Oxygen and the thermal stability of thin CoSi2 layers

The thermal stability of thin ${\mathrm{CoSi}}_{\mathrm{2}}$ layers is demonstrated to improve with the use of oxygen-containing annealing ambients. Pinhole formation observed in 11–27 nm thick ${\mathrm{CoSi}}_{\mathrm{2}}$ layers after anneals at 800 °C in nitrogen and vacuum is found to be eliminated when oxygen is used as the annealing ambient. A thin ${\mathrm{SiO}}_{\mathrm{2}}$ layer grown during oxygen anneals, which curbs surface diffusion and reduces the rates of kinetic processes, is thought to be the primary reason for the retardation of layer agglomeration. The beneficial effect of air exposure and wet etches to the integrity of thin ${\mathrm{CoSi}}_{\mathrm{2}}$ layers is also shown. These findings suggest the inclusion of oxygen in certain Co salicide processing steps.