CN115055846B - Real-time monitoring system and method for laser stripped ingot - Google Patents
Real-time monitoring system and method for laser stripped ingot Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 62
- 238000012544 monitoring process Methods 0.000 title claims abstract description 36
- 238000012545 processing Methods 0.000 claims abstract description 104
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- 238000003384 imaging method Methods 0.000 claims abstract description 24
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- 238000001228 spectrum Methods 0.000 description 8
- 230000009286 beneficial effect Effects 0.000 description 4
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000009659 non-destructive testing Methods 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 229910052594 sapphire Inorganic materials 0.000 description 2
- 239000010980 sapphire Substances 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 229910002601 GaN Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/50—Working by transmitting the laser beam through or within the workpiece
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/50—Working by transmitting the laser beam through or within the workpiece
- B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/70—Auxiliary operations or equipment
- B23K26/702—Auxiliary equipment
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Abstract
The invention discloses a real-time monitoring system and method for laser stripping ingot, which comprises the steps of firstly, performing fixed focus through a CCD imaging system, then, setting an acoustic emission sensor and a laser to ensure that laser spots are aligned to positions of the ingot sample to be processed, then, setting a plurality of different laser single pulse energies to respectively perform laser surface scanning processing on a plurality of different areas of a sample, so that the acoustic emission sensor obtains corresponding characteristic parameter graphs to be displayed in a computer, then, performing splitting treatment on the processed sample to obtain cross section morphology corresponding to a plurality of energies, analyzing crack conditions on the cross section morphology of each energy, combining analysis of the cross section morphology to obtain correlation between the cross section morphology and the characteristic parameter graphs, and finding out that the distribution characteristics of acoustic emission signals can perform real-time monitoring on the processing process of laser stripping and pre-judge 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 in a laser processing process, and particularly relates to a real-time monitoring system and method for laser stripping ingot.
Background
The laser stripping technology is an emerging ingot stripping method, and is characterized in that high-peak power pulse laser with higher 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 effect of the force is exerted on the modified layer, so that a wafer is stripped from the ingot along the modified layer. Compared with the traditional diamond wire-electrode cutting ingot method, the laser stripping method has the remarkable advantages of reducing the loss of the stripping surface, improving the processing efficiency and the yield, improving the surface quality of the stripping surface, being beneficial to the next process, and having the advantages of no waste liquid pollution, environmental protection and the like.
However, in the laser stripping process, the processing process of the laser in the material is very complex, and the problems that the processing mechanism is not clear, the processing process is difficult to monitor in real time, the processing state cannot be fed back, and the classification and characterization of the internal modified structure are not available in the processing process exist at present. In order to promote the continuous progress of the laser stripping technology, the problems are to be solved, the acoustic emission technology is a dynamic nondestructive testing method, acoustic emission signals generated by internal laser processing contain rich information, but no systematic research work exists in the field of internal laser processing in the acoustic emission monitoring technology, and how to use the acoustic emission technology to efficiently monitor the internal processing process when the ingot is stripped by the laser in real time and realize the processing structure prediction technology in the internal laser processing process is the problem to be solved currently.
Disclosure of Invention
The invention provides a real-time monitoring system and a real-time monitoring method for a laser stripped ingot, which are used for obtaining the relation between an acoustic emission signal and a laser-induced internal modification structure from the analysis of characteristic parameters of the acoustic emission signal, so as to realize the monitoring of the acoustic emission signal and the prejudgment technology of the processing process in the laser internal processing process of the laser stripped ingot, and solve 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 laser stripping ingot comprises a laser, a diaphragm, a first reflecting mirror, an attenuator, a second reflecting mirror, a third reflecting mirror, an objective lens, an X-Y-Z three-dimensional moving platform, a CCD imaging system, an acoustic emission sensor, a preamplifier, a data acquisition card and a computer;
the laser instrument is connected with the computer, and the laser that just shoots loops through diaphragm, first speculum, attenuator, second speculum, third speculum, objective reach place the upper surface of the ingot sample piece on the three-dimensional moving platform of X-Y-Z, CCD imaging system's illumination light passes through third speculum, objective is right the ingot sample piece on the three-dimensional removal of X-Y-Z is illuminated and is fixed the burnt, is used for assisting the facula alignment of laser instrument, acoustic emission sensor loops through preamplifier, data acquisition card with the computer links to each other, acoustic emission sensor is used for placing and acquires acoustic emission signal and transmits for on the ingot sample piece the computer.
