A second asymmetric etching process is performed to remove a portion of the first oxide layer by using {TAIL ~ the remaining nitride layer} as a mask until about 50% to 90% portion of {HEAD ~ the first oxide layer} is removed 
A second asymmetric etching process is performed to remove a portion of the first oxide layer by using { TAIL ~ the remaining nitride layer } as a mask until about 50 % to 90 % portion of { HEAD ~ the first oxide layer } is removed
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH