Etch rate and surface morphology of plasma etched glass and glass-ceramic substrates

Micromachined transparent components are of interest for optical MEMS and miniaturized biological systems. The glass-ceramic GC6 developed by Corning is optically transparent, has a softening point in excess of 900 °C, and a thermal expansion coefficient matched to silicon. These properties make it useful for the construction of devices that combine thin film silicon electronics with MEMS systems. Both the precursor (‘green’) glass and the glass-ceramic etch at a similar rate, about 1/3 to 1/4 of that of SiO2 dry etched under identical conditions, indicating that chemistry rather than microstructure controls the etch rate. The cleaning steps used to clean the glass precursor profoundly influence the degree of surface roughness that develops during plasma etching. In glass-ceramics, however, the morphology of plasma etched surface is always very smooth, independent of the cleaning steps used. An etch model postulating that the removal of spinel crystals is the rate-limiting step can explain this observation.