A new film thickness sensor material, single crystal gallium orthophosphate (GaPO4), has been investigated for use as a high temperature piezoelectric microbalance suitable for monitoring chemical vapor deposition (CVD) thin film processes. Our initial work has shown that gallium phosphate can operate at temperatures up to 930degreesC, and a reusable sensor housing can be constructed to hold the crystal for repeated runs. A significant shortcoming is that commercial film thickness monitors are not capable of accurately controlling GaPO4 above 600degreesC due to the limitations of the oscillator electronics used in such monitors.
