The influence of internal stresses in tungsten-gate electrodes on the degradation of MOSFET characteristics caused by hot carriers

The characteristic degradation of MOSFET´s with tungsten-gate electrodes caused by hot carriers is shown to be enhanced by internal stresses in gate electrodes. These stresses introduce strains in silicon substrates under the edges of gate electrodes, which increases the number of surface states at the Si-SiO2interfaces. As a result, these internal stresses enhance the degradation of MOSFET characteristics due to hot carriers. A new technique for reducing the strains induced in the region under the gate electrodes is presented. With this technique (namely, annealing before patterning tungsten films for gate electrodes), the degradation of tungsten-gate MOSFET´s can be decreased to a level compatible with that of conventional silicon gate MOSFET´s.