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