In-situ X-ray diffraction during rapid thermal annealing at rates from 3 to 20 degrees C s(-1) was used to study the formation of titanium silicide phases from a thin film of Ti and doped single-crystal or undoped polycrystalline silicon substrates. In all cases, a metal-rich silicide (identified as either Ti5Si4 or Ti5Si3) was the first crystalline phase to form between 500 and 550 degrees C, followed by C49-TiSi2 between 575 and 600 degrees C. The formation of C49-TiSi2 completely consumed the metal-rich silicide before transforming into the low-resistance C54-TiSi2 phase at approximately 800 degrees C. These results indicate that while there is sufficient thermodynamic driving forces to nucleate both a metal-rich silicide and C49-TiSi2 the subsequent growth of C49-TiSi2 is kinetically favored over the growth of Ti5Si4 or Ti5Si3.