The invention also provides a laser stripped ingot real-time monitoring method, which comprises the steps of monitoring by the laser stripped ingot real-time monitoring system, wherein the steps of:
s1: placing and fixing the ingot on an X-Y-Z three-dimensional moving platform, and enabling an illumination focus of a CCD imaging system to be aligned with the upper surface of the ingot;
s2: after the acoustic emission sensor is coated with the coupling agent, the acoustic emission sensor is placed at a position 4-8mm away from the to-be-processed area on the upper surface of the ingot sample;
s3: setting processing parameters of a laser through a computer;
S4: starting a laser, wherein the emitted light spot is focused according to an illumination focus of a CCD imaging system, so that the light spot is focused in a region to be processed in the ingot sample;
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 by using the plurality of different energies; simultaneously, an acoustic emission sensor is utilized to synchronously collect acoustic emission signals and the acoustic emission signals are uploaded to a computer for processing and analysis, so that an average frequency-amplitude correlation diagram and a count-duration correlation diagram are obtained;
s6: after the laser processing is finished, performing splitting treatment on the ingot sample piece to obtain a corresponding cross section morphology after internal modification processing of each laser single pulse energy;
S7: performing crack analysis according to the cross section morphology corresponding to each laser single pulse energy;
S8: carrying out joint observation on crack analysis conditions of each laser single pulse energy and corresponding average frequency-amplitude correlation graphs and count-duration correlation graphs respectively to obtain correlation between the cross section morphology and the characteristic parameter graphs;
S9: the correlation of the average frequency-amplitude correlation diagram, the count-duration correlation diagram and the cross section morphology and the corresponding stripping effect in the step S8 are used for monitoring the laser stripping process of the ingot in real time and pre-judging the internal processing structure.
According to the invention, firstly, a focus is fixed on a crystal ingot sample piece through a CCD imaging system, then an acoustic emission sensor is placed, processing parameters of a laser are set, the crystal ingot sample piece is aligned according to a focus positioning position, so that the position of a light spot to be processed is ensured, then a plurality of different levels of laser single pulse energy are set to respectively carry out laser surface scanning processing on a plurality of different areas of a sample, so that the acoustic emission sensor obtains a corresponding characteristic parameter graph (an average frequency-amplitude correlation graph and a count-duration correlation graph) to be displayed in a computer, then the processed sample is subjected to splitting treatment to obtain a plurality of cross section morphologies corresponding to the energy, the analysis of the cross section morphology of each energy is combined, the correlation between the cross section morphology and the characteristic parameter graph is obtained, and the distribution characteristics of acoustic emission signals are found to monitor the processing process of laser stripping in real time and pre-judge the internal processing.
The acoustic emission signal in the invention mainly generates physical phenomena such as melting and recondensing, plasma and the like when laser acts in the ingot sample, and generates internal pressure change along with micro-crack cracking.
The processing parameters of the laser are different from each other, so that the corresponding signal distribution also shows a large difference, and the characteristics can be used for the prejudgment of the internal processing structure when the ingot is stripped by the laser.
Further, in step S5, three different laser single pulse energies are set to be 6.9 μj, 11.6 μj, and 16.2 μj, respectively;
And three different energy processes of scanning the laser surface for three times on different positions inside the crystal ingot sample piece are as follows:
After the processing of the previous surface structure is completed, the surface structure is moved 0.3mm away from the processing area to process the next surface structure.
Further, in step S7, the process of crack analysis according to the cross-sectional morphology is as follows;
According to a first cross-sectional morphology corresponding to the pulse energy of 6.9 mu J, the ingot sample piece is observed to form transverse expansion cracks only between the uppermost explosion points, and the cracks are completely overlapped, so that the ingot sample piece is beneficial to stripping up and down along the transverse cracks;
According to the second section morphology corresponding to the pulse energy of 11.6 mu J, the transverse crack is observed to exist between the explosion points below besides the transverse expansion crack formed between the explosion points at the uppermost layer of the ingot sample piece, and the crack lap joint of the transverse explosion points is incomplete;
According to the third cross section morphology corresponding to the pulse energy of 16.2 mu J, the cross section of the ingot sample piece is observed to form double-layer transverse cracks;
the uneven lateral crack surfaces of the second and third cross-sectional shapes cause uneven peeling force during peeling and reduced flatness of the peeled surface, and therefore are disadvantageous to the effect of laser peeling.
