Morphological Instability Of Ag Films Caused By Phase Transition In The Underlying Ta Barrier Layer

Wide-bandgap (WBG) semiconductor technologies are maturing and may provide increased device performance in many fields of applications, such as high-temperature electronics. However, there are still issues regarding the stability and reliability of WBG devices. Of particular importance is the high-temperature stability of interconnects for electronic systems based on WBG-semiconductors. For metallization without proper encapsulation, morphological degradation can occur at elevated temperatures. Sandwiching Ag films between Ta and/or TaN layers in this study is found to be electrically and morphologically stabilize the Ag metallization up to 800 degrees C, compared to 600 degrees C for uncapped films. However, the barrier layer plays a key role and TaN is found to be superior to Ta, resulting in the best achieved stability, whereas the difference between Ta and TaN caps is negligible. The beta-to-alpha phase transition in the underlying Ta barrier layer is identified as the major cause responsible for the morphological instability observed above 600 degrees C. It is shown that this phase transition can be avoided using a stacked Ta/TaN barrier. (C) 2014 AIP Publishing LLC.