Chemical Mechanical Polishing Optimization for 4H-SiC

Scratch free surfaces are required for substrates used in epitaxial growth. Silicon carbide SiC is a substrate material that is used in the epitaxial growth of SiC, GaN, and InGaN electronic devices. Preliminary chemical mechanical polishing CMP studies of 1 38 4H-SiC wafers were performed in an attempt to identify the polishing parameter values that result in a maximum material removal rate and thus reduce substrate polishing time. Previous studies reported increased material removal rates associated with increasing polishing temperature, slurry pH, pressure, and polishing pad speed. In the current study, the effects of temperature, slurry pH, polishing pressure, and polishing pad speed were examined independently while keeping other polishing parameters constant. Material removal rates were determined using pre and post-polish wafer mass measurements. Photographs at specific wafer locations were obtained before and after each polishing period and compared to calculated removal rates. The current study indicated that different temperatures affect the removal rate by changing pad fiber dynamic shear modulus and not by altering the chemical reaction rate between the polishing slurry and wafer surface atoms. Also, in contradiction to other studies, a decrease in material removal was observed for increasing slurry pH levels. Increased applied pressure resulted in higher removal rates and unwanted polishing pad damage. Higher pad rotational speeds produced non-linear increases in material removal rates and appeared to have the greatest impact on material removal rates. High pressures and rotational speeds introduced variability and randomness in the calculated removal rates.