CN102144284A - Method and apparatus for defect detection - Google Patents

Abstract

Methods are presented for determining an indicator of shunt resistance of a solar cell or a solar cell precursor. The methods involve applying at least one low intensity illumination to the cell or precursor to produce photoluminescence, detecting a resulting level of the photoluminescence, and calculating from the level of detected photoluminescence the likely level of shunt resistance of the solar cell. Preferred methods are applicable to in-line measurement of samples during solar cell manufacture, enabling a number of corrective or remedial actions to be taken. Methods are also presented for monitoring edge isolation processes in solar cell manufacture. Lock-in techniques can be employed to filter noise from the photoluminescence signal.

Description

The method and apparatus that is used for defects detection

Technical field

The present invention relates to the field that solar cell is made, more particularly, relate to and use photoluminescence measurement and detect defective such as bypass influence that handled fully or the solar cell that section processes is crossed.

Background technology

In the manufacture process of silicon solar cell, be the FAQs that reduces average productive capacity and average production efficiency by the battery of bypass." bypass (shunt) " is the partial short-circuit of diode.Bypass occurs with local mode usually, and it is for example caused by the silicon nitride or the growth of carborundum impurity of the production period of silicon ingot.These bypasses can be called " bypass that material causes ".Another bypass source is unfavorable processing, for example in the silicon solar cell of silk screen printing is handled, when the silver of silk screen printing unfavorable sintering (firing) when sintering passes the pn knot immodestly can cause bypass.These bypasses can be called " bypass that processing causes ".

In the industrial silicon solar cell of several types, around the edge of battery, observe bypass usually.If emitter diffusion holds at Waffer edge, then can cause these bypasses, thereby between the front-side metallization of finished product device and back face metalization, form low-resistance channel.Therefore, the various edge isolation technology of each battery applications in producing (for example comprising edge plasma isolation, laser isolation and the one-sided etching of wet chemistry) is to interrupt battery edge potential bypass channel on every side.Undesirable processing in this edge isolation step also will make the finished product battery have too low bypass resistance, even the finished product battery is by bypass.Relating to by photoetching, ink jet printing or laser doping coming locally to form doped region and two kinds of contacts and be arranged in more complicated battery notion on the same battery surface sometimes, exist several other potential processing to produce the source of bypasses.

Before shown and to have used the so-called predicted current voltage characteristic that luminescence generated by light (PL) measures measure portion solar cell that handled or that handled fully on big voltage range.Use light source to shine sample, and use detector from illuminated side or detect the PL response of wafer from opposite side with variable intensity.According to following equation, PL intensity (I _PL) can be interpreted as predicted voltage U:

$I_{\mathrm{PL}}=C\·\exp \left(\frac{\mathrm{eU}}{\mathrm{kT}}\right)+C_{\mathrm{offset}}---\left(1\right)$

Wherein C is mainly by the definite constant 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 _OffsetExpression is at the correction coefficient of the existence of the charge carrier that is subjected to diffusion-restricted.Scanning exposure intensity and side by side measure the PL signal with exposure intensity and can draw out prediction IV curve on specified intensity range is promptly as the exposure intensity of the function of the predicted voltage that obtains from the PL signal.This technology can obtain the quantitative data of the electrical characteristic of the battery that relative section handled, otherwise these data are merely able to could obtain after battery production technology finishes.At T.Trupke, R.A.Bardos, " the Suns-photoluminescence:Contactless determination of currentvoltage characteristics of silicon wafers " of M.D Abbott and J.E.Cotter, Appl.Phys.Lett.87, described this " Suns-PL " technology in 093503 (2005) in detail, document content is incorporated this paper at this in the quoted passage mode.Yet, though this process can be used for detecting the defect influence such as bypass, for in-service monitoring wherein output be about may be too slow the manufacture of solar cells line of a battery of per second.

In principle, can also determine the predicted current voltage measurement according to photoconductivity or other minority carrier lifetime measurements.Yet in great majority were used for the interested voltage range (low-voltage) of bypass detection, these measurements are caught the various artefacts that cause with so-called depleted region mudulation effect by minority carrier to be influenced significantly.The final result of these artefacts is that with regard to prediction IV curve, the analysis that photoconductivity is measured might be very inaccurate.On the contrary, PL can not influenced by these artefacts, thereby makes PL become the ideal tools that obtains little predicted voltage value.The classic predictive voltage of the detected silicon device of the enough PL of energy is in 250mV to the 750mV scope.

The Suns-PL of the battery crossed by the battery of bypass or by the section processes of bypass measured to be influenced by the diffusion-restricted of so-called minority carrier lifetime.When having bypass, this introduces a contribution can for the PL signal that is directly proportional with incident intensity at very little luminous intensity place.This signal comes C by the skew in the equation (1) _OffsetDescribe and be directly proportional with incident intensity.Realize the correction of this influence simply by the product that from the PL intensity that measures, deducts invariant and incident intensity.

Its content is incorporated this paper into by cross reference exercise question discloses a kind of form that realizes the realization of photoluminescence measurement for the open WO 07/041758A1 of the PCT patent application of " Method and System forInspecting Indirect Bandgap Semiconductor Structure ".In this case, the many pixel detectors such as the CCD camera are used to the luminous intensity distribution on the test sample zone.The luminescent image that produces can show the position of bypass, this be because by in the zone of bypass or the luminous intensity around it decrease with not compared by the zone of bypass.Yet, as at O.Breitenstein, J.Bauer, " the On the Detection of Shunts in Silicon Solar Cells byPhoto-and Electroluminescence Imaging " of T.Trupke and R.A.Bardos, among the 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 Luminescence Imaging for the Detection of Shunts onSilicon Solar Cells " of M.D.Abbott and W.Warta, that is discussed among the Prog.Photovolt:Res.Appl.16:297-305 (2008) is such, and PL is imaged on and shows that on the bypass position be not reliable always.

