Air gap isolation in non-volatile memory
View Patent ↗Air gap isolation in non-volatile memory arrays and related fabrication processes are provided. Electrical isolation between adjacent active areas of a substrate can be provided, at least in part, by bit line air gaps that are elongated in a column direction between the active areas. At least one cap is formed over each isolation region, at least partially overlying air to provide an upper endpoint for the corresponding air gap. The caps may be formed at least partially along the sidewalls of adjacent charge storage regions. In various embodiments, selective growth processes are used to form capping strips over the isolation regions to define the air gaps. Word line air gaps that are elongated in a row direction between adjacent rows of storage elements are also provided.
1. A method of fabricating non-volatile storage, comprising:
forming a first layer stack column and a second layer stack column elongated in a column direction over a substrate, each layer stack column having two vertical sidewalls and including a charge storage strip over a tunnel dielectric strip, the first layer stack column overlying a first active area of the substrate and the second layer stack column overlying a second active area of the substrate;
etching the substrate to define an isolation region between the first active area and the second active area;
modifying a surface of at least a portion of the two vertical sidewalls of each layer stack column by ion implantation prior to etching the substrate;
growing a cap between the first layer stack column and the second layer stack column, the cap extending vertically along at least a portion of the charge storage strip of the first column and the charge storage strip of the second column; and
forming a bit line air gap in the isolation region having an upper endpoint defined at least partially by the cap.
2. A method according to claim 1 , wherein growing the cap between the first layer stack column and the second layer stack column includes:
selectively growing the cap using the modified surface of the two vertical sidewalls to form the cap between the charge storage strip of the first layer stack column and the charge storage strip of the second layer stack column.
3. A method according to claim 1 , wherein selectively growing the cap includes:
providing ozone and tetraethyl orthosilicate in a first ratio to form a nucleation layer on the modified surface of the two vertical sidewalls; and
changing the ratio of the ozone to the tetraethyl orthosilicate to induce selective growth of the cap along the nucleation layer.
4. A method according to claim 1 , further comprising:
recessing the cap below a level of an upper surface of the charge storage strips;
forming an intermediate dielectric layer over the upper surface and along the vertical sidewalls of the charge storage strips; and
forming a control gate layer over the intermediate dielectric layer, the control gate layer extending below the upper surface of the charge storage strips between adjacent portions of the intermediate dielectric layer.
5. A method according to claim 4 , further comprising:
etching the control gate layer into a plurality of control gates;
etching the charge storage strip for the first column into a first plurality of charge storage regions;
etching the charge storage strip for the second column into a second plurality of charge storage regions;
wherein the plurality of control gates includes a first control gate separated from a first charge storage region of the first plurality and a first charge storage region of the second plurality;
wherein the plurality of control gates includes a second control gate separated from a second charge storage region of the first plurality and a second charge storage region of the second plurality.
6. A method according to claim 5 , wherein:
etching the control gate layer, the charge storage strip for the first column and the charge storage strip for the second column is orthogonal to a direction of the first layer stack column and the second layer stack column.
7. A method according to claim 6 , wherein:
etching the control gate layer, the charge storage strip for the first column and the charge storage strip for the second column forms a plurality of layer stack rows including a first layer stack row and a second layer stack row;
the first layer stack row includes the first control gate, a first intermediate dielectric strip, and the first plurality of charge storage regions; and
the second layer stack row includes the second control gate, a second intermediate dielectric strip, and the second plurality of charge storage regions.
8. A method according to claim 7 , further comprising:
forming a plurality of word line air gaps including a first word line air gap formed between the first layer stack row and the second layer stack row.
9. A method according to claim 8 , wherein:
the first word line air gap extends vertically, with respect to the substrate surface, from a level above the substrate surface to at least a level of an upper surface of the first and second control gate.
10. A method according to claim 9 , further comprising, after etching the control gate layer and before etching the charge storage strip for the first column and the charge storage strip for the second column:
forming a catalytic layer on a first and a second sidewall of each control gate.
11. A method according to claim 10 , further comprising, after etching the charge storage strip for the first column and the charge storage strip for the second column and before forming the plurality of word line air gaps:
selectively growing a temporary cap between each pair of adjacent control gates;
recessing the temporary caps below an upper surface of each control gate;
siliciding the control gates after recessing the temporary caps.
