Semiconductor device and method forming the same

A semiconductor device includes: a first metal layer; a second metal layer; and an inter-metal dielectric (IMD) layer, disposed between the first metal layer and the second metal layer. The inter-metal dielectric layer includes: a first dielectric layer disposed on the first metal layer, and in direct contact with the first metal layer, wherein the first dielectric layer has a stress value less than 0; a second dielectric layer disposed on the first dielectric layer, wherein the second dielectric layer has a stress value greater than 0; and a third dielectric layer disposed on the second dielectric layer, wherein the third dielectric layer has a stress value less than 0, wherein a thickness of the third dielectric layer is greater than a thickness of the second dielectric layer, and the thickness of the second dielectric layer is greater than a thickness of the first dielectric layer.