Any discussion of relevant prior art should be understood to never to admit that this prior art is well-known or forms a part of common practise in this field in the whole specification.

Summary of the invention

The objective of the invention is to overcome or revise at least one shortcoming of prior art, a kind of useful replacement scheme perhaps is provided.The purpose of preferred form of the present invention provides a kind ofly to be discerned by the method and apparatus of the wafer of bypass in early days the processing stage reliably with short Measuring Time.

According to a first aspect of the invention, provide a kind of method that is used for the index of the one or more electrical quantitys in definite solar cell or the solar cell precursor (precursor), said method comprising the steps of:

(a) described solar cell or solar cell precursor are applied at least one low-intensity irradiation, from described solar cell or solar cell precursor, to produce the luminescence generated by light radiation;

(b) level of the described luminescence generated by light of detection generation; And

(c) index of the possible electrical quantity in the solar cell that produces as described solar cell or from described solar cell precursor of the luminescence generated by light level that arrives of applying detection, wherein the intensity of each described at least one low-intensity irradiation is less than or equal to a Sun (one sun, a dual intensity).

Preferably, step (a) is carried out with the conductor of the different piece on the surface that is electrically connected solar cell or solar cell precursor at least.More preferably, by solar cell or solar cell precursor are installed in the different piece that is electrically connected the surface on the metal vacuum sucker.Alternatively, by solar cell or solar cell precursor are completely or partially immersed the different piece that is electrically connected the surface in the conductive liquid.

In a preferred form, the low-intensity irradiation comprises predetermined modulation, and described this predetermined modulation of detection step application is filtered the noise in the detected luminescence generated by light level.In another preferred form, step (a) also comprises to solar cell or solar cell precursor and applies predetermined electrical modulation, and uses this electrical modulation the noise in the detected luminescence generated by light level is filtered.Preferably, the filtration of noise comprises detected luminescence generated by light level application locking signal treatment technology.

In a preferred form, step (c) also comprises according to detected luminescence generated by light level calculates solar cell or the possible level of one or more electrical quantitys of the solar cell that produces from the solar cell precursor.Preferably, one or more electrical quantitys comprise open circuit voltage.In another preferred form, step (c) also comprises with the next background doped concentration divided by described solar cell or solar cell precursor of described detected luminescence generated by light level, and described one or more electrical quantity comprises short circuit current.In another preferred form, step (c) comprises that also the relative luminescence generated by light level that different samples are measured the production of solar cell or solar cell precursor same the processing stage compares.

Described one or more electrical quantity preferably includes the parallel connection or the bypass resistance of solar cell or solar cell precursor.Preferably, passing through to carry out this 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 was less than 3 seconds.In a preferred form, solar cell or solar cell precursor are the silicon wafers that the silicon solar cell handled fully or section processes are crossed.Preferably, the incident photon flux of low-intensity irradiates light is approximately less than 10 ¹⁷Cm ^-2s ^-1

Preferably, the emitter in the manufacture of solar cells line is used this method after forming step.In a preferred form, carry out this method under the situation of any phosphorus glass layer that in not removing emitter formation step, produces.Alternatively, carry out this method removing after emitter forms any phosphorus glass layer that forms the step from the back side of solar cell or solar cell precursor at least, this back side with its on be formed with the surperficial relative of emitter.Preferably, after natural oxidizing layer is removed at the back side of solar cell or solar cell precursor, carrying out this method at least, this back side with its on formation emitter surperficial relative.

In a preferred form, use this method after the edge isolation step in the manufacture of solar cells line.Preferably, described edge isolation step comprises edge plasma isolation, laser edge isolation or floating (floating) edge isolation.Alternatively, use this method during the floating edge isolation step in the manufacture of solar cells line, wherein the etching liquid of using in floating edge isolation step conducts electricity.

Preferably, on the surface of solar cell or solar cell precursor, use this method in the spatial discrimination mode.

Preferably, the irradiation of described low-intensity comprises that the duration was less than 3 seconds radiation pulses.

In a preferred form, step (c) also comprises the prediction I-V curve that makes up solar cell or solar cell precursor.Preferably, use a plurality of different low-intensity irradiations, make up the corresponding prediction I-V curve of solar cell or solar cell precursor in the mode that repeats.

Preferably, this method is further comprising the steps of: the index of (d) using possible electrical quantity is carried out quality control, technology controlling and process or technology supervision in the production process of solar cell or silicon wafer.Preferably, this method of online execution in the manufacture of solar cells line, and detected luminescence generated by light level is used for solar cell or solar cell precursor are categorized in a plurality of quality categories (quality bin).

According to a second aspect of the invention, provide a kind of method that is used to measure the attribute of solar cell material, said method comprising the steps of:

(a) described solar cell material is shone in the irradiation that is less than or equal to a Sun with intensity, to produce luminescence generated by light from described solar cell material;

(b) modulate the level or the described solar cell material of electrical modulation of described irradiation with predetermined modulation, with the modulation that in described luminescence generated by light, bears results;

(c) detect described luminescence generated by light; And

(d) based on described predetermined modulation detected luminescence generated by light is filtered.

Preferably, predetermined modulation is included in the modulation of preset frequency, and described filtration step is used lock-in techniques so that the noise that is associated with detected luminescence generated by light is filtered to described preset frequency.

According to a third aspect of the invention we, provide a kind of method that is used for monitoring the edge isolation technology of manufacture of solar cells line, said method comprising the steps of: (a) before described edge isolation technology, apply irradiation to the solar cell precursor; (b) luminescence generated by light that sends as described irradiation result and from described solar cell precursor of monitoring is to obtain the first luminescence generated by light level; (c) repeating step (a) and (b) after the described edge isolation technology is to obtain the second luminescence generated by light level; And (d) more described first and second luminescence generated by light level, to obtain measurement to the validity of described edge isolation technology.Preferably, the intensity of described irradiation is less than or equal to a Sun.

