A low-impurity uniformity control rod based on a zone-melting single crystal silicon rod and a preparation and application method thereof

Abstract

The present application relates to the field of polysilicon quality detection, and more particularly to a low-impurity uniformity quality control rod based on a zone-melting single crystal silicon rod and a preparation and application method thereof. The quality control rod is made of a zone-melting single crystal silicon rod meeting the uniformity standard, has a diameter of 20±0.05 mm and a length of 160±0.1 mm, and the impurity content meets the following requirements: phosphorus <100 ppta, boron <20 ppta, carbon <20 ppba, and oxygen <20 ppba; the variation coefficients of the impurity contents of phosphorus, boron, carbon, and oxygen in the quality control rod and between batches are all ≤3%. The present application overcomes the influence of the radial impurity unevenness of the traditional polysilicon raw material, ensures that the key impurity contents of the prepared quality control rod are highly consistent, the variation coefficient (CV) can be stably controlled within 5%, and a stable and reliable measurement reference is obtained.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline silicon quality testing, and in particular to a low-impurity uniformity control rod based on zone-melted single-crystal silicon rod, and its preparation and application methods. Background Technology

[0002] In the production of high-purity polycrystalline silicon and semiconductor-grade monocrystalline silicon, continuous and stable monitoring of the cleanliness of the polycrystalline silicon raw material cleaning process and the suspension zone melting monocrystalline growth process is crucial to ensuring that the final product achieves ultra-high purity. Current monitoring methods typically rely on quality control rods: a batch of silicon rods with known and uniformly stable impurity content is used, and these rods undergo the same cleaning and suspension zone melting crystal pulling processes as the production materials. Subsequently, precise analytical methods such as low-temperature infrared spectroscopy are used to measure the changes in impurity content after the processing, thereby inferring the level of contamination introduced into the process or the purification efficiency.

[0003] Currently, quality control rods are generally prepared using polycrystalline silicon rods produced by industrial-grade chemical vapor deposition as raw materials. The specific method involves drilling a cylindrical sample rod along the axial direction of the polycrystalline silicon rod to obtain a sample representing the overall impurity level of the rod. However, this method has inherent and insurmountable drawbacks: First, because the temperature field and the gas flow field inside the reactor cannot be absolutely uniform during the chemical vapor deposition process, there is a significant radial impurity concentration gradient inside the deposited polycrystalline silicon rod. That is, from the center of the silicon rod to the edge, the concentration of key Group III / V impurities such as phosphorus (P) and boron (B) shows a systematic change.

[0004] Secondly, the existence of the aforementioned radial gradient means that the impurity concentration of any axially drilled sample rod is not uniformly distributed. More seriously, even if multiple sample rods are drilled closely adjacent to each other from the same mother rod, the average impurity content between the obtained sample rods will vary greatly due to the unavoidable slight deviation in the radial position of the drilling path at the microscopic level. The coefficient of variation is usually more than 50%.

[0005] The inherent, uncontrollable high degree of inhomogeneity and batch-to-batch inconsistency of these quality control bars render them unsuitable as stable reference materials. When using such control bars for process monitoring, the significant fluctuations in test data primarily stem from the differences within the control bars themselves, rather than actual changes in the process. This makes it impossible to establish effective statistical process control charts, depriving long-term cleanliness monitoring and trend analysis of the process of a reliable data foundation. Consequently, the quality control system has blind spots, making it difficult to provide timely warnings of subtle process drift or accidental contamination events.

[0006] In addition, even if the quality control rods are prepared, they are easily affected by the environmental atmosphere and precipitates from packaging materials during storage and transportation, which can cause uncontrollable drift in the content of surface and even bulk impurities. This results in the known impurity content of the quality control rods being distorted before they are put into use, thus affecting the accuracy of process monitoring results.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The first objective of this invention is to provide a low-impurity, uniform quality control rod based on zone-melted single-crystal silicon rods, which overcomes the influence of radial impurity inhomogeneity in traditional polycrystalline silicon raw materials, and ensures that the content of key impurities in the prepared quality control rods is highly consistent within each rod, between rods, and between batches, with its coefficient of variation (CV) being stably controlled within 5%, thereby obtaining a stable and reliable measurement benchmark.

