In-situ polymer buildup monitoring in plasma etching systems [micromachined sensor]

This paper reports a micromachined sensor for the direct in-situ measurement of polymer buildup in plasma etching systems. The sensor is based on an electrothermal oscillator that measures the thermal mass change as polymer builds up on a stress-compensated dielectric window containing metal film heating and sensing resistors. The change in the thermal mass of the window can be detected as a variation in the pulse width (cooling time) of the oscillation. The device operates with a typical cooling time of 2.7 msec and has a measurement resolution of <1 nm. The device is flush-mounted in the chamber wall with the exposed window area protected by a thin film of iridium against damage by the plasma