Dry Selective Etching of Si_0.7Ge_0.3 for Horizontal GAA Inner Spacer Module

Aiming at the issue that it is difficult to accurately control the size and profile of the inner spacer cavity etching of Si_0.7Ge_0.3 in Gate-All-Around (GAA) process flow, based on the conventional inductively coupled plasma (ICP) etching tool, dry isotropic selective etching experiment of Si_0.7Ge_0.3 was carried out with CF₄/O₂/He mixed gas. The effects and mechanisms of factors such as the power of SRF (source radio frequency), gas pressure, and the sidewall cleaning process before etching were explored. The results show that there are linear and quasi-saturated regions in the effect of SRF on the etching rate, and there is a quadratic function relationship between gas pressure and etching rate in the experimental range. Diluted HF (DHF) and O₃ alternate cycle cleaning process has a better performance than the single DHF cleaning in the removal of the interface passivation layer and the control of the etching profile. After the optimization of the process scheme, better process results are obtained: the etching accuracy reaches 0.61 nm/s, the optimal roughness R_q is 0.101 nm, and the rectangle of the etching profile is high (d/t~83.3%). This study provides a solution for the inner spacer cavity etching.