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