An impurity-diffused layer having an extension structure is formed first by implanting
Sb ion as an impurity for forming a pocket region; then by implanting N as a diffusion-suppressive
substance so as to produce two peaks in the vicinity of the interface with a gate
electrode and at an amorphous/crystal interface which serves as an defect interface
generated by the impurity in the pocket region; and by carrying out ion implantations
for forming an extension region and deep source and drain regions.