A first portion of {TAIL ~ the intrinsic base layer} is masked while a second portion of {HEAD ~ an intrinsic base layer} is etched 
A first portion of { TAIL ~ the intrinsic base layer } is masked while a second portion of { HEAD ~ an intrinsic base layer } is etched
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH