Macro and micro-nano machining mechanism for ultrasonic vibration assisted chemical mechanical polishing of sapphire

Abstract

Ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) has been proven to achieve better sapphire polishing performance. However, its polishing mechanism is still ambiguous. Few studies about pads and slurries have been reported in the field of sapphire UV-CMP. Thus the effects of the pad material and structure, abrasive material and size, and slurry pH on UV-CMP were explored in this paper. The influences of each factor on the material removal rate and surface roughness were analyzed and compared. Transmission electron microscopy images reveal the types of subsurface damage including amorphous layers, dislocations, residual stresses, stacking faults and lattice distortions. The sapphire subsurface damage layer after UV-CMP (123 nm) is much thinner and more uniform than that after CMP (199 nm). The chemical products during sapphire UV-CMP are softer than those in sapphire CMP. And the chemical compounds are detected on the sapphire surface by X-ray photoelectron spectroscopy. This article deeply explores the machining mechanism of sapphire UV-CMP and provides the important theoretical and practical guidance for sapphire ultra-precision polishing.