Seedless electrochemical deposition of copper on liner materials for ULSI devices

The parameters for electrochemical deposition (ECD) of copper directly on air exposed metal nitride materials are reported. ECD of copper in damascene features for microprocessor manufacturing has historically been performed in acid bath chemistries on copper seeded features. However, when plating directly on the nitride liner surfaces, in the traditional acid baths, the atmosphere-exposed liner surfaces exhibit a significant nucleation barrier, presumed to be due to air formed passivating type films. This study demonstrates that copper can be deposited directly on metal nitride barrier layer films that have been exposed to ambient atmosphere, by utilizing complex alkaline bath chemistries. The results indicate that adhesion of copper on air exposed metal nitride liner materials is directly related to the reduction of copper-ammonia complexes at the metal nitride surface. High nucleation density and 2D type growth of copper films with good resistivity have been demonstrated in a citrate ammonia based electrolyte.