Direct-liquid-evaporation chemical vapor deposition of smooth, highly conformal cobalt and cobalt nitride thin films

Abstract

By a direct-liquid-evaporation chemical vapor deposition (DLE-CVD) method, we deposited smooth low-resistance cobalt (Co) and cobalt nitride (Co_xN) thin films with excellent conformality at low temperatures down to 200 °C. In the DLE process, a cobalt amidinate precursor solution, bis(N,N′-diisopropylacetamidinato)cobalt(II) dissolved in tetradecane, was vaporized as it flowed smoothly, without boiling, inside heated tubing. This DLE process avoids creating unwanted particles that are generated when droplets from a nebulizer evaporate in a conventional direct-liquid-injection (DLI) process. The vapor then mixed with ammonia (NH₃) and hydrogen (H₂) and flowed over substrates in a tubular CVD reactor, resulting in metallic Co or Co_xN films by tuning the NH₃/H₂ co-reactant ratio. This process deposited pure and highly conformal Co or Co_xN films in trenches with 60 : 1 or 45 : 1 aspect ratio respectively. The good conformality is crucial towards realizing potential applications, such as in 3D contacts and interconnects in microelectronics.