Atomic layer defect-free etching for germanium using HBr neutral beam

The authors developed extremely selective etching for making an atomically flat, defect-free germanium fin (Ge Fin) structure. The etching uses a hydrogen bromide (HBr) neutral beam (NB), and they investigated the etching reaction differences between the HBr NB and a Cl₂ NB. No sidewall etching by HBr NB occurred at 90 °C, although that by Cl₂ NB occurred at more than 90 °C. This was due to the different boiling points of GeBr₄ and GeCl₄ as the reacted layer was formed by NB irradiation on the Ge surface. As a result, the Ge sidewall etching by Cl₂ NB occurred above 90 °C, whereas that by HBr NB did not occur at 90 °C. Additionally, nonvolatile bromide protected layers, such as GeBr₄ and SiBr_xO_y, were deposited on the Ge sidewall and the SiO₂ top surface in case of using HBr, respectively. Then, the authors succeeded in fabricating the atomically flat, defect-free Ge Fin structure with the extremely selective HBr NB etching. This result shows that HBr NB can more precisely achieve sub-10-nm scale atomic layer Ge etching for 3D Fin-type MOSFETs.