A method and system for detecting defects of single crystal silicon rods
By acquiring and analyzing the reflection and transmission echo of the single crystal silicon rod and calculating the dislocation index, the problem of low ultrasonic detection accuracy in the existing technology is solved, and high accuracy detection and distinction of dislocation defects of single crystal silicon rods is achieved. , improves the efficiency of the preparation process.
Patent Information
- Application Number
- CN202411245894.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-06
- Publication Date
- 2024-12-10
- Estimated Expiration
- 2044-09-06
AI Technical Summary
Existing ultrasonic detection methods only consider one type of echo in single crystal silicon rods, resulting in low defect detection accuracy and inability to accurately identify dislocation defects.
The digital ultrasonic flaw detector collects reflected echoes and transmission echoes at each height of the single crystal silicon rod, obtains the initial wave, bottom wave and defect waves of each wave, calculates the dislocation lateral index and longitudinal index, and performs dislocation defects based on these indexes. Test.
It improves the identification accuracy and distinction ability of dislocation defects, enhances the analysis of the internal defect distribution characteristics of single crystal silicon rods, and improves the detection accuracy and efficiency.
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Figure CN118759050B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of silicon rod defect detection, and in particular to a method and system for detecting defects in a single crystal silicon rod. Background Art
[0002] During the preparation of single crystal silicon rods, there are changes in the longitudinal and transverse temperature gradients in the quartz crucible. The temperature changes will cause thermal stress; and the silicon single crystal will also introduce mechanical internal stress during the machining process. These internal stresses will cause defects such as dislocations in the single crystal silicon rods, which will in turn affect the performance and reliability of the final product. Among the various defects caused by internal stress, dislocation defects are the most common and will seriously affect the performance of single crystal silicon rods. Therefore, the detection and identification of dislocation defects are crucial in the production and preparation of single crystal silicon rods.
[0003] Ultrasonic testing has the characteristics of non-destructive testing, the ability to detect defects inside single crystal silicon rods, and fast detection speed, making it suitable for mass production and quality control applications. Therefore, ultrasonic testing has become one of the commonly used means in the existing technology for single crystal silicon rod defect detection. In the existing ultrasonic testing process, only one type of echo is often considered, resulting in low defect detection accuracy. Summary of the invention
[0004] In order to solve the above technical problems, the purpose of this application is to provide a single crystal silicon rod defect detection method and system, and the technical solutions adopted are as follows:
[0005] The reflected echo and transmitted echo at each height of the single crystal silicon rod are collected by a digital ultrasonic flaw detector;
[0006] For the reflected echo and the transmitted echo at any height, the initial wave of the reflected echo, the bottom wave of the transmitted echo, and the defect wave and the bottom wave of the reflected echo are obtained respectively according to the heights of the wave peaks in the reflected echo and the transmitted echo; the integral area of the initial wave and the bottom wave of the reflected echo, and the integral area of the bottom wave of the transmitted echo are calculated by the integral operation rule; the center time of each wave is taken as the appearance time of each wave; based on the difference between the integral areas of different waves, and the difference between the appearance time of the defect wave and the initial wave and the bottom wave, the dislocation lateral index of the single crystal silicon rod at any height is constructed;
[0007] Calculate the dislocation longitudinal index of the single crystal silicon rod according to the variation trend of the dislocation transverse index at each height;
[0008] A segmentation threshold is obtained according to the longitudinal index of dislocation of each single crystal silicon rod, and dislocation defect detection is performed on the single crystal silicon rod based on the segmentation threshold.
[0009] In one embodiment, the process of acquiring the initial wave of the reflected echo is:
[0010] The sequence composed of all peak values in the reflected echo is recorded as the first peak sequence; each peak point in the first peak sequence is taken as the first data point in the moving window to obtain the moving window corresponding to each peak point; the average value of all data points in each moving window is taken as the moving average value corresponding to each peak point; the peak point whose moving average value is greater than the preset first threshold is recorded as a marking point, and the continuous marking points are combined to obtain each marking point set; all peak points in the marking point set with the earliest time sequence are recorded as the starting wave marking points, all data points in the moving window corresponding to all the starting wave marking points are recorded as the starting wave peak points, and the waveform between all the starting wave peak points in the reflected echo is taken as the starting wave of the reflected echo.
[0011] In one embodiment, the process of acquiring the bottom wave of the transmission echo is:
[0012] The sequence composed of all peaks in the transmission echo is recorded as the second peak sequence; based on the second peak sequence, the moving window, moving average and starting wave marking point of each peak point of the second peak sequence are obtained in the same manner as the moving window, moving average and starting wave marking point of each peak point of the first peak sequence;
[0013] Among all the remaining peak points except the initial wave marking point in the second peak sequence, the peak point whose moving average value is greater than the preset second threshold value is obtained and recorded as the secondary marking point; the set composed of continuous secondary marking points is recorded as the secondary marking point set, all the peak points in the secondary marking point set with the latest time sequence are recorded as bottom wave marking points, all the data points in the moving window corresponding to all the bottom wave marking points are recorded as bottom wave peak points, and the waveform between all the bottom wave peak points in the transmitted echo is used as the bottom wave of the transmitted echo.
[0014] In one embodiment, the process of acquiring the defect wave and the bottom wave of the reflected echo is as follows:
[0015] The starting wave of the reflected echo is recorded as the reflection starting wave, and the bottom wave of the transmitted echo is recorded as the transmitted bottom wave; the central moment of the time interval where the transmitted bottom wave is located is taken as the reflection midpoint moment; for the reflected echo, the time period of the corresponding moving window of all the peak points in each corresponding mark point set is obtained, and the mark point set in the time period between the reflection starting wave and the reflection midpoint moment is called the defect mark point set; all data points in the moving window corresponding to all the peak points in each defect mark point set are recorded as defect wave peak points, and the waveform between all the defect wave peak points in each defect mark point set is taken as a defect wave to obtain each defect wave in the reflected echo;
[0016] All peak points in the set of all defect marking points are recorded as defect wave marking points, and all remaining peak points except the initial wave marking point and the defect marking point in the first peak sequence are obtained; based on the remaining peak points, the same acquisition method as that for obtaining the transmitted bottom wave based on the remaining peak points in the second peak sequence is adopted to obtain the bottom wave of the reflected echo.
[0017] In one embodiment, the process of obtaining the dislocation lateral index at any height is:
[0018] The bottom wave of the reflected echo is recorded as the reflected bottom wave, the difference between the integrated area of the reflected initial wave and the reflected bottom wave is taken as the attenuation of the reflected bottom wave, and the difference between the integrated area of the reflected initial wave and the transmitted bottom wave is taken as the attenuation of the transmitted bottom wave; the difference between the attenuation of the reflected bottom wave and the transmitted bottom wave is calculated and recorded as the bottom wave attenuation difference;
[0019] Based on the appearance of the defect wave and the differences between the appearance time of the defect wave and the initial wave and the midpoint of the reflection, combined with the difference in the bottom wave attenuation, the dislocation lateral index of the single crystal silicon rod at any height is determined.
[0020] In one embodiment, the process of obtaining the dislocation lateral index is:
[0021] Calculate the difference between the appearance time of each defect wave and the initial reflection wave, which is recorded as the first time difference; calculate the difference between the appearance time of each defect wave and the midpoint of the reflection, which is recorded as the second time difference; obtain the minimum value between the first time difference and the second time difference of each defect wave; calculate the chaos degree of the minimum value of all defect waves in the reflected echo, which is recorded as the first chaos degree;
[0022] The dislocation transverse index is positively correlated with the number of defect waves in the reflected echo, and negatively correlated with the bottom wave attenuation difference and the first disorder degree.
[0023] In one embodiment, the process of obtaining the dislocation longitudinal index of the single crystal silicon rod is:
[0024] Starting from the tail of the single crystal silicon rod, the height is used as the horizontal coordinate, and the dislocation lateral index corresponding to the height is used as the vertical coordinate to obtain each coordinate point, and all the coordinate points are fitted by a polynomial fitting algorithm to obtain a fitting curve; the interval between the i-th to the i+s-th height in the fitting curve is used as the neighborhood interval at the i-th height, where s is a preset positive integer; the fitting curve in the neighborhood interval at each height is integrated to obtain the integral area of the neighborhood interval at each height;
[0025] The difference between the integral area of each height value and the neighborhood interval corresponding to the next height value is calculated and recorded as the first difference; the dislocation longitudinal index of the single crystal silicon rod is recorded as B, and the calculation expression of B is: , where is the number of heights for data collection, For the the sign function value of the first difference between the ith height and the ith height, is the height and The sign function value of the first difference between the heights, is the lateral index of the dislocation at the ith height.
[0026] In one embodiment, the sign function value is: when the first difference is greater than or equal to zero, the sign function value of the first difference is 1; when the first difference is less than zero, the sign function value of the first difference is 0.
[0027] In one embodiment, the process of performing dislocation defect detection on a single crystal silicon rod is as follows:
[0028] The dislocation longitudinal index of a preset number of single crystal silicon rods is used as the input of the threshold segmentation algorithm, and the segmentation threshold is output; if the dislocation longitudinal index of the single crystal silicon rod is greater than the segmentation threshold, the single crystal silicon rod has a dislocation defect; otherwise, the single crystal silicon rod does not have a dislocation defect.
[0029] In a second aspect, an embodiment of the present application further provides a defect detection system for a single crystal silicon rod, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor implements the steps of any one of the above methods when executing the computer program.
[0030] The embodiments of the present application have at least the following beneficial effects:
[0031] The present application analyzes the connection between the reflected echo and the transmitted echo at the same height according to the height change of the wave peaks in the reflected echo and the transmitted echo, determines the initial wave and the bottom wave of the two types of echoes, and the defect wave in the reflected echo; constructs a dislocation transverse index based on the distribution difference between each wave, analyzes the transverse characteristics of the dislocation defect distribution, measures the defect changes inside the single crystal silicon rod at the same height, improves the recognition of the dislocation defect characteristics, and helps to improve the accuracy of subsequent dislocation defect detection; calculates the dislocation longitudinal index of the single crystal silicon rod according to the change trend of the dislocation transverse index at each height, analyzes the longitudinal distribution characteristics of the dislocation defect, and helps to further improve the ability to distinguish dislocation defects; performs dislocation defect detection based on the dislocation longitudinal index, improves the ability to distinguish and judge dislocation defects in the single crystal silicon rod, improves the accuracy of dislocation defect detection in the single crystal silicon rod, and is conducive to improving the efficiency of the single crystal silicon rod preparation process. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0033] Figure 1 A flowchart of a defect detection method for a single crystal silicon rod provided in one embodiment of the present application;
[0034] Figure 2 is a schematic diagram of the position of the ultrasound probe;
[0035] Figure 3 This is a schematic diagram of the attenuation of the two probes in the absence of defects;
[0036] Figure 4 Schematic diagram of the attenuation of two probes when there are defects;
[0037] Figure 5 Schematic diagram for determining the initial wave and bottom wave using moving average;
[0038] Figure 6 Schematic diagram of transmission echo. DETAILED DESCRIPTION
[0039] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following is a detailed description of a single crystal silicon rod defect detection method and system proposed in the present application, its specific implementation, structure, features and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.
[0040] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
[0041] The specific scheme of a single crystal silicon rod defect detection method and system provided by the present application is described in detail below with reference to the accompanying drawings.
[0042] See also Figure 1 , which shows a flow chart of the steps of a defect detection method for a single crystal silicon rod provided by an embodiment of the present application, the method comprising the following steps:
[0043] Step S1, collecting reflected echoes and transmitted echoes at various heights of the single crystal silicon rod by a digital ultrasonic flaw detector.
[0044] The single crystal silicon rod is inspected for defects by a digital ultrasonic flaw detector. Two ultrasonic probes are placed on both sides of the single crystal silicon rod. The center lines of the two ultrasonic probes coincide with the axis of the single crystal silicon rod. The schematic diagram of the position of the ultrasonic probes is shown in the figure. Figure 2 As shown, 1 is a single crystal silicon rod; 2 is an ultrasonic probe, which is an integrated transceiver probe, denoted as the first ultrasonic probe, capable of emitting ultrasonic waves and receiving echoes at the same time, and the echo received by the ultrasonic probe is called a reflected echo; 3 is another ultrasonic probe, which is only responsible for receiving echoes, denoted as the second ultrasonic probe, and the echo received by the ultrasonic probe is called a transmitted echo; 4 is a probe fixing bracket; 5 is a displacement controller, which can control the up and down movement of the ultrasonic probe.
[0045] Ultrasonic testing is performed starting from the bottom of the single crystal silicon rod, and the ultrasonic probe is raised by 5mm each time, and ultrasonic testing is performed at different heights. At each height, the A-type ultrasonic signal received by the two ultrasonic probes during the digital ultrasonic flaw detector detection process is obtained, where the bottom of the single crystal silicon rod corresponds to the tail of the single crystal silicon rod after it is drawn. It should be noted that the height of the ultrasonic probe raised each time can be set by the implementer, and this application does not impose specific restrictions.
[0046] Preferably, in one embodiment of the present application, when collecting ultrasonic signals, the sampling frequency of the echo is 50 MHz, the chip diameter of the ultrasonic probe is 6 mm, the center frequency is 5 MHz, and the bandwidth is 15%. In other embodiments of the present application, the sampling frequency of the echo and the parameters of the ultrasonic probe can be set by the implementer according to actual conditions.
[0047] Step S2, determining the initial wave, bottom wave and defect wave of the reflected echo, and the initial wave and bottom wave of the transmitted echo according to the change of the wave peaks in the reflected echo and the transmitted echo at the same height; constructing the dislocation lateral index of the single crystal silicon rod at each height based on the difference in distribution characteristics of different waves.
[0048] When ultrasonic testing is performed on a single crystal silicon rod, two probes are symmetrically set on both sides of the single crystal silicon rod to receive reflected echoes and transmitted echoes, and defect detection is performed based on the relationship between the two echoes. However, ultrasonic echoes can only reflect whether there are defects, but cannot accurately identify whether they are dislocation defects, so further identification and judgment is required based on the distribution characteristics of dislocation defects.
[0049] When there are no defects inside the single crystal silicon rod, the ultrasonic signal is emitted from one side of the single crystal silicon rod, and there is almost no reflection inside the single crystal silicon rod until the ultrasonic signal contacts the other side of the single crystal silicon rod and is reflected back. The bottom waves finally received by the first ultrasonic probe and the second ultrasonic probe have a certain attenuation, but the signal strength is still large; and the attenuation of the bottom wave received by the first ultrasonic probe is close to 2 times the attenuation of the bottom wave of the second ultrasonic probe, and the time it takes for the first ultrasonic probe to receive the bottom wave is also close to 2 times the time it takes for the second ultrasonic probe to receive the bottom wave. When there are defects in the single crystal silicon rod, the defects will cause the reflection of the ultrasonic signal, so that the first ultrasonic probe will receive the corresponding defect wave; and the defect wave will also cause the attenuation of the signal, such as Figure 3 , Figure 4 As shown, the bottom waves finally received by the first ultrasonic probe and the second ultrasonic probe have a greater attenuation, and the signal attenuation between the first ultrasonic probe and the second ultrasonic probe no longer presents a multiple relationship. Secondly, according to the direction of the ultrasonic signal, it can be determined that the defect wave of the first ultrasonic probe only exists in the first half of the entire echo.
[0050] During crystal growth, the stress in the edge area is greater, and the stress in the center area is smaller, and dislocations tend to gather in the area with greater stress. Therefore, according to the growth law of dislocations, the dislocation density in the center area is generally smaller, while the dislocation density around is relatively larger.
[0051] (1) Obtain the initial waves in the reflected echo and the transmitted echo respectively according to the height of all wave peaks in the echo:
[0052] (1.1) The sequence obtained by arranging all the peaks in the reflected echo in ascending time order is recorded as the first peak sequence, and the sequence obtained by arranging all the peaks in the transmitted echo in ascending time order is recorded as the second peak sequence.
[0053] set up Preferably, in one embodiment of the present application, The value of is set to 10. In other embodiments of the present application, the implementer can set it according to the actual situation. The value of .
[0054] Each peak point in the first peak sequence is taken as the first data point in the moving window, and the moving window when each peak point is the first data point is taken as the moving window corresponding to each peak point; the average value of all data points in the moving window is taken as the moving average value of the first data point in the moving window, thereby obtaining the moving average value of each peak point in the first peak sequence. When the first to last peak point is the first data point in the moving window, some data in the moving window is missing, so the first peak sequence is not correct. The moving average is calculated from the first to the last peak point.
[0055] Based on the second peak sequence, the moving average value of each peak point in the second peak sequence is obtained in the same manner as that of obtaining the moving average value of each peak point in the first peak sequence.
[0056] (1.2) For the first peak sequence, in the embodiment of the present application, the mean of the moving average values of all peak points in the sequence is used as the first threshold value. It should be noted that in other embodiments of the present application, the first threshold value can be set by the implementer according to the actual situation. The peak points whose moving average value is greater than the first threshold value are marked to obtain each marking point, and the set obtained by combining the marking points that are continuous in time is recorded as the marking point set, thereby obtaining each marking point set of the first peak sequence; all the peak points in the marking point set that is the earliest in time sequence are recorded as the starting wave marking points, and all the data points in the moving window corresponding to all the starting wave marking points are recorded as the starting wave peak points, and the waveform between all the starting wave peak points in the reflected echo is taken as the starting wave of the reflected echo, which is recorded as the reflected starting wave.
[0057] Since the initial wave is the first continuous waveform in the echo, and the moving window size is fixed, the window length is not set according to the length of the initial wave, so the entire initial wave may be in multiple moving windows, but due to the continuity of the initial wave, the peak points of the initial wave are also continuous, so the moving window corresponding to the first continuous mark point is used as the moving window where the initial wave is located. Figure 5 As shown in the initial wave window.
[0058] Based on the moving average of each peak point in the second peak sequence, the same acquisition method as the start wave mark point of the first peak sequence and the reflection start wave is adopted to obtain the start wave mark point of the second peak sequence and the start wave of the transmission echo, which are recorded as the transmission start wave.
[0059] (2) Obtain the bottom wave of the transmission echo:
[0060] Since the echo collected by the second ultrasonic probe is a transmission echo, there will be no defect wave, so the two obvious peaks on the entire echo correspond to the initial wave and the bottom wave respectively. When there are defects in the single crystal silicon rod, the peak value of the bottom wave may be very small, so it is impossible to determine the initial wave and the bottom wave at the same time through a single average, so a secondary average is performed to determine the bottom wave. Specifically:
[0061] Obtain all remaining peak points except the initial wave marking point in the second peak sequence. In the embodiment of the present application, the mean of the moving averages of all the remaining peak points is used as the second threshold. It should be noted that in other embodiments of the present application, the implementer of the setting of the second threshold can set it according to the actual situation. Mark the peak points whose moving averages are greater than the second threshold among all the remaining peak points as secondary marking points, record the set of secondary marking points that are continuous in time as the secondary marking point set, record all peak points in the set of secondary marking points with the latest time sequence as bottom wave marking points, record all data points in the moving window corresponding to all bottom wave marking points as bottom wave peak points, and use the waveform between all bottom wave peak points in the transmitted echo as the bottom wave of the transmitted echo, recorded as the transmitted bottom wave, such as Figure 5 , Figure 6 As shown. Among them, Figure 5 The middle bottom wave window is the bottom wave moving window composed of moving windows corresponding to the consecutive secondary marking points at the latest time sequence.
[0062] (3) Obtain the defect wave and bottom wave of the reflected echo:
[0063] The center value of the entire time interval of the transmitted bottom wave is taken as the appearance time of the transmitted bottom wave. On the reflected echo, the moment that is the same as the appearance time of the transmitted bottom wave is marked as the reflection midpoint moment. The time period of the corresponding moving window of all peak points in each mark point set is obtained, and the mark point set in the time period between the reflection start wave and the reflection midpoint moment is called the defect mark point set;
[0064] All data points in the moving window corresponding to all peak points of each defect mark point set are recorded as defect wave peak points, and the waveform between all the defect wave peak points of each defect mark point set in the reflected echo is regarded as a defect wave, so as to obtain each defect wave in the reflected echo;
[0065] All peak points in the set of all defect marking points are recorded as defect wave marking points, and all remaining peak points in the first peak sequence except the initial wave marking point and the defect marking point are obtained; based on the remaining peak points in the first peak sequence, the same acquisition method as that for acquiring the transmitted bottom wave based on the remaining peak points in the second peak sequence is adopted to obtain the bottom wave of the reflected echo, which is recorded as the reflected bottom wave.
[0066] (4) Based on the initial reflection wave, the transmitted bottom wave and the reflected bottom wave, the integral area of the initial reflection wave, the transmitted bottom wave and the reflected bottom wave is calculated in combination with the trapezoidal rule:
[0067] Take uniformly on the reflected initial wave point, this The time and amplitude corresponding to each point are used as the input of the trapezoidal rule, and the output is the integrated area of the initial reflection wave. The value of is set to 100. In other embodiments of the present application, the value of n can be set by the implementer according to the actual situation. Among them, the trapezoidal rule is a well-known technology, and the specific process is not repeated. Based on the transmitted bottom wave and the reflected bottom wave, the integrated area of the transmitted bottom wave and the reflected bottom wave is obtained in the same way as the integrated area of the reflected initial wave.
[0068] (5) Each wave is not instantaneous, but has a duration. In the embodiments of the present application, the center time of each wave is taken as the appearance time of each wave. In other embodiments of the present application, the implementation of each wave can set the appearance time of each wave by itself, and the present application does not impose any specific restrictions. Since the propagation speed of ultrasound waves in the same material is the same, the appearance time of each wave can represent the position of each wave in the echo.
[0069] (6) Based on the difference in the integrated area between each initial wave and the bottom wave, and the difference in the appearance time between the defect wave and the initial wave and the bottom wave, the dislocation lateral index at each height of the single crystal silicon rod is constructed:
[0070] The dislocation lateral index at each height of the single crystal silicon rod is used to measure whether there are defects at each height of the single crystal silicon rod and whether the defects meet the lateral characteristics of the dislocation. The specific construction process is as follows:
[0071] (6.1) For the reflected echo and transmitted echo at each height of the single crystal silicon rod, the difference between the integrated area of the reflected initial wave and the reflected bottom wave is taken as the attenuation of the reflected bottom wave, and the difference between the integrated area of the reflected initial wave and the transmitted bottom wave is taken as the attenuation of the transmitted bottom wave.
[0072] (6.2) Based on the difference between the attenuation amounts of different echoes at different heights of the single crystal silicon rod, the appearance of the defect wave, and the difference between the appearance time of the defect wave and the initial wave and the reflection midpoint, the dislocation lateral index at each height of the single crystal silicon rod is determined:
[0073] For the reflected echo and the transmitted echo at each height of the single crystal silicon rod, the difference between the attenuation of the reflected bottom wave and the transmitted bottom wave is calculated and recorded as the bottom wave attenuation difference;
[0074] In the reflected echo at each height of the single crystal silicon rod, the difference between the appearance time of each defect wave of the echo and the initial wave is calculated, which is recorded as the first time difference; the difference between the appearance time of each defect wave of the echo and the moment of the midpoint of reflection is calculated, which is recorded as the second time difference; the minimum value between the first time difference and the second time difference of each defect wave is obtained; the chaos degree of the minimum value of all defect waves in the reflected echo is calculated, which is recorded as the first chaos degree. It should be understood that the difference described in the present application can be the absolute value of the difference, the square of the difference, etc.; the chaos degree is the degree of chaos of the data distribution, which can be the information entropy, variance and standard deviation of the data; preferably, in one embodiment of the present application, the first chaos degree can be the variance of the minimum value of all defect waves in the reflected echo; the difference in the attenuation of the bottom wave can be the absolute value of the difference between the attenuation of the reflected bottom wave and the transmitted bottom wave; the first time difference can be the absolute value of the difference between the appearance time of each defect wave and the initial wave; the second time difference can be the absolute value of the difference between the appearance time of each defect wave and the moment of the midpoint of reflection.
[0075] In other embodiments of the present application, the first disorder degree may be a standard deviation of the minimum values of all defect waves in the reflected echo.
[0076] The dislocation lateral index at each height of the single crystal silicon rod is positively correlated with the number of defect waves in the reflected echo at each height of the single crystal silicon rod, and is negatively correlated with the difference in bottom wave attenuation at each height of the single crystal silicon rod and the first degree of chaos. It should be noted that the positive correlation and negative correlation in this application refer to the relationship between the independent variable and the dependent variable. The positive correlation is that the independent variable increases (decreases) as the dependent variable increases (decreases); the negative correlation is that the independent variable decreases (increases) as the dependent variable increases (decreases); the specific positive correlation and negative correlation can be determined according to actual conditions during the application process, and this application does not impose any special restrictions.
[0077] Preferably, as an embodiment of the present application, the dislocation lateral index at each height of the single crystal silicon rod can be: calculating the product of the difference in bottom wave attenuation at each height of the single crystal silicon rod and the first degree of disorder, and taking the ratio of the number of defect waves in the reflected echo at each height of the single crystal silicon rod to the product as the dislocation lateral index at each height of the single crystal silicon rod.
[0078] In other embodiments of the present application, the dislocation lateral index at each height of the single crystal silicon rod can be: calculating the result of an exponential function with a natural constant as the base and the negative of the product as the exponent, and taking the product of the number of defect waves in the reflected echo at each height of the single crystal silicon rod and the calculation result as the dislocation lateral index at each height of the single crystal silicon rod.
[0079] It is understandable that when the height of the single crystal silicon rod When there is a high possibility that there are dislocation defects at the defect, the defect will reflect the ultrasonic wave, so that a defect wave will appear on the reflected echo, and the greater the density of dislocation defects, the greater the number of defect waves; when there are more defects, the more ultrasonic signals will be reflected at the defects, and the more serious the signal attenuation will be, so that the transmitted bottom wave and the reflected bottom wave will be smaller, but because a large number of signals are reflected by the defects, the difference between the transmitted bottom wave and the reflected bottom wave will be smaller, so the attenuation of the two is no longer in a multiple relationship, and the ratio is smaller; and the lateral distribution characteristics of dislocation defects are high density around and low density in the center, so the smaller the distance between the defect wave and the reflected initial wave or the midpoint of the reflected echo, the more it conforms to the characteristics of dislocation defects, that is, the smaller the variance; so when the height of the single crystal silicon rod is When the possibility of dislocation defects is greater, the dislocation lateral index is larger, and the larger the dislocation lateral index, the more likely it is that a dislocation defect exists and the more serious the defect is. Conversely, the smaller the dislocation lateral index, the less likely it is that a dislocation defect exists.
[0080] Step S3, calculating the dislocation longitudinal index of the single crystal silicon rod according to the variation trend of the dislocation transverse index at different heights, which is used to measure the longitudinal characteristics of the dislocation defect.
[0081] The dislocation transverse index only considers the characteristics of dislocation defects at the same height. However, the reflection ultrasonic detection has limited ability to detect defects near the surface, which affects the ultrasonic detection's ability to identify dislocation defects. Therefore, it is impossible to accurately identify dislocation defects based on the characteristics of a certain height. It is necessary to further determine the longitudinal distribution characteristics of dislocation defects. According to the dislocation migration theory, after the single crystal silicon rod is pulled, a large number of dislocations will be generated at the tail due to thermal stress, extending upward along the single crystal. Therefore, on the single crystal silicon rod, the closer to the tail, the greater the density of dislocation defects.
[0082] (1) Starting from the tail of the single crystal silicon rod, the height is used as the horizontal coordinate, and the dislocation lateral index corresponding to the height is used as the vertical coordinate to obtain a series of coordinate points. These coordinate points are fitted by a polynomial fitting algorithm to obtain a fitting curve function, which is recorded as a dislocation fitting curve function. Among them, polynomial fitting is a well-known technology, and the specific process is not repeated. It should be noted that for the curve fitting of coordinate points, this application only provides a curve fitting method. There are many existing curve fitting methods. The implementer can also use other curve fitting algorithms to perform curve fitting of coordinate points. This application does not make specific restrictions.
[0083] Theoretically, the closer to the tail, the greater the dislocation defect density. However, due to the complexity of the internal situation of the single crystal silicon rod, this monotonic change cannot be fully guaranteed. Therefore, the change in the integral area is used to smooth the local abnormal fluctuations on the curve, reduce the impact of abnormal noise, and measure the overall change trend.
[0084] (2) Based on the local data changes of the dislocation fitting curve and combined with the integral operation, the integral area of the neighborhood interval at each height is calculated:
[0085] The interval between the i-th and i+s-th heights in the dislocation fitting curve is used as the neighborhood interval at the i-th height. For the value of s, when s is smaller, the description of the change of the curve trend is more accurate, but the influence of abnormal fluctuation noise is greater. When s is larger, the smoothness of the curve trend is better, but the accuracy of some trends will be lost. Preferably, in one embodiment of the present application, the value of s is set to 3. In other embodiments of the present application, the implementer can set the value of s according to actual conditions. Among them, the interval between the s+1th to the last height is used as the neighborhood interval at any height from the sth to the last height.
[0086] The dislocation fitting curve in the neighborhood interval at each height is integrated, and the integration result is used as the integrated area of the neighborhood interval at each height.
[0087] (3) Based on the difference in the size of the integrated area of the neighborhood intervals at adjacent heights, combined with the dislocation lateral index at each height, the dislocation longitudinal index of the single crystal silicon rod is constructed to measure the change trend of the dislocation lateral index of the single crystal silicon rod at different heights, so as to determine the dislocation distribution characteristics in the longitudinal direction, specifically:
[0088] Calculate the difference between the integrated area of each height value and the neighborhood interval of the next height value, and record it as the first difference; obtain the sign function value of the first difference based on the positive and negative conditions of the first difference. In the embodiment of the present application, the sign function is defined as follows: when the independent variable is a non-negative number, the sign function value is 1, and in other cases the sign function value is 0. That is, when the first difference is greater than or equal to zero, the sign function value of the first difference is 1; when the first difference is less than zero, the sign function value of the first difference is 0.
[0089] The calculation expression of the dislocation longitudinal index of a single crystal silicon rod is:
[0090] , where is the longitudinal index of dislocation of the single crystal silicon rod, is the number of heights for data collection, For the the sign function value of the first difference between the ith height and the ith height, is the height and The sign function value of the first difference between the heights, is the transverse index of dislocation at the ith height. The denominator is used to eliminate the influence of the number of heights and avoid the problem that different evaluation criteria are required when the number of heights for data collection in ultrasonic testing is different.
