Methods for epitaxially growing active regions between STI regions
A method includes forming a hard mask over a substrate, patterning the hard mask to form a first plurality of trenches, and filling a dielectric material into the first plurality of trenches to form a plurality of dielectric regions. The hard mask is removed from between the plurality of dielectric regions, wherein a second plurality of trenches is left by the removed hard mask. An epitaxy step is performed to grow a semiconductor material in the second plurality of trenches.
1. A method comprising:
forming a hard mask over a substrate;
patterning the hard mask to form a first plurality of trenches;
filling a dielectric material into the first plurality of trenches to form a plurality of dielectric regions;
removing the hard mask from between the plurality of dielectric regions, wherein a second plurality of trenches is left by the removed hard mask; and
performing an epitaxy step to grow a semiconductor material in the second plurality of trenches.
2. The method of claim 1 , wherein the step of patterning the hard mask comprises:
forming a mandrel layer over the hard mask;
patterning the mandrel layer to form a plurality of mandrels;
forming a spacer layer comprising top portions on top surfaces of the plurality of mandrels and sidewall portions on sidewalls of the plurality of mandrels;
etching the spacer layer to remove the top portions of the spacer layer, wherein parts of the sidewall portions of the spacer layer are left un-etched; and
etching the hard mask using the parts of the sidewall portions of the spacer layer as an etching mask.
3. The method of claim 1 further comprising:
before the step of forming the hard mask, forming a pad oxide layer over the substrate; and
after the step of removing the hard mask and before the step of performing the epitaxy step, etching portions of the pad oxide layer to expose a top surface of the substrate.
4. The method of claim 1 , wherein the substrate comprises a semiconductor material.
5. The method of claim 1 , wherein the substrate and the semiconductor material grown in the epitaxy step are formed of essentially a same material.
6. The method of claim 5 , wherein the substrate is a crystalline silicon substrate, and the semiconductor material is formed of crystalline silicon.
7. The method of claim 1 further comprising, forming a transistor at a top surface of one of the semiconductor material.
8. The method of claim 1 , wherein the second plurality of trenches extends into the dielectric regions, with bottoms of the second plurality of trenches lower than top surfaces of the dielectric regions.
9. The method of claim 1 further comprising, after the epitaxy step, forming a gate stack of a transistor over the semiconductor material.
10. The method of claim 3 , wherein the semiconductor material is grown from the top surface of the substrate, with a bottom surface of the semiconductor material in physical contact with the top surface of the substrate.
11. The method of claim 1 , wherein the hard mask is formed over a planar top surface of the substrate, and wherein after the patterning the hard mask, the first plurality of trenches have bottom surfaces level with or higher than the planar top surface of the substrate.
12. The method of claim 11 , wherein entireties of the dielectric material are deposited over the planar top surface of the substrate.