Activation-free electroless solution for deposition of cobalt and method for deposition of cobalt capping/passivation layer on copper

An electroless deposition solution for deposition of a cobalt layer onto copper, comprising:

• at least one metal ion source consisting of cobalt;
• at least one second metal ion source selected from the second group of metals consisting of chromium, molybdenum, and tungsten;
• at least one reducing agent used as initiator for initiating deposition of an initial layer of cobalt and of said second group of metals required for deposition of subsequent layers without said initiator from said electroless deposition solution;
• and
• at least one reducing agent for reducing metal ions of cobalt and of said second group of metals onto said initial layer and onto subsequent layers from said electroless deposition solution.

A single-stage method for electroless deposition of a cobalt layer on copper using at least one initiator and at least one reducing agent, comprising the steps of:

• preparing an electroless deposition solution for deposition of cobalt onto said copper, said deposition solution comprising at least one cobalt ion source, an initiator for initiating deposition of an initiation layer of said cobalt on said copper for deposition of subsequent layers onto said initiation layer, and a reducing agent for reducing said cobalt into said subsequent layers;
• bringing said copper into contact with the electroless deposition solution to form on said copper said initiation layer;
• and
• depositing said cobalt onto said copper by reducing said cobalt into said cobalt layer;
• said electroless deposition solution having a pH value not exceeding 10.