The influence of heat treatment and of different deposition paramaters on the phase transformation of $TiSi_2$ thin film has been investigated. And stress variations during C49 and C54 phase transformation were measured and analysed.
Ti and Si were cosputtered onto a Si＜100＞ substrate, using alloy target of $TiSi_{2+α}$ in a dc magnetron sputtering apparatus. As-deposited thin films were heat-treated in a vacuum furnace holding a pressure $＜1×10^{-5}$ torr. Phase transformation has been monitored using a XRD and sheet resistance measurement apparatus. Stress variation has been monitored using an laser apparatus measuring curvature variation. The evolution of grain size and phase transformation has been further characterized using SEM and TEM.
Transformation temperature of C49 to C54 was affected by the variation of film thickness, stress, and composition. For thicker films, polymorphic transformation temperature was decreased. And C49 structure in a higher tensile stress state required a longer time to be transformed to the stable C54 structure at a given temperature. Heat treatment temperature to obtain a stable C54 configuration was decreased as the alloy target composition was slightly Si-excess(i.e., $TiSi_{2.1}$).
Two-step heat treatment consisting of 1st temperature below ~650℃ and 2nd temperature above ~650℃ suggested that the increasing first heat treatment temperature tends to enhance the transformation rate of C49→C54 at the second (high) heat treatment temperature. This is closely correlated with an initial tensile stress level of C49 film especially in the case where amorphous→C49 transformation is complete.
The structure of as-deposited thin film was amorphous. The heat treatment below ~650℃ induces a crystallization of this film into C49 structure. The heat treatment above ~650℃ leads to a further transformation of C49 to C54 structure. The results indicate that the C54 structure rarely evolve directly from amorphous structure and that it almost always evolves from the C49 structure. The result further indicates that the transformation of amorphous→C49 (preceeding C49→C54) at above ~650℃ occurs so rapidly that the transformation of C49→C54 appears to start after a complete transformation of amorphous→C49.
Phase transformation of C49 to C54 was significantly retarded in thin films deposited under an application of certain bias. Bias-sputtered specimen assumed a (004) (of C54) preferred texture after the transformation and severely grooved at the grain boundaries with an occasional formation of hole and hillock. The appearance of this texture and morphology is closely related with a high intrinsic tensile stress found in the initial film of C49 structure. Since the transformation of C49 to C54 induces an additional tensile stress, this case will lead to an abnormally higher tensile stress acting on thin film during the phase transformation. Room temperature stress for bias-sputtered specimen deposited from $TiSi_2$ composite target, was down to 640MPa in the stage of C54.
And cosputtered thin film initiated C49→C54 transformation as the amorphous film transformed to C49 phase up to a certain constant point. This was confirmed by the C49 vs C54 XRD intensity variations.
At 680℃, intrinsic tensile stress induced by the polymorphic transformation of C49→C54 was estimated to be ~700MPa.
