Dual contact etch stop layer process

A dual contact etch stop layer (dual CESL) process, comprising:

• providing a substrate having thereon a first device region, a second device region and a shallow trench isolation (STI) region between the first and second device regions, wherein a gate structure overlies the first device region, the second device region and the STI region, and wherein the gate structure comprises a contact region on the STI region, which is approximately at a middle point between the first and second device regions;
• forming a first-stress imparting film with a first stress over the substrate, wherein the first-stress imparting film does not cover the second device region;
• and
• forming a second-stress imparting film with a second stress over the substrate, wherein the second-stress imparting film does not cover the first device region, an overlapped boundary between the first- and second-stress imparting films is created directly above the STI region, and wherein the overlapped boundary is placed in close proximity to the second device region and does not overlap with the contact region.