Recycling method of monocrystalline silicon circulating material

Abstract

The embodiment of the invention relates to the technical field of photovoltaics, and provides a single crystal silicon circulating material recycling method which comprises the following steps: collecting a circulating material, taking the resistivity of a single crystal to be prepared as the target resistivity, and taking the variable range of the target resistivity as the target control precision; performing elemental analysis on the circulating material to obtain types and doping concentrations of doped elements at different lengths in the circulating material and electrical resistivity at different lengths; if the target resistivity is larger than the preset resistivity or the target control precision is smaller than or equal to the first preset precision, the circulating materials are divided into M levels based on element analysis of the circulating materials; if the target resistivity is smaller than or equal to the preset resistivity or the target control precision is smaller than or equal to the second preset precision, the circulating materials are divided into S grades based on element analysis of the circulating materials, and at least improvement of the quality of the single crystal to be prepared and the utilization rate of the circulating materials is facilitated.

Description

Technical Field

[0001] The disclosed embodiments relate to the field of photovoltaic technology, and in particular to a method for recovering recycled monocrystalline silicon material. Background Art

[0002] At present, in the process of preparing single crystal silicon rods, scraps and bottom materials are collected as recycled materials for recycling. However, before using the recycled materials, it is necessary to remove or reduce various stains on the surface of the recycled materials, such as metal impurities, particles, organic pollution, etc.

[0003] However, the composition or performance parameters of the recycled materials produced in different production links are different. In the subsequent process of adding the recycled materials to prepare single crystal silicon, it is easy to cause large fluctuations in the resistivity of the single crystal silicon prepared with the help of the recycled materials, thereby affecting the uniformity of the resistivity of the prepared single crystal silicon. Summary of the invention

[0004] The disclosed embodiment provides a method for recovering recycled single crystal silicon material, which is at least beneficial for improving the quality of the single crystal to be prepared while increasing the utilization rate of the recycled material.

[0005] According to some embodiments of the present disclosure, the embodiments of the present disclosure provide a method for recycling recycled single crystal silicon material, comprising: collecting the recycled material, and using the recycled material as a raw material for subsequent preparation of a single crystal, using the resistivity of the single crystal to be prepared as a target resistivity, and using the variable range of the target resistivity as a target control accuracy; performing elemental analysis on the recycled material to obtain and record the types and doping concentrations of doping elements at different lengths in the recycled material and the resistivity at different lengths in the recycled material; if the target resistivity is greater than a preset resistivity, or the target control accuracy is less than or equal to a first preset accuracy, Based on the types and doping concentrations of the doping elements at different lengths in the circulating material and the differences in resistivity at different lengths in the circulating material, the circulating material is divided into M levels; if the target resistivity is less than or equal to the preset resistivity, or the target control accuracy is less than or equal to the second preset accuracy, based on the types and doping concentrations of the doping elements at different lengths in the circulating material and the differences in resistivity at different lengths in the circulating material, the circulating material is divided into S levels; wherein M is greater than S, and both M and S are positive integers; the resistivity of the circulating material at any level is less than the preset resistivity.

[0006] In some embodiments, the process of preparing a single crystal includes at least a crystal pulling step and a machining step; the step of collecting the recycled material includes: collecting the recycled material generated by the crystal pulling step, and collecting the recycled material generated by the machining step.

[0007] In some embodiments, the step of collecting the recycled material generated by the machining process includes: cutting the prepared crystal into T segments of crystal blanks, each segment of the crystal blank will produce a portion of sub-recycled material after machining, T is a positive integer less than or equal to M; the step of performing elemental analysis on the recycled material includes: performing elemental analysis on each portion of the sub-recycled material.

[0008] In some embodiments, the types of doping elements in the recycled material include antimony and phosphorus; the step of performing elemental analysis on the recycled material also includes: obtaining the doping concentration of antimony in the recycled material as a first doping concentration, and the sum of the doping concentration of antimony in the recycled material and the doping concentration of phosphorus in the recycled material as a second doping concentration, so as to record the recycled material coefficient; wherein the recycled material coefficient is the ratio of the first doping concentration to the second doping concentration.

[0009] In some embodiments, the difference in resistivity of the recycled materials of different grades is less than 0.2 Ω·cm.

[0010] In some embodiments, the recycling method also includes: performing cleaning treatments on the recycled materials divided into different levels respectively; the cleaning treatment steps include: using a first cleaning liquid to perform a first cleaning treatment on the recycled materials divided into M levels, the cleaning temperature of the first cleaning treatment is a first temperature, and the cleaning time of the first cleaning treatment is a first time; first using a second cleaning liquid to perform a second cleaning treatment on the recycled materials divided into S levels, and then using the first cleaning liquid to perform a third cleaning treatment on the recycled materials divided into S levels, the cleaning temperature of the second cleaning treatment is a second temperature, the cleaning time of the second cleaning treatment is a second time, the cleaning temperature of the third cleaning treatment is a third temperature, and the cleaning time of the third cleaning treatment is a third time; wherein, the second temperature is greater than the first temperature, the second time is greater than or equal to the first time, and the third time is greater than or equal to the first time; the acidity of the first cleaning liquid is lower than the acidity of the second cleaning liquid.

[0011] In some embodiments, after the recycled material is subjected to the cleaning treatment, the recycling method further includes: performing heat treatment on the recycled material divided into different levels respectively; the heat treatment step includes: performing a first heat treatment on the recycled material divided into M levels, the treatment temperature of the first heat treatment is a fourth temperature, and the treatment time of the first heat treatment is a fourth time; performing a second heat treatment on the recycled material divided into S levels, the treatment temperature of the second heat treatment is a fifth temperature, and the treatment time of the second heat treatment is a fifth time; wherein, the fourth temperature is lower than the fifth temperature, and the fourth time is lower than the fifth time.

[0012] In some embodiments, after the recycled material is heat-treated, the recycling method further includes: performing impurity analysis on the recycled material to obtain and record the actual purity of the recycled material; if the actual purity is lower than the preset purity, marking the recycled material as unqualified recycled material, and performing the cleaning treatment and the heat treatment on the unqualified recycled material again until the actual purity of the unqualified recycled material is greater than or equal to the preset purity.

[0013] In some embodiments, the collected recycled materials include multiple batches; the step of performing the impurity analysis on the recycled materials also includes: obtaining and recording the total impurity content of iron, copper and nickel in any batch of the recycled materials; the recovery method also includes: based on the total impurity content of each batch of the recycled materials, allocating at least two batches of the recycled materials into a group for the same round of single crystal preparation, and controlling the average value of the total impurity content of each group of the recycled materials to be less than or equal to 80 ppb.

[0014] In some embodiments, the recycling method also includes: providing silicon material; based on the grading of the recycled material, selecting the recycled material of the corresponding level that better matches the target resistivity and the target control accuracy; mixing the selected recycled material with the silicon material in a preset ratio to prepare a new round of single crystal preparation; wherein the preset ratio is 45% to 55%: 55% to 45% of the weight of the selected recycled material to the weight of the silicon material.

[0015] The technical solution provided by the embodiments of the present disclosure has at least the following advantages:

[0016] On the basis of elemental analysis of the recycled materials to distinguish the performance parameters of different recycled materials, based on the different target resistivities or target control accuracies of the single crystals to be prepared, preset resistivities, first preset accuracies and second preset accuracies are set, and the single crystals to be prepared are divided into at least two grades according to the different performance parameters, and based on the different performance parameters of the single crystals to be prepared, different grading logics are performed on the collected recycled materials according to the different performance parameters of the recycled materials, thereby effectively avoiding large fluctuations in the resistivity inside the single crystals to be prepared so as to improve the quality of the single crystals to be prepared, while making full use of the recycled materials with different performance parameters to improve the utilization rate of the recycled materials, and simplifying the grading process of the collected recycled materials to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings, and these exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise specified, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the traditional technology, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic flow chart of a method for recovering single crystal silicon recycled material provided in an embodiment of the present disclosure;

[0019] Figure 2 A curve relationship diagram of doping concentration and resistivity of different doping elements at different lengths in the recycling material in the recycling method provided by the embodiment of the present disclosure;

[0020] Figure 3 Another schematic diagram of a process for recovering a single crystal silicon recycling material provided in an embodiment of the present disclosure;

[0021] Figure 4 Another schematic flow chart of the method for recovering recycled single crystal silicon material provided in the embodiment of the present disclosure. DETAILED DESCRIPTION

[0022] As can be seen from the background technology, the quality of single crystal silicon prepared by using recycled materials needs to be improved.

[0023] The present disclosure provides a method for recovering single crystal silicon recycled material. On the basis of performing elemental analysis on the recycled material to distinguish the performance parameters of different recycled materials, a preset resistivity, a first preset accuracy and a second preset accuracy are set based on the target resistivity or target control accuracy of the single crystal to be prepared. The single crystal to be prepared is divided into at least two grades according to the different performance parameters. Based on the different performance parameters of the single crystal to be prepared, different grading logics are performed on the collected recycled material according to the different performance parameters of the recycled material. This is beneficial for effectively avoiding a large fluctuation in the resistivity inside the single crystal to be prepared to improve the quality of the single crystal to be prepared, while making full use of the recycled material with different performance parameters to improve the utilization rate of the recycled material and simplifying the grading process of the collected recycled material to a certain extent.

[0024] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0025] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0026] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0027] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0028] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0029] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0030] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​the layer are magnified for better understanding and ease of description. When describing a component (such as a layer, film, region or substrate) on another component or on the surface of another component, the component can be "directly" located on the surface of the other component, or a third component can be present between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a partial edge of the entire surface.

[0031] In the description of the embodiments of the present application, when a component "includes" another component, unless otherwise specified, other components are not excluded, and other components may be further included. In addition, when a component such as a layer, a film, a region, or a plate is referred to as being "on / located on" another component, it may be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may exist in between. In addition, when a component such as a layer, a film, a region, a plate, etc. is "directly located on" another component, or when a component such as a layer, a film, a region, a plate, etc. is located on the surface of another component, it means that no other components are located in between.

[0032] The terms used in the description of the various embodiments described herein are only used to describe specific embodiments and are not intended to be limiting. As used in the description of the various embodiments described and in the appended claims, "the components" are also intended to include plural forms unless the context clearly indicates otherwise. Among them, components include components such as layers, films, regions, or plates.

[0033] The following will describe the various embodiments of the present disclosure in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present disclosure, many technical details are provided in order to enable the reader to better understand the embodiments of the present disclosure. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the embodiments of the present disclosure can be implemented.

[0034] The embodiment of the present disclosure provides a method for recovering a monocrystalline silicon recycled material. The method for recovering a monocrystalline silicon recycled material provided by the embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0035] refer to Figure 1 , Figure 1 A schematic flow chart of a method for recovering a monocrystalline silicon recycling material provided in an embodiment of the present disclosure is provided. The method for recovering a monocrystalline silicon recycling material comprises at least the following steps:

[0036] S1: Collect the recycled material and use it as the raw material for the subsequent preparation of single crystals. The resistivity of the single crystal to be prepared is used as the target resistivity, and the variable range of the target resistivity is used as the target control accuracy.

[0037] It is worth noting that in the process of pulling single crystal silicon rods, many production links will produce residual materials, which can be used as recycled materials. In some cases, both the crystal pulling link and the subsequent machining link will produce recycled materials. For example, the recycled materials produced in the crystal pulling link may include crucible bottom materials, shoulder lifting materials or crucible lifting materials, and the recycled materials produced in the machining link may include edge materials, recycled tail materials or cut block materials. The recycled materials generated in different production links will be divided into different batches in the future, and the recycled materials of different batches will be described in detail.

[0038] Moreover, the composition or performance parameters of the recycled materials produced in different production links are different, for example, the content of the same doping element in the recycled materials produced in different production links is different, or the resistivity of the recycled materials produced in different production links is different, etc.; the composition or performance parameters of different recycled materials produced at different parts of the same production link are also different. If the various types of recycled materials are not properly distinguished, it is easy to make it difficult to control the resistivity of the single crystal silicon rod prepared by adding the recycled materials. It should be noted that the recycled materials collected in step S1 include different recycled materials under the above-mentioned various situations.

[0039] Based on this, the resistivity of the single crystal to be prepared and the variable range of the resistivity of the single crystal to be prepared are first determined, that is, the resistivity of the single crystal to be prepared is taken as the target resistivity, and the variable range of the target resistivity is taken as the target control accuracy. Based on the target resistivity and target control accuracy of the single crystal to be prepared, the various types of recycled materials mentioned above are divided into different levels, so as to facilitate the subsequent preparation of single crystal silicon with different performance parameters using recycled materials of different levels.

[0040] S2: Performing element analysis on the recycled material to obtain and record the types and doping concentrations of the doping elements at different lengths in the recycled material and the resistivity at different lengths in the recycled material.

[0041] S3: If the target resistivity is greater than the preset resistivity, or the target control accuracy is less than or equal to the first preset accuracy, the circulating material is divided into M levels based on the types and doping concentrations of the doping elements at different lengths in the circulating material and the differences in resistivity at different lengths in the circulating material; If the target resistivity is less than or equal to the preset resistivity, or the target control accuracy is less than or equal to the second preset accuracy, the circulating material is divided into S levels based on the types and doping concentrations of the doping elements at different lengths in the circulating material and the differences in resistivity at different lengths in the circulating material; wherein M is greater than S, and both M and S are positive integers; the resistivity of any level of circulating material is less than the preset resistivity.

[0042] It is worth noting that based on the types and doping concentrations of doping elements at different lengths in various types of circulating materials, as well as the resistivity at different lengths in the circulating materials, circulating materials with different performance parameters are distinguished, wherein the performance parameters of single crystal silicon include but are not limited to its target resistivity and target control accuracy. In addition, based on the different requirements for the target resistivity and target control accuracy of the single crystal silicon to be prepared, the grading logic of circulating materials with different performance parameters is divided into at least two types:

[0043] The first classification logic of the circulating material: if the target resistivity is greater than the preset resistivity, or if the target control accuracy is less than or equal to the first preset accuracy, the circulating material is divided into M levels based on the types and doping concentrations of the doping elements at different lengths in the circulating material and the different resistivities at different lengths in the circulating material.

[0044] The second classification logic of the recycled material: If the target resistivity is less than or equal to the preset resistivity, or if the target control accuracy is less than or equal to the second preset accuracy, the recycled material is divided into S levels based on the types and doping concentrations of the doping elements at different lengths in the recycled material and the different resistivities at different lengths in the recycled material.

[0045] It is worth emphasizing that in the first classification logic of the recycled material, the resistivity of the single crystal to be prepared is relatively large, that is, the target resistivity is greater than the preset resistivity. Since the resistivity of any level of recycled material is less than the preset resistivity, the difference between the target resistivity of the single crystal to be prepared and the resistivity of any level of recycled material is relatively large. Therefore, it is necessary to classify the collected recycled materials with different performance parameters more carefully to avoid excessive differences in resistivity between different recycled materials in the same level, which greatly affect the resistivity of the single crystal to be prepared. For example, avoid large fluctuations in the resistivity inside the single crystal to be prepared, so as to improve the uniformity of the resistivity inside the single crystal to be prepared, thereby maintaining the high quality of the single crystal to be prepared.

[0046] Compared with the first grading logic of recycled materials, in the second grading logic of recycled materials, the resistivity of the single crystal to be prepared is relatively small, that is, the target resistivity is less than or equal to the preset resistivity, then the difference between the target resistivity of the single crystal to be prepared and the resistivity of any level of recycled materials is relatively small, and therefore the grading of the collected recycled materials with different performance parameters does not have to be as detailed as in the first grading logic of recycled materials, that is, S is less than M, and it can also ensure that the fluctuation range of the resistivity of the single crystal to be prepared is small, so as to improve the uniformity of the resistivity inside the single crystal to be prepared, and it is conducive to simplifying the grading process of the collected recycled materials.

