The power electronics has been driving the improvement of the performance and SDGs of electric cars, trains, ships, and so on. The maximum density of current is about 1000 A/cm2, and the expected lifetime at 250oC is longer than 1000 h. The expected lifetime under the temperature cycle between -40oC and 250oC is longer than 1000 cycles. Even under these harsh condition, Al-base material is still mainstream interconnection material from the perspectives of processability and cost of power devices to be installed in electric vehicles, etc., which are expected to be widely used in the future. Therefore, it is essential to ensure the reliability of Al-interconnections under the high current density condition. Under such high current density condition, electromigration (EM) dominates the effective lifetime of the interconnections. The lifetime of the interconnections was quantitatively evaluated by using Black’s law, in which the lifetime is mainly dominated by temperature and current density. In addition, the main diffusion path under EM was grain boundaries. Recently, it was found, however, that effective lifetime of the electroplated copper and gold thin-film interconnections varied by about 100 times strongly depending on the crystallinity of grain boundaries in the polycrystalline thin films. The effective activation energy of the diffusion of component atoms along grain boundaries was found to decrease drastically with the decrease of the crystallinity.In this study, the correlation between the quality of grain boundaries and EM resistance of Al thin films fabricated by sputtering as a thin-film interconnection material was investigated by evaluating the crystallinity and crystal orientation using EBSD (Electron Back-Scatter Diffraction) analysis. The test interconnection structures were fabricated on a 2-inch diameter Si wafer and 200-nm thick TiN was deposited as the base layer by RF sputtering in Ar with pressure of 0.5 Pa, and power of 300 W. The deposition temperature was varied from room temperature t 300oC. Next, 1-μm thick Al film was deposited on the TiN layer by sputtering under the same conditions. After the deposition of the thin films, to control the crystallinity of the thin film materials, they were annealed in N2 environment for 30 min at 300°C. After that, the surface of the samples was polished appropriately in order to evaluate the crystallinity of the micro texture by the EBSD method using a scanning electron microscope.It was confirmed that the crystallinity of the Al interconnections deposited at room temperature was rather low and the most grain boundaries consisted of random grain boundaries with low crystallinity. Since these random grain boundaries were found to be the main diffusion path under EM, the degradation of the crystallinity under EM was confirmed to be almost uniform in the interconnections as was reported in a lot of previous researches. When the interconnections were annealed at 300oC, however, their crystallinity, in particular, the crystallinity of grain boundaries was found to improve drastically. In addition, the average grain size and crystallographic orientation of the interconnections also changed drastically by the annealing. As a result, the EM resistance of the Al interconnections varied drastically strongly depending on their fabrication process. Therefore, the further improvement of the crystallinity of grain boundaries is essential for the improvement of the EM resistance of Al interconnections.&nbsp;

Crystallinity-Induced Acceleration of Intergranular Cracking in Thin-Film Interconnections Under High Current Density

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.