An integration flow for LDD and spacer fabrication on a sacrificial amorphous carbon gate structure, form first spacer by way of depositing on the si substrate which have gate structure first. Gate is provided above the N-well and P-well on substrate. Spin coating a layer of photoresist in the first spacer, patterning the photoresist, and the gate structure above the N-well or P-well is exposed, ion lightly dope treatment is then used to the whole device. Remove the redundant photoresist and the first spacer layer, form the second spacer layer by depositing on the surface of the si substrate and gate, and spin coating another photoresist layer on the second spacer layer. Pattern the another photoresist layer, and another side of the gate structure is exposed, ion lightly dope treatment is then used to the whole device. Remove the redundant photoresist and the second spacer layer, form the third spacer layer and SiN layer by depositing on the gate and the Si substrate in turn. Form spacer by removing the redundant the third spacer layer and SiN layer.