Thin film stresses in TiW/AlCuSi/TiW sandwich structures

A highly reliable metallization for high current bipolar integrated circuits was developed with the aid of thin film stress analysis to optimize the process. The final structure was a sandwich layer of TiW and AlCuSi alloy. Film stresses were measured for individual TiW layers as well as for the sandwich layers of TiW/AlCuSi/TiW. In this paper, it will be shown how sputter deposition pressure can drastically affect film stress. For individual TiW layers, the film stress can be varied between compressive and highly tensile by adjusting the Argon pressure. Meanwhile, the AlCuSi layers were always tensile under the normal range of sputtering pressure. By controlling the individual film stresses, a sandwich layer can be designed so that the overall structure has a very low average stress. This work also shows how a TiW capping layer has a major effect on the final average stress of the sandwich structure