Partial barrier free vias for cobalt-based interconnects and methods of fabrication thereof

A method comprising:

• forming a first interconnect feature in a dielectric layer;
• forming a via in the dielectric layer, wherein the forming the via includes:
• forming a via opening in the dielectric layer, wherein the via opening exposes the first interconnect feature,
• depositing a first via plug layer in the via opening, wherein the first via plug layer fills a lower portion of the via opening,
• depositing a via barrier layer in the via opening, wherein the via barrier layer is disposed over the first via plug layer, wherein the via barrier layer partially fills an upper portion of the via opening,
• depositing a second via plug layer over the via barrier layer, wherein the second via plug layer partially fills the upper portion of the via opening, and
• performing a planarization process that removes the via barrier layer and the second via plug layer from over a top surface of the dielectric layer;
• and
• forming a second interconnect feature in the dielectric layer, wherein the via connects the first interconnect feature to the second interconnect feature.

A method for forming an interconnect structure of a multilayer interconnect (MLI) feature, the method comprising:

• forming a dielectric layer over a substrate;
• forming a cobalt-comprising device-level contact in the dielectric layer;
• and
• forming a partial barrier-free via in the dielectric layer over the cobalt-comprising device-level contact, wherein the forming the partial barrier-free via includes:
• forming a first via plug portion in the dielectric layer over the cobalt-comprising device-level contact, wherein the first via plug portion physically contacts the dielectric layer,
• forming a via barrier layer in the dielectric layer over the first via plug portion, and
• forming a second via plug portion in the dielectric layer over the via barrier layer, wherein the via barrier layer is disposed between the first via plug portion and the second via plug portion and is further disposed between the second via plug portion and the dielectric layer.