Mechanistic Insights Into Oxidation-Regulated Material Removal of Soft-Brittle CdS in Chemical Mechanical Polishing

Abstract

Cadmium sulfide (CdS) is a typical soft and brittle semiconductor widely used in infrared detection and optoelectronic devices. However, its low hardness and high brittleness make ultra-precision machining with low damage highly challenging. Chemical mechanical polishing (CMP) effectively yields atomically smooth surfaces, yet the coupling mechanism of surface reactions and crystallographic characteristics in material removal remains unclear. In this study, hexagonal wurtzite CdS single crystals were selected as model materials, and NaClO was introduced as an oxidant. Material removal rate measurements, AFM/SEM characterization, XPS analysis, electrochemical tests, and density functional theory calculations were combined to investigate the oxidation-driven anisotropic removal mechanism. The results show that NaClO significantly alters the polishing behavior of the two polar surfaces. The S surface shows higher removal rate yet prone to polyhedral corrosion defects, while the Cd surface delivers better surface flatness. XPS, electrochemical analyses, and DFT calculations reveal that the distinct stability and solubility of oxidation products govern the different removal behaviors. The S surface undergoes continuous oxidation-dissolution reactions, while the Cd surface is removed through mechanical stripping of a chemically softened Cd(OH)2 layer. These findings provide atomic-scale insights into the synergistic effect of surface chemistry and crystal polarity during CdS CMP.