Cleaning method for keeping silicon surface bright and improving conduction voltage drop and silicon wafer

Abstract

The invention discloses a cleaning method for keeping silicon surface brightness and improving conduction voltage drop and a silicon wafer, the cleaning method comprises first acid pickling, first water washing, second acid pickling and second water washing which are carried out in sequence, the first acid pickling is used for removing silicon / silicon slag on the silicon surface, and the specific method is as follows: the silicon wafer subjected to a back thinning process is vertically placed in a first acid pickling tank; a nitric acid mixed solution is circularly introduced into the first pickling tank from bottom to top; inert gas is continuously introduced into the bottom of the first pickling tank, so that bubbles are formed in the nitric acid mixed solution; and vibrating the silicon wafer to enable the silicon wafer to vibrate up and down in the pickling tank 1. According to the silicon wafer wet cleaning method and device, the cooperative adjustment design of liquid medicine circulation, acid tank bubbling and silicon wafer vibration frequency and amplitude is carried out on the first acid pickling procedure in silicon wafer wet cleaning, a good bright state of the silicon surface can be obtained, meanwhile, low contact resistance is formed, and low conduction voltage drop is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chip processing. Specifically, it relates to a cleaning method and a silicon wafer for maintaining the brightness of the silicon surface and improving the on-state voltage drop. Background Art

[0002] The on-state voltage drop of semiconductor power devices is an important indicator determining the power consumption of the devices. A lower on-state voltage drop can greatly reduce the on-state power consumption of the devices, thereby achieving energy conservation, consumption reduction, and green development.

[0003] In addition to reducing the on-state voltage drop at the device design level, during the processing of semiconductor chips, the quality and characteristics of some processing steps also directly affect the magnitude and stability of the on-state voltage drop. These include the bulk resistance of the silicon wafer, the contact resistance between silicon and metal, the resistance of metal electrodes, other internal resistances, etc., all of which affect the on-state resistance of the device to a certain extent, thereby affecting the on-state voltage drop of the device.

[0004] The contact resistance between silicon and metal can be divided into two categories: the contact resistance between silicon and front-side metal, and the contact resistance between silicon and back-side metal. The contact resistance between silicon and front-side metal is affected by factors such as silicon impurity concentration, silicon interface states, the state of the silicon surface, and the quality of metal silicides; the contact resistance between silicon and back-side metal is restricted by the process flow and generally depends only on the silicon impurity concentration and the state of the silicon surface.

[0005] Improving the state of the silicon surface requires specific surface treatment processes. For the contact resistance between silicon and back-side metal, generally two types of methods are used to improve the state of the silicon surface. One is plasma treatment under vacuum to obtain a fresh silicon surface, which requires expensive semiconductor equipment; the other is treatment with chemical solutions / or steam, which can also obtain a good silicon surface, with relatively low cost and controllable quality. The chemical solution treatment method can be further divided into two types: nitric acid mixture and sulfuric acid mixture. Among them, the sulfuric acid mixture has better treatment effect and can obtain a lower and more stable contact resistance between silicon and back-side metal, but the obtained surface color is dull, commonly known as a matte surface. The treatment effect of the nitric acid mixture is relatively poor, and problems such as high and unstable contact resistance often occur, but the obtained surface color is bright, commonly known as a bright surface.

[0006] In view of this, the present application is specifically proposed. Summary of the Invention

[0007] The problem existing in the prior art is that although the sulfuric acid mixture treatment has a better effect and can obtain a lower and more stable contact resistance between silicon and the back metal, the color of the obtained silicon surface is dull. The present invention provides a cleaning method and a silicon wafer for maintaining the brightness of the silicon surface and improving the conduction voltage drop. By treating and cleaning with a nitric acid mixture and designing multiple dimensions of process parameters, it is possible to maintain the brightness of the silicon surface, simultaneously improve the state of the silicon surface, reduce the contact resistance between silicon and the back metal, thereby obtaining a stable and low conduction resistance and achieving a stable low conduction voltage drop.

[0008] The present invention is realized through the following technical solutions:

[0009] In a first aspect, the present invention provides a cleaning method for maintaining the brightness of the silicon surface and improving the conduction voltage drop, including a first pickling, a first water washing, a second pickling, and a second water washing performed in sequence. The first pickling is used to remove silicon / silicon slag on the silicon surface, and the specific method is as follows:

[0010] Vertically place the silicon wafer after the back thinning process into the first pickling tank;

[0011] Circulate the nitric acid mixture from the bottom to the top in the first pickling tank;

[0012] Continuously introduce an inert gas into the bottom of the first pickling tank to form bubbles in the nitric acid mixture;

[0013] Vibrate the silicon wafer to make it vibrate up and down in the first pickling tank.

