Method for film thickness endpoint control

Abstract

Endpoint control of thickness of a film being deposited or etched is achieved by use of an ellipsometer that derives delta and psi coordinates of a polarized light beam reflected from the work piece during the course of processing. Measured film thickness is a function of the delta and psi coordinates and other parameters. Delta and psi coordinates of a selected end point (final film thickness) of the process are calculated, and an unbounded line through the endpoint perpendicular to the direction of a plot of delta and psi coordinates adjacent the endpoint is defined. As the processing continues, an ERROR is generated that becomes zero when measured delta and psi coordinates are on the line. When this error changes sign, in the appropriate cycle and within a reasonable range of the endpoint, the desired thickness has been attained, and the process is stopped. The improved film thickness endpoint control is used in a rapid thermal processing system wherein temperatures are changed at a rate of 100.degree. C. or more to deposit or etch film on a substrate. Instead of using a fixed time and other fixed parameters to control film thickness, the described precision endpoint control is employed to obtain increased accuracy of control of the rapid thermal processing system.