INFLUENCE OF PARTICLE BOMBARDMENT ON MICROSTRUCTURE AND INTERNAL-STRESSES OF REFRACTORY-METAL SILICIDES ON SILICON

First results on microstructural changes and stress relaxation in thin refractory metal silicide films (TaSi2 and MoSi2) caused by particle bombardment are reported. The polycrystalline films had initial tensile stresses of some 10(9) Pa. Exposed to irradiation with Ge ions of 400 keV, both silicides showed a similar stress relaxation behaviour as a function of dose. During room-temperature implantation the initial tensile stress rapidly decreased and turned into compressive stress. Continuous irradiation partly relaxed the compressive stress and resulted in a saturation value of some -10(8) Pa. With increasing implantation temperature, the buildup of compressive stress gradually vanished, leaving only the initial decrease of tensile stress which finally approached zero. Based on microstructural investigations (TEM and X-ray diffraction) it is proposed to explain this behaviour by the combined action of two processes: relaxation of tensile stress by a volume increase due to irradiation-induced amorphization, and Frenkel defect production and relaxation of compressive stress by irradiation-induced densification of amorphous regions and/or Frenkel defect elimination.