Semiconductor device including capacitor and method of fabricating same

1. A method of fabricating a capacitor for a semiconductor device, the method comprising:

forming a bottom electrode;

forming a dielectric layer on the bottom electrode;

forming a doped poly-Si 1-x Ge x layer on the dielectric layer;

epitaxially depositing a first doped polysilicon layer on the doped poly-Si 1-x Ge x layer, the doped poly-Si 1-x Ge x layer and the first doped polysilicon layer included in a top electrode of the capacitor; and

forming a contact plug that is physically connected to the first doped polysilicon layer, the contact plug including a metal layer.

2. The method of claim 1 , wherein forming the bottom electrode comprises depositing a second doped polysilicon layer.

3. The method of claim 2 , wherein forming the dielectric layer comprises depositing a material selected from the group consisting of HfO 2 , Al 2 O 3 , and a combination of HfO 2 and Al 2 O 3 .

4. The method of claim 1 , further comprising, before forming the doped poly-Si 1-x Ge x layer, depositing a TiN layer on the dielectric layer.

5. The method of claim 1 , wherein forming the doped poly-Si 1-x Ge x layer comprises activating the dopant concurrently with forming the doped poly-Si 1-x Ge x layer, wherein forming the doped poly-Si 1-x Ge x layer and activating the dopant is performed at a temperature ranging from approximately 400° C. to approximately 550° C.

6. The method of claim 1 , wherein forming the doped poly-Si 1-x Ge x layer comprises forming the doped poly-Si 1-x Ge x layer so that 0.1≦x≦0.9.

7. The method of claim 6 , wherein the doped poly-Si 1-x Ge x layer has a thickness ranging from approximately 100 Å to approximately 500 Å and the first doped polysilicon layer has a thickness ranging from approximately 1,000 Å to approximately 1,500 Å.

8. The method of claim 7 , wherein forming the doped poly-Si 1-x Ge x layer comprises Low Pressure Chemical Vapor Deposition (LPCVD) at a temperature ranging from approximately 400° C. to approximately 550° C. using SiH 4 and GeH 4 gases and a dopant selected from a group consisting of PH 3 , AsH 3 , BCl 3 , and B 2 H 6 .

9. The method of claim 8 , wherein epitaxially depositing the first doped polysilicon layer comprises LPCVD at a temperature ranging from approximately 400° C. to approximately 550° C. using SiH 4 gas and a dopant selected from a group consisting of PH 3 , AsH 3 , BCl 3 , and B 2 H 6 .

10. The method of claim 6 , wherein the doped poly-Si 1-x Ge x layer has a thickness ranging from approximately 1,000 Å to approximately 1,500 Å and the first doped polysilicon layer has a thickness ranging from approximately 100 Å to approximately 500 Å.

11. The method of claim 1 , wherein epitaxially depositing the first doped polysilicon layer is performed in-situ after forming the doped poly-Si 1-x Ge x layer.

12. The method of claim 1 , further comprising forming a silicon nitride layer between the bottom electrode and the dielectric layer.

13. The method of claim 1 , wherein a thickness of the top electrode ranges from approximately 1,100 Å to approximately 2,000 Å.

14. The method of claim 1 , wherein epitaxially depositing the first doped polysilicon layer comprises activating the dopant concurrently with forming the first doped polysilicon layer, wherein epitaxially depositing the first doped polysilicon layer and activating the dopant is performed at a temperature ranging from approximately 400° C. to approximately 550° C.

15. A method of fabricating a capacitor for a semiconductor device, the method comprising:

forming a bottom electrode;

forming a dielectric layer on the bottom electrode;

forming a doped poly-Si 1-x Ge x layer on the dielectric layer;

epitaxially depositing a first doped polysilicon layer on the doped poly-Si 1-x Ge x layer, the doped poly-Si 1-x Ge x layer and the first doped polysilicon layer included in a top electrode of the capacitor; and

forming a contact plug that is physically connected to the first doped polysilicon layer, the contact plug including a metal layer, wherein forming the contact plug comprises:

etching the first doped polysilicon layer to form a trench; and

filling the trench with the contact plug.

16. The method of claim 15 , wherein etching the first doped polysilicon layer comprises etching the first doped polysilicon layer so that the trench does not extend through a thickness of the first doped polysilicon layer.

17. The method of claim 15 , wherein etching the first doped polysilicon layer comprises etching the first doped polysilicon layer so that the trench extends through a thickness of the first doped polysilicon layer.