[0047] In some cases, the first preset accuracy is less than the second preset accuracy. From the above analysis, it can be seen that compared with the second classification logic of the recycled material, in the first classification logic of the recycled material, the difference between the target resistivity of the prepared single crystal and the resistivity of any level of the recycled material is relatively large, which easily leads to a large fluctuation in the target resistivity of the prepared single crystal due to a slight change in the performance parameters of the incorporated recycled material. Therefore, the requirements for the target control accuracy of the prepared single crystal are also high. Based on this, whether the target resistivity is greater than the preset resistivity or the target control accuracy is less than or equal to the first preset accuracy, the first classification logic is executed on the collected recycled material, that is, the recycled material is divided into M levels, which is conducive to effectively avoiding a large fluctuation in the resistivity inside the single crystal to be prepared, so as to improve the uniformity of the resistivity inside the single crystal to be prepared. Different from this, for the case where the target control accuracy is greater than, less than or equal to the second preset accuracy, that is, the resistivity fluctuation range is required to be lower, or the target resistivity is less than or equal to the preset resistivity, the second grading logic can be executed on the collected recycled material, that is, the recycled material is divided into S levels, which is beneficial to effectively avoid large fluctuations in the resistivity inside the single crystal to be prepared so as to improve the uniformity of the resistivity inside the single crystal to be prepared, while simplifying the grading process of the collected recycled material.

[0048] In summary, on the basis of elemental analysis of the recycled materials to distinguish the performance parameters of different recycled materials, based on the different target resistivity or target control accuracy of the single crystal to be prepared, the preset resistivity, the first preset accuracy and the second preset accuracy are set, and the single crystal to be prepared is divided into at least two grades according to the different performance parameters, and based on the different performance parameters of the single crystal to be prepared, different grading logics are performed on the collected recycled materials according to the different performance parameters of the recycled materials, which is beneficial to effectively avoid large fluctuations in the resistivity inside the single crystal to be prepared, so as to improve the quality of the single crystal to be prepared, while making full use of the recycled materials with different performance parameters to improve the utilization rate of the recycled materials, and to simplify the grading process of the collected recycled materials to a certain extent.

[0049] The following is a more detailed description of the method for recovering the single crystal silicon recycled material provided by the embodiment of the present disclosure in conjunction with the accompanying drawings.

[0050] In some embodiments, in step S2, the recycled material may be subjected to elemental analysis using equipment such as ICP-MS (inductively coupled plasma mass spectrometry) or XRF (X-ray fluorescence spectroscopy).

[0051] In some cases, elemental analysis of recycled materials generally includes the following steps: a sampling step, i.e. taking representative samples from the recycled materials; a pretreatment step, including but not limited to grinding, dissolving or melting the recycled material samples for elemental analysis; an analysis step, i.e. performing elemental analysis using equipment such as ICP-MS or XRF; a data processing step: analyzing the data collected by the equipment to obtain and record the types and doping concentrations of the doping elements at different lengths in the recycled materials and the resistivity at different lengths in the recycled materials; and a reporting step, i.e. organizing the analysis results into a report.

[0052] In some cases, reference Figure 2 , Figure 2 The graph of the relationship between the doping concentration and resistivity of different doping elements at different lengths in the circulating material in the recycling method provided in the embodiment of the present disclosure is a curve. The types and doping concentrations of the doping elements at different lengths in the circulating material will fluctuate, which will cause the resistivity at different lengths in the circulating material to fluctuate.

[0053] In some examples, the prepared single crystal silicon is N-type single crystal silicon, and the doping element doped into the single crystal silicon may be at least one of the VA Group elements such as P (phosphorus), As (arsenic) or Sb (antimony), thereby causing the doping element in the recycled material formed by the preparation of the single crystal silicon to also be at least one of the VA Group elements such as P (phosphorus), As (arsenic) or Sb (antimony). Figure 2 In the example, the doping elements in the recycled material are P (phosphorus) and Sb (antimony), where the doping concentrations of P (phosphorus) and Sb (antimony) at different lengths in the recycled material are different, and the resistivity at different lengths in the recycled material is inversely correlated with the sum of the doping concentrations of P (phosphorus) and Sb (antimony) at this location. In other words, the greater the sum of the doping concentrations of P (phosphorus) and Sb (antimony) at different locations in the recycled material, that is, at different lengths, the lower the resistivity of the recycled material at this location.

[0054] In some embodiments, the preset resistivity may be any value in the range of 2Ω·cm to 4Ω·cm, for example, the preset resistivity may be 2.2Ω·cm, 2.5Ω·cm, 2.8Ω·cm, 3Ω·cm, 3.2Ω·cm, 3.5Ω·cm or 3.6Ω·cm, etc. It is worth noting that the target resistivity for preparing a single crystal is different from the preset resistivity. The preset resistivity is set in order to determine how to grade the recycled material later. The target resistivity for preparing a single crystal may be set arbitrarily according to actual needs and is not controlled by the preset resistivity. For example, the target resistivity for preparing a single crystal may be 1Ω·cm or 7Ω·cm, etc.

[0055] In some embodiments, the first preset accuracy may be any value between 4% and 6%. For example, the first preset accuracy may be 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.3%, 5.5%, 5.6% or 5.8%, etc.

[0056] In some embodiments, the second preset accuracy may be 10% to 20%. For example, the second preset accuracy may be 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% or 19%, etc.

