Acidic electroless Cu deposition in CuSO4-NH4F solution

Acidic electroless Cu deposition on a TiN/Ti/SiN/Si/SiN substrate in CuSO4-NH4F solution is examined. In this study, SiN insulator layers in the substrate and the reaction agent, NH4F, are employed to reduce the corrosive influence of F- ions on the substrate. During the plating, a Si wafer is used as a reducing agent and is oxidized by F- ions. The Cu2+ ions accept the electrons released via the oxidation of Si and then deposit as Cu metal on the TiN barrier. The plating solution enables the activation of the TiN surface for direct electroless Cu deposition, due to its corrosion on the oxygen-rich layer of the barrier. The increased plating time and the NH4F concentration elevate the nucleation rate of Cu on TiN, resulting in the finer Cu grains and better surface coverage of Cu films. Plating at higher bath temperatures causes the agglomeration of Cu clusters by providing more thermal energy for growth but not for nucleation. X-ray diffraction analysis indicates no Cu2O in the Cu films deposited on TiN. Also, the adhesion of Cu/TiN is improved as shown by the tape-peel test. (C) 2006 The Electrochemical Society.