CN115055846A - Laser-stripped crystal ingot real-time monitoring system and method - Google Patents
Laser-stripped crystal ingot real-time monitoring system and method Download PDFInfo
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Abstract
The invention discloses a real-time monitoring system and a method for laser peeling crystal ingots, which firstly carry out fixed focus through a CCD imaging system, then setting an acoustic emission sensor and a laser to ensure that laser spots are aligned with the positions of the crystal ingot samples to be processed, then setting a plurality of different laser single pulse energies to respectively carry out laser surface scanning processing on a plurality of different areas of the samples so as to enable the acoustic emission sensor to obtain corresponding characteristic parameter graphs to be displayed in a computer, then the processed sample is processed by splinter treatment to obtain the section appearance corresponding to a plurality of energies, the section appearance of each energy is analyzed for the situation of crack, the correlation between the cross-sectional morphology and the characteristic parameter graph is obtained by combining the analysis of the cross-sectional morphology, and the distribution characteristics of the acoustic emission signals are found to be capable of monitoring the laser peeling processing process in real time and prejudging the internal processing. The invention solves the problem that the prior art does not have systematic real-time monitoring.
Description
Technical Field
The invention belongs to the technical field of nondestructive testing of a laser processing process, and particularly relates to a laser stripping crystal ingot real-time monitoring system and method.
Background
The laser stripping technology is a novel ingot stripping method, firstly, high-peak power pulse laser with high transmittance to a processing material is focused in the material for processing, the temperature of the material is rapidly increased after the material absorbs laser energy, a high-temperature and high-pressure environment atmosphere is formed in an inner closed area, a laser-induced inner modified layer is further formed, and then, the action of force is exerted on the modified layer, so that a wafer is stripped from an ingot along the modified layer. Compared with the traditional diamond wire cutting ingot method, the laser stripping method has remarkable advantages of reducing the loss of the stripping surface, improving the yield due to high processing efficiency, improving the surface quality of the stripping surface, facilitating the next process, having no waste liquid pollution, being green and environment-friendly and the like.
However, in the laser lift-off process, the laser processing process inside the material is very complex, and at present, the problems that the processing mechanism is not clear, the processing process is difficult to monitor in real time and cannot feed back the processing state, the classification and characterization of an internal modified structure are lacked in the processing process, and the like exist. In order to promote the continuous progress of the laser peeling technology, the existing problems need to be solved urgently, the acoustic emission technology is a dynamic nondestructive detection method, acoustic emission signals generated by laser internal processing contain rich information, but the acoustic emission monitoring technology has no systematic research work in the field of laser internal processing, and the problem that how to utilize the acoustic emission technology to efficiently monitor the internal processing process when a laser ingot is peeled off in real time and realize a processing structure prejudgment technology in the laser internal processing process is needed to be solved urgently at present.
Disclosure of Invention
The invention provides a real-time monitoring system and a real-time monitoring method for a laser stripped crystal ingot, which are used for obtaining the relation between an acoustic emission signal and a laser-induced internal modified structure from the characteristic parameter analysis of the acoustic emission signal, realizing the acoustic emission signal monitoring and processing process prejudging technology in the laser internal processing process of the laser stripped crystal ingot and solving the problem that the prior art does not have systematic real-time monitoring.
The technical scheme of the invention is as follows:
a real-time monitoring system for a laser stripped ingot comprises a laser, a diaphragm, a first reflector, an attenuator, a second reflector, a third reflector, an objective lens, an X-Y-Z three-dimensional mobile platform, a CCD imaging system, an acoustic emission sensor, a preamplifier, a data acquisition card and a computer;
the laser is connected with a computer, emitted laser sequentially passes through the diaphragm, the first reflector, the attenuator, the second reflector, the third reflector and the objective lens to reach the upper surface of an ingot sample piece placed on the X-Y-Z three-dimensional moving platform, illumination light of the CCD imaging system illuminates and focuses the ingot sample piece on the X-Y-Z three-dimensional moving platform through the third reflector and the objective lens to assist in aligning light spots of the laser, the acoustic emission sensor is connected with the computer sequentially passes through the preamplifier and the data acquisition card, and the acoustic emission sensor is used for being placed on the ingot sample piece to acquire acoustic emission signals and transmitting the acoustic emission signals to the computer.
