Optical emission spectroscopy end point detection in plasma etching

Abstract

A method for etching a batch of semiconductor wafers to end point using optical emission spectroscopy is described. The method is applicable to any form of dry plasma etching which produces an emission species capable of being monitored. In a preferred embodiment, as well as a first alternative embodiment, a computer simulation is performed using an algorithm describing the concentration of the monitored etch species within the etching chamber as a function of time. The simulation produces a time period for continuing the etching process past a detected time while monitoring the intensity of emission of the etch species. In a second alternative embodiment, this latter time period is calculated using mathematical distributions describing the parameters of the etching process. In all three embodiments, the actual time that end point of an etching process is reached is closely approximated. In this manner, all wafers in a batch of wafers being etched reach end point while at the same time, the amount of over etching is greatly minimized.