Application of Confocal Microscopy to Evaluate the Morphology of Acidic Etched Mc-silicon

The acidic texturization using HF/HNO3/H2SiF6 mixtures is the standard treatment of as-cut multicrystalline silicon (mc-Si) wafers to remove the saw damage and to reveal the undisturbed bulk material. Furthermore, by the texturization a certain surface morphology at the bulk silicon should be generated that leads to an enhanced light trapping by multi-reflection of the incident light within the surface. The present paper work is focused on the development of the surface morphology formed during the horizontal etching of an as-cut multicrystalline silicon wafer in a common HF/HNO3/H2SiF6 etch mixture. In a procedure of stepwise etching about 1 μm silicon was removed per etching step. After each step the same spot of the silicon surface, one on the upper side and one on the lower side, was measured by confocal microscopy. The obtained micrographs were treated with image analytical methods and line profiles and other relevant morphology sensitive parameters were extracted. It can be shown, that the resulting morphology depends on the blueprint of the microcracks under the as cut structure, and that the first microns of saw damage removal are the important steps to generate an effective texture. Furthermore, a statistically significant relationship between the reflectivity of the wafer surface and a morphology parameter was derived.