Direct electroless plating of Cu on barrier metals

We succeeded in electroless deposition of Cu directly on barrier metals such as TaN, WN, and TiN, without any sputtered Cu layer or Pd catalysis adsorption pretreatment. Electroless deposition was possible when the barrier metal surface was lightly wet etched to remove a surface oxygen-rich layer. The measured REDOX potentials of the barrier metals suggest that displacement plating of Cu is a dominant mechanism for TaN and WN. Electroless deposited Cu on sputtered TaN had good adhesion properties to endure against CMP. Electrical resistivity of 0.42 μm damascene interconnection formed by electroless deposition only was 2.2 μΩcm. Filling characteristics into fine holes are rather conformal and we succeeded in the filling of holes with an aspect ratio up to 5 without the use of electroplating.