an impurity layer formed between {TAIL ~ said first semiconductor substrate} and epitaxial layer extending to {HEAD ~ 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 
an impurity layer formed between { TAIL ~ said first semiconductor substrate } and epitaxial layer extending to { HEAD ~ 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
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH