Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/9501—Semiconductor wafers
  • G01N21/9505—Wafer internal defects, e.g. microcracks
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/64—Fluorescence; Phosphorescence
  • G01N21/6489—Photoluminescence of semiconductors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions

Definitions

• the present invention relates to systems and methods for monitoring laser processing steps in the manufacture of solar cells, and in particular to the use of photoluminescence imaging for process control and quality control of such steps.
• a laser beam 1 can be used to etch a trench 2 through an emitter layer 4 of a silicon wafer 6 in an edge isolation process as shown in Figure 1 , or through a thin amorphous silicon layer 8 on a glass substrate 10 as shown in Figure 2, for example to separate thin film solar cells.
• Certain high efficiency solar cell designs require holes 12 to be drilled through a wafer 6 for wrap through of an emitter layer 4 or metallization 14 as shown in Figures 3 and 4 respectively, while a laser can also be used to form local openings in a dielectric layer (e.g. silicon nitride or oxide) for improved back surface passivation. Lasers are also commonly used for spot isolation and for wafer marking and cutting.
• a dielectric layer e.g. silicon nitride or oxide
• An emitter layer e.g. an n ++ -type layer on a p-type wafer formed for example by diffusing a suitable dopant (e.g. phosphorus for n-doping) into the surface, is typically required to transport charge carriers to and into the metal finger contacts.
• a suitable dopant e.g. phosphorus for n-doping
• the emitter layer also absorbs a significant proportion of the high energy (blue) portion of the solar spectrum, causing a reduction in cell efficiency of about 2% in absolute terms (e.g. from 17% to 15%).
• this process comprises the steps of: coating the front surface of a silicon wafer 6 with one or more dielectric layers 16 that serve as a diffusion source for the emitter layer and as a metallization mask (Figure 5); heating the wafer to form a lightly doped emitter layer 4 ( Figure 6); exposing the wafer to a laser beam 1 to melt a localised portion of the silicon and the overlying dielectric layer to produce one or more regions 20 with a higher doping density than the surrounding emitter layer 4 ( Figure 7); and finally a self-aligned metallization step where metal contacts 22 are produced, e.g. by electroplating, on top of the highly-doped regions (Figure 8).
• the self- alignment occurs by virtue of the dielectric layer 16 doubling as a metallization mask, with metallization occurring only in those regions where the dielectric layer has been disrupted by the laser.
• processing steps involve the ablation or melting of material, necessitating high intensity laser beams, e.g. from Nd:YAG lasers (1064 nm) or frequency-doubled Nd:YAG lasers (532 nm) operating in continuous wave or pulsed mode.
• high intensity laser beams e.g. from Nd:YAG lasers (1064 nm) or frequency-doubled Nd:YAG lasers (532 nm) operating in continuous wave or pulsed mode.
• These processing steps have a number of complications that can compromise cell efficiency.
• the localised heating from the laser beam causes thermal stress in the surrounding silicon, possibly leading to dislocations that reduce carrier lifetime or cracks that interrupt current flow and potentially grow to cause catastrophic cell failure.
• the heating can also volatilise hydrogen in passivated samples, resulting in de-passivation of carrier recombination sites such as surfaces, grain boundaries and point defects, and furthermore the hydrogen can migrate to the boundary of the molten silicon causing micro channels that, after metallization, can result in shunts.
• Insufficient laser exposure can also cause problems such as incomplete edge isolation or, in the LDSE process, incomplete mixing of the molten silicon and the emitter dopant resulting in a mixed phase with a high concentration of recombination sites.
• these problems can be ameliorated individually, they are on occasion counter-optimised. For example the shunting problem can be reduced by driving hydrogen off locally with an initial low power laser beam pass, but this contributes to the de-passivation problem.
• the technique should be sufficiently fast to be used in-line to inspect all or a significant fraction of the precursor cells passing through a laser processing station.
• the present invention provides a method for processing a semiconductor sample, said method comprising the steps of:
• the method further comprises the step of (d) adjusting a parameter of the laser processing step based on the information.
