In situ ellipsometry study of the kinetics of hydrogen plasma interaction with a-Si:H thin films: A particular temperature-dependence

摘要

We performed H_2 plasma treatment of hydrogenated amorphous silicon (a-Si:H) thin films and followed by in situ spectroscopic ellipsometry measurements the kinetics of hydrogen-induced film modifications at temperatures varying from 100 to 250 ℃. The time-dependence of the H-modified layer thickness d_H(t) follows an exponential relation of the form d_H~0[l -exp(-t / τ)]. The temperature-dependence of dH~0 and t shows a discontinuity at 7=200 ℃. While the activation energy of dH~0 changes from 0.19 eV at T<200 ℃ to 0.05 eV at higher temperatures, the activation energy of τ suddenly changes from 0.15 eV to a negative value (-0.26 eV). Such a discontinuity should be linked to the thermal equilibrium temperature of undoped a-Si:H. Moreover, we found that the rate of formation of the H-modified layer r_H=d_H~0/τ varies in inverse proportion to the etching rate, indicating a balance between hydrogen insertion and film etching at the steady state.