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