We used tapping-mode AFM to study TiSi2 formation on an Si(lll) surface in an ultrahigh vacuum with Ti film thicknesses ranging from 0.05 to 20 nn. Observation of the surface morphology confirms the presence of three kinds of silicide structures: small hemispheric C49-TiSi2, 2D island C54-TiSi2, and strip-like C54-TiSi2. The phase transition from C49-TiSi2 to C54-TiSi2 is dependent on the Ti film thickness as well as the temperature. Ti evaporation on high-temperature substrate is an effective method for lowering the phase transition temperature.