12. A method according to claim 11 , further comprising:
removing the temporary caps after siliciding the control gates;
nonconformally depositing a capping layer to form permanent word line air gap caps that overlie air between adjacent layer stack rows, the permanent word line air gap caps defining an upper endpoint of the corresponding word line air gap.
13. A method of fabricating non-volatile storage, comprising:
forming a first layer stack column and a second layer stack column elongated in a column direction over a substrate, each layer stack column having two vertical sidewalls and including a charge storage strip over a tunnel dielectric strip, the first layer stack column overlying a first active area of the substrate and the second layer stack column overlying a second active area of the substrate;
etching the substrate to define an isolation region between the first active area and the second active area;
growing a cap between the first layer stack column and the second layer stack column, the cap extending vertically along at least a portion of the charge storage strip of the first column and the charge storage strip of the second column;
recessing the cap below a level of an upper surface of the charge storage strips;
forming an intermediate dielectric layer over the upper surface and along the vertical sidewalls of the charge storage strips;
forming a control gate layer over the intermediate dielectric layer, the control gate layer extending below the upper surface of the charge storage strips between adjacent portions of the intermediate dielectric layer; and
forming a bit line air gap in the isolation region having an upper endpoint defined at least partially by the cap.
14. A method according to claim 13 , further comprising:
etching the control gate layer into a plurality of control gates;
etching the charge storage strip for the first column into a first plurality of charge storage regions;
etching the charge storage strip for the second column into a second plurality of charge storage regions;
wherein the plurality of control gates includes a first control gate separated from a first charge storage region of the first plurality and a first charge storage region of the second plurality;
wherein the plurality of control gates includes a second control gate separated from a second charge storage region of the first plurality and a second charge storage region of the second plurality.
15. A method according to claim 14 , wherein:
etching the control gate layer, the charge storage strip for the first column and the charge storage strip for the second column is orthogonal to a direction of the first layer stack column and the second layer stack column.
16. A method according to claim 15 , wherein:
etching the control gate layer, the charge storage strip for the first column and the charge storage strip for the second column forms a plurality of layer stack rows including a first layer stack row and a second layer stack row;
the first layer stack row includes the first control gate, a first intermediate dielectric strip, and the first plurality of charge storage regions; and
the second layer stack row includes the second control gate, a second intermediate dielectric strip, and the second plurality of charge storage regions.
17. A method according to claim 16 , further comprising:
forming a plurality of word line air gaps including a first word line air gap formed between the first layer stack row and the second layer stack row.
18. A method according to claim 17 , wherein:
the first word line air gap extends vertically, with respect to the substrate surface, from a level above the substrate surface to at least a level of an upper surface of the first and second control gate.
19. A method according to claim 18 , further comprising, after etching the control gate layer and before etching the charge storage strip for the first column and the charge storage strip for the second column:
forming a catalytic layer on a first and a second sidewall of each control gate.
20. A method according to claim 19 , further comprising, after etching the charge storage strip for the first column and the charge storage strip for the second column and before forming the plurality of word line air gaps:
selectively growing a temporary cap between each pair of adjacent control gates;
recessing the temporary caps below an upper surface of each control gate;
siliciding the control gates after recessing the temporary caps.
21. A method according to claim 20 , further comprising:
removing the temporary caps after siliciding the control gates;
nonconformally depositing a capping layer to form permanent word line air gap caps that overlie air between adjacent layer stack rows, the permanent word line air gap caps defining an upper endpoint of the corresponding word line air gap.
22. A method according to claim 13 , further comprising:
modifying a surface of at least a portion of the two vertical sidewalls of each layer stack column by ion implantation prior to etching the substrate.
23. A method according to claim 22 , wherein growing the cap between the first layer stack column and the second layer stack column includes:
selectively growing the cap using the modified surface of the two vertical sidewalls to form the cap between the charge storage strip of the first layer stack column and the charge storage strip of the second layer stack column.
24. A method according to claim 23 , wherein selectively growing the cap includes:
providing ozone and tetraethyl orthosilicate in a first ratio to form a nucleation layer on the modified surface of the two vertical sidewalls; and
changing the ratio of the ozone to the tetraethyl orthosilicate to induce selective growth of the cap along the nucleation layer.