Germanium FinFETs Having Dielectric Punch-Through Stoppers

A method of forming a semiconductor structure, the method comprising:

• providing a bulk silicon substrate;
• epitaxially growing a silicon germanium (SiGe) layer on the bulk silicon substrate;
• and
• performing a first condensation to the SiGe layer to form a condensed SiGe layer at a temperature between about 825° C. and about 880° C.

A method of forming a semiconductor structure, the method comprising:

• providing a bulk silicon substrate;
• epitaxially growing a silicon germanium (SiGe) layer on the bulk silicon substrate;
• performing a first condensation to the SiGe layer to form a condensed SiGe layer, wherein the first condensation is performed at an elevated temperature;
• etching the condensed SiGe layer and a top portion of the bulk silicon substrate to form a recess and a composite fin in the recess, wherein the composite fin comprises a silicon fin and a condensed SiGe fin over the silicon fin;
• filling a first dielectric material into the recess;
• etching the first dielectric material until the condensed SiGe fin is exposed;
• forming a mask to cover a top surface and sidewalls of the condensed SiGe fin;
• recessing the first dielectric material to expose sidewalls of a portion of the silicon fin;
• oxidizing the portion of the silicon fin to form an insulator;
• filling a second dielectric material on the first dielectric material, wherein a top surface of the second dielectric material is substantially level with a top surface of the insulator;
• and
• performing a second condensation to the condensed SiGe fin to form a substantially pure germanium fin.