An acid pickling method for electronic grade polysilicon gradient

Abstract

The application discloses an acid pickling method for electronic-grade polysilicon gradient, which comprises the following steps: carrying out three-stage acid pickling on polysilicon blocks, using the discharge liquid of the next stage acid pickling as the acid pickling liquid of each stage; carrying out high-purity water cleaning on the polysilicon blocks before each acid pickling, and carrying out high-purity water spraying after the first high-purity water cleaning and the last high-purity water cleaning; and finally, carrying out nitrogen drying on the polysilicon blocks after the spraying cleaning. The method has the advantages that the utilization rate of the acid pickling liquid is effectively improved, and the operation cost is reduced through the orderly and multi-stage acid pickling utilization mode. Meanwhile, the acid concentration of the multi-stage utilized acid pickling liquid is reduced, the ion concentration is high, the surface tension of the acid pickling liquid is effectively reduced, the wettability of the acid pickling liquid is higher, the acid pickling liquid can be more deeply in the gaps of the silicon blocks, and the cleaning quality is improved. Compared with other electronic-grade polysilicon processes, the process is simple, the acid preparation links are reduced, the acid discharge is reduced, the treatment cost is saved, the method is more environmentally friendly, and the personnel safety problem is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polysilicon pickling, and particularly relates to a pickling method for electronic-grade polysilicon gradient. BACKGROUND

[0002] Electronic-grade polysilicon is a kind of polysilicon with very high purity, and with the continuous progress of semiconductor process technology, the purity and quality of electronic-grade polysilicon are required to be higher and higher. The electronic-grade polysilicon produced by the vapor deposition method is in the form of a rod with a large volume, which needs to be broken into blocks before being supplied to downstream users. In the current silicon rod breaking process, whether manual breaking or mechanical breaking, or in the subsequent screening process, various impurities will inevitably be introduced. If the impurities on the surface of the silicon block are not removed, the impurities will enter the silicon rod body during crystal pulling, resulting in a decrease in purity.

[0003] In the current production process of polysilicon, the cleaning process is mainly realized through the following procedures: first, multiple passes of high-purity water spraying and water washing, then nitric acid and hydrofluoric acid mixed acid etching, and then again high-purity water spraying and water washing. After multiple cleaning processes, drying is finally performed.

[0004] When cleaning polysilicon, the following two problems have not been effectively solved:

[0005] 1. With the increase of cleaning batches, the acid concentration of the mixed acid etched off the surface layer of the silicon block decreases, resulting in a decrease in the cleaning quality of the polysilicon, and the polysilicon cleaning cannot achieve the required etching thickness. The existing solution is to continuously supplement and replace newly prepared nitric acid / hydrofluoric acid mixed acid to maintain the reaction rate, so as to meet the etching thickness of the silicon block within the time limit defined by the process production rhythm.

[0006] However, frequent acid replacement results in high cleaning cost and reduces cleaning efficiency.

[0007] 2. There are small gaps and cracks on the surface of the broken polysilicon silicon block, and metal particles in the air or particles on the utensils in contact with the silicon block will gradually diffuse into the gaps and cracks of the silicon block over time. Due to the surface tension of the mixed acid solution, it cannot enter the gaps, and it is difficult to remove. If you want to clean the impurities diffused into the gaps and cracks of the silicon block, you need to use nitric acid and hydrofluoric acid mixed acid, increase the concentration of the mixed acid in the solution, and then increase the reaction etching time to increase the etching thickness, until the outer part of the silicon block containing the gaps and cracks is etched, so as to eliminate the impurities in the gaps.

[0008] However, this method increases the reaction time, slows down the yield, and causes waste of high-purity nitric acid and hydrofluoric acid, resulting in cost waste. SUMMARY

[0009] The application aims to provide an acid pickling method for electronic-grade polysilicon gradient.

[0010] The application is implemented by the following technical solutions:

[0011] Primary cleaning:

[0012] The polysilicon block is subjected to three-stage acid pickling, the acid pickling solution used in each stage is a newly configured acid pickling solution, and the acidity of the acid pickling solution used in each stage is lower than that of the acid pickling solution in the previous stage; the polysilicon block is subjected to high-purity water cleaning before each acid pickling, and high-purity water spraying is performed after the first high-purity water cleaning and the last high-purity water cleaning; and finally, the polysilicon block is subjected to nitrogen drying after the spraying cleaning is completed.

[0013] Normal cleaning:

[0014] The primary cleaning process is still adopted, and after one process of primary cleaning is completed, the acid pickling solutions after the acid pickling of the first stage and the second stage are discharged, the acid pickling solution of the first stage adopts the discharge solution of the acid pickling of the second stage, the acid pickling solution of the second stage adopts the discharge solution of the acid pickling of the third stage, and then the normal cleaning process is performed.

[0015] Preferably, the device used for the acid pickling of the first stage is a first-stage acid pickling tank, the device used for the acid pickling of the second stage is a second-stage acid pickling tank, and the device used for the acid pickling of the third stage is a third-stage acid pickling tank.

[0016] Preferably, the acid pickling time of the third-stage acid pickling is 150-300s.

[0017] Preferably, the acid pickling solutions in the first-stage acid pickling tank, the second-stage acid pickling tank and the third-stage acid pickling tank are mixed acid solutions mixed by nitric acid and hydrofluoric acid.

[0018] Preferably, the device used for the high-purity water cleaning is a high-purity water cleaning tank.

[0019] Preferably, the cleaning time of the high-purity water cleaning is 150-300s.

[0020] Preferably, the device used for the high-purity water spraying is a high-purity water spraying tank and a self-rotating cleaning head.

[0021] Preferably, the water pressure of the high-purity water spraying is 0.2Mpa, and the flushing time is 150-300s.

[0022] Preferably, the nitrogen drying is performed by nitrogen hot air blowing in a nitrogen drying tank, the hot air temperature is 60-120℃, the air volume is 1000m³ / h, and the drying time is 150-300s.

[0023] The present application has the advantages that the utilization rate of the pickling solution is effectively improved and the operation cost is reduced by using the pickling method in an orderly and multi-stage manner. Meanwhile, the pickling solution used in the multi-stage manner has a reduced acid concentration and a high ion concentration, effectively reduces the surface tension of the pickling solution, has a higher wettability, can penetrate into the gaps of the silicon blocks more deeply, and improves the cleaning quality. Compared with other electronic-grade polysilicon processes, the process is simple, the acid preparation process is reduced, the acid discharge is reduced, the treatment cost is saved, the process is more environmentally friendly, and the personnel safety problem is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and all other drawings can be obtained by those skilled in the art without any creative effort.

[0025] Figure 1 is a schematic diagram of the overall structure of the present application.

[0026] In the figure: first-stage pickling tank 1, second-stage pickling tank 2, third-stage pickling tank 3, high-purity water cleaning tank 4, high-purity water spraying tank 5, nitrogen drying tank 6. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present application.

[0028] As shown in Figure 1 , an electronic-grade polysilicon gradient pickling method, the initial cleaning is:

[0029] The polysilicon blocks are subjected to three-stage pickling, the pickling solution used in each stage is a newly prepared pickling solution, and the acidity of the pickling solution used in each stage is lower than that of the pickling solution in the previous stage. The polysilicon blocks are subjected to high-purity water cleaning before each pickling, and high-purity water spraying is performed after the first high-purity water cleaning and the last high-purity water cleaning. Finally, the polysilicon blocks are subjected to nitrogen drying after the spraying cleaning is completed.

[0030] Normal cleaning:

[0031] The initial cleaning process is still used for cleaning. After one process of initial cleaning is completed, the pickling solutions after the first-stage and second-stage pickling are discharged. The first-stage pickling uses the discharge solution of the second-stage pickling, and the second-stage pickling uses the discharge solution of the third-stage pickling, and then the normal cleaning process is performed.

[0032] The equipment for the first-stage acid pickling is a first-stage acid pickling tank 1, the equipment for the second-stage acid pickling is a second-stage acid pickling tank 2, and the equipment for the third-stage acid pickling is a third-stage acid pickling tank 3.

[0033] The acid pickling time of the third-stage acid pickling is 150-300s.

[0034] The acid pickling liquid in the first-stage acid pickling tank 1, the second-stage acid pickling tank 2 and the third-stage acid pickling tank 3 is a mixed acid liquid mixed by nitric acid and hydrofluoric acid.

[0035] The equipment for the high-purity water cleaning is a high-purity water cleaning tank 4.

[0036] The cleaning time of the high-purity water cleaning is 150-300s.