Further, in step S8, the process of obtaining the correlation between the cross-sectional morphology and the characteristic parameter map is as follows:
when the laser single pulse energy is 6.9 mu J, the laser internal modification structure is favorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is longitudinally distributed along the scattered points, the count-duration correlation diagram is linearly distributed along the scattered points, the duration time is distributed below 250 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment favorable for laser stripping;
When the laser single pulse energy is 11.6 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is longitudinally distributed at dense points, the count-duration correlation diagram is linearly distributed at dense points, the duration of the count-duration correlation diagram is distributed below 350 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment unfavorable for stripping of the laser;
When the laser single pulse energy is 16.2 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is in transverse dense point distribution, the count-duration correlation diagram is in linear dense point distribution with duration time distribution below 550 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping.
Further, in step S4, when the illumination focus of the CCD imaging system is located on the upper surface of the ingot, the X-Y-Z three-dimensional moving platform is moved by 100 μm in the Z-axis direction to focus the light spot of the laser into the ingot, and the actual focusing position of the light spot does not coincide with the upward movement distance of the X-Y-Z three-dimensional moving platform due to the self-focusing effect of the ingot, the light spot is actually focused at a depth of 330 μm in the ingot.
In step S1, the CCD imaging system is started, so that the illumination light of the CCD imaging system reaches the upper surface of the ingot sample 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 regulated, so that the visual field picture of the CCD imaging system can 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 channel parameters for signal acquisition are set for the acoustic emission sensor, where the channel parameters are set as follows:
the signal gain is 40dB, the acquisition threshold is 35dB, the sampling rate is 5MHz, the sampling length is 4k, the acoustic emission timing parameter adopts the recommended value of nonmetallic materials according to the material characteristics of the ingot sample piece, the peak value definition time is 50 mu s, the impact definition time is 200 mu s and the impact locking time is 300 mu s.
Further, in step S3, the laser is an infrared ultrafast laser, and the processing parameters thereof are set as follows:
the wavelength of the emitted laser is 1030nm, the pulse width is 290fs-15ps, the frequency range of the laser is 0.1-610kHz, and the diameter of a focusing spot of the laser is 2 μm after the focusing action of an objective lens (7).
Further, other laser processing parameters in step S5 are: the laser scans the single line length to be 3mm, the line lap joint interval to be 45 mu m, the scanning line quantity to be 10, the scanning speed to be 2mm/s, the laser pulse width to be 15ps and the repetition frequency to be 1kHz.
The beneficial effects of the invention are as follows:
(1) The invention introduces the acoustic emission detection technology into the laser internal processing process of the laser stripped ingot, establishes the relation between the acoustic emission signal characteristics 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 ingot.
(2) The method for monitoring the laser stripped ingot in real time based on the acoustic emission technology provided by the invention has the advantages that the detection energy is derived from the material, the detected material is free from stress and radiation damage, the signal is easy to understand, the signal processing is simple, and the processing process is easy to judge.
(3) The real-time monitoring method of the laser stripped ingot based on the acoustic emission technology provided by the invention is simple in field operation, can evaluate the laser stripping processing process, can monitor the laser stripping process of other transparent materials such as sapphire, gallium nitride, silicon and the like, and can monitor the laser stripping process of the monitored laser stripped object without being limited to the internal processing of the ingot.
Drawings
FIG. 1 is a schematic diagram of a laser-stripped ingot real-time monitoring system of the present invention;
FIG. 2 is a plot of average frequency versus amplitude for a sample ingot at 6.9 μJ;
FIG. 3 is a plot of average frequency versus amplitude for a sample ingot at 11.6 μJ;
FIG. 4 is a plot of average frequency versus amplitude for a sample ingot at 16.2 μJ;
FIG. 5 is a plot of count versus duration for a sample ingot at 6.9 μJ;
FIG. 6 is a plot of count versus duration for a sample ingot at 11.6 μJ;
FIG. 7 is a plot of count versus duration for a sample ingot at 16.2 μJ;
FIG. 8 is a first cross-sectional profile of the ingot sample at 6.9 μJ;
FIG. 9 is a second cross-sectional profile of the ingot sample at 11.6 μJ;
FIG. 10 is a third cross-sectional profile of the ingot sample at 16.2 μJ.
In the figure: the device comprises a laser 1, a diaphragm 2, a first reflecting mirror 3, an attenuator 4, a second reflecting mirror 5, a third reflecting mirror 6, an objective lens 7, an 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 present patent; for the purpose of better illustrating the embodiments, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the actual product dimensions; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted. The positional relationship depicted in the drawings is for illustrative purposes only and is not to be construed as limiting the present patent.
Example 1:
As shown in fig. 1, a system for implementing a laser stripped ingot real-time monitoring method is firstly built, and comprises a laser 1, a diaphragm 2, a first reflecting mirror 3, an attenuator 4, a second reflecting mirror 5, a third reflecting mirror 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 the computer 14, the emitted laser sequentially passes through the diaphragm 2, the first reflecting mirror 3, the attenuator 4, the second reflecting mirror 5, the third reflecting mirror 6 and the objective 7 to reach the upper surface of the crystal ingot sample 8 placed on the X-Y-Z three-dimensional moving platform 9, the CCD imaging system 10 illuminates and focuses the crystal ingot sample 8 on the X-Y-Z three-dimensional moving platform 9 through the third reflecting mirror 6 and the objective 7 to assist in light spot alignment 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 crystal ingot sample 8 to acquire acoustic emission signals and transmit the acoustic emission signals to the computer 14.
The embodiment also provides a real-time monitoring method for the laser stripped ingot based on the acoustic emission technology, which comprises the system, and the steps of monitoring by using the system are as follows:
S1: placing and fixing the 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 ingot sample 8 to reach the upper surface of the ingot sample 8 through refraction of a third reflector 6 and an objective lens 7 in sequence, enabling an illumination focus to appear on the upper surface of the ingot sample 8, and adjusting the position of the X-Y-Z three-dimensional moving platform 9 to enable a visual field picture of the CCD imaging system 10 to clearly observe the upper surface of the sample;
s2: setting an acoustic emission sensor 11, coating a coupling agent on the acoustic emission sensor 11, placing the acoustic emission sensor 11 at a position 4-8mm away from a region to be processed on the upper surface of the 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 on the acoustic emission sensor 11;
s3: setting processing parameters of a laser through a computer;
S4: starting the laser 1 to emit laser beams, sequentially passing through the diaphragm 2, the first reflecting mirror 3, the attenuator 4, the second reflecting mirror 5, the third reflecting mirror 6 and the objective lens 7 to reach the upper surface of the ingot sample 8 to form light spots, when the illumination focus of the CCD imaging system 10 is positioned on the upper surface of the ingot sample 8, moving 100 mu m in the Z axis direction through the X-Y-Z three-dimensional moving platform 9 to enable the light spots of the laser 1 to be focused in the ingot sample 8, and because of the self-focusing effect of the ingot sample 8, the actual focusing positions of the light spots do not coincide with the upward moving distance of the X-Y-Z three-dimensional moving platform 9, and then the light spots are actually focused at the depth of 330 mu m in the ingot sample 8;
S5: varying the laser monopulse energy of the laser 1, including three of 6.9 μj, 11.6 μj and 16.2 μj, with other laser processing parameters remaining unchanged; respectively carrying out laser surface scanning processing on three different positions inside the ingot sample 8 by using the three different energies, and moving the position 0.3mm away from a processing area after the processing of the previous surface structure is finished to process the next surface structure; simultaneously, the acoustic emission sensor 11 is utilized to synchronously collect acoustic emission signals and upload the acoustic emission signals to the computer 14 for processing and analysis to obtain an average frequency-amplitude correlation diagram and a count-duration correlation diagram, and the effect and quality of an internal modified structure during laser stripping are determined according to the change of the two correlation diagrams along with the laser single pulse energy;
S6: after the laser processing is finished, performing splitting treatment on the ingot sample 8 to obtain a corresponding cross section morphology after each laser single pulse energy is subjected to internal modification processing, wherein the cross section morphology comprises a first cross section morphology, a second cross section morphology and a third cross section morphology;
S7: performing crack analysis according to the cross section morphology corresponding to each laser single pulse energy;
As shown in fig. 8, according to the first cross-sectional morphology corresponding to the pulse energy of 6.9 μj, it was observed that the ingot 8 formed only laterally expanding cracks between the uppermost explosion points, and the cracks were complete in overlap, which is beneficial for the peeling required up and down along the lateral cracks;
