High-density hollow cathode plasma etching for large area multicrystalline silicon solar cells

Abstract

Multicrysalline silicon (mc-Si) materials are commercially important photovoltaic material. This material consists of number of grains and grain boundaries. The orientation is generally random and the size of the grain varies between a few millimeters to several centimeters. So for multicrysalline silicon, surface texturization is not possible with help of standard NaOH/KOH or other anisotropic chemical enchant. Actually texturing for enhanced absorption in silicon has been obtained by creating randomly distributed pyramids using anisotropic wet enchants, but this works well only on single crystalline silicon because of its crystallographic orientation. Various surface texturization method has been used during surface preparation of mc-Si solar cell research, including mechanical grinding, laser-structuring, porous silicon etching, photolithographically defined etching etc. We developed a mask less plasma texturing technique for mc-Si solar cells using high-density hollow cathode plasma etching technique. We used SF/sub 6/ and O/sub 2/ gases in hollow cathode plasma (HCP) dry etching process. This paper demonstrates very high plasma density of 2/spl times/10/sup 12/ cm/sup -3/ at a discharge current of 20mA. Silicon etch rate of 1.3/spl mu/m/min. was achieved with SF/sub 6//O/sub 2/ plasma conditions of total gas pressure =50 mTorr, gas flow rate=40 sccm, and RF power=100W. In this paper, we also reported the surface etching characteristics of monocrystalline silicon and large area multicrystalline silicon (mc-Si) wafer.