Patent ID: 7306696

Claim:
A substrate etching apparatus comprising: (a) a chamber comprising: (1) a substrate support to support a substrate having a layer; (2) a gas distributor to introduce an etchant gas into the chamber; (3) a gas energizer to energize the etchant gas to etch the substrate or layer; and (4) a gas exhaust port; (b) a controller programmed to determine at the beginning of an etching process, a wavelength of light reflected from the substrate at which a local intensity of the reflected intensity signal trace is maximized, by: (1) scanning through a sequence of successive wavelengths of light reflected from the substrate until a local maximum of an intensity of the light reflected from the substrate is detected; or (2) calculating a wavelength of light based on a path length in a thickness of the layer on the substrate that provides a local maximum of intensity when light having the wavelength is reflected from the substrate; and (c) a light detector adapted to detect an intensity of the light having the determined wavelength that is reflected from the substrate, and generate an intensity signal trace during the etching process; wherein the controller receives and evaluates the intensity signal trace during the etching process to determine an endpoint of the etching process.