Non-volatile storage with substrate cut-out and process of fabricating
View Patent ↗Shallow trench isolation regions are positioned between NAND strings (or other types of non-volatile storage). These isolation regions include sections that form concave cut-out shapes in the substrate for the NAND string (or other types of non-volatile storage). The floating gates (or other charge storage devices) of the NAND strings hang over the sections of the isolation region that form the concave cut-out shape in the substrate. To manufacture such a structure, a two step etching process is used to form the isolation regions. In the first step, isotropic etching is used to remove substrate material in multiple directions, including removing substrate material underneath the floating gates. In the second step, anisotropic etching is used to create the lower part of the isolation region.
1. A non-volatile storage device, comprising:
a first active area including a first substrate region and a first floating gate, said first floating gate includes a lowest surface;
a second active area including a second substrate region and a second floating gate, said second floating includes a lowest surface; and
an isolation region between said first substrate region and said second substrate region, said isolation region includes a first section that forms a concave cut-out shape in said first substrate region, said isolation region includes a second section that forms a concave cut-out shape in said second substrate region, said lowest surface of said first floating gate hangs over said first section, said lowest surface of said second floating gate hangs over said second section.
2. A non-volatile storage device according to claim 1 , wherein:
said lowest surface of said first floating gate is positioned higher than said isolation region in its entirety.
3. A non-volatile storage device according to claim 2 , further comprising:
a word line, said word line having a lowest surface that is at a same level as said lowest surface of said first floating gate and said lowest surface of said second floating gate.
4. A non-volatile storage device according to claim 1 , wherein:
said concave cut-out shape in said second substrate region is formed from horizontal isotropic etching underneath said second floating gate while said second floating gate was in place.
5. A non-volatile storage device according to claim 1 , wherein:
said first active area is a first NAND string;
said second active area is a second NAND string;
said isolation region is filled with a dielectric; and
said first NAND string, said second NAND string and said isolation region are in a common well.
6. A non-volatile storage device according to claim 1 , wherein:
said first active area includes a channel in said first substrate region, a tunnel dielectric layer above said channel, a set of floating gates above said tunnel dielectric layer, a set of control gates, and an inter-gate dielectric layer between said floating gates and said control gates; and
said set of floating gates includes said first floating gate.
7. A non-volatile storage device according to claim 1 , wherein:
said isolation region includes a third section that includes all of said isolation region other than said first section and said second section; and
said lowest surface of said first floating gate and said lowest surface of said second floating gate do not hang over said third section of said isolation region.
8. A non-volatile storage device according to claim 1 , wherein:
said first floating gate and said second floating gate are narrower on top and wider on bottom.
9. A non-volatile storage device, comprising:
a set of NAND strings, each of said NAND strings is formed on a substrate and includes floating gates, each floating gate has a lowest surface; and
isolation regions in said substrate and between said NAND strings, said isolation regions include sections that form concave shapes in said substrate, said lowest surfaces of said floating gates hang over said sections of said isolation region that form concave shapes in said substrate, said lowest surfaces of said floating gates are positioned above said isolation regions in their entirety.
10. A non-volatile storage device according to claim 9 , wherein:
said sections of said isolation regions that form concave shapes in said substrate have rounded profiles;
said isolation regions each include a main section that includes all of a respective isolation region other than said sections that form concave shapes in said substrate; and
said lowest surface of said floating do not hang over said main sections of said isolation regions.
11. A non-volatile storage device according to claim 10 , wherein:
said concave shapes are formed from horizontal isoptropic etching underneath said floating gates while said floating gates are in place.
12. A non-volatile storage element according to claim 11 , wherein:
each of said NAND strings includes a channel in said substrate, a tunnel dielectric layer above said channel such that said floating gates are positioned above said tunnel dielectric layer, a set of control gates, and a inter-gate dielectric layer between said floating gates and said control gates.
13. A non-volatile storage device according to claim 12 , wherein:
said floating gates are narrower on top and wider on bottom, said bottom is closer to said substrate than said top.
14. A non-volatile storage device, comprising:
a first substrate region having a first top surface;
a first lower dielectric layer on said first top surface;
a first floating gate on said first lower dielectric layer;
a first upper dielectric layer on said first floating gate;
a first control gate layer on said first upper dielectric layer;
a second substrate region having a second top surface;
a second lower dielectric layer on said second top surface;
a second floating gate on said second lower dielectric layer;
a second upper dielectric on said second floating gate;
a second control gate layer on said second upper dielectric layer; and
an isolation region between said first substrate region and said second substrate region, a first portion of said isolation region forms a concave cut-out in said first substrate region, a second portion of said isolation region forms a concave cut-out in said second substrate region, said isolation region includes a third portion that includes all of said isolation region except said first portion and said second portion, said first floating gate overhangs said first portion of said isolation region without overhanging said third portion of said isolation region, said second floating gate overhangs said second portion of said isolation region without overhanging said third portion of said isolation region.
15. A non-volatile storage device according to claim 14 , wherein:
said first portion of said isolation region and said second portion of said isolation region are formed from horizontal isotropic etching underneath said first and second floating gates while said first and second floating gates are in place.
16. A non-volatile storage device according to claim 14 , wherein:
said first floating gate and said second floating gate are narrower on top and wider on bottom;
said second control gate layer is above said second upper dielectric layer and on two sides of said second floating gate.
17. A non-volatile storage device according to claim 16 , wherein:
said first floating gate and said second floating gate are positioned higher than said isolation region in its entirety.
18. A non-volatile storage device according to claim 17 , wherein:
said first substrate region, said first lower dielectric layer, said first floating gate, said first upper dielectric layer and said first control gate layer comprise a first NAND string;
said second substrate region, said second lower dielectric layer, said second floating gate, said second upper dielectric layer and said second control gate layer comprise a second NAND string;
said isolation region is filled with a dielectric; and
said first NAND string, said second NAND string and said isolation region are in a common well.
19. A non-volatile storage device according to claim 17 , wherein:
said first floating gate and said second floating gate have bottom surfaces;
said bottom surface of said first floating gate hangs over said first section of said isolation region; and
said bottom surface of said second floating gate hangs over said second section of said isolation region.
20. A non-volatile storage device according to claim 14 , wherein:
said first floating gate has a bottom surface in contact with said first lower dielectric layer;
said second floating gate has a bottom surface in contact with said second lower dielectric layer;
said bottom surface of said first floating gate overhangs said first portion of said isolation region; and
said bottom surface of said second floating gate overhangs said second portion of said isolation region.
21. A non-volatile storage device, comprising:
a first substrate region having a first top surface;
a first lower dielectric layer on said first top surface;
a first floating gate layer on said first lower dielectric layer, said first floating gate layer has a bottom surface in contact with said first lower dielectric layer;
a first upper dielectric layer on said first floating gate layer;
a first control gate layer on said first upper dielectric layer;
a second substrate region having a second top surface;
a second lower dielectric layer on said second top surface;
a second floating gate layer on said second lower dielectric layer, said second floating gate layer has a bottom surface in contact with said second lower dielectric layer;
a second upper dielectric on said second floating gate layer;
a second control gate layer on said second upper dielectric layer; and
an isolation region between said first substrate region and said second substrate region, a first portion of said isolation region forms a cut-out in said first substrate region, a second portion of said isolation region forms a cut-out in said second substrate region, said bottom surface of said first floating gate layer overhangs said first portion of said isolation region, said bottom surface of said second floating gate layer overhangs said second portion of said isolation region.