Strained semiconductor using elastic edge relaxation of a stressor combined with buried insulating layer
An SOI wafer contains a compressively stressed buried insulator structure. In one example, the stressed buried insulator (BOX) may be formed on a host wafer by forming silicon oxide, silicon nitride and silicon oxide layers so that the silicon nitride layer is compressively stressed. Wafer bonding provides the surface silicon layer over the stressed insulator layer. Preferred implementations of the invention form MOS transistors by etching isolation trenches into a preferred SOI substrate having a stressed BOX structure to define transistor active areas on the surface of the SOI substrate. Most preferably the trenches are formed deep enough to penetrate through the stressed BOX structure and some distance into the underlying silicon portion of the substrate. The overlying silicon active regions will have tensile stress induced due to elastic edge relaxation.
1. A semiconductor device comprising:
a substrate comprising silicon and having first and second walls of one or more trench isolation structures extending partially into the substrate, a substrate interface region extending between the first and second walls;
an electrically conductive buried stressor layer on the substrate interface region and extending over a lateral extent between the first and second walls, the conductive buried stressor layer being a metallic thin film with built-in in-plane compressive stress;
a buried insulation layer over the buried stressor layer;
a surface semiconductor layer over the buried insulation layer, the surface semiconductor layer extending between the first and second walls and having in-plane tensile strain induced within a first portion of the surface semiconductor layer extending between the first and second walls, the strain induced by edge relaxation of the buried stressor layer; and
an active semiconductor device circuit device having an active region at least partially in the first portion of the surface semiconductor layer.
2. The device of claim 1 , wherein the electrically conductive buried stressor layer comprises at least one of tungsten, molybdenum, titanium, cobalt, nickel, hafnium, and lanthanum.
3. The device of claim 1 , wherein the electrically conductive buried stressor layer comprises a refractory metal.
4. The device of claim 1 , wherein the electrically conductive buried stressor layer comprises a metal boride, or a metal carbide, or a metal nitride.
5. A semiconductor device comprising:
a substrate comprising silicon and having first and second walls of one or more trench isolation structures extending partially into the substrate, a substrate interface region extending between the first and second walls;
an electrically conductive buried stressor layer on the substrate interface region and extending over a lateral extent between the first and second walls, the conductive buried stressor layer being a conductive thin film with built-in in-plane compressive stress;
a buried insulation layer over the buried stressor layer;
a surface semiconductor layer over the buried insulation layer, the surface semiconductor layer extending between the first and second walls and having in-plane tensile strain induced within a first portion of the surface semiconductor layer extending between the first and second walls, the strain induced by edge relaxation of the buried stressor layer; and
an active semiconductor device circuit device having an active region at least partially in the first portion of the surface semiconductor layer
wherein the electrically conductive buried stressor layer comprises heavily doped polycrystalline silicon which is under compressive stress.
6. The device as in any one of claims 1 - 5 , wherein the active semiconductor device is a semiconductor-on-insulator (SOI) MOSFET.
7. The device of claim 6 , wherein the electrically conductive buried stressor layer is a back gate of the SOI MOSFET.
8. The device as in any one of claims 1 - 5 , wherein the surface semiconductor layer comprises silicon.
9. The device as in any one of claims 1 - 5 , wherein the surface semiconductor layer comprises germanium.
10. The device as in any one of claims 1 - 5 , wherein the surface semiconductor layer comprises a compound semiconductor, and wherein the compound semiconductor is a II-VI or a III-V compound semiconductor.
11. The device as in any one of claims 1 - 5 , wherein the buried insulation layer is silicon oxide.