RAPID THERMAL ANNEALING OF WSIX - INSITU RESISTANCE MEASUREMENTS

In-situ sheet resistance measurements have been performed on amorphous WSi2.5 alloy films deposited by low pressure chemical vapour deposition either on thermal oxide or on polysilicon. The heat treatments were performed in vacuum up to 1000-degrees-C at a heating rate ranging from 5 to 6000-degrees-C/min. The temperature was measured with a thermocouple placed underneath and in contact with the sample; the film sheet resistance was measured with a four-point probe in van der Pauw configuration. The in-depth elemental composition was determined by 2 MeV He-4+ backscattering technique. Nuclear reaction was used to monitor the quantity of fluorine present in the sample. The phases formed were identified by X-ray diffraction. The sheet resistance versus temperature curves are all similar and present, after a small initial decrease, first a sharp increase followed, after about 200-degrees-C, by a decrease. X-ray diffraction measurements indicate that the increase is due to the amorphous-hexagonal phase transformation; the decrease is due to the formation of the tetragonal WSi2 phase. The temperature at which the two variations occur increases with the heating rate indicating thermally activated processes. The activation energies are 1.4 +/- 0.1 and 2.4 +/- 0.1 eV for the amorphous-hexagonal and hexagonal-tetragonal transformation, respectively. Silicon segregation at the inner interface occurs only on the samples where the silicide alloy was deposited on polysilicon and for heating rates lower than 200-degrees-C/min. The total fluorine content is not affected by the kind of heat treatment performed.