Quasi-pyramidal texturing using phase-segregated masks

Abstract

Surface texturing processes for thin silicon solar cells ideally remove as little Si as possible relative to amount of topography generated. Here we describe how a micron-scale quasi-pyramidal texture may be achieved in Si layers with arbitrary crystallinity using a phase-segregated mask in combination with reactive ion etching (RIE). The Si to be textured is coated with a thin barrier layer followed by a layer of Al-Si alloy which phase-segregates into micron-sized regions of Al and Si after low temperature (<450 °C) annealing. One omponent of the mask is selectively etched away and the Si under the exposed barrier regions is etched by a process that gives the desired depth and lateral undercut. In this paper we show the dependence of the segregated Al-Si morphology on Al-Si alloy composition, thickness, and annealing conditions, and then present examples of texturing produced in single crystal Si by these masks in combination with CF₄/O₂ reactive ion etching.