Basic Study on the high-Temperature Deformation in Thin Metallic Films and Wires

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To elucidate the difference in the deformation and fracture mechanisms between connect lines in microelectronic circuits and bulk materials, effects of specimen thickness, t, and grain size, d, on the high-temperature creep deformation behavior in Al-1%Si-0.5%Cu alloy thin sheets and foils have been investigated. The alloy is frequently used for connect lines in the form of sputtered thin film line. The primary issue of this study is whether the high-temperature deformation mechanism of simply thin aluminum materials is different from that of the bulk material or not, and whether the same type of fracture as in what is called stress induced voiding takes place in such thin materials or not.The results showed that steady-state creep rate was proportional to the -α-th power of t/d, and that the exponent α was approximately constant and unity at the applied stress σ of 30 MPa and over. The value of α decreased with decreasing the applied stress but was always positive in the range of the … More present experimental condition. This means that the creep rate increases with increasing grain size and with decreasing specimen thickness. Although apparent stress exponent was a value as high as from 7.9 to 10.4, taking the threshold stress into account, true stress exponent was deduced to be 5. The result that the dispersion of silicon phase particles was observed supports the existence of threshold stress, and the true stress exponent of 5 (dislocation creep controlled by recovery or dislocation climb ) was supported by the TEM observation that the microstructure during the steady-state creep consists of subgrains. Fractograpy showed that intergranular fracture as was observed in the case of stress induced voiding did not occur. The fracture morphology was dimple-forming type in the near-bulk specimens where t≧200μm, and chisel-line type, typical to the extremely ductile materials, in thinner specimens where t≦100μm. From these results, it has been deduced that high-temperature deformation in such thin materials proceeds in a newly proposed model based on heterogeneity in the subgrain structure during the deformation, where subgrains are finer in the vicinity of the grain boundary and coarser near the free surface. This model is expected to become one of the fundamental theories in the field of high- temperature deformation in metallic materials where merely homogeneous microstructure has been taken into account so far. Less