Method for forming isolation regions in a semiconductor device

A method for forming a semiconductor device comprising:

• providing a silicon substrate having a vertical wall surface;
• forming a single-crystal SiGe sidewall spacer overlying the vertical wall surface;
• selectively depositing a silicon layer to form a single-crystal silicon region spaced apart from the vertical wall surface by the SiGe spacer;
• and
• selectively etching away the SiGe spacer leaving the selectively deposited silicon region.

A method for forming a semiconductor device comprising:

• providing a single-crystalline silicon substrate of a first conductivity type;
• forming an insulating layer overlying the surface of the substrate;
• etching a trench into the substrate, the trench having a wall surface;
• forming a SiGe sidewall layer overlying the wall surface;
• selectively forming a single-crystal silicon layer in the trench;
• removing the SiGe sidewall layer leaving a space between the vertical wall surface and the single-crystal silicon layer;
• and
• filling the space with a dielectric material.