Modeling of surface damage at the Si/SiO2-interface of irradiated MOS-capacitors

Surface damage caused by ionizing radiation in SiO2 passivated silicon particle detectors consists mainly of the accumulation of a positively charged layer along with trapped-oxide-charge and interface traps inside the oxide and close to the Si/SiO2-interface. High density positive interface net charge can be detrimental to the operation of a multi-channel n-on-p sensor since the inversion layer generated under the Si/SiO2-interface can cause loss of position resolution by creating a conduction channel between the electrodes. In the investigation of the radiation-induced accumulation of oxide charge and interface traps, a capacitance-voltage characterization study of n/gamma- and gamma-irradiated Metal-Oxide-Semiconductor (MOS) capacitors showed that close agreement between measurement and simulation were possible when oxide charge density was complemented by both acceptor- and donor-type deep interface traps with densities comparable to the oxide charges. Corresponding inter-strip resistance simulations of a n-on-p sensor with the tuned oxide charge density and interface traps show close agreement with experimental results. The beneficial impact of radiation-induced accumulation of deep interface traps on inter-electrode isolation may be considered in the optimization of the processing parameters of isolation implants on n-on-p sensors for the extreme radiation environments.