Comparative studies of As and B diffusion in polysilicon-on-monocrystal systems were performed by means of cross-sectional transmission electron microscopy and secondary ion mass spectrometry. The As and BF2 which were implanted into 300nm polysilicon, deposited via low-pressure chemical vapor deposition, were diffused into the underlying Si substrate by using rapid thermal annealing or furnace annealing. The As diffusion profiles were continuous across the polysilicon/monocrystal interface, except for a peak at the interface. They exhibited a gradual increase towards the interface, within the polysilicon layer, due to an inhomogeneous distribution of grain sizes in As-implanted polysilicon. At low annealing temperatures, the B profiles in monocrystalline Si were shallower than the As profiles. This then reduced the effect of grain boundaries with regard to high diffusivities. During high thermal budget annealing, B diffusion into the substrate was greater than As diffusion because of higher B diffusivities in monocrystalline Si. At high annealing temperatures, the native oxide at the interface broke up and caused the polysilicon layer to align epitaxially with the underlying substrate. The elapsed time up to the break-up of the interfacial oxide depended upon the dopant species and the annealing temperature. The oxide break-up took longer in As-doped samples than in B-doped samples.

K.Park, S.Batra, S.Banerjee, G.Lux, R.Manukonda: Journal of the Electrochemical Society, 1991, 138[2], 545-9