Multiple-depth sti trenches in integrated circuit fabrication

A method of fabricating isolation trenches of varying depth within an integrated circuit device, the method comprising:

• defining areas of a substrate for future trenches, wherein a first area has a first width and a second area has a second width wider than the first width;
• forming a first trench in the first area of the substrate and a second trench in the second area of the substrate;
• forming a first dielectric fill layer overlying the substrate to fill the first trench and to leave the second trench open;
• removing a portion of the first dielectric fill layer to expose a portion of the substrate at a bottom of the second trench;
• extending the second trench into the exposed portion of the substrate;
• and
• forming a second dielectric fill layer overlying the substrate to fill the second trench.

A method of fabricating trenches within an integrated circuit device, comprising:

• forming a plurality of trenches in a substrate to a first depth, wherein the plurality of trenches includes first trenches having a width less than some first value, second trenches having a width greater than the first value and less than a second value, and third trenches having a width greater than the second value;
• forming a first dielectric layer overlying the substrate to fill the first trenches and to leave open the second and third trenches;
• removing a portion of the first dielectric layer to expose portions of the underlying substrate at bottoms of the second and third trenches while leaving the first trenches filled;
• removing exposed portions of the underlying substrate to extend the second and third trenches to a second depth;
• forming a second dielectric layer overlying the substrate to fill the second trenches and to leave open the third trenches;
• removing a portion of the second dielectric layer to expose portions of the underlying substrate at the bottoms of the third trenches while leaving the first and second trenches filled;
• removing exposed portions of the underlying substrate to extend the third trenches to a third depth;
• and
• forming a third dielectric layer overlying the substrate to fill the third trenches.