FinFET devices with unique fin shape and the fabrication thereof

A semiconductor device, comprising:

• a p-channel metal-oxide-semiconductor (PMOS) FinFET that includes:
• a substrate;
• a silicon germanium layer disposed over the substrate;
• a silicon layer disposed over the silicon germanium layer;
• and
• a PMOS fin disposed over the silicon layer, wherein the PMOS fin contains silicon germanium;
• and
• an n-channel metal-oxide-semiconductor (NMOS) FinFET that includes:
• the substrate;
• a silicon germanium oxide layer disposed over the substrate;
• a silicon oxide layer disposed over the silicon germanium oxide layer;
• and
• an NMOS fin disposed over the silicon oxide layer, wherein the NMOS fin contains silicon, and wherein the silicon germanium oxide layer and the silicon oxide layer collectively define a concave recess in a horizontal direction, the concave recess being partially disposed below the NMOS fin.

A semiconductor device, comprising:

• a substrate;
• a dielectric layer disposed over the substrate;
• and
• a fin structure disposed over the dielectric layer;
• wherein:
• the dielectric layer includes a silicon germanium oxide layer disposed over the substrate and a silicon oxide layer disposed over the silicon germanium oxide layer;
• the fin structure contains a semiconductor material;
• and
• the dielectric layer disposed below the fin structure includes a lateral recess.