[0057] It is worth noting that both the first preset accuracy and the second preset accuracy can be regarded as a specific threshold of the target control accuracy. The target control accuracy refers to the variable range of the target resistivity of the single crystal to be prepared, and the first preset accuracy and the second preset accuracy are both specific ranges thereof. In one example, the first preset accuracy can be 5%, and the target resistivity of the single crystal to be prepared is 8Ω·cm, then the first preset accuracy refers to the actual output of the single crystal to be prepared. The head-controlled resistivity of the crystal rod is 8±0.05Ω·cm; in another example, the second preset accuracy can be 15%, and the target resistivity of the single crystal to be prepared is 1Ω·cm, then the second preset accuracy refers to the actual output of the single crystal to be prepared. The head-controlled resistivity of the crystal rod is 1±0.15Ω·cm.

[0058] In some embodiments, M may be any value between 6 and 10, for example, M may be 7; S may be any value between 1 and 4, for example, S may be 1.

[0059] In some embodiments, the process of preparing a single crystal includes at least a crystal pulling step and a machining step; the step of collecting recycled materials may include: collecting recycled materials generated by the crystal pulling step, and collecting recycled materials generated by the machining step.

[0060] It is worth noting that the composition or performance parameters of the recycled materials generated in different production links are different. The collected recycled materials can be roughly divided into different groups according to the different production links, such as crystal pulling group recycled materials or machining group recycled materials, and then the recycled materials can be classified in detail based on steps S2 and S3.

[0061] In some cases, step S1 of collecting recycled materials generated in the machining process may include: cutting the prepared crystal into T segments of crystal blanks, each segment of the crystal blank will produce a portion of sub-recycled material after machining, T is a positive integer less than or equal to M; step S2 of performing elemental analysis on the recycled materials may include: performing elemental analysis on each portion of the sub-recycled material.

[0062] In some examples, the cross section of the crystal is circular or elliptical. In order to prepare a crystal blank with a rectangular cross section including four chamfers, each section of the crystal blank will generate more sub-circulated materials at least when preparing the chamfers.

[0063] In some examples, along the extension direction X of the crystal, the length of each section of the crystal blank may be 780 mm.

[0064] In some examples, the sub-circulated materials produced by each 780 mm crystal rod to form a crystal blank can be regarded as one level, that is, T equals M. In other embodiments, after performing step S2, based on the different performance parameters of the sub-circulated materials produced by each section of the crystal blank, the T-molecule sub-circulated materials produced by the T-section crystal blank can be divided into (T-1), (T-2) or (T-3) levels. For example, based on the element analysis in step S2, if the types and doping concentrations of the doping elements at different lengths and the resistivity at different lengths in at least two sub-circulated materials among the T-molecule sub-circulated materials are relatively close, then the at least two sub-circulated materials can be divided into the same level.

[0065] In one example, the crystal is cut into 780 mm sections, which can be divided into 7 sections of crystal blanks. Each section of the crystal blank will produce a portion of sub-circulating material. The 7 portions of sub-circulating material can be divided into 7 levels at most and at least 1 level.

[0066] In some embodiments, the types of doping elements in the recycled material may include antimony and phosphorus; the step of performing elemental analysis on the recycled material may also include: obtaining the doping concentration of antimony in the recycled material as a first doping concentration, and the sum of the doping concentration of antimony in the recycled material and the doping concentration of phosphorus in the recycled material as a second doping concentration, to record the recycled material coefficient; wherein the recycled material coefficient is the ratio of the first doping concentration to the second doping concentration.

[0067] From the above analysis, it can be seen that the resistivity at different lengths in the circulating material is inversely correlated with the sum of the doping concentrations of P (phosphorus) and Sb (antimony) here. Based on this, the circulating material coefficient can reflect the proportion of the doping concentrations of P (phosphorus) and Sb (antimony) in the circulating material here to a certain extent, as well as the resistivity of the circulating material here. Subsequently, the circulating material coefficients of different circulating materials recorded in step S2 can be used to classify them.

[0068] In some embodiments, the difference in resistivity of recycled materials of different levels is less than 0.2 Ω·cm. This is conducive to achieving detailed division of recycled materials with the help of step S2 and step S3, avoiding excessive difference between recycled materials of different levels, and thus helping to reduce the variation range of resistivity of single crystals prepared with the help of recycled materials.

[0069] In some embodiments, reference Figure 3 , Figure 3 Another schematic flow diagram of the method for recycling the monocrystalline silicon recycled material provided in the embodiment of the present disclosure, the recycling method may further include step S4: washing the recycled materials divided into different levels respectively; the washing process may include the following steps:

[0070] A first cleaning liquid is used to perform a first cleaning treatment on the circulating material divided into M levels. The cleaning temperature of the first cleaning treatment is a first temperature, and the cleaning time of the first cleaning treatment is a first time.

[0071] First, the second cleaning liquid is used to perform a second cleaning treatment on the circulating material divided into S levels, and then the first cleaning liquid is used to perform a third cleaning treatment on the circulating material divided into S levels. The cleaning temperature of the second cleaning treatment is the second temperature, the cleaning time of the second cleaning treatment is the second time, the cleaning temperature of the third cleaning treatment is the third temperature, and the cleaning time of the third cleaning treatment is the third time; wherein, the second temperature is greater than the first temperature, the second time is greater than or equal to the first time, and the third time is greater than or equal to the first time; the acidity of the first cleaning liquid is lower than the acidity of the second cleaning liquid.

[0072] It is worth noting that, based on the different target resistivity or target control accuracy of the single crystal to be prepared, different grading logics are executed on the circulating material, and different cleaning treatments are also performed on the circulating material after being graded by different grading logics. Specifically, only the first cleaning liquid is used to clean the circulating material divided into M levels, and the first cleaning liquid and the second cleaning liquid are used to clean the circulating material divided into S levels, respectively, wherein not only the second temperature is controlled to be greater than the first temperature, the second time length is greater than or equal to the first time length, and the third time length is greater than or equal to the first time length, and the acidity of the first cleaning liquid is controlled to be lower than the acidity of the second cleaning liquid, so as to effectively increase the cleaning strength of the circulating material divided into S levels, so as to reduce the difference in performance parameters between the circulating materials of different levels in the S levels of circulating materials to a certain extent.

[0073] In some cases, the second duration may be equal to the third duration.

[0074] In some cases, due to the fact that the resistivity of the single crystal to be prepared in the first grading logic of the recycled material is relatively large, that is, the target resistivity is greater than the preset resistivity, the doping concentrations of the doping elements in the recycled material divided into M levels, such as antimony and phosphorus, are relatively low. Based on this, a first cleaning liquid is used to perform a first cleaning treatment on the recycled material divided into M levels, which is sufficient to remove surface impurities and slight internal impurities in the recycled material.

[0075] Due to the second grading logic of the recycled material, the resistivity of the single crystal to be prepared is itself small, that is, the target resistivity is less than or equal to the preset resistivity, and the doping concentrations of the doping elements, such as antimony and phosphorus, in the recycled material divided into S levels are relatively high. The recycled material is prone to contain more insoluble impurities. Based on this, the second cleaning liquid is first used to perform a second cleaning treatment on the recycled material divided into S levels, and then the first cleaning liquid is used to perform a third cleaning treatment on the recycled material divided into S levels, so as to increase the cleaning intensity of the recycled material divided into S levels, so as to thoroughly decompose and remove impurities in the recycled material, such as removing oxide type impurities and organic type impurities in the recycled material.

[0076] In some examples, the chemical composition of the first cleaning solution may be HCl, H 2 O 2 and H 2 O, the volume ratio of the three can be HCL:H 2 O 2 :H 2 O=1:1:6~1:2:8; the chemical composition of the second cleaning solution can be NH 4 OH, H 2 O 2 and H 2 O, the volume ratio of the three can be NH 4 OH:H 2 O 2 :H 2 O=1:1:5~1:2:7.

[0077] In some examples, the first temperature may be 80°C to 90°C, for example, the first temperature may be 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C or 89°C, etc.; the first time length may be 10min to 15min, for example, the first time length may be 11min, 12min, 13min or 14min, etc.

[0078] In some examples, the second temperature may be 100°C to 120°C, for example, the second temperature may be 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C or 119°C, etc.; the second time length may be 15min to 20min, for example, the second time length may be 16min, 17min, 18min or 19min, etc.; the third temperature may be 80°C to 90°C, for example, the third temperature may be 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C or 89°C, etc.; the third time length may be 15min to 20min, for example, the third time length may be 16min, 17min, 18min or 19min, etc.

[0079] In some embodiments, reference Figure 4 , Figure 4 Another flow chart of the method for recycling monocrystalline silicon recycled material provided in the embodiment of the present disclosure is as follows. After the recycled material is cleaned, the recycling method may further include step S5: performing heat treatment on the recycled material divided into different levels respectively; the heat treatment step may include: performing a first heat treatment on the recycled material divided into M levels, the treatment temperature of the first heat treatment is a fourth temperature, and the treatment time of the first heat treatment is a fourth time; performing a second heat treatment on the recycled material divided into S levels, the treatment temperature of the second heat treatment is a fifth temperature, and the treatment time of the second heat treatment is a fifth time; wherein the fourth temperature is lower than the fifth temperature, and the fourth time is lower than the fifth time.

[0080] It is worth noting that by adjusting the treatment temperature and treatment time of the heat treatment, the degree of heat treatment of the recycled material divided into S levels is higher than that of the recycled material divided into M levels, so as to further improve the performance parameters of the recycled material divided into S levels with higher doping elements.

[0081] For recycled materials divided into M levels, the processing temperature and processing time of the first heat treatment are reduced accordingly, which can avoid unnecessary energy consumption and time waste caused by excessive heat treatment; for recycled materials divided into S levels, higher processing temperatures and longer processing times are used, which are conducive to promoting the evaporation and diffusion of impurities in the recycled materials, ensuring that the impurities inside the recycled materials are fully treated.

[0082] In addition, both the first heat treatment and the second heat treatment can improve the quality of the recycled material from at least the following three aspects to improve the performance parameters of the recycled material:

[0083] First, the lattice integrity of the recycled material can be improved by heat treatment. For example, the dislocation density in the crystal of the recycled material can be reduced to improve the lattice integrity. Moreover, the optimized lattice integrity means fewer dislocations and defects in the recycled material, which is conducive to improving the electrical properties of the crystals formed later with the recycled material.

[0084] Secondly, the impurity concentration in the recycled material can be reduced by heat treatment. For example, the diffusion and removal of impurities in the recycled material can be promoted to reduce the impurity concentration in the crystal. Moreover, reducing the impurity concentration in the recycled material helps to reduce non-radiative recombination centers, thereby improving the carrier lifetime and conductivity in the crystal formed subsequently with the recycled material.

[0085] Third, the conductivity of the recycled material can be improved by heat treatment. For example, the mobility and life of the carriers in the recycled material can be improved, thereby optimizing the conductivity of the crystal. Moreover, the optimization of the conductivity of the recycled material means better carrier transport, which is conducive to improving the electrical properties of the crystals formed with the recycled material, which is crucial for the performance of subsequent electronic devices and photovoltaic cells formed based on the crystals.

