Semiconductor device and manufacturing method thereof

A method of manufacturing a semiconductor device, the method comprising:

• forming a source/drain structure over a substrate;
• forming a first interlayer dielectric (ILD) layer including one or more first insulating layers over the source/drain structure;
• forming a first opening in the first ILD layer to at least partially expose the source/drain structure;
• filling the first opening with a first conductive material to form a source/drain contact in contact with the source/drain structure;
• forming a second ILD layer including a first layer and a second layer disposed on the first layer over the source/drain contact and the first ILD layer;
• forming a second opening in the second ILD layer to at least partially expose the source/drain;
• partially recessing the source/drain contact to form a recess, the recess extending below the first layer;
• performing a cleaning operation on the recess and the first layer;
• and
• filling the second opening and the recess with ruthenium to form an upper contact in direct contact with the source/drain contact and in direct contact with the second ILD layer without an interposing conductive barrier layer.

A semiconductor device comprising:

• a gate electrode;
• a source/drain structure;
• a lower contact contacting either of the gate electrode or the source/drain structure;
• and
• an upper contact disposed in an opening formed in an interlayer dielectric (ILD) layer and in direct contact with the lower contact;
• wherein the upper contact is in direct contact with the ILD layer without an interposing conductive barrier layer, and
• the upper contact includes ruthenium.