Tuning strain in semiconductor devices

A device comprising:

• a substrate;
• and
• a Fin Field-Effect Transistor (FinFET) comprising:
• a first silicon germanium oxide layer over the substrate, wherein the first silicon germanium oxide layer has a first germanium percentage, and wherein the first silicon germanium oxide layer has a first width;
• a second silicon germanium oxide layer over the first silicon germanium oxide layer, wherein the second silicon germanium oxide layer has a second germanium percentage greater than the first germanium percentage, and wherein the second silicon germanium oxide layer has a second width smaller than the first width, with the first width and the second width being measured in a channel width direction of the FinFET;
• a silicon layer over the second silicon germanium oxide layer, wherein the silicon layer forms a channel of the FinFET;
• a gate dielectric on sidewalls and a top surface of the silicon layer;
• and
• a gate electrode over the gate dielectric.

A device comprising:

• a substrate;
• a first silicon germanium oxide layer over the substrate;
• a second silicon germanium oxide layer over the first silicon germanium oxide layer, with opposite edges of the second silicon germanium oxide layer recessed from respective edges of the first silicon germanium oxide layer;
• and
• a silicon layer over the second silicon germanium oxide layer.