Changes in Optical Properties during Nickel Silicide Formation and Potential Impact on Process Results using Various Heating Methods

Nickel silicide was formed by heating sputtered Ni film on Si wafers in a stacked hotplate-based low temperature annealing system under 1 atm N₂. The annealing temperature was varied in the range of 200 ~ 450degC. Sheet resistance, spectral reflectance and spectral absorbance of Ni film on Si wafers were measured before and after annealing. Formation of desirable stoichiometric NiSi was observed by sheet resistance measurement, X-ray diffraction and cross-sectional transmission electron microscopy over the wide temperature range of 300 ~ 450degC. Phase change from Ni₂Si to NiSi was observed at approximately 300 ~ 350degC. The optical properties of nickel film, in particular spectral reflectance and absorbance, showed dramatic change during various stages of nickel silicide formation. Strong diffraction was observed from the patterned wafers. Microscopic reflectance and absorbance variation was observed from the patterned wafers as a result of the selective nature of silicidation. To minimize the negative impact of changes in optical properties during silicidation, radiation-based heating should be avoided as much as possible