CN102144284B - For the method and apparatus of defects detection - Google Patents
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- CN102144284B CN102144284B CN200980134896.XA CN200980134896A CN102144284B CN 102144284 B CN102144284 B CN 102144284B CN 200980134896 A CN200980134896 A CN 200980134896A CN 102144284 B CN102144284 B CN 102144284B
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- 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
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- 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
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- 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
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Abstract
The present invention proposes the finger calibration method of the multiple bypass resistance for determining solar cell or solar cell precursor.These methods relate at least one low-intensity to irradiate and are applied to battery or precursor to produce luminescence generated by light, detect the luminescence generated by light level of generation, and calculate the possible level of the bypass resistance of solar cell according to the luminescence generated by light level detected.Preferred method is applicable to on-line measurement sample during solar cell manufactures, thus can take a large amount of corrective action or remedial measure.The invention allows for the multiple method monitoring edge isolation technique in solar cell manufacture.Lock-in techniques can be adopted to filter noise from luminescence generated by light signal.
Description
Technical field
The present invention relates to the field that solar cell manufactures, more particularly, relate to defect that application photoluminescence measurement detects such as bypass and so on processed completely or the impact of solar cell that part processed.
Background technology
In the manufacture process of silicon solar cell, the battery be bypassed is the FAQs reducing average productive capacity and average production efficiency." bypass (shunt) " is the partial short-circuit of diode.Bypass occurs with local mode usually, and it is such as grown by the silicon nitride of the production period of silicon ingot or carborundum impurity and causes.These bypasses can be called " bypass that material causes ".Another bypass source is undesirable process, such as, in the silicon solar cell process of silk screen printing, when the silver of silk screen printing sintered immodestly tie through pn time undesirable sintering (firing) can bypass be caused.These bypasses can be called " bypass that process causes ".
In the industrial silicon solar cell of several types, usually observe bypass at the perimeter of battery.If emitter diffusion holds at Waffer edge, then can cause these bypasses, thus form low-resistance channel between the front-side metallization and back face metalization of finished device.Therefore, to the various different edge isolation technology of each battery applications (such as comprising edge plasma isolation, laser isolation and the one-sided etching of wet chemistry) in production, to interrupt the potential bypass channel around battery edge.Undesirable process in this edge isolation step also by making resultant battery have too low bypass resistance, even if resultant battery is bypassed.Relate to be partially formed doped region by photoetching, ink jet printing or laser doping and two kinds contact the more complicated cells concepts be sometimes arranged on same battery surface, there is the source that other potential process several produce bypass.
Previously showed the so-called predicted current voltage characteristic can applying solar cell that is that luminescence generated by light (PL) measures in large voltage range measure portion process or that processed completely.Use light source to irradiate sample with variable intensity, and use detector from illuminated side or from opposite side to detect the PL response of wafer.According to following equation, PL intensity (I
pL) can predicted voltage U be interpreted as:
Wherein C is the constant determined primarily of sample geometry (specifically thickness, superficial makings and surface reflectivity).In equation (1), e represents elementary charge, and k represents Boltzmann constant, and T represents sample temperature, C
offsetrepresent the correction coefficient of the existence for the charge carrier by diffusion-restricted.Specified intensity range scans exposure intensity and side by side measures PL signal with exposure intensity and can draw out and predict IV curve, namely as the exposure intensity of the function of the predicted voltage from PL signal acquisition.This technology can obtain the quantitative data of the electrical characteristic of the battery of relative section process, otherwise these data are merely able to could obtain after battery production technology terminates.At T.Trupke, R.A.Bardos, " the Suns-photoluminescence:Contactlessdeterminationofcurrent voltagecharacteristicsofsiliconwafers " of M.DAbbott and J.E.Cotter, Appl.Phys.Lett.87, describe in detail this " Suns-PL " technology in 093503 (2005), document content is incorporated to herein in quoted passage mode at this.But, although this process can be used for detecting the impact of the defect of such as bypass and so on, for in-service monitoring wherein output be about a battery per second manufacture of solar cells line may be too slow.
In principle, predicted current voltage measurement can also be determined according to photoconductivity or other minority carrier lifetime measurements.But in the interested voltage range (low-voltage) that great majority are used for bypass detection, these measurements are caught by minority carrier the various artefacts caused with so-called depleted region mudulation effect to be affected significantly.The final result of these artefacts is, with regard to prediction IV curve, likely very inaccurate to photoconductivity survey quantitative analysis.On the contrary, PL can not be affected by these artefacts, thus makes PL become the ideal tools obtaining little predicted voltage value.The classic predictive voltage of the silicon device that can detect with PL is in 250mV to 750mV scope.
The Suns-PL of the battery that the battery be bypassed or the part be bypassed processed is measured and is affected by the diffusion-restricted of so-called minority carrier lifetime.When there is bypass, this introduces one can to the PL signal be directly proportional to incident intensity at very little luminous intensity place and contribute.This signal carrys out C by the skew in equation (1)
offsetdescribe and be directly proportional to incident intensity.The correction of this impact is realized simply by the product deducting invariant and incident intensity from the PL intensity measured.
Its content discloses WO07/041758A1 by the PCT patent application that the cross reference exercise question be incorporated to herein be " MethodandSystemforInspectingIndirectBandgapSemiconductor Structure " and discloses a kind of form realizing the realization of photoluminescence measurement.In this case, many pixel detectors of such as CCD camera and so on are used to the luminous intensity distribution in detection sample area.The luminescent image produced can show the position of bypass, this is because the luminous intensity in the region be bypassed or around it decreases compared with the region be not bypassed.But, as at O.Breitenstein, J.Bauer, " the OntheDetectionofShuntsinSiliconSolarCellsbyPhoto-andElec troluminescenceImaging " of T.Trupke and R.A.Bardos, in Prog.Photovolt:Res.Appl.16:325-330 (2008) and at M.Kasemann, D.Grote, B.Walter, W.Kwapil, T.Trupke, Y.Augarten, R.A.Bardos, E.Pink, " the LuminescenceImagingfortheDetectionofShuntsonSiliconSolar Cells " of M.D.Abbott and W.Warta, that discusses in Prog.Photovolt:Res.Appl.16:297-305 (2008) is such, it is not always reliable that PL is imaged in display bypass position.
About any discussion of prior art never should be understood to admit that this prior art is well-known or forms a part of common practise in this field in whole specification.
Summary of the invention
The object of the invention is at least one shortcoming overcoming or revise prior art, or a kind of useful replacement scheme is provided.The object of preferred form of the present invention be to provide a kind of with shorter Measuring Time in early days processing stage reliably identify the method and apparatus of the wafer be bypassed.
According to a first aspect of the invention, providing a kind of for determining the finger calibration method of the one or more electrical quantitys in solar cell or solar cell precursor (precursor), said method comprising the steps of:
A () applies at least one low-intensity to described solar cell or solar cell precursor and irradiates, to produce photoluminescent emission from described solar cell or solar cell precursor;
B () detects the level of the described luminescence generated by light produced; And
C () applies the luminescence generated by light level that the detects index as the possible electrical quantity in described solar cell or the solar cell that produces from described solar cell precursor, the intensity that wherein each at least one described low-intensity is irradiated is less than or equal to a Sun (onesun, a dual intensity).
Preferably, at least step (a) conductor of different piece on the surface of electrical connection solar cell or solar cell precursor performs.More preferably, by solar cell or solar cell precursor being arranged on the different piece of electric connection surface on metal vacuum sucker.Alternatively, by solar cell or solar cell precursor are completely or partially immersed in conductive liquid the different piece carrying out electric connection surface.
In a preferred form, low-intensity is irradiated and is comprised predetermined modulation, and described detecting step is applied this predetermined modulation and filtered the noise in the luminescence generated by light level detected.In another preferred form, step (a) also comprises and applies predetermined electrical modulation to solar cell or solar cell precursor, and applies this electrical modulation and filter the noise in the luminescence generated by light level detected.Preferably, the filtration of noise comprises the luminescence generated by light level application locking signal treatment technology to detecting.
In a preferred form, step (c) also comprises the possible level calculating solar cell or the one or more electrical quantitys from the solar cell of solar cell precursor generation according to the luminescence generated by light level detected.Preferably, one or more electrical quantity comprises open circuit voltage.In another preferred form, step (c) also comprise with described in the luminescence generated by light level that detects carry out divided by described solar cell or solar cell precursor background doped concentration, and described one or more electrical quantity comprises short circuit current.In another preferred form, the relative photoluminescence level that step (c) also comprises different sample obtains at the same process phase measuring of the production of solar cell or solar cell precursor compares.
Described one or more electrical quantity preferably includes parallel connection or the bypass resistance of solar cell or solar cell precursor.Preferably, by performing the method on each sample of manufacture of solar cells line or on the sample of predetermined portions, wherein the overall measurement time of each sample is less than 3 seconds.In a preferred form, solar cell or solar cell precursor are the silicon solar cell processed completely or the silicon wafer partly processed.Preferably, the incident photon flux of low-intensity irradiation light is about less than 10
17cm
-2s
-1.
Preferably, the method is applied after the emitter forming step in manufacture of solar cells line.In a preferred form, perform the method when not removing any phosphorus glass layer produced in emitter forming step.Alternatively, after any phosphorus glass layer formed emitter forming step is removed at the back side at least from solar cell or solar cell precursor, perform the method, this back side is relative with the surface it being formed with emitter.Preferably, after natural oxidizing layer is removed at the back side at least from solar cell or solar cell precursor, perform the method, this back side is relative with the surface it forming emitter.
In a preferred form, the method is applied after the edge isolation step in manufacture of solar cells line.Preferably, described edge isolation step comprises edge plasma isolation, Laser edge isolation or floating (floating) edge isolation.Alternatively, apply the method during the floating edge isolation step in manufacture of solar cells line, the etching liquid wherein applied in floating edge isolation step is conduction.
Preferably, on the surface of solar cell or solar cell precursor, the method is applied in a spatially resolved manner.
Preferably, described low-intensity is irradiated and is comprised the radiation pulses that the duration is less than 3 seconds.
In a preferred form, step (c) also comprises the prediction I-V curve building solar cell or solar cell precursor.Preferably, apply multiple different low-intensity in a repetitive fashion and irradiate, build the corresponding prediction I-V curve of solar cell or solar cell precursor.
Preferably, the method is further comprising the steps of: the index that (d) applies possible electrical quantity carries out quality control, technology controlling and process or process monitor in the production process of solar cell or silicon wafer.Preferably, in manufacture of solar cells line, perform the method online, and the luminescence generated by light level detected is used for solar cell or solar cell precursor to be categorized in multiple quality category (qualitybin).
According to a second aspect of the invention, providing a kind of method of the attribute for measuring solar cell material, said method comprising the steps of:
A () irradiates described solar cell material with the irradiation that intensity is less than or equal to a Sun, to produce luminescence generated by light from described solar cell material;
B () modulates solar cell material described in the level of described irradiation or electrical modulation, with the modulation that bears results in described luminescence generated by light with predetermined modulation;
C () detects described luminescence generated by light; And
D () filters the luminescence generated by light detected based on described predetermined modulation.
Preferably, predetermined modulation is included in the modulation of preset frequency, and described filtration step to described preset frequency application lock-in techniques to filter the noise be associated with the luminescence generated by light detected.
According to a third aspect of the invention we, providing a kind of method for monitoring the edge isolation technique in manufacture of solar cells line, said method comprising the steps of: (a) applies to irradiate at the forward direction solar cell precursor of described edge isolation technique; B () monitors the luminescence generated by light sent from described solar cell precursor as described irradiation result, to obtain the first luminescence generated by light level; C () repeats step (a) and (b) after described edge isolation technique, to obtain the second luminescence generated by light level; And (d) more described first and second luminescence generated by light level, to obtain the measurement of the validity to described edge isolation technique.Preferably, the intensity of described irradiation is less than or equal to a Sun.
According to a forth aspect of the invention, providing a kind of method for monitoring the edge isolation technique in manufacture of solar cells line, said method comprising the steps of: (a) applies to irradiate to solar cell or solar cell precursor at the rear of described edge isolation technique; B () obtains the image of the luminescence generated by light sent from described solar cell or solar cell precursor as described irradiation result; And (c) relative intensity to the luminescence generated by light that the peripheral part from described solar cell or solar cell precursor sends is analyzed, to obtain the measurement of the validity to described edge isolation technique.
Preferably, the method is further comprising the steps of: this image compares to the corresponding photoluminescence image obtained before edge isolation step by (d).Preferably, the intensity of described irradiation is less than or equal to a Sun.
According to a fifth aspect of the invention, providing a kind of method of the progress for monitoring the edge isolation technique in manufacture of solar cells line, said method comprising the steps of: (a) very first time in described edge isolation technique applies to irradiate to solar cell precursor; B () monitors the luminescence generated by light sent from described solar cell precursor as described irradiation result, to obtain the first luminescence generated by light level; C () second more late time in described edge isolation technique repeats step (a) and (b), to obtain the second luminescence generated by light level for described solar cell precursor; And (d) more described first and second luminescence generated by light level.
In a preferred form, before edge isolation technique starts, perform step (a).Preferably, the intensity of described irradiation is less than or equal to a Sun.
According to a sixth aspect of the invention, provide a kind of when implementing according to of the present invention first, second, third, fourth or the 5th system of method of aspect.
In order to the object of this specification, term " on-line measurement " can represent to be measured by each wafer of manufacture of solar cells line, or takes out sample (such as, taking out in every 20 wafers) with predetermined space from production line and measure.
Accompanying drawing explanation
Basis exemplary embodiment subsequently and the description of claims by reference to the accompanying drawings, for belonging to technical staff that the invention relates to the field, benefit of the present invention and advantage will become obvious, wherein:
Fig. 1 shows the prediction IV curve for bypass diode in various degree;
Fig. 2 diagrammatically illustrates some frequent origins of the bypass in solar cell;
Fig. 3 shows the PL image of the silicon wafer of emitter diffusion, and wherein the bright area of perimeter represents the bypass that potential process causes; And
The different operating that Fig. 4, Fig. 5 and Fig. 6 diagrammatically illustrate preferred embodiment is arranged.
Embodiment
Such as Suns-PL technology carries out measuring the existence that the prediction IV curve obtained can disclose bypass to solar cell.Fig. 1 shows the figure with three simulation and forecast IV curves, one (curve 1) be there is infinitely great bypass resistance ideal battery (namely, bypass on battery performance without any impact), two (curves 2,3) be calculate for two different limited bypass resistance values, wherein the bypass resistance of curve 2 is less than the bypass resistance of curve 3.The figure shows, especially under low exposure intensity, low bypass resistance reduces diode voltage (be equivalent to low luminous signal, thus cause low-voltage), and the IV curve under large voltage is only bypassed value impact in edge.In other words, bypass is the most obvious on the impact of solar cell under low-light (level).Even if before battery is metallized, the whole predicted current voltage response under low irradiation as shown in Figure 1 also can be used for obtaining the quantitative information about bypass resistance.Therefore, Suns-PL is a kind of measure based on PL, bypass potential in its early stage announcement solar cell that can manufacture at solar cell.
Impurity is the common form causing the material of bypass in a kind of solar cell.Such as in polycrystalline silicon wafer, typical impurity comprises carborundum and silicon nitride.These impurity are generally N-shaped, and occur with the form of not only long but also narrow pin.As schematically shown in Figure 2, impurity 20 can connect front 21 and the back side 22 of the silicon wafer 23 being processed to solar cell.Fig. 2 also show the common cause of " process causes bypass " in solar cell, the side effect of emitter diffusion.Be the silicon solar cell of p-type for base stage, emitter will be N-shaped, be generally phosphorus, and for N-shaped base stage, emitter will be p-type, be generally boron.Ideally, emitter layer 24 should exist only on the front of wafer.But in the emitter formation process of typical such as thermal diffusion, diffusion zone holds, thus form doped region on the peripheral part 26 at wafer side 25 and the back side.Low resistance path should can be formed by " holding " emitter layer between the front-side metallization of finished device and back face metalization.
Fig. 3 shows and carries out irradiating from chip back surface and PL detects is launched the PL image 31 got of silicon wafer spread pole.Bright area 32 around this image border discloses the region two sides being all launched accidentally pole diffusion.Luminous intensity higher in these regions is the result of the field effect passivation on two sides, and at middle section, the irradiated back side is not passivated, thus causes low count rate (countrate).Therefore, PL imaging is the another kind of measure based on PL, bypass potential in its early stage announcement solar cell that can manufacture at solar cell.
But, importantly to recognize, the interface of shown in Fig. 2 two kind of bypass source (that is, impurity and careless emitter hold) only between p-type base stage and N-shaped emitter (or) or between base stage and impurity just becomes when connecting with metal 27 or other conductor a certain and is fully active in N-shaped battery vice versa.Such as, in the solar cell of finished silk reticulated printing, when this aluminium rear-face contact appeared on the whole back side is deposited and is then sintered.All pn knots in this process below metal or impurity are shorted, and they are only potential bypass heretofore.This has important implication for supervision bypass problem early stage during solar cell manufacture.For early stage supervision reliably, potential bypass must be shorted, or at least connects with low resistance path, detectable to make them become.Preferably, the measure based on PL of the present invention performs with the conductor different piece at the sample back side be electrically connected.In one embodiment, potential bypass is by sucking sample or being pressed into metal chuck (such as, vacuum chuck) and being activated.In an alternative embodiment, sample can be dipped into or swim on the surface of conducting liquid, or sample is inhaled or is pressed on conducting sample retainer, and has thin layer conducting liquid between sample and conducting sample retainer.
