Hole Transport and Recovery Characteristics of SiO2 Gate Insulators

The transient response, or flat-band voltage recovery, in a number of pedigreed SiO2 gate insulator MOS capacitors following exposure to a pulsed 13-MeV electron beam was studied as a function of time, temperature, and applied bias. A quantitative comparison of the response characteristics of the different oxides is made. It is found generally that the response consists of two stages. The first (early time) stage in most cases encompasses most of the recovery and is dominated by hole transport through the insulator film to the interface. This hole transport recovery stage in all the oxides studied is well described by the stochastic model of hopping transport based on a continuous time random walk used previously in the analysis of hole transport in SiO2. It is further shown that all the main features of the hole transport are consistent with a model of the holes moving via polaron hopping between localized sites in the SiO2. The second or long-term stage of recovery commences after cessation of the hole transport in the oxide and is found to vary significantly in its importance and time of onset among the various oxides. This stage involves a radiation-induced buildup of interface states and possibly, in some cases, an annealing of a trapped-hole distribution near the SiO2/Si interface.