As shown in fig. 9, according to the second cross-sectional morphology corresponding to the pulse energy of 11.6 μj, it is observed that the transverse crack exists between the explosion points below in addition to the transverse expansion crack formed between the explosion points at the uppermost layer of the ingot sample 8, and the crack lap joint of the transverse explosion points is incomplete;
as shown in fig. 10, according to the third cross-sectional profile corresponding to the pulse energy of 16.2 μj, it was observed that the cross section of the ingot 8 formed a double-layered transverse crack;
the uneven transverse crack surfaces of the second and third cross-sectional shapes can cause uneven stripping force during stripping and reduced flatness of the stripped surface, so that the effect on laser stripping is unfavorable;
S8: the crack analysis condition of each laser single pulse energy is respectively combined with the corresponding average frequency-amplitude correlation diagram and count-duration correlation diagram to obtain the correlation between the cross section morphology and the characteristic parameter diagram, and the correlation can be known:
when the laser single pulse energy is 6.9 mu J, the laser internal modification structure is favorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is in longitudinal scattered point distribution, as shown in fig. 2, the count-duration correlation diagram is in linear scattered point distribution, the duration distribution is below 250 mu s, as shown in fig. 5, and the acoustic emission signal distribution characteristics at the moment can be used as processing judgment favorable for laser stripping;
When the laser single pulse energy is 11.6 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is in longitudinal dense point distribution, as shown in fig. 3, the count-duration correlation diagram is in linear dense point distribution, the duration distribution is below 350 mu s, as shown in fig. 6, and the acoustic emission signal distribution characteristics at the moment can be used as processing judgment unfavorable for laser stripping;
when the laser single pulse energy is 16.2 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is in transverse dense point distribution, as shown in fig. 4, the count-duration correlation diagram is in linear dense point distribution with duration time distribution below 550 mu s, as shown in fig. 7, and the distribution characteristics of the acoustic emission signals at the moment can be used as processing judgment unfavorable for laser stripping;
S9: the correlation of the average frequency-amplitude correlation diagram, the count-duration correlation diagram and the cross section morphology and the corresponding stripping effect in the step S8 are used for monitoring the laser stripping process of the ingot in real time and pre-judging the internal processing structure.
According to the invention, firstly, focusing is carried out on a crystal ingot sample 8 through a CCD imaging system 10, then an acoustic emission sensor 11 is placed, processing parameters of a laser 1 are set, and the crystal ingot sample is aligned according to a focusing position to ensure that light spots are aligned to positions 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 a sample, so that the acoustic emission sensor 11 obtains corresponding characteristic parameter graphs (an average frequency-amplitude correlation graph and a counting-duration correlation graph) to be displayed in a computer 14, then the processed sample is subjected to splitting treatment to obtain three energy-corresponding section morphologies, crack conditions are analyzed on the section morphology of each energy, the correlation between the section morphology and the characteristic parameter graphs is obtained by combining the analysis of the section morphologies, and the distribution characteristics of acoustic emission signals are found to be capable of carrying out real-time monitoring on the processing process of laser stripping and carrying out pre-judgment on internal processing.
The acoustic emission signal in the present invention is mainly generated by physical phenomena such as melting and recondensing, plasma, etc. generated when laser acts inside the ingot 8, and by internal pressure change caused by micro-crack cracking.
The modified structure with larger variation of different shapes of processing parameters of the laser 1 and corresponding signal distribution also shows larger variation, and the characteristics can be used for prejudging the internal processing structure when the ingot is stripped by laser.
In the present embodiment, the ingot sample 8 includes a silicon carbide ingot, a silicon ingot, a sapphire ingot, or the like, and the sample to which the present embodiment is applied is specifically a silicon carbide ingot.
In this embodiment, more than three types of laser single pulse energy may be set to perform laser processing to obtain a corresponding cross-sectional morphology and a correlation diagram, and this embodiment only lists three types of energy with larger gap for representation, and does not limit this, and different laser single pulse energies may be set according to actual needs.
In this embodiment, in step S5, the obtained acoustic emission signals are uploaded to the computer 14 for processing and analysis, and the process principle of obtaining the average frequency-amplitude correlation chart and the count-duration correlation chart is well known to those skilled in the art, and the correlation chart can be formed by using commonly used chart software (for example, EXCEL), and the data of the acoustic emission signals are input into the chart software, so that the chart can be formed by making the chart according to the longitudinal and transverse 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 4k; according to the material characteristics of the ingot, the acoustic emission timing parameters adopt recommended values of nonmetallic materials: peak definition time 50 mus, strike definition time 200 mus, strike lockout time 300 mus.
In this embodiment, the acoustic emission sensor 11 is a Nano-30 single-ended resonant acoustic emission sensor, and the coupling agent is vaseline.
In this embodiment, the laser 1 is an infrared ultrafast laser, the laser wavelength is 1030nm, the pulse width is 290fs-15ps, the laser frequency range is 0.1-610kHz, and the focused spot diameter of the laser is 2 μm after the laser is focused by the objective lens 7.
In this example, the ingot 8 had dimensions of 10mm×10mm×0.5mm, and the Si surface thereof was subjected to chemical mechanical polishing treatment with a roughness of 1nm or less, and laser light was incident from the Si surface.
In this embodiment, the other laser processing parameters in step S5 are: the laser scans the single line length to be 3mm, the line lap joint interval to be 45 mu m, the scanning line quantity to be 10, the scanning speed to be 2mm/s, the laser pulse width to be 15ps and the repetition frequency to be 1kHz.
Example 2:
The present embodiment is similar to embodiment 1, except that in step S5, the pulse number of the laser 1 may be changed, and the pulse numbers n=20, 50, 100, 200, 500, 800 are set, respectively, while other processing parameters (specifically, the laser pulse width 15ps, the repetition frequency 1kHz, and the single pulse energy 19 μj) are kept unchanged. And respectively carrying out laser multi-pulse dotting processing on six areas on the sample, and simultaneously adopting an acoustic emission sensor 11 to process acoustic emission amplitude signals, waveforms and frequency spectrum signals which are synchronously collected to obtain an amplitude calendar graph, a waveform and a frequency spectrum graph, wherein the change of the amplitude calendar graph, the waveform and the frequency spectrum graph along with the number of pulses reflects the evolution process of the multi-pulse point modification processing state in the laser. And after the processing is finished, the sample is subjected to splitting treatment, and the section morphology corresponding to each pulse number is also obtained.
Under different laser pulse numbers, the amplitude of the acoustic emission signal at the moment can be proved to form a corresponding relation with the evolution process of the internal multi-pulse point modification processing state by comparing the amplitude history map with the corresponding section morphology.
When the number of pulses is within 100, the height of the modified region increases rapidly, and after the number of pulses is greater than 100, the height of the modified region rises relatively slowly until reaching the surface. The amplitude rising trend within 100 pulses is fast, and the highest amplitude is 44dB; the amplitude history is gentle after the pulse number is more than 100, and when the laser is ablated on the surface of the sample, the corresponding amplitude reaches 48dB at the maximum, and then the laser pulse continuously acts until an ablated pit is formed on the surface, the amplitude is still 48dB at the maximum, so that the amplitude signal characteristic of the acoustic emission can be used as the characterization of the internal processing evolution process of the laser.
In order to better utilize the acoustic emission signals to reflect the distinction and connection of different laser processing states, the acoustic emission signals with the pulse number within 20 and the pulse number above 500 are respectively selected to analyze the 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 mu s, and the peak value of the frequency spectrum is about 0.2 mV; when the number of pulses is 500 or more, the waveform distribution range is expanded to-25 to 25mV, the waveform oscillation time is increased to approximately 500 mu s, and the peak value of the frequency spectrum is also increased to about 1 mV. The method shows that the acoustic emission signals of the laser in different processing states have obvious differences, and proves that the processing states can be prejudged by adopting the waveform and the frequency of the acoustic emission signals.
According to the corresponding relation between the pulse number and the section morphology, the relation between the acoustic emission amplitude signal and the processing effect is analyzed by combining the amplitude signal, the waveform and the frequency spectrum characteristics, and the waveform and the frequency spectrum difference during internal or surface processing are combined, so that the acoustic emission technology can be used for monitoring the prejudgment of the processing state in the laser internal processing process.
