A study was made of heavily-doped polycrystalline Si which was used as a transistor gate in standard complementary metal-oxide semiconductor technology. The aim was to study the redistribution and activation of B during thermal annealing in thin Si films implanted and deposited by low-pressure chemical vapor deposition using a disilane (Si2H6) gaseous source. The B concentration was monitored by secondary ion mass spectrometry. The resistivity measurements by the four-probe method showed that the films become conductors after annealing. Carrier mobility and active doping fraction were obtained by Hall effect measurements. In order to investigate the SIMS profiles, a model was proposed which was based upon the 1-dimensional numerical resolution of Fick's laws. This model took account of phenomena which were due to the effects of very heavy doping; such as that of clusters. The B diffusion coefficient and its activation percentage were deduced from the adjustment of simulated profiles with SIMS experimental ones. SUPREM IV software was used to estimate the B diffusion coefficients in these films and compare them to the results. A small gap between the profiles simulated by the present model and by SUPREM IV was observed, in particular in the region where the B limit solubility was exceeded. Nevertheless, the diffusion coefficient values obtained using the two methods were of the same order of magnitude.

Boron Diffusion and Activation during Heat Treatment in Heavily Doped Polysilicon Thin Films for P+ Metal-Oxide-Semiconductor Transistors Gates. R.Mahamdi, F.Mansour, E.Scheid, P.T.Boyer, L.Jalabert: Japanese Journal of Applied Physics - 1, 2001, 40[12], 6723-7