[0037] The equipment for the high-purity water spraying is a high-purity water spraying tank 5 and a self-rotating cleaning head.

[0038] The water pressure of the high-purity water spraying is 0.2Mpa, and the flushing time is 150-300s.

[0039] The nitrogen drying is carried out by blowing nitrogen hot air in a nitrogen drying tank 6, the hot air temperature is 60-120℃, the air volume is 1000m³ / h, and the drying time is 150-300s.

[0040] The advantages of the present application are as follows: by using the ordered and multi-stage acid pickling method, the utilization rate of the acid pickling liquid is effectively improved, and the operation cost is reduced. Meanwhile, the acid concentration of the multi-stage used acid pickling liquid is reduced, the ion concentration is high, the surface tension of the acid liquid is effectively reduced, the wettability of the acid pickling liquid is higher, the cleaning quality is improved, the process is simple compared with other electronic-grade polysilicon processes, the acid preparation process is reduced, the acid liquid discharge is reduced, the treatment cost is saved, the process is more environmentally friendly, and the personnel safety problem is greatly reduced.

[0041] Working principle: when the present application is used,

[0042] The acid pickling process direction is as follows: the silicon block material is placed in a PVDF material cuboid basket, is grabbed by a mechanical hand, and is sequentially passed through a first high-purity water cleaning tank 4, a first high-purity water spraying tank 5, a first-stage acid pickling tank 1, a second high-purity water cleaning tank 4, a second-stage acid pickling tank 2, a third high-purity water cleaning tank 4, a third-stage acid pickling tank 3, a fourth high-purity water cleaning tank, a second high-purity water spraying tank 5 and a nitrogen drying tank 6. The impurity removal and other water washing, soaking and spraying purposes are all for removing the impurity residues or solution residues of the previous process, and are not recycled and used.

[0043] (1) The polysilicon block material is immersed in the first high-purity water cleaning tank 4 to precipitate surface impurities, particulate matters and the like. The high-purity water conductivity is required to reach 15-18MΩ / CM;

[0044] (2) The polysilicon block is sprayed and washed in the first high-purity water spraying tank 5, with the purpose of removing the granular silicon on the surface of the silicon block and other particulate impurities which fall off after soaking in high-purity water;

[0045] (3) The first-stage pickling tank 1 can use pickling liquid with lower acidity than the second-stage pickling tank 2 in the initial start-up stage, and use the discharge liquid of the second-stage pickling tank 2 after the production is stable, which can clean the impurities in the gap with low surface tension and save acid and reduce cost;

[0046] (4) The polysilicon block is cleaned in the second high-purity water cleaning tank 4, using high-purity water to clean the residual liquid in the first-stage pickling tank 1, so as to avoid the impurities in the first-stage pickling tank 1 from being introduced into the second-stage pickling tank 2 and prevent cross contamination.

[0047] (5) The second-stage pickling tank 2 is pickled, which can use pickling liquid with lower acidity than the third-stage pickling tank 3 in the initial start-up stage, and use the discharge liquid of the third-stage pickling tank 3 after the production is stable, which still has high acid concentration and can perform one-step light etching to improve the etching thickness, while saving acid and reducing cost;

[0048] (6) The polysilicon block is cleaned in the third high-purity water cleaning tank 4, using high-purity water to clean the residual liquid in the second-stage pickling tank 2, so as to avoid the impurities in the second-stage pickling tank 2 from being introduced into the third-stage pickling tank 3 and prevent cross contamination.

[0049] (7) The third-stage pickling tank 3 is pickled, which is the main working tank and contains mixed acid pickling liquid composed of nitric acid and hydrofluoric acid, with strong acidity. The polysilicon block first reacts with nitric acid to generate silicon dioxide, and the generated silicon dioxide reacts with hydrofluoric acid to generate hexafluorosilicate, while releasing a certain amount of nitrogen oxide. The molar mass ratio of hydrofluoric acid to nitric acid is 1:5~1:10, the mass concentration of hydrofluoric acid is 15~25wt%, the mass concentration of nitric acid is 45~75wt%, and the rest is water;

[0050] (8) The polysilicon block is soaked and cleaned in the fourth high-purity water cleaning tank;

[0051] (9) The polysilicon block is uniformly sprayed and washed in the second high-purity water spraying tank 5;

[0052] (10) The polysilicon block is dried in the nitrogen drying tank 6 using nitrogen hot air blowing.

