Method to form self-aligned high density nanocrystals
Methods for fabricating dense arrays of electrically conductive nanocrystals that are self-aligned in depressions at target locations on a substrate, and semiconductor devices configured with nanocrystals situated within a gate stack as a charge storage area for a nonvolatile memory (NVM) device, are provided.
1. A method of forming nanocrystals on a substrate, comprising:
forming a plurality of depressions in a surface of the substrate, the depressions having a depth and sidewalls;
forming a first insulating layer over the substrate;
forming a semiconductor layer over the first insulating layer;
annealing the semiconductor layer to form a plurality of spaced apart nanocrystals on the first insulating layer;
forming a second insulating layer over the nanocrystals and the first insulating layer; and
forming a semiconductor layer over the second insulating layer;
wherein density of the nanocrystals within the depressions is higher than density of the nanocrystals on the surface of the first insulating layer outside the depressions.
2. The method of claim 1 , wherein forming the depressions comprises masking and etching the surface of the substrate.
3. The method of claim 1 , wherein the substrate comprises a semiconductor material.
4. The method of claim 3 , wherein the semiconductor material is selected from the group consisting of polycrystalline silicon, monocrystalline silicon, amorphous silicon, gallium arsenide, silicon germanium, and silicon-on-insulator (SOI).
5. The method of claim 1 , wherein the depressions are in a form selected from the group consisting of trenches, grooves, pits, indentations, cavities, concavities, and V-shapes.
6. The method of claim 1 , wherein sidewalls of the depressions are angled at greater than zero.
7. The method of claim 1 , wherein the depth of the depressions is about 3-80 nm.
8. The method of claim 1 , wherein the semiconductor layer comprises amorphous silicon.
9. The method of claim 1 , wherein the nanocrystals within the depressions have an average diameter of about 3-20 nm.
10. The method of claim 1 , wherein the nanocrystals are separated from each other by a distance of about 5-20 nm.
11. The method of claim 1 , wherein the density of the nanocrystals is about 1E11 to 5E11 nanocrystals per cm 2 .
12. The method of claim 11 , wherein the density of the nanocrystals on the first insulating layer on the depressions is greater than the density of nanocrystals outside the depressions.
13. The method of claim 12 , wherein about 1.5 times more nanocrystals are situated on the first insulating layer on the depressions.
14. A method of forming a nonvolatile memory device, comprising:
providing a semiconductor substrate having a source region, a drain region and a channel region therebetween;
patterning and etching a plurality of depressions in a surface of the semiconductor substrate opposite the channel region, the depressions having a depth and sidewalls;
forming a first insulating layer over the semiconductor substrate including on the depressions;
forming a semiconductor layer over the first insulating layer;
annealing the semiconductor layer to form a plurality of nanocrystals on the insulating layer;
forming a second insulating layer over the nanocrystals;
forming a semiconductor layer over the second insulating layer; and
patterning the semiconductor layer and the second insulating layer to form a gate stack;
wherein the plurality of nanocrystals on the depressions are capable of storing an electrical charge.
15. The method of claim 14 , wherein a select gate is situated on the semiconductor substrate, and the depressions are patterned and etched in the surface of the semiconductor substrate laterally adjacent sidewalls of the select gate.