{HEAD ~ an impurity layer} formed between {TAIL ~ said first semiconductor substrate} and epitaxial layer extending to the surface of said composite substrate, said impurity layer having an etching rate different from etching rates of said first semiconductor substrate and epitaxial layer 
{ HEAD ~ an impurity layer } formed between { TAIL ~ said first semiconductor substrate } and epitaxial layer extending to the surface of said composite substrate , said impurity layer having an etching rate different from etching rates of said first semiconductor substrate and epitaxial layer
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH