Real time control of etch rate and selectivity using two colors laser interferometry

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Abstract
Summary form only given, as follows. Single point two color laser interferometry is used to determine in-situ the etch rate of transparent thin films in real time. The objective of this study is to implement real time control of etch rate and selectivity in a magnetically confined inductively coupled plasma tool. This non-invasive and nondestructive technique is very useful for monitoring the plasma processed surface. It is advantageous to use two lasers operating with different colors, as opposed to one, in order to gain a more accurate etch rate estimation. This is achieved by partially avoiding the peak parts of the interference pattern which are less sensitive to the etch rate. Moreover, the phase difference between the interference pattern of the two colors provides a reasonable measure of the film thickness, and is used for end-point estimation. The two laser beams as well as the detected interference signals are introduced perpendicular to the wafer surface through the quartz plate on top of the processing tool. This arrangement simplifies the data analysis and could be used in industrial processing tools. The real time control variables are the RF power to the wafer stage and to the inductive coil. In the future the gas mixture and flow rates will be used as extra variables for etch rate and selectivity control.

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