Diamond Coated Wire Cutting of Solar Si Ingots: New Insights Using Raman Microspectroscopy

Diamond embedded abrasive wire (henceforth called diamond wire) sawing process of Si is a highly efficient technique for rapid wafering of solar Si ingots. However, the root causes for cutting efficiency losses are unknown. One approach to understanding this complex process is to study 1) diamond particles on diamond coated wire (DCW) and 2) Si swarf collected during cutting process. In this thesis, we use confocal, micro Raman spectroscopy to unravel loss mechanisms of wafer sawing efficiency. In the first part, we analyze the diamond microparticles which perform the sawing. By analyzing the phase transformation and stress distribution on single diamond particle, graphitization (i.e. softening of diamond) and residual stresses are observed. By studying the individual Si particles (swarf), correlations between particle shape and phase is established. Fibrillar Si particles are found to be amorphous – indicative of a ductile cut; while spherical Si articles are crystalline – indicative of a brittle cut. This important find helps to quantify the rates of cutting efficiency by simply measuring the entire Si swarf cluster; its phase distribution and stress change, as a function of Si swarf extraction time during the cutting process