The term etching factor refers to {HEAD ~ the ratio} of {TAIL ~ etching depth} with respect to the amount of side etching 
of
The term etching factor refers to { HEAD ~ the ratio } of { TAIL ~ etching depth } with respect to the amount of side etching
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH