Etch stop layers and methods of forming the same

1. A semiconductor device, comprising:

a metal-oxide-silicon field-effect transistor (MOSFET); and

a plurality of stress layers disposed on the MOSFET,

wherein the plurality of stress layers include a first stress layer disposed on the MOSFET, and a second stress layer disposed on the first stress layer, the first stress layer having a first stress and the second stress layer having a second stress,

wherein the plurality of stress layers further include a third stress layer disposed on the second stress layer and a fourth stress layer disposed on the third stress layer, the third stress layer having a third stress and the fourth stress layer having a fourth stress, and

wherein the first stress is higher than each of the second and fourth stresses, and the third stress is higher than each of the second and fourth stresses.

2. The semiconductor device of claim 1 , wherein the first stress is about 1.5 Gpa to about 1.7 Gpa tensile stress, and the second stress is about 1.2 Gpa to about 1.4 Gpa tensile stress.

3. The semiconductor device of claim 2 , wherein the first stress layer and the second stress layer comprise a same material.

4. The semiconductor device of claim 3 , wherein the same material comprises silicon nitride.

5. The semiconductor device of claim 2 , wherein the first stress layer and the second stress layer comprise a different material.

6. The semiconductor device of claim 5 , wherein the first stress layer comprises silicon nitride and the second stress layer comprises at least one of silicon or silicon oxide.

7. The semiconductor device of claim 6 , wherein the first stress layer and the second stress layer have a substantially same thickness.

8. The semiconductor device of claim 1 , wherein the third stress is substantially the same as the first stress and the fourth stress is substantially the same as the second stress.

9. The semiconductor device of claim 1 , wherein each of the first and third stresses is about 1.5 Gpa to about 1.7 Gpa tensile stress, and each of the second and fourth stresses is about 1.2 Gpa to about 1.4 Gpa tensile stress.

10. The semiconductor device of claim 9 , wherein the first, second, third and fourth stress layers comprise silicon nitride.

11. The semiconductor device of claim 9 , wherein each of the first and third stress layers comprises silicon nitride and each of the second and fourth stress layers comprises at least one of silicon or silicon oxide.

12. The semiconductor device of claim 1 , wherein the MOSFET comprises a MOS capacitor and impurity regions.

13. A method of forming a semiconductor device, the method comprising:

forming a MOSFET;

forming a first stress layer having a first stress on the MOSFET;

forming a second stress layer having a second stress on the first stress layer,

forming a third stress layer having a third stress on the second stress layer, and

forming a fourth stress layer having a fourth stress on the third stress layer,

wherein the first stress is higher than each of the second and fourth stresses, and the third stress is higher than each of the second and fourth stresses.

14. The method of claim 13 , wherein forming the first stress layer comprises depositing a first silicon nitride layer under a first pressure, and forming the second stress layer comprises depositing a second silicon nitride layer under a second pressure, wherein the first pressure is higher than the second pressure.

15. The method of claim 14 , wherein the first pressure is about 5 Torr to about 10 Torr, and the second pressure is about 2 Torr to about 4 Torr.

16. The method of claim 13 , wherein forming the first stress layer comprises depositing a first silicon nitride layer, and forming the second stress layer comprises converting a surface of the first silicon nitride layer into a second silicon nitride layer using an N 2 plasma process.

17. The method of claim 13 , wherein forming the first stress layer comprises depositing a first silicon nitride layer, and forming the second stress layer comprises depositing a second silicon nitride layer and performing an N 2 plasma process over the second silicon nitride layer.

18. The method of claim 13 , wherein forming the first stress layer comprises depositing a silicon nitride layer, and forming the second stress layer comprises depositing at least one of a silicon layer or a silicon oxide layer.

19. The method of claim 13 , wherein the third stress layer has a third stress which is substantially the same as the first stress and the fourth stress layer has a fourth stress which is substantially the same as the second stress.

20. A semiconductor device, comprising: a MOSFET; and a plurality of stress layers disposed on the MOSFET, wherein the plurality of stress layers include a pair of stress layers having a first stress layer and a second stress layer disposed on the first stress layer, the first stress layer having a first stress and the second stress layer having a second stress which is lower than the first stress, and the pair of stress layers are repeatedly stacked on top of each other.

21. The semiconductor device of claim 20 , wherein the first stress is about 1.5 Gpa to about 1.7 Gpa tensile stress, and the second stress is about 1.2 Gpa to about 1.4 Gpa tensile stress.

22. A system for transmitting or receiving data, the system comprising:

a memory device for storing a program;

a processor in communication with the memory device, wherein the memory device comprises:

a MOSFET; and

a plurality of stress layers disposed on the MOSFET,

wherein the plurality of stress layers include a pair of stress layers having a first stress layer and a second stress layer disposed on the first stress layer, the first stress layer having a first stress and the second stress layer having a second stress which is lower than the first stress, and the pair of stress layers are repeatedly stacked on top of each other.

23. The system of claim 22 , wherein the system comprises at least one of a mobile system, a portable computer, a web tablet, a mobile phone, a digital music player, or a memory card.