Tracing the Ti-silicide formation by in situ ellipsometric measurements

Abstract

In situ multi-wavelength ellipsometry is employed to trace the reaction of Ti/Si to C49-TiSi 2 as well as the polymorphic C49-to-C54-TiSi 2 transformation by thermal annealing up to 900°C for Ti layers of different thickness (10– 80 nm ) on Si (1 0 0). Ti deposition, annealing and ellipsometry were performed in the same ultrahigh vacuum system. In this way, the silicidation process could be studied without the influence of oxygen and carbon contamination. Characteristic changes in the ellipsometric angles as a function of temperature were correlated with phase changes in the Ti/Si system by halting the heating ramp at the corresponding temperatures and performing structural analysis by X-ray diffraction and Raman spectroscopy. The first change, completed at around 530–600°C, is due to the reaction of Ti with Si to form C49-TiSi 2, whereas the one shortly afterwards is caused by the polymorphic transformation of C49–TiSi 2 to the C54 phase at 600–650°C. After C54-TiSi 2 formation both ellipsometric angles keep changing slowly but continuously. At these temperatures, the silicide surface undergoes serious roughening. With increasing ramp rates the transformation temperatures are shifted to higher temperatures. In addition, the C49–C54 transformation is retarded relative to the C49 phase formation with decreasing Ti thickness. An as yet unassigned phase is observed to appear with C49-TiSi 2 formation and to be consumed by C49-TiSi 2 in a narrow temperature interval. Additionally, the optical constants of the constituent phases Ti, C49- and C54-TiSi 2 were calculated from spectroscopic ellipsometry measurements in the range from 415 to 750 nm .