Radiation damage on MOS devices

Radiation damage on metal oxide semiconductor (MOS) films due to ionizing radiation is studied. In general radiation damage is made up of surface damage and bulk damage. The former one can be explained by two components that are mainly located at the interface between oxide and silicon: positive oxide charge and interface trap. From the microscopic point of view a physical model is proposed to describe the whole generation process of such radiation damage. On the other hand, the observed characteristic parameters are measured that record the macroscopic change of the MOS devices after irradiation. Bulk damage is normally not relevant for low energy X-ray irradiation, and consequently is not covered within the scope of this presentation. In order to study the radiation effect on MOS films different MOS devices are irradiated with X-ray up to a total dose of about 1 Mrad (SiO2). As a result a series of radiation effect are analyzed: oxide thickness dependence; dose rate effect; electric field dependence; saturation effect and improvement of radiation hardness through additional nitride layer. The main goal of the study on radiation effect is not only to give a comprehensive understanding of radiation damage but also to improve the radiation hardness of MOS devices, and moreover to improve the technology design. Because of the same processing for different MOS devices one could make a prediction of the feasibility of MOSDEPFET as a candidate for the vertex detector in the international linear collider in the end