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