Development of a Multistep SiO2 Plasma Etching Process in a Minibatch Reactor Using Response‐Surface Methodology

Abstract

A multistep process to etch uniformly and selectively over silicon has been developed with a Drytek 202 mini‐batch, parallel plate reactor using experimental design and response‐surface methodology. Glow discharges, formed at a radio frequency of 13.56 MHz with mixtures of and with He in the first process step but without He in the second process step, were used to achieve etch rates of ∼2500 and 1750 Å/min for a deposited, doped oxide in the first and second steps, respectively. Etch uniformities are < ± 5% within a wafer for both steps and < ± 8 and < ± 10% across the reactor for the first and second steps, respectively. The etch rate of masked single crystal silicon (>95% surface coverage) in the second step is ∼300 Å/min, so that selectivity of etch in this step is >5:1. To minimize reactor cleaning and to insure process uniformity and repeatability, the process is completed with a brief plasma cleaning step after the etching of each batch of wafers. Plots and contour maps of etch rates and etch uniformity in the regions about optimized parameter settings which were derived from response‐surface models indicate that these settings represent positions of high process stability.