Study on the improvement of silicon wafering using diamond wire process

Abstract

Finding a means of clean, efficient and environmentally sustainable energy is a

matter of global concern. Of the various forms of clean energy, solar energy has

matured greatly as an industry. The key component of photovoltaic cells is ultra thin

silicon (Si) wafers that are sliced from Si ingots using the multi-wire sawing

technique that uses loose abrasive slurry. However, this method has several

limitations in the form of high consumables cost and low productivity. Technological

advancements and continued research in this field has led to the development of an

innovative technique whereby diamond impregnated wires are used for sawing thus

doing away with the need for loose slurry. However, this technique also needs further

improvements for cost reduction, improved quality yield and high productivity. The

surface quality and damage are also areas of concern, which needs further study.

In this study, the author designed an experiment to investigate the interaction of

diamond with Si surface. The author used diamond tips, with included angle of 42°

and radius of 15-30μm, to perform multiple scratches on n-type single crystal Si(100)

wafers. The tips were vibrated at frequencies, 486Hz and 2kHz, to study the effect of

vibration on the scratch and wafer surface quality. In addition, the effect of varying

the cutting speed of the tool tips and effect of crystallographic orientation on the

extent of damage of the wafer surface was also examined.

The scratched wafer surfaces were analyzed under the Scanning Electron Microscope

(SEM) to study the surface morphologies of the scratches. Quantitative results of the

width and depth of scratches were obtained using the Confocal Imaging Profiler

(CIP) and finally the wafers were analyzed for possible phase transformations using

Raman Spectroscopy. It was concluded that the scratch at resonant frequency showed

maximum brittle damage while the vibration-less scratch showed dominance of

ductile damage and the width and depth of scratches increased with the increase in

cutting speed.