Use of Multifunctional Carboxylic Acids and Hydrogen Peroxide To Improve Surface Quality and Minimize Phosphine Evolution During Chemical Mechanical Polishing of Indium Phosphide Surfaces

During the chemical mechanical polishing (CMP) of an indium phosphide buffer layer for the fabrication of InGaAs n -channels in CMOS devices, there is interest in controlled removal of In and P atoms from the surface and avoidance of the generation of toxic phosphine (PH 3 ) gas. We report InP removal rates and phosphine generation during InP CMP in hydrogen peroxide based silica particle dispersions in the presence and absence of three different multifunctional chelating carboxylic acids, namely oxalic acid, tartaric acid, and citric acid. The presence of these acids in the polishing slurry resulted in highly smooth surfaces (about 0.1 nm RMS surface roughness) with good InP removal rates (about 400 nm min –1 ) and very low phosphine generation (<15 ppb). The optimized slurry compositions are reported herein. We use chemical dissolution measurements, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements to discuss the InP removal rate and phosphine generation data and to propose InP removal and phosphine generation mechanisms. Thermodynamic calculations of the Gibbs free energy of reaction are used to validate the proposed reactions.