Wet Chemical Etching of Si, Si1 − xGex, and Ge in HF : H2O2 : CH3COOH

Abstract

Device concepts are applied to strained layers ranging from pure Si to pure Ge to achieve higher carrier mobilities. Strain is generated by growth on buffer layers with an appropriate Ge content. Processing of these heterostructures requires selective removal of individual layers. Different approaches to the etch Si, , and Ge layers have been evaluated in terms of the etch rate, selectivity, and isotropy. All investigated etching methods used highly selective chemical etching solutions composed of HF, hydrogen peroxide, and acetic acid . The effect of the different HF content on the etch rate of pure Si, pure Ge, and alloys with Ge mole fractions between 20 and 75% is presented. In general, the etch rate increases significantly with the increase in Ge content. As an example, the etch rate increases by a factor of more than 100 when the Ge content increases from 20 up to 75 atom %.