Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. IV. Effects of substrate temperature in a CF4 plasma

Abstract

Effects of substrate temperature on the redeposition of bottom-emitted particles to the sidewall surface and the resulting changes in the sidewall properties during SiO2 etching in a CF4 plasma were investigated. A Faraday cage and specially designed, step-shaped substrates located in a plasma etcher allowed us to observe lateral and vertical etch rates, the temperature dependence of redeposition, and resulting changes in the chemical composition of the sidewall surface. We conducted two sets of experiments under different process conditions to observe changes in the temperature effect with ion energy and plasma density. Process (I), which was carried out with a 200 W source power and a −400 V bias voltage, represented a typical reactive ion etching condition for low plasma density and high ion energy, and process (II), with 500 W and −200 V, represented an inductively coupled plasma condition of high plasma density and low ion energy. Lateral etching was more sensitive to substrate temperature than vertical etching. As the substrate temperature was raised, the redep-effect, which was defined as the difference in deposition rates between two sidewalls, either affected by bottom-emitted particles or not, was slightly decreased in process (I) but was significantly increased in process (II). The chemical composition of the sidewall surface was highly dependent on substrate temperature. The carbon content and the F/C ratio of the surface carbon-containing layer formed on the sidewall increased and decreased, respectively, with substrate temperature. The O/Si ratio of the redep-etch combined layer formed beneath the surface carbon-containing layer decreased when the substrate temperature was increased.