Another difficult problem that early stage bypass detects is that the thermal diffusion of emitter is easy to leave thin highly doped oxide layer from the teeth outwards.Such as, for the emitter layer of phosphorus doping, this oxide layer is so-called " phosphorus glass ".This oxide layer can be electric insulation, and the said method that this means to set up the contact between sample and solid or liquid conductor always can not set up electrical contact (thus, activate potential bypass) after and then emitter diffusion technique.In certain embodiments, after phosphorus glass or similar oxide layer are removed in the back side at least from sample, the measure based on PL of the present invention is performed.An extra difficult problem results from the following fact: natural oxidizing layer is formed after a certain time on the surface of silicon wafer, normally such as being formed formation in a few minutes after naked surface (baresurface) by etching.At least from the back side, also must remove this natural oxidizing layer, reliably to detect potential bypass.
Because diffused emitter layer holds the characteristic of Waffer edge, usually give each battery applications edge isolation technology in producing to interrupt potential bypass channel.Be called as in this technology of Laser edge isolation at one, use laser that thin groove is cut into emitter.In current manufacturing lines, this process is performed to resultant battery, but this process can be performed immediately after phosphorus glass is removed in principle.Another edge isolation technology is edge plasma isolation, and wherein plasma etch process removes emitter layer from Waffer edge.Usually this process is performed when a large amount of wafer be stacked up one by one.In another edge isolation technology, based on wet chemical etch, wafer, by floating or be supported on the surface of etching bath, make the part at the only back side and edge soak and is etched in the etch solution.This technology will be called as " floating edge isolation ".
Next, the measure based on PL of the present invention can be used for monitoring edge isolation technology, if potential bypass disappears, then this edge isolation is effective.On the other hand, with reference to the PL image shown in Fig. 3, if bright neighboring area 32 exists after edge isolation, then edge isolation may not exclusively effectively.In certain embodiments, in edge plasma isolation step or in Laser edge isolation step or the tolerance that performs after floating edge isolation step based on PL.Alternatively, the result " performing method of the present invention after above-mentioned isolation step " can compare with the corresponding result obtained before isolation step.If etching solution enough conducts electricity, then the tolerance based on PL can also be used to the progress monitoring floating edge isolation step, this is because the whole rear-face contact of etching solution and wafer.Alternatively, if wafer is such as inhaled into or is pressed in the retainer of conduction, then can be used for the progress of monitoring laser edge isolation step based on the tolerance of PL.
In another measure based on PL, by formula (1), the single luminescence under a specific shot intensity is measured and can be used for acquisition predicted voltage value.Then this predicted voltage can be used as quality factor or be used as decision criterion of next step action in production.
The conversion from luminous intensity to predicted voltage according to formula (1) needs known constant C and deviant C
offset.But for wherein measuring speed and important application on site thereof, luminous signal itself (obtaining with given experimental provision measurement) can be used as decision criterion.Such as, a specific luminous intensity values can be used as threshold reference, with by wafer or cell classification in different quality categories.That is, for assessing such as bypass or potential bypass to may the affecting of battery performance, the absolute value knowing predicted voltage is not needed.
In certain embodiments, luminous measurement can be performed when carrying out irradiating and detecting from the same side of wafer, and in other embodiments, luminous measurement can be performed when carrying out irradiating and detecting from the relative both sides of wafer.In various embodiments, can in a spatially resolved manner (such as, use the luminescence imaging of CCD camera) or with non-space resolved way (such as, using broad-area photodiode in conjunction with preamplifier) or measure luminescence by mapping.In certain embodiments, it is uniform for whole chip area irradiating.In an alternative embodiment, only there is Partial wafer illuminated, as at exercise question for " Materialordevicecharacterizationwithnon-homogeneousexcit ation " and described in the Australian Provisional Patent application No.2009902178 be incorporated herein by reference, if there is emitter, then this at least will excite whole wafer with low-light (level).
Luminous measurement can occur very fast, and exemplary Measuring Time for being less than for 2 seconds, thus can monitor each wafer by manufacture of solar cells line.This monitoring process even can occur while wafer on a moving belt movement.In this case, optics and detection system can be parallel mobile with sample.Alternatively, irradiation and detection system can be static, in this case, will measure along the line scanning of each wafer or build still image from 2-D photodetector.Alternatively, during measuring, sample can keep static, and this is suitable for regional imaging and measures.
Then, can according to threshold value predicted voltage or luminous signal by be bypassed and the wafer that is not bypassed sort out.Such as, predicted voltage can be categorized as lower than the wafer of threshold signal the wafer be bypassed lower than threshold voltage or luminous signal.Usually, under low-light (level), perform single luminescence measure, preferably incident photon flux < 3 × 10
17cm
-2s
-1(being approximately a dual intensity (Sun)), more preferably < 10
17cm
-2s
-1, this is because as shown in Figure 1 bypass on the impact of diode voltage, thus the impact on luminous signal, more obvious under low-light (level).In order to the object of this specification, 3 × 10
17cm
-2s
-1incident photon flux be considered to 1Sun.
Although it should be noted that bypass is especially the possible cause of wafer " Low threshold " under low-light (level), also there is other reasons, the low life materials of such as bulk zone.Therefore, although the measure based on PL of the present invention is designed to be mainly used to detect the impact of bypass on solar cell and solar cell precursor, be not limited thereto.
In principle, the bypass based on PL detects can be carried out in two kinds of fundamentally different modes, and these two kinds of modes are spatial discrimination mode or non-space resolved way.In both cases, use irradiation source to irradiate whole wafer or Partial wafer, and use luminescence generated by light (PL) detector to catch the luminescence sent.Described detector can be positioned on any side of wafer relative to irradiation source.Under the first sample situation shown in Fig. 4, irradiation source 40 and detector 41 are positioned on the same side of sample 42.In the second example shown in Fig. 5, irradiation source 40 is arranged on the first side of sample 42, and detector 41 is directly installed on after sample, and in this case, detector picks up most of PL and launches from region 50, wherein detector is installed in below this region 50.Alternatively, as shown in Figure 6, detector 41 is arranged on the position separated by a distance with sample 42, and this gathers the luminous signal compared with small part by causing, but from comparatively large sample area collection.
For the layout of Fig. 5, luminescence detector 41 is (such as 2 × 2cm dimensionally
2) sample 42 (usual > 10 × 10em can be less than significantly
2).Therefore, because in fact emitter to be electrically connected in battery parallel different piece (be bypassed and be not bypassed), therefore because the impact of the bypass being arranged in the region beyond the region 50 above wafer detector will make the luminous intensity on whole wafer area reduce, so advantageously perform luminous measurement with low exposure intensity.Therefore, the region be bypassed drags down from the PL intensity not being bypassed region.But, along with exposure intensity increases, the limited conductance of emitter little by little lateral isolation be bypassed and the region that is not bypassed.Because emitter is typically designed to the exposure intensity for about Sun (dual intensity) equivalent, therefore preferably under the exposure intensity being less than a Sun equivalent (that is, to be less than 3 × 10
17cm
-2s
-1incident photon flux) perform single PL and measure.
Special optical filter can be used avoid to measuring the contributive exciting light of PL signal obtained.Usually, this realizes by using the long-pass filter before transducer to carry out long-pass filtration to the luminous signal detected, this long-pass filter transmission major part luminous signal still stops exciting light.The short-pass filter that cut-off wavelength is less than long-pass filter cut-off wavelength is used to filter exciting light, to stop any long wavelength component in excitation spectrum, described excitation spectrum can be detected by described transducer after sample surfaces reflection (or being conveyed through wafer).Due to the luminous intensity several order of magnitude more weak than exciting light usually of the indirect bandgap material from such as silicon and so on, and exciting light is approximately several percentage points to tens percentage points from the reflection of silicon wafer, therefore filters needs highly effective.In the geometry shown in Fig. 5 and 6, silicon wafer itself can be used as effective long-pass filter.Such as, if use the excitation wavelength of 800nm, then for 200 μm of thick silicon wafers, the exciting light part of transmission will be less than 10
-6.No longer need further long-pass to filter in this case, but still need effectively to filter the short-pass of exciting light.
Several light source is likely for exciting, and these light sources comprise laser, light-emitting diode, Halogen lamp LED and photoflash lamp.
Non-space resolved way is measured: in certain embodiments, use a photodetector to carry out the average luminescence generated by light signal of capture space.The example that can be used for detecting the typical light electric diode launched from the PL of silicon sample is the detector be made up in conjunction with low-noise preamplifier of crystalline silicon (Si), indium gallium arsenide (InGaAs), germanium (Ge) or SiGe alloy.Other specimen materials will send the PL of different wavelength range usually, and suitable detector is known to those of ordinary skill in the art.In the embodiment adopting time resolution mode to measure, can detector be used to catch time dependent luminous intensity during irradiation light pulse and afterwards.Usually, the duration of radiation pulses be one millisecond to a few second.In an alternative embodiment, detector can be used for detecting the constant PL signal by producing with constant intensity irradiate wafer.In other embodiments, modulate irradiation with known frequency period, to perform PL ionization meter by lock-in techniques.Adopt which, the impact of the surround lighting in production environment can be reduced significantly.
Spatial discrimination mode is measured: PL imaging for luminous intensity Quick air between resolved way measure be a kind of attractive measuring technique.In this case, the luminous intensity values of each spatial discrimination part of battery in a luminescent image is measured.The local prediction diode voltage of each pixel of luminescent image can be calculated so in principle.If several PL imaging measurement adopts different exposure intensities to carry out, then can calculate the luminous intensity correlation of each detector pixel, therefore can calculate the prediction IV curve of each detector pixel.Because the impact of bypass under low predicted voltage (that is, in the low exposure intensity that PL signal is low) is the most remarkable, then may need the longer time of integration.In order to avoid the longer time of integration (thus being longer Measuring Time), the spatial resolution that combination of pixels (pixelbinning) reduces camera can be passed through.Such as, 5 × 5 pixels are synthesized a pixel and make count rate increase 25 times, but will spatial resolution be reduced.Alternatively, more highly sensitive camera can be used.
Preferably on one or two surface that emitter had been diffused or had been processed in addition sample with the processing stage that to be formed after pn ties arbitrary time or apply the above-mentioned measure based on PL afterwards.With reference to Fig. 4, Fig. 5 and Fig. 6, the illuminated surface of sample 42 does not need the surface corresponding to emitter diffusion, but can choose illuminated surface so that measure.In the battery design of such as screen printed cells and so on, non-space resolved way is measured not to be needed to occur distinguishing between other bypasses that the edge bypass of (at least before edge isolation) and such as impurity cause in almost each battery.Therefore, after edge isolation, suitably apply the bypass of non-space resolved way detect, in this case, the qualitative or quantitative bypass analysis based on PL can provide the information about other bypasses in non-optimal edge isolation or relevant sample.
Measure the PL data obtained can be used for obtaining about the quantitative information of bypass intensity or about bypass intensity is relative to the qualitative information of threshold value.In qualitative examples, do not exist from measuring the conversion to predicted voltage or any other physical parameter of the PL signal that obtains, but the luminous signal of spatial discrimination or space average itself can as quality factor.The wafer sending the PL signal more high or low than specific threshold will be classified in independent quality category.In a preferred embodiment, measure enough fast, thus to each wafer by production equipment or described measurement can be performed online to most chip yield.
