Vertical NAND and method of making thereof using sequential stack etching and landing pad

1. A method of making a vertical NAND device, comprising:

forming a lower portion of a memory stack over a substrate;

forming a lower portion of memory openings in the lower portion of the memory stack;

widening a top part of the lower portion of the memory openings;

forming at least one additional portion of the memory stack over the lower portion of the memory stack;

forming at least one additional portion of the memory openings in the at least one additional portion of the memory stack;

forming a lower portion of the semiconductor channels in the lower portion of the memory openings;

forming semiconductor or electrically conductive landing pads in the widened top parts of the lower portion of the memory openings, wherein the landing pads have a larger width than a widest portion of the memory openings and are in contact with the lower semiconductor channel portions; and

forming at least one additional portion of the semiconductor channels in the at least one additional portion of the memory openings, such that the at least one additional portion of the semiconductor channels contacts the respective landing pads.

2. The method of claim 1 , wherein the at least one additional portion of the memory stack comprises an upper portion of the stack, and the at least one additional portion of the memory openings comprises an upper portion of the memory openings.

3. The method of claim 1 , wherein the memory stack contains more than two portions, the at least one additional portion of the memory stack comprises one or more middle portions and an upper portion of the stack, and the at least one additional portion of the memory openings comprises one or more middle portion and an upper portion of the memory openings.

4. The method of claim 1 , wherein the lower portion of the memory openings is formed by etching using a first hard mask, and the at least one additional portion of the memory openings is formed by etching using at least one second hard mask different from the first hard mask.

5. The method of claim 1 , wherein the lower and the at least one additional portions of the memory stack comprise alternating insulating and sacrificial layers, and wherein the sacrificial material layers are removed and replaced with a memory film and control gate electrodes.

6. The method of claim 1 , wherein the lower and the at least one additional portions of the memory stack comprise alternating insulating and control gate material layers.

7. The method of claim 1 , further comprising forming a memory film which comprises at least one charge storage region located between blocking and tunneling dielectric layers.

8. The method of claim 7 , wherein:

the lower portion of the channels are formed in the lower portion of the memory openings prior to forming the at least one additional portion of the memory stack;

the landing pads are formed after forming the lower portion of the channels prior to forming the at least one additional portion of the memory stack;

the at least one additional portion of the stack is formed over the landing pads;

the at least one additional portion of the memory openings are formed to expose the landing pads; and

the at least one additional portion of the channels are formed in contact with the landing pads.

9. The method of claim 1 , further comprising forming a current boosting layer electrically connected to the landing pads, wherein the landing pad is thicker than the current boosting layer.

10. The method of claim 1 , wherein:

the landing pad is located between an upper select gate electrode of an upper select transistor in the at least one additional portion of the memory stack and an upper most control gate electrode in the lower portion of the memory stack; and

a channel of the upper select transistor is formed by a non-damascene process.

11. A method of making a vertical NAND device, comprising:

forming a lower portion of the memory stack over a substrate;

forming a lower portion of memory openings in the lower portion of the memory stack;

forming at least one additional portion of the memory stack over the lower portion of the memory stack;

forming at least one additional portion of the memory openings in the at least one additional portion of the memory stack;

forming a lower portion of the semiconductor channels in the lower portion of the memory openings;

forming semiconductor or electrically conductive landing pads in contact with the lower semiconductor channel portions;

forming at least one additional portion of the semiconductor channels in the at least one additional portion of the memory openings, such that the at least one additional portion of the semiconductor channels contacts the respective landing pads;

filling lower parts of the lower portion of the memory openings with a sacrificial material;

widening remaining exposed top parts of the lower portion of the memory openings where the landing pads will be subsequently formed; and

filling the widened top parts of the lower portion of the memory openings with a sacrificial material.

12. The method of claim 11 , wherein:

the at least one additional portion of the stack is formed over the lower portion of the stack containing the lower portion of the memory openings filled with the sacrificial material; and

the at least one additional portion of the memory openings is formed by etching the additional portion of the memory stack to expose the sacrificial material in the top part of the lower portion of the memory openings.

13. The method of claim 12 , further comprising removing the sacrificial material from the entire memory openings and forming entire memory films in the memory openings.

14. The method of claim 13 , wherein the lower portion of the channels, the landing pads and the at least one additional portion of the channels are formed in the memory openings in the same growth step, such that entire channels and the landing pads built into the channels are formed in one step.

15. The method of claim 14 , wherein:

the semiconductor channel has a U-shaped side cross section;

two wing portions of the U-shaped semiconductor channel extend substantially perpendicular to a major surface of the substrate are connected by a connecting portion which extends substantially parallel to the major surface of the substrate; and

an insulating fill is located over the connecting portion and separating two wing portions of the U-shaped semiconductor channel.

16. The method of claim 15 , wherein the device further comprises:

a tunnel dielectric portion of the memory film located adjacent to the semiconductor channel;

a charge storage region portion of the memory film located adjacent to the tunnel dielectric;

a blocking dielectric portion of the memory film located adjacent to the charge storage region; and

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.

17. The method of claim 13 , wherein the device further comprises:

a tunnel dielectric located adjacent to the semiconductor channel;

a charge storage region located adjacent to the tunnel dielectric;

a blocking dielectric located adjacent to the charge storage region; and

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.

18. The method of claim 17 , wherein the lower portion of each of the memory openings is misaligned with respect to the respective at least one additional portion of each of the memory openings.

19. The method of claim 17 , wherein the device comprises at least a 3×3 array of NAND strings, the first control gate electrode and the second control gate electrode are continuous in the array, and the first control gate electrode and the second control gate electrode do not have an air gap or a dielectric filled trench in the array.

20. The method of claim 17 , wherein:

each semiconductor channel has a pillar shape; and

the entire pillar-shaped semiconductor channel extends substantially perpendicularly to the major surface of the substrate.

21. The method of claim 13 , further comprising forming a current boosting layer comprising a conductive or semiconducting material electrically connected to the landing pads.

22. The method of claim 13 , wherein the memory films comprise at least one charge storage region.