Interconnect with recessed dielectric adjacent a noble metal cap

A method of forming an interconnect structure, comprising:

• depositing a first dielectric layer of ultra low-k material;
• forming a sacrificial dielectric layer over said first dielectric layer;
• forming an interconnect feature in said sacrificial dielectric layer and first dielectric layer by:
• etching an opening in said sacrificial dielectric layer and first dielectric layer;
• depositing a liner over said sacrificial dielectric layer and within said opening;
• overfilling said opening with a conductive material;
• and,
• performing a chemical mechanical polishing process to remove a portion of said conductive material, a portion of said liner, and said sacrificial dielectric layer such that top surface of said conductive material filled opening is coplanar with said first dielectric layer;
• depositing a noble metal layer on top of said interconnect feature;
• annealing said interconnect feature such that an alloy layer forms in said conductive material adjacent said noble metal layer;
• removing said noble metal layer and a portion of said first dielectric layer using a gas cluster ion beam, leaving a portion of said liner and said alloy layer protruding from said first dielectric layer;
• and,
• depositing a second dielectric layer over said first dielectric layer and said protruding liner and alloy layer.