Atomic Interdiffusion and Diffusive Stabilization of Cobalt by Copper During Atomic Layer Deposition from Bis(N-tert-butyl-N'-ethylpropionamidinato) Cobalt(II).

Abstract

Electromigration of copper in integrated circuits leads to device failure. Potential solutions involve capping the copper with ultrathin cobalt films. We report the properties of cobalt films after deposition on polycrystalline Cu at 265 °C by atomic layer deposition from H2 and bis(N-tert-butyl-N'-ethylpropionamidinato) cobalt(II) (CoAMD). We find intermixing of Co and Cu producing a transition layer on the Cu nearly as thick as the Co-rich overlayer. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry depth profiling reveal that a finite amount of Cu continuously segregates to the progressing Co surface, minimizing the free surface energy, throughout deposition up to at least 16 nm. The Cu-stabilized Co film initially follows 2D growth and strain-relieving 3D crystal formation is apparent beyond 2 nm of film growth. Depth profiling indicates that Cu likely diffuses within the Co film and along the polycrystalline Co grain boundaries.