TMAH wet etching of silicon micro- and nano-fins for selective sidewall epitaxy of III-Nitride semiconductors

We describe wet etch experiments to form silicon micro- and nano-fins, with (111)-plane sidewall facets, to be used in selective epitaxy of III-Nitride semiconductors. Starting material was (110)-oriented silicon wafers. Silicon dioxide is used for producing a hard mask and patterned using photo- and electron-beam lithography for micro- and nano-fins, respectively. Wet etching to produce silicon fins was carried out using tetramethyl ammonium hydroxide (TMAH) diluted with isopropyl alcohol (IPA). We experimented with silicon doped TMAH/IPA solution, using a sacrificial wafer, and with surfactant (Triton X-100). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to determine the morphology including surface roughness of the area between fins and etching rate of silicon. By controlling the etching time, temperature, percentage of IPA and concentration of Triton X-100 we obtain good surface morphology on both (111) and (110) planes. Nanofins as small as 30 nm in width and ∼ 250 nm in height are prepared, with corresponding aspect ratio of ∼ 8:1.