Formation of mesa-type vertically aligned silicon nanowire bundle arrays by selective-area chemical oxidation and etching processes

Abstract

A novel top-down scheme for post patterning of vertically aligned silicon nanowires (VA-SiNWs) is proposed and demonstrated by means of chemical oxidation, photolithographic patterning, and chemical etching processes. The authors discovered that only ∼1.4 nm chemical oxide layer is sufficient to protect SiNWs from the attack of KOH etchant. VA-SiNWs can simultaneously serve as an optical antireflective layer between photoresist and silicon substrate for eliminating the backreflection during photolithographic patterning due to the strong optical absorption and light trapping behavior at ultraviolet spectral region. After selective-area SiNW removal with chemical etching procedures, SiNWs at unmasked areas are drastically shortened with a decreased wire number density while oxide masked SiNWs are still vertically aligned with high wire number density and good uniformity. The patterned SiNWs preserves the superior antireflective performance of original SiNWs which makes every SiNW bundle to have dark appearance. Contrary to prepatterning scheme which creates embedded VA-SiNW patterns, this post patterning scheme enables the synthesis of patterned mesa-type SiNWs on silicon surface. The patterned VA-SiNW bundles can be employed for applications in arrayed sensors, arrayed photodiodes, or arrayed field emitters.