Electrical resistivity change in amorphous Ta42Si13N45 films by stress relaxation
In a first experiment, a reactively sputtered amorphous Ta42Si13N45 film about 260 nm thick deposited on a flat and smooth alumina substrate was thermally annealed in air for 30 min and let cooled again repeatedly at successively higher temperatures from 200 to 500 °C. This treatment successively and irreversibly increases the room temperature resistivity of the film monotonically from its initial value of 670 μΩ cm to a maximum of 705 μΩ cm (+5.2 %). Subsequent heat treatments at temperatures below 500 °C and up to 6 h have no further effect on the room temperature resistivity. The new value remains unchanged after 3.8 years of storage at room temperature. In a second experiment, the evolution of the initially compressive stress of a film similarly deposited by reactive sputtering on a 2-inch silicon wafer was measured by tracking the wafer curvature during similar thermal annealing cycles. A similar pattern of irreversible and reversible changes of stress was observed as for the film resistivity. Transmission electron micrographs and secondary ion mass profiles of the film taken before and after thermal annealing in air establish that both the structure and the composition of the film scarcely change during the annealing cycles. We reason that the film stress is implicated in the resistivity change. In particular, to interpret the observations, a model is proposed where the interface between the film and the substrate is mechanically unyielding.
The Ta36Si14N50 film was deposited and patterned by Dietmar Bertsch at NTB, Buchs (SG). Peter van der Wal and Sylviane Pochon of the IMT, University of Neuchâtel, sliced the alumina substrate. The secondary ion mass profiles reproduced in Fig. 3 were obtained from Jen-Sue Chen, Natl. Cheng Kung University, Taiwan. Konrad Samwer, University of Göttingen, offered constructive suggestions how to better the manuscript (e.g. Fig. 5). We thank them all five for their generous participation.
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