Chemical Mechanical Polishing Slurries for Chemically Vapor-Deposited Diamond Films

Abstract

The objective of this study is to investigate slurries for chemical mechanical polishing (CMP) of chemically vapor-deposited (CVD) diamond films based on the principle of thermokinetics combined with physical and chemical properties. The study uses the mechanical work, surface energy and oxidability of a slurry with diamond carbon as the main physical-chemical indicators in selecting the slurries. The study indentifies 10 CMP slurries of different oxidants, such as potassium ferrate, potassium permanganate, chromium trioxide and potassium dichromate, for CVD diamond film polishing. Prior to a CMP process, prepolishing with a boron carbide plate is performed to prepare a CVD diamond film with acceptable surface finish and flatness. After polishing with the CMP process a CVD diamond film is examined with optical microscopy, surface profilometry, atomic force microscopy and X-ray photoelectron spectroscopy for information on surface finish and quality, material removal and mechanisms. The study demonstrates that among the ten CMP slurries, the one with potassium ferrate as an oxidant provides the highest material removal rate of 0.055 mg/hour, and the best surface finish (Ra = 0.187 nm) and surface quality (no surface scratches nor pits), which is followed by potassium permanganate. It then discusses how mechanical stress may promote the chemical oxidation of an oxidant with diamond by forming “C-O” and “C=O” on diamond surface. The study concludes that chemical mechanical polishing is effective for CVD diamond films.