Method to induce strain in finFET channels from an adjacent region
Methods and structures for forming strained-channel finFETs are described. Fin structures for finFETs may be formed using two epitaxial layers of different lattice constants that are grown over a bulk substrate. A first thin, strained, epitaxial layer may be cut to form strain-relieved base structures for fins. The base structures may be constrained in a strained-relieved state. Fin structures may be epitaxially grown in a second layer over the base structures. The constrained base structures can cause higher amounts of strain to form in the epitaxially-grown fins than would occur for non-constrained base structures.
1. A device, comprising:
a substrate having a pedestal;
a fin-shaped structure over the pedestal of the substrate, the fin-shaped structure including a first layer of a first semiconductor material and a second layer of a second material, the first layer stacked on the second layer with the second layer between the first layer and the substrate in a first direction, and the second material different from a material of the substrate;
two constraining structures, one on each of two sides of the fin-shaped structure in a second direction that crosses the first direction, wherein each constraining structure is adjacent to all of the pedestal, all of the second layer, and a lower portion of the first layer in the second direction; and
a gate structure contacting at least the first layer of the fin-shaped structure.
2. The device of claim 1 wherein each constraining structure has a Young's modulus greater than 50 Gpa.
3. The device of claim 1 wherein each constraining structure is a nitride material.
4. The device of claim 1 wherein the gate structure includes a gate dielectric layer and a conductive layer, the gate dielectric layer positioned on the two constraining structures and between the conductive layer and the first layer of the fin-shaped structure.
5. The device of claim 1 wherein the second material of the second layer has a lattice mismatch with the first semiconductor material of the first layer.
6. The device of claim 5 wherein the second material of the second layer has a lattice mismatch with a material of the substrate.
7. The device of claim 5 wherein the first semiconductor material is silicon and the second material is silicon germanium.
8. The device of claim 7 wherein the first layer is an epitaxial silicon layer.
9. The device of claim 7 wherein the second layer has a germanium concentration of about 25% and has a thickness of about 40 nm in the first direction.
10. The device of claim 7 wherein the second layer has a germanium concentration of about 30% and has a thickness of about 30 nm in the first direction.
11. A device, comprising:
a substrate of a first material at a first surface of the substrate, the substrate having a pedestal;
a first structure of a second material on the pedestal of the substrate, the second material having a lattice mismatch with the first material;
a second structure of a third material on the first structure, the third material having a lattice mismatch with the second material;
two constraining structures, one on each of two sides of the first structure, wherein each constraining structure is adjacent to all of the pedestal, all of the first structure, and a lower portion of the second structure; and
a gate structure adjacent to the second structure.
12. The device of claim 11 , each constraining structure has a Young's modulus greater than 50 Gpa.
13. A method, comprising:
forming a substrate having a pedestal;
forming a first fin-shaped structure over the pedestal of the substrate, the first fin-shaped structure having a first material that includes a lattice mismatch with the first surface of the substrate;
forming two constraining structures, each laterally adjacent to one of two sides of the first fin-shaped structure;
forming a second fin-shaped structure on the first fin-shaped structure, the second fin-shaped structure having a second material that includes a lattice mismatch with the first material of the first fin-shaped structure, wherein each constraining structure is laterally adjacent to all of the pedestal, all of the first fin-shaped structure, and a lower portion of the second fin-shaped structure; and
forming a gate structure contacting the second fin-shaped structure.
14. The method of claim 13 wherein the forming the second fin-shaped structure includes:
forming the second fin-shaped structure within a space at least partially defined by the two constraining structures; and
etching each constraining structure down to a height that is above an interface between the first fin-shaped structure and the second fin-shaped structure.