Method for detecting layered impurities in granular silicon

Abstract

The application discloses a granular silicon layered impurity detection method in the field of high-purity single silicon product preparation, and aims to solve the problem that in the existing granular silicon impurity detection, only total impurity content can be detected, and specific sources of impurities from surface adhesion, internal matrix or seed introduction cannot be effectively distinguished. The method comprises the following steps: selecting a granular silicon sample with a preset diameter range, and performing etching and evaporation concentration on the granular silicon sample to obtain a first detection solution; performing cleaning and drying on the granular silicon sample subjected to surface etching treatment, and then performing digestion and evaporation drying to obtain a second detection solution; performing digestion and evaporation drying again on the granular silicon sample remaining after the matrix digestion to obtain a third detection solution; and using an inductively coupled plasma mass spectrometer to detect the content of impurity elements in the first detection solution, the second detection solution and the third detection solution respectively. The application can realize layered and accurate quantitative analysis of impurities with different sources in the granular silicon.

Description

Technical Field

[0001] This invention relates to a method for detecting layered impurities in particulate silicon, belonging to the technical field of high-purity elemental silicon product preparation. Background Technology

[0002] The production process of granular silicon takes place in a fluidized bed, where silicon atoms generated from the decomposition of silane gas are continuously deposited onto pre-added seed crystals. After cooling, the granular silicon undergoes sieving and surface de-dusting to complete the production. Non-silicon impurities, especially metallic impurities, are the most important control indicator for granular silicon. In the quality improvement process, it is necessary to accurately identify the sources of contamination for various impurities, especially metallic impurities. Specifically, current methods for detecting metallic impurities in granular silicon only perform overall metal detection of the granular silicon as a whole. This cannot quickly pinpoint the source of contamination during quality improvement, whether it originates from the matrix during the granular silicon deposition process, surface contamination during de-dusting, or introduction from the seed crystals used for deposition. Therefore, effective process adjustments cannot be made for several key steps. Due to the small particle size of granular silicon, mechanical breaking of the particles is not feasible, and the introduction of contamination during breaking cannot be avoided. Therefore, the technical challenge of this method is to etch the granular silicon layer by layer without introducing contamination and to detect impurities, especially metallic impurities, in each layer. Summary of the Invention

[0003] The purpose of this invention is to provide a method for detecting layered impurities in particulate silicon, which can solve the problem that when the total metal impurity content of particulate silicon is high, it is impossible to accurately identify and distinguish whether the impurities originate from the matrix during the particulate silicon growth process, surface contamination during the powder removal process, or the introduction of seed crystals used for growth.

[0004] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution.

[0005] On the one hand, a method for detecting particulate silicon layering impurities includes:

[0006] Select a silicon particle sample within a preset diameter range;

[0007] The particulate silicon sample is subjected to etching and evaporation treatment to obtain a first detection solution for determining surface impurities of the particulate silicon sample.

[0008] After the surface-etched particulate silicon sample is cleaned and dried, it is then digested and evaporated to obtain a second detection solution for determining matrix impurities in the particulate silicon sample.

[0009] The remaining particulate silicon sample after digestion of the matrix is ​​digested and evaporated again to obtain a third detection solution for determining seed crystal impurities in the particulate silicon.

[0010] The content of impurity elements in the first detection solution, the second detection solution, and the third detection solution were measured respectively to obtain the layered impurity content of the particle silicon surface, the matrix, and the seed crystal.

[0011] Preferably, the diameter of the silicon particles is in the range of 1500 μm to 2500 μm.

[0012] Preferably, obtaining the first detection solution for determining surface impurities in the particulate silicon sample comprises:

[0013] Weigh out the predetermined mass of granular silicon sample;

[0014] The particulate silicon sample was subjected to surface etching treatment using a mixed acid solution prepared by hydrofluoric acid, nitric acid and water in a certain volume ratio to remove surface impurities and form a mixed solution.

