Morphology and phase stability of TiSi2 on Si

The formation mechanisms and properties of TiSi2 on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi2 films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either by in situ annealing or deposition onto heated substrates. The island formation of TiSi2 and surface and interface morphologies of TiSi2 were examined by scanning electron microscopy and transmission electron microscopy. The TiSi2 formation process was monitored with in situ Auger electron spectroscopy and low-energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi2. Titanium film thicknesses from 50 to 400 Å were examined. For all thicknesses studied, the C49 TiSi2 phase is observed to nucleate. Immediately after low-temperature deposition, the interface morphology was smooth, but after reaction and nucleation of the C49 TiSi2 phase a rough interface was observed. After higher-temperature annealing the transition to the C54 TiSi2 phase was observed. For TiSi2 on Si(111), the interface becomes smooth and flat. The temperature of the C49-to-C54 transition was observed to vary as a function of film thickness and substrate orientation. The films exhibited island formation after high-temperature annealing. For similar Ti thicknesses and annealing temperature, different areal coverages and island morphologies of TiSi2 on Si(100) and Si(111) were observed. The island morphologies are modeled and analyzed based on a liquid-liquid model, and the surface and interface energies for different TiSi2 island structures are deduced from contact angle measurements. The C49 nucleation, interface morphologies, surface morphologies, and the C49-to-C54 structural phase transition are discussed in terms of surface and bulk free-energy considerations.