A second polishing step is performed to remove {HEAD ~ a portion} of {TAIL ~ the remaining portion} of the silicon oxide layer until the silicon nitride layer is exposed 
of
A second polishing step is performed to remove { HEAD ~ a portion } of { TAIL ~ the remaining portion } of the silicon oxide layer until the silicon nitride layer is exposed
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