Abstract

We have investigated low-temperature (≤500 °C) gettering in combination with phosphorus diffusion gettering with a view to improving poor quality multicrystalline silicon. Low-temperature gettering applied after standard phosphorus diffusion gettering is found to provide a >40% improvement in minority carrier lifetime in samples from the top and bottom of an ingot. The best results are achieved at 300 °C with very long annealing times (>24 h). Improvements in the lifetime do not correlate with changes in interstitial iron concentration. Experiments are performed to assess whether the presence of a phosphorus-diffused emitter affects low-temperature gettering, and results from sister samples show the low-temperature gettering behavior is not affected by the existence of an emitter. Further experiments show that low-temperature gettering prior to phosphorus diffusion results in a 20% higher lifetime after phosphorus diffusion. Low-temperature gettering can, therefore, enhance lifetime even when used in conjunction with standard phosphorus diffusion gettering.

Highlights

  • M ULTICRYSTALLINE silicon contains both structural crystal defects and impurity-related defects including point-like defects and precipitates

  • We aim to investigate whether low-temperature gettering used either before or after a standard phosphorus diffusion step can result in a lifetime improvement

  • We have conducted three separate carefully designed experiments to understand the combination of low-temperature gettering with phosphorus diffusion gettering (PDG) with the aim of developing processes to improve low-lifetime M ULTICRYSTALLINE silicon (mc-Si) wafers

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Summary

Introduction

M ULTICRYSTALLINE silicon (mc-Si) contains both structural crystal defects (grain boundaries and dislocations) and impurity-related defects including point-like defects and precipitates. Impurities can interact with structural defects by segregation to their associated strain fields. Impurities in the bulk, or when segregated to or precipitated at structural defects, are often associated with recombination activity and degrade the minority carrier lifetime ( referred to as just “lifetime”).

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