Hi Andrea Mazzolari i do not know what is the purpose for 1um silicon layer but i suggest you are right to start with SOI wafer and then if do not need Si handle etch that with KOH but first protect front Si thin layer with some oxide other you lose that too by using wet etching. at alst you can remove oxide from both sides of thin Si film. best regards Imran Ali Institute of MicroElectronics, Tsinghua University, Beijing, China