X-ray study of reactive ion etch damage to 〈100〉 silicon

Abstract

Contact resistance measurements, x-ray double-crystal diffraction, and Auger electron spectroscopy were used to evaluate reactive ion etch (RIE) damage to silicon wafers. Wafers were exposed to plasmas at different powers with gas mixtures of CHF3/O2 and O2 only. The CHF3/O2 mixture was typical of a gas mixture used for etching contacts to silicon. The O2 alone was used as a damaging, bombarding gas. Some oxidation of silicon occurs during the O2 bombardment. However, O2 was used to determine the effects of ion bombardment at conditions similar to those that occur during RIE etching of contacts. It has been found that the depth of damage to the underlying silicon increases with cathode bias and that at −550 V the damage is 200–250 Å deep. The damage at −550 V consists of two layers: one is an amorphous and/or polycrystalline silicon layer at the surface 100–125 Å thick. The surface layer contains impurities as a result of the reactive ion etch process. The second single-crystal dilated layer, 100–125 Å thick, lies beneath the amorphous/poly Si layer. The thickness of these layers is the same when either CHF3/O2 or O2 alone are used as the etchant gases.