DIFFUSION OF AS, P, AND B FROM DOPED POLYSILICON THROUGH THIN SIO2-FILMS INTO SI SUBSTRATES

Diffusion characteristics of As, P, and B in SiO2 films as thin as 35 angstrom have been studied using doped polysilicon/SiO2/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 DSiO2-As (cm2 s-1) = 2.3 x 10(3) exp (-5.3 eV/kT), m(As) = 1.8 x 10(7) exp (-1.3 eV/kT), DSiO2-P (cm2 s-1) = 1.2 x 10(-2) exp (-4.1 eV/kT), m(P) = 9.2 x 10(5) exp (-1.0 eV/kT), DSiO2-B (cm2 s-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 SiO2 film thickness. Based on the change of bond characteristics in SiO2 observed by SIMS and ESCA, the enhancement has been explained by assuming that the changed layer with a high diffusion coefficient grows in SiO2 with a thickness d(F) = square-root kt, where the rate constant k is given typically by k(cm2 s-1) = 2.5 x 10(7) exp (-6.4 eV/kT) for a B concentration in polysilicon C(poly) = 2.5 x 10(20) cm-3.