Dependence of the C49-C54 TiSi₂ phase transition temperature on film thickness and Si substrate orientation

The C49 to C54 phase transition and the surface and interface morphologies were examined for titanium silicides formed on atomically clean Si substrates. The properties were explored as a function of the Ti film thickness, deposition temperature and Si substrate orientation. Ti films of thicknesses between 5 nm and 40 nm were deposited at elevated temperatures from 500°C to 900°C in increments of 100°C onto Si(100) and Si(111) wafers. The titanium silicides are analyzed with X-ray diffraction, Raman, scanning and transmission electron microscopy for phase identification and measurement of the surface and interface morphologies. The C49 to C54 TiSi₂ phase transition is observed to occur between 600°C and 700°C for the thickest films on (100) wafers, but the transition temperature is observed to increase as the film thickness is decreased or for films formed on Si(111) substrates. For a 20 nm Ti film deposited onto Si(100), the transition temperature occurs between 600°C and 700°C. However, for the same thickness of Ti on Si(111), the transition temperature is found between 700°C and 800°C. This retardation of the phase transition is discussed in terms of surface and volume free-energy considerations.