Split charge storage node outer spacer process
View Patent ↗Memory cells containing two split sub-lithographic charge storage nodes on a semiconductor substrate and methods for making the memory cells are provided. The methods can involve forming two split sub-lithographic charge storage nodes by using spacer formation techniques. By removing an exposed portion of a fist poly layer between sloping side surfaces or outer surfaces of spacers while leaving portions of the first poly layer protected by the spacers, the method can provide two split sub-lithographic first poly gates. Further, by removing an exposed portion of a charge storage layer between sloping side surfaces or outer surfaces of spacers, the method can provide two split, narrow portions of the charge storage layer, which subsequently form two split sub-lithographic charge storage nodes.
1. A method of making a memory cell comprising two split sub-lithographic charge storage nodes, comprising sequentially performing the acts of:
forming first openings in a first poly layer and a charge storage layer on a semiconductor substrate using only a patterned first mask layer as a mask, thereby forming a patterned first poly layer ( 300 );
forming a center oxide layer and a second poly in the first opening;
removing the patterned first mask layer;
forming spacers adjacent side surfaces of the center oxide layer and on portions of the upper surface of the patterned first poly layer, wherein the surfaces of the spacers which are not adjacent to the side surfaces of the center oxide layer or on portions of the upper surface of the patterned first poly layer, are sloping; and
forming two split sub-lithographic first poly gates, two split sub-lithographic charge storage nodes, and bit line openings by removing exposed portions of the patterned first poly layer and at least portion of the exposed portions of the charge storage layer that are not covered with the spacer.
2. The method of claim 1 , wherein forming two split sub-lithographic first poly gates comprises removing the exposed portion of the fist poly layer that is between the sloping surfaces of the spacers.
3. The method of claim 1 , wherein forming two split sub-lithographic charge storage nodes comprises removing the exposed portion of the charge storage layer that is between the sloping surfaces of the spacers.
4. The method of claim 1 further comprising implanting portions of the semiconductor substrate through the bit line openings.
5. The method of claim 1 further comprising forming a bit line dielectric in the bit line opening.
6. The method of claim 1 further comprising forming a third poly gate over the semiconductor substrate.
7. The method of claim 1 , wherein forming the center oxide layer comprises a high temperature oxide deposition process.
8. The method of claim 1 , wherein forming the bit line dielectric comprises a high temperature oxide deposition process.
9. The method of claim 1 , wherein the charge storage layer comprises a first oxide layer a nitride layer, and a second oxide layer.
10. The method of claim 1 wherein the center oxide layer is formed around the patterned first mask layer and in the first openings, and the second poly is formed between portions of the center oxide layer.
11. The method of claim 1 where the surface of the spacers on the upper surface of the patterned first poly layer has a length of about 5 nm or more and about 50 nm or less.
12. The method of claim 9 wherein the second oxide layer, the nitride layer, and an upper portion of the first oxide layer of the exposed portion of the charge storage layer are removed, and the rest of the first oxide layer remains.
13. The method of claim 5 further comprising:
removing upper portions of the second poly;
removing upper portions of the spacer; and
removing upper portions of the bit line dielectric
14. The method of clam 1 wherein The upper surface of the second poly is substantially coplanar with the upper surface of the center oxide layer.
15. The method of claim 1 wherein the second poly has a length perpendicular to the substrate of about 10 nm or more and about 100 nm or less.