[0015] The mixture is evaporated to dryness at a certain temperature to obtain a first residue. The first residue is then dissolved in a nitric acid solution of a certain concentration. The dissolved solution is then allowed to stand to obtain a surface impurity detection sample solution.

[0016] A certain proportion of the surface impurity detection sample solution was transferred into a clean beaker, and then a mixed acid prepared by hydrofluoric acid and nitric acid in a certain volume ratio was added. The mixture was then evaporated to dryness again at a certain temperature to obtain the second residue.

[0017] The second residue was dissolved in a nitric acid solution of a certain concentration, and after mixing, the first test solution was obtained.

[0018] Preferably, obtaining the second detection solution for determining matrix impurities in the particulate silicon sample includes:

[0019] The particulate silicon sample, after surface etching, cleaning and drying, was digested in a mixture of hydrofluoric acid, nitric acid and water in a certain volume ratio.

[0020] After the digestion reaction is complete, the digested mixture is transferred to a heating plate to evaporate to dryness, and then dissolved and evaporated to dryness using a nitric acid solution of a certain concentration to obtain the third residue. The third residue is then allowed to stand to obtain the matrix impurity detection sample solution.

[0021] A certain proportion of the matrix impurity detection sample solution was transferred into a clean beaker, and a digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio was added. The solution was then evaporated to dryness again at a certain temperature to obtain the fourth residue.

[0022] The fourth residue was dissolved in a nitric acid solution of a certain concentration to obtain the second test solution.

[0023] Preferably, obtaining the third detection solution for determining seed crystal impurities includes:

[0024] The remaining particulate silicon sample after matrix digestion was added to a digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio for the first digestion to obtain the first digestion solution.

[0025] After the first digestion reaction is completed, the first digestion solution is evaporated to dryness at a certain temperature to obtain the fifth residue;

[0026] A second digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio is added to the fifth residue to obtain a second digestion solution.

[0027] After the second digestion reaction is completed, the second digestion solution is evaporated to dryness for the second time at a certain temperature to obtain the sixth residue;

[0028] The sixth residue was dissolved in a certain proportion of nitric acid solution to obtain the third detection solution.

[0029] Preferably, the volume of the digestion solution prepared in the second step is smaller than the volume of the digestion solution prepared in the first step.

[0030] Preferably, the percentage of silicon particles removed by surface etching is controlled between 5% and 6%.

[0031] Preferably, the settling process is carried out under conditions that do not require heating.

[0032] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0033] This invention selects granular silicon samples within a specific diameter range and sequentially performs surface etching and evaporation concentration treatments to obtain a first detection solution for analyzing surface impurities. Subsequently, the surface-treated samples are cleaned, dried, digested, and evaporated to obtain a second detection solution for determining matrix impurities. The remaining granular silicon samples after matrix digestion are further digested and evaporated to obtain a third detection solution for detecting seed crystal impurities. Finally, inductively coupled plasma mass spectrometry (ICP-MS) is used to quantitatively analyze the impurity element content, particularly the content of metallic impurity elements, in each solution. This method achieves efficient separation and accurate determination of surface-adhered, matrix-internal, and seed crystal-introduced impurities in granular silicon, effectively solving the problem that existing technologies cannot distinguish the specific source of impurities, and providing a reliable analytical basis for impurity control and source traceability in granular silicon production processes. Attached Figure Description

[0034] Figure 1 The diagram shown is a flowchart of a method for detecting layered impurities in particulate silicon according to an embodiment of the present invention.

[0035] Figure 2The figure shown is a graph showing the relationship between the removal of 4%-6.5% of particulate silicon by etching according to an embodiment of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0037] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship. Example 1

[0038] This embodiment describes a method for detecting layered impurities in particulate silicon. First, particulate silicon samples within a specific diameter range are selected. Then, through three main steps—surface etching, matrix digestion, and seed crystal digestion—three types of detection solutions are prepared to measure surface impurities, matrix impurities, and seed crystal impurities in the particulate silicon sample, respectively. Finally, inductively coupled plasma mass spectrometry (ICP-MS) is used to accurately determine the content of impurity elements in each detection solution. Specifically, the method includes etching and evaporating the particulate silicon sample with a mixed acid solution prepared in a specific volume ratio to obtain a first detection solution for measuring its surface impurities.