[0091] When there is a defect and it is a dislocation defect, the distribution of the dislocation defect is that the closer to the tail, the greater the density, that is, the lower the height, the greater the value of the dislocation transverse index, and the larger the integral area of the neighborhood interval at the corresponding height, so that the integral area of the neighborhood intervals arranged from high to low in height shows a decreasing trend, then the value of the sign function of the first difference value at each height should be 1, so the larger the numerator, the more heights that meet the dislocation longitudinal distribution characteristics, and then the larger the dislocation longitudinal index. Conversely, when it is not a dislocation defect, it does not meet the dislocation longitudinal distribution characteristics, so the numerator is small and the dislocation longitudinal index is also small.
[0092] Step S4, obtaining a segmentation threshold according to the dislocation longitudinal index of each single crystal silicon rod, and performing dislocation defect detection on the single crystal silicon rod based on the segmentation threshold.
[0093] According to the echo signals of ultrasonic detection of m single crystal silicon rods, the dislocation longitudinal index of each single crystal silicon rod is calculated respectively, and the dislocation longitudinal index of these m single crystal silicon rods is used as the input of the Otsu method, and the output is the segmentation threshold. Preferably, in the embodiment of the present application, the value of m is set to 100. In other embodiments of the present application, the implementer can set the value of m according to the actual situation. Among them, the Otsu method is a well-known technology, and the specific process is not repeated. It should be noted that the present application only provides a method for obtaining a segmentation threshold. There are many existing methods for obtaining the segmentation threshold. The implementer can also use other threshold segmentation algorithms to obtain the segmentation threshold, and the present application does not make specific restrictions. When the defect detection of the single crystal silicon rod is performed subsequently, the dislocation longitudinal index of the single crystal silicon rod is calculated according to the echo signals of ultrasonic detection of different heights of the single crystal silicon rod. When the dislocation longitudinal index is greater than the segmentation threshold, the single crystal silicon rod has a dislocation defect; when the dislocation longitudinal index is less than or equal to the segmentation threshold, the single crystal silicon rod does not have a dislocation defect.
[0094] Based on the same inventive concept as the above method, an embodiment of the present application also provides a defect detection system for a single crystal silicon rod, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor implements the steps of any one of the above-mentioned methods for defect detection of a single crystal silicon rod when executing the computer program.
[0095] In summary, the embodiment of the present application provides a defect detection method for a single crystal silicon rod. According to the height change of the wave peaks in the reflected echo and the transmitted echo, the connection between the reflected echo and the transmitted echo at the same height is analyzed to determine the initial wave and the bottom wave of the two types of echoes, as well as the defect wave in the reflected echo; a dislocation transverse index is constructed based on the distribution difference between each wave, the transverse characteristics of the dislocation defect distribution are analyzed, the defect changes inside the single crystal silicon rod at the same height are measured, the recognition of the dislocation defect characteristics is improved, and it is helpful to improve the accuracy of subsequent dislocation defect detection; the dislocation longitudinal index of the single crystal silicon rod is calculated according to the change trend of the dislocation transverse index at each height, and the longitudinal distribution characteristics of the dislocation defect are analyzed, which is helpful to further improve the ability to distinguish dislocation defects; dislocation defect detection is performed based on the dislocation longitudinal index, the accuracy of dislocation defect judgment is improved, thereby improving the ability to distinguish and judge dislocation defects in the single crystal silicon rod, which is beneficial to improving the efficiency of the single crystal silicon rod preparation process.
[0096] It should be noted that the above-mentioned sequence of the embodiments of the present application is only for description and does not represent the advantages and disadvantages of the embodiments. The above-mentioned specific embodiments of the present application are described. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.
[0097] The various embodiments in the present application are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.
[0098] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present application should be included in the protection scope of the present application.
Claims
1. A method for detecting defects in a single crystal silicon rod, It is characterized in that The method comprises the following steps: The reflected echo and transmitted echo at each height of the single crystal silicon rod are collected by a digital ultrasonic flaw detector; For the reflected echo and the transmitted echo at any height, the initial wave of the reflected echo, the bottom wave of the transmitted echo, and the defect wave and the bottom wave of the reflected echo are obtained respectively according to the heights of the wave peaks in the reflected echo and the transmitted echo; the integral area of the initial wave and the bottom wave of the reflected echo, and the integral area of the bottom wave of the transmitted echo are calculated by the integral operation rule; the center time of each wave is taken as the appearance time of each wave; based on the difference between the integral areas of different waves, and the difference between the appearance time of the defect wave and the initial wave and the bottom wave, the dislocation lateral index of the single crystal silicon rod at any height is constructed; Calculate the dislocation longitudinal index of the single crystal silicon rod according to the variation trend of the dislocation transverse index at each height; Obtaining a segmentation threshold according to the longitudinal index of dislocation of each single crystal silicon rod, and performing dislocation defect detection on the single crystal silicon rod based on the segmentation threshold; The process of obtaining the initial wave of the reflected echo is as follows: Record the sequence composed of all peak values in the reflected echo as the first peak sequence; take each peak point in the first peak sequence as the first data point in the moving window to obtain the moving window corresponding to each peak point; take the average value of all data points in each moving window as the moving average value corresponding to each peak point; record the peak point whose moving average value is greater than the preset first threshold as a marking point, and combine the continuous marking points to obtain each marking point set; record all peak points in the marking point set that is the earliest in time order as the initial wave marking points, record all data points in the moving window corresponding to all the initial wave marking points as the initial wave peak points, and take the waveform between all the initial wave peak points in the reflected echo as the initial wave of the reflected echo; The acquisition process of the bottom wave of the transmission echo is as follows: The sequence composed of all peaks in the transmission echo is recorded as the second peak sequence; based on the second peak sequence, the moving window, moving average and starting wave marking point of each peak point of the second peak sequence are obtained in the same manner as the moving window, moving average and starting wave marking point of each peak point of the first peak sequence; Among all the remaining peak points except the initial wave mark point in the second peak sequence, obtain the peak point whose moving average value is greater than the preset second threshold value, and record it as the secondary mark point; record the set composed of continuous secondary mark points as the secondary mark point set, record all the peak points in the secondary mark point set with the latest time sequence as the bottom wave mark points, record all the data points in the moving window corresponding to all the bottom wave mark points as the bottom wave peak points, and use the waveform between all the bottom wave peak points in the transmission echo as the bottom wave of the transmission echo; The acquisition process of the defect wave and bottom wave of the reflected echo is as follows: The starting wave of the reflected echo is recorded as the reflection starting wave, and the bottom wave of the transmitted echo is recorded as the transmitted bottom wave; the central moment of the time interval where the transmitted bottom wave is located is taken as the reflection midpoint moment; for the reflected echo, the time period of the corresponding moving window of all the peak points in each corresponding mark point set is obtained, and the mark point set in the time period between the reflection starting wave and the reflection midpoint moment is called the defect mark point set; all data points in the moving window corresponding to all the peak points in each defect mark point set are recorded as defect wave peak points, and the waveform between all the defect wave peak points in each defect mark point set is taken as a defect wave to obtain each defect wave in the reflected echo; All peak points in the set of all defect mark points are recorded as defect wave mark points, and all other peak points except the initial wave mark point and the defect mark point in the first peak sequence are obtained; based on all other peak points, the bottom wave of the reflected echo is obtained in the same acquisition method as that of acquiring the transmitted bottom wave based on all remaining peak points in the second peak sequence; The process of obtaining the dislocation lateral index at any height is as follows: The bottom wave of the reflected echo is recorded as the reflected bottom wave, the difference between the integrated area of the reflected initial wave and the reflected bottom wave is taken as the attenuation of the reflected bottom wave, and the difference between the integrated area of the reflected initial wave and the transmitted bottom wave is taken as the attenuation of the transmitted bottom wave; the difference between the attenuation of the reflected bottom wave and the transmitted bottom wave is calculated and recorded as the bottom wave attenuation difference; Based on the appearance of the defect wave and the difference between the appearance time of the defect wave and the initial wave and the midpoint time of the reflection, combined with the difference in the attenuation of the bottom wave, the dislocation lateral index of the single crystal silicon rod at any height is determined; The process of obtaining the dislocation lateral index is as follows: Calculate the difference between the appearance time of each defect wave and the initial reflection wave, which is recorded as the first time difference; calculate the difference between the appearance time of each defect wave and the midpoint of the reflection, which is recorded as the second time difference; obtain the minimum value between the first time difference and the second time difference of each defect wave; calculate the chaos degree of the minimum value of all defect waves in the reflected echo, which is recorded as the first chaos degree; The dislocation transverse index is positively correlated with the number of defect waves in the reflected echo, and negatively correlated with the difference in bottom wave attenuation and the first disorder degree; The process of obtaining the dislocation longitudinal index of the single crystal silicon rod is as follows: Starting from the tail of the single crystal silicon rod, the height is used as the horizontal coordinate, and the dislocation lateral index corresponding to the height is used as the vertical coordinate to obtain each coordinate point, and all the coordinate points are fitted by a polynomial fitting algorithm to obtain a fitting curve; the interval between the i-th to the i+s-th height in the fitting curve is used as the neighborhood interval at the i-th height, where s is a preset positive integer; the fitting curve in the neighborhood interval at each height is integrated to obtain the integral area of the neighborhood interval at each height; The difference between the integral area of each height value and the neighborhood interval corresponding to the next height value is calculated and recorded as the first difference; the dislocation longitudinal index of the single crystal silicon rod is recorded as B, and the calculation expression of B is: , where is the number of heights for data collection, For the the sign function value of the first difference between the ith height and the ith height, is the height and The sign function value of the first difference between the heights, is the lateral index of the dislocation at the ith height.
2. A method for detecting defects in a single crystal silicon rod according to claim 1, It is characterized in that The sign function value is: when the first difference is greater than or equal to zero, the sign function value of the first difference is 1; when the first difference is less than zero, the sign function value of the first difference is 0.
3. A method for detecting defects in a single crystal silicon rod according to claim 1, It is characterized in that The process of detecting dislocation defects on a single crystal silicon rod is as follows: The dislocation longitudinal index of a preset number of single crystal silicon rods is used as the input of the threshold segmentation algorithm, and the segmentation threshold is output; if the dislocation longitudinal index of the single crystal silicon rod is greater than the segmentation threshold, the single crystal silicon rod has a dislocation defect; otherwise, the single crystal silicon rod does not have a dislocation defect.
4. A defect detection system for a single crystal silicon rod, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, It is characterized in that When the processor executes the computer program, the steps of the method according to any one of claims 1 to 3 are implemented.