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