**4. Summary**

This Chapter descried the influence of the applied EB energy density used for the recrystallization process on the surface morphology of the ploy-silicon film system. At a low EB energy density, the voids were formed in the capping layer and the SiO2 capping layer exhibited a rougher and droplet morphology. With the increase of EB energy density, the capping layer became smooth and the size of the voids decreased. The size and amount of pinholes increased again if the EB energy density was too high. This also led to the formation of larger voids in the capping layer as well as coarser and wider spreading of a WSi2/Si eutectic crystallite at the grain boundaries.

This Chapter also gave the details about the formation of Tungstendisilicide (WSi2). The tungstendisilicide precipitates/silicon eutectic structures were mainly localized in at the tungsten/silicon interface but also at the grain boundaries of the silicon throughout all the EB energy density range, as well as the relationship between energy density and microstructure of WSi2/W areas. Tungstendisilicide forms in its tetragonal by the reaction of tungsten with silicon. WSi2 improves the wetting and adhesion of the silicon melt but the tungsten layer may degrade the electrical properties of the solar absorber. The formation and distribution of the eutectic depended on the crystallization and the growth dynamic of the tungsten enriched silicon melt. This is a nonequilibrium solidification process.

A tungstendisilicide layer was formed between the tungsten layer and the silicon layer for all EB energy densities used. The higher the applied EB energy density, the thicker the tungstendisilicide layer grows and the thinner the tungsten layer left. It is important to perform the recrystallization process at a moderate energy density to suppress the formation of both WSi2/Si eutectic and pinholes. In addition, there are no chlorine and hydrogen in the area surrounding a pinhole after recrystallization because of outgassing during the solidification.
