Dependence of Si-SiO2 interface state density on oxide thickness in structures with ultrathin (79–227 Å) oxides

Abstract

Admittance voltage characteristics of Si/79–227 Å SiO2/metal structures were measured in dark and under optical illumination in the frequency range of 30 Hz–100 kHz. For fabricating the structures, thermal oxidation was carried out in dry oxygen at 900 °C at 1 atm. The interface state versus band-gap energy profiles of the unannealed samples exhibited peaked distributions near the valence and conductance-band edges, overlying a concave background. The interface state density versus oxide thickness profile was observed to go through a minimum and a maximum instead of decreasing in a monotonic fashion.

Process Dependence of the Si ‐ SiO2 Interface Trap Density for Thin Oxides

“…For the 1050~ samples, the effect of oxide thickness is important only when the oxide is thinner than 200/~. The general trend of thickness dependence is consistent with the measurement by Kar et al on thin (79-227A) as-grown oxides on n-type substrates, except they found that the Dit values go through a maximum around the oxide thickness of 150A, rather than varying in a monotonic fashion (10). The minor disagreement is probably due to different processing conditions and materials.…”

“…Results of the annealed samples indicate that the peak structures can be readily removed by a low temperature hydrogen annealing. Similar density peaks occurring in the lower half of bandgap have been frequently observed for as-oxidized samples (5,10,17). Employing the electron paramagnetic resonance (EPR) and quasi-static techniques, Gerardi et al observed a direct correlation between the bandgap distribution of the Pb centers and interface traps for as-grown oxides (18).…”

“…However, not much has been reported about the effects of reducing the oxide thickness on the process dependence of the interface trap density (D~t). There are conflicting results on the thickness dependence of Dit for thin oxides (9,10). An investigation of the process dependence of interface trap density for thin oxides has another far-reaching implication for scaled devices.…”