Methods of forming gate structures for semiconductor devices using a replacement gate technique and the resulting devices

1. A method, comprising:

forming a sacrificial gate structure above a surface of a semiconductor substrate, said sacrificial gate structure comprising a sacrificial gate insulation layer, a lower sacrificial gate electrode positioned above said sacrificial gate insulation layer and an upper sacrificial gate electrode positioned above said lower sacrificial gate electrode;

forming a sidewall spacer adjacent opposite sides of at least said lower sacrificial gate electrode and said upper sacrificial gate electrode;

forming a layer of insulating material adjacent said sidewall spacers;

performing at least one first etching process through a patterned mask layer so as to thereby define a patterned upper sacrificial gate electrode comprised of a plurality of trenches that each expose a portion of a surface of said lower sacrificial gate electrode; and

performing at least one second etching process through said patterned upper sacrificial gate electrode to remove said lower sacrificial gate electrode and said sacrificial gate insulation layer and thereby define a first portion of a replacement gate cavity that is at least partially positioned under said patterned upper sacrificial gate electrode.

2. The method of claim 1 , further comprising, with the patterned upper sacrificial gate electrode in position, performing at least one deposition process through said trenches in said patterned upper sacrificial gate electrode to form a first portion of a replacement gate structure positioned in at least the first portion of said replacement gate cavity under said patterned upper sacrificial gate electrode.

3. The method of claim 2 , wherein performing said at least one deposition process comprises:

performing a first deposition process to deposit a layer of high-k insulating material on an upper surface of said substrate, on a bottom surface of said patterned upper sacrificial gate electrode and on sidewalls of said trenches; and

performing a second deposition process to deposit at least one work-function adjusting material layer on said high-k insulating material.

4. The method of claim 3 , further comprising performing at least one third etching process to remove portions of said high-k gate insulation layer and said at least one work-function adjusting material layer so as to define at least a lower portion of said replacement gate structure that is at least partially positioned within said first portion of said replacement gate cavity.

5. The method of claim 4 , further comprising, after performing said at least one third etching process, performing at least one fourth etching process to remove said patterned upper sacrificial gate electrode so as to expose portions of said high-k gate insulation layer that were positioned under said patterned upper sacrificial gate electrode.

6. The method of claim 5 , further comprising, after performing said at least one fourth etching process, performing a fifth etching process to remove said exposed portions of said high-k gate insulation layer so as to expose an upper surface of said work-function adjusting material layer of said lower portion of said replacement gate structure.

7. The method of claim 6 , further comprising forming at least one layer of conductive material above said exposed upper surface of said lower portion of said replacement gate structure, wherein a final replacement gate structure for a transistor device is comprised of at least said lower replacement gate structure and said at least one layer of conductive material.

8. The method of claim 1 , wherein said upper sacrificial gate electrode and said lower sacrificial gate electrode are made of materials that are selectively etchable relative to one another.

9. The method of claim 1 , wherein said upper sacrificial gate electrode is comprised of silicon, amorphous silicon or polysilicon, and said lower sacrificial gate electrode is comprised of silicon-germanium.

10. A method, comprising:

forming a sacrificial gate structure above a surface of a semiconductor substrate, said sacrificial gate structure comprising a sacrificial gate insulation layer, a lower sacrificial gate electrode positioned above said sacrificial gate insulation layer and an upper sacrificial gate electrode positioned above said lower sacrificial gate electrode, wherein said upper sacrificial gate electrode and said lower sacrificial gate electrode are made of materials that are selectively etchable relative to one another;

forming a sidewall spacer adjacent opposite sides of at least said lower sacrificial gate electrode and said upper sacrificial gate electrode;

forming a layer of insulating material adjacent said sidewall spacers;

performing at least one first etching process through a patterned mask layer so as to thereby define a patterned upper sacrificial gate electrode comprised of a plurality of trenches that each expose a portion of a surface of said lower sacrificial gate electrode;

performing at least one second etching process through said patterned upper sacrificial gate electrode to remove said lower sacrificial gate electrode and said sacrificial gate insulation layer and thereby define a first portion of a replacement gate cavity that is at least partially positioned under said patterned upper sacrificial gate electrode; and

performing at least one process operation to form a first portion of a replacement gate structure positioned in at least the first portion of said replacement gate cavity under said patterned upper sacrificial gate electrode.

11. The method of claim 10 , wherein performing said at least one process operation comprises:

performing a first deposition process to deposit a layer of high-k insulating material on an upper surface of said substrate, on a bottom surface of said patterned upper sacrificial gate electrode and on sidewalls of said trenches;

performing a second deposition process to deposit at least one work-function adjusting material layer on said high-k insulating material; and

performing at least one third etching process to remove portions of said high-k gate insulation layer and said at least one work-function adjusting material layer so as to define at least a lower portion of said replacement gate structure that is at least partially positioned within said first portion of said replacement gate cavity.

12. The method of claim 11 , further comprising:

after performing said at least one third etching process, performing at least one fourth etching process to remove said patterned upper sacrificial gate electrode so as to expose portions of said high-k gate insulation layer that were positioned under said patterned upper sacrificial gate electrode;

after performing said at least one fourth etching process, performing a fifth etching process to remove said exposed portions of said high-k gate insulation layer so as to expose an upper surface of said work-function adjusting material layer of said lower portion of said replacement gate structure; and

forming at least one layer of conductive material above said exposed upper surface of said lower portion of said replacement gate structure, wherein a final replacement gate structure for a transistor device is comprised of at least said lower replacement gate structure and said at least one layer of conductive material.

13. The method of claim 10 , wherein said upper sacrificial gate electrode is comprised of silicon, amorphous silicon or polysilicon, and said lower sacrificial gate electrode is comprised of silicon-germanium.

14. A method, comprising:

forming a sacrificial gate structure above a surface of a semiconductor substrate, wherein forming said sacrificial gate structure comprises:

forming a sacrificial gate insulation layer above said surface of said semiconductor substrate;

forming a lower sacrificial gate electrode comprising one of silicon, amorphous silicon and polysilicon above said sacrificial gate insulation layer; and

forming an upper sacrificial gate electrode comprising silicon-germanium above said lower sacrificial gate electrode;

forming a sidewall spacer adjacent opposite sides of at least said lower sacrificial gate electrode and said upper sacrificial gate electrode;

forming a layer of insulating material adjacent said sidewall spacers;

forming a plurality of trenches in said upper sacrificial gate electrode so as to form a patterned upper sacrificial gate electrode, each of said plurality of trenches exposing an upper surface portion of said lower sacrificial gate electrode;

performing at least one etching process through said patterned upper sacrificial gate electrode to remove said lower sacrificial gate electrode and said sacrificial gate insulation layer from said sacrificial gate structure and to form a first portion of a replacement gate cavity that is at least partially defined by a bottom surface of said patterned upper sacrificial gate electrode and inner sidewall surfaces of said sidewall spacer;

forming a layer of high-k gate insulation material inside of said first portion of said replacement gate cavity through said patterned upper sacrificial gate electrode; and

forming at least one work-function adjusting material layer inside of said cavity and on said layer of high-k gate insulation material through said patterned upper sacrificial gate electrode.

15. The method of claim 14 , further comprising removing said patterned upper sacrificial gate electrode and forming a layer of conductive material above said at least one work-function adjusting material layer.

16. The method of claim 15 , further comprising forming a dielectric gate cap layer above said layer of conductive material.