Three dimensional NAND device with silicide containing floating gates
A monolithic three dimensional NAND string includes a semiconductor channel located over a substrate, a plurality of control gates extending substantially parallel to the major surface of the substrate including a first control gate located in a first device level and a second control gate located in a second device level located over the substrate and below the first device level, a charge storage material including a silicide layer located in the first device level and in the second device level, a blocking dielectric located between the charge storage material and the plurality of control gates, and a tunnel dielectric located between the charge storage material and the semiconductor channel. The tunnel dielectric has a straight sidewall, portions of the blocking dielectric have a clam shape, and each of the plurality of control gates is located at least partially in an opening in the clam-shaped portion of the blocking dielectric.
1. A monolithic three dimensional NAND string, comprising:
a semiconductor channel located over a substrate, at least one end of the semiconductor channel extending substantially perpendicular to a major surface of the substrate;
a plurality of control gates extending substantially parallel to the major surface of the substrate, wherein the plurality of control gates comprise at least a first control gate located in a first device level and a second control gate located in a second device level located over the substrate and below the first device level;
a charge storage material comprising a silicide layer located in the first device level and in the second device level;
a blocking dielectric located between the charge storage material and the plurality of control gates; and
a tunnel dielectric located between the charge storage material and the semiconductor channel;
wherein:
the tunnel dielectric has a straight sidewall;
portions of the blocking dielectric have a clam shape; and
each of the plurality of control gates is located at least partially in an opening in the clam-shaped portion of the blocking dielectric.
2. The NAND string of claim 1 , further comprising one of a source or drain electrode which contacts the semiconductor channel from above, and another one of a source or drain electrode which contacts the semiconductor channel from below.
3. The NAND string of claim 1 , wherein the charge storage material comprises a floating gate material and wherein the NAND string is configured to store at least four bits per cell.
4. The NAND string of claim 3 , wherein the floating gate material further comprises a first layer of polysilicon.
5. The NAND string of claim 4 , wherein the floating gate comprises the silicide layer between the first layer of polysilicon and a second layer of polysilicon.
6. The NAND string of claim 5 , wherein:
the NAND string comprises a plurality of discrete, vertically separated floating gates; and
each of the plurality of discrete, vertically separated floating gates comprising a discrete portion of the first polysilicon layer, a discrete portion of the second polysilicon layer and a discrete portion of the silicide layer located between the discrete portions of the first and the second polysilicon layers.
7. The NAND string of claim 6 , wherein each of the plurality of discrete, vertically separated floating gates is located in a recess between insulating layers, and the straight sidewall of the tunnel dielectric layer contacts the discrete portion of the first polysilicon layer in each floating gate.
8. The NAND string of claim 1 , wherein the plurality of control gates comprise conductive or semiconductor control gate material.
9. The NAND string of claim 8 , wherein the plurality of control gates comprise tungsten, copper, aluminum, tantalum, titanium, cobalt, titanium nitride or alloys thereof, and wherein the silicide layer comprises nickel, titanium, cobalt or tungsten silicide.
10. The NAND string of claim 9 , wherein the plurality of control gates comprise tungsten.
11. A monolithic three dimensional NAND string, comprising:
a semiconductor channel located over a substrate, at least one end of the semiconductor channel extending substantially perpendicular to a major surface of the substrate;
a plurality of control gates extending substantially parallel to the major surface of the substrate, wherein the plurality of control gates comprise at least a first control gate located in a first device level and a second control gate located in a second device level located over the substrate and below the first device level;
a charge storage material comprising a silicide layer located in the first device level and in the second device level;
a blocking dielectric located between the charge storage material and the plurality of control gates; and
a tunnel dielectric located between the charge storage material and the semiconductor channel;
wherein:
the tunnel dielectric has a straight sidewall;
portions of the blocking dielectric have a clam shape; and
each of the plurality of control gates is located at least partially in an opening in the clam-shaped portion of the blocking dielectric;
the substrate comprises silicon;
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 the first device level of the three dimensional array of NAND strings is located over another memory cell in the 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.