[0014] By synergistically adjusting the design of liquid circulation, acid tank bubbling, and the vibration frequency and amplitude of the silicon wafer in the first pickling process of the wet cleaning of the silicon wafer, the present invention can obtain a good bright state of the silicon surface, simultaneously form a low contact resistance, and obtain a lower conduction voltage drop.

[0015] In a specific embodiment, the vibration frequency of the silicon wafer is 10 - 30 times / min, and the vibration amplitude is 3 - 4 cm. Specifically, the silicon wafer is placed in a basket and immersed in the circulated nitric acid mixture. By vibrating the basket, the silicon wafer can move up and down in the first pickling tank. The up and down movement of the silicon wafer can promote the exchange rate of the acid solution on the silicon wafer surface, thereby improving the chemical reaction efficiency and uniformity between the acid solution and the silicon wafer surface. During the up and down vibration process, based on the fluid characteristics of the liquid, the reaction products of the chemical reaction can be simultaneously removed away from the silicon wafer surface, without interfering with further chemical reactions.

[0016] Among them, the vibration frequency and amplitude of the basket cannot be too large and must be controlled within the above range; if the vibration frequency and amplitude are too large, the surface of the silicon after the chemical reaction is too smooth. Although a bright surface is obtained, it is not conducive to reducing the contact resistance; conversely, if the vibration frequency and amplitude are too small, both the chemical reaction and the elimination of the reaction products are insufficient, and abnormalities such as contamination and particles will occur.

[0017] In a specific embodiment, the inert gas is nitrogen.

[0018] In a specific embodiment, the flow rate of nitrogen introduced is 1-2 L / min, the distance between the nitrogen introduction holes at the bottom of the first pickling tank is 1-2 cm, and the diameter of the nitrogen introduction holes is 0.5-1 cm.

[0019] In the present invention, nitrogen is introduced from the bottom of the first pickling tank, and the nitrogen bubbles gradually rise from the bottom of the first pickling tank. On the way, they will pass through the contact surface between the acid solution and the silicon wafer, improving the uniformity of the local chemical reaction.

[0020] In the present invention, by limiting the nitrogen introduction flow rate and the size of the nitrogen introduction holes, the size of the nitrogen bubbles can be controlled; if the bubbles are too large, the reaction on the contact surface is uneven, and color differences will form on the silicon surface; while if the bubbles are too small, the efficiency of the chemical reaction will be hindered, and the local reaction is uneven. Therefore, in the present invention, the size of the bubbles is controlled by the nitrogen flow rate, the hole spacing, and the hole diameter, so as to obtain a bright surface with uniform reaction and no color difference.

[0021] In a specific embodiment, the circulation flow rate of the nitric acid mixture is 3-4 L / min.

[0022] In a specific embodiment, the component ratio of the nitric acid mixture is as follows: the volume ratio of HNO3, HF, CH3COOH, and H2O is 6-40:1:1-2:10-20.

[0023] In the present invention, an external circulation pump is used to make the nitric acid mixture circulate in the first pickling tank, which can promote the exchange of the acid solution on the silicon surface and improve the rate of the chemical reaction; at the same time, a filter element is provided on the circulation pump to remove particles in the acid solution and avoid the generation of particles on the silicon surface.

[0024] Among them, in the present invention, by limiting the circulation flow rate of the acid solution, the control range of the flow rate is very crucial. If the flow rate is too large, the surface of the silicon after the chemical reaction is too smooth, which is not conducive to reducing the contact resistance; if the flow rate is too low, the rate of the chemical reaction is low, and reactant particles may appear, and the reaction is uneven.

[0025] In a specific embodiment, the working temperature of the first pickling is room temperature, and the cleaning time is 5-7 min.

[0026] In a specific embodiment, the second pickling is performed by circulating and cleaning with a hydrofluoric acid solution at room temperature for 5 - 7 minutes, and the volume ratio of HF to H₂O in the hydrofluoric acid solution is 1:10 - 50.