[0086] In some examples, the fourth temperature may be 90°C to 100°C, for example, the fourth temperature may be 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C or 99°C, etc.; the fourth time may be 15min to 20min, for example, the fourth time may be 16min, 17min, 18min or 19min, etc.; the fifth temperature may be 100°C to 120°C, for example, the fifth temperature may be 101°C, 102°C, 103°C , 104°C, 105°C, 106°C, 107°C, 108°C, 109°, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C or 119°C, etc.; the fifth time length can be 20min~30min, for example, the fifth time length can be 21in, 22min, 23min, 24min, 25min, 26min, 27min, 28min or 29min, etc.

[0087] In some embodiments, after the recycled material is heat treated, the recycling method may further include: performing an impurity analysis on the recycled material to obtain and record the actual purity of the recycled material; if the actual purity is lower than the preset purity, marking the recycled material as unqualified recycled material, and performing a cleaning process and a heat treatment on the unqualified recycled material again until the actual purity of the unqualified recycled material is greater than or equal to the preset purity. In this way, after the cleaning process and the heat treatment, the recycled material is also subjected to a strict impurity analysis to control the recycled material after the treatment to reach the required impurity control level, so as to further improve the quality of the single crystal to be prepared.

[0088] In some cases, ICP-MS equipment can be used to conduct in-depth testing of the recycled material after cleaning and heat treatment to obtain and record the actual purity of the recycled material.

[0089] In some examples, the preset purity may be 7N, in other words, the preset purity may be 99.99999%, and the proportion of impurities in the recycled material is less than 0.00001%.

[0090] It is worth noting that in the step of again cleaning and heat treating the unqualified recycled material, if the unqualified recycled material is one of the recycled materials divided into M levels, the cleaning and heat treatment of the M levels of recycled materials are repeated until the actual purity of the unqualified recycled material is greater than or equal to the preset purity; if the unqualified recycled material is one of the recycled materials divided into S levels, the cleaning and heat treatment of the S levels of recycled materials are repeated until the actual purity of the unqualified recycled material is greater than or equal to the preset purity.

[0091] In some embodiments, the collected recycled materials include multiple batches; the step of performing impurity analysis on the recycled materials may also include: obtaining and recording the total impurity content of iron, copper and nickel in any batch of recycled materials; the recovery method may also include: based on the total impurity content of each batch of recycled materials, allocating at least two batches of recycled materials into a group for the same round of single crystal preparation, and controlling the average value of the total impurity content of each group of recycled materials to be less than or equal to 80 ppb.

[0092] It is worth noting that the collected recycled materials include recycled materials generated in multiple production links. Based on the aforementioned steps S2 and S3, the recycled materials have been divided into multiple levels. A batch of recycled materials includes at least one level of recycled materials. The correspondence between batches and levels can be adjusted according to actual needs.

[0093] Based on this, the average value of the total impurity content of multiple batches of recycled materials allocated to the same round of single crystal preparation process is controlled to be less than or equal to 80 ppb, so as to further control the impurity content of the recycled material in each round of single crystal preparation process, so as to further improve the uniformity of the resistivity inside the single crystal prepared with the help of the recycled material, thereby maintaining the high quality of the single crystal to be prepared.

[0094] In one example, if the impurity content of a batch of recycled materials among multiple batches of recycled materials allocated to the same round of single crystal preparation process is higher, for example, greater than 80 ppb, then the recycled materials of other batches in the same group are adjusted to be less than 80 ppb, and based on the degree of excess impurity content of a batch of recycled materials, the difference between the impurity content of other batches in the same group and 80 ppb can be matched to ensure that the average value of the total impurity content of each group of recycled materials is less than or equal to 80 ppb.

[0095] It should be noted that the average value of the total impurity content of each group of recycled materials is less than or equal to 80 ppb, which means that the average value of the total impurity content of each group of recycled materials is 1 μg / kg, that is, the mass of impurities contained in each 1 kg of recycled materials is not higher than 1 μg.

[0096] In some embodiments, the recycling method may further include: providing silicon material; based on the classification of the recycled material, selecting the recycled material of the corresponding level that better matches the target resistivity and the target control accuracy; mixing the selected recycled material with the silicon material in a preset ratio to prepare a new round of single crystal preparation; wherein the preset ratio is 45% to 55% of the weight of the selected recycled material to the weight of the silicon material: 55% to 45%. In this way, it is beneficial to improve the quality of the single crystal to be prepared while allowing more recycled materials to be reused to prepare the single crystal, thereby improving the utilization rate of the recycled material.

[0097] In some examples, the ratio of the weight of the selected recycled material to the weight of the silicon material is 50%:50%.

[0098] To summarize, on the basis of elemental analysis of the recycled materials to distinguish the performance parameters of different recycled materials, based on the different target resistivity or target control accuracy of the single crystal to be prepared, the preset resistivity, the first preset accuracy and the second preset accuracy are set, and the single crystal to be prepared is divided into at least two grades according to the different performance parameters, and based on the different performance parameters of the single crystal to be prepared, different grading logics are performed on the collected recycled materials according to the different performance parameters of the recycled materials, which is beneficial to effectively avoid large fluctuations in the resistivity inside the single crystal to be prepared, so as to improve the quality of the single crystal to be prepared, while making full use of the recycled materials with different performance parameters to improve the utilization rate of the recycled materials, and to simplify the grading process of the collected recycled materials to a certain extent.

