A micromachined sensor for in-situ monitoring of plasma etching

We present a prototype plasma etch rate sensor which correlates film thickness with the change in resonant frequency that occurs in a micromachined platform during etching. This approach is similar to the use of crystal oscillators to monitor deposition processes. The platform is suspended over a drive electrode on the surface of the wafer and electrically excited into resonance. As material is etched from the platform, its fundamental resonance frequency shifts, thus allowing etch rate to be inferred. The sensor has the potential to allow in-situ process monitoring of both etch rate and uniformity at a nominal cost.