After the diffusion contact endpoint has been reached, the second etch step is initiated using a CHF3 /O2 mixture which etches silicon nitride with {HEAD ~ a very high etch rate ratio} to both BPSG and {TAIL ~ titanium disilicide} 
to
After the diffusion contact endpoint has been reached , the second etch step is initiated using a CHF3 /O2 mixture which etches silicon nitride with { HEAD ~ a very high etch rate ratio } to both BPSG and { TAIL ~ titanium disilicide }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL