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