[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A low-impurity uniformity quality control rod based on a zone-melted single-crystal silicon rod is provided. The quality control rod is manufactured by processing a zone-melted single-crystal silicon rod that meets the uniformity standard. Its diameter is 20±0.05mm and its length is 160±0.1mm. The impurity content must meet the following requirements: phosphorus (P) < 100 ppta, boron (B) < 20 ppta, carbon (C) < 20 ppba, and oxygen (O) < 20 ppba; the coefficients of variation for the phosphorus, boron, carbon, and oxygen impurities within the quality control rod and between batches must all be ≤ 3%.

[0010] This invention utilizes the inherent characteristics of zone-melted single-crystal silicon—its perfect crystal structure and macroscopically uniform impurity distribution—to replace polycrystalline silicon raw materials with grain boundaries and radial concentration gradients used in traditional methods. By defining ultra-low impurity content thresholds and uniformity indicators, an ideal and stable background reference is established for process monitoring, fundamentally solving the problem of excessive background noise in traditional polycrystalline silicon quality control rods caused by raw material inhomogeneity.

[0011] Preferably, the zone-melted single-crystal silicon rods that meet the uniformity standard are raw materials whose coefficients of variation for phosphorus, boron, carbon, and oxygen impurities in both radial and axial directions are ≤5%. In this invention, uniformity is expressed as the coefficient of variation, i.e., the percentage of standard deviation to mean (CV). Specifically, electronic-grade zone-melted intrinsic single-crystal silicon rods (conductivity type N-type, crystal orientation...) are used. <111> or <100> By pre-screening the raw materials, silicon rods that do not meet the basic uniformity requirements are avoided from being put into the subsequent ultra-clean processing, thereby reducing the overall preparation cost and improving the yield.

[0012] The second objective of this invention is to provide a method for preparing a low-impurity, uniform quality control rod based on a zone-melted single-crystal silicon rod. This system can strictly isolate processing contamination and precisely control the physical dimensions of the product, enabling stable and repetitive production of high-quality quality control rods. Furthermore, it can be effectively packaged and stored to ensure long-term stability and reliability.

[0013] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for preparing a quality control rod includes the following steps: S1. Raw Material Selection: A combination of secondary ion mass spectrometry and low-temperature infrared spectroscopy is used to conduct full-rod testing on zone-melted single-crystal silicon rods. Silicon rods with phosphorus <80ppta, boron <15ppta, carbon <15ppba, oxygen <15ppba, and impurity variation coefficients of each impurity content ≤5% in the radial / axial direction are selected as raw materials to avoid the risk of excessive impurities and uneven distribution from the source. In this step, the upper limit of impurities in the raw materials is lower than that in the finished product of the quality control rod. This is because the process from raw materials to finished products involves a series of physical and chemical treatments, such as cutting, grinding, polishing, cleaning, and packaging. Even in a Class 1000 cleanroom and under argon protection, there is still a very small risk of introducing contamination during these processes. The above limits ensure that even if there are slight fluctuations within an acceptable range during the processing of a certain batch, the final product can still meet the standards.

[0014] S2. Directional Cutting and Precision Forming: In a Class 1000 cleanroom environment, the raw material is cut into bars, which are then subjected to rough grinding, fine grinding, and polishing processes to obtain billets of predetermined dimensions. The entire process is carried out under a high-purity argon protective atmosphere, and the surface roughness Ra of the processed billets is ≤0.01μm. Preferably, in step S2, a high-precision wire cutting device with a positioning accuracy of ±0.01mm is used to cut along the axial direction at a rate of 0.5~1mm / min. The length of the cut blank is 160mm±0.1mm and the initial diameter is 22mm, which ensures the uniformity of the blank size and reduces the introduction of impurities during the cutting process. Subsequently, coarse grinding, fine grinding, and polishing were performed sequentially to obtain a billet with a diameter of 20±0.05mm, a length of 160±0.1mm, and a surface roughness Ra≤0.01μm, thus achieving precise dimensional and surface quality control of the quality control rod.

