Cryogenic electron cyclotron resonance plasma etching

Abstract

A cryogenic electron cyclotron resonance (ECR) plasma etching system has been built to study wafer temperature in the Si etching characteristics. The wafer temperature was controlled from −150 to +30 °C during etching using the liquid nitrogen cooled helium gas. Although Si was etched isotropically in SF6 plasmas at room temperatures, we found that it is possible to suppress the etch undercut in Si by reducing a substrate temperature without sidewall passivation. In addition, the selectivity of silicon to photoresist was improved considerably at a low wafer temperature. ECR etching generates less damage in the gate oxide than reactive ion etching does under comparable etching conditions.