According to a forth aspect of the invention, a kind of method that is used for monitoring the edge isolation technology of manufacture of solar cells line is provided, has said method comprising the steps of: (a) after described edge isolation technology, apply irradiation to solar cell or solar cell precursor; (b) obtain as described irradiation result and the image of the luminescence generated by light that sends from described solar cell or solar cell precursor; And the relative intensity of the luminescence generated by light that (c) peripheral part from described solar cell or solar cell precursor is sent analyzes, to obtain the measurement to the validity of described edge isolation technology.

Preferably, this method is further comprising the steps of: (d) this image and the corresponding light photoluminescence image that obtained before the edge isolation step are compared.Preferably, the intensity of described irradiation is less than or equal to a Sun.

According to a fifth aspect of the invention, a kind of method of progress of the edge isolation technology that is used for monitoring the manufacture of solar cells line is provided, and said method comprising the steps of: (a) very first time in described edge isolation technology applies irradiation to the solar cell precursor; (b) luminescence generated by light that sends as described irradiation result and from described solar cell precursor of monitoring is to obtain the first luminescence generated by light level; (c) the second later time in described edge isolation technology at described solar cell precursor repeating step (a) and (b), to obtain the second luminescence generated by light level; And (d) more described first and second luminescence generated by light level.

In a preferred form, execution in step before edge isolation technology begins (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 system of the method for the 5th aspect.

For the purpose of this specification, each wafer by the manufacture of solar cells line can be represented to measure in term " on-line measurement ", perhaps takes out sample (for example, taking out in per 20 wafers) with predetermined space from production line and measure.

Description of drawings

According to subsequently the exemplary embodiment and the description of claims, for the technical staff who belongs to field involved in the present invention, benefit of the present invention and advantage will become obviously in conjunction with the accompanying drawings, wherein:

Fig. 1 shows the prediction IV curve in various degree bypass diode;

Fig. 2 has schematically shown some common sources of the bypass in the solar cell;

Fig. 3 has shown the PL image of the silicon wafer of emitter diffusion, and wherein the bright area around the edge is represented the bypass that potential processing causes; And

Fig. 4, Fig. 5 and Fig. 6 have schematically shown the different operating setting of preferred embodiment.

Embodiment

For example Suns-PL technology prediction IV curve that solar cell is measured acquisition can disclose the existence of bypass.Fig. 1 shows the figure with three simulation and forecast IV curves, one (curve 1) be have an infinitely great bypass resistance ideal battery (promptly, bypass to battery performance without any the influence), two (curves 2,3) be to calculate at 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 has reduced diode voltage (be equivalent to low luminous signal, thereby cause low-voltage), and the IV curve under the big voltage is only influenced by the bypass value in edge.In other words, bypass is the most tangible to the influence of solar cell under low-light (level).Even before battery is metallized, the whole predicted current voltage response under the low irradiation as shown in Figure 1 also can be used for obtaining the quantitative information of relevant bypass resistance.Therefore, Suns-PL is a kind of measure based on PL, and it can potential bypass in the early stage announcement solar cell that solar cell is made.

Impurity is the common form of the material that causes bypass in a kind of solar cell.For example in polycrystalline silicon wafer, typical impurity comprises carborundum and silicon nitride.These impurity are generally the n type, and occur with the form of not only long but also narrow pin.Schematically show as Fig. 2, impurity 20 can connect the front 21 and the back side 22 of the silicon wafer 23 that is processed to solar cell.Fig. 2 also shows the common cause of " processing causes bypass " in the solar cell, the side effect of emitter diffusion.For base stage is the silicon solar cell of p type, and emitter will be generally phosphorus, and for n type base stage, emitter will be the p type, be generally boron for the n type.Ideally, emitter layer 24 should exist only on the front of wafer.Yet, forming in the technology at typical emitter such as thermal diffusion, diffusion zone holds, thereby forms doped region on the peripheral part 26 at the wafer side 25 and the back side.Should " holding " emitter layer can between the front-side metallization of finished product device and back face metalization, form low resistance path.

Fig. 3 shows from chip back surface and shines the PL image of getting with the silicon wafer that is launched utmost point diffusion of PL detection 31.Bright area 32 around this image border has disclosed and all has been launched the zone that the utmost point spreads on two sides accidentally.Higher luminous intensity is the result of two field effect passivation on the side in these zones, and at middle section, the irradiated back side is not passivated, thereby causes low count rate (count rate).Therefore, the PL imaging is another kind of measure based on PL, and it can potential bypass in the early stage announcement solar cell that solar cell is made.

Yet, importantly to recognize, two kinds of bypasses sources shown in Figure 2 (that is, impurity and careless emitter hold) only just become during with metal 27 or a certain other conductor connection between p type base stage and the n type emitter (perhaps in n type battery vice versa) or the interface between base stage and impurity to be activated fully.For example, in the solar cell of finished silk reticulated printing, this aluminium back side contact that appears on the whole back side is deposited when being sintered then.All pn knots in this process below the metal or impurity are by short circuit, and they are only potential bypass heretofore.This has important implication early stage supervision bypass problem during the solar cell manufacturing.For reliable early stage the supervision, potential bypass must perhaps be connected with low resistance path at least by short circuit, so that they become is detectable.Preferably, the measure based on PL of the present invention uses the conductor that the different piece at the sample back side is electrically connected to carry out.In one embodiment, potential bypass is by sucking sample or being pressed into metal chuck (for example, vacuum chuck) and being activated.In optional embodiment, sample can be dipped into or swim on the surface of conducting liquid, perhaps sample inhale or be pressed on the conducting sample retainer, and have the thin layer conducting liquid between sample and the conducting sample retainer.

Another difficult problem that early stage bypass detects is that the thermal diffusion of emitter is easy to stay from the teeth outwards thin highly doped oxide layer.For example, for the emitter layer of phosphorus doping, this oxide layer is so-called " phosphorus glass ".This oxide layer can be an electric insulation, this means that the said method of setting up the contact between sample and solid or the liquid conductor always can not set up and electrically contact (thereby, activate potential bypass) after emitter diffusion technology and then.In certain embodiments, at least after phosphorus glass or similar oxide layer are removed in the back side of sample, carry out the measure based on PL of the present invention.An extra difficult problem results from the following fact: natural oxidizing layer forms on the surface of silicon wafer after sometime, normally forms in a few minutes afterwards for example forming naked surface (bare surface) by etching.At least from the back side, also must remove this natural oxidizing layer, to detect potential bypass reliably.

Because the diffused emitter layer holds the characteristic of Waffer edge, give each battery applications edge isolation technology in producing usually to interrupt potential bypass channel.In a this technology that is called as the laser edge isolation, use laser that thin groove is cut into emitter.In current production line, the finished product battery is carried out this processing, but can after phosphorus glass is removed, carry out this processing immediately in principle.Another edge isolation technology is that edge plasma is isolated, and wherein plasma etch process is removed emitter layer from Waffer edge.Usually under the situation of a large amount of wafers that pile up one by one, carry out this processing.In another edge isolation technology, based on wet chemical etch, wafer is by floating or be supported on the surface of etching bath, makes that only the part at the back side and edge is immersed in the etching solution etched.This technology will be called as " floating edge isolation ".

Next, the measure based on PL of the present invention can be used for monitoring the edge isolation technology that if potential bypass disappears, then this edge isolation is effective.On the other hand, with reference to PL image shown in Figure 3, if bright neighboring area 32 exists after edge isolation, then edge isolation may be not exclusively effectively.In certain embodiments, carry out tolerance in the edge plasma isolation step or in laser edge isolation step or after floating edge isolation step based on PL.Alternatively, the result who " carries out method of the present invention after above-mentioned isolation step " can compare with the result who obtained before isolation step accordingly.If etching solution enough conducts electricity, then can also be used to monitoring the progress of floating edge isolation step based on the tolerance of PL, this is because etching solution contacts with the whole back side of wafer.Alternatively, if wafer for example is 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 luminous measurement under specific shot intensity can be used for obtaining a predicted voltage value.This predicted voltage can be used as quality factor then or be used as the decision criterion of next step action in the production.

The conversion from the luminous intensity to the predicted voltage according to formula (1) needs known constant C and deviant C _OffsetYet for wherein measuring speed and important online application thereof, luminous signal itself (measuring with given experimental provision) can be used as decision criterion.For example, a specific luminous intensity values can be used as the threshold value benchmark, with wafer or cell classification in different quality categories.That is, concerning may the influencing of battery performance, do not need to know the absolute value of predicted voltage for assessment such as bypass or potential bypass.

In certain embodiments, can under the situation of shining from the same side of wafer and detecting, carry out luminous measurement, and in other embodiments, can under the situation of shining from the relative both sides of wafer and detecting, carry out luminous measurement.In each embodiment, can differentiate mode (for example, using broad-area photodiode) or measure luminous in spatial discrimination mode (for example, using the luminescence imaging of CCD camera) or with non-space by mapping in conjunction with preamplifier.In certain embodiments, irradiation is uniform on the entire wafer area.In optional embodiment, only there is the part wafer illuminated, as at exercise question for " Material ordevice characterization with non-homogeneous excitation " and incorporate into way of reference described in the Australian temporary patent application No.2009902178 of this paper, if there is emitter, then this will excite entire wafer with low-light (level) at least.

Luminous measurement can take place very fast, and exemplary Measuring Time is less than 2 seconds, thereby can monitor each wafer by the manufacture of solar cells line.This monitoring process even can when wafer moves on conveyer belt, take place.In this case, optics and detection system can move with sample is parallel.Alternatively, irradiation and detection system can be static, in this case, make up still image with measuring along the line scanning of each wafer or from the 2-D photodetector.Alternatively, sample can keep static during measuring, and this is suitable for regional imaging and measures.

Then, can according to threshold value predicted voltage or luminous signal will by bypass and do not sorted out by the wafer of bypass.For example, predicted voltage is lower than the wafer that threshold voltage or luminous signal be lower than threshold signal and can be categorized as by the wafer of bypass.Usually, under low-light (level), carry out single luminous measurement, preferably incident photon flux＜3 * 10 ¹⁷Cm ^-2s ^-1(being approximately a dual intensity (Sun)), more preferably＜10 ¹⁷Cm ^-2s ^-1, this is because bypass is to the influence of diode voltage as shown in Figure 1, thereby to the influence of luminous signal, more obvious under low-light (level).For the purpose of this specification, 3 * 10 ¹⁷Cm ^-2s ^-1The incident photon flux be considered to 1Sun.

Though should be noted that bypass especially is the possible cause of wafer " low threshold value " under low-light (level), also has other reasons, for example the low life-span material of bulk zone.Therefore, though measure based on PL of the present invention is designed to be mainly used to detect the influence of bypass to solar cell and solar cell precursor, be not limited thereto.

In principle, can carry out in two kinds of fundamentally different modes based on the bypass detection of PL, this dual mode is that spatial discrimination mode or non-space are differentiated mode.In both cases, use irradiation source to shine entire wafer or part wafer, and use luminescence generated by light (PL) detector to catch send luminous.Described detector can be positioned on any side of wafer with respect to irradiation source.Under first sample situation shown in Figure 4, irradiation source 40 and detector 41 are positioned on the same side of sample 42.In second example shown in Figure 5, irradiation source 40 is arranged on first side of sample 42, and detector 41 is directly installed on the sample back, and in this case, detector picks up most of PL emission from zone 50, and wherein detector is installed in this 50 belows, zone.Alternatively, as shown in Figure 6, detector 41 is installed in the position separated by a distance with sample 42, and this will cause gathering the luminous signal than small part, but from gathering than the large sample area.

