Nondestructive detection of titanium disilicide phase transformation by picosecond ultrasonics

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Abstract
We demonstrate that picosecond ultrasonics is a sensitive nondestructive probe of the formation of TiSi2 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 TiSi2 are formed. The longitudinal sound velocity is measured to be (8.3±0.2)×105 cm/s for C49 TiSi2, and about 5% lower for the C54 phase.