Endpoint detection in plasma etching

Plasma etching is a main stream technology in integrated circuit fabrication. The general trend towards fine linewidths and decreasing thickness of underlying layers (etch stops) results in an increasing dependence on highly controlled plasma etch processes. Such tight control requires in situ process monitoring, particularly, for determination of the etch endpoint. This paper reviews the various methods for endpoint detection. A novel application of interferometric principles for very precise etch endpoint determination in high density circuits is described. A comparison of several methods used simultaneously in a plasma planarization process is presented. The etch endpoint can also be determined by monitoring the pressure change in the chamber upon completion of the etch. An application of this method to dielectric etching is demonstrated.