• the parameter preferably comprises laser power, pulse repetition rate and/or scanning rate.
• the method further comprises the step of (e) adjusting the position or orientation of the sample relative to a subsequent processing station based on the information.
• the method further comprises the step of (f) determining a destination of the sample based on the information.
• the destination preferably comprises a reject bin, a high quality cell line, a standard quality cell line, or a remediation line.
• the present invention provides a method for processing a semiconductor sample, said method comprising the steps of:
• the method further comprises the step of (f) adjusting a parameter of the laser processing step based on the information.
• the parameter preferably comprises laser power, pulse repetition rate and/or scanning rate.
• the method further comprises the step of (g) adjusting the position or orientation of the sample relative to an apparatus used to perform the laser processing step based on the information.
• the defects may comprise dislocations, cracks, micro-channels, impurity-rich areas, shunts and/or areas of reduced minority carrier lifetime.
• the semiconductor sample may comprise a multicrystalline silicon wafer, a monocrystalline silicon wafer, or a thin film comprising amorphous silicon, crystalline silicon, an amorphous silicon-germanium alloy, a crystalline silicon-germanium alloy, crystalline germanium, cadmium telluride, CIGS, or a III-V semiconductor based on gallium, aluminium and/or indium arsenide.
• the laser processing step occurs during a stage in the manufacture of a solar cell, said stage comprising edge isolation, spot isolation, cell isolation, selective emitter formation, emitter wrap through, metallization wrap through, back surface passivation, laser marking or laser cutting.
• the present invention provides a method for processing a semiconductor sample, said method comprising the steps of:
• the data comprises the quantity, type and/or location of defects induced in the sample.
• the method further comprises the step of (g) adjusting a parameter of the laser processing step based on the data.
• the parameter preferably comprises laser power, pulse repetition rate and/or scanning rate.
• the method further comprises the step of (h) determining a destination of the sample based on the data.
• the destination preferably comprises a reject bin, a high quality cell line, a standard quality cell line, or a remediation line.
• sample illuminating at least said region with a predetermined illumination to produce photoluminescence from said sample in response to said illumination;
• step (c) comprises obtaining information on defects present in the sample before the laser processing step and/or defects being induced in the sample by the laser processing step.
• the method further comprises the step of (d) adjusting a parameter of the laser processing step based on the information.
• the parameter preferably comprises laser power, pulse repetition rate and/or scanning rate.
• the method further comprises the step of (e) determining, based on the information, a destination of the sample after completion of the laser processing step.
• the destination preferably comprises a reject bin, a high quality cell line, a standard quality cell line, or a remediation line.
• the methods of the invention are performed in-line on a solar cell manufacturing line.
• the present invention provides a system for processing a semiconductor sample, said system comprising a photoluminescence imaging apparatus and a laser processing station, wherein said photoluminescence imaging apparatus comprises:
• an illumination source for illuminating said sample with a predetermined illumination to produce photoluminescence from said sample in response to said illumination
• an image acquisition device for acquiring at least one image of the
• said laser processing station comprises:
• a controller for controlling said laser for controlling said laser.
• the photoluminescence imaging apparatus and the laser processing station are housed within a common laser safety enclosure.
• the controller is configured to adjust a parameter of the laser in response to the information on defects present or induced in the sample.
• system further comprises:
• a sample handling mechanism provided between the photoluminescence imaging apparatus and the laser processing station.
• the sample handling mechanism is configured to direct the sample to a reject bin in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to a remediation line in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to an alternate process line in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to adjust the position or orientation of the sample relative to the laser processing station in response to the information on defects present or induced in the sample.
• system further comprises: a transport mechanism for transporting the sample from the laser processing station to the photoluminescence imaging apparatus; and
• the sample handling mechanism is configured to direct the sample to a reject bin in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to a remediation line in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to an alternate process line in response to the information on defects present or induced in the sample.
• the photoluminescence imaging apparatus and the laser processing station are co-located.
• system further comprises a sample handling mechanism for directing the semiconductor sample to a destination after the sample exits the photoluminescence imaging apparatus and the laser processing station.
• the sample handling mechanism is configured to direct the sample to a reject bin in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to a remediation line in response to the information on defects present or induced in the sample.
• the sample handling mechanism is configured to direct the sample to an alternate process line in response to the information on defects present or induced in the sample.
• system further comprises a sample handling mechanism configured to adjust the position or orientation of the sample relative to a subsequent processing station in response to the information on defects present or induced in the sample.
• a single optical source serves as the illumination source and as the laser.
• the present invention provides a system when used to implement the method according to any one of the first to fifth aspects.
• the present invention provides a semiconductor sample when processed by the method according to any one of the first to fourth aspects, or by the system according to the fifth aspect.
• Fig. 1 shows in side view a laser edge isolation process
• Fig. 2 shows in side view the laser scribing of a trench through a thin semiconductor layer on glass
• Fig. 3 shows in side view a section of a solar cell with a wrap through emitter layer
• Fig. 4 shows in side view a section of a solar cell with a wrap through metallization path
• Fig. 5 shows in side view a phosphorus-containing dielectric layer on the surface of a boron-doped silicon wafer
• Fig. 6 shows the formation of a lightly doped emitter layer on the silicon surface by thermal treatment of the dielectric layer shown in Fig. 5 ;
• Fig. 7 shows the selective formation of a highly doped emitter region by laser exposure of the lightly doped emitter layer shown in Fig. 6;
• Fig. 8 shows a conductor track formed by metallization of the highly doped emitter region shown in Fig. 7;
• Fig. 9 shows a flowchart illustrating 'post-exposure' process monitoring methods according to certain embodiments of the invention.
• Fig. 10 shows a flowchart illustrating 'pre-exposure' process monitoring methods according to certain embodiments of the invention
• Fig. 11 shows a flowchart illustrating process monitoring methods according to certain embodiments of the invention.
• Fig. 12 shows in side view a system for monitoring a laser processing step in a solar cell manufacture line
• Fig. 13 shows a system for monitoring a laser processing step in a solar cell manufacture line according to a preferred embodiment of the invention.
• Fig. 14 shows a system for monitoring a laser processing step in a solar cell manufacture line according to another preferred embodiment of the invention.
• Photoluminescence (PL) imaging is known to be a rapid and convenient technique for characterising semiconductor samples such as silicon bricks, wafers and thin films, and in particular silicon-based solar cells both during and after manufacture.
• semiconductor samples such as silicon bricks, wafers and thin films, and in particular silicon-based solar cells both during and after manufacture.
• the PL emission from silicon samples can provide information on many material and electrical parameters of relevance to solar cell performance, including minority carrier diffusion length, minority carrier lifetime, series resistance, shunts, impurities, dislocations and cracks.
• the PL emission from silicon arises primarily from band-to-band recombination, in the wavelength range 900 to 1300 nm, although emission at longer wavelengths can also occur from defects such as dislocations.
• Suitable apparatus and methods for performing PL imaging of silicon and other semiconductor materials are described in PCT Publication No WO 2007/041758 Al entitled 'Method and System for Inspecting Indirect Bandgap Semiconductor Structure' and incorporated herein by reference.
• PL imaging of a semiconductor sample typically involves exposing a surface of the sample to an illumination chosen to produce PL (typically above band-gap light for generating band-to-band PL), acquiring or capturing an image of the PL emitted from the sample in response to the illumination, and processing the image to highlight or obtain a measure of one or more features of interest.
• a description of the imaging process may on occasion omit the illumination or optical excitation step, but it will be implicitly present in the acquisition or capture of a PL image.
• Luminescence generated from a combination of optical and electrical excitation e.g. current injection or extraction at the terminals of a solar cell, discussed for example in PCT Publication No WO 2007/128060 Al entitled 'Method and System for Testing Indirect Bandgap Semiconductor Devices Using
• Luminescence Imaging' and incorporated herein by reference, is also considered to be photoluminescence for the purposes of this specification.
