DIFFERENTIAL MEASUREMENTS FOR ENDPOINT SIGNAL ENHANCEMENT

Provided is a method of etching a layer. A substrate is provided in a chamber. Etching plasma for etching the layer on the substrate is generated. Light from a first region of the chamber is measured in order to provide a first signal. Light from a second region of the chamber is measured in order to provide a second signal. The first signal is compared with the second signal to determine an etching end point. [Reference numerals] (104) Arrange a substrate in a chamber; (108) Enable gas to flow into a chamber; (112) Form gas with plasma; (116) Measure light from a first region to provide a first signal; (120) Measure light from a second region to provide a second signal; (124) Compare a first signal with a second signal to detect an endpoint; (128) Perform a next process in case the endpoint is detected; (132) Remove the substrate from the chamber; (AA) Start; (BB) End