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 {TAIL ~ both BPSG} and 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 { TAIL ~ both BPSG } and 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 TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH