Low-temperature ALD of metallic cobalt using the CoCOhept precursor: Simulation-assisted process development for deposition on temperature sensitive 3D-structures

This work presents the development and implementation of a low-temperature atomic layer deposition (ALD) process for metallic cobalt thin films. The works are based on a set of five different Co precursors with alkyne ligands. Computational analysis identified CoCOhept ( [ Co<inf>2</inf>( CO )<inf>6</inf> HC ≡ CC<inf>5</inf>H<inf>11</inf>] ) as the most promising candidate among a series of potential precursors. Using density functional theory calculations, we examined the surface chemistry of Co<inf>2</inf>( CO )<inf>6</inf>HC ≡ CCH<inf>3</inf> during Co ALD. The precursor undergoes dissociative adsorption on Co(001), followed by efficient ligand removal via a hydrogenation reaction with surface H atoms. Simultaneously to the process development with CoCOhept, the chamber geometry has been co-optimized using computational fluid dynamics simulation. By this, the chamber height was identified as a critical factor for a homogenous precursor distribution. We show that a minimum height is mandatory in order to avoid local concentration hot-spots under the gas inlets. The predictions by the model are in good agreement with experiments employing varying chamber geometries. Further experimental tests show the influence of the precursor flow and the plasma pulse duration. We demonstrate the integration of the process in high aspect-ratio silicon structures and on temperature sensitive 3D-photoresist structures.