• lasers can be used in a number of process stages in solar cell manufacture.
• PL imaging There are several aspects of PL imaging that make it suitable for monitoring a laser-based processing step.
• the PL signal emitted from silicon is known to be sensitive to the presence of most if not all of the types of defects likely to be caused by the laser exposure. For example dislocations act as minority carrier recombination sites, and appear as 'dark' areas in a PL image because the locally enhanced non-radiative recombination rate, equivalent to a locally reduced carrier lifetime, reduces the concentration of carriers available for radiative recombination.
• PL measurements can also be useful for detecting potential shunts, i.e. in partially processed cells before metallization. It should be noted that shunts and potential shunts can also be detected globally by their influence on the overall PL signal from a sample. PL imaging also has the ability to detect cracks in solar cells or solar cell precursors, as described for example in PCT Publication Nos WO 2009/026661 Al and WO
• a high concentration of recombination sites resulting from incomplete mixing of the molten silicon and the emitter dopant because of insufficient laser exposure in an LDSE process will be detectable from a local reduction in PL signal, for reasons explained above. Incomplete mixing may also result in a high local series resistance, detectable by methods disclosed in PCT Publication Nos WO 2007/128060 Al and WO 2009/129575 Al.
• PL imaging is used to monitor a laser processing step by inspecting samples after the laser exposure, looking for any of the above-described defects that may have been induced by the exposure. In certain embodiments this 'post-exposure' inspection is used for process control purposes.
• a PL image of a laser-processed sample is acquired in a PL imaging step 26 and analysed in an image processing step 28 to identify and assess the presence of defects in the sample.
• This image processing step may for example comprise electronic filtering, line detection algorithms or deconvolution with point spread functions that can reveal features such as dislocations and cracks more clearly.
• a parameter of the laser processing step such as laser power, pulse rate or scan speed is adjusted if required. While there is a possibility that a given defect (e.g. a crack or a low lifetime region) in a given sample may have been pre-existing, the presence of such a defect in repeated samples is a more certain indicator of a problem with the laser exposure.
• the process control step can comprise adjusting the position or orientation of the sample relative to a subsequent processing station in a solar cell manufacture line. In other embodiments the 'post-exposure' inspection is used for quality control purposes.
• a quality determination of the sample followed by some action is performed in a quality control step 31.
• severely defective samples can be transported to a reject bin to avoid wasting further resources on them, while other samples can be sent to high efficiency cell lines, standard cell lines or remediation lines depending on the quality assessment.
• a remediation line may for example be used to ameliorate defects induced by the laser processing step.
• the process control step 30 and the quality control step 31 may be viewed as alternatives, although in other embodiments both are implemented.
• PL measurements are performed after the metallization step, either additionally or alternatively to image acquisition after the laser doping step.
• luminescence can also be generated by electrical excitation if required, by connecting the contact terminals to a voltage source.
• PL imaging is used to monitor a laser processing step by inspecting samples before the laser exposure, looking for defects that may compromise the outcomes of this step. In certain embodiments this 'pre-exposure' inspection is used for process control purposes. As shown in Figure 10, a PL image of a sample prior to laser-processing is acquired in a PL imaging step 32 and analysed in an image processing step 28 to identify the presence of defects in the sample.
• a parameter of the laser processing step such as laser power, pulse rate or scan speed is adjusted if required for example to mitigate the risk of an adverse effect such as crack propagation.
• the process control step can comprise adjusting the position or orientation of the sample relative to the laser processing station, e.g. by turning or moving the sample or moving the laser beam, to avoid a defect-rich or impurity-rich region or a micro-crack.
• the 'pre-exposure' inspection is used for quality control purposes. Referring again to Figure 10, after the occurrence of any defects in a sample has been determined in the image processing step 28, a quality determination of the sample followed by some action is performed in a quality control step 31.
• PL imaging is used to monitor a laser processing step by inspecting samples both before and after the laser exposure, for example to provide more certainty that a given defect was actually caused by the laser exposure or to determine whether the laser exposure enlarged a micro-crack. Again, this inspection process can be used for quality control or process control purposes.
