Study of temperature dependence of positive charge generation in thin dielectric film of MOS structure under high-fields

Abstract

In this work, the temperature effect on positive charge generation under high-field electron injection in MOS structures is studied using a new multilevel current stress technique. In our experiments, we used commercially made test MOS capacitors based on thermal silicon dioxide film with thickness in the range from 7 to 100 nm. Using the proposed multilevel current stress technique one can investigate the positive charge generation in MOS structure gate dioxide under high electric fields. The technique is different from the standard constant current stress technique, as it includes two levels of current: the stress current level, which provides the generation of positive charge, and the additional measuring current level, which allows to monitor the change of dielectric charge. Due to the additional measuring current level, it is possible to decrease significantly the error of positive charge density measurement in the dielectric. The latter error is caused by the positive charge trapped in the initial stage of electron injection while the steady-state of the stress mode is being reached. It was found that the rise of sample temperature leads to a decrease of the density of the positive charge generated in SiO 2 film under high-field injection of electrons from the silicon substrate. A model of the positive charge generation in MOS structures under high-field electron injection has been proposed. The new model of the positive charge generation in MOS structures takes into account the temperature effect and the subsequent phenomena of dielectric charge state change: the band-to-band impact ionization in SiO 2 with the creation of electron-hole pairs and the subsequent trapping of holes in traps in the oxide; the trapping of injected electrons by trapped holes as well as the thermal release of trapped holes from the traps.