Dielectric back passivated solar cells with local Al-BSF (Back Surface Field) are investigated to lead the way on achieving higher efficiencies. However the formation of efficient and uniform local BSF needs a proper opening of the dielectric passivation layers. In this paper the laser ablation mechanisms with green and ultraviolet laser sources are studied to locally remove dielectric stacks such as SiO2/SiNx. Green laser process parameters are found to lower silicon surface damages but highlight the importance of using a post-laser cleaning step based on an alkaline etching solution. The impact of this additional step on BSF formation is studied by extracting the local internal quantum efficiency from LBIC mappings of a fabricated PERC solar cell.