Metal Gates of Transistors Having Reduced Resistivity

An integrated circuit device comprising:

• a gate electrode;
• a source/drain region adjacent to the gate electrode;
• and
• a source/drain contact plug over and electrically coupling to the source/drain region, wherein the source/drain contact plug comprises:
• a metal nitride layer;
• a metal silicide layer over a bottom portion of the metal nitride layer;
• and
• a metal-containing layer over the metal silicide layer.

An integrated circuit device comprising:

• a transistor comprising:
• a semiconductor region;
• a gate stack overlying the semiconductor region;
• a source/drain region extending into the semiconductor region and on a side of the gate stack;
• and
• a contact plug electrically connected to one of the gate stack and the source/drain region, wherein the contact plug comprises:
• a cobalt nitride layer;
• a cobalt silicide layer over and contacting the cobalt nitride layer;
• and
• a cobalt-containing layer over and contacting the cobalt silicide layer.