Microstructure analysis of plasma enhanced atomic layer deposition-grown mixed-phase RuTaN barrier for seedless copper electrodeposition

Abstract

Plasma enhanced atomic layer deposition (PEALD)-grown mixed phase RuTaN films has been studied as a direct plate material for Cu electroplating within interconnects. It was seen that these liners behaved as excellent Cu diffusion barrier and could be scaled down to sub-5 nm thicknesses. High resolution TEM based structural analysis of these films showed islands of Ru surrounded by amorphous region. The selected area electron diffraction pattern corresponds to the hcp phase of Ru with (101) as the primary crystallographic orientation. Scanning tunneling microscopy and atomic force microscopy suggested the Volmer–Weber growth mechanism of these liners. A series of electroplating experiments with various plating current density and time showed that a uniform bottom-up filling could be achieved in trenches with RuTaN as direct plate liners. Trenches with aspect-ratio as high as 10 could be filled uniformly. The conformality of the PEALD RuTaN process within the trenches was also found to be very promising with step-coverage over 85%.