Semiconductor device and method for forming the same

A complementary metal-oxide-semiconductor (CMOS) device, comprising:

• a first gate and a second gate over a substrate;
• a first source/drain in the substrate at two sides of the first gate and a second source/drain in the substrate at two sides of the second gate;
• a metal silicide layer in the first source/drain and the second source/drain, respectively;
• a first insulating layer over sidewalls of the first gate and at least a portion of a surface of the first source/drain substrate;
• and
• a second insulating layer over sidewalls of the second gate and at least a portion of a surface of the second source/drain,
• wherein the first insulating layer and the second insulating layer respectively cover a portion of the metal silicide layer, the first source/drain and the first insulating layer comprise first dopants, the second source/drain and the second insulating layer comprise second dopants, and conductivity types of the first dopants and the second dopants are complementary to each other.

A method for forming a semiconductor device, comprising:

• receiving a substrate having a gate formed thereon;
• forming an insulating layer over the substrate and sidewalls and a top of the gate, wherein the insulating layer has a first side facing the gate or the substrate, and a second side opposite to the first side;
• forming a source/drain in the substrate at two sides of the gate;
• forming an interlayer dielectric (ILD) layer on the insulating layer;
• and
• forming a metal silicide layer after the forming of the ILD layer,
• wherein the source/drain and the insulating layer comprise same dopants, and a concentration of the dopants in the insulating layer is reduced from the second side to the first side of the insulating layer.