Patterning of vertical nanowire transistor channel and gate with directed self assembly
Directed self-assembly (DSA) material, or di-block co-polymer, to pattern features that ultimately define a channel region a gate electrode of a vertical nanowire transistor, potentially based on one lithographic operation. In embodiments, DSA material is confined within a guide opening patterned using convention lithography. In embodiments, channel regions and gate electrode materials are aligned to edges of segregated regions within the DSA material.
1. A method of forming a nanowire transistor on a substrate, the method comprising:
forming a guide opening in a mask layer disposed over a dielectric layer disposed over a doped semiconductor layer disposed over a substrate;
depositing a directed self-assembly (DSA) material into the guide opening;
segregating the DSA material into a first interior polymer region and a second interior polymer region, the first interior polymer region and the second interior polymer region completely surrounded by an exterior polymer region within the guide opening;
removing the first interior polymer region and the second interior polymer region selectively to the exterior polymer region to form a first opening and a second opening;
forming a first trench and a second trench in the dielectric layer and the doped semiconductor layer, wherein the first trench and the second trench are defined by the first opening and the second opening, respectively;
removing the mask layer and a peripheral portion of the dielectric layer beneath the mask layer to form an annular portion of the dielectric layer surrounding the first trench and the second trench;
removing the exterior polymer region;
forming a first source/drain semiconductor material in the first trench and in the second trench;
forming a channel semiconductor material on the first source/drain semiconductor material in the first trench and in the second trench;
forming a second source/drain semiconductor material on the channel semiconductor material in the first trench and in the second trench;
removing at least a portion of the annular portion of the dielectric layer surrounding the first trench and the second trench to form a gate trench surrounding the channel semiconductor material; and
forming a gate electrode in the gate trench.
2. The method of claim 1 , further comprising:
prior to forming the gate electrode in the gate trench, forming a gate dielectric in the gate trench adjacent to and surrounding the channel semiconductor material, wherein the gate electrode is formed on the gate dielectric.
3. The method of claim 2 , wherein removing at least the portion of annular portion of the dielectric layer comprises removing only a portion of the annular portion of the dielectric layer and leaving a lower portion of the annular portion of the dielectric layer, and wherein forming the gate dielectric layer comprises forming the gate dielectric layer on the lower portion of the annular portion of the dielectric layer.
4. The method of claim 1 , wherein removing at least the portion of the annular portion of the dielectric layer comprises removing all of the annular portion of the dielectric layer.
5. The method of claim 1 , wherein each of the first interior polymer region and the second interior polymer region has a cylindrical geometry.
6. The method of claim 1 , wherein forming the guide opening comprises lithographically patterning a curved guide.
7. The method of claim 1 , wherein segregating the DSA material comprises baking and/or curing the DSA material.
8. The method of claim 1 , further comprising:
polishing the second source/drain semiconductor material so that the second source/drain semiconductor material in the trench is planar with a top surface of the annular portion of the dielectric layer.
9. The method of claim 1 , wherein depositing the DSA material into the guide opening further comprises spin coating a DSA material comprising first and second polymeric materials; and
wherein segregating the DSA material further comprises curing the DSA material at a temperature and for a duration sufficient to permit the first polymeric material to migrate into the interior polymer portion while the second polymeric material migrates into the exterior polymer portion.
10. The method of claim 9 , wherein one of the first and second polymeric materials comprises PMMA.
11. The method of claim 10 , wherein the other of the first and second polymeric material comprises polystyrene.
12. The method of claim 9 , wherein the mask layer comprises one of the first and second polymeric materials.