Interconnect structure having a multi-deck conductive feature and method of forming the same

A semiconductor device structure, comprising:

• a semiconductor substrate having an active region;
• a gate stack disposed on the active region, wherein the gate stack includes a high-k gate dielectric layer and a metal gate electrode;
• a source/drain (S/D) feature formed on the active region and disposed on an edge of the gate stack;
• a conductive via landing on the metal gate electrode;
• and
• a conductive feature landing on the conductive via and electrically connected to the metal gate electrode, wherein the conductive feature includes:
• a bottom metal feature of a first metal that includes cobalt;
• a top metal feature of a second metal that includes copper over the bottom metal feature, wherein the second metal is different from the first metal in composition;
• a barrier layer directly contacting a bottom surface of the bottom metal feature;
• and
• a liner layer of the first metal that includes cobalt directly contacting a top surface of the bottom metal feature and directly contacting a bottom surface of the top metal feature,
• wherein a portion of the liner layer is disposed between the top metal feature and the barrier layer.

A semiconductor device structure, comprising:

• a semiconductor substrate having an active region;
• a gate stack disposed on the active region, wherein the gate stack includes a gate dielectric layer and a gate electrode;
• a source/drain (S/D) feature formed on the active region and disposed on an edge of the gate stack;
• and
• a conductive feature electrically connected to the S/D features, wherein the conductive feature is embedded within a first interlayer dielectric (ILD) layer having a first etch stop layer and a first low-k dielectric layer over the first etch stop layer, the conductive feature includes:
• a bottom metal feature of a first metal that includes cobalt;
• a top metal feature of a second metal that includes copper over the bottom metal feature, wherein the second metal is different from the first metal in composition;
• a barrier layer surrounding both the top metal feature and the bottom metal feature, wherein the barrier layer is in direct contact with the bottom metal feature without directly contacting the top metal feature, wherein the barrier layer lands on a top surface of a second ILD layer having a second etch stop layer and a second low-k dielectric layer over the second etch stop layer;
• and
• a liner of the first metal that includes cobalt surrounding the top metal feature, wherein the barrier layer surrounds the liner and the bottom metal feature, wherein the barrier layer and the liner are different in composition.