Semiconductor device and method of forming the same

1. A semiconductor device comprising:

a semiconductor substrate;

a gate insulating film formed on a surface of the semiconductor substrate;

a gate electrode formed on the gate insulating film;

a first sidewall insulating film formed on a side surface of the gate electrode; and

source and drain regions, each of the source and drain regions comprising:

a pocket diffusion layer of a first conductivity type in the semiconductor device;

a first diffusion layer of a second conductivity type extending over the pocket diffusion layer, and the first diffusion layer facing toward the gate electrode through the first sidewall insulating film; and

a second diffusion layer of the second conductivity type being higher in impurity concentration than the first diffusion layer, the second diffusion layer extending over the first diffusion layer, the second diffusion layer being separated by the first diffusion layer from the pocket diffusion layer, the second diffusion layer having a side surface which faces toward the first sidewall insulating film through the first diffusion layer.

2. The semiconductor device according to claim 1 , wherein the second diffusion layer has a bottom surface which is higher than the surface of the semiconductor substrate.

3. The semiconductor device according to claim 1 , wherein the second diffusion layer has a bottom surface which is higher than the gate insulating film.

4. The semiconductor device according to claim 1 , wherein the first diffusion layer contacts the pocket diffusion layer.

5. The semiconductor device according to claim 1 , further comprising:

a second sidewall insulating film extending along the first sidewall insulating film, the second sidewall insulating film being positioned on a top portion of the first diffusion layer.

6. The semiconductor device according to claim 1 , further comprising:

an isolation layer in the semiconductor substrate, the isolation layer defining an active region in which the source and drain regions are positioned, the isolation layer having a bottom surface which is deeper than a bottom surface of the pocket diffusion layer.

7. A semiconductor device comprising:

a first circuit region comprising a first transistor; and

a second circuit region comprising a second transistor, the second circuit region being isolated from the first circuit region,

the first transistor comprising:

a first active region;

a first gate insulating film formed on a surface of the first active region;

a first gate electrode formed on the first gate insulating film;

a first sidewall insulating film formed on a side surface of the first gate electrode; and

first source and drain regions, each of the first source and drain regions comprising:

a pocket diffusion layer of a first conductivity type in the first active region;

a first diffusion layer of a second conductivity type extending over the pocket diffusion layer, and the first diffusion layer facing toward the gate electrode through the first sidewall insulating film; and

a second diffusion layer of the second conductivity type being higher in impurity concentration than the first diffusion layer, the second diffusion layer extending over the first diffusion layer, the second diffusion layer being separated by the first diffusion layer from the pocket diffusion layer, the second diffusion layer having a side surface which faces toward the first sidewall insulating film through the first diffusion layer, and

the second transistor comprising:

a second active region;

a second gate electrode formed in the second active region;

a semiconductor layer on a surface of the second active region; and

second source and drain regions that formed in the semiconductor layer and in the second active region, and the second source and drain regions being lower in impurity concentration than the first diffusion layer.

8. The semiconductor device according to claim 7 , wherein the second diffusion layer has a bottom surface which is higher than the surface of the semiconductor substrate.

9. The semiconductor device according to claim 7 , wherein the second diffusion layer has a bottom surface which is higher than the gate insulating film.

10. The semiconductor device according to claim 7 , wherein the first diffusion layer contacts the pocket diffusion layer.

11. The semiconductor device according to claim 7 , further comprising:

a second sidewall insulating film extending along the first sidewall insulating film, the second sidewall insulating film being positioned on a top portion of the first diffusion layer.

12. The semiconductor device according to claim 7 , wherein the first circuit region comprises a peripheral circuit region,

the second circuit region comprises a memory cell region,

the first transistor is a planer transistor,

the second transistor is a trench transistor, and

the second gate electrode is partially buried in the semiconductor substrate.

13. The semiconductor device according to claim 12 , further comprising:

a bit line connected to a first one of the second source and drain regions in the memory cell region; and

a capacitor element connected to a second one of the second source and drain regions in the memory cell region.

14. A semiconductor device comprising:

a semiconductor substrate;

a gate insulating film on a surface of the semiconductor substrate;

a gate electrode on the gate insulating film;

a first sidewall insulating film on a side surface of the gate electrode;

a pocket diffusion layer of a first conductivity type in the semiconductor device;

a first diffusion layer of a second conductivity type facing toward the gate electrode through the first sidewall insulating film; and

a second diffusion layer of the second conductivity type being higher in impurity concentration than the first diffusion layer, the second diffusion layer having a side surface which faces toward the first sidewall insulating film through the first diffusion layer.

15. The semiconductor device according to claim 14 , wherein the first diffusion layer comprises first and second portions, the first portion extends over the pocket diffusion layer, and the second portion extends along the first sidewall insulating film,

the second diffusion layer extends over the first portion of the first diffusion layer, the second diffusion layer is separated by the first portion of the first diffusion layer from the pocket diffusion layer, the second diffusion layer is separated by the second portion of the first diffusion layer and the first sidewall insulating film from the gate electrode.

16. The semiconductor device according to claim 14 , wherein the second diffusion layer has a bottom surface which is higher than the surface of the semiconductor substrate.

17. The semiconductor device according to claim 14 , wherein the first diffusion layer contacts the pocket diffusion layer.

18. The semiconductor device according to claim 14 , further comprising:

a second sidewall insulating film extending along the first sidewall insulating film, the second sidewall insulating film being positioned on a top portion of the side surface of the second diffusion layer.

19. The semiconductor device according to claim 14 , further comprising:

a bit line connected to the second diffusion layer.

20. The semiconductor device according to claim 14 , further comprising:

a capacitor element connected to the second diffusion layer.