• PL imaging is used to monitor a laser processing step by inspecting samples during the laser exposure, looking for defects induced by the laser. In certain embodiments this inspection is used for process control purposes.
• one or more PL images of a sample are acquired during laser-processing in a PL imaging step 35 and analysed in an image processing step 28 to identify and assess the presence of defects induced in the sample.
• a parameter of the laser processing step such as laser power, pulse rate or scan speed is adjusted if required, e.g. to reduce the rate of defect formation.
• the inspection is used for quality control purposes.
• a quality determination of the sample followed by some action is performed in a quality control step 31.
• the process control step 30 and the quality control step 31 may be viewed as alternatives, although in other embodiments both are implemented.
• Performing PL imaging during a laser processing step may require some care, particularly if the laser wavelength is sufficiently short (i.e. above the band gap of the semiconductor material) to induce photoluminescence.
• the laser wavelength is sufficiently short (i.e. above the band gap of the semiconductor material) to induce photoluminescence.
• a frequency-doubled Nd:YAG laser (532 nm) could induce photoluminescence from silicon, which has a band gap of approximately 1.1 eV (-1125 nm), whereas a C0 2 laser (10.6 ⁇ ) could not.
• This potential problem can be avoided by acquiring PL images when the laser beam is off, e.g. between pulses or while the laser is being moved to another portion of the sample.
• the acquisition of PL images 'during' a laser processing step does not necessarily mean that the PL images are acquired while the laser beam is actually interacting with the sample, although this may be the case. It may also be advantageous for the PL emission to be collected from the back surface of the sample, so that the sample itself helps to shield the detector from the laser light. In any event it should be relatively simple to prevent laser light entering the camera by means of appropriate filters, and in many cases the long pass filter commonly used in PL imaging to prevent the excitation light entering the camera will suffice.
• PL images of silicon samples can be acquired and processed on a timescale of fractions of a second to 2 seconds, especially for the post-passivation samples that will usually be encountered at a laser-processing stage of a solar cell line such as edge isolation or selective emitter formation. This is because passivation significantly increases the radiative quantum efficiency, and hence the PL signal, of silicon wafers.
• This timescale is fast enough for in-line characterisation of samples on silicon solar cell manufacturing lines that currently operate with a throughput of order 1 wafer per second. Accordingly, in certain embodiments of the invention measurements are performed in an 'in-line' manner where PL images are acquired from all or a significant fraction of the samples before or after laser processing. In yet other embodiments PL images can be acquired during the laser processing.
• measurements are performed in an Off-line' manner, applicable for example to optimising the laser processing conditions or examining failure modes for process development purposes before the laser processing station is introduced into a solar cell manufacturing line, or to process monitoring/quality control purposes where selected samples are removed from a solar cell manufacturing line.
• the measurement time available in these situations is obviously much greater than in an in-line situation, enabling the use of a greater number of PL measurement and image processing techniques.
• quantitative series resistance imaging can take of order 30 seconds or longer depending on the desired spatial resolution and accuracy among other factors.
• Other lasers could also be trialled to determine whether the precise wavelength or operating mode (e.g. pulsed versus continuous wave) has a significant effect on the laser processing and possible side effects.
• a system 33 comprises a combination of a laser processing station 34 and a PL imaging apparatus 36 as shown in Figure 12.
• Suitable PL imaging apparatus are described in the above-mentioned PCT Publication No WO 2007/041758 Al, and typically comprise an excitation module 38 comprising an illumination source, a short pass filter and collimating optics, an imaging module 40 comprising focussing optics, a long pass filter and a suitable camera, and an image processor 42 for processing the PL images.
• a typical laser processing station comprises a laser 44 and a controller 46 for controlling the power, pulse rate (if applicable) and direction of the laser beam among other parameters.
• the system 33 further comprises a transport mechanism 48 such as a transport belt for transporting a sample 50 between the laser processing station and the PL imaging apparatus, and a sample handling mechanism 52 for moving or turning a sample or for directing samples to a reject bin or another process line.