Example 3:
The present embodiment is similar to embodiment 1, except that in step S5, the repetition frequency of the laser 1 may be changed, and the repetition frequencies f=1, 100, 200 are set, respectively, while other processing parameters (specifically, the laser pulse width 15ps, the pulse number 50, and the single pulse energy 15.2 μj) are kept unchanged. And respectively carrying out laser multi-pulse dotting processing on three areas on the sample, and simultaneously adopting an acoustic emission sensor 11 to process the acoustic emission amplitude signals and the frequency signals which are synchronously acquired to obtain the corresponding relation between the amplitude history chart and the average frequency-amplitude correlation chart and the internal point modification processing structure. And after the processing is finished, the sample is subjected to splitting treatment, and the cross section morphology corresponding to each repetition frequency is also obtained.
Under different repetition frequencies, the amplitude history chart and the average frequency-amplitude correlation chart are compared with the corresponding cross-sectional morphologies, so that three cross-sectional morphology signal points can be obtained from the chart and distributed in different areas, and the phenomenon that the signal points overlap occurs in two cross-sectional morphologies with higher repetition frequencies, namely different structures show different signal distributions, and similar structures show similar signal distributions even when laser processing parameters are different, and the clustering characteristics of acoustic emission signals are proved to be closely related to the internal modified structure.
Therefore, the analysis again proves that the clustering characteristics of the acoustic emission signals of the modified structures of different types are closely related to the internal modified structures, and the acoustic emission signals can be used for respectively classifying and characterizing the internal modified structures of different types, so that acoustic emission signal monitoring and processing structure prejudging in the laser internal processing process are realized.
It is to be understood that the above examples of the present invention are provided by way of illustration only and are not intended to limit the scope of the invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (5)
1. The real-time monitoring method for the laser stripped ingot is characterized by comprising a real-time monitoring system for the laser stripped ingot, wherein the system comprises a laser (1), a diaphragm (2), a first reflecting mirror (3), an attenuator (4), a second reflecting mirror (5), a third reflecting mirror (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 device (1) is connected with a computer (14), emitted laser sequentially passes through the diaphragm (2), the first reflecting mirror (3), the attenuator (4), the second reflecting mirror (5), the third reflecting mirror (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) carries out illumination focusing on the ingot sample piece (8) on the X-Y-Z three-dimensional moving platform (9) through the third reflecting mirror (6) and the objective lens (7) so as to assist light spot alignment of the laser device (1), the acoustic emission sensor (11) sequentially passes through the preamplifier (12) and the data acquisition card (13) to be connected with the computer (14), and the acoustic emission sensor (11) is used for being placed on the ingot sample piece (8) to acquire acoustic emission signals and is transmitted to the computer (14);
The steps of monitoring by the laser stripped ingot real-time monitoring system are as follows:
S1: placing and fixing the ingot (8) on an X-Y-Z three-dimensional moving platform (9) and focusing the illumination of a CCD imaging system (10) on the upper surface of the ingot (8);
s2: the acoustic emission sensor (11) is coated with a coupling agent and then is placed at a position 4-8mm away from the to-be-processed area on the upper surface of the crystal ingot sample piece (8);
s3: setting processing parameters of the laser (1) through a computer (14);
S4: starting a laser (1), wherein the emitted light spot focuses according to an illumination focus of a CCD imaging system (10) so as to enable the light spot to be focused in 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 inside the ingot sample piece (8) by using the plurality of different energies; simultaneously, an acoustic emission sensor (11) is utilized to synchronously collect acoustic emission signals and the acoustic emission signals are uploaded to a computer (14) for processing and analysis, so that an average frequency-amplitude correlation diagram and a count-duration correlation diagram are obtained;
S6: after the laser processing is finished, performing splitting treatment on the ingot sample piece (8) to obtain a corresponding cross 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: carrying out joint observation on crack analysis conditions of each laser single pulse energy and corresponding average frequency-amplitude correlation graphs and count-duration correlation graphs respectively to obtain correlation between the cross section morphology and the characteristic parameter graphs;
s9: the method comprises the steps of (1) carrying out real-time monitoring on the laser stripping process of an ingot and pre-judging an internal processing structure through the correlation of an average frequency-amplitude correlation diagram, a count-duration correlation diagram and a cross section morphology and the corresponding stripping effect in the step S8;
In step S5, three different laser monopulse energies are set to be 6.9 mu J, 11.6 mu J and 16.2 mu J respectively; and three different energy processes of three laser surface scanning processes to different positions inside the ingot (8) are as follows: after the processing of the previous surface structure is finished, moving the surface structure by 0.3mm from a processing area to process the next surface structure;
Other laser processing parameters in step S5 are: the laser scans the single line length to be 3mm, the line lap joint interval to be 45 mu m, the scanning line quantity to be 10, the scanning speed to be 2mm/s, the laser pulse width to be 15ps and the repetition frequency to be 1kHz;
In step S7, the process of crack analysis according to the cross-sectional morphology is as follows: according to the first section morphology corresponding to the pulse energy of 6.9 mu J, the crystal ingot sample piece (8) is observed to form transverse expansion cracks only between the uppermost explosion points, and the cracks are completely overlapped; according to the second section morphology corresponding to the pulse energy of 11.6 mu J, the transverse crack is observed to exist between the explosion points below besides the transverse expansion crack formed between the explosion points at the uppermost layer of the ingot sample piece (8), and the crack lap joint of the transverse explosion points is incomplete; according to the third cross section morphology corresponding to the pulse energy of 16.2 mu J, the cross section of the ingot sample piece (8) is observed to form double-layer transverse cracks;
in step S8, the process of obtaining the correlation between the cross-sectional morphology and the characteristic parameter map is as follows: when the laser single pulse energy is 6.9 mu J, the laser internal modification structure is favorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is longitudinally distributed along the scattered points, the count-duration correlation diagram is linearly distributed along the scattered points, the duration time is distributed below 250 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment favorable for laser stripping; when the laser single pulse energy is 11.6 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is longitudinally distributed at dense points, the count-duration correlation diagram is linearly distributed at dense points, the duration of the count-duration correlation diagram is distributed below 350 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment unfavorable for stripping of the laser; when the laser single pulse energy is 16.2 mu J, the laser internal modification structure is unfavorable for stripping, and in the acoustic emission signal characteristics corresponding to the laser single pulse energy, the average frequency-amplitude correlation diagram is in transverse dense point distribution, the count-duration correlation diagram is in linear dense point distribution with duration time distribution below 550 mu s, and the distribution characteristic of the acoustic emission signal at the moment can be used as processing judgment unfavorable for laser stripping.
2. The method for monitoring a laser lift-off ingot in real time according to claim 1, 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 100 μm in the Z-axis direction by the X-Y-Z three-dimensional moving platform (9), and the actual focusing position of the spot is not coincident 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), so that the spot is actually focused at a depth of 330 μm inside the ingot sample (8).
3. The method for monitoring the ingot by laser stripping in real time according to claim 1, wherein in the step S1, a CCD imaging system (10) is started, so that illumination light carried by the system sequentially passes through a third reflecting mirror (6) and refraction of an objective lens (7) to reach the upper surface of an ingot sample (8), and the position of an X-Y-Z three-dimensional moving platform (9) is adjusted so that a visual field picture of the CCD imaging system (10) can clearly observe the upper surface of the sample.
4. The method for monitoring a laser-stripped ingot in real time according to claim 1, wherein in step S2, the position of the acoustic emission sensor (11) is fixed by using an adhesive tape or a jig, and channel parameters for signal acquisition are set for the acoustic emission sensor (11), and the channel parameters are set as follows: the signal gain is 40dB, the acquisition threshold is 35dB, the sampling rate is 5MHz, the sampling length is 4k, the acoustic emission timing parameter adopts the recommended value of nonmetallic materials according to the material characteristics of the ingot sample piece, the peak value definition time is 50 mu s, the impact definition time is 200 mu s and the impact locking time is 300 mu s.
5. The method for monitoring a laser-stripped ingot in real time according to claim 1, wherein in step S3, the laser (1) is an infrared ultrafast laser, and the processing parameters are set as follows: the wavelength of the emitted laser is 1030nm, the pulse width is 290fs-15ps, the frequency range of the laser is 0.1-610kHz, and the diameter of a focusing spot of the laser is 2 μm after the focusing action of an objective lens (7).
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