the epitaxial wafer.

[0051] Preferably, the method for eliminating static electricity includes ionizing air to generate positive and negative charges, and neutralizing the static electricity on the surface of the epitaxial wafer and the unpaired electrons on the surface of dangling bonds through the positive and negative charges, thereby reducing the impact of the pretreatment process on the minority carrier lifetime, which is beneficial to improving the minority carrier lifetime.

[0052] Preferably, the primary drying and the secondary drying both include spin drying and oven drying.

[0053] Preferably, the method of rinsing the epitaxial wafer with deionized water includes rinsing the epitaxial wafer three times with cold, hot and cold water flows, the cold water flow temperature is 25°C, and the hot water flow temperature is 55°C. By rinsing the epitaxial wafer multiple times with cold, hot and cold deionized water, the surface of the epitaxial wafer can be fully cleaned.

[0054] Preferably, the chemical passivation method includes passivation layer deposition, heat treatment and local field oxidation (LFO) process. After the epitaxial wafer is cleaned once and twice, a passivation layer is deposited. Commonly used passivation materials include silicon oxide or silicon nitride. Silicon oxide or silicon nitride is deposited on the epitaxial wafer by chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD). After the passivation layer is deposited, a heat treatment process is performed to make the passivation layer and the surface of the epitaxial wafer better interact and bond, thereby improving the passivation effect. Finally, local field oxidation (LFO) is performed. The local field oxidation (LFO) method includes forming a local oxide layer on the surface of the device to effectively control the surface electric field and reduce surface recombination. The chemical passivation step takes 150 seconds.

[0055] Preferably, after the chemical passivation step is completed, a final performance test is performed on the epitaxial wafer to ensure that the passivation effect meets the device performance requirements. The performance test is based on physical, chemical and / or electrochemical principles, and the passivation effect is evaluated by measuring the electrochemical behavior, corrosion resistance and mechanical performance parameters of the epitaxial wafer surface. The performance test lasts for 150 seconds.

[0056] like Figure 3 The figure shows the minority carrier lifetime before the method of the present invention is adopted. When the conventional method in the industry is used for processing, the minority carrier lifetime of the epitaxial wafer is 1484.1us.

[0057] like Figure 4 This is the minority carrier lifetime diagram after adopting the method of the present invention. The minority carrier lifetime of the epitaxial wafer is 2697.3us. Compared with the minority carrier lifetime of the epitaxial wafer processed by the conventional industry method, the minority carrier lifetime of the epitaxial wafer processed by the method of the present invention is increased by 1213.2us. It can be seen that the epitaxial wafer processed by the method of the present invention can effectively improve the minority carrier lifetime and reduce the measurement deviation of the minority carrier.

[0058] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A static elimination device, characterized in that: The device comprises: Air ionization components, used to ionize the air to produce positive and negative charges; The circulating ion wind drainage component is used to drain the ionized air at one end of the interior of the air ionization component and blow it back into the interior of the circulating ion wind drainage component.

2. The static eliminator according to claim 1, characterized in that: The air ionization assembly includes a first electrode, a second electrode and an electrostatic elimination chamber, wherein the first electrode and the second electrode are fixed to the inner wall of the electrostatic elimination chamber, and the distance between the discharge ends of the first electrode and the second electrode is no more than 1 mm, and the voltage loaded on the discharge ends of the first electrode and the second electrode is no less than 300 volts.

3. The static eliminator according to claim 2, characterized in that: The lower end of the static elimination chamber is connected to an elimination channel, the bottom of the elimination channel is connected to an elimination pipe, a second valve is installed at the opening of the elimination pipe, and the elimination channel is adapted to a sheet component through the bottom opening of the elimination pipe.

4. The static eliminator according to claim 3, characterized in that: The circulating ion wind drainage component includes a drainage tube and a drainage pump. The drainage tube is connected to the top and bottom of the static elimination chamber. The air inlet and air outlet of the drainage pump are respectively connected to the middle part of the drainage tube. A pressure gauge is installed on the surface of the drainage tube.

5. The static eliminator according to claim 4, characterized in that: An air pressure regulating structure is connected through the surface of the drainage tube, and the air pressure regulating structure includes a pressurized airbag and a first valve installed at the connection between the pressurized airbag and the drainage tube. The drainage tube includes a first pipeline connected to one end of the static elimination chamber and a second pipeline connected to the other end of the static elimination chamber. The drainage pump is connected to the connection between the first pipeline and the second pipeline.

6. A method for pre-processing epitaxial wafer minority carrier lifetime measurement, characterized in that: The static electricity elimination device according to any one of claims 1 to 5 is used to eliminate static electricity, and the method comprises the steps of: Eliminate dangling bonds; Eliminate static electricity; Chemical passivation.

7. The epitaxial wafer minority carrier lifetime measurement pre-processing method according to claim 6, characterized in that: The method for eliminating dangling bonds includes primary cleaning and secondary cleaning, wherein the primary cleaning includes primary immersion and primary drying, and the secondary cleaning includes secondary immersion and secondary drying. The primary cleaning is used to remove organic compounds and metal impurities attached to the surface of the epitaxial wafer, and the secondary cleaning is used to remove alkali metal particles, heavy metal ions and oxide layers on the surface of the epitaxial wafer. The secondary cleaning also includes immersing the epitaxial wafer after the secondary immersion with a hydrofluoric acid solution, the immersion time is 50 seconds to 100 seconds, and rinsing the epitaxial wafer with deionized water after the immersion cleaning, the rinsing time is 50 seconds to 100 seconds, and the rinsed epitaxial wafer is secondary dried, the secondary drying temperature is 45°C-65°C, the secondary drying time is 50 seconds to 100 seconds, and the dilution ratio of the hydrofluoric acid solution is 1:10-20.

8. The epitaxial wafer minority carrier lifetime measurement pre-processing method according to claim 7, characterized in that: The one-time immersion includes immersing the epitaxial wafer in a No. 1 solution for cleaning, and the cleaning time is 50 seconds to 100 seconds. The No. 1 solution is composed of ammonia water, hydrogen peroxide and pure water, and the volume ratio of ammonia water, hydrogen peroxide and pure water is ammonia water: hydrogen peroxide: pure water = 1:1:5-8. After cleaning, the epitaxial wafer is rinsed with deionized water, and the rinsing time is 50 seconds to 100 seconds. After the one-time immersion is completed, the epitaxial wafer is dried once, the drying temperature is 40°C-65°C, and the drying time is 50 seconds to 100 seconds.

9. The epitaxial wafer minority carrier lifetime measurement pre-processing method according to claim 8, characterized in that: The secondary immersion includes immersing the epitaxial wafer after the primary cleaning in a No. 2 solution for cleaning, the cleaning time is 25 seconds to 50 seconds, the No. 2 solution is composed of hydrochloric acid, hydrogen peroxide and pure water, the volume ratio of hydrochloric acid, hydrogen peroxide and pure water is hydrochloric acid: hydrogen peroxide: pure water = 1:1:5-9, and after cleaning, the epitaxial wafer is rinsed again with deionized water, the rinsing time is 25 seconds to 50 seconds.

10. The epitaxial wafer minority carrier lifetime measurement pre-processing method according to claim 9, characterized in that: The static electricity elimination method comprises using the static electricity elimination device to ionize the air to generate positive and negative charges, and neutralizing the static electricity on the surface of the epitaxial wafer and the unpaired electrons on the surface of the dangling bonds by the positive and negative charges.

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