Selective self-initiating electroless capping of copper with cobalt-containing alloys

摘要

Embodiments of the invention generally provide compositions of plating solutions, methods to mix plating solutions and methods to deposit capping layers with plating solutions. The plating solutions described herein may be used as electroless deposition solutions to deposit capping layers on conductive features. The plating solutions are rather dilute and contain strong reductants to self-initiate on the conductive features. The plating solutions may provide in-situ cleaning processes for the conductive layer while depositing capping layers free of particles. In one embodiment, a method for forming an electroless deposition solution is provided which includes forming a conditioning buffer solution with a first pH value and comprising a first complexing agent, forming a cobalt-containing solution with a second pH value and comprising a cobalt source, a tungsten source and a second complexing agent, forming a buffered reducing solution with a third pH value and comprising a hypophosphite source and a borane reductant, combining the conditioning buffer solution, the cobalt-containing solution and the buffered reducing solution to form the electroless deposition solution. The electroless deposition solution includes the cobalt source in a concentration range from about 1 mM to about 30 mM, the tungsten source in a concentration range from about 0.1 mM to about 5 mM, the hypophosphite source in a concentration range from about 5 mM to about 50 mM, the borane reductant in a concentration range from about 5 mM to about 50 mM, and has a total pH value in a range from about 8 to about 10.