Observation of radiation induced changes in stress and electrical properties in MOS devices

Abstract

Strain measurements using x-ray diffraction were performed on irradiated commercial and radiation hardened metal gate CMOS devices in addition to polysilicon gate NMOS devices. I-V curves were taken and Vot and Vi, were separated using the subthreshold slope method for all devices. A correlation has been shown to exist between physical strain relaxation and the electrical properties as a function of radiation dose and recovery. Data shown suggest that the physical response (strain relaxation) in the silicon at the oxide interface is a measure of the type of damage induced and the recovery mechanism. Post radiation measurements of AVit and AVot taken immediately after irradiation support the conclusions of Zekeriya and Ma and Kasama, et al.; compressive stress at the silicon/SiO, interface does reduce radiation damage in the device. "

Enhanced thermally induced stress effect on an ultrathin gate oxide

“…On the other hand, when oxide thickness of the stressed samples increases, the J sat increment due to irradiation decreases. This result is consistent with the previous research results of Shaw et al 16 Increased exterior compressive stress in the silicon substrate will reduce the total net ͑tensile͒ stress, which results in less radiation damage in the device. The exterior compressive stress in the silicon substrate under a thicker oxide region enhanced the lattice mismatch, which resulted in a large initial fixed oxide charge density Q f , but released the strained bondings.…”