Methods of fabricating integrated circuit device with fin transistors having different threshold voltages

A method of forming an integrated circuit device, comprising:

• forming a plurality of Si and SiGe fins on a substrate including an isolation layer thereon;
• forming a mask layer covering at least one among the plurality of Si and SiGe fins and covering at least a portion of the isolation layer;
• forming a compound semiconductor layer comprising Si and Ge directly on sidewalls of some of the plurality of Si and SiGe fins not covered by the mask layer and directly on the isolation layer and the mask layer;
• oxidizing the entire compound semiconductor layer to oxidize Si therein for a sufficient duration to drive at least a portion of Ge within the compound semiconductor layer into the sidewalls of the some of the plurality of Si and SiGe fins not covered by the mask;
• and
• removing oxidized portions of the compound semiconductor layer to thereby expose the mask, the isolation layer covered by the compound semiconductor layer and the sidewalls of the some of the plurality of Si and SiGe fins not covered by the mask.

A method of forming an integrated circuit device, comprising:

• epitaxially growing a plurality of semiconductor fins from a corresponding plurality of semiconductor seed regions within an oxide-based isolation layer;
• covering at least some of the semiconductor fins with a mask layer;
• depositing a compound SiGe layer on the mask layer, an upper surface of the oxide-based isolation layer and directly onto sidewalls of the semiconductor fins not covered by the mask layer;
• oxidizing the compound SiGe layer for a sufficient duration to drive at least some of the Ge within the compound SiGe layer into the semiconductor fins not covered by the mask layer, using the mask layer to block transfer of Ge from the compound SiGe layer into semiconductor fins covered by the mask layer;
• and
• etching oxidized portions of the compound SiGe layer to thereby expose the sidewalls of the semiconductor fins not covered by the mask layer and expose the upper surface of the oxide-based isolation layer.