The aim of this study is to optimize processes suitable for production of extremely thin cells focusing in two of the solar cell fabrication steps: P and Al diffusion for pn junction and BSF formation respectively. SEM analysis has been used to monitor BSF junction uniformity and EDX to determine composition of the diffused Al layer formed by screen-printing. The influence of the preparation conditions is studied in order to avoid the formation of an eutectic Al-Si alloy, that is the responsible for the bow of thin wafers. Phosphorus deposition has been carried out by spray coating, a technique that allows in-line implementation and reduces manipulation of the cell. Samples were prepared on 250 and 100 μm silicon wafers, comparing various mixtures of H3PO4 as precursor, the resulting emitters were characterized measuring their surface resistivity and analyzing surface composition by XPS and FTIR.