For the layout of Fig. 5, luminescence detector 41 is (2 * 2cm for example dimensionally ²) can be (common＞10 * 10em less than sample 42 significantly ²).Therefore, since emitter in fact be electrically connected in the battery parallel different piece (by bypass and not by bypass), therefore will make the luminous intensity on the entire wafer zone reduce owing to be arranged in the influence of the bypass in the zone beyond the zone 50 of wafer detector top, so advantageously carry out luminous measurement with low exposure intensity.Therefore, by the zone of bypass from not dragged down by the PL intensity of by-pass area.Yet, along with exposure intensity increases, the having of emitter ration the power supply lead lateral isolation little by little by bypass and not by the zone of bypass.Because emitter is typically designed to exposure intensity at an about Sun (dual intensity) equivalent, therefore preferably under exposure intensity less than a Sun equivalent (that is, with less than 3 * 10 ¹⁷Cm ^-2s ^-1The incident photon flux) carry out single PL and measure.

Can use special-purpose optical filter to avoid the contributive exciting light of PL signal to measuring.Usually, this long-pass filter by using the transducer front carries out long-pass to detected luminous signal and filters and realize that but this long-pass filter transmits most of luminous signal stops exciting light.Cut-off wavelength is used to exciting light is filtered less than the short-pass filter of long-pass filter cut-off wavelength, stopping any long wave component in the excitation spectrum, described excitation spectrum from after the sample surfaces reflection (perhaps wafer is passed through in transmission) can by described sensor to.Because usually than several magnitude a little less than the exciting light, and exciting light is approximately several percentage points to tens percentage points from the reflection of silicon wafer from the luminous intensity of the indirect bandgap material such as silicon, therefore filter need highly effective.In the geometry shown in Fig. 5 and 6, silicon wafer itself can be used as effective long-pass filter.For example, if use the excitation wavelength of 800nm, then for the thick silicon wafer of 200 μ m, the exciting light of transmission part will be less than 10 ^-6No longer need further long-pass to filter in this case, yet still need effectively the short-pass of exciting light to be filtered.

Several light sources might be used to excite, and these light sources comprise laser, light-emitting diode, Halogen lamp LED and photoflash lamp.

Non-space resolution mode is measured: in certain embodiments, use a photodetector to come the average luminescence generated by light signal of capture space.The example that can be used for detecting from the typical light electric diode of the PL emission of silicon sample is the detector of being made in conjunction with low-noise preamplifier by 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 that adopts the time resolution mode to measure, can and use detector to catch time dependent luminous intensity afterwards at the irradiates light impulse duration.Usually, the duration of radiation pulses be one millisecond to several seconds.In optional embodiment, detector can be used for detecting the constant PL signal by producing with the constant intensity irradiate wafer.In other embodiments, with known frequency period ground modulation irradiation, to carry out the PL ionization meter by lock-in techniques.Adopt this mode, can reduce the influence of the surround lighting in the production environment significantly.

The spatial discrimination mode is measured: the PL imaging is a kind of attractive measuring technique for the quick spatial discrimination mode measurement of luminous intensity.In this case, measure the luminous intensity values of each the spatial discrimination part of battery in a luminescent image.Can calculate each local prediction of pixels diode voltage of luminescent image so in principle.If several PL imaging measurements are to adopt 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 influence of bypass is the most remarkable under low predicted voltage (that is, in the low low exposure intensity of PL signal), then may need the long time of integration.For fear of the long time of integration (thereby being long Measuring Time), can reduce the spatial resolution of camera by combination of pixels (pixel binning).For example, make count rate increase 25 times the synthetic pixel of 5 * 5 pixels, but will reduce spatial resolution.Alternatively, can use more highly sensitive camera.

Be preferably in that emitter has been spread or one or two surface of being processed into sample in addition with form arbitrary after pn knot when processing stage or use above-mentioned measure afterwards based on PL.With reference to Fig. 4, Fig. 5 and Fig. 6, the illuminated surface of sample 42 need be corresponding to the surface of emitter diffusion, but can choose illuminated surface so that measure.In the battery design such as the silk screen printing battery, non-space resolution mode is measured not and need be distinguished between other bypasses that the edge bypass that almost all occurs (at least before the edge isolation) in each battery and for example impurity cause.Therefore, after edge isolation, suitably use non-space and differentiate mode bypass detection, in this case, can provide the information of other bypasses in relevant non-best edge isolation or the relevant sample based on the qualitative or quantitative bypass analysis of PL.

The PL data that measure can be used for obtaining the quantitative information of relevant bypass intensity or the relevant bypass intensity qualitative information with respect to threshold value.In qualitative embodiment, do not have conversion, but the luminous signal of spatial discrimination or space average itself can be used as quality factor from the PL signal that measures to predicted voltage or any other physical parameter.The wafer that sends the PL signal high or lower than specific threshold value will be classified in the independent quality category.In a preferred embodiment, measure enough fast, thereby can be to each wafer of passing through production equipment or to the described measurement of the online execution of most chip yield.

The information of bypass can cause may moving in a large number subsequently from the relevant wafer that the measure based on PL of the present invention is derived.For example, can remove wafer,, perhaps sample be classified to carry out the treatment step of back to reprocess or to turn back to wafer supplier from production line.In other examples, defective causes if bypass is technical process, then can take corrective action to processing step or instrument, and if bypass is a fault in material causes, then can take corrective action by material supplier.In other examples, can handle again to carry out bypass wafer and remedy, " tag " perhaps for online state-variable, to reduce the influence of bypass.

