Diffusion of As, P, and B from Doped Polysilicon through Thin Si02 Films into Si Substrates

Diffusion characteristics of As, P, and B in SiO2 films as thin as 35 A have been studied using doped polysil icon/ S iOJS i structure samples. A two-boundary model can well characterize the As and P diffusion and low concentrat ion B diffusion, where the derived iffusion.coefficients and segregation coefficients are given by Dsio~As (cm 2 S 1) = 2.3 x 103 exp (-5.3 eV/kT), mA ~ = 1.8 X 10 ~ exp (--1.3 eV/kT), Dsio2-P (cm 2 s-l) = 1.2 x 10 2 exp (-4.1 eV/k'l'), mp = 9.2 x 105 exp (-1.0 eV/kT), Dsio2-u (cm 2 s-l) = 0.31 exp (-4.2 eV/kT), mB = 30 exp (-0.33 eV/kT). For diffusion of high B concentrations, anomalous enhancement of diffusion has been observed at long diffusion t imes t, and thin SiO2 film thickness. Based on the change of bond characteristics in SiO2 observed by SIMS and ESCA, the enhancement has beenexp la ined by assum-ing that the changed layer with a high diffusion coefficient grows in SiO2 with a thickness dr = Vkt, where the rate con-stant k is g iven typical ly by k(cm2s-~) = 2.5 x 107 exp (-6.4eV/kT) for a B concentrat ion in polysi l icon Cpoly = 2.5 x 1020 cm-3. A l though a thin gate oxide is necessary for ultra large scale integration (ULSI) (1), it has a weaker masking effect on impurity penetrat ion compared with conventional oxide geometries. Therefore, it is necessary to clarify th