Biaxial strained field effect transistor devices
A process for forming contacts to a field effect transistor provides edge relaxation of a buried stressor layer, inducing strain in an initially relaxed surface semiconductor layer above the buried stressor layer. A process can start with a silicon or silicon-on-insulator substrate with a buried silicon germanium layer having an appropriate thickness and germanium concentration. Other stressor materials can be used. Trenches are etched through a pre-metal dielectric to the contacts of the FET. Etching extends further into the substrate, through the surface silicon layer, through the silicon germanium layer and into the substrate below the silicon germanium layer. The further etch is performed to a depth to allow for sufficient edge relaxation to induce a desired level of longitudinal strain to the surface layer of the FET. Subsequent processing forms contacts extending through the pre-metal dielectric and at least partially into the trenches within the substrate.
1. A method of manufacturing a semiconductor device, comprising:
providing a substrate having a semiconductor surface layer, the substrate having a stressor layer positioned at a depth within the substrate and positioned adjacent the semiconductor surface layer, the buried stressor layer provided in a stressed state in comparison to the semiconductor surface layer;
forming a field effect transistor on the semiconductor surface layer, the field effect transistor comprising source and drain regions and a gate structure;
forming a pre-metal dielectric layer over the field effect transistor;
etching openings in the pre-metal dielectric layer and etching to expose contact portions of the substrate on either side of the gate structure;
etching into the substrate within the openings in the pre-metal dielectric, the etching proceeding to sufficient depth so that the stressor layer induces stress in the semiconductor surface layer to provide longitudinal stress to the upper semiconductor layer in a channel region of the field effect transistor through edge relaxation; and
forming electrical contacts to the source and drain regions with the contacts formed at least partially within the substrate.
2. The method of claim 1 , wherein the etching into the substrate extends through the stressor layer and into the substrate below the stressor layer.
3. The method of claim 1 , wherein the etching into the substrate is performed through an orientation-selective wet etch.
4. The method of claim 1 , wherein the etching is performed through an anisotropic etch.
5. The method of claim 1 , wherein the semiconductor surface region is silicon and the stressor layer is silicon germanium alloy.
6. The method of claim 1 , wherein the buried stressor layer is a layer of silicon nitride in a state of compressive built-in stress.
7. The method of claim 1 , wherein the buried stressor layer is a layer of silicon nitride in a state of tensile built-in stress.
8. The method of claim 1 , wherein the buried stressor layer is selectively deposited on a portion of a surface following definition of trenches for trench isolation structures.
9. The method of claim 1 , wherein the buried stressor layer and the semiconductor surface layer are selectively deposited on a portion of a surface following definition of trenches for trench isolation structures.
10. The method of claim 9 , wherein the semiconductor surface region is silicon and the stressor layer is silicon germanium alloy.
11. The method of claim 1 , wherein the field effect transistor is an n-channel field effect transistor.
12. The method of claim 11 , wherein the channel region is silicon.
13. The method of claim 1 , wherein the stressed state of the stressor layer is in-plane compressive stress and the longitudinal stress of the surface semiconductor region is tensile stress.
14. The method of claim 12 , wherein the field effect transistor is an n-channel field effect transistor.
15. The method of claim 13 , wherein the channel region is silicon.