Layers of Si-B were used as a new B diffusion source for polysilicon/silicon systems. The layer was deposited onto polysilicon in an ultrahigh-vacuum chemical vapor deposition system at 550C. The characteristics of B diffusion in Si-B/polysilicon/silicon systems were investigated by using secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. In order to remove the Si-B layer, after the drive-in step, the Si-B layer was completely oxidized during the drive-in stage and was removed using HF. It was found that the B profiles within the polysilicon were slightly dependent upon the oxidation of the Si-B layer. The polysilicon grain size, after using a Si-B layer source, was greater than that after using conventional BF2+-implanted polysilicon sources. This was attributed to the effects of O gettering by the Si-B layer, and to secondary grain growth during Si-B layer oxidation. The B diffusion profiles in the Si substrate, after using a Si-B layer source, also exhibited a shallower junction depth and a lower sensitivity to the thermal budget; as compared with a BF2+-implanted polysilicon source. This was attributed to the effect of a smaller surface concentration in the Si substrate, in the case of a Si-B layer source.

Characteristics of Boron Diffusion in Polysilicon/Silicon Systems with a Thin Si-B Layer as Diffusion Source. T.P.Chen, T.F.Lei, H.C.Lin, C.Y.Chang: Journal of the Electrochemical Society, 1995, 142[2], 532-7