A method for detecting metal impurities on a polysilicon surface

Abstract

The application provides a method for detecting metal impurities on a polysilicon surface, comprising the following steps: soaking a polysilicon sample to be detected in a leaching solution to obtain a soaked sample; heating the soaked sample to perform a surface metal leaching reaction, and then cooling to room temperature to obtain a sample solution; and detecting the sample solution according to a preset method corresponding to the type of the polysilicon sample to be detected to complete the detection of metal impurities. The application classifies the polysilicon sample to be detected in advance, and detects different polysilicon samples by shunting, so that different polysilicon samples can be suitable for the same concentration of leaching solution, the lengthy process of preparing a standard solution with a proper concentration and diluting the sample solution is reduced, the detection cost is reduced, and the linear range limitation of a single detection method is broken through.

Description

Technical Field

[0001] This application belongs to the field of polycrystalline silicon technology, specifically relating to a method for detecting metallic impurities on the surface of polycrystalline silicon. Background Technology

[0002] In the production of polycrystalline silicon, the content of metallic impurities on the surface of silicon materials is one of the most important technical indicators. Strictly controlling its content can significantly extend the minority carrier lifetime of polycrystalline silicon, improve the photoelectric conversion efficiency of photovoltaic solar cells, and enhance the performance of electronic devices. However, current national standards are not applicable to the detection of surface metallic content in granular polycrystalline silicon. When detecting the surface metallic content of granular polycrystalline silicon, it is often necessary to prepare detection solutions of different concentrations according to different surface metallic concentrations, resulting in material waste and increased time consumption.

[0003] Therefore, how to provide a method suitable for detecting metallic impurities on the surface of granular polycrystalline silicon is a problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a method for detecting metallic impurities on the surface of polycrystalline silicon, aiming to solve the problem that existing methods for detecting the content of metallic impurities on the surface of silicon materials are not suitable for detecting granular polycrystalline silicon.

[0005] This application provides a method for detecting metallic impurities on the surface of polycrystalline silicon, comprising the following steps:

[0006] The polycrystalline silicon sample to be tested was soaked in the leachate to obtain the soaked sample;

[0007] The soaked sample is heated to carry out a surface metal leaching reaction, and then cooled to room temperature to obtain a sample solution;

[0008] Depending on the type of polycrystalline silicon sample to be tested, the sample solution is tested using a corresponding preset method to complete the detection of the metal impurities.

[0009] In some embodiments, the step of detecting the sample solution using a corresponding preset method according to the type of the polycrystalline silicon sample to be tested further includes:

[0010] If the polycrystalline silicon sample is a Class I sample, then inductively coupled plasma mass spectrometry is used to detect the sample solution.

[0011] If the polycrystalline silicon sample is a type II sample, then inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to detect the sample solution.

[0012] The metal impurity content of the first type of sample is less than that of the second type of sample.

[0013] In some embodiments, the surface metal impurity content of the first type of sample is C1, which satisfies: 0ppb≤C1<100ppb;

[0014] The surface metal impurity content of the second type of sample is C2, which satisfies the following condition: 100ppb≤C2≤10000ppb.

[0015] In some embodiments, the first type of sample is a polycrystalline silicon sample that has not come into contact with a source of contamination during any of the processes of preparation, processing, post-processing, packaging, and transportation;

[0016] The second type of sample is a polycrystalline silicon sample that has come into contact with a contamination source during at least one of the processes of preparation, processing, post-treatment, packaging, and transportation.

[0017] In some embodiments, the leachate includes nitric acid, hydrofluoric acid, and ultrapure water;

[0018] The volume ratio of the nitric acid, the hydrofluoric acid, and the ultrapure water is 1:1:(100-130).

[0019] In some embodiments, the mass of the polycrystalline silicon sample to be tested is 10-20g.

[0020] In some embodiments, the volume of the leachate is 30 to 50 mL.

[0021] In some embodiments, the surface metal leaching reaction time is 20 to 40 minutes.

[0022] In some embodiments, the temperature of the surface metal leaching reaction is 60–70°C.

