Nondestructive detection of titanium disilicide phase transformation by picosecond ultrasonics

We demonstrate that picosecond ultrasonics is a sensitive nondestructive probe of the formation of TiSi, from the reaction of titanium films on silicon annealed at temperatures of 300-800 “C. From the measured change in optical reflectivity, the responses due to electronic excitation, acoustic echoes, and thermal coupling to the underlying Si are resolved. The results show significant differences in the electronic response and the ultrasonic echo pattern before and after the structural phases C49 and C54 TiSi, are formed. The longitudinal sound velocity is measured to be (8.3 *0.2) X lo5 cm/s for C49 TiSiz, and about 5% lower for the C54 phase.