• the transport mechanism operates in the direction indicated by the arrow 54 such that a sample is inspected by the PL imaging apparatus before the laser processing, while in other embodiments the transport mechanism operates in the direction indicated by the arrow 56 such that a sample is inspected by the PL imaging apparatus after laser processing.
• a PL imaging apparatus is provided before and after the laser processing station.
• the PL imaging apparatus and the laser processing station are co-located so that PL images can be acquired before, during or after a laser processing step as required, potentially improving processing speed by removing the requirement to transport a sample between separate laser processing and PL imaging stations.
• automated transport and sample handling mechanisms may not be required.
• PL imaging of silicon or other indirect bandgap semiconductors generally requires relatively high intensity illumination sources, frequently but not necessarily lasers.
• the light safety requirements for the laser processing station are therefore unlikely to be less stringent than those for the PL imaging apparatus, reducing the amount of engineering required to combine a PL imaging apparatus with a laser processing station.
• a system 33 comprising a laser processing station 34 and a PL imaging apparatus 36 is provided in a common laser safety enclosure 58 as shown in Figure 13. It will be appreciated that the enclosure will have manual or automatic doors or shutters to allow insertion or removal of samples.
• the provision of a common laser safety enclosure is a further advantage of having co-located laser processing and PL imaging stations.
• a substantial area of a sample is illuminated in a single illumination step with light suitable for exciting photoluminescence from the sample, and a PL image of the area acquired in a single exposure with an area camera such as a silicon CCD camera.
• an area camera such as a silicon CCD camera.
• a sample area can be illuminated in line-scanning fashion, i.e. line-by-line with a linear light source, say as a sample moves along a process line, and a PL image acquired line-by-line with a line camera.
• a linear light source say as a sample moves along a process line
• a PL image acquired line-by-line with a line camera.
• a PL image can also be acquired in point- wise fashion with a small area excitation beam (e.g. a focused laser beam) scanned across the sample surface, in which case a simple photo-detector can be used to detect the PL emission from each point; we refer to this situation as 'PL mapping' rather than PL imaging.
• broad area illumination allows PL images to be acquired more rapidly, while small area (high intensity) illumination generates a stronger PL signal.
• Line-scanning configurations are particularly suitable for in-line applications.
• the laser used for the laser processing step is of a suitable wavelength and intensity for generating PL from the sample, it may be possible to use a single laser for both purposes, i.e. the laser processing station and the PL imaging apparatus could share a laser source. To this end it may be advantageous to have two interchangeable sets of optics for the laser, one to provide a focused beam for the laser processing and one to provide a broad area or line illumination for the PL imaging.
• the invention has been described in terms of silicon wafer-based solar cells, but is not so limited. It could for example be applicable to other silicon-based devices or solar cells or other devices based on other indirect bandgap semiconductors such as germanium or silicon-germanium alloys or on direct bandgap semiconductors such as GaAs.
• Thin film solar cells based on a variety of semiconductor materials are also known, including amorphous silicon, crystalline silicon, amorphous silicon-germanium alloys, crystalline silicon-germanium alloys, crystalline germanium, cadmium telluride, Cu(In,Ga)Se 2 (CIGS), or III-V semiconductors based on gallium, aluminium and/or indium arsenide.
• lasers are used for cell separation, edge ablation, substrate cutting, marking sample identification, structuring the semiconductor and metal layers, and isolating poor areas of performance to reduce their impact on module efficiency, amongst other uses.
• Each of these processes can adversely affect the thin film solar cell via damage to the semiconductor, the substrate (often glass), the metal layers, or other layers.
• features detected by PL imaging prior to laser processing, during laser processing or after interactions with the laser in laser processing can lead to further site specific issues.
• PL imaging before, after or during laser processing, or some combination thereof can lead to both quality control and process control actions.

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• 2011
  • 2011-03-30 WO PCT/AU2011/000364 patent/WO2011120089A1/en active Application Filing
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