[0023] In some embodiments, the step of detecting the sample solution further includes:

[0024] Identify the target metallic element;

[0025] Prepare standard curve working solutions for each of the target metal elements;

[0026] Based on the standard curve working fluid, plot the standard working curve for each of the target metal elements;

[0027] Obtain the detection signal of the target metal element in the sample solution;

[0028] The content of the target metal element is obtained by comparing the detection signal of the target metal element with the standard working curve of the target metal element.

[0029] In some embodiments, if the polycrystalline silicon sample is a first type of sample, the content gradient of the standard curve working solution is 0 ppb, 0.05 ppb, 0.1 ppb, 0.3 ppb, 0.5 ppb, 1 ppb, 3 ppb, 5 ppb;

[0030] If the polycrystalline silicon sample is a type II sample, then the content gradient of the standard curve working solution is: 0 ppm, 0.02 ppm, 0.04 ppm, 0.06 ppm, 0.08 ppm, 0.1 ppm, 0.2 ppm.

[0031] In some embodiments, after completing the step of detecting the metallic impurities, the method further includes:

[0032] Several sets of blank experiments and parallel experiments were performed on the provided polycrystalline silicon sample.

[0033] The blank experiment was repeated 2 to 3 times.

[0034] The number of parallel experiments is 2 to 3.

[0035] This application provides a method for detecting metallic impurities on the surface of polycrystalline silicon, comprising the following steps: immersing the polycrystalline silicon sample to be tested in a leaching solution to obtain an immersed sample; heating the immersed sample to perform a surface metal leaching reaction, and then cooling it to room temperature to obtain a sample solution; and detecting the sample solution using a corresponding preset method according to the type of polycrystalline silicon sample to be tested, thereby completing the detection of metallic impurities. This invention pre-classifies the polycrystalline silicon samples to be tested and performs separate detection on different polycrystalline silicon samples, enabling different polycrystalline silicon samples to be used with the same concentration of leaching solution. This reduces the lengthy process of preparing appropriate concentration standard solutions and diluting sample solutions, lowers detection costs, and overcomes the linear range limitations of single detection methods. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0038] Figure 1 This is a flowchart of a method for detecting metallic impurities on the surface of polycrystalline silicon, provided in an embodiment of this application. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0040] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection, an indirect connection through an intermediate medium, or an indirect connection through a pipe or conduit; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0041] As one of the mainstream polycrystalline silicon production technologies in the market, the silane fluidized bed process eliminates the crushing process of the traditional modified Siemens process. The product is granular polycrystalline silicon, which has the characteristics of good fluidity and high filling capacity. Due to the relatively uniform temperature distribution in the silane fluidized bed, the surface area for silicon deposition in the reactor is large and the deposition rate is fast. The granular polycrystalline silicon produced can fully meet the requirements of N-type single crystal and has stable quality.

[0042] For the detection of metallic impurities on the surface of polycrystalline silicon, inductively coupled plasma mass spectrometry (ICP-MS) in GB / T 24582-2023 can be used. However, the applicable sample mass for this standard is approximately 120g, with a size range of (3cm×3cm×1cm) to (3cm×3cm×3cm). The particle size of granular polycrystalline silicon is 0.15mm to 4mm, making the aforementioned ICP-MS detection method unsuitable. Furthermore, due to its small size and large surface area, and the fact that granular polycrystalline silicon easily contains fine powder, impurities can be introduced into the product during raw material quality, process environment, post-processing environment, and product packaging, thus affecting the quality of granular polycrystalline silicon products. Therefore, if it comes into contact with contaminants during any process such as preparation, processing, post-processing, packaging, and transportation, the content of metallic impurities on the surface of some granular polycrystalline silicon may be too high. When using the same leaching solution for ICP-MS detection, inaccurate detection of metallic impurities on the surface of some samples may occur.

[0043] This invention application has discovered through research that by pre-classifying polycrystalline silicon materials before testing granular polycrystalline silicon, and then performing flow separation testing, different polycrystalline silicon samples can be matched with different testing methods and / or testing instruments, which can effectively solve the problem of inaccurate detection of metal impurities on the surface of granular polycrystalline silicon.

[0044] This application provides a method for detecting metallic impurities on the surface of polycrystalline silicon, such as... Figure 1 As shown, it includes the following steps:

[0045] The polycrystalline silicon sample to be tested was soaked in the leachate to obtain the soaked sample;

[0046] The sample was heated and immersed to carry out a surface metal leaching reaction, and then cooled to room temperature to obtain a sample solution.

[0047] Depending on the type of polycrystalline silicon sample to be tested, the corresponding preset method is used to detect the sample solution in order to complete the detection of metal impurities.

[0048] By classifying the polycrystalline silicon samples to be tested and performing split detection on different polycrystalline silicon samples, different polycrystalline silicon samples can be used in leaching solutions of the same concentration. This reduces the lengthy process of preparing appropriate concentration standard solutions and diluting sample solutions, thereby reducing detection costs and overcoming the linear range limitations of single detection methods.

[0049] In some embodiments, the step of detecting the sample solution further includes:

[0050] Identify the target metallic element;

[0051] Configure the standard curve working solution for each target metallic element;

[0052] Based on the standard curve working fluid, plot the standard working curve for each target metallic element;

[0053] Acquire the detection signal of the target metal element in the sample solution;

[0054] The content of the target metal element is obtained by comparing the detection signal of the target metal element with the standard working curve of the target metal element.

[0055] The target metal element refers to the metal impurity element whose content needs to be confirmed. By identifying the target metal element and preparing a standard curve working solution to plot a standard working curve, a precise quantitative analysis model can be established. Subsequently, the detection signal of the sample solution (such as the spectral signal or ion signal emitted by the target metal element in the sample solution) is obtained and compared with the standard working curve, thereby achieving a precise conversion from sample to data.

[0056] In some embodiments, the step of detecting the sample solution using a corresponding preset method according to the type of polycrystalline silicon sample to be tested further includes:

[0057] If the polycrystalline silicon sample is a Class I sample, then inductively coupled plasma mass spectrometry (ICP-MS) is used to detect the sample solution;

[0058] If the polycrystalline silicon sample is a type II sample, then inductively coupled plasma optical emission spectrometry (ICP-OES) is used to detect the sample solution;

[0059] Among them, the metal impurity content of the first type of sample is lower than that of the second type of sample.

[0060] ICP-MS boasts ultra-high sensitivity, capable of detecting trace elements at the ppt level. For polycrystalline silicon samples with extremely low metal impurity content, it can precisely capture minute amounts of metal impurities, ensuring the accuracy and reliability of the detection results. However, when the impurity content of the sample is too high, the detection curve should be adjusted, and the sample may need to be diluted before detection to avoid contaminating the instrument and affecting its detection limit and precision. ICP-OES, on the other hand, features a wide linear range and fast analysis speed when detecting higher levels of metal impurities. It is suitable for Class II samples with relatively high metal impurity content, meeting detection requirements while improving detection efficiency and reducing detection costs. Based on the differences in metal impurity content on the surface of different polycrystalline silicon samples, this application rationally selects ICP-MS and ICP-OES for split detection. This avoids the enhancement and inhibition phenomena caused by excessively high impurity content in the leaching solution and silicon-based content contaminating the instrument. Furthermore, it reduces the lengthy process of preparing appropriate concentration standard solutions and diluting sample solutions, thus lowering detection time costs.

[0061] In some embodiments, the surface metal impurity content of the first type of sample is C1, which satisfies: 0ppb≤C1<100ppb;

[0062] The surface metal impurity content of the second type of sample is C2, which satisfies the following condition: 100ppb≤C2≤10000ppb.

[0063] It is understandable that the surface metal impurity C1 value (unit: ppb) of the first type of sample can be any value or any range between two values ​​from 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 99, and the surface metal impurity content C2 value (unit: ppb) of the second type of sample can be any value or any range between two values ​​from 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000. Using 100 ppb as the dividing line for metal impurity content to classify polycrystalline silicon samples into first and second type samples, and selecting ICP-MS or ICP-OES to detect surface metal impurities in polycrystalline silicon samples based on this pre-classification, can ensure accurate detection of low-content impurities while efficiently processing high-content impurity samples, achieving the best balance between detection accuracy, efficiency, and cost.

[0064] Specifically, the surface metal impurity content of polycrystalline silicon can be pre-determined before ICP-MS or ICP-OES, which can be achieved by X-ray fluorescence spectroscopy (XRF) or scanning electron microscopy (SEM). Without damaging the sample, the metal impurity content on the surface of granular polycrystalline silicon can be roughly measured at the ppm level, thereby achieving the pre-classification of polycrystalline silicon samples into first-class and second-class samples.

[0065] In some embodiments, the first type of sample is a polycrystalline silicon sample that has not come into contact with a contaminant source during any of the processes of preparation, processing, post-processing, packaging, and transportation;

[0066] The second category of samples consists of polycrystalline silicon samples that have come into contact with a contamination source during at least one of the processes of preparation, processing, post-treatment, packaging, and transportation.

[0067] It is understandable that contamination sources refer to industrial impurities, dust, and gaseous impurities. If a polycrystalline silicon sample experiences raw material impurities, container contamination, or spillage during at least one of the processes of preparation, processing, post-processing, packaging, or transportation, it can be considered a source of contamination and thus classified as a Category II sample. Using the above method to classify polycrystalline silicon samples eliminates the need for coarse measurements using instruments, and more accurately categorizes samples into two classes based on the level of surface metal impurities, making them suitable for both ICP-MS and ICP-OES.

[0068] In some embodiments, the target metal element may be a plurality of metal elements, including at least one of Na, Mg, Al, K, Ca, Cr, Mn, Fe, Ni, Co, Cu, Zn, and W.

[0069] It is worth noting that when there are multiple target metal elements, C1 and C2 both refer to the content of each individual target metal element. For example, when the target metal elements include five elements: Na, Mg, Al, K, and Ca, the content of these five elements on the surface of the single crystal silicon sample is judged sequentially. If the content of each target metal element is less than 100 ppb, the single crystal silicon sample is judged to be a first-class sample; if the content of any target metal element is greater than or equal to 100 ppb, the single crystal silicon sample is judged to be a second-class sample.

[0070] Specifically, the method for detecting metallic impurities on the surface of polycrystalline silicon provided in this application can be implemented through the following steps:

[0071] S1. Identify several target metal elements and set the detection parameters for each target metal element in the ICP device;

[0072] S2. Prepare standard curve working solutions for each target metal element corresponding to ICP-OES and ICP-MS.

[0073] S3. Prepare the leachate;

[0074] S4. Provide granular polycrystalline silicon raw material, weigh a certain mass from it, and use it as the polycrystalline silicon sample to be tested, and place it in a covered beaker.

[0075] S5. Immerse the polycrystalline silicon sample to be tested in the leaching solution to obtain the immersion sample;

[0076] S6. Place the soaked sample on a hot plate and keep it at a constant temperature for a certain period of time to carry out the surface metal leaching reaction, and then cool it to room temperature to obtain the sample solution.

[0077] S7. Determine whether to use ICP-OES or ICP-MS to detect the sample solution based on the type of polycrystalline silicon sample to be tested.

[0078] S8. Optimize the performance of the ICP instrument by tuning and plotting the standard working curve for each target metal element based on the standard curve working fluid.

[0079] S9. Use an ICP device to directly aspirate the sample solution for testing. Measure the content of the target metal element every 10 minutes to complete the detection of metal impurities.

[0080] In some embodiments, the leachate includes nitric acid, hydrofluoric acid, and ultrapure water;

[0081] The volume ratio of nitric acid, hydrofluoric acid and ultrapure water is 1:1:(100-130).

[0082] Understandably, the volume ratio of nitric acid, hydrofluoric acid, and ultrapure water can be any value or any two values ​​within the range of 1:1:100, 1:1:105, 1:1:110, 1:1:115, 1:1:120, 1:1:125, and 1:1:130. Granular polycrystalline silicon has a small volume and large surface area, resulting in a large contact area with the leaching solution and a fast reaction rate. If the leaching solution concentration is too high, the granular polycrystalline silicon will be leached to an excessive depth, dissolving some of the matrix metal in the leaching solution. This affects the ionization of the sample solution in the ICP-MS plasma, leading to matrix inhibition or matrix gain. Conversely, if the leaching solution concentration is too low, incomplete leaching may occur, and impurities on the polycrystalline silicon surface may not dissolve completely. When the volume ratio of nitric acid, hydrofluoric acid, and ultrapure water meets the above-mentioned range, it ensures complete dissolution of surface impurities (>98%) while controlling the dissolution of the silicon matrix below the detection interference threshold.

[0083] Based on the above embodiments, after obtaining the sample solution, the sample solution is not evaporated to dryness, but directly subjected to ICP-MS or ICP-OES detection.

[0084] Understandably, when the volume ratio of nitric acid, hydrofluoric acid, and ultrapure water in the leachate is 1:1:(100-130), the acid content in the leachate is relatively low and will not cause corrosion to the ICP equipment. Therefore, the evaporation step can be skipped, and the sample solution can be directly tested, thereby effectively reducing the overall time consumption of the testing process and improving the testing efficiency.

[0085] In some embodiments, the mass of the polycrystalline silicon sample to be tested is 10–20 g.

[0086] It is understood that the mass of the polycrystalline silicon sample to be tested refers to the mass weighed from the granular polycrystalline silicon material each time. The mass of the polycrystalline silicon sample to be tested (unit: g) can be any value or a range between any two of 10, 12, 14, 16, 18, and 20. When the mass of the polycrystalline silicon sample to be tested meets the above value range, it can be ensured that the content of metallic impurities on its surface is within a reasonable range that can be accurately detected by ICP equipment.

[0087] In some embodiments, the volume of the leachate is 30 to 50 mL.

[0088] It is understood that the volume of the leachate (in mL) can be any value or a range between any two of 30, 35, 40, 45, and 50. When the volume of the leachate meets the above range, it can match the mass of the polycrystalline silicon sample to be tested, ensuring complete coverage of the polycrystalline silicon sample while avoiding excessive dissolution of the silicon matrix.

[0089] In some embodiments, the surface metal leaching reaction time is 20 to 40 minutes.

[0090] It is understandable that the time (in minutes) for the surface metal leaching reaction can be any value or a range between any two of the following: 20, 24, 28, 32, 36, and 40.

[0091] In some embodiments, the temperature of the surface metal leaching reaction is 60–70°C.

[0092] It is understandable that the temperature (unit: °C) of the surface metal leaching reaction can be any value or a range between any two of the following: 60, 62, 64, 66, 68, 70.

[0093] In some embodiments, if the polycrystalline silicon sample is a first type of sample, the content gradient of the standard curve working solution is 0 ppb, 0.05 ppb, 0.1 ppb, 0.3 ppb, 0.5 ppb, 1 ppb, 3 ppb, and 5 ppb.

[0094] If the polycrystalline silicon sample is a type II sample, the concentration gradient of the standard curve working solution is: 0 ppm, 0.02 ppm, 0.04 ppm, 0.06 ppm, 0.08 ppm, 0.1 ppm, 0.2 ppm.

[0095] In some embodiments, after completing the step of detecting metallic impurities, the method further includes:

[0096] Several sets of blank experiments and parallel experiments were performed on the provided polycrystalline silicon samples.

[0097] The blank experiment was repeated 2 to 3 times;

[0098] The number of parallel experiments is 2 to 3.

