Semiconductor devices

1. A semiconductor device, comprising:

a substrate including an isolation layer pattern and an active pattern;

a buffer insulation layer pattern on the substrate;

a polysilicon structure on the active pattern and the buffer insulation layer pattern, the polysilicon structure contacting a portion of the active pattern, and the polysilicon structure extending in a direction parallel to an upper surface of the substrate;

a first diffusion barrier layer pattern on an upper surface of the polysilicon structure, the first diffusion barrier layer pattern including polysilicon doped with at least carbon;

a second diffusion barrier layer pattern on the first diffusion barrier layer pattern, the second diffusion barrier layer pattern including at least a metal; and

a first metal pattern and a first capping layer pattern stacked on the second diffusion barrier layer pattern.

2. The semiconductor device as claimed in claim 1 , wherein the first diffusion barrier layer pattern has a thickness less than a thickness of the second diffusion barrier layer pattern.

3. The semiconductor device as claimed in claim 1 , wherein the second diffusion barrier layer pattern has a thickness of about 10 angstroms to about 50 angstroms.

4. The semiconductor device as claimed in claim 1 , wherein the carbon in the first diffusion barrier layer pattern is in a range of about 1 at. % to about 5 at. %, based on a total amount of atoms in the first diffusion barrier layer pattern.

5. The semiconductor device as claimed in claim 1 , wherein the first diffusion barrier layer pattern further includes nitrogen.

6. The semiconductor device as claimed in claim 5 , wherein the nitrogen in the first diffusion barrier layer pattern is in a range of about 2 at. % to about 10 at. %, based on a total amount of atoms in the first diffusion barrier layer pattern.

7. The semiconductor device as claimed in claim 1 , wherein the second diffusion barrier layer pattern includes at least one of silicon-doped titanium nitride, Ti, TiN, TaC, TaCN, TaSiN, TaN, and WN.

8. The semiconductor device as claimed in claim 1 , further comprising a contact plug contacting the active pattern, the contact plug including at least polysilicon,

wherein the polysilicon structure, the first diffusion barrier layer pattern, the second diffusion barrier layer pattern, the first metal pattern, and the first capping layer pattern are stacked to define a bit line structure, and

wherein the contact plug is spaced apart from the bit line structure, an upper surface of the contact plug being higher than an upper surface of the bit line structure.

9. A semiconductor device, comprising:

a substrate including an isolation layer pattern and an active pattern;

a gate structure in a gate trench at the isolation layer pattern and the active pattern, the gate structure extending in a first direction parallel to an upper surface of the substrate;

buffer insulation layer patterns on the isolation layer pattern, the active pattern, and the gate structure;

a bit line structure contacting an upper surface of at least one of the buffer insulation layer patterns and an upper surface of the active pattern between the buffer insulation layer patterns, the bit line structure extending in a second direction parallel to the upper surface of the substrate and perpendicular to the first direction;

a contact plug contacting the active pattern and being spaced apart from the bit line structure, the contact plug including at least polysilicon; and

a capacitor contacting an upper surface of the contact plug,

wherein the bit line structure includes:

a polysilicon structure on the active pattern and the buffer insulation layer pattern,

a first diffusion barrier layer pattern on an upper surface of the polysilicon structure, the first diffusion barrier layer pattern including polysilicon doped with at least carbon, and

a second diffusion barrier layer pattern, a first metal pattern, and a first capping layer pattern sequentially stacked on the first diffusion barrier layer pattern.

10. The semiconductor device as claimed in claim 9 , wherein the first diffusion barrier layer pattern has a thickness less than a thickness of the second diffusion barrier layer pattern.

11. The semiconductor device as claimed in claim 9 , wherein the second diffusion barrier layer pattern has a thickness of about 10 angstroms to about 50 angstroms.

12. The semiconductor device as claimed in claim 9 , wherein the carbon in the first diffusion barrier layer pattern is in a range of about 1 at. % to about 5 at. %, based on a total amount of atoms in the first diffusion barrier layer pattern.

13. The semiconductor device as claimed in claim 9 , wherein the first diffusion barrier layer pattern further includes nitrogen.

14. The semiconductor device as claimed in claim 13 , wherein the nitrogen in the first diffusion barrier layer pattern is in a range of about 2 at. % to about 10 at. %, based on a total amount of atoms in the first diffusion barrier layer pattern.

15. The semiconductor device as claimed in claim 9 , wherein the first diffusion barrier layer pattern includes no metal, and the second diffusion barrier layer pattern includes at least metal.

16. The semiconductor device as claimed in claim 9 , wherein the polysilicon structure extends in the second direction, and the upper surface of the polysilicon structure is substantially flat.

17. The semiconductor device as claimed in claim 9 , wherein the polysilicon structure includes:

a first polysilicon pattern contacting the upper surface of the active pattern; and

a second polysilicon pattern on the buffer insulation layer pattern, the second polysilicon pattern contacting an upper sidewall of the first polysilicon pattern.