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