[0099] By conducting blank and parallel experiments and averaging the results of each test, the accuracy of detecting metal impurities on the surface of polycrystalline silicon samples can be further ensured. Specifically, the content of metal impurities on the polycrystalline silicon surface can be calculated using the following formula:

[0100] M v = (wK)×V / m;

[0101] In the formula:

[0102] M v The mass concentration of metal elements on the surface of polycrystalline silicon is expressed in nanograms per gram (ng / g).

[0103] w represents the volume concentration of the metal element in the sample solution, expressed in nanograms per milliliter (ng / mL).

[0104] K is the volume concentration of the element to be tested in the blank solution, expressed in nanograms per milliliter (ng / mL).

[0105] V represents the volume of the leaching liquid, in milliliters (mL);

[0106] m represents the mass of the polycrystalline silicon sample, expressed in grams (g).

[0107] Performing blank experiments and parallel experiments two or three times has a positive impact on the accuracy of the final test results.

[0108] The method for detecting metallic impurities on the surface of polycrystalline silicon provided in this application is described below with reference to specific embodiments:

[0109] Example 1

[0110] This embodiment provides a method for detecting metallic impurities on the surface of polycrystalline silicon, and the specific steps are as follows:

[0111] S1. Identify 12 target metal elements: Na, Mg, Al, K, Ca, Cr, Mn, Fe, Ni, Co, Cu, and Zn, and set the detection parameters for each target metal element in the ICP device;

[0112] S2. Prepare standard curve working solutions for each target metal element corresponding to ICP-OES and ICP-MS.

[0113] S3. Prepare the leachate, with the volume ratio of each component in the leachate being HNO3:HF:H2O = 1:1:100;

[0114] S4. Provide granular polycrystalline silicon raw material, weigh 20g from it as the polycrystalline silicon sample to be tested, and place it in a covered beaker.

[0115] S5. Immerse the polycrystalline silicon sample to be tested in the leaching solution to obtain the immersion sample;

[0116] S6. Place the soaked sample on a hot plate and heat it at a constant temperature of 70°C for 30 minutes to carry out the surface metal leaching reaction. Then cool it to room temperature to obtain the sample solution.

[0117] S7. Based on whether the polycrystalline silicon samples come into contact with contaminants during any process of preparation, processing, post-processing, packaging and transportation, the polycrystalline silicon samples to be tested are divided into Class I samples and Class II samples. It is determined that ICP-MS will be used to detect Class I samples and ICP-OES will be used to detect Class II samples.

[0118] S8. Optimize the performance of the ICP instrument by tuning and plotting the standard working curve for each target metal element based on the standard curve working fluid.

[0119] S9. Use an ICP device to directly aspirate the sample solution for testing. Measure the content of the target metal element every 10 minutes to complete the detection of metal impurities.

[0120] Example 2

[0121] Example 2 is identical to the detection method provided in Example 1, and the polycrystalline silicon sample to be tested is weighed from the same group of polycrystalline silicon materials. The only difference is that the volume ratio of each component in the leachate and the time for placing the soaked sample on the hot plate for constant temperature heating are adjusted.

[0122] Comparative Examples 1-4

[0123] Comparative Examples 1 to 4 follow the same detection method and steps as those provided in Example 1, and the polycrystalline silicon samples to be tested are weighed from the same group of polycrystalline silicon materials. The only difference is that the volume ratio of each component in the leachate is adjusted.

[0124] The relevant process parameters in Examples 1-2 and Comparative Examples 1-4 are shown in Table 1.

[0125] Table 1

[0126]

[0127] The detection results of Examples 1-2 and Comparative Examples 1-4 are shown in Table 2.

