I looking for a "dry process" by which I can change the hydrophobicity of the silicon wafer, to limit the hazardous wet process of using piranha solution.
This is possible. I have used oxygen plasma or UV-ozone (oxygen plasma is more powerfull). Note that the surface treatment keeps the hydrophilic properties for a short time (less than 15 minutes), after this contamination in the air will decrease your wettabilty.