[0053] The acid solution flows as follows: after the first start or after the overhaul, the acid solution in the second pickling tank 2 is 50% of that in the third pickling tank 3, the acid solution in the first pickling tank 1 is 25% of that in the third pickling tank 3, and the third pickling tank 3 is the main working tank, in which the mixed acid solution is a new solution, nitric acid and hydrofluoric acid are mixed uniformly in the solution pool and then are delivered to the third pickling tank 3 by an acid solution pump; the solution in the second pickling tank 2 is the discharge solution of the third pickling tank 3, when the acid solution in the third pickling tank 3 needs to be completely discharged and replaced, the discharge solution is delivered to the second pickling tank 2 by a delivery pump for the second pickling tank 2 to use; the original acid solution in the second pickling tank 2 is delivered to the first pickling tank 1 by a delivery pump for the first pickling tank 1 to use again; and the original acid solution in the first pickling tank 1 is discharged and abandoned. From the third pickling tank 3 to the first pickling tank 1, the acid concentration decreases successively, the ion concentration increases successively, the surface tension decreases, the wettability increases, the etching capacity for the silicon block decreases, the etching thickness of the silicon block decreases, but the ability to enter the micro gap increases, and the impurities in the gap of the cleaned silicon material are more effectively removed.

[0054] The acid solution is replaced: the solution in the third pickling tank 3 has great corrosion and high acid concentration, and direct measurement is costly, so the etching capacity of the acid solution can be indirectly measured by the weight change of a standard block, that is, a standard silicon block with a size of 2*2*2 cm is put into the acid washing process together with the normal silicon block to be cleaned, and after the acid washing for the specified time, the weight difference G before and after the acid washing is obtained by an analytical balance to represent the etching capacity of the acid solution. For each fixed acid washing process, the weight difference G of the standard block is basically consistent, and when the actual weight difference g is less than or equal to Gx%, it indicates that the quality of the acid solution does not meet the requirements of the third pickling tank 3, and the acid solution needs to be replaced, wherein G is the standard difference value required by the process, x is between 85 and 99, and the actual weight should be greater than or equal to 90% of the standard weight difference, for example, the standard weight difference is G X =0.05 g, and the actual weight should be greater than or equal to 90% of the standard weight difference, and when the actual weight difference g is less than or equal to 0.045, the acid is replaced, and x=90.

[0055] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An acid pickling method for an electronic-grade polysilicon gradient, characterized by, The polysilicon blocks are subjected to three-stage acid pickling, the acid pickling solution used in each stage is the discharge solution of the next stage; the polysilicon blocks are subjected to high-purity water cleaning before each acid pickling, and high-purity water spraying is performed after the first high-purity water cleaning and the last high-purity water cleaning; and finally the polysilicon blocks are subjected to nitrogen drying after the spraying cleaning; The acid concentration of the acid pickling solution of the three-stage acid pickling is arranged in a sequence from low to high; The equipment used for the high-purity water spraying is a high-purity water spraying tank and a self-rotating cleaning head; The water pressure of the high-purity water spraying is 0.2 Mpa, and the flushing time is 150-300 s.

2. The method of claim 1, wherein the acid pickling method is characterized by: The equipment used for the three-stage acid pickling is a first-stage acid pickling tank, a second-stage acid pickling tank and a third-stage acid pickling tank in sequence.

3. The method of claim 1, wherein the acid pickling method is characterized by: The acid pickling time of the three-stage acid pickling is 150-300 s.

4. The acid pickling method for electronic grade polysilicon gradient according to claim 2 or 3, characterized in that: The acid pickling solution in the three-stage acid pickling tank is a mixed acid solution of nitric acid and hydrofluoric acid.

5. The method of pickling an electronic grade polysilicon gradient according to claim 1, wherein: The equipment used for the high-purity water cleaning is a high-purity water cleaning tank.

6. The method of pickling an electronic grade polysilicon gradient according to claim 1, wherein: The cleaning time of the high-purity water cleaning is 150-300 s.

7. The method of pickling an electronic grade polysilicon gradient according to claim 1, wherein: The nitrogen drying is carried out by blowing hot air of 60-120℃ in a nitrogen drying tank at a flow rate of 1000m 3 / h for 150-300s.

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