Nanosphere lithography on silicon oxide for high aspect ratio cryo etching of vertically-align silicon structures

Abstract

Nowadays, classical silicon solar cell achieved efficiencies close to theoretical limit and new design of silicon solar cell is required. Vertically aligned silicon solar cells seems to be a promising design of future silicon multijunction solar cells. These structures can be produce with dry etching technics. However, dry etching requires high quality mask. Mask can be archived with classical photolithography, but photolithography is multistep process and cannot be used in mass production of solar cells, because of the price. Nanosphere lithography is a powerful one-step method to produce periodic mask on silicon, but polystyrene spheres does not have enough selectivity in silicon etching process. Etching depth in silicon that can be archived in cryo process with 900 nm polystyrene sphere is about 3 μm. For deep silicon etching, we have to use hard mask. In this paper, we investigated nanosphere lithography on 500 nm thick PECVD deposed silicon oxide on silicon. Influence of isopropyl content in nanosphere solution were investigated. The effect of process conditions is discussed in the paper.