The first step of the contact etch is accomplished using a boron trichloride BCL3 etch gas which selectively etches {TAIL ~ BPSG} without etching {HEAD ~ the underlying silicon nitride} 
The first step of the contact etch is accomplished using a boron trichloride BCL3 etch gas which selectively etches { TAIL ~ BPSG } without etching { HEAD ~ the underlying silicon nitride }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD