Wet etching silicon nanofins with (111)-oriented sidewalls

A systematic study of the chemical etching of Si(111) fins is reported. Optimized wet etching of Si(110) with isopropyl alcohol and tetramethyl ammonium hydroxide produces 30 nm wide silicon nanofins with (111)-oriented sidewalls. The addition of a sacrificial silicon wafer for “doping” the etchant reduces the surface roughness of the interfin region. Atomic force microscopy indicates interfin roughness of <2 nm (root-mean square) based on scan areas of 5 μm × 5 μm. The addition of a commercial surfactant helps in reducing the presence of shoulders where the (111) and (110) crystallographic surfaces meet. Smooth sidewalls are obtained as a consequence of the directional etching process. Using electron-beam lithography and SiO₂ as a hard mask, fin aspect ratio of >8:1 with 30 nm wide fins is achieved.