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