Method to form strained channel in thin box SOI structures by elastic strain relaxation of the substrate
Methods and structures for forming strained-channel FETs are described. A strain-inducing layer may be formed under stress in a silicon-on-insulator substrate below the insulator. Stress-relief cuts may be formed in the strain-inducing layer to relieve stress in the strain-inducing layer. The relief of stress can impart strain to an adjacent semiconductor layer. Strained-channel, fully-depleted SOI FETs and strained-channel finFETs may be formed from the adjacent semiconductor layer. The amount and type of strain may be controlled by etch depths and geometries of the stress-relief cuts and choice of materials for the strain-inducing layer.
1. A strained-channel FET comprising:
a source region;
a drain region;
a channel region;
a strain-inducing layer of a first semiconductor material adjacent the channel region and extending laterally across an area that includes the source, channel, and drain regions; and
at least one stress-relief trench formed in the strain-inducing layer such that a region of the strain-inducing layer at which stress is relieved by the at least one stress-relief trench imparts strain to the channel region, wherein the at least one stress-relief trench comprises a first plurality of trenches extending in a first direction and a second plurality of trenches extending in a second direction that is different from the first direction.
2. The strained-channel FET of claim 1 , wherein the source, drain, and channel regions are formed in an ultrathin semiconductor layer disposed on an ultrathin buried oxide layer.
3. The strained-channel FET of claim 2 , wherein the strain-inducing layer comprises SiGe or SiC and the source, drain, and channel regions are formed in Si.
4. The strained-channel FET of claim 3 , wherein the thickness of the strain-inducing layer is between 10 nm and 100 nm and the thickness of the ultrathin semiconductor layer is between 1 nm and 25 nm.
5. The strained-channel FET of claim 1 , wherein the first semiconductor material comprises an epitaxial layer formed on a substrate having a second semiconductor material that is chemically different from the first semiconductor material.
6. The strained-channel FET of claim 5 , wherein the first semiconductor material has a first lattice constant that differs from a second lattice constant in the second semiconductor material, wherein the difference in first and second lattice constants determine a stress in the strain-inducing layer prior to formation of the at least one stress-relief trench.
7. The strained-channel FET of claim 5 , wherein the first semiconductor material is SiGe or SiC and the second semiconductor material is Si.
8. The strained-channel FET of claim 1 , wherein the first plurality of trenches extends in a first lateral direction and the second plurality of trenches extends in a second lateral direction that is different from the first lateral direction.
9. The strained-channel FET of claim 8 , wherein the first plurality of trenches and the second plurality of trenches are filled with an electrical insulator.
10. The strained-channel FET of claim 9 , wherein the electrical insulator exhibits compressive or tensile stress.
11. The strained-channel FET of claim 8 , wherein the first plurality of trenches further extend through the strain-inducing layer and the second plurality of trenches do not extend through the strain-inducing layer.