Methods for forming contact plugs with reduced corrosion

An integrated circuit structure comprising:

• a semiconductor region;
• a gate stack over the semiconductor region;
• an Inter-layer Dielectric (ILD) having portions on opposite sides of the gate stack;
• a contact plug in the ILD, the contact plug comprising:
• a metal layer comprising first sidewall portions over and connected to the first bottom portion;
• a first metal nitride layer comprising:
• a bottom portion between the first sidewall portions;
• and
• second sidewall portions over, and connected to, the bottom portion;
• a first metal region over the bottom portion and between the second sidewall portions of the first metal nitride layer;
• and
• a first metal cap overlapping the first metal region, wherein the first metal cap comprises a first portion having a bottom surface contacting the first metal region, and second portions extending lower than the bottom surface.

An integrated circuit structure comprising:

• a semiconductor region;
• a gate stack over the semiconductor region;
• a source/drain region on a side of the gate stack;
• a source/drain contact plug over and electrically coupling to the source/drain region, the source/drain contact plug comprising:
• a metal region;
• and
• a metal nitride layer comprising sidewall portions on opposite sidewalls of the metal region;
• a metal cap overlapping the metal region and the sidewall portions of the metal nitride layer;
• and
• a metal layer comprising sidewall portions on opposites sidewalls of the source/drain contact plug, wherein the metal cap is spaced apart from the sidewall portions of the metal layer by the sidewall portions of the metal nitride layer.