Spatially resolved fluorine actinometry

A method has been developed to obtain spatially resolved optical emission spectra. This method is used ina diagnostic known as actinometry, where the relative concentration of fluorine can be obtained by examining the ratio of two spectral lines having similar excitation thresholds and excitation cross sections. Generally, the etch rate of silicon is correlated to the concentration of fluorine. In this modified actinometry method, radial emissivity profiles of the discharge are obtained 1 cm above the wafer surface by using a rotating stage to capture small wedges of light from the etching discharge, and analyzing these wedges using a regularized reconstruction algorithm. The relative fluorine concentration is obtained by comparing the ratio of a fluorine (703.75 nm) to argon (750.39 nm) emission line. The atomic fluorine radial profiles correlate to hard masked silicon etch radial profiles processed in a Lam TCP 9400 SE inductively coupled plasma processing tool using an SF6/Ar chemistry. Fluorine loading on the radial fluorine concentration profile over the wafer surface was investigated and found to affect the radial actinometry profile. (C) 1999 American Vacuum Society. [S0734-2101(99)04105-6].