Optimization of polishing parameters for surface roughness and material removal in chemical mechanical polishing of hard optical materials

Abstract

In this work, a comprehensive chemo-mechanical polishing (CMP) study was conducted on two technologically important materials, the glass ceramic Zerodur® and a transparent Spinel ceramic under strictly controlled and identical process conditions. The novelty of this study lies in its mechanistic, side-by-side evaluation of two materials with fundamentally different hardness, microstructure, and chemical reactivity, enabling new insight into the governing abrasive–workpiece interactions during CMP. Systematic parametric analyses were performed to quantify the influence of pressure, relative velocity, slurry concentration, polishing time, and abrasive type (alumina vs. ceria) on both material removal rate and surface evolution. Particular attention is given to the distinct mechanical and chemical contributions of the two abrasives, revealing why ceria despite its known chemical reactivity with silicate systems performs sub-optimally on Zerodur® compared to alumina. The optimized CMP conditions yielded ultra-smooth surfaces, achieving RMS roughness values below 1 nm for Zerodur® and below 3 nm for spinel. The results establish a unified mechanistic framework for understanding and optimizing the CMP of advanced hard optical materials, and establishing a mechanistic framework that supports the optimization of CMP processes for advanced hard optical materials.