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