Scattered light measurements on textured crystalline silicon substrates using an angle-resolved Mueller matrix polarimeter

Abstract

Dry plasma etching is a promising technique for crystalline silicon surface texturing aimed at improving solar cell efficiencies by reducing incident light reflection and backscattering at the cell front surface. In this work we present a new optical characterization technique for textured surfaces based on a Mueller polarimeter coupled with a high numerical aperture microscope operated either in real or in angular spaces. This tool provides both the specularly reflected and the angle-resolved backscattered intensities in a very efficient manner, due to the absence of moving parts. Three different silicon samples were etched in a standard reactor with SF(6)/O(2) plasmas at various RF powers, resulting in different textures that were characterized by scanning electron microscopy, standard reflectometry, and by our tool. The three techniques yielded consistent results. However, reflectometry could not take into account the backscattered light from highly textured surfaces, leading to significant underestimation of the overall amount of the reflected light. In contrast, our tool has demonstrated the potential to measure both reflected and backscattered light quickly and efficiently for all samples, paving the way for a new characterization technique for textured solar cells both at the development and at the production stage.