Floating gate ultrahigh density vertical NAND flash memory

1. A method of making a monolithic three dimensional NAND string, comprising a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate, a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprise at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level, a blocking dielectric located over the plurality of control gates, a tunnel dielectric in contact with the semiconductor channel, and at least one charge storage region located between the blocking dielectric and the tunnel dielectric, wherein each control gate comprises copper;

wherein the method comprises:

providing a stack of alternating first material layers and second material layers over a substrate, wherein the first material layers comprise an insulating material and the second material layers comprise sacrificial layers;

forming a back side opening in the stack;

selectively removing the second material layers through the back side opening to form back side recesses between adjacent first material layers;

forming the blocking dielectric inside the back side recesses and the back side opening, the blocking dielectric having a clam shaped regions inside the back side recesses; and

forming the plurality of copper control gate electrodes in the respective clam shell shaped regions of the blocking dielectric in the back side recesses.

2. The method of claim 1 , further comprising:

forming a first barrier layer over the blocking dielectric inside the back side recesses and the back side opening, the first barrier layer having clam shaped regions inside the clam shaped regions in the blocking dielectric the back side recesses, wherein the plurality of copper control gate electrodes are formed in the respective clam shell shaped regions of the first barrier layer in the back side recesses.

3. The method of claim 2 , further comprising:

forming at least one front side opening in the stack;

forming the at least one charge storage region in the at least one opening;

forming the tunnel dielectric layer over the at least one charge storage region in the front side opening; and

forming the semiconductor channel on the tunnel dielectric in the front side opening.

4. The method of claim 3 , further comprising:

forming a cover layer on a sidewall of front side opening prior to forming the at least one charge storage layer; and

forming an insulating fill material in the central part of the at least one opening to completely fill the at least one opening.

5. The method of claim 2 , wherein the blocking dielectric comprises Al 2 O 3 and the first barrier layer comprises Ta, Ti, TiN, TaN, TaCN, TaMnN, Ru, WN or MnN.

6. The method of claim 5 , wherein the first barrier layer is formed by atomic layer deposition.

7. The method of claim 2 , wherein forming a plurality of copper control gate electrodes comprises:

forming a copper seed layer by chemical vapor deposition on the clam shell shaped regions of the barrier layer;

forming a sacrificial film on the copper seed layer in the back side recesses;

recessing the first barrier layer and the copper seed layer in the back side recesses to remove the barrier layer and the copper seed layer from the back side opening;

removing the sacrificial layer; and

selectively electrochemically depositing copper on the copper seed layer to fill the remaining clam shaped regions of the blocking dielectric with copper.

8. The method of claim 7 , wherein the sacrificial film comprises polysilicon, silicon nitride or SiO 2 .

9. The method of claim 2 , wherein forming a plurality of copper control gate electrodes comprises:

forming a sacrificial film on the first barrier layer in the back side recesses, wherein the first barrier layer is a copper nucleation layer;

recessing the first barrier layer in the back side recesses;

removing the sacrificial layer; and

selectively electrochemically depositing copper on the first barrier layer using the first barrier layer as a copper nucleation layer.

10. The method of claim 2 , wherein forming a plurality of copper control gate electrodes comprises:

forming a sacrificial film on the first barrier layer in the back side opening and the back side recesses, wherein the first barrier layer is a copper nucleation layer;

anisotropically etching the sacrificial layer in the back side opening and recessing the sacrificial layer in the back side recesses to expose the first barrier layer in the back side opening and a portion of the first barrier layer in the back side recesses;

oxidizing the exposed first barrier layer in the back side opening and the back side recesses;

removing the sacrificial layer to expose the remaining first barrier layer in the back side recesses; and

selectively electrochemically depositing copper on the remaining first barrier layer using the first barrier layer as a copper nucleation layer without depositing copper on the oxidized portions of the first blocking layer.

11. The method of claim 2 , wherein forming a plurality of copper control gate electrodes comprises:

non-selectively depositing copper in the back side opening and the back side recesses;

removing copper from the back side opening; and

removing the first barrier layer from the back side opening.

