Thermal ALD of Cu via reduction of CuxO films for the advanced metallization in spintronic and ULSI interconnect systems

In this work, an approach for copper atomic layer deposition (ALD) via reduction of Cu_xO films was investigated regarding applications in ULSI interconnects, like Cu seed layers directly grown on diffusion barriers (e. g. TaN) or possible liner materials (e. g. Ru or Ni) as well as non-ferromagnetic spacer layers between ferromagnetic films in GMR sensor elements, like Ni or Co. The thermal Cu_xO ALD process is based on the Cu (I) β-diketonate precursor [(ⁿBu₃P)₂Cu(acac)] and a mixture of water vapor and oxygen (“wet O₂”) as co-reactant at temperatures between 100 and 130°C. Highly efficient conversions of the Cu_xO to metallic Cu films are realized by a vapor phase treatment with formic acid (HCOOH), especially on Ru substrates. Electrochemical deposition (ECD) experiments on Cu ALD seed/Ru liner stacks in typical interconnect patterns are showing nearly perfectly filling behavior. For improving the HCOOH reduction on arbitrary substrates, a catalytic amount of Ru was successful introduced into the Cu_xO films during the ALD with a precursor mixture of the Cu (I) β-diketonate and an organometallic Ru precursor. Furthermore, molecular and atomic hydrogen were studied as promising alternative reducing agents.