JP2006041282A - Crack detecting method for silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detecting method capable of inspecting the existence of crack on a silicon wafer within a short time with a good accuracy. <P>SOLUTION: The crack on the silicon wafer is detected by a method wherein the silicon wafer is twisted and the frequency distribution of strength of a sound generated upon twisting the silicon wafer is measured to detect the existence of crack on the silicon wafer. In this case, the existence of a point whereat the frequency distribution of the strength of sound exceeds a predetermined level within the range of a frequency of 4-35 kHz is measured to detect the existence of the crack on the silicon wafer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for detecting a crack in a silicon wafer, and more particularly to a method for detecting a crack in a silicon wafer that detects the presence or absence of a crack in a silicon wafer by twisting the silicon wafer.

  Silicon wafers used as substrates for single crystal or polycrystalline crystal solar cell elements are being made larger and thinner for reasons such as cost reduction and reduction of silicon materials. For this reason, cracks are likely to occur in the process of manufacturing a silicon wafer and the device process.

  For example, in the case of a solar cell element, when the solar cell elements are assembled in series and parallel to form a module, if even one solar cell element with such a crack exists, the output power of the module is greatly reduced. For this reason, it is important to inspect the presence or absence of a crack before modularizing the solar cell element, accurately detect and remove the cracked one.

As a method for detecting such a crack in a silicon wafer, a vibration is generated by applying an impact to the silicon wafer, and the vibration frequency of the silicon wafer is converted into an electric signal through a microphone. The applicant has proposed a method of calculating an integral value and comparing it with an integral value of a power spectrum of a vibration frequency obtained in advance. (See Patent Document 1)
FIG. 5 is a diagram showing an example of the configuration of an apparatus according to the above-described silicon wafer crack detection method.

  In FIG. 5, 1 is a silicon wafer, 2 is an obstacle, 3 is a microphone, 4 is an analyzer, and 5 is a computer. In many cases, the silicon wafer 1 is usually a square or rectangle having a side of about 100 to 200 mm or a circle having a diameter of 50 to 200 mm. The obstacle 2 is preferably a spherical shape having a diameter of about 3 cm. A hole having a diameter of about 1 cm is formed in the obstacle 2 and is made of aluminum or the like and is provided with a rod and a base having a length of about 10 to 20 cm.

  An operator holds one side of the silicon wafer 1 with a finger, hits the obstacle 2 in a state of dropping from a height of 1 to 5 cm, applies an impact to the silicon wafer 1, Generate vibration. The vibration is collected by the microphone 3 disposed in the vicinity and converted into an electric signal. This is analyzed by an FFT (Fast Fourier Transform) analyzer 4 and a computer 5, and an integrated value of the power spectrum is calculated.

  The silicon wafer 1 to be inspected is compared by comparing the calculated integral value of the power spectrum with the integral value of the power spectrum of the vibration frequency of the silicon wafer in which cracks are determined in advance and the size of the crack is measured. The presence / absence of cracks and the size of cracks in the case of cracks can be understood.

Prior art document information related to the invention of this application includes the following.
JP 2004-28859 A

  However, as described above, an impact is applied to the silicon wafer to generate vibration, the vibration frequency of the silicon wafer is converted into an electric signal via a microphone, and the integral value of the power spectrum of the vibration frequency is calculated. In the method of comparing with the integral value of the power spectrum of the vibration frequency obtained in advance, in order to improve the detection accuracy, it is necessary to apply the silicon wafer as described above to an obstacle at several places on one silicon wafer. For example, if the silicon wafer is about 150 mm square, it is necessary to hit four obstacles against the obstacle. As described above, if it is necessary to hit several obstacles on one silicon wafer, it takes time to inspect the cracks, which increases the inspection cost of the silicon wafer.

  In view of such problems, it is an object of the present invention to provide a method for detecting a crack in a silicon wafer that can accurately inspect the presence or absence of a crack in the silicon wafer in a short time.

  In order to achieve the above object, the silicon wafer crack detection method of the present invention adds a twist to the silicon wafer, further measures the frequency distribution of the intensity of sound generated when the silicon wafer is twisted, and A silicon wafer crack detection method for detecting the presence or absence of cracks, wherein the presence or absence of a point where the frequency distribution of the sound intensity exceeds a predetermined level within a frequency range of 4 to 35 kHz is measured to detect cracks in the silicon wafer. The presence or absence is detected.

  In another crack detection method for a silicon wafer according to the present invention, it is desirable to twist the silicon wafer while the silicon wafer is in contact with a detection body incorporating a microphone.

  According to the silicon wafer crack detection method of the present invention, a twist is applied to the silicon wafer, and the frequency distribution of the intensity of sound generated when the silicon wafer is twisted is measured to detect the presence or absence of cracks in the silicon wafer. A method for detecting cracks in a silicon wafer, wherein the presence or absence of a crack in the silicon wafer is detected by measuring the presence or absence of a point where the frequency distribution of the sound intensity exceeds a predetermined level within a frequency range of 4 to 35 kHz. As a result, only one twist is required for one silicon wafer, so that cracks in the silicon wafer can be detected in a short time.

  Further, according to another method for detecting a crack in a silicon wafer of the present invention, a twist is applied to the silicon wafer in a state where the silicon wafer is in contact with a detection body incorporating a microphone. Can be raised.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a view showing an example of an apparatus for detecting cracks in a silicon wafer according to the present invention.

  In FIG. 1, 11 is a detector, 12 is a microphone, 14 is an amplifier, 15 is a computer, and 16 is a traffic light.

  The detection body 11 is for detecting the sound emitted from the silicon wafer. The detection body 11 is made of rubber, resin, or the like, and the microphone 12 is built therein. As shown in FIG. 1, the shape may be rounded at the tip or may be cylindrical. The microphone 12 converts sound into an electrical signal. The amplifier 14 is for amplifying a weak electric signal. The computer 15 compares the frequency distribution of the detected sound intensity with a predetermined level of intensity to determine whether or not there is a crack in the silicon wafer. The traffic light 16 informs the operator of whether there is a crack or not by blinking a separate lamp, and a buzzer or the like may be used together.

  FIG. 2 is a diagram showing an example of a crack detection method for a silicon wafer according to the present invention.

  Reference numerals 11 and 12 are the same as in FIG. 1, 11 is a detection body, 12 is a microphone, 20 is a silicon wafer, 21 is a metal hollow rod for supporting the detection body 11, 22 is a pedestal, 23 is Lead wires 24 a and 24 b connected to the microphone 12 indicate the twist direction of the silicon wafer 20.

  The lead wire 23 connected to the microphone 12 passes through the inside of the hollow bar 21 for supporting the detection body 11 and the lower part of the base 22 and is led out to the outside.

  The detection body 11 is held so that the center of the silicon wafer 20 is in contact with each other, and the opposite sides of the silicon wafer 20 rotate in directions different from each other in the directions indicated by 24a and 24b, preferably about 3 to 15 degrees. Twist 5-10 degrees. According to the results of experiments conducted repeatedly by the present inventors, if the twist angle is smaller than 3 degrees, no sound may be generated even if there is a crack in the silicon wafer 20, and if it exceeds 15 degrees, the silicon wafer 20 will break. There is a case. When the twisting angle is 5 to 10 degrees, cracks can be detected with high accuracy without damaging the silicon wafer 20.

  Further, even if the position where the silicon wafer 20 is twisted is not on the detection body 11 incorporating the microphone 12, it can be detected at a position slightly away from the detection body 11, but the silicon wafer 20 is in contact with the detection body 11. By doing so, since the sound generated when the silicon wafer 20 is twisted can be transmitted to the microphone 12 without being affected by the surrounding noise so much, the silicon wafer crack detection method according to the present invention incorporates the microphone 12. It is desirable to twist the silicon wafer 20 on the detected body 11.

  Thus, the sound generated by twisting the silicon wafer 20 on the detection body 11 is converted into an electrical signal by the microphone 12.

  FIG. 3 shows an example of a waveform of a frequency distribution of sound intensity measured when a certain silicon wafer is twisted.

  This is amplified to the required level by the amplifier 14 and sent to the computer 15.

  FIG. 4 shows an example of a waveform of a silicon wafer having no cracks obtained in advance.

  In order to improve the crack detection accuracy, about 10-20 wafers of the same type, thickness, size and shape as the silicon wafer to be inspected are used as much as possible for this crack-free silicon wafer whose waveform is obtained in advance. It is desirable to do.

  For such a silicon wafer without cracks, the waveform of the frequency distribution of the sound intensity of each silicon wafer is obtained by the above method. For these, the maximum value P of the frequency distribution of the sound intensity in the frequency region to be detected is obtained.

  The computer 15 is inputted with the maximum value P of the frequency distribution of the sound intensity as a reference for the determination, and is programmed to check whether there is a portion exceeding the maximum value P of the frequency distribution of the intensity. To do.

  For example, in the polycrystalline silicon wafer for solar cell elements before the device process having a size of 150 × 150 mm and a thickness of about 0.26 to 0.29 mm, the crack detection method according to the present invention is the result of no cracks. The sound intensity was all less than 30 dB in the frequency region between 4 kHz and 35 kHz with 20 measurements. On the other hand, with cracks, the number of measurements was 50, and the sound intensity was 33 to 45 dB in the same frequency range between 4 kHz and 35 kHz.

  In addition, at a frequency lower than 4 kHz or a frequency higher than 35 kHz, a silicon wafer having a crack and a silicon wafer having no crack could not be discriminated from the frequency distribution of sound intensity.

