Towards Structural Analysis of Polymeric Contaminants in Electrodeposited Cu films

Abstract

The incorporation of plating additives into Cu films was studied by means of complementary Laser Ablation/Ionization Mass Spectrometry (LIMS) and Secondary Ion Mass Spectrometry (SIMS) depth profiling techniques combined with Focused Ion Beam (FIB) analysis.Cu test samples were electrodeposited in the presence of a new prototypical two-component additive package for advanced Damascene applications consisting of a hybrid-type suppressor additive (Imep: polymerizate of epichlorohydrin and imidazole) and its essential co-additive (SPS: bis-(sodium-sulfopropyl)-disulfide). The tunable non-linear interplay between the Imep and the SPS during oscillatory Cu electrodeposition is used to fabricate samples bearing spatially confined layers with sequential high and marginal additive embedment. These test samples constitute an excellent platform to conduct true quantitative chemical depth profiling analysis of electrodeposited Cu films. In particular LIMS depth profiling measurements with an unmatched nano-meter depth-resolution demonstrate a preferential inclusion and accumulation of contaminants at grain boundaries inside the Cu deposit whereas the Cu grains remain largely contamination-free. A novel LIMS desorption approach is presented which allows for a molecular structure analysis of the polymeric additive ensembles preferentially embedded at grain boundaries of the Cu deposit. Our LIMS analysis confirms a recently discussed mechanism on the action of these hybrid additives which relies on their interaction with thiolate-stabilized Cu(I) intermediates.