Integrated circuit devices including backside power rail and methods of forming the same

An integrated circuit device, comprising:

• first and second active regions;
• first and second source/drain regions on the first and second active regions, respectively;
• an isolation layer between the first and second active regions;
• an etch stop layer on the isolation layer, wherein the etch stop layer does not extend between the first and second source/drain regions;
• a front contact that is on the first source/drain region and comprises a front contact plug that is between the first and second source/drain regions;
• and
• a back contact plug that extends through the isolation layer and is electrically connected to the front contact plug.

An integrated circuit device, comprising:

• first and second active regions spaced apart from each other in a first direction;
• first and second source/drain regions on the first and second active regions, respectively;
• an isolation layer between the first and second active regions;
• a front contact comprising a first portion that is on the first source/drain region and comprises a first width in the first direction, and a front contact plug that is between the first and second source/drain regions and comprises a second width in the first direction that is narrower than the first width;
• and
• a back contact comprising a back contact plug that extends through the isolation layer to contact the front contact plug and comprises a third width in the first direction, and a back-side power rail that is on the back contact plug and comprises a fourth width in the first direction that is wider than the third width.