[0099] Those skilled in the art can understand that the above-mentioned embodiments are specific examples for implementing the present disclosure, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the embodiments of the present disclosure. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present disclosure, so the protection scope of the embodiments of the present disclosure shall be based on the scope defined in the claims.

Claims

1. A method for recovering single crystal silicon recycled material, characterized in that: include: Collecting recycled materials and using the recycled materials as raw materials for subsequent preparation of single crystals, using the resistivity of the single crystal to be prepared as the target resistivity, and using the variable range of the target resistivity as the target control accuracy; Performing element analysis on the recycled material to obtain and record the type and doping concentration of the doping element at different lengths in the recycled material and the resistivity at different lengths in the recycled material; If the target resistivity is greater than the preset resistivity, or the target control accuracy is less than or equal to the first preset accuracy, the recycled material is divided into M levels based on the types and doping concentrations of the doping elements at different lengths in the recycled material and the resistivity at different lengths in the recycled material; If the target resistivity is less than or equal to the preset resistivity, or the target control accuracy is less than or equal to a second preset accuracy, the recycled material is divided into S levels based on the types and doping concentrations of the doping elements at different lengths in the recycled material and the resistivity at different lengths in the recycled material; Wherein, M is greater than S, and both M and S are positive integers; the resistivity of the recycled material at any level is less than the preset resistivity.

2. The recycling method according to claim 1, characterized in that: The process of preparing a single crystal includes at least a crystal pulling step and a machining step; The step of collecting the recycled material comprises: The recycled material generated in the crystal pulling step is collected, and the recycled material generated in the machining step is collected.

3. The recycling method according to claim 2, characterized in that: The step of collecting the recycled material generated in the machining process comprises: Cutting the prepared crystal into T segments of crystal blanks, each segment of the crystal blank will produce a portion of sub-circulated material after machining, and T is a positive integer less than or equal to M; The step of performing elemental analysis on the recycled material comprises: performing elemental analysis on each portion of the sub-recycled material.

4. The recycling method according to claim 1, characterized in that: The types of doping elements in the recycled material include antimony and phosphorus; The step of performing elemental analysis on the recycled material also includes: The doping concentration of the antimony element in the recycled material is obtained as a first doping concentration, and the sum of the doping concentration of the antimony element in the recycled material and the doping concentration of the phosphorus element in the recycled material is obtained as a second doping concentration, so as to record a recycled material coefficient; The recycling factor is the ratio of the first doping concentration to the second doping concentration.

5. The recovery method according to claim 1 or 4, characterized in that: The difference in resistivity of the recycled materials of different levels is less than 0.2 Ω·cm.

6. The recycling method according to claim 1, characterized in that: Also includes: The recycled materials divided into different levels are cleaned respectively; The steps of the cleaning process include: Using a first cleaning liquid to perform a first cleaning treatment on the circulating material divided into M levels, the cleaning temperature of the first cleaning treatment is a first temperature, and the cleaning time of the first cleaning treatment is a first time; First, the second cleaning liquid is used to perform a second cleaning treatment on the circulating material divided into S levels, and then the first cleaning liquid is used to perform a third cleaning treatment on the circulating material divided into S levels, the cleaning temperature of the second cleaning treatment is a second temperature, the cleaning time of the second cleaning treatment is a second time, the cleaning temperature of the third cleaning treatment is a third temperature, and the cleaning time of the third cleaning treatment is a third time; The second temperature is greater than the first temperature, the second time period is greater than or equal to the first time period, and the third time period is greater than or equal to the first time period; and the acidity of the first cleaning liquid is lower than the acidity of the second cleaning liquid.

7. The recycling method according to claim 6, characterized in that: After the recycling material is cleaned, the recycling method further comprises: Heat treating the recycled materials divided into different grades respectively; The heat treatment steps include: Performing a first heat treatment on the recycled material divided into M levels, wherein the treatment temperature of the first heat treatment is a fourth temperature, and the treatment duration of the first heat treatment is a fourth duration; Performing a second heat treatment on the recycled material divided into S levels, wherein the treatment temperature of the second heat treatment is a fifth temperature, and the treatment duration of the second heat treatment is a fifth duration; The fourth temperature is lower than the fifth temperature, and the fourth duration is lower than the fifth duration.

8. The recycling method according to claim 7, characterized in that: After the recycled material is heat treated, the recycling method further comprises: Performing impurity analysis on the recycled material to obtain and record the actual purity of the recycled material; If the actual purity is lower than the preset purity, the recycled material is marked as unqualified recycled material, and the unqualified recycled material is again subjected to the cleaning treatment and the heat treatment until the actual purity of the unqualified recycled material is greater than or equal to the preset purity.

9. The recycling method according to claim 8, characterized in that: The collected recycled materials include multiple batches; The step of performing the impurity analysis on the recycled material further includes: obtaining and recording the total impurity content of iron, copper and nickel in any batch of the recycled material; The recycling method further comprises: Based on the total impurity content of each batch of the recycled material, at least two batches of the recycled material are allocated as a group for the preparation of the same round of single crystals, and the average value of the total impurity content of each group of the recycled material is controlled to be less than or equal to 80 ppb.

10. The recycling method according to claim 7 or 9, characterized in that: Also includes: Provide silicon materials; Based on the classification of the recycled material, selecting the recycled material of the corresponding grade that better matches the target resistivity and the target control accuracy; Mixing the selected recycled material with the silicon material in a preset ratio to prepare a new round of single crystal preparation; The preset ratio is 45% to 55%: 55% to 45% of the weight of the selected recycled material to the weight of the silicon material.

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