Optimization of inline processes for the production of freestanding epitaxially grown thin films for solar cells
In this publication we discuss inline aspects of fabricating freestanding epitaxially grown thin silicon for solar cells. Especially the inline electrochemical porosification and its limitations are discussed and homogeneity improvements achieved with aid of electric simulations are presented. Different types of inhomogeneity for porous silicon layers lead to difficulties when forming a proper separation layer through reorganization and the detachment yield of the epitaxial thin film is affected. One of the solutions to ensure good detachment of the films is to form several local separation layers in a kind of puff pastry like structure where detachment of epitaxial film might proceed in any of the separation layers thus increasing yield. However, in case of too high porosity of the highly porous layer, large cavities without smaller supporting silicon pillars can collapse during reorganization and the surface layer can re-attach to the substrate making detachment of this area impossible. Additionally, local warping of the reorganized template before epitaxy can lead to detrimental defects like stacking faults.