Extremely high selective Si1−xGex-film wet etchant generating highly dissolved oxygen via peracetic acid oxidant for lateral gate-all-around FETs with a logic node of less than 3-nm

For lateral gate-all-around (LGAA) field-effect transistors (FETs) having design rules of logic devices below 3-nm and 3D-DRAM below 10-nm, multi-stacked Si1−xGex/Si-films should be epitaxially grown on the Si surfaces, and a highly selective wet etching of Si1−xGex-film is essentially followed for forming nanoscale-thick (5–7 nm) Si channel multi-sheets. A high selective etchant has required a lateral Si1−xGex etch rate of >30 nm·min−1 and etch rate selectivity between Si1−xGex- and Si-films of >200:1 at patterned multi-stacked Si1−xGex/Si-films. The selective Si1−xGex-film etchant using an etching agent (HF), a selectivity enhancing agent (CH3COOH), and a strong oxidant peracetic acid (PAA; CH3COOOH) unlike a conventional oxidant (H2O2 or HNO3) presented an extremely high Si0.5Ge0.5-film etch rate (82 nm·min−1@5 wt% of PAA) and etch rate selectivity between the Si0.5Ge0.5- and Si-films (265:1). Thus, it performed sufficient lateral Si1−xGex-film etching in the 3 multi-stacked Si0.5Ge0.5/Si-films line pattern and satisfied the requirement for a selective etching of Si1−xGex-film for LGAA having a logic-node of less than 2.1-nm. The excellent Si1−xGex-film etch rate using PAA was driven by a lower decomposition energy, lower Gibbs free energy, and higher standard reduction potential compared to the oxidant H2O2. Therefore, the amount of diffused dissolved oxygen using 5 wt% PAA was ∼1.48 times higher than that of H2O2; hence, the chemical oxidation degree (GeOx, and SiOx-bonds on the Si0.5Ge0.5-film surface) for 5 wt% PAA was ∼1.1 times higher than that of H2O2. Furthermore, the etch rate of the Si0.5Ge0.5-film using 5 wt% PAA was ∼5.4 times higher than that of H2O2; thus, we provide a cost effective Si1−xGex-film etching process for LGAA.