Etch Rate Characterization of Borosilicate Glasses as Diffusion Sources

For diffusion of boron into silicon from a doped oxide diffusion source, the surface concentration of boron in silicon and in the glass at the glass‐silicon interface are independent of diffusion time. In the temperature range studied, the surface concentrations are also independent of temperature and depend only on the dopant concentration in the deposited glass. This dependence is observed as long as the glass thickness is large enough so that the impurity source approximates a semi‐infinite source. The concentration dependence of the diffusion coefficients of the in the glass and the boron in silicon are determined, the diffusion coefficient for boron in silicon being about 100 times that of the diffusion in the oxide. Heating under an oxidizing ambient oxidizes the silicon at the silicon‐glass interface with the thickness growth rate of the undoped layer being nearly independent of the original glass thickness. No such interface barrier to the boron diffusion process occurs when argon is used as an ambient.