The invention also provides a real-time monitoring method of the laser stripped crystal ingot, which comprises the following steps of monitoring by the real-time monitoring system of the laser stripped crystal ingot:
s1: placing and fixing the crystal ingot sample piece on an X-Y-Z three-dimensional moving platform, and aligning an illumination focus of a CCD imaging system to the upper surface of the crystal ingot sample piece;
s2: coating a couplant on an acoustic emission sensor, and then placing the acoustic emission sensor at a position 4-8mm away from a region to be processed on the upper surface of the crystal ingot sample piece;
s3: setting processing parameters of the laser through a computer;
s4: starting a laser, and focusing light spots emitted by the laser according to an illumination focus of a CCD imaging system so as to focus the light spots on a region to be processed in an ingot sample piece;
s5: setting multiple different laser single pulse energies, keeping other laser processing parameters unchanged, and respectively carrying out laser surface scanning processing on multiple different positions in the crystal ingot sample by using the multiple different energies; meanwhile, an acoustic emission sensor is used for synchronously acquiring acoustic emission signals and uploading the acoustic emission signals to a computer for processing and analysis to obtain an average frequency-amplitude correlation diagram and a counting-duration correlation diagram;
s6: after the laser processing is finished, splitting the ingot sample piece to obtain the corresponding section morphology of each laser single pulse energy after internal modification processing;
s7: carrying out crack analysis according to the cross section morphology corresponding to each laser single pulse energy;
s8: carrying out joint observation on the crack analysis condition of each laser single pulse energy and the corresponding average frequency-amplitude correlation diagram and the corresponding count-duration correlation diagram respectively to obtain the correlation between the section morphology and the characteristic parameter diagram;
s9: the correlation between the average frequency-amplitude correlation diagram and the counting-duration correlation diagram and the section morphology and the corresponding stripping effect in the step S8 are used for monitoring the laser stripping process of the crystal ingot in real time and prejudging the internal processing structure.
The invention firstly focuses on a crystal ingot sample piece through a CCD imaging system, then a sound emission sensor is placed, processing parameters of a laser are set, the laser is aligned according to a focus position to ensure that light spots are aligned with positions needing to be processed, then laser surface scanning processing is respectively carried out on a plurality of different areas of the sample by setting a plurality of levels of laser single pulse energy, so that the sound emission sensor obtains corresponding characteristic parameter graphs (average frequency-amplitude correlation graph and counting-duration correlation graph) to be displayed in a computer, then the processed sample is subjected to splitting processing to obtain section morphologies corresponding to a plurality of energies, the section morphologies of each energy are analyzed for crack conditions, the correlation between the section morphologies and the characteristic parameter graphs is obtained by combining the analysis of the section morphologies, and the distribution characteristics of the sound emission signals are found to be capable of monitoring the processing process of laser peeling in real time and carrying out pre-judging on internal processing .
The acoustic emission signal in the invention is mainly generated by physical phenomena such as melting and re-condensing and plasma generated when laser acts in the ingot sample piece, and internal pressure change caused by microcrack cracking.
The processing parameters of the laser are different to form a modified structure with larger morphology difference, the corresponding signal distribution also shows larger difference, and the characteristics can be used for prejudging the internal processing structure when the crystal ingot is stripped by the laser.
Further, in step S5, the three different laser single pulse energies are set to be 6.9 μ J, 11.6 μ J, and 16.2 μ J, respectively;
and the three laser surface scanning processes of different positions in the crystal ingot sample piece by three different energies are as follows:
and moving the distance of 0.3mm from the processing area after the processing of the previous surface structure is finished to process the next surface structure.
Further, in step S7, the process of performing crack analysis according to the cross-sectional profile is as follows;
according to the first section morphology corresponding to the pulse energy of 6.9 muJ, the ingot sample piece is observed to form transverse expansion cracks only between the uppermost explosion points, and the lap joints of the cracks are complete, so that the ingot sample piece is beneficial to the peeling up and down along the transverse cracks;
according to a second section morphology corresponding to the pulse energy of 11.6 muJ, transverse expansion cracks are observed to be formed between the uppermost layer of explosion points of the crystal ingot sample piece, transverse cracks also exist between the lower explosion points, and the overlap joint of the cracks of the transverse explosion points is incomplete;
according to the third section morphology corresponding to the pulse energy of 16.2 muJ, the section of the crystal ingot sample piece is observed to form a double-layer transverse crack;
the effect of laser lift-off is disadvantageous because the transverse crack planes of the second and third cross-sectional features are not uniform, resulting in non-uniform lift-off force during lift-off and reduced flatness of the lift-off surface after lift-off.
Further, in step S8, the process of obtaining the correlation between the cross-sectional profile and the feature parameter map is as follows:
when the laser single pulse energy is 6.9 muJ, the laser internal modification structure is beneficial to stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram shows longitudinal scatter distribution, the count-duration correlation diagram shows linear scatter distribution, the duration distribution is below 250 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment beneficial to laser stripping;
when the laser single pulse energy is 11.6 muJ, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram shows longitudinal dense point distribution, the count-duration correlation diagram shows linear dense point distribution, the duration time of the count-duration correlation diagram is distributed below 350 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping;
when the laser single pulse energy is 16.2 muJ, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram shows transverse dense point distribution, and the count-duration correlation diagram shows linear dense point distribution with the duration distribution below 550 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping.
