Migration-resistant amorphous AlY metallizations for surface acoustic wave filters

Surface acoustic wave (SAW) filters, delay lines, resonators or convolvers play a key role in consumer and communication systems such as video sets and mobile phones. The interconnects of such devices are exposed to considerable mechanical strains, which initiate fatigue. Amorphous aluminium-rare earth alloy metallizations are especially promising for replacing polycrystalline aluminium-copper interconnects, which are actually used for these micro-electromechanical systems (MEMS), because of their resistance against stress-migration and diffusion which should lead to a substantial improvement of lifetime and reliability of such devices, and their cost-effective processing. In this work, first experimental results for amorphous Al₈₄Y₁₆ alloy thin films deposited at room temperature (RT) by ultra-high vacuum (UHV) electron beam evaporation are presented. The composition of the films was validated by Rutherford backscattering (RBS) spectroscopy, and their amorphous structure was confirmed by X-ray diffraction (XRD) analysis. The roughness and hardness of the metallization, both important parameters for wire bonding, were investigated by scanning probe microscopy (SPM) and depth-sensing nanoindentation. The electrical resistivity was determined by four-point probe measurements. The amorphous films were annealed in UHV, and their crystallization temperature was investigated by XRD