Tapered nanowire structure with reduced off current
Non-planar semiconductor devices including at least one semiconductor nanowire having a tapered profile which widens from the source side of the device towards the drain side of the device are provided which have reduced gate to drain coupling and therefore reduced gate induced drain tunneling currents.
1. A method of forming a non-planar semiconductor device comprising:
forming at least one semiconductor nanowire suspended above an insulator layer of a semiconductor-on-insulator substrate, wherein an end segment of said at least one semiconductor nanowire is attached to a first semiconductor-on-insulator pad region and another end segment of said at least one semiconductor nanowire is attached to a second semiconductor-on-insulator pad region, said first and second semiconductor-on-insulator pad regions are both located atop said insulator layer;
forming at least one semiconductor nanowire into at least one suspended and tapered semiconductor nanowire comprising a first semiconductor nanowire portion having a first width, a second semiconductor nanowire portion having a second width and a third semiconductor nanowire portion having a third width, wherein said third semiconductor nanowire portion is located between the first and second semiconductor nanowire portions, and said first width is less than the third width, and wherein said third width is less than the second width;
forming a gate on a portion of said third semiconductor nanowire portion of said at least one semiconductor nanowire, wherein said first semiconductor nanowire portion is located on a first side of the gate and said second semiconductor nanowire portion is located on a second side of the gate that is opposite to said first side;
forming a source region on said first side of the gate and forming a drain region on the second side of the gate; and
forming a polysilicon line on a surface of said gate and having a bottommost surface directly contacting a surface of said insulator layer.
2. The method of claim 1 , wherein said forming the at least one tapered semiconductor nanowire comprises selective removal of semiconductor material from a portion of said at least one semiconductor nanowire that is located nearest to the first semiconductor-on-insulator pad region relative to at least another portion of the at least one semiconductor nanowire that is located nearest the second semiconductor-on-insulator pad region, and annealing.
3. The method of claim 1 , wherein said forming the at least one tapered semiconductor nanowire comprises forming a mask on a portion of the at least one semiconductor nanowire that is located nearest the second semiconductor-on-insulator pad region, annealing and removing said mask.
4. The method of claim 1 , further comprising forming a spacer on both sides of the gate.
5. The method of claim 1 , wherein said forming the source region and forming the drain region comprises forming an in-situ doped epitaxial semiconductor material atop the first and second semiconductor-on-insulator pad regions and atop exposed surfaces of the first semiconductor nanowire portion and the second semiconductor nanowire portion.
6. The method of claim 1 , further comprising forming a metal semiconductor alloy material atop the source region and the drain region.
7. The method of claim 1 , wherein said forming the gate comprises forming at least one gate dielectric material, followed by forming at least a metal gate film atop the at least one gate dielectric material.
8. The method of claim 1 , wherein said forming said at least one semiconductor nanowire comprises:
performing a first lithography and etching sequence to form a slab of semiconductor material; and
performing a second lithography and etching sequence to convert a portion of said slab of semiconductor material into said at least one semiconductor nanowire.
9. The method of claim 2 , wherein said selective removal is performed by subjecting a preselected portion of said at least one semiconductor nanowire to an oxidation process that is performed at a temperature of greater than 700° C.
10. The method of claim 1 , further comprising forming a hard mask line on said polysilicon line.
11. A method of forming a non-planar semiconductor device comprising:
forming at least one tapered semiconductor nanowire suspended above an insulator layer of a semiconductor-on-insulator substrate, wherein an end segment of said at least one tapered semiconductor nanowire is attached to a first semiconductor-on-insulator pad region and another end segment of said at least one tapered semiconductor nanowire is attached to a second semiconductor-on-insulator pad region, said first and second semiconductor-on-insulator pad regions are both located atop said insulator layer, and wherein said at least one tapered semiconductor nanowire comprises a first semiconductor nanowire portion having a first width, a second semiconductor nanowire portion having a second width and a third semiconductor nanowire portion having a third width, wherein said third semiconductor nanowire portion is located between the first and second semiconductor nanowire portions, and wherein said first width is less than the third width, and said third width is less than the second width;
forming a gate atop said third semiconductor nanowire portion of said at least one tapered semiconductor nanowire, wherein said first semiconductor nanowire portion is located on a first side of the gate and said second semiconductor nanowire portion is located on a second side of the gate that is opposite to said first side;
forming a source region on said first side of the gate and forming a drain region ef on the second side of the gate; and
forming a polysilicon line on a surface of said gate and having a bottommost surface directly contacting a surface of said insulator layer.
12. The method of claim 11 wherein said forming the at least one tapered semiconductor nanowire comprises lithography wherein a strain is induced in said at least one tapered semiconductor nanowire that results in curvature of said at least one tapered semiconductor nanowire, wherein said strain forms said first semiconductor nanowire portion, said second semiconductor nanowire portion and said third semiconductor nanowire portion of said at least one tapered semiconductor nanowire.
13. The method of claim 12 , wherein said lithography is optical lithography.
14. The method of claim 12 , wherein said lithography is E-beam lithography.
15. The method of claim 11 , wherein said forming the at least one semiconductor nanowire further comprises annealing.
16. The method of claim 11 , further comprising forming a metal semiconductor alloy material atop the source region and the drain region.
17. The method of claim 11 , further comprising forming a hard mask line on said polysilicon line.
18. A method of forming a non-planar semiconductor device comprising:
forming at least one semiconductor nanowire suspended above an insulator layer of a semiconductor-on-insulator substrate, wherein an end segment of said at least one semiconductor nanowire is attached to a first semiconductor-on-insulator pad region and another end segment of said at least one semiconductor nanowire is attached to a second semiconductor-on-insulator pad region, each of said first and second semiconductor-on-insulator pad regions having a first bottommost surface portion located on a surface of said insulator layer and a second bottommost surface portion separated from said insulator layer by an undercut region;
forming at least one semiconductor nanowire into at least one tapered semiconductor nanowire comprising a first semiconductor nanowire portion having a first width, a second semiconductor nanowire portion having a second width and a third semiconductor nanowire portion having a third width, wherein said third semiconductor nanowire portion is located between the first and second semiconductor nanowire portions, and said first width is less than the third width, and wherein said third width is less than the second width;
forming a gate on a portion of said third semiconductor nanowire portion of said at least one semiconductor nanowire, wherein said first semiconductor nanowire portion is located on a first side of the gate and said second semiconductor nanowire portion is located on a second side of the gate that is opposite to said first side;
forming a first spacer portion of each side of said gate and second spacer portion in each undercut region, wherein a topmost surface of said second spacer portion within each undercut region directly contacts said second bottommost surface portion of said first and second semiconductor-on-insulator pad regions; and
forming a source region on said first side of the gate and forming a drain region on the second side of the gate.