Method of making ultrahigh density vertical NAND memory device
Monolithic, three dimensional NAND strings include 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 having a strip shape extending substantially parallel to the major surface of the substrate, the blocking dielectric comprising a plurality of blocking dielectric segments, a plurality of discrete charge storage segments, and a tunnel dielectric located between each one of the plurality of the discrete charge storage segments and the semiconductor channel.
1. A method of making a monolithic three dimensional NAND string, comprising:
providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate, the stack comprising at least one opening containing a charge storage material over a sidewall of the at least one opening, a tunnel dielectric on the charge storage material in the at least one opening, and a semiconductor channel on the tunnel dielectric in the at least one opening;
selectively removing the second material layers without removing the first material layers from the stack; and
forming control gates between the first material layers.
2. The method of claim 1 , further comprising forming a blocking dielectric between the first material layers and a side wall of the charge storage material exposed between the first material layers.
3. The method of claim 2 , further comprising forming a cut area on a back side of stack.
4. The method of claim 3 , wherein:
the second material layers are selectively removed through the cut area;
the blocking dielectric is formed through the cut area such that the blocking dielectric contacts the sidewall of the charge storage material exposed between the first material layers; and
the control gates are formed through the cut area.
5. The method of claim 4 , wherein portions of the blocking dielectric between the first material layers have a clam shape, and wherein each of the control gates is located at least partially in an opening in a respective clam-shaped portion of the blocking dielectric.
6. The method of claim 1 , wherein the tunnel dielectric has a straight sidewall and a uniform thickness.
7. The method of claim 1 , wherein the charge storage material comprises a charge storage dielectric material.
8. The method of claim 1 , wherein the charge storage material comprises a floating gate material.
9. The method of claim 8 , wherein the floating gate material comprises polysilicon, metal, metal alloy or metal silicide.
10. The method of claim 1 , wherein the charge storage material comprises conductive nanoparticles.
11. The method of claim 1 , wherein one of the first material layers and the second material layers comprise an oxide and the other of the first material layers and the second material layers comprise a nitride.
12. The method of claim 1 , wherein the semiconductor channel in the at least one opening completely fills the at least one opening with a semiconductor channel material.
13. The method of claim 1 , wherein the semiconductor channel in the at least one opening forms a semiconductor channel material on the side wall of the at least one opening but not in a central part of the at least one opening such that the semiconductor channel material does not completely fill the at least one opening.
14. The method of claim 13 , further comprising forming an insulating fill material in the central part of the at least one opening to completely fill the at least one opening.
15. The method of claim 1 , furthering comprising forming an upper electrode over the semiconductor channel and forming a lower electrode below the semiconductor channel.
16. The method of claim 1 , wherein the control gates comprise conductive or semiconductor control gate material.
17. The method of claim 16 , wherein the control gates comprise tungsten, copper, aluminum, tantalum, titanium, cobalt, titanium nitride or alloys thereof.
18. The method of claim 17 , wherein the control gates comprise tungsten.
19. The method of claim 1 , wherein the step of providing the stack comprises:
etching the stack to form the at least one opening in the stack;
forming the charge storage material over a sidewall of the at least one opening;
forming the tunnel dielectric on the charge storage material in the at least one opening; and
forming the semiconductor channel on the tunnel dielectric in the at least one opening.
20. The method of claim 1 , wherein:
the semiconductor channel extends substantially perpendicular to a major surface of the substrate;
the NAND string comprises a plurality of device levels over the substrate;
the NAND string is vertically oriented, such that at least one memory cell is located over another memory cell in the NAND string; and
each of the plurality of device levels comprises a respective control gate, a respective blocking dielectric portion adjacent to the respective control gate, a respective charge storage material portion adjacent to respective blocking dielectric portion, a respective tunnel dielectric portion adjacent to the respective charge storage material portion, and a respective portion of the semiconductor channel.