Formation and thermal stability of CoSi2 on polycrystalline Si

Abstract

The high temperature stability of CoSi2/polycrystalline‐Si/SiO2 structures has been explored by techniques of Rutherford backscattering, scanning, and transmission electron microscopy. Results indicate that the silicide formed by reacting 400 Å of Co with 3300 Å of poly‐Si is metallurgically stable up to 30 min at 900 °C. A 30‐min 1000 °C sinter causes intermixing of the silicide/Si phase, although the SiO2 layer is not visibly damaged. More severe forming‐gas anneals result in Si loss from the metallization and a complete destruction of the multilayered geometry. This Si loss can be prevented by sintering in a partially oxidizing ambient, which forms an encapsulating SiO2 surface layer. The stability of co‐sputtered films on Si is critically dependent on the as‐deposited Si/Co ratio. Si/Co2 are both unstable for temperature excursions in excess of 800 °C. In contrast, Si/Co≂2 composites form stable co‐sputtered silicides with thermal characteristics similar to those of thin Co on polycrystalline Si.