US EPA

8412794 

Journal Article 

Controlled phosphorus diffusion into silicon from P2O5 vapour using a red phosphorus source 

Nassibian, AG; Whiting, G 

1965 

1 

Solid-State Electronics
ISSN: 0038-1101 

8 

11 

843-853 

English 

10.1016/0038-1101(65)90094-8 

A single-stage method for low concentration diffusion of phosphorus into silicon using a red phosphorus source is described. When accurately controlled vapour of red phosphorus is combined with oxygen in the diffusion furnace to form a P2O5 vapour, accurate control of surface concentration on silicon slices from 1017 atoms cm-3 to greater than 3 × 1020 atoms cm-3 can be achieved. Results of sheet resistivity and surface concentrations are presented as a function of partial pressure of oxygen and source temperature. It is concluded from these results that the surface concentration is dependent on the oxide thickness grown on the slice during the diffusion. Results on surface concentration as a function of diffusion time at constant pressures of oxygen are also presented. From these results a definite relationship between surface concentration and the rate of oxidation and diffusion time has been demonstrated. A mechanism for this system of diffusion is described in terms of the diffusion rate of the phosphorus through the oxide and the rate of oxidation of the silicon slice. A condition for constant surface concentration for all diffusion times has been deduced and from this condition a value for the diffusion coefficient of phosphorus in the oxide has been calculated. The shape of the impurity profiles of diffused layers has been studied and show that at low concentrations, impurity distribution characterized by erfc can be obtained. Finally the application of this method in two stage diffusion is described to indicate that it can replace the conventional P2O5 diffusion system. © 1965.