Design guidelines for releasing silicon nanowire arrays by liquid and vapor phase hydrofluoric acid

Silicon nanowires of various geometries are fabricated using top-down approach starting from silicon-on-insulator substrate. Arrays of nanowires presenting widths from 25 up to 100 nm regularly spaced by 50 nm up to 1 μm are patterned and released. A comparison of various release methodologies, based on scanning electron microscopy images, namely wet release in hydrofluoric acid - 5% with rinse in water or iso-propanol followed by drying by evaporation in air or using a critical point dryer, and dry release using vapor phase hydrofluoric acid is presented. Forces acting on suspended wires during release are calculated. Increase of successful release length by increasing spacing between the wires is observed for both wet and vapor phase hydrofluoric acid release techniques. Maximum detachment length of 9 μm is achieved for 50 × 100 nm2 array of nanowires spaced by 1 μm using vapor phase hydrofluoric acid etching method