Patent ID: 6881644

Claim:
A semiconductor substrate producing method comprising: forming a first porous silicon layer on at least one surface of a silicon substrate; forming a non-porous layer over said first porous layer; forming a second porous layer having a larger porosity than the first porous silicon layer at a constant depth from a surface of said first porous silicon layer, said second porous layer forming step comprising implanting ions into said first porous silicon layer with a given projection range; bonding said non-porous layer and a support substrate together, the support substrate being different than the silicon substrate; separating said silicon substrate into two portions at said second porous layer; removing at least said first porous layer provided over said support substrate to expose said non-porous layer; and smoothing said exposed non-porous layer by subjecting a surface of said non-porous layer using an etchant species during a thermal treatment.