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