Abstract: The present invention is directed to a process for device fabrication in which a pattern is transferred from a photoresist mask into an underlying layer of silicon dioxide. A plasma containing a fluorocarbon gas is used to etch the pattern into the underlying silicon dioxide layer. The plasma is monitored using optical emission spectroscopy to effect control of the etch process. The optical emission is monitored at select wavelengths. To control the process based on an observation of photoresist etch rate, two wavelengths are monitored. One is associated with a species that is produced by the interaction between the photoresist and the plasma, and one is associated with a species related to the plasma intensity.