DOPANT AND CARRIER CONCENTRATION IN SI IN EQUILIBRIUM WITH MONOCLINICSIP PRECIPITATES

The behavior of silicon slices very heavily implanted (1.5 x 10(17) cm (-2)) with phosphorus was investigated by transmission electron micros copy and secondary neutral mass spectrometry (SNMS) after annealing at 800, 850, 900, and 1000 degrees C. Precipitation of large monoclinic, and partially orthorhombic, SiP particles takes place in the most hea vily doped region. From the shape of the SNMS profiles in the dissolut ion stage of these precipitates, we determined the concentration C-sat of P in equilibrium with the conjugate phase: C-sat = 2.45 x 10(23)ex p(-0.62/kT) cm(-3). This concentration has to be compared with the equ ilibrium concentration n(e) of the electrically active dopant. To this end, more accurate determinations of n(e) were performed on heavily P -doped polysilicon films. It was found that n(e) = 1.3 x 10(22)exp(-0. 37/kT) cm(-3). Hence for T > 750 degrees C, C-sat exceeds n(e) and the concentration (C-sat - n(e)) of inactive mobile P increases with temp erature. The formation and the diffusion behavior of this inactive dop ant are in keeping with a preprecipitation phenomenon.