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

为了阐明微电子电路中连接线与块状材料在变形和断裂机制上的差异，研究了试样厚度t和晶粒尺寸d对Al-1%Si-0.5%Cu合金薄板和箔高温蠕变行为的影响。该合金经常以溅射薄膜线的形式用于连接线。本研究的主要问题是单薄铝材料的高温变形机制是否与块状材料的高温变形机制不同，以及单薄铝材料是否发生与应力诱导空化相同类型的断裂。结果表明，稳态蠕变速率与-α-t /d的次幂成正比，在外加应力σ为30 MPa及以上时，α指数近似为常数和单位。α值随外加应力的减小而减小，但在此范围内始终为正值。这意味着蠕变速率随晶粒尺寸的增大和试样厚度的减小而增大。虽然表观应力指数高达7.9 ~ 10.4，但考虑阈值应力，真实应力指数为5。观察到硅相颗粒弥散的结果支持了阈值应力的存在，TEM观察到稳态蠕变过程中微观组织由亚晶粒组成，支持了5（位错蠕变受恢复或位错爬升控制）的真应力指数。断口形貌显示，在应力引起的空化情况下观察到的晶间断裂没有发生。当t≥200μm时，近大块试样的断口形貌为韧窝型；当t≤100μm时，较薄试样的断口形貌为极延性材料的典型断口凿线型。从这些结果可以推断出，这种薄材料的高温变形是在一种基于变形过程中亚晶结构非均质性的新模型中进行的，其中亚晶在晶界附近更细，在自由表面附近更粗。该模型有望成为金属材料高温变形研究领域的基本理论之一，目前该领域只考虑均匀微观结构。少

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