Study on diamond wire wear, surface quality, and subsurface damage during multi-wire slicing of c-plane sapphire wafer

Abstract

This paper aims on slicing of c-plane mono-crystalline aluminum oxide using reciprocating electroplated diamond wire in rocking mode sawing process. Effect of process parameters and wire characteristics on the surface morphology, surface roughness, and subsurface damage had been investigated. The machined wafer topography, wire wear, and subsurface damage are observed using scanning confocal microscopy (CCI), electron microscopy (SEM), and focused ion beam machining (FIB) respectively. Raman spectroscopy is used to observe the distribution of amorphous regions as a measure of dominant material removal mode. Results show that with reduced diamond size, higher wire speed, and uniform grit distribution, the wafer exhibits lower surface roughness and subsurface damage. The effect of wire speed is more pronounced than abrasive size and distribution density on surface quality. The wafers have shown lower roughness and greater evidence of ductile removal with increased wire wear. However, subsurface cracks are more and slightly deeper for wafers with increased wire wear. The wire characteristics in the form of abrasive size and distribution have dominant effect on subsurface damage. Wire wear analysis has shown that the pulled out diamond abrasive from the nickel bonding layer is the main reason for wire wear. Higher wire speed, lower ingot feed rate, and lower diamond grits size are suggested for lower subsurface damage.