The influence of different deposition parameters on the microstructure and the residual stress of Ti thin films has been investigated. Ti films were deposited onto Si (001) wafers by dc magnetron sputtering. The sputtering rate, the microstructure and the residual stress as determined respectively by α-step, TEM and X-ray, was varied by changing the Ar sputtering pressure $P_{Ar}$ between 0.5 and 7mtorr, and by applying a negative substrate bias -$V_{bias}$ between 0 and 200V. For $V_{bias}$=0V, the sputtering rate has maximum value at $P_{Ar}$=2.7mtorr. At $P_{Ar}$=2.7mtorr, the sputtering rate decreases with an increase in -$V_{bias}$. The as-deposited films showed strong (002) preferred orientation. The residual stress in the films were determined by the XRD $\sin^2\psi$ method. For the case of $V_{bias}$=0V, the residual stress in the films changed abruptly from compressive to tensile stress at about $P_{Ar}$=2mtorr. A maximum tensile stress of about 600MPa was obtained at $P_{Ar}$=2.7mtorr. The compressive stress at $P_{Ar}$=0.5mtorr measured to be about 400MPa. The results of TEM showed an accompanying structural change at grain boundaries: the amount of observed voids was large at $P_{Ar}$=2.7mtorr while it was small at $P_{Ar}$=0.5mtorr. For the case of $P_{Ar}$=2.7mtorr, where the largest tensile stress was obtained, the application of a negative substrate bias resulted in a transition from tensile to compressive stress state. The tensile stress was believed to arise from the presence of regions of low atom density at grain boundaries. The compressive stress is believed to be due to the shot peening effect of the Ar atoms and/or sputtered Ti atoms. Compressive stresses develop for the case of -$V_{bias}$>50V. TEM observations showed a dense film structure for that case. The residual stress was saturated to about 500MPa at -$V_{bias}$>75V. This phenomenon could be interpreted as plastic deformation of Ti films.
$TiSi_2$ formation study has been performed using Ti thin film deposited at $P_{Ar}$=1mtorr and $P_{Ar}$=2.7mtorr for -$V_{bias}$=0V. Thin films of Ti were fully transformed to C49 $TiSi_2$ on annealing at 660℃ for 1.5hr and to C54 $TiSi_2$ on annealing at 750℃ for 0.5hr. The transition temperature of C49 to C54 $TiSi_2$ was measured to be lower at $P_{Ar}$=1mtorr, where a large compressive stress is present, as compared to that at $P_{Ar}$=2.7mtorr, where a large tensile stress is measured. This decrease of transition temperature with deposition conditions is believed to arise from the presence of different types of residual stress in Ti thin film. The transition of C49 → C54 induces a tensile residual stress due to the volume contraction during the transition. Therefore the compressive residual stress present in the Ti thin film can be facilitate the transition of C49 → C54, whereas the tensile residual stress exerts an adverse effect. The temperature and film thickness can affect the magnitude of the residual stress in the film. The consideration of theses effects however has led us a similar conclusion because the expected direction of change is similar for both case.