Can also be at the PL signal that intermediate processing steps measures as allowing and final battery open circuit voltage V _OcThe tolerance that is associated.In manufacture of solar cells, this can use by set up statistical relationship between the PL of particular process step signal and final battery data.This information can be used for the source that the final battery performance of quick identification is lowered, and has for example occurred after which definite procedure of processing and obviously the departing from of expection statistical relationship by discerning.This statistical relationship can also be used as a kind of more effective ways of machined parameters of tuning each procedure of processing.The PL signal that measures with low exposure intensity can also be used as the input parameter in the manufacturing execution system (MES).

As mentioned above, luminous intensity can be understood as the measurement of cell voltage, and these two is connected by equation (1).On the other hand, the luminous intensity (being called the normalized PL signal that mixes) of being divided by by the background doped concentration of base material is relevant with the excess minority carrier life-span, therefore with the battery short circuit electric current I _ScRelevant.Therefore, can the normalized PL signal of doping spatial discrimination or space average, and the electric current that extracts when short circuit current or maximum power point between set up similar correlation and the analytical applications described in the last paragraph.In this case, and only compare from the signal of part wafer, the area of the luminous intensity of the wafer of partly processing from whole quilt on average is preferred.

Single non-space is differentiated mode PL and is measured following carrying out.Step 1:, preferably be less than or equal to 1Sun, more preferably less than 10 with given exposure intensity irradiate wafer or part wafer ¹⁷Cm ^-2s ^-1This irradiation can be constant for steady state measurement, perhaps can be pulse for the time resolution mode is measured.Alternatively, can modulate exposure intensity and carry out PL by lock-in techniques and measure.In this case, this signal can be modulated fully or be added that by modulated share systematic offset forms.Step 2: measure the average luminous intensity (using above-mentioned area to detect one of geometry) of area that is produced.Step 3: luminous intensity and the threshold value luminous intensity that measures compared, and be categorized into by bypass or not by in the classification of bypass or be categorized in the better bypass classification.

A plurality of non-spaces are differentiated mode PL and are measured and can carry out with following steps.Step 1: be generally the pulse of 1ms to 5s or with several discrete exposure intensity sequence irradiate wafer with the duration.Step 2: measure time dependent exposure intensity and measure time dependent luminous intensity.Step 3: calculating prediction IV curve as discussed previously.This need know calibration factor (C in the equation (1)), and this calibration factor is similar for a plurality of samples of same type.Therefore, only need to determine the primary calibration factor, this is will only influence accuracy a little because same calibration factor is used for a plurality of samples of same type.Alternatively, PL signal itself can be used as quality factor.Step 4: make up the 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: with a specific shot intensity wafer is carried out the PL imaging, this specific shot intensity preferably is equal to or less than 1Sun, more preferably is lower than 10 ¹⁷Cm ^-2s ^-1Step 2: carry out analysis to average canbdle power.Step 3: average canbdle power and the threshold value average canbdle power that measures compared, and with sample classification to by bypass or not by in the classification of bypass.

A plurality of spatial discrimination mode PL image measurements can carry out with following steps.Step 1: measure several PL images with different stable state exposure intensities, each intensity preferably is equal to or less than 1Sun, more preferably is lower than 10 ¹⁷Cm ^-2s ^-1Step 2:, draw exposure intensity as the predicted voltage function at each pixel.Step 3: for each pixel is determined prediction IV curve.Step 4: according to prediction IV curve, carry out analysis of statistical data, based on IV curve result wafer is sorted out subsequently based on the prediction IV curve of spatial discrimination.

In a word, the measure based on PL of preferred embodiment provides a kind of and has been used for determining that described defective will reduce the finished product Solar cell performance by the existence of the defective of the solar cell of processing fully or partly being processed (especially bypass or potential bypass) or the technology of influence.These methods can be applicable to the wafer or the film in any solar cell process segment after the emitter diffusion.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 to the resistance value of bypass or potential bypass, perhaps provide qualitative analysis based on threshold value.These methods can be used for producing, and carry out quality control, technology controlling and process and technology and monitor.Preferably, use these methods, PL is wherein produced by the exposure intensity that is less than or equal to a Sun (one Sun, a dual intensity).

In certain embodiments, machining chain (processing train) is used the processing environment that " locking " signal processing provides high anti-interference.There is not locking processing, the background noise of detector may be the exciting light of surround lighting (if owing to the laser safety reason detects when occurring in lighttight box, this surround lighting minimum) and prior reflection and anyly come from sample stage and around the summation of the PL of the radiation of thing.This needs to use the combination of precise optical filter to come the 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 the short-pass filter.The combination of filter and the selection of camera at be to make the interested extremely optionally bandpass filters that has.

In the embodiment that uses locking processing, require so not strict.Described method can use other light source (for example, visible light source and non-laser light source) and not too special-purpose camera installation to realize.Also can not need optical filter, and if using visible light or non-laser light source, then do not need laser safety equipment.And, can use in sample stage or rapidoprint on every side with remarkable PL radiation.A key factor of open design constraint is to use the locking signal processing method in these optional embodiment.The example that locking signal is handled is known, can 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 the exciting light.In another example embodiment, for example by electrically contacting via the back or the top electrically contacts or apply electromotive force or electric current for wafer or battery by the two, thereby locking signal is added to from the PL radiation of sample as disturbance.Electromotive force that is applied or electric current do not need to be enough to produce electroluminescent (EC), but only need produce the variation that can observe in the PL signal that measures, and this variation that can observe is the signature (signature) of locking carrier signal.Back a kind of method in these two kinds of methods is preferred, and this is because this method makes that PL radiation (comprising in the sample area any PL radiation from the sample stage material) can be from from deconvolution (de-convoluted) surround lighting and the catoptrical noise.