12. The method of claim 11 , wherein removing the first barrier layer is performed by selective isotropic wet etching, anisotropic reaction ion etching or a combination thereof.

13. The method of claim 11 , further comprising forming a second tungsten barrier layer by atomic layer deposition over the first barrier layer prior to non-selectively depositing copper, wherein the first barrier layer comprises TiN.

14. The method of claim 2 , wherein forming a plurality of copper control gate electrodes comprises:

forming a second tungsten barrier layer by atomic layer deposition over the first barrier layer in the back side opening and the back side recesses, wherein the first barrier layer comprises TiN;

selectively removing the first and second barrier layers from the back side opening and recessing the first and second barrier layers in the back side recesses; and

(i) selectively electrolessly plating copper on the recessed second tungsten barrier layer or (ii) depositing a copper seed layer by CVD on the recessed second tungsten barrier layer followed by selective electrochemical deposition of copper.

15. The method of claim 2 , wherein forming the plurality of copper control gate electrodes comprises:

forming a plurality of first control gate layers in the respective clam shell shaped regions of the first barrier layer in the back side recesses, wherein the first barrier layers and the first control gate layers completely fill the back side recesses;

selectively recessing the first control gate layer and the first barrier layer in the back side recesses; and

forming a plurality of second control gate layers in the respective clam shell shaped regions of the blocking dielectric in the back side recesses.

16. The method of claim 2 , wherein forming the plurality of copper control gate electrodes comprises:

forming a plurality of first control gate layers in the respective clam shell shaped regions of the first barrier layer in the back side recesses, wherein the first barrier layers and the first control gate layers partially fill the back side recesses;

selectively recessing the first control gate layers and the first barrier layers in the back side recesses; and

forming a plurality of second control gate layers in the respective clam shell shaped regions of the blocking dielectric in the back side recesses.

17. The method of claim 2 , wherein:

the substrate comprises a silicon substrate;

the monolithic three dimensional NAND string is located in an array of monolithic three dimensional NAND strings over the silicon substrate;

at least one memory cell in a first device level of the three dimensional array of NAND strings is located over another memory cell in a second device level of the three dimensional array of NAND strings; and

the silicon substrate contains an integrated circuit comprising a driver circuit for the memory device located thereon.

18. A monolithic three dimensional NAND string, comprising:

a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate;

a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprise at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level;

a blocking dielectric located over the plurality of control gates;

a tunnel dielectric in contact with the semiconductor channel; and

at least one charge storage region located between the blocking dielectric and the tunnel dielectric;

wherein each control gate comprises copper.

19. The NAND string of claim 18 , further comprising a first barrier layer between the plurality of control gate electrodes and the blocking dielectric.

20. The NAND string of claim 19 , further comprising a cover layer located between the blocking dielectric and the at least one charge storage layer.

21. The NAND string of claim 19 , wherein further comprising an insulating fill material adjacent a surface of the channel.

22. The NAND string of claim 19 , wherein the blocking dielectric comprises Al 2 O 3 and the first barrier layer comprises Ta, Ti, TiN, TaN, TaCN, TaMnN, Ru, WN or MnN.

23. The NAND string of claim 19 , further comprising a second barrier layer located between the first barrier layer and the control gate electrodes, wherein the first barrier layer comprises TiN and the second barrier layer comprises tungsten.

24. The NAND string of claim 19 , wherein the first barrier layer comprises a copper nucleating layer.

25. The NAND string of claim 19 , wherein the first barrier layer comprises a conductive clam shaped first portion in contact with the control gate electrodes and a non-conductive metal oxide second portion adjacent insulating layers separating the control gates from each other.

26. The NAND string of claim 19 , wherein the control gate electrodes comprise a first portion having a first thickness perpendicular to a major surface of the substrate and a second portion having a second thickness perpendicular to the major surface of the substrate, wherein the second thickness is greater than the first thickness and the first portion is closer to the semiconductor channel than the second portion.

27. The NAND string of claim 25 , wherein the control gate electrodes do not have a seam.