Mechanical Stress Dependence of Radiation Effects in MOS Structures

The effects of mechanical stress on radiation damage in polycide-gate MOS capacitors have been investigated as a function of gate-oxide thickness and silicide-gate electrode material (TiSi2, MoSi2 and WSi2). It was found that compressive stress on the SiO2/Si interfacial region reduces both positive charge build-up and interface-trap generation. The positive charge build-up exhibits a smaller stress effect, as compared with the interface-trap generation. The magnitude of stress effect depends only on the compressive strength, and not on the silicide material, if the annealing conditions are the same. In addition, as the gate-oxide thickness decreases, the stress effect on positive charge build-up increases, while the interface-trap generation remains nearly constant. These results can be explained on the basis of the bond reformation process, i. e., in a region where compressive stress exists, the broken bonds are reformed with high probability. Futhermore, radiation response of MOS transistors with different gate-oxide stress values have been evaluated, and compared with those observed in MOS capacitors. Similar stress effects were also obtained.