{HEAD ~ A bonding surface} of {TAIL ~ first semiconductor substrate} 11 , and a bonding surface of second semiconductor substrate 12 are mirror finished to provide a surface roughness of below 500 Å each 
of
{ HEAD ~ A bonding surface } of { TAIL ~ first semiconductor substrate } 11 , and a bonding surface of second semiconductor substrate 12 are mirror finished to provide a surface roughness of below 500 Å each
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