[0039] The particulate silicon sample that has undergone surface etching is cleaned and dried. The cleaned and dried particulate silicon sample is digested and evaporated using a mixture prepared in a specific volume ratio to obtain a second detection solution for determining its matrix impurities.

[0040] The remaining particulate silicon sample after digestion of the matrix is ​​digested with a digestion solution prepared in a specific volume ratio and then evaporated to dryness to obtain a third detection solution for determining its seed crystal impurities.

[0041] The content of impurity elements in the first, second, and third detection solutions was determined by inductively coupled plasma mass spectrometry to obtain the content of layered impurities, especially metallic impurity elements, on the surface of the particulate silicon, in the matrix, and in the seed crystal.

[0042] In summary, this method effectively distinguishes and quantifies impurities from different sources (surface adhesion, matrix interior, or seed crystal origin) in granular silicon by precisely controlling the volume ratio of mixed acid or digestion solution and reaction conditions at each stage. It overcomes the limitation of existing technologies that can only determine the overall impurity content of granular silicon but cannot identify the specific source of impurities, and provides a reliable basis for impurity tracing and process control for the improvement of granular silicon production processes. Example 2

[0043] Silicon particles with a diameter ranging from 1500 μm to 2500 μm were selected. The samples underwent sequential processing including surface metal impurity extraction, matrix metal impurity elimination, and seed crystal metal impurity treatment. Finally, inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the metal content at each layer. The specific process included:

[0044] First, weigh out 2.0g ± 0.0050g of particulate silicon sample.

[0045] 1. Surface impurities

[0046] a. The particulate silicon sample is surface etched using a mixed acid solution prepared by hydrofluoric acid, nitric acid and water in a volume ratio of 5:3:90. The volume of the mixed acid is 10 mL. The etching time is controlled to remove 4%-6.5% of the mass of particulate silicon. In this embodiment of the invention, the mass of particulate silicon removed by etching is controlled to be between 5% and 6% in order to peel off the surface metal and form a mixed solution.

[0047] Specifically, to establish an accurate particle size-corrosion quality relationship model for better control of the corrosion process, the particle size range (1300-2700 μm) selected in this experiment covers and includes the target range (1500-2500 μm). See [link to relevant documentation] Figure 2 Corrosion tests were conducted on silicon particles with particle sizes ranging from 1300-1500 μm, 1500-1700 μm, 1700-1900 μm, 1900-2100 μm, 2100-2300 μm, 2300-2500 μm, and 2500-2700 μm, respectively. Corrosion was performed using mixed acid of the same concentration, and a curve showing the relationship between particle size range and the proportion of surface metallic impurities after corrosion was established to control the corrosion quality. The results are shown in Table 1 below. The data within the 1500-2500 μm target range represent the key application area targeted by this invention.

[0048] Table 1

[0049] Particle size range (μm) Sample mass (g) Mass (g) of surface metallic impurities after corrosion Percentage of surface metallic impurities after corrosion (%) 1300-1500 2.0035 1.8733 6.5% 1500-1700 2.0005 1.8865 5.7% 1700-1900 1.9997 1.8957 5.2% 1900-2100 2.0001 1.8901 5.5% 2100-2300 2.0012 1.8951 5.3% 2300-2500 2.0023 1.9022 5.0% 2500-2700 1.9995 1.9115 4.4%

[0050] b. Heat the mixture on a heating plate at 200°C to dryness to obtain the first residue. While it is still hot, add 12 ml of 1% nitric acid solution to dissolve the first residue. Let the dissolved solution stand for 30 min (without heating) to obtain the surface detection sample solution.

[0051] c. Transfer 10 mL of the surface test sample solution into a clean beaker, add 2 mL of a mixed acid prepared by hydrofluoric acid and nitric acid in a volume ratio of 2:1, and evaporate to dryness twice at 200℃ to obtain the second residue;

[0052] d. Dissolve the second residue twice with 5 mL of 1% nitric acid solution, and mix well to obtain the first test solution;

[0053] e. Use ICP-MS to detect the content of impurity elements in the first test solution, especially the content of metallic impurity elements.

[0054] In summary, the method of "micro-etching + double evaporation" is used to peel off the outermost impurity elements of the granular silicon for detection, thereby completely separating them from the impurities of the internal matrix and seed crystal, and achieving independent quantification of surface impurities, especially metallic impurities.

[0055] 2. Matrix impurities

[0056] a. The surface-etched particulate silicon sample was washed and dried with ultrapure water, and then digested with 21 mL of a mixture of hydrofluoric acid, nitric acid and water in a volume ratio of 2:1:2.

[0057] b. After the digestion reaction is complete, transfer the digested mixture to a heating plate and evaporate it to dryness at 200℃. While it is still hot, use 12mL of 1% nitric acid (HNO3) solution to dissolve and evaporate it to dryness to obtain the third residue. Let the third residue stand for 30min (without heating) to obtain the matrix impurity detection sample solution.

[0058] c. Transfer 10 ml of the matrix impurity detection sample solution into a clean beaker, add 4 ml of digestion solution prepared by hydrofluoric acid and nitric acid in a volume ratio of 2:1, and evaporate to dryness twice at 200℃ to obtain the fourth residue;

[0059] d. Dissolve the fourth residue in a nitric acid solution of a certain concentration to obtain the second test solution;

[0060] e. Use ICP-MS to detect the content of impurity elements, especially metallic impurity elements, in the second test solution.

[0061] In summary, this matrix impurity detection method achieves efficient extraction and accurate determination of matrix impurities inside the particulate silicon matrix by precisely controlling the digestion solution ratio, evaporation temperature, and settling conditions, effectively avoiding interference from surface impurity residues on the detection results.

[0062] 3. Seed crystal impurities

[0063] a. After the matrix digestion is completed, the remaining particulate silicon sample (accounting for about 10%-15% of the total mass) is added to about 4 mL of a digestion solution prepared by hydrofluoric acid and nitric acid in a volume ratio of 2:1 for the first digestion to obtain the first digestion solution;

[0064] b. After the first digestion reaction is completed, the first digestion solution is evaporated to dryness at 200℃ to obtain the fifth residue;

[0065] c. Add 1 mL of a digestion solution prepared by hydrofluoric acid and nitric acid in a volume ratio of 2:1 to the residue obtained after the first evaporation, i.e., the fifth residue, and perform a second digestion to obtain the second digestion solution;

[0066] d. After the second digestion reaction is completed, the second digestion solution is evaporated to dryness for the second time at 200℃ to obtain the sixth residue;

[0067] e. Dissolve the sixth residue in 4 mL of nitric acid solution to obtain the third test solution;

[0068] f. Use ICP-MS to detect the content of impurity elements, especially metallic impurities, in the third test solution.

[0069] In summary, the seed crystal impurity detection method, by employing a two-stage digestion and evaporation process and strictly controlling the proportion, amount, and reaction temperature of the digestion solution, ensures the complete dissolution and effective enrichment of impurities in the seed crystal, significantly improving the sensitivity and accuracy of detecting impurities introduced into the seed crystal.

[0070] It should be noted that although the detection method of this application can detect metallic (such as surface impurities, matrix impurities, and seed crystal impurities) and non-metallic (such as boron, phosphorus, and arsenic) impurities, it is mainly applicable to the analysis of metallic impurities. The detection data of non-metallic impurities are for reference and comparison only.

[0071] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for detecting impurities in particulate silicon stratification, characterized in that, include: Select a silicon particle sample within a preset diameter range; The particulate silicon sample is subjected to etching and evaporation treatment to obtain a first detection solution for determining surface impurities of the particulate silicon sample. After the surface-etched particulate silicon sample is cleaned and dried, it is then digested and evaporated to obtain a second detection solution for determining matrix impurities in the particulate silicon sample. The remaining particulate silicon sample after digestion of the matrix is ​​digested and evaporated again to obtain a third detection solution for determining seed crystal impurities in the particulate silicon. The content of impurity elements in the first detection solution, the second detection solution, and the third detection solution were measured respectively to obtain the layered impurity content of the particle silicon surface, the matrix, and the seed crystal.

2. The method for detecting particulate silicon layering impurities according to claim 1, characterized in that, The diameter of the silicon particles ranges from 1500 μm to 2500 μm.

3. The method for detecting particulate silicon layering impurities according to claim 1, characterized in that, The first detection solution for determining surface impurities in the particulate silicon sample includes: Weigh out the predetermined mass of granular silicon sample; The particulate silicon sample was subjected to surface etching treatment using a mixed acid solution prepared by hydrofluoric acid, nitric acid and water in a certain volume ratio to remove surface impurities and form a mixed solution. The mixture is evaporated to dryness at a certain temperature to obtain a first residue. The first residue is then dissolved in a nitric acid solution of a certain concentration. The dissolved solution is then allowed to stand to obtain a surface impurity detection sample solution. A certain proportion of the surface impurity detection sample solution was transferred into a clean beaker, and then a mixed acid prepared by hydrofluoric acid and nitric acid in a certain volume ratio was added. The mixture was then evaporated to dryness again at a certain temperature to obtain the second residue. The second residue was dissolved in a nitric acid solution of a certain concentration, and after mixing, the first test solution was obtained.

4. The method for detecting particulate silicon layering impurities according to claim 1, characterized in that, The process of obtaining a second detection solution for determining matrix impurities in the particulate silicon sample includes: The particulate silicon sample, after surface etching, cleaning and drying, was digested in a mixture of hydrofluoric acid, nitric acid and water in a certain volume ratio. After the digestion reaction is complete, the digested mixture is transferred to a heating plate to evaporate to dryness, and then dissolved and evaporated to dryness using a nitric acid solution of a certain concentration to obtain the third residue. The third residue is then allowed to stand to obtain the matrix impurity detection sample solution. A certain proportion of the matrix impurity detection sample solution was transferred into a clean beaker, and a digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio was added. The solution was then evaporated to dryness again at a certain temperature to obtain the fourth residue. The fourth residue was dissolved in a nitric acid solution of a certain concentration to obtain the second detection solution.

5. The method for detecting particulate silicon layering impurities according to claim 1, characterized in that, The method for obtaining the third detection solution for determining seed crystal impurities includes: The remaining particulate silicon sample after matrix digestion was added to a digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio for the first digestion to obtain the first digestion solution. After the first digestion reaction is completed, the first digestion solution is evaporated to dryness at a certain temperature to obtain the fifth residue; A second digestion solution prepared by hydrofluoric acid and nitric acid in a certain volume ratio is added to the fifth residue to obtain a second digestion solution. After the second digestion reaction is completed, the second digestion solution is evaporated to dryness for the second time at a certain temperature to obtain the sixth residue; The sixth residue was dissolved in a certain proportion of nitric acid solution to obtain the third detection solution.

6. The method for detecting particulate silicon layering impurities according to claim 5, characterized in that, The volume of the digestion solution prepared in the second batch was smaller than that prepared in the first batch.

7. The method for detecting particulate silicon layering impurities according to claim 3, characterized in that, The percentage of silicon particles removed by surface etching was controlled between 5% and 6%.

8. The method for detecting particulate silicon layering impurities according to any one of claims 3 to 5, characterized in that, All the resting periods were carried out under conditions that did not require heating.

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