From the regarding wafer that the measure based on PL of the present invention is derived, the information of bypass can cause possibility action in a large number subsequently.Such as, wafer can be removed from production line, to reprocess or to turn back to wafer supplier, or classify to carry out treatment step below to sample.In other examples, if bypass is technical process, defect causes, then can take corrective action to processing step or instrument, and if bypass is fault in material causes, then can take corrective action by material supplier.In other examples, reprocessing can be carried out to wafer and remedy to carry out bypass, or " tag ", to reduce the impact of bypass to online state-variable.
The PL signal measured in intermediate processing steps can also be used as to allow and final battery open circuit voltage V
octhe tolerance be associated.In manufacture of solar cells, this can by setting up statistical relationship to use between the PL signal and final battery data of particular process step.This information can be used for identifying the source that final battery performance is lowered fast, such as, to have occurred after which definite procedure of processing and obviously the departing from of expection statistical relationship by identifying.This statistical relationship can also be used as a kind of more effective ways of machined parameters of each procedure of processing tuning.The PL signal measured by low exposure intensity can also be used as the input parameter in manufacturing execution system (MES).
As mentioned above, luminous intensity can be understood as the measurement of cell voltage, and both is connected by equation (1).On the other hand, the luminous intensity (being called the normalized PL signal of doping) of being divided by by the background doped concentration of base material is relevant to the excess minority carrier life-span, therefore with battery short circuit electric current I
screlevant.Therefore, can spatial discrimination or the doping normalized PL signal of space average and short circuit current or maximum power point time the electric current that extracts between set up the similar correlation described in last paragraph and analytical applications.In this case, with only from Partial wafer signal compared with, the area of the luminous intensity of the wafer partly processed from whole quilt is on average preferred.
Single non-space resolved way PL measures and carries out as follows.Step 1: with given exposure intensity irradiate wafer or Partial wafer, be preferably less than or equal to 1Sun, more preferably less than 10
17cm
-2s
-1.This irradiation can be constant for steady state measurement, or can be pulse for time resolution mode is measured.Alternatively, exposure intensity can be modulated and perform PL by lock-in techniques and measure.In this case, this signal can be fully modulated or add that systematic offset forms by modulated share.Step 2: the luminous intensity (using one of above-mentioned area detecting geometry) that the area that measurement produces is average.Step 3: the luminous intensity measured and threshold luminance intensity are compared, and be categorized in classification that is that be bypassed or that be not bypassed or be categorized in better bypass classification.
Multiple non-space resolved way PL measures and can carry out with following steps.Step 1: with the duration be generally 1ms to 5s pulse or by several discrete exposure intensity sequence irradiate wafer.Step 2: measure time dependent exposure intensity and measure time dependent luminous intensity.Step 3: computational prediction IV curve as discussed previously.This needs to know calibration factor (C in equation (1)), and this calibration factor is similar for multiple samples of same type.Therefore, the multiple samples same calibration factor being used for same type only need to determine primary calibration factor, this is because only will affect accuracy a little.Alternatively, PL signal itself can be used as quality factor.Step 4: build Suns-PL curve and analyze this curve to obtain quantitative bypass resistance data.
Single spatial discrimination mode PL image measurement can carry out with the following step.Step 1: carry out PL imaging to wafer by a specific shot intensity, this specific shot intensity is preferably equal to or less than 1Sun, more preferably lower than 10
17cm
-2s
-1.Step 2: perform the analysis to average canbdle power.Step 3: the average canbdle power measured and threshold value average canbdle power are compared, and by sample classification to be bypassed or in the classification that is not bypassed.
Multiple spatial discrimination mode PL image measurement can carry out with following steps.Step 1: with the several PL image of different steady-state irradiation ionization meters, each intensity is preferably equal to or less than 1Sun, more preferably lower than 10
17cm
-2s
-1.Step 2: for each pixel, draws the exposure intensity as predicted voltage function.Step 3: for each pixel determines prediction IV curve.Step 4: according to prediction IV curve, the prediction IV curve based on spatial discrimination performs analysis of statistical data, is sorted out by wafer subsequently based on IV Dependence Results.
In a word, the measure based on PL of preferred embodiment provides a kind of for determining to be processed completely or by the existence of defect (especially bypass or potential bypass) in the solar cell partly processed or the technology of impact, described defect will reduce the performance of finished product solar cell.These methods can be applicable to emitter diffusion after the wafer in any solar cell process segment or film.Can use these methods with spatial discrimination or non-space resolved detection mode, and these methods are suitable for single intensity or are suitable for up to whole Suns-PL curve.These methods can provide the quantitative analysis of the resistance value to bypass or potential bypass, or provide qualitative analysis based on threshold value.These methods may be used for, in production, carrying out quality control, technology controlling and process and process monitor.Preferably, use these methods, PL is wherein produced by the exposure intensity being less than or equal to a Sun (oneSun, a dual intensity).
In certain embodiments, machining chain (processingtrain) application " locking " signal transacting provides the processing environment of high interference immunity.There is no locking processing, the background noise of detector may be surround lighting (if due to laser safety reason detect occur in lighttight box time, this surround lighting is minimum) and the exciting light of prior reflection and any summation coming from the PL of the radiation of sample stage and surroundings thereof.This needs the combination using precise optical filter to come exciting light and the surround lighting of filtering reflection from the PL signal of camera usually.If camera is based on silicon, then himself serve as short-pass filter.The combination of filter and the selection of camera for be manufacture the interested bandpass filters with extreme selective.
In the embodiment using locking processing, require so not strict.Described method can use other light source (such as, visible light source and non-laser light source) and not too special camera installation to realize.Also can not need optical filter, and if using visible light or non-laser light source, then not need laser safety equipment.And, can be used in the sample stage with remarkable PL radiation or rapidoprint around.In these embodiment, a key factor of open design constraint is application locking signal processing method.The example of locking signal process is known, Ke Yi
http:// en.wikipedia.org/wiki/Lock-in_amplifierfind roughly reference.
At least can use lock-in techniques in two ways.In an example embodiment, by modulated light source intensity, locking signal is superimposed on exciting light.In another example embodiment, such as, pass through via back electrical contact or electrical top contact or apply electromotive force or electric current by the two to wafer or battery, thus locking signal is added to from the PL radiation of sample as disturbance.The electromotive force applied or electric current do not need to be enough to produce electroluminescent (EC), but only need to produce the change that can observe in the PL signal measured, and this change that can observe is the signature (signature) of locking carrier signal.Rear a kind of method in these two kinds of methods is preferred, this is because the method make PL radiation (comprising any PL radiation from sample stage material in sample area) can from the noise from surround lighting and reverberation deconvolution (de-convoluted).
Another advantage using locking processing to use instant camera detector, this instant camera detector can within a second repeatedly integrated signal, thus accelerate pendulous frequency significantly, thus enhance and manufacture in application fast online the measure used based on PL.
Explanation
Unless contrary situation pointed out clearly in context, in whole specification and claim, word " comprises ", " comprising " etc. should understand with the implication comprised, instead of understand with implication that is exclusive or limit; That is, understand with the meaning of " including, but are not limited to ".
In whole specification, quoting of " embodiment " or " embodiment " is meaned that special characteristic, structure or the characteristic described relatively with this embodiment comprises at least one embodiment of the present invention.Therefore, the statement " in one embodiment " that diverse location occurs in whole specification or " in an embodiment " not necessarily refer to same embodiment completely, but have this possibility.And, can in any appropriate manner in conjunction with the special characteristic in one or more embodiment, structure or characteristic, according to of the present invention open, this is obvious to those of ordinary skill in the art.
Similarly, be to be understood that, in the above-mentioned description to exemplary embodiment of the present invention, one or more in order to what simplify the disclosure and contribute to understanding in various inventive aspect, various feature of the present invention is combined in during embodiment, accompanying drawing or an accompanying drawing describes sometimes.But disclosed method not should be understood to reflect following intention: the feature clearly recorded in each claim of aspect ratio of invention needs required for protection is many.But, as claim reflect, the aspect of invention is to be less than whole features of an above-mentioned disclosed embodiment.Therefore, claim is incorporated in this embodiment herein clearly, and wherein each claim itself is as an independent embodiment of the present invention.
And, although embodiments more described herein comprise some features included in other embodiment, do not comprise other features, the combination of the feature of different embodiment belongs to scope of the present invention, and form different embodiments, as those skilled in the art is understandable.Such as, in the claims, embodiment claimed arbitrarily can be used with any combination.
And, the combination of method key element that some embodiments are described as method at this or can be realized by the processor of computer system or other devices performing this function.Therefore, the processor of the required instruction had for performing this method or method key element constitutes the device for performing the method or method key element.And in order to realize the present invention, the key element described in apparatus embodiments is the example of the device for performing the function performed by this key element.
In the description provided herein, set forth various detail.But, should be appreciated that and can put into practice embodiments of the invention when there is no these details.In other instances, in order to not obscure the understanding to this description, known method, structure and technology is not shown specifically.
As used herein, ordinal adjectives " first ", " second ", " the 3rd " etc. is used to describe public object unless otherwise expressly stated, otherwise these ordinal adjectives only represent the different instances of referred to similar object, its intention does not represent that the object so described must be in given order, or the time is upper, spatially, in grade or in any other manner.
In the claims and specification, it is open-ended term that term " comprises ", and it represents the elements/features at least comprised subsequently, but does not get rid of other elements/features.Therefore, when with time in the claims, term " comprises " and not should be understood to be limited to after this listed device or key element or step.Such as, the scope stating " comprising the equipment of A and B " should not be limited to the equipment be only made up of key element A and B.Term " comprises ", " it comprises " or " it comprises " be also open-ended term, and it also means the elements/features at least comprised subsequently.Therefore, comprising with comprising is synonym, and implication is identical.
Similarly, it should be noted that term " couples " and not should be understood to be only limitted to direct connection when using in the claims.Term can be used " to couple " and " connection " and derivatives thereof.Should be appreciated that these terms not synonym each other.Therefore, the output that the scope of " device A is coupled to equipment B " stated should not be limited to wherein device A is connected directly to equipment or the system of the input of equipment B.There is path in its expression, this path may be the path comprising other equipment or device between the output and the input of B of A." couple " and can represent that two or more key element or direct physical connect or electrical connection, or represent that two or more key element does not directly connect each other, but still cooperation or interact with each other mutually.
Although describe the present invention with reference to some preferred embodiment of the present invention, modification of the present invention and change belong to claim thought and scope in.
Claims (29)
1., for determining a finger calibration method for the one or more electrical quantitys in solar cell or solar cell precursor, said method comprising the steps of:
A () applies at least one low-intensity to described solar cell or described solar cell precursor and irradiates, to produce charge carrier at described solar cell or described solar cell precursor;
B () detects the luminescence generated by light level produced by the radiation recombination of described charge carrier; And
C the luminescence generated by light level detected is used as described solar cell or the index from the possible electrical quantity in the solar cell of described solar cell precursor generation by (),
The intensity that wherein each at least one low-intensity described is irradiated is less than or equal to a Sun,
The electrical contact that wherein said step (a) also comprises to described solar cell or described solar cell precursor applies predetermined electrical modulation, and utilizes described electrical modulation to filter the noise in the described luminescence generated by light level detected.
2. the method for claim 1, wherein at least step (a) adopts the conductor of the different piece on the surface of the described solar cell of electrical connection or described solar cell precursor to perform.
3. method as claimed in claim 2, wherein by described solar cell or described solar cell precursor are arranged on described different piece metal vacuum sucker being electrically connected described surface.
4. method as claimed in claim 2, wherein by by described solar cell or described solar cell precursor fully or partly immerse the described different piece being electrically connected described surface in conducting liquid.
5. the method as described in any one in aforementioned claim, wherein said low-intensity is irradiated and is comprised predetermined modulation, and described detecting step utilizes described predetermined modulation to filter the noise in the described luminescence generated by light level detected.
6. method as claimed in claim 5, the step of wherein filtering noise comprises to the described luminescence generated by light level application locking signal treatment technology detected.
7. the method as described in any one in Claims 1-4, wherein said step (c) also comprises the possible level that the luminescence generated by light level detected described in basis calculates described solar cell or the described one or more electrical quantity from the solar cell of described solar cell precursor generation.
8. method as claimed in claim 7, wherein said one or more electrical quantity comprises open circuit voltage.
9. method as claimed in claim 7, wherein step (c) also comprise with described in the luminescence generated by light level that detects carry out divided by described solar cell or solar cell precursor background doped concentration, and described one or more electrical quantity comprises short circuit current.
10. the method as described in any one in power Claims 1-4, wherein said step (c) also comprises and being compared by the relative photoluminescence level measured by the different samples in the same process segment of the production to described solar cell or described solar cell precursor.
11. the method as described in any one in Claims 1-4, wherein said one or more electrical quantity comprises parallel resistance or the bypass resistance of described solar cell or described solar cell precursor.
12. methods as described in any one in Claims 1-4, wherein perform described method online to by each sample of manufacture of solar cells line or predetermined a part of sample, wherein the Measuring Time of each sample is less than 3 seconds.
13. methods as described in any one in Claims 1-4, wherein said solar cell or solar cell precursor are the silicon wafers that the silicon solar cell handled well completely or part processed.
14. methods as described in any one in Claims 1-4, the incident photon flux that wherein said low-intensity is irradiated is less than 10
17cm
-2s
-1.
15. methods as described in any one in Claims 1-4, using said method after the emitter forming step wherein in manufacture of solar cells line.
16. methods as claimed in claim 15, wherein said method is used to detect that the emitter layer that formed in described emitter forming step carries out holds.
17. method as claimed in claim 15, wherein performs described step when not removing the arbitrary phosphorus glass layer produced in described emitter forming step.
18. methods as claimed in claim 15, wherein after the arbitrary phosphorus glass layer produced is removed described emitter forming step at the back side at least from described solar cell or described solar cell precursor, perform described method, the described back side is relative with the surface it forming emitter.
19. method as claimed in claim 15, wherein after natural oxidizing layer is removed at the back side at least from described solar cell or described solar cell precursor, perform described method, the described back side is relative with the surface it forming emitter.
20. methods as claimed in claim 15, using said method after the edge isolation step wherein in manufacture of solar cells line.
21. methods as claimed in claim 20, wherein said edge isolation step comprises edge plasma isolation, Laser edge isolation or floating edge isolation.
22. method as claimed in claim 15, using said method during the floating edge isolation step wherein in manufacture of solar cells line, the etching liquid applied in wherein said floating edge isolation step is conduction.
23. methods as described in any one in Claims 1-4, wherein using said method in a spatially resolved manner on the surface of described solar cell or described solar cell precursor.
24. methods as described in any one in Claims 1-4, wherein said low-intensity is irradiated and is comprised the radiation pulses that the duration is less than 3 seconds.
25. the method as described in any one in Claims 1-4, wherein said step (c) also comprises the prediction I-V curve building described solar cell or described solar cell precursor.
26. the method for claim 1, wherein apply multiple different low-intensity in a repetitive fashion and irradiate, to build the corresponding prediction I-V curve of described solar cell or described solar cell precursor.
27. methods as described in any one in Claims 1-4, wherein said method is further comprising the steps of: the index of the possible electrical quantity described in (d) application carries out quality control in the production of solar cell or silicon wafer, technology controlling and process or process monitor.
28. methods as described in any one in Claims 1-4, perform described method wherein online in manufacture of solar cells line, and described in the luminescence generated by light level that detects be used to described solar cell or described solar cell precursor to be categorized in quality case.
The system of the method for 29. 1 kinds of realizations as described in any one in claim 1 to 28.
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| PCT/AU2009/001054 WO2010019992A1 (en) | 2008-08-19 | 2009-08-18 | Method and apparatus for defect detection |
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| WO2011123469A1 (en) * | 2010-03-29 | 2011-10-06 | Intevac, Inc. | Time resolved photoluminescence imaging systems and methods for photovoltaic cell inspection |
| CN203055871U (en) * | 2010-03-30 | 2013-07-10 | Bt成像股份有限公司 | System used for processing semiconductor samples |
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| US9246434B2 (en) | 2011-09-26 | 2016-01-26 | First Solar, Inc | System and method for estimating the short circuit current of a solar device |
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| US9885662B2 (en) * | 2012-07-06 | 2018-02-06 | Bt Imaging Pty Ltd | Methods for inspecting semiconductor wafers |
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|---|---|---|---|---|
| GB9618897D0 (en) * | 1996-09-10 | 1996-10-23 | Bio Rad Micromeasurements Ltd | Micro defects in silicon wafers |
| US6534774B2 (en) * | 2000-09-08 | 2003-03-18 | Mitsubishi Materials Silicon Corporation | Method and apparatus for evaluating the quality of a semiconductor substrate |
| US6812717B2 (en) * | 2001-03-05 | 2004-11-02 | Boxer Cross, Inc | Use of a coefficient of a power curve to evaluate a semiconductor wafer |
| GB0216815D0 (en) * | 2002-07-19 | 2002-08-28 | Aoti Operating Co Inc | Detection method and apparatus |
| US7187186B2 (en) * | 2004-03-22 | 2007-03-06 | Kla-Tencor Technologies Corp. | Methods and systems for determining one or more properties of a specimen |
| US20070000434A1 (en) * | 2005-06-30 | 2007-01-04 | Accent Optical Technologies, Inc. | Apparatuses and methods for detecting defects in semiconductor workpieces |
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2009
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- 2009-08-18 WO PCT/AU2009/001054 patent/WO2010019992A1/en active Application Filing
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| WO2010019992A1 (en) | 2010-02-25 |
| CN102144284A (en) | 2011-08-03 |
| KR20110055631A (en) | 2011-05-25 |
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