Referring to FIG 4A, {TAIL ~ a predetermined area} of {HEAD ~ a substrate} 31 is etched to form a trench 
Referring to FIG 4A , { TAIL ~ a predetermined area } of { HEAD ~ a substrate } 31 is etched to form a trench
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH