In-Situ Tem-Investigations of Electromigration Induced Mass Transport in “Near-Bamboo” Al-Interconnects

Abstract

ABSTRACTElectromigration(EM)-driven mass transport in “near-bamboo” Al-lines, which consist mostly of “blocking grains” is an important topic of research on ULSI-metallizations. Because the most easy diffusion path, i.e. grain boundaries parallel to the line, is suppressed in bamboo-like Al-lines other paths have to be considered. In this work two other possible paths of diffusion were examined by in-situ observations in a transmission electron microscope (TEM). For these experiments a special sample holder had to be constructed.One path is EM-driven intragranular diffusion in Al-lines. In this experiment, inert gas-filled voids with a mean diameter of about lOnm, so-called bubbles, which were created after gas implantation and annealing of the Al-lines, serve as indicators of mass (or vacancy) transport. The in-situ EM-tests reveal no intragranular void motion over a period of more than 100h at current densities of l-1.75MA/cm2 and temperatures of 150–225°C. This leads to an estimation of the maximum void diffusion velocity which was compared with calculated values of surface and volume diffusion controlled void motion, respectively. The second point of interest was the behavior of dislocations in Al-lines under an applied EM-force. The importance of their observed motion for intragranular mass transport will be discussed.