Using another advantage of locking processing is to use the instant camera detector, this instant camera detector can be in a second integrated signal repeatedly, thereby accelerate significantly to measure number of times, thereby strengthened the measure that in quick online manufacturing is used, uses based on PL.

Explanation

Unless opposite situation pointed out clearly in context, in whole specification and claim, word " comprises ", " comprising " etc. should understand with the implication that comprises, rather than understand with implication exclusive or limit; That is to say, understand with the meaning of " including, but are not limited to ".

In the whole specification quoting of " embodiment " or " embodiment " meaned that special characteristic, structure or the characteristic described relatively with this embodiment comprise at least one embodiment of the present invention.Therefore, diverse location occurs in whole specification statement " in one embodiment " or " in an embodiment " not necessarily refer to same embodiment fully, but this possibility is arranged.And, can be in any appropriate manner in conjunction with the special characteristic among 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 above-mentioned description to exemplary embodiment of the present invention, in order to simplify the disclosure and to help to understand one or more in the various inventive aspects, various features of the present invention are combined in during an embodiment, accompanying drawing or accompanying drawing describe sometimes.Yet disclosed method not should be understood to reflect following intention: clearly the feature of record is many in each claim of the aspect ratio of invention needs required for protection.But, reflect that as claim the aspect of invention is the whole features less than 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, though embodiment more described herein comprise some included among other embodiment features, do not comprise other features, the combination of the feature of different embodiment belongs to scope of the present invention, and form different embodiment, as the those skilled in the art is understandable.For example, in the claims, can use claimed arbitrarily embodiment with any combination.

And some embodiment are described as method or can be by the processor of computer system or carry out the combination of the method key element that other devices of this function realize at this.Therefore, have the processor that must instruct that is used to carry out this method or method key element and constituted the device that is used to carry out this method or method key element.And in order to realize the present invention, the key element described in the apparatus embodiments is the example that is used to carry out the device of the performed function of this key element.

In the description that provides herein, various details have been set forth.Yet should be appreciated that not to have putting into practice embodiments of the invention under the situation of these details.In other examples,, be not shown specifically known method, structure and technology in order not obscure understanding to this description.

As used herein, unless adjective " first ", " second ", " the 3rd " wait and describe public object in proper order to spell out use in addition, otherwise the different instances of the similar object that refers to only represented in these order adjectives, its intention does not represent that the object of so describing must be in given order, perhaps the time go up, on the space, on the grade or in any other mode.

In claim and specification, it is open-ended term that term " comprises ", and its expression comprises elements/features subsequently at least, but does not get rid of other elements/features.Therefore, when with in the claims the time, term " comprises " and not should be understood to be limited to after this listed device or key element or step.For example, the scope of statement " equipment that comprises A and B " should not be limited to the equipment of only being made up of key element A and B.Term " comprises ", " it comprises " or " it comprises " also be open-ended term, and it also means the elements/features that comprises at least subsequently.Therefore, comprise that with comprising be synonym, and implication is identical.

Similarly, should be noted that term " couples " and not should be understood to only limit to direct connection when using in the claims.Can use term " to couple " and " connection " and derivatives thereof.Should be appreciated that these terms synonym not each other.Therefore, the scope of statement " device A is coupled to equipment B " should not be limited to equipment or the system that the wherein output of device A is connected directly to the input of equipment B.It is illustrated between the input of the output of A and B and has the path, and this path may be the path that comprises other equipment or device." couple " and can represent that two or more key elements or direct physical connect or electrical connection, represent that perhaps two or more key elements directly do not connect each other, but still cooperation or interact with each other mutually.

Though described the present invention with reference to some preferred embodiment of the present invention, modification of the present invention and variation belong in the thought and scope of claim.

Claims (39)

1. method that is used for determining the index of the one or more electrical quantitys in solar cell or the solar cell precursor said method comprising the steps of:

(a) apply at least one low-intensity irradiation to described solar cell or described solar cell precursor, to produce the luminescence generated by light radiation from described solar cell or described solar cell precursor;

(b) detect the luminescence generated by light level that produces; And

(c) index of possible the electrical quantity in the solar cell that detected luminescence generated by light level is produced as described solar cell or from described solar cell precursor, wherein each described at least one low-intensity intensity of shining is less than or equal to a Sun.

2. the method for claim 1, wherein step (a) adopts the conductor of the different piece on the surface that is electrically connected described solar cell or described solar cell precursor to carry out at least.

3. method as claimed in claim 2 is wherein by being installed in the described different piece that is electrically connected described surface on the metal vacuum sucker with described solar cell or described solar cell precursor.

4. method as claimed in claim 2 is wherein by fully or partly immersing the described different piece that is electrically connected described surface in the conducting liquid with described solar cell or described solar cell precursor.

5. any described method in the claim as described above, wherein said low-intensity irradiation comprises predetermined modulation, and described detection step utilizes described predetermined modulation to come the noise in the described detected luminescence generated by light level is filtered.

6. as any described method in the claim 1 to 4, wherein said step (a) also comprises to described solar cell or described solar cell precursor and applies predetermined electrical modulation, and utilizes described electrical modulation to come the noise in the described detected luminescence generated by light level is filtered.

7. as claim 5 or the described method of claim 6, the wherein said step that noise is filtered comprises to described detected luminescence generated by light level application locking signal treatment technology.

8. any described method in the claim as described above, wherein said step (c) also comprise according to described detected luminescence generated by light level calculates described solar cell or the possible level of described one or more electrical quantitys of the solar cell that produces from described solar cell precursor.

9. method as claimed in claim 8, wherein said one or more electrical quantitys comprise open circuit voltage.

10. method as claimed in claim 8, wherein step (c) also comprises with the next background doped concentration divided by described solar cell or solar cell precursor of described detected luminescence generated by light level, and described one or more electrical quantity comprises short circuit current.

