Silver under-layers for electroless cobalt alloys

A composition of a deposition solution for depositing a cobalt tungsten alloy comprising:

• calcium tungstate;
• a cobalt source at a concentration within a range from about 50 mM to about 500 mM;
• a complexing agent at a concentration within a range from about 100 mM to about 700 mM;
• and
• a buffering agent at a concentration within a range from about 50 mM to about 500 mM.

A method for depositing a capping layer on a substrate surface containing a copper layer, comprising:

• exposing the substrate surface to a zinc solution;
• exposing the substrate surface and the copper layer to a silver solution to form a silver layer on the copper layer;
• and
• depositing the capping layer on the silver layer during a deposition process comprising exposing the substrate surface to a deposition solution containing calcium tungstate.

A method for depositing a capping layer on a substrate surface containing a copper layer, comprising:

• exposing the substrate surface to a silver solution to form a silver layer on the copper layer;
• exposing the substrate surface to a deposition solution containing calcium tungstate to deposit the capping layer on the silver layer;
• and
• forming a second silver layer on the capping layer.