Saw Damage Gettering for Improved Multicrystalline Silicon

Martins, George; Macdonald, Phi; Burton, Toby; Wilshaw, Peter R.

doi:10.1016/j.egypro.2015.07.087

Cited by 9 publications

(12 citation statements)

References 4 publications

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“…, annealing at 850 °C is seen to be more effective than at 900 °C. One explanation proposed to account for this , is that at the higher temperature some of the saw damage is annealed away so reducing its effectiveness as a site for precipitate nucleation on cooling. An alternative explanation is that at the higher temperature some precipitates release significant quantities of slow diffusing impurities, such as titanium, which on cooling diffuse too slowly to be effectively gettering to the saw damage region.…”

Section: Resultsmentioning

confidence: 99%

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Saw Damage Gettering for industrially relevant mc‐Si feedstock

Shaw

Hamer

Collett

et al. 2017

Physica Status Solidi (a)

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The silicon photovoltaic industry is currently shifting towards lightly doped emitters. These have electrical properties that benefit solar cells, compared to the traditional heavily doped emitters. This move brings new challenges, as gettering efficiencies of impurities are lowered as the doping reduces. This is particularly problematic in multicrystalline silicon (mc-Si) since cell performance is typically boosted by the effective gettering of such impurities. In prior work, we proposed the novel gettering technique, saw damage gettering (SDG), which improved effective carrier lifetime of standard performance mc-Si red zone material. In this work, we expand the study of SDG to various types of industrially relevant mc-Si: upgraded metallurgical grade (UMG), high performance bottom red zone (HPRZ), and diamond sawn high performance (DHP). The optimal condition for SDG is found to be an annealing temperature of 850 8C. With this condition it was demonstrated that the effective carrier lifetime can be increased in all silicon types upon SDG. The largest increase was observed for HPRZ material by a factor of 10, and the largest final effective lifetime post SDG was that of UMG, with t eff ¼ 61.3 ms. SDG is a potentially viable gettering method to work in conjunction with lightly doped emitters in removing the impurities of mc-silicon feedstock and thus, improving the efficiency of the cells made therefrom.

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Section: Resultsmentioning

confidence: 99%

“…One such method has been proposed in prior work , and termed saw damage gettering (SDG). This is a simple and effective gettering method.…”

Section: Introductionmentioning

confidence: 99%

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Shaw

Hamer

Collett

et al. 2017

Physica Status Solidi (a)

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“…In particular, a high-temperature anneal 900-1100 °C in temperature and 10-30 min in length was performed prior to the PDG step. [37][38][39][40] The purpose of this step is to dissolve iron precipitates and leave a majority of iron atoms in a dissolved, mobile state, in which they can easily be gettered by the PDG. Figure 4 shows the hard core width of the QM-Si wafers after the high-temperature anneal and PDG.…”

Section: Resultsmentioning

confidence: 99%

Electronic Quality Improvement of Highly Defective Quasi‐Mono Silicon Material by Phosphorus Diffusion Gettering

Liu

Vähänissi

Laine

et al. 2017

Adv Elect Materials

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Quasi‐mono silicon (QM‐Si) attracts interest as a substrate material for silicon device processing with the promise to yield single‐crystalline silicon quality with multicrystalline silicon cost. A significant barrier to widespread implementation of QM‐Si is ingot edge‐contamination caused by the seed material and crucible walls during crystal growth. This work aims to recover the scrap material in QM‐Si manufacturing with a process easily adaptable to semiconductor device manufacturing. A phosphorus diffusion process at 870 °C for 60 min significantly improves the electronic quality of a QM‐Si wafer cut from a contaminated edge brick. The harmonic minority carrier recombination lifetime of the wafer, a key predictor of ultimate device performance, experiences a tenfold increase from 17 to 178 µs, which makes the scrap QM‐Si material usable for device fabrication. Local areas with suboptimal (<50 µs) lifetimes remaining can be further improved by a high temperature anneal before the phosphorus diffusion process.

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“…This approach, called saw damage gettering (SDG), has been recently studied at high temperatures (≥800 °C) by a group at the University of Oxford, who have demonstrated an improvement in lifetime, with the best results achieved at 850 °C followed by a relatively slow cool . However, adding another high‐temperature process step may be commercially unattractive in the context of cell production.…”

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“…It is not straightforward to compare our results to high temperature SDG experiments due to the different material types, different surface passivation schemes, and because the high temperature SDG studies used a relatively slow cool from the peak processing temperature during which impurity gettering occurs. The “standard performance bottom red zone” used in Ref.…”

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Low‐Temperature Saw Damage Gettering to Improve Minority Carrier Lifetime in Multicrystalline Silicon

Al‐Amin

Grant

Murphy

2017

Physica Rapid Research Ltrs

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The minority carrier lifetime in multicrystalline silicon − a material used in the majority of today's manufactured solar cells − is limited by defects within the material, including metallic impurities which are relatively mobile at low temperatures (≤700 °C). Addition of an optimised thermal process which can facilitate impurity diffusion to the saw damage at the wafer surfaces can result in permanent removal of the impurities when the saw damage is etched away. We demonstrate that this saw damage gettering is effective at 500 to 700 °C and, when combined with subsequent low‐temperature processing, lifetimes are improved by a factor of more than four relative to the as‐grown state. The simple method has the potential to be a low thermal budget process for the improvement of low‐lifetime “red zone” wafers.

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Saw Damage Gettering for Improved Multicrystalline Silicon

Cited by 9 publications

References 4 publications

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Electronic Quality Improvement of Highly Defective Quasi‐Mono Silicon Material by Phosphorus Diffusion Gettering

Low‐Temperature Saw Damage Gettering to Improve Minority Carrier Lifetime in Multicrystalline Silicon

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