This article reports the use of an optical emission diagnostic as an in situ monitor of the photoresist etch rate during contact etch in a commercial, hot wall high density plasma reactor. The chamber was conditioned by prior photoresist etch and postetch oxygen clean to achieve reproducible conditions. The etch rate of photoresist and thermal oxide was measured, along with the optical emission observed for Si, SiO2 and photoresist wafers. With the rf bias power fixed at 600 W (125 mm wafers), the chamber roof temperature (240-260 degrees C) and source power (2350-2800 W) were varied in an experimental array to produce a range of photoresist etch rates (700-2800 Angstrom/min). C-2 and SiF optical emissions were measured for blanket Si, SiO2 and photoresist wafers. A procedure which ratioed the C-2 to SiF emissions of a blanket photoresist wafer and normalized this ratio to the C,to SiF emission ratio of a Si wafer, measured under the same conditions,, was used. A strong correlation observed between the amount of C-2 optical emission, and the removal rate of photoresist in the etching plasma was observed. This correlation provides a real time diagnostic that can be used for monitoring and controlling the contact etching process conditions.