Dual storage node memory
View Patent ↗An embodiment of the present invention is directed to a memory cell. The memory cell includes a first charge storage element and a second charge storage element, wherein the first and second charge storage elements include nitrides. The memory cell further includes an insulating layer formed between the first and second charge storage elements. The insulating layer provides insulation between the first and second charge storage elements.
1. A method of fabricating spaced storage nodes on a surface of a substrate between two adjacent bit lines, the method comprising:
forming a first oxide layer over the substrate extending between the two adjacent bit lines;
forming a charge storage layer over the first oxide layer,
wherein the charge storage layer comprises a nitride; forming a second oxide layer over the charge storage layer; removing a center portion of the second oxide layer; and after removing the center portion of the second oxide layer,
chemically converting the nitride of a center portion of the charge storage layer into an oxide thereby replacing the center portion of the charge storage layer with an insulating layer between two side portions of the charge storage layer and over the first oxide layer extending between the two adjacent bit lines,
wherein chemically converting the nitride of the center portion of the charge storage layer into the oxide is performed while retaining the two side portions of the charge storage layer and while retaining the first oxide layer extending between the two adjacent bit lines.
2. The method as recited in claim 1 further comprising:
forming silicon oxide pillars on the surface of the substrate over each bit line prior to forming the charge storage layer.
3. The method as recited in claim 1 wherein the insulating layer electrically isolates a first portion of the charge storage layer from a second portion of the charge storage layer.
4. The method as recited in claim 1 further comprising:
forming conductive word lines over the bit lines, a first portion of the charge storage layer and a second portion of the charge storage layer.
5. The method as recited in claim 1 wherein the nitride is selected from the group consisting of silicon nitride and silicon enriched nitride.
6. The method as recited in claim 1 further comprising:
forming shallow trenches in the substrate between the adjacent bit lines prior to forming the charge storage layer.
7. The method as recited in claim 1 wherein forming the charge storage layer comprises forming a nitride layer with a thickness between 50 A and 120 A.
8. The method as recited in claim 7 wherein forming the first oxide layer comprises forming a first silicon oxide layer with a thickness between 30 A and 100 A.
9. The method as recited in claim 8 wherein forming the second oxide layer comprises forming a second silicon oxide layer with a thickness between 30 A and 100 A.
10. The method as recited in claim 1 wherein the insulating layer between two side portions of the charge storage layer and over the first oxide layer is operable as a gate oxide.