Cobalt first layer advanced metallization for interconnects

A method for fabricating an advanced metal conductor structure comprising:

• providing a pattern in a dielectric layer, wherein the pattern includes a set of features in the dielectric for a set of metal conductor structures;
• creating an adhesion promoting layer disposed over the patterned dielectric;
• depositing a ruthenium metal layer disposed over the adhesion promoting layer;
• using a physical vapor deposition process to deposit a cobalt layer disposed over the ruthenium layer;
• performing a thermal anneal which reflows the cobalt layer to fill a first portion of the set of features leaving a second, remaining portion of the set of features unfilled, wherein the reflowed cobalt layer has a u-shaped cross-section having a thicker bottom layer than side layers;
• and
• depositing a second metal layer to fill the second, remaining portion of the set of features, wherein the second metal is a metal other than cobalt;
• wherein a thickness of the reflowed cobalt layer from the ruthenium layer to a bottom of the second metal layer and a thickness of the second metal layer after planarization are substantially equal.