A first asymmetric etching process is performed to remove {HEAD ~ a portion} of {TAIL ~ the nitride layer} until a portion of a top surface of the first oxide layer is exposed 
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A first asymmetric etching process is performed to remove { HEAD ~ a portion } of { TAIL ~ the nitride layer } until a portion of a top surface of the first oxide layer is exposed
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH