Microstructure of Al-Cu thin-film interconnect

Abstract

The precipitate structure of bulk aluminum alloys was heavily studied with x-ray diffraction commencing in the 1930s and via direct observation with the development of transmission electron microscopy (TEM) techniques in the 1950s. In 1970, recognition of the electromigration performance benefits of Cu additions to Al interconnect in integrated circuit devices precipitated studies on Al-Cu thin films. However, the microstructure of these films remains only partially known, in part due to the many process and interconnect geometry variables. In particular, there has been minimal attempt to study films which mimic as closely as possible the environment and thermal history of real interconnect (prior studies typically have examined unpatterned or unpassivated films.) In the present work, Al-Cu films in standard life test devices have been studied. This work is directed at understanding the evolution of microstructure during device processing and life testing and application of this knowledge to a better understanding of the role of microstructure in electromigration in Al-Cu interconnect. The present contribution describes initial microstructural observations on a variety of annealed samples.