Further, in step S4, after the illumination focus of the CCD imaging system is located on the upper surface of the ingot sample, the spot of the laser is focused inside the ingot sample by moving the X-Y-Z three-dimensional moving stage up by 100 μm in the Z-axis direction, and the actual focusing position of the spot is not coincident with the upward moving distance of the X-Y-Z three-dimensional moving stage due to the self-focusing effect of the ingot sample, and then the spot is actually focused at a depth of 330 μm inside the ingot sample.
Further, in step S1, the CCD imaging system is started to make the illumination light from the CCD imaging system reach the upper surface of the sample of the ingot through the refraction of the third reflector and the objective lens in sequence, and the position of the X-Y-Z three-dimensional moving platform is adjusted to make the view picture of the CCD imaging system clearly observe the upper surface of the sample.
Further, in step S2, the position of the acoustic emission sensor is fixed by using an adhesive tape or a clamp, and the acoustic emission sensor is set with channel parameters for signal acquisition, and the channel parameters are set as follows:
the method comprises the steps of obtaining a signal with the gain of 40dB, obtaining the threshold of 35dB, obtaining the sampling rate of 5MHz, obtaining the sampling length of 4k, adopting the recommended value of a non-metal material as an acoustic emission timing parameter according to the material characteristics of an ingot sample, and obtaining the peak value definition time of 50 mus, the impact definition time of 200 mus and the impact locking time of 300 mus.
Further, in step S3, the laser is an infrared ultrafast laser, and the processing parameters thereof are set as:
the transmitting laser wavelength is 1030nm, the pulse width is 290fs-15ps, the laser frequency range is 0.1-610kHz, and the diameter of a focusing spot of the laser is 2 mu m after the laser is focused by the objective lens (7).
Further, the other laser processing parameters in step S5 are: the laser scanning single line length is 3mm, the line lapping interval is 45 mu m, the scanning line number is 10, the scanning speed is 2mm/s, the laser pulse width is 15ps, and the repetition frequency is 1 kHz.
The invention has the following beneficial effects:
(1) the invention introduces the acoustic emission detection technology into the laser internal processing process of the laser stripped crystal ingot, establishes the relation between the acoustic emission signal characteristic and the processing structure, can monitor the laser stripping processing process and make the pre-judgment of the processing structure, and provides a novel monitoring method for the laser stripped crystal ingot.
(2) According to the real-time monitoring method for the laser stripped crystal ingot based on the acoustic emission technology, the detection energy comes from the material, the detected material is free of stress and radiation damage, signals are popular and easy to understand, signal processing is simple, and the machining process is easy to judge.
(3) The method for monitoring the laser-peeled crystal ingot in real time based on the acoustic emission technology is simple in field operation, can evaluate the laser peeling process, can monitor the laser peeling process of other transparent materials such as sapphire, gallium nitride and silicon without being limited to the internal processing of the crystal ingot.
Drawings
FIG. 1 is a schematic diagram of a laser lift-off ingot real-time monitoring system of the present invention;
FIG. 2 is a graph of the average frequency-amplitude correlation at 6.9 μ J for an ingot sample;
FIG. 3 is a graph of the average frequency-amplitude correlation at 11.6 μ J for an ingot sample;
FIG. 4 is a graph of the average frequency-amplitude correlation at 16.2 μ J for an ingot sample;
FIG. 5 is a count-duration correlation at 6.9 μ J for an ingot sample;
FIG. 6 is a count-duration correlation at 11.6 μ J for an ingot sample;
FIG. 7 is a count-duration correlation at 16.2 μ J for an ingot sample;
FIG. 8 is a first cross-sectional profile of the ingot sample at 6.9 μ J;
FIG. 9 is a second cross-sectional profile of the ingot sample at 11.6 μ J;
FIG. 10 is a third cross-sectional profile of the ingot sample at 16.2 μ J.
In the figure: the device comprises a laser 1, a diaphragm 2, a first reflector 3, an attenuator 4, a second reflector 5, a third reflector 6, an objective lens 7, a crystal ingot sample 8, an X-Y-Z three-dimensional moving platform 9, a CCD imaging system 10, an acoustic emission sensor 11, a preamplifier 12, a data acquisition card 13 and a computer 14.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent; for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted. The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent.
