Formation of mesa-type vertically aligned silicon nanowire bundle arrays by selective-area chemical oxidation and etching processes
(Color online) Schematic diagram of state-of-art fabrication techniques for realizing patterned SiNWs: (a) mesa-type SiNW bundles by selective-area deposition of metal particles followed by bottom-up growth method (Ref. 9); (b) embedded SiNW bundles by prepatterning metal catalyst followed by top-down chemical etching (Ref. 10); (c) mesa-type SiNW bundles by fabricating silicon mesas with sidewall and bottom surface protection followed by top-down chemical etching (Ref. 13); (d) mesa-type SiNW bundles by post selective-area protection of blank SiNWs followed by top-down chemical etching (this work).
(Color online) Schematic diagram of (a) top-down VA-SiNW patterning concept and (b) detailed process procedures for the realization of patterned VA-SiNWs.
(Color online) Cross-sectional SEM views of resultant SiNWs with residual silver catalysts after (a) 12 s of etching and (b) 6 min of etching, respectively.
(Color online) Cross-sectional SEM views of (a) original 5.98-μm tall VA-SiNWs and (b) 50-s KOH sharpened SiNWs. (c) Comparison of resultant heights of SiNW with and without thin SiO2 protection under different KOH etching time.
(Color online) (a) Tilted and (b) cross-sectional SEM views of VA-SiNWs covered with photoresist patterns. SiNW height is about 1.18 μm. The exposure wavelength of photolithography process is 405 nm. (c) Comparison of measured total optical reflectance of VA-SiNWs with different wire lengths for the wavelengths of 365 nm (i-line), 405 nm (h-line), and 436 nm (g-line). The inset figure compares the measured total optical reflectance of SiNWs and commercial ARC on silicon substrate under different SiNW heights/ARC thicknesses.
(Color online) Photographs of (a) dark SiNW sample on which is covered with patterned oxide masks and (b) its resultant surface appearance after KOH etch.
(Color online) (a) Top optical microscope view of hexagonal two-dimensional VA-SiNW bundles with a periodicity of 40 μm, a bundle diameter of 20 μm, and a SiNW height of 1.18 μm. Top SEM views of (b) individual VA-SiNW bundle and KOH-etched surfaces of (c) unmasked and (d) masked VA-SiNWs. Resultant unmasked and masked VA-SiNW surface have nanowire volume fill factors of 0.074 and 0.414, respectively.
(Color online) Measured EDX spectrum of patterned SiNW bundle.
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