Method for fabricating a thin, free-standing semiconductor device layer and for making a three-dimensionally integrated circuit

Field of the Invention In a method for fabricating a silicon-on-insulation wafer having fully processed devices in its upper-most silicon layer, the wafer is reduced in thickness from a surface opposite to the device layer surface by performing a first etching step of etching the semiconductor substrate to the insulation layer, so that the insulation layer functions as an etch stop layer, and a second etching step of etching the insulation layer to the semiconductor device layer, so that the semiconductor device layer functions as an etch stop layer. The semiconductor device layer is then separated into individual chips for fabricating a three-dimensionally integrated circuit thereof.