Epitaxial CoSi2 films on Si(100) by solid-phase reaction

Abstract

The inversion of a bilayer of Co on top of Ti and a Si(100) substrate upon steady-state annealing, and the resultant formation of an epitaxial CoSi2 layer have been studied using both reactive (N2, N2+5% H2, He+14% H2) and nonreactive (vacuum) annealing ambients. In nitrogen, a high-quality, single-crystalline CoSi2 layer forms above 600 °C for 30 min, with an abrupt interface to the substrate. As the fraction of hydrogen in the ambient increases, the abruptness of the interface deteriorates slightly. On top of this silicide, the Ti is chemically bound with oxygen present as a contaminant. In the case of a nonreactive annealing ambient, the Co/Ti inversion still takes place, although it is only partial. Moreover, the interface is very rough. The structure is unstable above 800 °C for 30 min annealing and transforms into a mixed layer of Co0.25Ti0.75Si2 and epitaxial CoSi2 grains. Using isothermal vacuum annealings with varying durations, a square-root time dependence is observed for the growth of the epitaxial CoSi2 in a temperature range around 700 °C. An activation energy of Ea=3.5 eV is found for that process, which is higher than the 2.3 eV reported for the polycrystalline growth of CoSi2 and is attributed to this structural dissimilarity.