Etched Shape Control of Single‐Crystal Silicon in Reactive Ion Etching Using Chlorine

Abstract

The trench shape formation mechanism is examined during reactive ion etching (RIE) of single‐crystal silicon using chlorine for the etching gas, and shape control is achieved through the mixing of the depositing gas. One problem with RIE is undercutting of the sidewall due to divergent ions from ion‐molecule collisions. Furthermore, sharp crevices are formed at the trench bottom edges because of the increase in radical concentration at these edges. From the experiment using chlorine, it is found that these problems are suppressed by a simultaneous deposition. Next, this deposition is shown to be enhanced by mixing hydrogen with the chlorine. However, for complete suppression of the crevice growth, silicon tetrachloride must be added to the mixture. Using this procedure, the desired tapering sidewall slope was obtained by controlling both the deposition rate and RF power density. Experimentation showed that the etched depth is independent of the trench width for trenches wider than 0.7 μm, although the sidewall slope only slightly decreased with increasing trench width. Consequently, silicon trench etching in a chlorine, hydrogen, and silicon tetrachloride mixture is a promising method for many silicon trench applications, because of its high shape controllability and less chance of contamination.