On the Size Effect in MOS Structures under Ionizing Irradiation

A quantitative model of the size effect, i.e., the dependence of surface states on the gate size, in metal-oxide-semiconductor (MOS) structures subjected to ionizing irradiation is developed. It is assumed that the size effect is induced by the escape of hydrogen released from hydrogen-containing hole traps through the ends of a two-dimensional MOS structure. The effect is described by a system of diffusion-kinetic equations solved together with the Poisson equation. The influence of processing treatments and thermal-oxidation modes on the magnitude of the effect is associated with different concentrations of hydrogen-containing traps in the gate oxide. It is shown that the main contribution to the effect is introduced by the diffusion of neutral hydrogen atoms accelerated by ionizing irradiation.