Diffusion of Phosphorus in silicon dioxide from a spin-on source

The diffusion of phosphorus in silicon dioxide was investigated. A phosphosilicate glass which was deposited from a solution containing a silicic ester was used as the source. Using radioactive ³²P it was possible to determine the dopant profile in silicon dioxide by measuring the β activity. The profiles obtained cannot be described by the usual solution of the diffusion equation. The phosphorus mobility in silicon dioxide was found to be markedly dependent on the oxygen content of the ambient gas during diffusion. Pre-annealing in nitrogen of the SiO₂ layer into which the diffusion took place similarly influences the diffusion profile. It is presumed that a free acid of phosphorus from the doping solution participates in the diffusion process.