  Therefore, in such a polycrystalline silicon wafer, when it is inspected by the silicon wafer crack detection method according to the present invention, at a frequency of 4 kHz to 35 kHz, those having less than 30 dB have no cracks, and those having 30 dB or more have cracks. What is necessary is just to determine with a thing. That is, the predetermined level at this time can be set to 30 dB as an example.

  In addition, in the case of a single crystal silicon wafer having a diameter of 100 mm and a thickness of about 0.28 to 0.30 mm before being subjected to a device process, as a result of testing using the silicon wafer crack detection method according to the present invention, In the frequency region between 4 kHz and 35 kHz with 20 sheets, the sound intensity was all less than 25 dB. On the other hand, with cracks, the number of measurements was 50, and the sound intensity was all 29 to 40 dB in the frequency region between 4 kHz and 35 kHz.

  In addition, at a frequency lower than 4 kHz or a frequency higher than 35 kHz, a silicon wafer having a crack and a silicon wafer having no crack could not be discriminated from the frequency distribution of sound intensity.

  Accordingly, when such a polycrystalline silicon wafer is inspected by the silicon wafer crack detection method according to the present invention, at a frequency of 4 kHz to 35 kHz, those having less than 25 dB have no cracks, and those having 25 dB or more have cracks. What is necessary is just to determine with a thing. That is, the predetermined level at this time can be set to 25 dB as an example.

  The above example shows a silicon wafer crack detection method for detecting a crack in a silicon wafer by measuring a frequency distribution of sound intensity in a frequency region of 4 to 35 kHz. It is also possible to determine the presence or absence of cracks in the silicon wafer by measuring the point where the frequency distribution of sound intensity in a frequency range narrower than ~ 35 kHz exceeds a predetermined level.

  If there is a crack in the silicon wafer inspected by the above-described method, the crack portion is rubbed by twisting the silicon wafer, and a specific sound is generated. Therefore, as shown in FIG. appear. However, in a silicon wafer without cracks, even if it is twisted, such a protruding portion does not appear because no specific sound is generated. Therefore, it is possible to accurately detect a crack in the inspected silicon wafer based on the presence / absence of the protrusion 28 having a certain level or higher in the vibration frequency band of the inspection region.

  Thereby, when the computer 15 determines that the inspected silicon wafer has a crack, the lamp with a crack of the traffic light 16 is turned on, and when it is determined that there is no crack, the lamp with no crack of the traffic light 16 is turned on. Inform the operator of the test results.

  As described above, according to the method for detecting a crack in a silicon wafer of the present invention, since one silicon wafer may be inspected once, several points of the silicon wafer are applied to an obstacle, and the sound at this time is subjected to a fast Fourier transform analyzer. A great effect is obtained in that less than half the inspection time is required as compared with the case of analyzing by the above method.

  Furthermore, since an expensive fast Fourier transform analyzer is not required, the inspection apparatus is also inexpensive, and in combination with the above effects, the inspection cost of the silicon wafer can be reduced.

  The method for detecting a crack in a silicon wafer according to the present invention can be performed before the device process, during the device process, or after the device process.

  In addition, this invention is not limited to the above-mentioned form, A various change, improvement, etc. are possible in the range which does not deviate from the summary of this invention.

It is a figure which shows an example of the apparatus for detecting the crack of the silicon wafer which concerns on this invention. It is a figure which shows an example of the crack detection method of the silicon wafer which concerns on this invention. 4 shows an example of a waveform of a frequency distribution of sound intensity measured when a silicon wafer according to the present invention is twisted. An example of the waveform of a silicon wafer without a crack is shown. It is a figure which shows an example of a structure of the apparatus which concerns on the crack detection method of the silicon wafer in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20: Silicon wafer 2; Obstacle 3, 12: Microphone 4; Analyzer 5, 15: Computer 11: Detection body 13: Filter 14: Amplifier 16: Signal device 21: Rod 22 for supporting a detection body: Base
23: Lead wires 24a, 24b: Twist direction of silicon wafer 28: Waveform protrusion

Claims (2)

A method for detecting a crack in a silicon wafer, wherein the silicon wafer is twisted, and further, the frequency distribution of the intensity of sound generated when the silicon wafer is twisted is measured, and the presence or absence of cracks in the silicon wafer is detected. A method for detecting cracks in a silicon wafer, wherein the presence or absence of cracks in the silicon wafer is detected by measuring the presence or absence of a point where the intensity frequency distribution exceeds a predetermined level within a frequency range of 4 to 35 kHz. 2. The method for detecting cracks in a silicon wafer according to claim 1, wherein a twist is applied to the silicon wafer in a state where the silicon wafer is in contact with a detection body incorporating a microphone.

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