Two-channel spectroscopic reflectometry for in situ monitoring of blanket and patterned structures during reactive ion etching

In this article we present a low-cost, high-speed, high-accuracy in situ th in film measurement system for real-time process monitoring and industrial process control. This sensor, the two-channel spectroscopic reflectometer ( 2CSR), is a hybrid of spectroscopic ellipsometry and spectroscopic reflecto metry. In 2CSR a polarized beam of white light is directed at the sample, T he reflected light is resolved into its two orthogonal components, s and p, using a Wollaston prism. These data, \R-s\(2) and \R-p\(2), are recorded s imultaneously as a function of wavelength using a two-channel spectrometer with linear array detectors. The fact that 2CSR has no moving parts, couple d with the use of the two-channel linear array detectors, enables high-accu racy data acquisition across the sensor's spectral range in 6 Ins. This mak es the 2CSR ideal for real-time high-speed process monitoring and control i n an industrial setting. We have used the 2CSR to make accurate in situ, hi gh speed film thickness measurements during the plasma etching of both sili con dioxide and polycrystalline silicon samples. We show that, in addition to our ability to measure blanket film thicknesses and etch rates, the accu racy of the 2CSR makes this a viable technique for patterned wafer analysis . (C) 2000 American Vacuum Society. [S0734-211X(00)19006-7].