Patent ID: 6828249
Filing Date: 2004-12-07
Classification: H01J

Abstract:
A method for monitoring an etch process of a substrate, the method comprising:receiving a first signal having a first wavelength; deriving a second signal based on said first signal; combining said first signal with said second signal to produce a composite signal having a composite wavelength less than said first wavelength; identifying one or more inflection points of said composite signal; determining an etch rate of an etch process by evaluating said inflection points and elapsed time between said inflection points; wherein said first signal is represented by the following equation: y(t)=A sin (kt+&phgr;), where y is an observed signal intensity, A is an amplitude of said first signal, k is a constant that defines a time period of said first signal, t is time, and &phgr; is a phase shift of said first signal; wherein said second signal is represented by the following equation: y(t)â€²=dy/dt=kA cos (kt+&phgr;); and wherein said combining comprises multiplying said first signal by said second signal to produce said composite signal.