METAL GATE FET HAVING REDUCED THRESHOLD VOLTAGE ROLL-OFF

• US 20110079828A1
• Filed: 10/05/2009
• Published: 04/07/2011
• Est. Priority Date: 10/05/2009
• Status: Active Grant

• Current Assignee: Globalfoundries US Incorporated (GlobalFoundries, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Nowak, Edward J., Anderson, Brent A., Rankin, Jed H.
• Granted Patent: US 8,546,252 B2
• Time in Patent Office: Days
• US Class Current: 257/288
• CPC Class Codes: H01L 21/28079 the final conductor layer next to the insulator being a single metal, e.g. Ta, W, Mo, Al
• CPC Class Codes: H01L 21/28088 the final conductor layer next to the insulator being a composite, e.g. TiN
• CPC Class Codes: H01L 21/28105 the final conductor next to the insulator having a lateral composition or doping variation, or being formed laterally by more than one deposition step
• CPC Class Codes: H01L 21/28114 characterised by the sectional shape, e.g. T, inverted-T
• CPC Class Codes: H01L 29/42376 characterised by the length or the sectional shape
• CPC Class Codes: H01L 29/495 the conductor material next to the insulator being a simple metal, e.g. W, Mo H01L29/4908, H01L29/4983 take precedence
• CPC Class Codes: H01L 29/4966 the conductor material next to the insulator being a composite material, e.g. organic material, TiN, MoSi2 H01L29/4908, H01L29/4983 take precedence
• CPC Class Codes: H01L 29/4983 with a lateral structure, e.g. a Polysilicon gate with a lateral doping variation or with a lateral composition variation or characterised by the sidewalls being composed of conductive, resistive or dielectric material
• CPC Class Codes: H01L 29/517 the insulating material comprising a metallic compound, e.g. metal oxide, metal silicate H01L29/518 takes precedence
• CPC Class Codes: H01L 29/66545 using a dummy, i.e. replacement gate in a process wherein at least a part of the final gate is self aligned to the dummy gate
• CPC Class Codes: H01L 29/78 with field effect produced by an insulated gate H01L29/7725, H01L29/775, H01L29/778 take precedence

Abstract

A structure and method to create a metal gate having reduced threshold voltage roll-off. A method includes: forming a gate dielectric material on a substrate; forming a gate electrode material on the gate dielectric material; and altering a first portion of the gate electrode material. The altering causes the first portion of the gate electrode material to have a first work function that is different than a second work function associated with a second portion of the gate electrode material.

Claims

1. A method of forming a semiconductor structure, comprising:

forming a gate dielectric material on a substrate;

forming a gate electrode material on the gate dielectric material; and

altering a first portion of the gate electrode material,

wherein the altering causes the first portion of the gate electrode material to have a first work function that is different than a second work function associated with a second portion of the gate electrode material.

2. The method of claim 1, further comprising filling a trench defined by the gate electrode material with a second gate electrode material different than the gate electrode material,

wherein the altering comprises diffusing the second gate electrode material into the first portion of the gate electrode material.

3. The method of claim 2, further comprising thinning the first portion of the gate electrode material before the filling the trench with the second gate electrode material.

4. The method of claim 3, wherein the thinning causes the first portion to have a vertical height that is less than a lateral thickness of a sidewall portion of the gate electrode material.

5. The method of claim 1, wherein:

the first portion comprises a central portion of the gate electrode material atop the gate dielectric material,

the second portion comprises lateral portions of the gate electrode material atop the gate dielectric material, and

the altering comprises an ion-implantation that dopes the first portion without doping the second portion.

6. The method of claim 1, further comprising:

forming a barrier layer over the gate electrode material;

thinning a second portion of the barrier layer relative to a first portion of the barrier layer; and

forming a metal replacement gate in a trench defined by the barrier layer.

7. The method of claim 6, wherein the altering comprises:

diffusing a first amount of the metal replacement gate through the first portion of the barrier layer into the first portion of the gate electrode material, and

diffusing a second amount of the metal replacement gate through the second portion of the barrier layer into the second portion of the gate electrode material.

8. The method of claim 7, wherein the second amount is different than the first amount due to the thinning.

9. The method of claim 6, wherein the thinning comprises:

masking the first portion of the barrier layer, and

etching the second portion of the barrier layer.

10. The method of claim 6, wherein the thinning comprises:

performing an angled ion-implant of the barrier layer such that ions are implanted in the second portion of the barrier layer, and

simultaneously etching the first and second portions of the barrier layer.

11. The method of claim 6, wherein the first and second portions of the gate electrode material provide an asymmetric work function for a FET comprising the metal replacement gate.

12. The method of claim 1, further comprising:

forming a diffusing material on the gate electrode material and on sidewalls of a gate trench containing the gate electrode material;

forming a barrier layer on the diffusing material; and

forming a metal replacement gate in a trench defined by the barrier layer.

13. The method of claim 12, wherein the altering comprise annealing the semiconductor structure.

14. The method of claim 13, wherein the annealing causes the diffusing material to diffuse into the first and second portions of the gate electrode material.

15. A method of forming a semiconductor structure, comprising:

forming a gate dielectric material on a substrate;

forming a first gate electrode material on the gate dielectric material and on sidewalls of a gate trench;

removing a first portion of the gate electrode material from atop a first portion of the gate dielectric material; and

forming a conductive material on the first portion of the gate dielectric material,

wherein a second portion of the gate electrode material remains on a second portion of the gate dielectric material after the removing,

the gate electrode material has a first work function, and

the conductive material has a second work function different than the first work function.

16. The method of claim 15, wherein the removing comprises etching the first portion of the gate electrode material using an anisotropic etch.

17. A method of forming a semiconductor structure, comprising:

forming a gate dielectric material on a substrate;

forming a gate electrode material on the gate dielectric material and on sidewalls of a gate trench;

forming a first reactive material on a first portion of the gate electrode material;

forming a second reactive material on a second portion of the gate electrode material; and

creating a non-uniform work function in the gate electrode material.

18. The method of claim 17, wherein the creating the non-uniform work function comprises annealing the semiconductor structure to diffuse the first reactive material and the second reactive material into regions of the gate electrode material.

19. The method of claim 18, wherein the forming the first reactive material on the first portion of the gate electrode material comprises:

conformally depositing a layer of the first reactive material on horizontal and vertical surfaces of the gate electrode material; and

removing the first reactive material from the horizontal surfaces of the gate electrode material.

20. A semiconductor structure, comprising:

a gate dielectric material on a substrate;

a gate electrode material on the gate dielectric material; and

a replacement gate formed on the gate electrode material;

wherein the gate electrode material comprises a reacted first portion having a first work function, and

the gate electrode material comprises a second portion having a second work function different than the first work function.