Diffusion of As, P, and B from Doped Polysilicon through Thin SiO2 Films into Si Substrates

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