Example 1:
as shown in fig. 1, a system for implementing a real-time monitoring method for laser peeling off an ingot is firstly built, and the system comprises a laser 1, a diaphragm 2, a first reflector 3, an attenuator 4, a second reflector 5, a third reflector 6, an objective lens 7, an X-Y-Z three-dimensional moving platform 9, a CCD imaging system 10, an acoustic emission sensor 11, a preamplifier 12, a data acquisition card 13 and a computer 14;
the laser 1 is connected with a computer 14, emitted laser sequentially passes through a diaphragm 2, a first reflector 3, an attenuator 4, a second reflector 5, a third reflector 6 and an objective lens 7 to reach the upper surface of an ingot sample 8 placed on an X-Y-Z three-dimensional moving platform 9, a CCD imaging system 10 illuminates and focuses the ingot sample 8 on the X-Y-Z three-dimensional moving platform 9 through the third reflector 6 and the objective lens 7 to assist in light spot alignment of the laser 1, an acoustic emission sensor 11 is connected with the computer 14 sequentially passes through a preamplifier 12 and a data acquisition card 13, and the acoustic emission sensor 11 is used for being placed on the ingot sample 8 to acquire acoustic emission signals and transmitting the acoustic emission signals to the computer 14.
The embodiment also provides a real-time monitoring method of a laser-stripped crystal ingot based on an acoustic emission technology, which comprises the following steps of:
s1: placing and fixing the crystal ingot sample 8 on an X-Y-Z three-dimensional moving platform 9, starting a CCD imaging system 10, enabling illumination light carried by the CCD imaging system to sequentially pass through a third reflector 6 and an objective lens 7 to reach the upper surface of the crystal ingot sample 8 so as to enable the upper surface of the crystal ingot sample 8 to have an illumination focus, and adjusting the position of the X-Y-Z three-dimensional moving platform 9 so as to enable a visual field picture of the CCD imaging system 10 to clearly observe the upper surface of the sample;
s2: arranging an acoustic emission sensor 11, coating a couplant on the acoustic emission sensor 11, placing the acoustic emission sensor 11 at a position 4-8mm away from the region to be processed on the upper surface of the crystal ingot sample 8, fixing the position of the acoustic emission sensor 11 by using an adhesive tape or a clamp, and setting channel parameters for signal acquisition for the acoustic emission sensor 11;
s3: setting processing parameters of the laser through a computer;
s4: starting a laser 1 to emit a laser beam, sequentially passing through a diaphragm 2, a first reflector 3, an attenuator 4, a second reflector 5, a third reflector 6 and an objective lens 7 to reach the upper surface of an ingot sample 8 to form a light spot, moving the light spot of the laser 1 in the Z-axis direction by 100 microns through an X-Y-Z three-dimensional moving platform 9 after an illumination focus of a CCD imaging system 10 is positioned on the upper surface of the ingot sample 8, so that the light spot is focused inside the ingot sample 8, wherein the actual focusing position of the light spot is not overlapped with the upward moving distance of the X-Y-Z three-dimensional moving platform 9 due to the self-focusing effect of the ingot sample 8, and the light spot is actually focused at the depth of 330 microns inside the ingot sample 8;
s5: changing laser single pulse energy of the laser 1, including three types of 6.9 muJ, 11.6 muJ and 16.2 muJ, and keeping other laser processing parameters unchanged; respectively carrying out laser surface scanning processing on three different positions in the ingot sample 8 by using the three different energies, and moving 0.3mm away from a processing area after the processing of the previous surface structure is finished to process the next surface structure; meanwhile, an acoustic emission sensor 11 is used for synchronously acquiring acoustic emission signals and uploading the acoustic emission signals to a computer 14 for processing and analysis to obtain an average frequency-amplitude correlation diagram and a counting-duration correlation diagram, and the effect and the quality of an internal modification structure during laser stripping are determined according to the changes of the two correlation diagrams along with the laser single pulse energy;
s6: after the laser processing is finished, splitting the ingot sample 8 to obtain corresponding cross-sectional appearances of each laser single pulse energy after internal modification processing, wherein the cross-sectional appearances comprise a first cross-sectional appearance, a second cross-sectional appearance and a third cross-sectional appearance;
s7: carrying out crack analysis according to the cross section morphology corresponding to each laser single pulse energy;
as shown in fig. 8, from the first cross-sectional profile corresponding to a pulse energy of 6.9 μ J, it was observed that the ingot sample 8 formed only laterally propagating cracks between the uppermost shots, and the cracks overlapped completely, which was beneficial for the desired peeling up and down the lateral cracks;
as shown in fig. 9, according to the second cross-sectional profile corresponding to the pulse energy of 11.6 μ J, it is observed that, in addition to the formation of the transverse expansion cracks between the uppermost explosion points of the ingot sample 8, transverse cracks also exist between the lower explosion points, and the lap joints of the cracks of the transverse explosion points are incomplete;
as shown in fig. 10, according to the third sectional morphology corresponding to the pulse energy of 16.2 μ J, it was observed that the section of the ingot sample 8 formed a double-layer transverse crack;
the transverse crack surfaces of the second and third cross-sectional shapes are not uniform, so that the peeling force during peeling is not uniform and the flatness of the peeled surface after peeling is reduced, and the laser peeling effect is not good;
s8: the crack analysis condition of each laser single pulse energy is respectively and jointly observed with the corresponding average frequency-amplitude correlation diagram and the corresponding count-duration correlation diagram to obtain the correlation between the section morphology and the characteristic parameter diagram, and the following results can be obtained:
when the laser single pulse energy is 6.9 muj, the laser internal modification structure is beneficial to stripping, in the corresponding acoustic emission signal characteristic, the average frequency-amplitude correlation diagram shows longitudinal scatter distribution, as shown in fig. 2, the count-duration correlation diagram shows linear scatter distribution, and the duration distribution is below 250 mus, as shown in fig. 5, the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment beneficial to laser stripping;
when the laser single pulse energy is 11.6 muj, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristic, the average frequency-amplitude correlation diagram shows longitudinal dense point distribution, as shown in fig. 3, the count-duration correlation diagram shows linear dense point distribution, and the duration distribution is below 350 mus, as shown in fig. 6, the distribution characteristic of the acoustic emission signal at this time can be used as processing judgment unfavorable for laser stripping;
when the laser single pulse energy is 16.2 muj, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristic, the average frequency-amplitude correlation diagram shows a transverse dense point distribution, as shown in fig. 4, the count-duration correlation diagram shows a linear dense point distribution with the duration distribution below 550 mus, as shown in fig. 7, the distribution characteristic of the acoustic emission signal at this time can be used as processing judgment unfavorable for laser stripping;
s9: the correlation between the average frequency-amplitude correlation diagram and the counting-duration correlation diagram and the section morphology and the corresponding stripping effect in the step S8 are used for monitoring the laser stripping process of the crystal ingot in real time and prejudging the internal processing structure.
The invention firstly focuses on a crystal ingot sample 8 through a CCD imaging system 10, then a sound emission sensor 11 is placed, processing parameters of a laser 1 are set and aligned according to a focusing position to ensure that light spots are aligned with positions needing to be processed, then three different laser single pulse energies are set to respectively carry out laser surface scanning processing on three different areas of the sample, so that the sound emission sensor 11 obtains corresponding characteristic parameter graphs (average frequency-amplitude correlation graph and counting-duration correlation graph) to be displayed in a computer 14, then the processed sample is subjected to splitting processing to obtain section morphologies corresponding to the three energies, the section morphology of each energy is analyzed for crack conditions, the analysis of the section morphology is combined to obtain the correlation between the section morphology and the characteristic parameter graph, and the distribution characteristics of the sound emission signals are found to be capable of monitoring the laser lift-off processing process in real time and carrying out the internal processing on the section morphology And (6) carrying out prejudgment.
The acoustic emission signal in the invention is mainly generated by physical phenomena such as melting and re-condensing and plasma generated when the laser acts in the ingot sample 8, and internal pressure changes caused by microcrack cracking.
The processing parameters of the laser 1 are different to form a modified structure with larger morphology difference, the corresponding signal distribution also shows larger difference, and the characteristics can be used for prejudging the internal processing structure when the crystal ingot is stripped by laser.
In the present embodiment, the ingot sample 8 includes a silicon carbide ingot, a silicon ingot, a sapphire ingot, and the like, and the sample applied to the present embodiment is specifically a silicon carbide ingot.
In this embodiment, more than three laser single-pulse energies may be set to perform laser processing to obtain the corresponding cross-sectional profile and the correlation diagram, but this embodiment only lists three energies with larger differences, and does not limit this, and different laser single-pulse energies may be set according to actual needs.
In the present embodiment, the principle of the process of uploading the obtained acoustic emission signals to the computer 14 for processing and analysis in step S5 to obtain the average frequency-amplitude correlation map and the count-duration correlation map is well known to those skilled in the art, and the correlation map may be formed by using conventional graphical software (for example, EXCEL), and the data of the acoustic emission signals may be input to the graphical software so as to be graphed according to the vertical and horizontal coordinates of the data.
In the present embodiment, the channel parameters of the acoustic emission sensor 11 are set as: the signal gain is 40dB, the acquisition threshold is 35dB, the sampling rate is 5MHz, and the sampling length is 4 k; according to the material characteristics of the crystal ingot sample piece, the acoustic emission timing parameter adopts the recommended value of a non-metal material: peak definition time 50 mus, impact definition time 200 mus and impact dwell time 300 mus.
In this embodiment, the acoustic emission sensor 11 is a Nano-30 single-end resonant acoustic emission sensor, and the applied coupling agent is vaseline.
In this embodiment, the laser 1 is an infrared ultrafast laser, the emitting laser wavelength is 1030nm, the pulse width is 290fs-15ps, the laser frequency range is 0.1-610kHz, and the diameter of the focused spot of the laser is 2 μm after the laser is focused by the objective lens 7.
In this embodiment, the ingot sample 8 has a size of 10mm × 10mm × 0.5mm, and the Si surface of the ingot sample is subjected to chemical mechanical polishing treatment to have a roughness of 1nm or less, and laser light is incident from the Si surface.
In this embodiment, the other laser processing parameters in step S5 are: the laser scanning single line length is 3mm, the line lapping interval is 45 mu m, the scanning line number is 10, the scanning speed is 2mm/s, the laser pulse width is 15ps, and the repetition frequency is 1 kHz.
Example 2:
this embodiment is similar to embodiment 1, except that in step S5, the number of pulses of the laser 1 may be changed, the number of pulses N may be set to 20, 50, 100, 200, 500, and 800, respectively, and other processing parameters may be kept unchanged (specifically, the laser pulse width 15ps, the repetition frequency 1kHz, and the single pulse energy 19 μ J). And respectively carrying out laser multi-pulse dotting processing on six areas on the sample, and simultaneously processing the acoustic emission amplitude signal, the waveform and the frequency spectrum signal which are synchronously acquired by adopting the acoustic emission sensor 11 to obtain an amplitude process diagram and an evolution process of the modification processing state of the multi-pulse points in the laser, wherein the evolution process is reflected by the change of the amplitude process diagram, the waveform and the frequency spectrum diagram along with the pulse number. And the sample is cracked after the processing is finished, and the section appearance corresponding to each pulse number is also obtained.
Under different laser pulse numbers, the amplitude history graph is compared with the corresponding section morphology, so that the corresponding relation between the amplitude of the acoustic emission signal and the evolution process of the internal multi-pulse point modification processing state can be proved.
When the number of pulses is 100 or less, the height of the modified region rapidly increases, and when the number of pulses is greater than 100, the height of the modified region rises more slowly until reaching the surface. Obtaining the rising trend of the amplitude within the pulse number of 100 from the corresponding detected amplitude process diagram, wherein the highest amplitude is 44 dB; the amplitude course is smooth after the pulse number is more than 100, when the laser ablates on the surface of the sample, the corresponding amplitude reaches 48dB at most, and then the laser pulse continuously acts until an ablation pit is formed on the surface, the amplitude is still 48dB at most, so that the amplitude signal characteristic of the acoustic emission can be used as the characteristic of the laser internal processing evolution process.
In order to better reflect the difference and the connection of different laser processing states by using acoustic emission signals, acoustic emission signals within the pulse number 20 and above the pulse number 500 are respectively selected to analyze original waveforms and frequency spectrums corresponding to internal processing and surface processing. When the pulse number is within 20, the waveform distribution range is within-5 mV, the waveform oscillation time is about 200 mus, and the peak value of the frequency spectrum is about 0.2 mV; when the pulse number is more than 500, the waveform distribution range is expanded to-25 mV, the waveform oscillation time is increased to nearly 500 mus, and the peak value of the frequency spectrum is also increased to about 1 mV. The acoustic emission signals of the laser in different processing states have obvious difference, and the waveform and the frequency of the acoustic emission signals can be used for pre-judging the processing states.
According to the corresponding relation between the pulse number and the cross section morphology, the acoustic emission technology is proved to be used for monitoring the prejudgment of the processing state in the laser internal processing process by combining the appearing amplitude signal and the waveform and frequency spectrum characteristics, analyzing the relation between the acoustic emission amplitude signal and the processing effect and combining the waveform and frequency spectrum difference in the internal or surface processing.
Example 3:
this embodiment is similar to embodiment 1, except that in step S5, the repetition frequency of the laser 1 is changed, and the repetition frequencies f are set to 1, 100, and 200, respectively, while keeping the other processing parameters (specifically, the laser pulse width 15ps, the pulse number 50, and the single pulse energy 15.2 μ J) unchanged. And respectively carrying out laser multi-pulse dotting processing on three areas on the sample, and simultaneously processing the acoustic emission amplitude signal and the frequency signal which are synchronously acquired by adopting the acoustic emission sensor 11 to obtain the corresponding relation formed by an amplitude process diagram, an average frequency-amplitude correlation diagram and an internal point modification processing structure. And the sample is subjected to splinter treatment after the processing is finished, and the section morphology corresponding to each repetition frequency is also obtained.
Under different repetition frequencies, the amplitude history diagram and the average frequency-amplitude correlation diagram are compared with corresponding section morphologies, so that the signal points of three section morphologies are distributed in different regions, the phenomenon that the signal points are overlapped occurs in two section morphologies with higher repetition frequencies can be obtained from the diagram, namely different structures show different signal distributions, and similar structures show similar signal distributions even if laser processing parameters are different, and the clustering characteristic of the acoustic emission signal is proved to be closely related to the internal modified structure.
Therefore, the analysis proves that the clustering characteristics of the acoustic emission signals of the modified structures of different types are closely related to the internal modified structure, and the acoustic emission signals can be used for classifying and representing the internal modified structures of different types respectively, so that the acoustic emission signal monitoring and the processing structure prejudgment in the laser internal processing process are realized.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. This need not be, nor should it be exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A laser stripping crystal ingot real-time monitoring system is characterized by comprising a laser (1), a diaphragm (2), a first reflector (3), an attenuator (4), a second reflector (5), a third reflector (6), an objective lens (7), an X-Y-Z three-dimensional moving platform (9), a CCD imaging system (10), an acoustic emission sensor (11), a preamplifier (12), a data acquisition card (13) and a computer (14);
the laser (1) is connected with a computer (14), emitted laser sequentially passes through the diaphragm (2), the first reflector (3), the attenuator (4), the second reflector (5), the third reflector (6) and the objective lens (7) to reach the upper surface of an ingot sample piece (8) placed on the X-Y-Z three-dimensional moving platform (9), illumination light of the CCD imaging system (10) illuminates and focuses the ingot sample piece (8) on the X-Y-Z three-dimensional moving platform (9) through the third reflector (6) and the objective lens (7) to assist in aligning light spots of the laser (1), the acoustic emission sensor (11) is sequentially connected with the computer (14) through the preamplifier (12) and the data acquisition card (13), and the acoustic emission sensor (11) is used for being placed on the ingot sample piece (8) to acquire acoustic emission signals and transmitting the acoustic emission signals to the computer (14) ).
2. A real-time monitoring method of a laser-stripped ingot, comprising the real-time monitoring system of claim 1, wherein the monitoring by the real-time monitoring system of a laser-stripped ingot comprises the following steps:
s1: placing and fixing the ingot sample (8) on an X-Y-Z three-dimensional moving platform (9), and aligning the illumination focus of a CCD imaging system (10) to the upper surface of the ingot sample (8);
s2: coating a couplant on an acoustic emission sensor (11), and then placing the acoustic emission sensor at a position 4-8mm away from a region to be processed on the upper surface of an ingot sample piece (8);
s3: setting processing parameters of the laser (1) through a computer (14);
s4: starting a laser (1), and focusing light spots emitted by the laser according to an illumination focus of a CCD imaging system (10) so as to focus the light spots on a region to be processed in an ingot sample piece (8);
s5: setting a plurality of different laser single pulse energies, keeping other laser processing parameters unchanged, and respectively carrying out laser surface scanning processing on a plurality of different positions in the ingot sample piece (8) by using the plurality of different energies; meanwhile, an acoustic emission sensor (11) is used for synchronously acquiring acoustic emission signals and uploading the acoustic emission signals to a computer (14) for processing and analysis to obtain an average frequency-amplitude correlation diagram and a counting-duration correlation diagram;
s6: after the laser processing is finished, the ingot sample piece (8) is subjected to splitting treatment to obtain the corresponding section morphology after each laser single pulse energy is subjected to internal modification processing;
s7: performing crack analysis according to the cross section morphology corresponding to each laser single pulse energy;
s8: respectively carrying out joint observation on the crack analysis condition of each laser single pulse energy and the corresponding average frequency-amplitude correlation diagram and the corresponding count-duration correlation diagram to obtain the correlation between the section morphology and the characteristic parameter diagram;
s9: the correlation between the average frequency-amplitude correlation diagram and the counting-duration correlation diagram and the section morphology and the corresponding stripping effect in the step S8 are used for monitoring the laser stripping process of the crystal ingot in real time and prejudging the internal processing structure.
3. A laser lift-off ingot real-time monitoring method as set forth in claim 2, wherein in step S5, three different laser single pulse energies are set to 6.9 μ J, 11.6 μ J and 16.2 μ J, respectively;
and three times of laser surface scanning processing is carried out on different positions in the ingot sample piece (8) by three different energies:
and moving 0.3mm away from the processing area after the processing of the previous surface structure is finished, and processing the next surface structure.
4. A real-time monitoring method of a laser lift-off ingot as set forth in claim 3, wherein in the step S7, the crack analysis is performed based on the cross-sectional profile as follows;
according to the first cross-sectional profile corresponding to the pulse energy of 6.9 muj, it was observed that the ingot sample (8) formed laterally propagating cracks only between the uppermost detonating points with complete lap joints, which was beneficial for the desired peeling up and down the lateral cracks;
according to the second section morphology corresponding to the pulse energy of 11.6 muJ, the ingot sample piece (8) is observed to form transverse expansion cracks between the uppermost layer of explosion points, transverse cracks also exist between the lower explosion points, and the lap joints of the transverse explosion points are incomplete;
observing that the cross section of the ingot sample (8) forms a double-layer transverse crack according to the third cross section morphology corresponding to the pulse energy of 16.2 mu J;
the effect of laser lift-off is disadvantageous because the transverse crack planes of the second and third cross-sectional features are not uniform, resulting in non-uniform lift-off force during lift-off and reduced flatness of the lift-off surface after lift-off.
5. A method for real-time monitoring of a laser lift-off ingot as set forth in claim 4, wherein in the step S8, the correlation between the cross-sectional profile and the characteristic parameter map is obtained as follows:
when the laser single pulse energy is 6.9 muJ, the laser internal modification structure is beneficial to stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram shows longitudinal scatter distribution, the count-duration correlation diagram shows linear scatter distribution, the duration distribution is below 250 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment beneficial to laser stripping;
when the laser single pulse energy is 11.6 muJ, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram is expressed as longitudinal dense point distribution, the count-duration correlation diagram is expressed as linear dense point distribution, the duration distribution is below 350 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping;
when the laser single pulse energy is 16.2 muJ, the laser internal modification structure is unfavorable for stripping, in the corresponding acoustic emission signal characteristics, the average frequency-amplitude correlation diagram shows transverse dense point distribution, and the count-duration correlation diagram shows linear dense point distribution with the duration distribution below 550 mus, and the distribution characteristics of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping.
6. The real-time monitoring method for laser lift-off of an ingot as set forth in claim 2, wherein in step S4, after the illumination focus of the CCD imaging system (10) is located on the upper surface of the ingot sample (8), the spot of the laser (1) is focused inside the ingot sample (8) by moving the X-Y-Z three-dimensional moving platform (9) 100 μm in the Z-axis direction, and the spot is actually focused at a depth of 330 μm inside the ingot sample (8) when the spot is not coincident with the moving distance of the X-Y-Z three-dimensional moving platform (9) due to the self-focusing effect of the ingot sample (8).
7. A real-time monitoring method for laser lift-off of an ingot as set forth in claim 2, characterized in that in step S1, the CCD imaging system (10) is activated to make its own illumination light reach the upper surface of the ingot sample (8) through the refraction of the third reflector (6) and the objective lens (7) in sequence, and the position of the X-Y-Z three-dimensional moving platform (9) is adjusted to make the view picture of the CCD imaging system (10) clearly observe the upper surface of the sample.
8. A real-time monitoring method for a laser lift-off ingot as set forth in claim 2, wherein in step S2, the acoustic emission sensor (11) is fixed in position by using a tape or a jig, and the acoustic emission sensor (11) is set with channel parameters for signal acquisition, the channel parameters being set as:
the method comprises the steps of obtaining a signal with the gain of 40dB, obtaining the threshold of 35dB, obtaining the sampling rate of 5MHz, obtaining the sampling length of 4k, adopting the recommended value of a non-metal material as an acoustic emission timing parameter according to the material characteristics of an ingot sample, and obtaining the peak value definition time of 50 mus, the impact definition time of 200 mus and the impact locking time of 300 mus.
9. A real-time monitoring method for laser lift-off ingot as set forth in claim 2, wherein in step S3, the laser (1) is an infrared ultrafast laser whose processing parameters are set as:
the transmitting laser wavelength is 1030nm, the pulse width is 290fs-15ps, the laser frequency range is 0.1-610kHz, and the diameter of a focusing spot of the laser is 2 mu m after the laser is focused by the objective lens (7).
10. A method for real-time monitoring of a laser stripped ingot as set forth in claim 2 wherein the other laser process parameters in step S5 are: the laser scanning single line length is 3mm, the line lapping interval is 45 mu m, the scanning line number is 10, the scanning speed is 2mm/s, the laser pulse width is 15ps, and the repetition frequency is 1 kHz.
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