Comparison Between Three Si1-xGex versus Si Selective Etching Processes

Abstract

Three very different approaches to laterally etch SiGe layers selectively versus Si have been evaluated in terms of etch rate, selectivity and isotropy. The first one calls upon a CF4 plasma at low pressure and room temperature. The second one consists in the use of gaseous HCl at relatively high temperature and pressure in an epitaxy reactor. The third one is based on the use of appropriate chemistries in a wet bench. Germanium concentration impact on processes has been studied in the 20 - 40% range. To allow a strict comparison between so different processes, common test structures have been fabricated and etching targets have been jointly defined. Each technique entails its strengths and drawbacks, which will have to be carefully weighted when selecting one instead of another for a given sacrificial material configuration.