[0128] Table 2

[0129]

[0130]

[0131] As shown in Tables 1 and 2, the method for detecting metal impurities on the surface of polycrystalline silicon provided in this application can effectively detect granular polycrystalline silicon samples with different surface impurity contents. Furthermore, when the volume ratio of nitric acid, hydrofluoric acid, and water is higher than 1:1:100, the metal impurity content in the resulting silicon surface metal leaching solution does not show an increasing trend; on the contrary, it decreases. This indicates that when using a volume ratio higher than 1:1:100 (1:1:70), the silicon-based content in the solution is too high, resulting in matrix inhibition. Although the metal impurity content in the solution increases when using a higher volume ratio (1:1:10), the effect is comparable to that of heating for 30 minutes with a volume ratio of 1:1:100. This is because the leaching solution concentration is too high, and the granular polycrystalline silicon is leached to a greater depth, dissolving some matrix metals in the leaching solution, which offsets the matrix inhibition caused by the high silicon-based content. Therefore, using the leaching solution formulation provided in this application can achieve the most ideal effect for extracting metal elements from the surface of polycrystalline silicon samples.

[0132] The method for detecting metallic impurities on the surface of polycrystalline silicon provided in the embodiments of this application has been described in detail above. Specific examples have been used in this application to illustrate the principle and implementation of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for detecting metallic impurities on the surface of polycrystalline silicon, characterized in that, Includes the following steps: The polycrystalline silicon sample to be tested was soaked in the leachate to obtain the soaked sample; The soaked sample is heated to carry out a surface metal leaching reaction, and then cooled to room temperature to obtain a sample solution; Depending on the type of polycrystalline silicon sample to be tested, the sample solution is tested using a corresponding preset method to complete the detection of the metal impurities.

2. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 1, characterized in that, The step of detecting the sample solution using a corresponding preset method based on the type of polycrystalline silicon sample to be tested further includes: If the polycrystalline silicon sample is a type I sample, then inductively coupled plasma mass spectrometry is used to detect the sample solution. If the polycrystalline silicon sample is a type II sample, then inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to detect the sample solution. The metal impurity content of the first type of sample is less than that of the second type of sample.

3. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 2, characterized in that, The surface metal impurity content of the first type of sample is C1, which satisfies: 0ppb≤C1<100ppb; The surface metal impurity content of the second type of sample is C2, which satisfies the following condition: 100ppb≤C2≤10000ppb.

4. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 2, characterized in that, The first type of sample is a polycrystalline silicon sample that has not come into contact with a source of contamination during any of the processes of preparation, processing, post-processing, packaging, and transportation; The second type of sample is a polycrystalline silicon sample that has come into contact with a contamination source during at least one of the processes of preparation, processing, post-treatment, packaging, and transportation.

5. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 1, characterized in that, The leachate includes nitric acid, hydrofluoric acid, and ultrapure water; The volume ratio of the nitric acid, the hydrofluoric acid, and the ultrapure water is 1:1:(100-130).

6. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 1, characterized in that, The mass of the polycrystalline silicon sample to be tested is 10–20 g; and / or, The volume of the leachate is 30-50 mL.

7. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 1, characterized in that, The surface metal leaching reaction time is 20–40 min; and / or, The surface metal leaching reaction is carried out at a temperature of 60–70°C.

8. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 2, characterized in that, The step of detecting the sample solution further includes: Identify the target metallic element; Prepare standard curve working solutions for each of the target metal elements; Based on the standard curve working fluid, plot the standard working curve for each of the target metal elements; Obtain the detection signal of the target metal element in the sample solution; The content of the target metal element is obtained by comparing the detection signal of the target metal element with the standard working curve of the target metal element.

9. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 8, characterized in that, If the polycrystalline silicon sample is a Class I sample, then the content gradient of the standard curve working solution is 0 ppb, 0.05 ppb, 0.1 ppb, 0.3 ppb, 0.5 ppb, 1 ppb, 3 ppb, 5 ppb; If the polycrystalline silicon sample is a type II sample, then the content gradient of the standard curve working solution is: 0 ppm, 0.02 ppm, 0.04 ppm, 0.06 ppm, 0.08 ppm, 0.1 ppm, 0.2 ppm.

10. The method for detecting metallic impurities on the surface of polycrystalline silicon according to claim 1, characterized in that, After completing the step of detecting the metallic impurities, the method further includes: Several sets of blank experiments and parallel experiments were performed on the provided polycrystalline silicon sample; The blank experiment was repeated 2 to 3 times; The number of parallel experiments is 2 to 3.

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