Diffusion of As, P, and B from Doped Polysilicon through Thin S1O² Films into Si Substrates

Diffusion characteristics of As, P, and B in SiO² films as thin as 35 A have been studied using doped polysilicon/ Si0²/Si structure samples. A two-boundary model can well characterize the As and P diffusion and low concentration B diffusion, where the derived diffusion coefficients and segregation coefficients are given by D^{SiO2 as} (cm² s^-l) = 2.3 x 10³ exp (-5.3 eV/kT), m^As = 1.8 x 10⁷ exp (-1.3 eV/fcT), D^sio²-p (^{cm2 s_1}) ⁼ 1.2 x 10² exp (-4.1 eV/kT), m^P = 9.2 x 10⁵ exp (-1.0 eV/kT), D^Sio²-B (cm²s^-1) = 0.31 exp (-4.2 eV/kT), m^B = 30 exp (-0.33 eV/kT). For diffusion of high B concentrations, anomalous enhancement of diffusion has been observed at long diffusion times t, and thin Si0² film thickness. Based on the change of bond characteristics in Si0² observed by SIMS and ESCA, the enhancement has been explained by assuming that the changed layer with a high diffusion coefficient grows in Si0² with a thickness d^F = V/ct, where the rate constant k is given typically by fc(cm² s’¹) = 2.5 x 10⁷ exp (—6.4 eV/kT) for a B concentration in polysilicon Cpoly = 2.5 X 10²⁰cm^-3.