[0027] In a specific embodiment, both the first water wash and the second water wash are performed by circulating and rinsing with pure water 5 times. Among them, the purpose of the first water wash is to remove the mixed solution remaining on the silicon surface after the first pickling process; the purpose of the second water wash is to remove the acid solution remaining on the silicon surface after the second pickling process.

[0028] In a second aspect, the present invention also provides a silicon wafer with a bright surface, low conduction voltage drop, and low contact resistance, which is prepared by using the above cleaning method.

[0029] The silicon obtained by the present invention using the above cleaning method has a bright surface and simultaneously has a low and uniform conduction voltage drop. It breaks the conventional cleaning methods: the silicon surface is bright, but the conduction voltage drop is high and uneven; or the conduction voltage drop is low and uniform, but the surface is matte. At the same time, it combines the properties of a bright silicon surface and a low and uniform conduction voltage drop.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. The cleaning method and silicon wafer for maintaining a bright silicon surface and improving the conduction voltage drop provided by the embodiments of the present invention can obtain a better bright state of the silicon surface and simultaneously form a low contact resistance and obtain a low conduction voltage drop through the coordinated adjustment design of the liquid medicine circulation, acid tank bubbling, and the vibration frequency and amplitude of the silicon wafer in the first pickling process of the wet cleaning of the silicon wafer.

[0032] 2. The cleaning method and silicon wafer for maintaining a bright silicon surface and improving the conduction voltage drop provided by the embodiments of the present invention can make the silicon wafer move up and down in the first pickling tank through the vibrating basket. The up and down movement of the silicon wafer can promote the exchange rate of the acid solution on the silicon wafer surface, thereby improving the chemical reaction efficiency and uniformity between the acid solution and the silicon wafer surface. During the up and down vibration process, based on the fluid characteristics of the liquid, the reaction products of the chemical reaction can be simultaneously removed away from the silicon wafer surface and will not interfere with further chemical reactions.

[0033] 3. The cleaning method and silicon wafer for maintaining a bright silicon surface and improving the conduction voltage drop provided by the embodiments of the present invention can introduce nitrogen gas from the bottom of the first pickling tank. The nitrogen gas bubbles gradually rise from the bottom of the first pickling tank and will pass through the contact surface between the acid solution and the silicon wafer on the way, improving the uniformity of the local chemical reaction, thereby obtaining a uniformly reactive and colorless bright surface.

[0034] 4. A cleaning method and silicon wafer for maintaining the brightness of the silicon surface and improving the on-state voltage drop provided by the embodiments of the present invention can promote the circulation of the nitric acid mixture in the first pickling tank through an external circulation pump, thereby promoting the exchange of the acid solution on the silicon surface and increasing the rate of the chemical reaction. At the same time, a filter element is provided in the circulation pump to remove particles in the acid solution and prevent particles from being generated on the silicon surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a schematic diagram of the wet cleaning process of the silicon surface provided by the embodiments of the present invention;

[0037] Figure 2 It is the on-state voltage drop data of the silicon wafer after being cleaned by the methods of Comparative Example 2, Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments and the drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not limit the present invention.

[0039] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that the present invention does not have to be practiced with these specific details. In other embodiments, well-known materials or methods are not specifically described to avoid obscuring the present invention.

[0040] Throughout the specification, the reference to "one embodiment", "embodiment", "one example" or "example" means that the specific features, structures or characteristics described in connection with the embodiment or example are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment", "embodiment", "one example" or "example" appearing throughout the specification do not necessarily refer to the same embodiment or example. In addition, the specific features, structures or characteristics can be combined in any appropriate combination and / or sub-combination in one or more embodiments or examples. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] At present, chemical liquid treatment methods are used to improve the state of the silicon surface, which are mainly divided into two types: nitric acid mixture and sulfuric acid mixture. Among them, the sulfuric acid mixture has a better treatment effect and can obtain a lower and more stable contact resistance between the silicon and the back metal, but the obtained surface color is dull, commonly known as a matte surface. The treatment effect of the nitric acid mixture is relatively poor, and there are often problems of high and unstable contact resistance, but the obtained surface color is bright, commonly known as a bright surface.

[0042] To solve the above technical problems,

[0043] In a first aspect, the present invention provides a cleaning method for maintaining the brightness of the silicon surface and improving the conduction voltage drop, which includes a first pickling, a first water washing, a second pickling, and a second water washing performed in sequence. The first pickling is used to remove silicon / silicon slag on the silicon surface, and the specific method is as follows:

[0044] Vertically place the silicon wafer after the back thinning process into the first pickling tank;

[0045] Circulate the nitric acid mixture from bottom to top into the first pickling tank;

[0046] Continuously introduce an inert gas into the bottom of the first pickling tank to form bubbles in the nitric acid mixture;

[0047] Vibrate the silicon wafer to make it vibrate up and down in the first pickling tank.

[0048] Through the coordinated adjustment design of liquid circulation, acid tank bubbling, and the vibration frequency and amplitude of the silicon wafer in the first pickling process of the wet cleaning of the silicon wafer, the present invention can obtain a good bright state of the silicon surface, simultaneously form a low contact resistance, and obtain a lower conduction voltage drop.

[0049] In a specific embodiment, the vibration frequency of the silicon wafer is 10 - 30 times / min, and the vibration amplitude is 3 - 4 cm (where the vibration amplitude refers to the height difference between the highest point and the lowest point of the movement of the silicon wafer). Specifically, the silicon wafer is placed in a basket and immersed in the circulated nitric acid mixture. By vibrating the basket, the silicon wafer can move up and down in the first pickling tank. The up and down movement of the silicon wafer can promote the exchange rate of the acid solution on the surface of the silicon wafer, thereby improving the chemical reaction efficiency and uniformity between the acid solution and the silicon wafer surface. During the up and down vibration process, based on the fluid characteristics of the liquid, the reaction products of the chemical reaction can be simultaneously removed and kept away from the silicon wafer surface, without interfering with further chemical reactions.

[0050] Among them, the vibration frequency and amplitude of the basket cannot be too large and must be controlled within the above range; if the vibration frequency and amplitude are too large, the silicon surface after the chemical reaction is too smooth. Although a bright surface is obtained, it is not conducive to reducing the contact resistance; on the contrary, if the vibration frequency and amplitude are too small, both the chemical reaction and the removal of the reaction products are not sufficient, and abnormalities such as contamination and particles will occur.

[0051] In a specific embodiment, the inert gas is nitrogen.

[0052] In a specific embodiment, the flow rate of nitrogen gas introduced is 1 - 2 L / min, the distance between the nitrogen gas inlet holes at the bottom of the first pickling tank is 1 - 2 cm, and the diameter of the nitrogen gas inlet holes is 0.5 - 1 cm.

[0053] In the present invention, by introducing nitrogen gas from the bottom of the first pickling tank, the nitrogen gas bubbles gradually rise from the bottom of the first pickling tank and will pass through the contact surface between the acid solution and the silicon wafer during the process, improving the uniformity of the local chemical reaction.

[0054] In the present invention, by limiting the flow rate of nitrogen gas introduced and the size of the nitrogen gas inlet holes, the control of the size of the nitrogen gas bubbles is achieved; if the bubbles are too large, the reaction on the contact surface is uneven, and color differences will form on the silicon surface; while if the bubbles are too small, the efficiency of the chemical reaction will be hindered and the local reaction will be uneven. Therefore, in the present invention, the size of the bubbles is controlled by the nitrogen gas flow rate, the hole spacing, and the hole diameter, thereby obtaining a bright surface with uniform reaction and no color difference.

[0055] In a specific embodiment, the circulation flow rate of the nitric acid mixture is 3 - 4 L / min.

[0056] In a specific embodiment, the components of the nitric acid mixture are as follows: the volume ratio of HNO3, HF, CH3COOH, and H2O is 6 - 40:1:1 - 2:10 - 20.

[0057] In the present invention, an external circulation pump is used to make the nitric acid mixture in a circulating state in the first pickling tank, thereby promoting the exchange of the acid solution on the silicon surface and improving the rate of the chemical reaction; at the same time, a filter element is provided in the circulation pump to remove particles in the acid solution and avoid the generation of particles on the silicon surface.

[0058] Among them, in the present invention, by limiting the circulation flow rate of the acid solution, the control range of the flow rate is very crucial. If the flow rate is too large, the silicon surface after the chemical reaction is too smooth, which is not conducive to reducing the contact resistance; if the flow rate is too low, the rate of the chemical reaction is low, and reactant particles may appear and the reaction may be uneven.

[0059] In a specific embodiment, the working temperature of the first pickling is room temperature, and the cleaning time is 5 - 7 min.

[0060] In a specific embodiment, the second pickling is carried out by circulating and cleaning with a hydrofluoric acid solution at room temperature for 5 - 7 min, and the volume ratio of HF and H2O in the hydrofluoric acid solution is 1:10 - 50.

[0061] In a specific embodiment, both the first water wash and the second water wash are performed by circulating and rinsing with pure water 5 times. Among them, the purpose of the first water wash is to remove the mixed liquid remaining on the silicon surface after the first pickling process; the purpose of the second water wash is to remove the acid solution remaining on the silicon surface after the second pickling process.

[0062] In a second aspect, the present invention also provides a silicon wafer with a bright surface, low conduction voltage drop, and low resistance, which is obtained by using the cleaning method described above.

[0063] The silicon obtained by the present invention using the above cleaning method has a bright surface and low and uniform conduction voltage drop. It breaks the conventional cleaning methods: the silicon surface is bright, but the conduction voltage drop is high and uneven; or the conduction voltage drop is low and uniform, but the surface is matte. At the same time, it combines the performance of a bright silicon surface and a low and uniform conduction voltage drop.

[0064] Example 1

[0065] An embodiment of the present invention provides a cleaning method for maintaining a bright silicon surface and improving the conduction voltage drop, including first pickling, first water wash, second pickling, and second water wash performed in sequence;

[0066] (1) First pickling

[0067] Put the silicon wafer after the back thinning process into a basket, and then vertically place it into pickling tank 1;

[0068] Circulate and introduce a nitric acid mixed solution (components are as follows: the volume ratio of HNO3, HF, CH3COOH, and H2O is 10:1:1:20) from bottom to top into pickling tank 1 at room temperature, and the circulation flow rate of the nitric acid mixed solution is 3 - 4 L / min;

[0069] Continuously introduce nitrogen gas into the bottom of pickling tank 1 to form bubbles in the nitric acid mixed solution. The introduction flow rate of nitrogen gas is 1 - 2 L / min, the distance between the nitrogen gas introduction holes at the bottom of pickling tank 1 is 1 - 2 cm, and the diameter of the nitrogen gas introduction holes is 0.5 - 1 cm;

[0070] Vibrate the basket to make the silicon wafer vibrate up and down in pickling tank 1 for 5 minutes. The vibration frequency of the silicon wafer is 10 - 30 times / min, and the vibration amplitude is 3 - 4 cm.

[0071] (2) First water wash

[0072] Use pure water to circulate and rinse the silicon wafer after the first pickling 5 times to remove the remaining nitric acid mixed solution on the silicon surface.

[0073] (3) Second pickling

[0074] At room temperature, use diluted hydrofluoric acid to circulate and clean the silicon wafer to remove the natural oxide layer on the silicon surface.

[0075] (4) Second water rinse

[0076] Use pure water to perform 5 - cycle rinsing on the silicon wafers that have undergone the second pickling to remove the residual hydrofluoric acid on the silicon surface.

[0077] After cleaning by the method of the present invention, observe the surface state of the silicon wafers and the surface state of the silicon wafers after the subsequent metal evaporation process. The surface shows a bright state.

[0078] Comparative Example 1

[0079] This comparative example provides a method for cleaning the silicon surface, including first pickling, first water rinse, second pickling, and second water rinse performed in sequence;

[0080] (1) First pickling

[0081] At room temperature, use a nitric acid mixture (volume ratio of HNO3, HF, CH3COOH, and H2O is 10:1:1:20) to perform cyclic cleaning on the silicon wafers to remove silicon / silicon slag on the silicon surface.

[0082] (2) First water rinse

[0083] Use pure water to perform 5 - cycle rinsing on the silicon wafers that have undergone the first pickling to remove the residual nitric acid mixture on the silicon surface.

[0084] (3) Second pickling

[0085] At room temperature, use diluted hydrofluoric acid to perform cyclic cleaning on the silicon wafers to remove the natural oxide layer on the silicon surface.

[0086] (4) Second water rinse

[0087] Use pure water to perform 5 - cycle rinsing on the silicon wafers that have undergone the second pickling to remove the residual hydrofluoric acid on the silicon surface.

[0088] After cleaning by the method of Comparative Example 1, observe the surface state of the silicon wafers and the surface state of the silicon wafers after the subsequent metal evaporation process. The surface shows a bright state.

[0089] Comparative Example 2

[0090] This comparative example provides a method for cleaning the silicon surface, including first pickling, first water rinse, second pickling, and second water rinse performed in sequence;

[0091] (1) First pickling

[0092] At room temperature, use a sulfuric acid mixture (volume ratio of H2SO4, HNO3, and HF is 6:1:1) to perform cyclic cleaning on the silicon wafers to remove silicon / silicon slag on the silicon surface.

[0093] (2) First water rinse

[0094] The silicon wafers after the first pickling are rinsed 5 times with pure water to remove the residual nitric acid mixture on the silicon surface.

[0095] (3) Second pickling

[0096] At room temperature, the silicon wafers are cleaned by circulating diluted hydrofluoric acid to remove the natural oxide layer on the silicon surface.

[0097] (4) Second water wash

[0098] The silicon wafers after the second pickling are rinsed 5 times with pure water to remove the residual hydrofluoric acid on the silicon surface.

[0099] After cleaning by the method of Comparative Example 2, the surface state of the silicon wafers and the surface state after the subsequent metal evaporation process are observed, and the surface is in a matte state.

[0100] As Figure 2 Table 1 shows the on-state voltage drop data of the silicon wafers after being cleaned by the methods of Example 1 and Comparative Examples 1 and 2.

[0101] Table 1

[0102]

[0103] It can be seen from the data in the table that the cleaning method of the nitric acid-based mixture of the present invention obtains a low and uniform on-state voltage drop while obtaining a bright silicon wafer surface. It breaks the conventional cleaning methods: the silicon surface is bright, but the on-state voltage drop is high and uneven; or the on-state voltage drop is low and uniform, but the surface is matte. At the same time, it has the properties of a bright silicon surface and a low and uniform on-state voltage drop.

[0104] The specific embodiments described above further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cleaning method for maintaining the brightness of the silicon surface and improving the on-state voltage drop, including first pickling, first water washing, second pickling, and second water washing carried out in sequence, characterized in that, The specific method of the first pickling is as follows: Vertically place the silicon wafers that have undergone the back thinning process into the first pickling tank; Circulate and introduce the nitric acid mixture into the first pickling tank from bottom to top; Continuously introduce an inert gas into the bottom of the first pickling tank to form bubbles in the nitric acid mixture; Vibrate the silicon wafers to make them vibrate up and down in the first pickling tank.

2. The cleaning method for maintaining the brightness of the silicon surface and improving the on-state voltage drop according to claim 1, characterized in that, The vibration frequency of the silicon wafers is 10 - 30 times / min, and the vibration amplitude is 3 - 4 cm.

3. A cleaning method for maintaining a bright silicon surface and improving the on-state voltage drop according to claim 1, characterized in that, The inert gas used is nitrogen.

4. A cleaning method for maintaining the brightness of a silicon surface and improving the on-state voltage drop according to claim 3, characterized in that, The flow rate of nitrogen introduced is 1 - 2 L / min, the distance between the nitrogen inlet holes at the bottom of the first pickling tank is 1 - 2 cm, and the diameter of the nitrogen inlet holes is 0.5 - 1 cm.

5. The cleaning method for maintaining the brightness of the silicon surface and improving the on-state voltage drop according to claim 3, wherein The circulation flow rate of the nitric acid mixture is 3 - 4 L / min.

6. A cleaning method for maintaining the brightness of the silicon surface and improving the on-state voltage drop according to claim 5, characterized in that The components of the nitric acid mixture include HNO3, HF, and CH3COOH.

7. A cleaning method for maintaining the brightness of the silicon surface and improving the on-state voltage drop according to claim 5, characterized in that, The working temperature of the first pickling is room temperature, and the cleaning time is 5 - 7 min.

8. A cleaning method for maintaining the brightness of a silicon surface and improving the on-state voltage drop according to claim 5, characterized in that, The second pickling is carried out by circulating and cleaning with a hydrofluoric acid solution at room temperature for 5 - 7 min. The volume ratio of HF to H2O in the hydrofluoric acid solution is 1:10 - 1:

50.

9. A cleaning method for maintaining the brightness of the silicon surface and improving the conduction voltage drop according to claim 5, characterized in that, Both the first water wash and the second water wash are carried out by circulating and rinsing with pure water.

10. A silicon wafer with a bright surface, good electrical conductivity and low voltage drop, characterized in that, Prepared by the method according to any one of claims 1 - 9.

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