Transistor contacts self-aligned in two dimensions
Embodiments of the present invention provide an improved semiconductor structure and methods of fabrication that provide transistor contacts that are self-aligned in two dimensions. Two different capping layers are used, each being comprised of a different material. The two capping layers are selectively etchable to each other. One capping layer is used for gate coverage while the other capping layer is used for source/drain coverage. Selective etch processes open the desired gates and source/drains, while block masks are used to cover elements that are not part of the connection scheme. A metallization line (layer) is deposited, making contact with the open elements to provide electrical connectivity between them.
1. A method of forming a semiconductor structure comprising:
covering a plurality of transistor gates with a first capping layer;
covering a plurality of source/drain contact areas with a second capping layer;
forming a first mask over the semiconductor structure, wherein the first mask exposes a plurality of gate contact locations;
removing the first capping layer from the plurality of gate contact locations;
forming a second mask over the semiconductor structure, wherein the second mask exposes a plurality of source/drain contact locations;
removing the second capping layer from the plurality of source/drain contact locations; and
depositing a metallization layer over the exposed source/drain contact locations and exposed gate contact locations.
2. The method of claim 1 , wherein covering a plurality of transistor gates with a first capping layer comprises depositing silicon nitride.
3. The method of claim 2 , wherein covering a plurality of source/drain contact areas with a second capping layer comprises depositing silicon oxide.
4. The method of claim 1 , wherein depositing a metallization layer comprises depositing tungsten.
5. The method of claim 1 , wherein depositing a metallization layer comprises depositing copper.
6. The method of claim 1 , further comprising forming a gate-SD stitch structure connecting one of the plurality of transistor gates to an adjacent source/drain contact area.
7. The method of claim 1 , further comprising connecting a first transistor gate of the plurality of transistor gates to a second transistor gate of the plurality of transistor gates.
8. The method of claim 1 , further comprising connecting a first source/drain contact area of the plurality of source/drain contact areas to a second source/drain contact area of the plurality of source/drain contact areas.
9. A method of forming a semiconductor structure comprising:
covering a plurality of transistor gates with a first capping layer;
covering a plurality of source/drain contact areas with a second capping layer;
forming a first mask over the semiconductor structure, wherein the first mask exposes a plurality of gate contact locations;
removing the first capping layer from the plurality of gate contact locations;
forming a second mask over the semiconductor structure, wherein the second mask exposes a plurality of source/drain contact locations;
removing the second capping layer from the plurality of source/drain contact locations; and
depositing a metallization line over the exposed source/drain contact locations and exposed gate contact locations, wherein the first capping layer comprises silicon oxide and the second capping layer comprises silicon nitride.
10. The method of claim 9 , wherein depositing a metallization line comprises depositing tungsten.
11. The method of claim 9 , further comprising forming a gate-SD stitch structure connecting one of the plurality of transistor gates to an adjacent source/drain contact area.
12. The method of claim 9 , further comprising connecting a first transistor gate of the plurality of transistor gates to a second transistor gate of the plurality of transistor gates.
13. The method of claim 9 , further comprising connecting a first source/drain contact area of the plurality of source/drain contact areas to a second source/drain contact area of the plurality of source/drain contact areas.
14. The method of claim 9 , further comprising connecting a first source/drain contact layer region comprising NMOS transistors to a second source/drain contact layer region comprising PMOS transistors using a passthrough interconnection.
15. A semiconductor structure comprising: a plurality of transistor gates; a plurality of transistor source/drain contact areas; a first capping layer disposed on a subset of the plurality of transistor gates; a second capping layer disposed on a subset of the plurality of transistor source/drain contact areas; and a metallization layer disposed on the first capping layer and second capping layer and a dielectric region comprised of silicon oxycarbide, and a plurality of spacers comprised of a material selected from the group consisting of silicon oxycarbide and silicon oxycarbonitride.
16. The semiconductor structure of claim 15 , wherein the metallization layer is in electrical contact with at least one transistor gate of the plurality of transistor gates.
17. The semiconductor structure of claim 15 , wherein the metallization layer is in electrical contact with at least one source/drain contact area of the plurality of transistor source/drain contact areas.
18. The semiconductor structure of claim 15 , wherein the dielectric region bounds the metallization layer.
19. The semiconductor structure of claim 18 , wherein the plurality of spacers are adjacent to each transistor gate of the plurality of transistor gates.
20. The semiconductor structure of claim 19 , wherein the first capping layer is comprised of silicon nitride, and the second capping layer is comprised of silicon oxide.