Multi-layer work function metal replacement gate
View Patent ↗Embodiments relate to a field-effect transistor (FET) replacement gate apparatus. The apparatus includes one or more of a substrate and insulator including a base and side walls defining a trench. A high-dielectric constant (high-k) layer is formed on the base and side walls of the trench. The high-k layer has an upper surface conforming to a shape of the trench. A first layer is formed on the high-k layer and conforms to the shape of the trench. The first layer includes an aluminum-free metal nitride. A second layer is formed on the first layer and conforms to the shape of the trench. The second layer includes aluminum and at least one other metal. A third layer is formed on the second layer and conforms to the shape of the trench. The third layer includes aluminum-free metal nitride.
1. A method of forming a replacement gate structure of a field-effect transistor, comprising:
forming a high-dielectric-constant (high-k) layer on a substrate;
forming a first layer on the high-k layer, the first layer being an aluminum-free metal nitride;
forming a second layer on the first layer, the second layer comprising aluminum and at least one other metal, wherein forming the second layer includes depositing layers of aluminum to the at least one other metal in a sequence such that a ratio of aluminum to the at least one other metal is a gradient having a higher ratio at a center portion of the second layer and a lower ratio at ends of the second layer; and
forming a third layer on the second layer, the third layer being an aluminum-free metal nitride.
2. The method of claim 1 , wherein the substrate includes a base and side walls extending from the base, and
wherein the high-k layer and the first, second and third layers are formed by a conforming process, such that an upper surface the high-k layer conforms to an upper surface of the base and the side walls and each of the first, second and third layers conforms to an upper surface of a respectively underlying layer.
3. The method of claim 2 , further comprising forming a metal gap fill layer on the third layer to fill a gap defined by the substrate and side walls via the high-k layer, and the first, second, and third layers.
4. The method of claim 2 , wherein the FET is a finFET and the side walls are at least one of source and drain structures and channels extending between the source and drain structures.
5. The method of claim 1 , wherein the high-k layer includes hafnium.
6. The method of claim 1 , wherein the first and third layers comprise one of titanium nitride (TiN) and tantalum nitride (TaN).
7. The method of claim 1 , wherein the second layer includes titanium and aluminum (TiAl).
8. The method of claim 1 , wherein the second layer does not include nitrogen.
9. The method of claim 1 , wherein forming the second layer includes forming the layers of aluminum in sequence with the layers of the at least one other metal such that the layers of the aluminum are formed with greater frequency at the center portion of the second layer relative to the ends of the second layer.
10. The method of claim 1 , further comprising preventing exposure of the first, second and third layers to oxygen during forming of the first, second and third layers.
11. A method of forming a replacement gate structure of a field-effect transistor, the replacement gate structure including a trench defined by a base and side walls, the method comprising:
forming a high-dielectric-constant (high-k) layer in the trench to conform to a shape of the trench;
forming a first layer on the high-k layer to conform to a shape of the trench, the first layer being an aluminum-free metal nitride;
forming a second layer on the first layer to conform to a shape of the trench, the second layer comprising aluminum and at least one other metal, wherein forming the second layer includes depositing layers of aluminum to the at least one other metal in a sequence such that a ratio of aluminum to the at least one other metal is a gradient having a higher ratio at a center portion of the second layer and a lower ratio at ends of the second layer; and
forming a third layer on the second layer to conform to a shape of the trench, the third layer being an aluminum-free metal nitride.
12. The method of claim 11 , further comprising forming a metal gap fill layer on the third layer to fill a gap defined by the substrate and side walls via the high-k layer, and the first, second, and third layers.
13. The method of claim 11 , wherein the FET is a finFET and the side walls are at least one of source and drain structures and channels extending between the source and drain structures.
14. The method of claim 11 , wherein the high-k layer includes hafnium.
15. The method of claim 11 , wherein the first and third layers comprise one of titanium nitride (TiN) and tantalum nitride (TaN).
16. The method of claim 11 , wherein the second layer includes titanium and aluminum (TiAl).
17. The method of claim 11 , wherein the second layer does not include nitrogen.
18. The method of claim 11 , wherein forming the second layer includes forming the layers of aluminum in sequence with the layers of the at least one other metal such that the layers of the aluminum are formed with greater frequency at the center portion of the second layer relative to the ends of the second layer.
19. The method of claim 11 , further comprising preventing exposure of the first, second and third layers to oxygen during forming of the first, second and third layers.