Retarded Diffusion of Phosphorus in Silicon-on-Insulator Structures

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Abstract
Phosphorus diffusion profiles in bonding silicon-on-insulator (SOI) structures are compared with those in bulk Si. Phosphorus diffusion is carried out at 900 and 1000°C, using a spin-on-glass source which enables achievement of a high surface concentration near solid solubility. The diffusion methods consist of both predeposition diffusion in N2 ambient and drive-in diffusion in N2 or O2 ambients following a short time predeposition. Results show that predeposition diffusion in the SOI structures is retarded at 900°C as compared with that in bulk Si, while it is not at 1000°C. The diffusion retardation appears more clearly for the SOI structure with a thinner active layer and longer diffusion time. In the drive-in diffusion at 900°C, retardation occurs in O2 ambient, but not in N2 ambient. These results are explained by considering the extinction of excess interstitial Si at the Si/SiO2 interface in the SOI structure.