Methods of forming MOSFETS using crystalline sacrificial structures

A method of forming a MOSFET, comprising:

• forming a first recess in a region of a semiconductor substrate having a crystalline structure;
• forming a sacrificial structure having the crystalline structure in the recess;
• forming an epitaxial semiconductor layer on the sacrificial structure and on the semiconductor substrate;
• patterning the epitaxial semiconductor layer and the semiconductor substrate to form a second recess to expose a lateral sidewall surface of the sacrificial structure;
• removing the sacrificial structure via the exposed lateral sidewall surface to form a void in the substrate in place of the sacrificial structure;
• and
• forming a device isolation layer in the void.

A method of forming a MOSFET comprising:

• forming a first mask pattern in a predetermined region of a semiconductor substrate having a crystalline structure;
• forming a first recess in the semiconductor substrate using the first mask pattern as an etch mask;
• epitaxially growing a crystalline sacrificial structure in the first recess using the first mask pattern to prevent epitaxial growth beneath the first mask pattern;
• removing the first mask pattern to expose an upper surface of the semiconductor substrate;
• epitaxially growing a semiconductor layer on an upper surface of the sacrificial structure and the semiconductor substrate;
• patterning the epitaxial semiconductor layer and the semiconductor substrate to form a second trench exposing a lateral surface of the sacrificial structure;
• removing the exposed sacrificial structure to form a void in the first recess;
• forming a device isolation layer in the void;
• forming a gate insulation layer on the epitaxial semiconductor layer;
• forming a gate pattern on the gate insulation layer to cross over a central portion of the epitaxial semiconductor layer;
• and
• forming source/drain regions in the epitaxial semiconductor layer on both sides of the gate pattern.

A method of forming a Metal-Oxide-Semiconductor Field-Effect-Transistor (MOSFET) comprising:

• forming a recess in an upper surface of a substrate;
• forming a sacrificial crystalline structure filling the recess;
• growing an epitaxial semiconductor layer on an upper surface of the sacrificial crystalline structure and on the substrate to form a buried sacrificial structure including in the recess wherein an upper surface of the buried sacrificial structure is above a lower surface of source/drain regions formed in the substrate;
• removing the buried sacrificial structure to form a void in place of the buried sacrificial structure;
• and
• forming a device isolation layer in the void, wherein forming a device isolation layer in the void comprises:
• forming the device isolation layer adjacent to a source region and/or a drain region;
• and
• avoiding forming the device isolation layer beneath a central portion of a channel region in the MOSFET.