Nanosheet field effect transistor with spacers between sheets
Methods form devices by creating openings in sacrificial gates between nanosheet stacks (alternating layers of a first material and channel structures), forming spacers in the openings, and removing the sacrificial gates to leave the spacers. The first material is then removed from between the channel structures. A first work function metal is formed around and between the channel structures. Next, first stacks (of the stacks) are protected with a mask to leave second stacks (of the stacks) exposed. Then, the first work function metal is removed from the second stacks while the first stacks are protected by the mask and the spacers. Subsequently, a second work function metal is formed around and between the channel structures of the second stacks. A gate material is then formed over the first work function metal and the second work function metal.
1. A method comprising:
patterning a multi-layer structure of alternating layers of a first material and a second material into first and second nanosheet stacks;
forming a sacrificial gate on the first and second nanosheet stacks;
forming an opening in the sacrificial gate;
forming a spacer between the first nanosheet stack and the second nanosheet stack;
removing the first material from between the layers of the second material of the first and second nanosheet stacks;
forming a first work function metal surrounding the layers of the second material;
covering the first work function metal surrounding the first nanosheet stack with a mask;
removing the first work function metal from the second nanosheet stack while protecting the first work function metal surrounding the first nanosheet stack by the mask, and the spacer;
forming a second work function metal surrounding the layers of the second material of the second nanosheet stack and on remaining portions of the first work function metal; and
forming a gate material over the second work function metal,
wherein the forming the spacer comprises:
forming a first spacer in a lower portion of the opening; and
forming a second spacer in an upper portion of the opening,
wherein forming the spacer results in the second spacer extending into a portion of the second nanosheet stack.
2. The method according to claim 1 ,
wherein the second spacer is removed before forming the gate material.
3. The method according to claim 1 ,
wherein the forming the spacer comprises
narrowing the upper portion of the opening before forming the second spacer in the upper portion of the opening, and
wherein the spacer comprises the first spacer and the second spacer on top of the first spacer.
4. The method according to claim 1 ,
wherein the forming the spacer comprises forming the second spacer over a portion of the second nanosheet stack.
5. The method according to claim 1 , wherein the first spacer and the second spacer are the same material.
6. The method according to claim 1 , wherein the removing the first work function metal from the second nanosheet stack comprises applying one of a wet etching process and a dry etching process.
7. A method comprising:
patterning a multi-layer structure of alternating layers of a first material and a second material into first and second nanosheet stacks;
forming a sacrificial gate on the first and second nanosheet stacks;
forming an opening in the sacrificial gate;
forming a spacer between the first nanosheet stack and the second nanosheet stack;
removing the first material from between the layers of the second material of the first and second nanosheet stacks;
forming a first work function metal surrounding the layers of the second material;
covering the first work function metal surrounding the first nanosheet stack with a mask;
removing the first work function metal from the second nanosheet stack while protecting the first work function metal surrounding the first nanosheet stack by the mask, and the spacer;
forming a second work function metal surrounding the layers of the second material of the second nanosheet stack and on remaining portions of the first work function metal; and
forming a gate material over the second work function metal,
wherein the forming the spacer comprises forming the spacer at least one of: over the second nanosheet stack such that the spacer is present over a topmost surface of the second nanosheet stack after the formation of the spacer; and into the second nanosheet stack,
wherein the forming the spacer comprises:
forming a first spacer in a lower portion of the opening; and
forming a second spacer in an upper portion of the opening,
wherein the forming the spacer forms the second spacer to extend into the second material of the second nanosheet stack.
8. The method according to claim 7 , wherein the second spacer is removed before forming the gate material.
9. The method according to claim 7 , wherein the forming the spacer comprises narrowing the upper portion of the opening before forming the second spacer in the upper portion of the opening, and
wherein the spacer comprises the first spacer and the second spacer on top of the first spacer.
10. The method according to claim 7 , wherein the forming the spacer comprises forming the second spacer over a portion of the second nanosheet stack.
11. The method according to claim 7 , wherein the first spacer and the second spacer are the same material.
12. The method according to claim 7 , wherein the removing the first work function metal from the second nanosheet stack comprises applying one of a wet etching process and a dry etching process.
13. A method of forming a device, comprising:
forming a first transistor on a substrate, wherein the first transistor is formed to comprise first source/drain structures on the substrate, first nanosheet channel structures formed to extend between the first source/drain structures, and first gate structures formed to surround each of the first nanosheet channel structures, wherein the first gate structures are formed to comprise a first work function metal;
forming a second transistor on the substrate adjacent the first transistor, wherein the second transistor is formed to comprise second source/drain structures on the substrate, second nanosheet channel structures formed to extend between the second source/drain structures, and second gate structures formed to surround the second nanosheet channel structures, wherein the second gate structures are formed to comprise a second work function metal different from the first work function metal; and
forming a spacer of dielectric material between the first nanosheet channel structures and the second nanosheet channel structures, wherein the forming the spacer comprises forming the spacer to be positioned into a portion of at least one of the second nanosheet channel structures of the second transistor.
14. The method in claim 13 , wherein the spacer is formed to be one of taller and the same height as the first nanosheet channel structures and the second nanosheet channel structures.
15. The method in claim 13 , wherein the spacer and a plurality of liners comprise different materials.