A silicon layer is etched using a plasma etcher equipped with an endpoint control device. CF.sub.4 and N.sub.2 are provided to the plasma etcher at lower flow rates than those typically used during fixed time etching processes. The endpoint control device monitors optical emissions from the etching chamber at a particular wavelength to detect a predetermined change in intensity. When the change in intensity is detected, the etching is terminated.
The present invention provides a method and an apparatus for establishing endpoint during an alternating cyclical etch process or time division multiplexed process. A substrate is placed within a plasma chamber and subjected to an alternating cyclical process having an etching step and a deposition step. A variation in plasma emission intensity is monitored using known optical emission spectrometry techniques. An amplitude information is extracted from a complex waveform of the plasma emission intensity using an envelope follower algorithm. The alternating cyclical process is discontinued when endpoint is reached at a time that is based on the monitoring step.
