The Study of Latex Sphere Lithography for High Aspect Ratio Dry Silicon Etching

Abstract

A method to obtain vertically aligned silicon structures with a high aspect ratio, which are interesting for photovoltaics, using nanosphere lithography and cryogenic plasma etching is explored. For the conventional nanosphere lithography, the etching of the latex spheres during the cryogenic plasma process limits the maximum ratio of Si wire length to the diameter at the level of 5:1. The maximum length of 2–3 μm can be obtained for Si wires with 0.45 μm diameter. An intermediate step of SiO2 hard mask formation before nanosphere lithography is proposed to increase the maximum length. The nanosphere lithography with the predeposited SiO2 layer allows to increase the maximum length/diameter ratio to at least 15:1. An array of Si wires with a diameter of 0.45 μm and a length of 6 μm is obtained on the entire surface of 4 in. Si wafers.