Surface characteristics and damage distributions of diamond wire sawn wafers for silicon solar cells

Bhushan Sopori; Srinivas Devayajanam; Prakash Basnyat; Bhushan Sopori; Srinivas Devayajanam; Prakash Basnyat

doi:10.3934/matersci.2016.2.669

AIMS Materials Science

2016, Volume 3, Issue 2: 669-685. doi: 10.3934/matersci.2016.2.669

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Research article Topical Sections

Surface characteristics and damage distributions of diamond wire sawn wafers for silicon solar cells

1.
National Renewable Energy Laboratory, Golden, CO 80401, USA
2.
New Jersey Institute of Technology, Newark, NJ 07102, USA

Received: 20 April 2016 Accepted: 08 June 2016 Published: 12 June 2016

This paper describes surface characteristics, in terms of its morphology, roughness and near-surface damage of Si wafers cut by diamond wire sawing (DWS) of Si ingots under different cutting conditions. Diamond wire sawn Si wafers exhibit nearly-periodic surface features of different spatial wavelengths, which correspond to kinematics of various movements during wafering, such as ingot feed, wire reciprocation, and wire snap. The surface damage occurs in the form of frozen-in dislocations, phase changes, and microcracks. The in-depth damage was determined by conventional methods such as TEM, SEM and angle-polishing/defect-etching. However, because these methods only provide local information, we have also applied a new technique that determines average damage depth over a large area. This technique uses sequential measurement of the minority carrier lifetime after etching thin layers from the surfaces. The lateral spatial damage variations, which seem to be mainly related to wire reciprocation process, were observed by photoluminescence and minority carrier lifetime mapping. Our results show a strong correlation of damage depth on the diamond grit size and wire usage.
- sawing damage,
- diamond wire sawing,
- silicon wafers
Citation: Bhushan Sopori, Srinivas Devayajanam, Prakash Basnyat. Surface characteristics and damage distributions of diamond wire sawn wafers for silicon solar cells[J]. AIMS Materials Science, 2016, 3(2): 669-685. doi: 10.3934/matersci.2016.2.669

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Abstract

This paper describes surface characteristics, in terms of its morphology, roughness and near-surface damage of Si wafers cut by diamond wire sawing (DWS) of Si ingots under different cutting conditions. Diamond wire sawn Si wafers exhibit nearly-periodic surface features of different spatial wavelengths, which correspond to kinematics of various movements during wafering, such as ingot feed, wire reciprocation, and wire snap. The surface damage occurs in the form of frozen-in dislocations, phase changes, and microcracks. The in-depth damage was determined by conventional methods such as TEM, SEM and angle-polishing/defect-etching. However, because these methods only provide local information, we have also applied a new technique that determines average damage depth over a large area. This technique uses sequential measurement of the minority carrier lifetime after etching thin layers from the surfaces. The lateral spatial damage variations, which seem to be mainly related to wire reciprocation process, were observed by photoluminescence and minority carrier lifetime mapping. Our results show a strong correlation of damage depth on the diamond grit size and wire usage.

References

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