The P doping of polycrystalline Si by the direct diffusion of PH3 at 685 and 785C, followed by rapid thermal annealing, was investigated. Contrary to the behavior at 785C, the dopant profile was not uniform at 685C, but became so after rapid thermal annealing (1050C, 10s); as revealed by secondary ion mass spectroscopic data. In the absence of any protective layer, rapid thermal annealing in N caused the out-diffusion of about 50% of the P from a sample which was diffused at 785C; but it activated almost 100% of the remaining P atoms (as indicated by Hall and secondary ion mass spectrometry measurements). On the other hand, rapid thermal annealing in O resulted in 95% activation of the incorporated P from the same sample, together with the oxidation of about 7nm of polycrystalline Si. In the case of samples diffused at 685C, rapid thermal annealing in N did not cause any out-diffusion, but it activated less than 80% of the incorporated P atoms. This difference in behavior was attributed to the tendency to produce equilibrium concentrations of P in the crystallites, and at the grain boundaries, at the rapid thermal annealing temperature. The highest active P concentration which was achieved was 2.0 x 1020/cm3 at 785C, followed by rapid thermal annealing in O to yield a resistivity which could be as low as 0.0009cm.

High Concentration Phosphorus Doping of Polycrystalline Silicon by Low Temperature Direct Vapor Phase Diffusion of Phosphine Followed by Rapid Thermal Annealing. S.Lourdudoss, S.L.Zhang: Applied Physics Letters, 1994, 64[25], 3461-3