11. as any described method of power in the claim 1 to 7, wherein said step (c) also comprises the measured relative luminescence generated by light level of different samples to same process segment of the production of described solar cell or described solar cell precursor is compared.

12. any described method in the claim as described above, wherein said one or more electrical quantitys comprise the parallel resistance or the bypass resistance of described solar cell or described solar cell precursor.

13. any described method in the claim as described above, wherein to by each sample of manufacture of solar cells line or the predetermined described method of the online execution of a part of sample, wherein the overall measurement time of each sample was less than 3 seconds.

14. any described method in the claim as described above, wherein said solar cell or solar cell precursor are the silicon wafers that the silicon solar cell handled well fully or section processes are crossed.

15. any described method in the claim as described above, the incident photon flux of wherein said low-intensity irradiation is less than about 10 ¹⁷Cm ^-2s ^-1

16. any described method in the claim as described above, wherein the emitter in the manufacture of solar cells line forms using said method after the step.

17. method as claimed in claim 16 is wherein carried out described step under the situation of the arbitrary phosphorus glass layer that is produced in not removing described emitter formation step.

18. method as claimed in claim 16, wherein carry out described method after forming the arbitrary phosphorus glass layer that is produced the step removing described emitter at least from the back side of described solar cell or described solar cell precursor, the described back side with its on formation emitter surperficial relative.

19. as any described method in the claim 16 to 18, wherein after natural oxidizing layer is removed at the back side of described solar cell or described solar cell precursor, carrying out described method at least, the described back side with its on formation emitter surperficial relative.

20. as any described method in the claim 16 to 19, using said method after the edge isolation step in the manufacture of solar cells line wherein.

21. method as claimed in claim 20, wherein said edge isolation step comprise edge plasma isolation, laser edge isolation or floating edge isolation.

22. as any described method in the claim 16 to 19, using said method during the floating edge isolation step in the manufacture of solar cells line wherein, the etching liquid of using in the wherein said floating edge isolation step conducts electricity.

23. any described method in the claim as described above, wherein on the surface of described solar cell or described solar cell precursor with spatial discrimination mode using said method.

24. any described method in the claim as described above, wherein said low-intensity irradiation comprise that the duration was less than 3 seconds radiation pulses.

25. any described method in the claim as described above, wherein said step (c) also comprise the prediction I-V curve that makes up described solar cell or described solar cell precursor.

26. the method for claim 1 is wherein used a plurality of different low-intensity irradiations in the mode that repeats, to make up the corresponding prediction I-V curve of described solar cell or described solar cell precursor.

27. any described method in the claim as described above, wherein said method is further comprising the steps of: (d) use described index quality control, technology controlling and process or the technology of carrying out in the production of solar cell or silicon wafer that may electrical quantity and monitor.

28. any described method in the claim as described above, the wherein described method of online execution in the manufacture of solar cells line, and described detected luminescence generated by light level is used to described solar cell or described solar cell precursor are categorized in the quality category.

29. the system of any one the described method in realization such as the claim 1 to 28.

30. a method that is used to measure the attribute of solar cell material said method comprising the steps of:

(a) irradiation that is less than or equal to a Sun with intensity is shone described solar cell material, to produce luminescence generated by light from described solar cell material;

(b) with predetermined modulation the level of described irradiation is modulated or described solar cell material is carried out electrical modulation, with the modulation that in described luminescence generated by light, bears results;

(c) detect described luminescence generated by light; And

(d) based on described predetermined modulation detected luminescence generated by light is filtered.

31. method as claimed in claim 30, wherein said predetermined modulation comprises the modulation of carrying out with preset frequency, and described filtration step is used lock-in techniques so that the noise that is associated with detected luminescence generated by light is filtered to described preset frequency.

32. the system of a realization such as claim 30 or the described method of claim 31.

33. a method that is used for monitoring the edge isolation technology of manufacture of solar cells line said method comprising the steps of: (a) before described edge isolation technology, apply irradiation to the solar cell precursor; (b) detect as the result of described irradiation and the luminescence generated by light that sends from described solar cell precursor, to obtain the first luminescence generated by light level; (c) repeating step (a) and (b) after the described edge isolation step is to obtain the second luminescence generated by light level; And (d) the relatively first luminescence generated by light level and the second luminescence generated by light level, with measuring of the validity that obtains described edge isolation technology.

34. a method that is used for monitoring the edge isolation technology of manufacture of solar cells line said method comprising the steps of: (a) after described edge isolation step, apply irradiation to solar cell or solar cell precursor; (b) obtain as the result of described irradiation and the image of the luminescence generated by light that sends from described solar cell or solar cell precursor; And the relative intensity of (c) analyzing the luminescence generated by light that sends from the peripheral part of described solar cell or solar cell precursor, with measuring of the validity that obtains described edge isolation technology.

35. method as claimed in claim 34, wherein said method is further comprising the steps of:

(d) described image and the corresponding light photoluminescence image that obtained before described edge isolation step are compared.

36. the method for the progress of an edge isolation technology that is used for monitoring the manufacture of solar cells line, said method comprising the steps of: (a) very first time in described edge isolation technology applies irradiation to the solar cell precursor; (b) detect as the result of described irradiation and the luminescence generated by light that sends from described solar cell precursor, to obtain the first luminescence generated by light level; (c) second time afterwards of described edge isolation technology to described solar cell precursor repeating step (a) and (b), to obtain the second luminescence generated by light level; And (d) the described first luminescence generated by light level and the second luminescence generated by light level are compared.

37. method as claimed in claim 36, wherein execution in step (a) before described edge isolation technology begins.

38. as any described method in the claim 33 to 37, the intensity of wherein said irradiation is less than or equal to a Sun.

39. the system of any described method in realization such as the claim 33 to 38.

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