Study of Isotropic and Si-Selective Quasi Atomic Layer Etching of Si _1−x Ge _x

Abstract

The lateral and vertical gate-all-around (GAA) field-effect transistors are considered the most promising candidates for next generation logic device at and beyond 3-nm technology node. SiGe plays an important role in these devices as the sacrificial layer or channel material and needs isotropic etching. In this paper, an advanced etching process termed quasi atomic layer etching (qALE) is developed with advantages of controllable etch rate and atomically smooth surfaces. The qALE of SiGe is based on wet chemical etching, in which H 2 O 2 is applied to oxidate the surface with cyclic manner, and diluted buffered oxide etchant (dBOE) is applied to remove the oxide. The profiles of SiGe qALE for quasi-self-limited behavior, etch rate and the effect in concentration and temperature of H 2 O 2 have been studied. The etch per cycle (EPC) of Si 0.7 Ge 0.3 is 0.50 nm and the etching selectivity between Si 0.7 Ge 0.3 and heavily p-type doped silicon is 4.99 in Si/SiGe/Si stacked layers with (110) sidewall. The etch rate and the selectivity are influenced by Ge fraction of SiGe and the boron doping in Si. The root mean square (RMS) roughness after 60 cycles qALE is 0.183 nm indicating atomically smooth surfaces. Finally, the application of qALE for vertical nanowire compared with wet continuous etching is discussed in this work.