[0015] The rough grinding process uses a diamond grinding wheel to trim the diameter of the blank to 20.1 mm. Then, the fine grinding uses a resin-bonded grinding wheel to trim the diameter of the blank to 20 mm ± 0.05 mm. Finally, the blank is polished with colloidal silica polishing liquid until the surface roughness Ra ≤ 0.01 μm.

[0016] Preferably, in step S2, the purity of high-purity argon gas is not less than 99.999%, which ensures that the extremely low oxygen and carbon background of the quality control rod is maintained, avoids the formation of irregular oxide layers, and makes the subsequent surface roughness control and cleaning effect better. The impurity detection results more accurately reflect the condition of the bulk material rather than surface contamination.

[0017] S3. Impurity Consistency Re-inspection: Using a secondary ion mass spectrometer, samples are taken from three locations on the billet obtained in step S2: 20mm from both ends and the center point, to re-inspect the billet and ensure that the coefficient of variation of each impurity content is ≤3% at different detection locations for the same billet; this is to remove unqualified products and ensure the consistency of quality control rods within the batch. Preferably, in step S3, the sampling depth for sampling detection is 10~50μm. This depth is intended to detect the subsurface region. If the depth is too shallow, it may only reflect surface cleaning or adsorbed impurities and not represent the bulk material; if the depth is too deep, it may complicate the detection signal and unnecessarily increase the detection time and cost.

[0018] Preferably, after step S3, step S3a is also included: batch consistency determination and identification; Batch consistency is determined as follows: In the same production batch, no less than 5% of the billets are randomly selected for re-inspection in step S3. All the sampled billets must meet the requirement that the coefficient of variation of each impurity within a single billet is ≤3%, and the deviation of the average value of the key impurity content of all finished products in the batch from the nominal value is also ≤3%. The marking method is as follows: Quality control bars that meet batch consistency requirements are uniquely identified using laser marking. By using random sampling of no less than 5% and combining the dual standards of single bar uniformity and batch average deviation, a reliable inference can be made statistically about the quality consistency of the entire batch of products.

[0019] S4. Clean Packaging: The qualified billets are sequentially ultrasonically cleaned with ultrapure water, dried with high-purity nitrogen, and finally sealed with a quartz tube for vacuum or inert gas protection.

[0020] Preferably, in step S4, the resistivity of ultrapure water is ≥18MΩ·cm, which can effectively dissolve and remove ionic impurities; the purity of high-purity nitrogen is ≥99.999%, which can quickly remove moisture by blowing it dry, avoid water stains, and form a temporary inert environment before packaging. Finally, a sealed quartz tube is used for packaging, which effectively isolates all external contamination pathways and facilitates safe transportation and long-term storage.

[0021] The third objective of this invention is to provide an application method for a low-impurity uniformity property control rod based on a zone-melted single-crystal silicon rod, specifically including its application in the stability monitoring of the zone-melted single-crystal silicon production process for electronic-grade polycrystalline silicon; and its application in the low-temperature infrared detection stability monitoring of P, B, C, and O impurities in electronic-grade polycrystalline silicon.

[0022] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for applying a quality control rod to monitor the cleanliness of the process of preparing single-crystal silicon rods using the zone melting method for electronic-grade polycrystalline silicon. The single-crystal silicon rod is used for subsequent detection of conductivity type, resistivity, group III-V impurities, and carbon-oxygen impurity content. The application method includes: Regularly use quality control rods with uniform impurities from the same batch and sequentially perform zone melting crystal pulling with the electronic-grade polycrystalline silicon sample rod to be tested under the same process conditions. Detect the impurity content in the quality control rod after zone melting and draw a quality control chart based on the test data. The quality control chart includes control lines and specification lines. The control lines are calculated based on test data after multiple quality control bars are drawn from the melt, while the specification lines are based on the impurity parameters of the quality control bars. If all the detected impurity indicators are within the control and specification lines, the zone melting process is stable and no additional impurities are introduced.

[0023] Specifically, the steps include the following: (1) Preparation: Select quality control rods from the same batch that meet the uniformity requirements, with a quantity of no less than 25 rods. After opening, use a low-temperature Fourier transform infrared spectrometer (LT-FTIR) to accurately determine the initial content of phosphorus, boron, carbon and oxygen impurities in each quality control rod and record it as the reference value for each quality control rod. (2) Co-processing: The single quality control rod and the electronic-grade polycrystalline silicon sample rod to be tested are subjected to the same standard cleaning process. After cleaning, in the same floating zone melting (FZ) single crystal furnace, the electronic-grade polycrystalline silicon sample rod to be tested is first subjected to zone melting pulling to grow a single crystal silicon rod. After the sample rod is pulled, the same process parameters as the sample rod pulling are immediately used to perform zone melting pulling on the quality control rod to ensure that the quality control rod and the electronic-grade polycrystalline silicon sample rod to be tested undergo the same zone melting process. (3) Impurity detection: Locate and remove the quality control rod from the single crystal silicon rod obtained by zone melting, and use LT-FTIR again to determine its phosphorus, boron, carbon and oxygen impurity content, and record it as the detection value after this zone melting process; (4) Quality control chart drawing: Repeat steps (2)-(3) to complete the zone melting drawing and impurity detection of at least 20-25 quality control bars. Calculate the control line of the quality control chart based on the impurity data obtained after zone melting. At the same time, formulate the specification line of the quality control chart based on the initial impurity parameters of the quality control bars to complete the drawing of the quality control chart. Among them, the control line is calculated based on the actual fluctuation data of the process itself and is used to determine whether the process is in a statistically controlled state. It is the natural boundary of fluctuation under normal process operation. The specification line is formulated based on the design parameters and product performance standards of the quality control bars themselves and is used to determine whether the process result is qualified. It is the hard tolerance boundary of the impurity content. (5) Daily process monitoring and evaluation: During the daily zone melting production process, the same batch of quality control bars are used regularly to complete the zone melting drawing and impurity detection according to steps (2)-(3), and the detection results are plotted on the above quality control chart; if all the impurity indicators obtained by detection are within the control line and specification line, it proves that the zone melting process is stable and no additional impurities are introduced; if the detection results exceed the control range, it is determined that there is a risk of contamination in the zone melting process, and process investigation is required.

[0024] This application method addresses the process characteristics of preparing single-crystal silicon rods from electronic-grade polycrystalline silicon using the floating zone melting method. It employs quality control rods with highly uniform impurities from the same batch, which undergo the same identical cleaning process as the electronic-grade polycrystalline silicon sample rods to be tested. Both are then sequentially subjected to zone melting crystal pulling using the same equipment and identical process parameters. This fundamentally eliminates the background noise in monitoring data caused by the inherent inhomogeneity of traditional quality control rods, ensuring that detected impurity changes accurately reflect the cleanliness level of the zone melting process. Furthermore, a dual-dimensional quality control chart system, using control lines and specification lines, is employed, with control lines calculated from the actual process measurement data of 20-25 quality control rods. It enables early warning of abnormal process fluctuations and uses the specification line established by the inherent impurity parameters of the quality control rod to achieve a hard judgment of the passability of process results. It not only conforms to the scientific norms of statistical process control, but also accurately captures the introduction of trace impurities at the ppba / ppta level in the zone melting process. It is suitable for the high-precision detection requirements of the conductivity type, resistivity, group III-V impurities and carbon and oxygen impurity content of the subsequent single crystal silicon rods. It can also realize long-term, continuous and quantitative monitoring of the cleanliness of the zone melting process, timely identify process drift and contamination risks, avoid batch product non-conformity, and significantly improve the process control capability and product quality consistency of electronic grade zone melting single crystal silicon production.

[0025] A method for using a quality control rod as a standard substance to monitor the stability of the determination of impurity content in silicon by low-temperature infrared spectroscopy. The method includes: periodically using the quality control rod to perform low-temperature infrared spectroscopy analysis, tracking the detection results of phosphorus, boron, carbon, and oxygen impurities, and plotting a quality control chart based on the results to determine the stability of the analytical instrument and method.

[0026] Specifically, the steps include the following: (1) Establishing a benchmark: Select a quality control bar as a long-term monitoring standard sample for the laboratory. A senior technician will use LT-FTIR to perform 10 repeated measurements on the bar under optimal instrument conditions. The average value will be taken as the acceptable value and uncertainty range of the standard sample, and an initial file will be established. (2) Daily monitoring: Every week or before each batch of important samples is tested, the testing personnel shall use the same LT-FTIR to measure the monitoring standard sample once under the same sample preparation conditions (such as sample thickness, cooling temperature) and instrument parameters; (3) Recording and plotting: Record the P, B, C and O content data obtained each time and plot a single-value moving range control chart (I-MRChart). Mark the upper and lower control limits on the chart with the acceptable value as the center line and ±3σ calculated from the historical data as the upper and lower limits. (4) Interpretation and action: Observe whether each new data point falls within the control limits and whether there is a continuous upward / downward trend. If the data point exceeds the control limits or shows an abnormal trend, an alarm will be issued immediately to indicate that the instrument may drift and needs to be recalibrated or maintained, thereby ensuring the accuracy and reliability of daily test data.

[0027] This method establishes a statistically based, objective, and quantitative benchmark for the stability of instruments and methods by drawing and continuously updating statistical process control charts (such as Xbar-R charts or I-MR charts). This greatly reduces the reliance on the experience of technical personnel, makes the quality control process standardized, trainable, and auditable, and improves the scientific level of laboratory management.

[0028] Compared with the prior art, the present invention has the following beneficial effects: This invention addresses the problem of traditional methods using polycrystalline silicon rods with radial impurity gradients to fabricate quality control rods. The inherent inhomogeneity of these rods leads to significant background noise in monitoring data, making it impossible to distinguish whether the signal originates from process fluctuations or inherent differences in the quality control rods. This invention designs a quality control rod that, leveraging the inherent perfect crystal structure and macroscopic uniformity of zone-melted single-crystal silicon, along with a stringent uniformity index of ≤3%, establishes an ideal and stable physicochemical benchmark. This ensures that any abnormal fluctuations in subsequent testing data can be reliably attributed to changes in the cleanliness of the monitored processes, such as cleaning or zone melting, thereby achieving effective process monitoring.

[0029] The combination of extremely low impurity content and ultra-high uniformity of the quality control rod in this invention achieves extreme sensitivity to process contamination and analytical errors. Its extremely low background makes it highly sensitive to trace contamination introduced by the process, capturing subtle process drifts that are undetectable by traditional methods, enabling early warning. Simultaneously, its high consistency ensures clear and unambiguous signals when used as measurement standards or process challenge samples, greatly improving the confidence level of monitoring signals and the analytical signal-to-noise ratio. Furthermore, the stable, consistent, and traceable reference material makes it possible to establish quality control charts with precise control limits, thereby enabling long-term, continuous, and quantitative trend monitoring and early warning of production processes or analytical instrument status. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the steps involved in preparing a low-impurity, uniform control rod based on a zone-melting single-crystal silicon rod. Detailed Implementation

[0032] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, features, and effects of a low-impurity uniform property control rod based on a zone-melting single-crystal silicon rod, and its preparation and application methods, are described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0033] Example 1: Preparation of quality control rods like Figure 1 As shown, this embodiment provides a method for preparing a low-impurity, uniform quality control rod based on a zone-melted single-crystal silicon rod. The specific steps are as follows: S1. Raw Material Selection: N-type zone-melted single-crystal silicon rods with a diameter of approximately 100 mm and a resistivity higher than 10000 Ω·cm were selected as initial raw materials. The silicon rods were scanned using a secondary ion mass spectrometer (SIMS) and a low-temperature Fourier transform infrared spectrometer (LT-FTIR). Detection points were taken every 10 cm along the length of the silicon rod, and the P, B, C, and O contents at each point were analyzed. The screening criteria were set as follows: the average impurity content at all detection points must meet the following requirements: P < 80 ppta, B < 15 ppta, C < 15 ppba, O < 15 ppba, and the coefficient of variation of the impurity content at each detection point must be ≤ 5%. Whole zone-melted single-crystal silicon rods meeting the above criteria were marked as qualified raw materials and proceeded to the next process. S2. Cleanroom forming process: Qualified zone-melting single-crystal silicon rods were sent to a Class 1000 cleanroom. Using a diamond wire cutter, under the protective atmosphere of high-purity argon (purity ≥99.999%), the silicon rods were cut into rods with a length of approximately 165 mm at a feed rate of 0.8 mm / min. The cut rods were then transferred to a precision centerless grinder with a continuous flow of high-purity argon (oxygen content <1 ppm). First, rough grinding was performed to remove the cutting damage layer and initially process the diameter to 20.2 mm. Then, fine grinding was performed to precisely control the diameter at 20.00 ± 0.05 mm, and the length was controlled at 160.0 ± 0.1 mm through end face grinding. The finely ground rods were then subjected to chemical mechanical polishing to achieve a surface roughness Ra ≤ 0.01 μm, resulting in a bright surface and a rod free of mechanical damage. S3. Uniformity re-inspection: From the batch of billets obtained in step S2, one billet is selected as a representative. Using a micro-area sampling device, samples are taken at three locations: both ends (20 mm from the end face) and the geometric center point of the billet. SIMS is used to perform depth profiling at each sampling point, analyzing the content of P, B, C, and O within a depth range of 10~50 μm. The relative standard deviation (RSD) of the detection results at the three locations is calculated, and its coefficient of variation is required to be ≤3%. This result represents the level of internal uniformity of a single billet in this batch. If the re-inspection is qualified, all billets in this batch proceed to the next step. S4. Clean Packaging: The re-inspected and qualified billet was placed in a Class 100 clean bench; the following cleaning steps were performed: first, ultrasonic cleaning was performed for 10 minutes in ultrapure water with a resistivity ≥18.2 MΩ·cm to remove adsorbed particles; then, the surface was dried with high-purity nitrogen gas with a purity ≥99.999%; the dried billet was quickly placed into a clean quartz glass tube; the quartz tube was evacuated until the pressure was below 1×10⁻⁶. -3 Pa, then fill with high-purity argon gas, and finally seal with an oxyhydrogen flame; a label is affixed to the outside of the sealed quartz tube, indicating the product batch number, specifications and nominal values ​​of key impurities.

[0034] Example 2: Application of quality control rods in monitoring the stability of zone melting process This embodiment utilizes the quality control rod prepared in Example 1 to monitor the cleanliness of the process for preparing single-crystal silicon rods using the electronic-grade polycrystalline silicon zone melting method. The single-crystal silicon rods are used for subsequent detection of conductivity type, resistivity, group III-V impurities, and carbon and oxygen impurity content, including the following steps: (1) Preparation: 30 quality control rods of the same batch (batch number A001) prepared in Example 1 were selected. All quality control rods met the requirements of phosphorus <100ppta, boron <20ppta, carbon <20ppba, oxygen <20ppba, and the coefficient of variation of impurity content within a single rod and between batches ≤3%. After opening, the initial content of phosphorus, boron, carbon and oxygen impurities in each quality control rod was accurately determined by LT-FTIR and recorded as the baseline value for each quality control rod to establish a baseline file. (2) Co-processing: Take one of the above quality control rods and perform the same standard RCA cleaning process together with the electronic-grade polycrystalline silicon sample rod to be tested. After cleaning, in the same floating zone melting (FZ) single crystal furnace, use the same equipment parameters, process conditions and environmental control to first perform zone melting pulling on the electronic-grade polycrystalline silicon sample rod to be tested to grow a single crystal silicon rod. After the sample rod is pulled, immediately use the same process parameters as the sample rod to perform zone melting pulling on the quality control rod to ensure that the quality control rod and the electronic-grade polycrystalline silicon sample rod to be tested undergo the same zone melting process. (3) Impurity detection: Locate and remove the quality control rod from the single crystal silicon rod obtained by zone melting, and use LT-FTIR again under the same detection conditions to determine the content of phosphorus, boron, carbon and oxygen impurities, and record it as the detection value after this zone melting process. (4) Quality control chart drawing: Repeat steps (2)-(3) to complete the zone melting drawing and impurity detection of 25 quality control bars. Based on the impurity detection data after 25 sets of zone melting, calculate the average value and standard deviation of each impurity content. With the average value as the center line and ±3σ as the upper and lower control lines, complete the formulation of the quality control chart control lines. At the same time, based on the initial impurity nominal parameters of this batch of quality control bars, formulate the upper and lower specification lines of each impurity. Finally, complete the drawing of the quality control chart for monitoring the cleanliness of the zone melting process. (5) Daily process monitoring and evaluation: During the daily zone melting production process, one quality control rod of the same batch (batch number A001) is used every week to complete the zone melting crystal pulling and impurity detection according to steps (2)-(3), and the detection results are plotted on the above quality control chart; if the detected impurity indicators of phosphorus, boron, carbon and oxygen are all within the control line and specification line, it proves that the zone melting process is stable and no additional impurities are introduced; if the detection results exceed the control range, or there is an abnormal trend of unidirectional increase / decrease of 7 consecutive data points, it is determined that there is a pollution risk in the zone melting process, production is stopped immediately and process investigation is carried out.

[0035] Example 3: Application of quality control rods in low-temperature infrared detection stability monitoring This embodiment uses the quality control rod prepared in Example 1 as a standard substance to monitor the stability of the low-temperature infrared spectroscopy analysis system, including the following steps: (1) Establishing a benchmark: Select a quality control rod from batch number A001 as the long-term monitoring standard sample of this laboratory. A senior technician will use LT-FTIR to perform 10 repeated measurements under the best instrument conditions. The average value will be taken as the acceptable value and uncertainty range of the standard sample to establish an initial file. It should be noted that the quality control rod needs to be sliced ​​and polished before testing to prepare a single crystal silicon wafer with a thickness of less than 10 mm. (2) Routine monitoring: Every week or before each batch of important samples is tested, the testing personnel shall use the same LT-FTIR to measure the monitoring standard sample once under the same sample preparation conditions and instrument parameters; (3) Recording and plotting: Record the P, B, C and O content data obtained each time and plot a single-value moving range control chart (I-MRChart). Mark the upper and lower control limits on the chart with the acceptable value as the center line and ±3σ calculated from the historical data as the upper and lower limits. (4) Interpretation and action: Observe whether each new data point falls within the control limits and whether there is a continuous upward / downward trend. If the data point exceeds the control limits or shows an abnormal trend, an alarm will be issued immediately to indicate that the instrument may drift and needs to be recalibrated or maintained, thereby ensuring the accuracy and reliability of daily test data.

[0036] Performance testing: A sampling survey was conducted on three batches (100 pieces per batch) of quality control bars prepared according to the method in Example 1: The average impurity content of the sampled products was: P: 65±3ppta, B: 12±1ppta, C: 10±0.5ppba, O: 12±0.8ppba; the average coefficient of variation of each impurity within a single sample (three-point detection) was 2.1%; the maximum deviation of the average impurity content between batches was 2.5%.

[0037] The above data proves that the quality control rods prepared by this invention have significantly lower coefficients of variation for impurities in single rods and between batches than those prepared by traditional methods, stably achieving the target of ≤3%, thus providing a reliable material basis for high-precision process monitoring and analytical quality control.

[0038] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A low-impurity, uniform property control rod based on a zone-melted single-crystal silicon rod, characterized in that, The quality control rod is made from a zone-melted single-crystal silicon rod that meets the uniformity standard, with a diameter of 20±0.05mm and a length of 160±0.1mm. The impurity content must meet the following requirements: phosphorus < 100 ppta, boron < 20 ppta, carbon < 20 ppba, and oxygen < 20 ppba; the coefficients of variation for phosphorus, boron, carbon, and oxygen impurities within the quality control rod and between batches must all be ≤ 3%.

2. The quality control bar according to claim 1, characterized in that, The zone-melting single-crystal silicon rod that meets the uniformity standard is a raw material whose coefficient of variation for phosphorus, boron, carbon, and oxygen impurities in the radial / axial directions is ≤5%.

3. A method for preparing a quality control rod as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Perform full-rod testing on zone-melted single-crystal silicon rods and screen out silicon rods with phosphorus <80ppta, boron <15ppta, carbon <15ppba, oxygen <15ppba, and the coefficient of variation of each impurity content in its radial / axial direction ≤5% as raw materials. S2. In a cleanroom environment, the raw material is sequentially cut, coarsely ground, finely ground, and polished to obtain a billet of a predetermined size; the entire process is carried out under a high-purity argon protective atmosphere, and the surface roughness Ra of the billet after processing is ≤0.01μm. S3. For the billet obtained in step S2, perform sampling re-inspection at three locations: 20mm from both ends and the center point, to ensure that the coefficient of variation of each impurity content is ≤3% at different inspection locations for the same billet; S4. The billets that pass the re-inspection are sequentially ultrasonically cleaned with ultrapure water, dried with high-purity nitrogen, and finally sealed with vacuum or inert gas protection using a sealed quartz tube.

4. The preparation method according to claim 3, characterized in that, In step S2, the cleanroom environment is a Class 1000 cleanroom. The raw material is cut into bars at a rate of 0.5~1mm / min, and then coarse grinding, fine grinding and polishing are performed in sequence to obtain a billet bar with a diameter of 20±0.05mm, a length of 160±0.1mm and a surface roughness Ra≤0.01μm.

5. The preparation method according to claim 3, characterized in that, In step S2, the purity of the high-purity argon gas is not less than 99.999%.

6. The preparation method according to claim 3, characterized in that, In step S3, the sampling depth for the sampling detection is 10~50μm.

7. The preparation method according to claim 3, characterized in that, Following step S3, step S3a is also included: batch consistency determination and identification; The batch consistency determination is as follows: in the same production batch, no less than 5% of the billets are randomly selected for re-inspection in step S3. All the sampled billets must meet the requirement that the internal variation coefficient of a single billet is ≤3%, and the deviation of the average value of the key impurity content of all finished products in the batch from the nominal value is also ≤3%. The identification method is as follows: quality control bars that meet batch consistency requirements are uniquely identified by laser marking.

8. The preparation method according to claim 3, characterized in that, In step S4, the resistivity of the ultrapure water is ≥18 MΩ·cm; the purity of the high-purity nitrogen gas is ≥99.999%.

9. A method for applying the quality control bar as described in claim 1 or 2, characterized in that, The method is used to monitor the cleanliness of the process for preparing single-crystal silicon rods using the electronic-grade polycrystalline silicon zone melting method, and includes: Regularly use quality control rods with uniform impurities from the same batch and sequentially perform zone melting crystal pulling with the electronic-grade polycrystalline silicon sample rod to be tested under the same process conditions. Detect the impurity content in the quality control rod after zone melting and draw a quality control chart based on the test data. The quality control chart includes control lines and specification lines. The control lines are calculated based on test data after multiple quality control bars are drawn from the melt zone, and the specification lines are based on the impurity parameters of the quality control bars. If all the detected impurity indicators are within the control and specification lines, the zone melting process is stable and no additional impurities are introduced.

10. A method for applying the quality control bar as described in claim 1 or 2, characterized in that, The method of using the quality control rod as a standard material to monitor the stability of the determination of impurity content in silicon by low-temperature infrared spectroscopy includes: periodically using the quality control rod to perform low-temperature infrared spectroscopy analysis, tracking the detection results of phosphorus, boron, carbon and oxygen impurities, and drawing a quality control chart based on the results to determine the stability of the analytical instrument and method.

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