Methods for Forming Semiconductor Regions in Trenches

A method comprising:

• forming an isolation region extending into a semiconductor substrate, wherein the semiconductor substrate has a (001) top surface, and the isolation region encircles an elongated portion of the semiconductor substrate, with the elongated portion having a long side and a short side;
• etching the elongated portion of the semiconductor substrate to form a recess, wherein after the etching, the elongated portion of the semiconductor substrate has a top surface comprising:
• a flat surface having a longitudinal direction parallel to the long side;
• and
• a slant surface having a (111) surface plane, wherein the slant surface comprises a bottom edge connected to the flat surface, and a top edge lower than a top surface of the isolation region;
• performing an epitaxy to grow a semiconductor material in the recess;
• planarizing the semiconductor material, wherein a top surface of the semiconductor material is substantially planar with the top surface of the isolation region;
• and
• recessing the isolation region until the top surface of the isolation region is lower than the top edge of the slant surface, wherein a top portion of the semiconductor material higher than the isolation region forms a semiconductor fin.

A method comprising:

• etching a semiconductor substrate to form a recess extending into a space between opposite isolation regions, wherein after the recessing, a portion of the semiconductor substrate underlying the recess has a top surface comprising:
• a flat surface parallel to a top surface of the semiconductor substrate;
• and
• a slant surface neither parallel to nor perpendicular to the top surface of the semiconductor substrate, wherein the slant surface comprises a bottom edge connected to the flat surface, and a top edge, wherein the top edge is at a first depth of the recess, and the bottom edge is at a second depth of the recess, and wherein the first depth and the second depth have a ratio smaller than about 0.6;
• and
• performing an epitaxy to grow a semiconductor material in the recess, wherein the semiconductor material is grown from the flat surface and the slant surface.