This will retard phosphorus from diffusing into an overlying epitaxial layer and retard {TAIL ~ other layers} formed on {HEAD ~ the substrate} from being auto doped 
This will retard phosphorus from diffusing into an overlying epitaxial layer and retard { TAIL ~ other layers } formed on { HEAD ~ the substrate } from being auto doped
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH