Three dimensional NAND device and method of charge trap layer separation and floating gate formation in the NAND device
A monolithic three dimensional NAND string includes a vertical semiconductor channel and a plurality of control gate electrodes in different device levels. The string also includes a blocking dielectric layer, a charge storage region and a tunnel dielectric. A first control gate electrode is separated from a second control gate electrode by an air gap located between the major surfaces of the first and second control gate electrodes and/or the charge storage region includes silicide nanoparticles embedded in a charge storage dielectric.
1. 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 having a strip shape with major surfaces 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, wherein the first control gate electrode is separated from the second control gate electrode by an air gap located substantially between the major surfaces of the first and second control gate electrodes;
a blocking dielectric layer located in contact with the plurality of control gate electrodes;
a plurality of spaced apart charge storage segments, wherein the plurality of spaced apart charge storage segments comprise at least a first spaced apart charge storage segment located in the first device level and a second spaced apart charge storage segment located in the second device level; and
a tunnel dielectric layer located between each one of the plurality of the spaced apart charge storage segments and the semiconductor channel.
2. The monolithic three dimensional NAND string of claim 1 , wherein the plurality of spaced apart charge storage segments comprise a plurality of vertically spaced apart floating gates or a plurality of vertically spaced apart dielectric charge storage segments.
3. The monolithic three dimensional NAND string of claim 1 , wherein:
the semiconductor channel has a pillar shape; and
the entire pillar-shaped semiconductor channel extends substantially perpendicularly to the major surface of the substrate.
4. The monolithic three dimensional NAND string of claim 3 , further comprising one of a source or drain electrode which contacts the pillar-shaped semiconductor channel from above, and another one of a source or drain electrode which contacts the pillar-shaped semiconductor channel from below.
5. The monolithic three dimensional NAND string of claim 1 , 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.
6. The monolithic three dimensional NAND string of claim 5 , further comprising one of a source or drain electrode which contacts the first wing portion of the semiconductor channel from above, another one of a source or drain electrode which contacts the second wing portion of the semiconductor channel from above, and a body contact electrode which contacts the connecting portion of the semiconductor channel from below.
7. The monolithic three dimensional NAND string of claim 1 , wherein:
at least a portion of the blocking dielectric layer has a clam shape which surrounds a respective control gate electrode; and
the plurality of spaced apart charge storage segments comprise silicon nitride segments or a composite segments comprising metal silicide nanoparticles embedded in a silicon nitride matrix.
8. The monolithic three dimensional NAND string of claim 1 , wherein the air gap is surrounded by an insulating layer which is located between the tunnel dielectric layer and the blocking dielectric layer.
9. A monolithic, three dimensional array of memory devices located over a silicon substrate, comprising an array of vertically oriented NAND strings in which at least one memory cell in a first device level of the array is located over another memory cell in a second device level, wherein at least one vertically oriented NAND string of the array of vertically oriented NAND strings comprises:
a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a silicon substrate;
a plurality of control gate electrodes having a strip shape with major surfaces extending substantially parallel to the major surface of the silicon 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 silicon substrate and below the first device level, wherein the first control gate electrode is separated from the second control gate electrode by an air gap located substantially between the major surfaces of the first and second control gate electrodes;
a blocking dielectric layer located in contact with the plurality of control gate electrodes;
a plurality of spaced apart charge storage segments, wherein the plurality of spaced apart charge storage segments comprise at least a first spaced apart charge storage segment located in the first device level and a second spaced apart charge storage segment located in the second device level;
a tunnel dielectric layer located between each one of the plurality of the spaced apart charge storage segments and the semiconductor channel; and
an integrated circuit comprising a driver circuit for the array of memory devices located on the silicon substrate.
10. The array of claim 9 , wherein the plurality of spaced apart charge storage segments of the at least one NAND string comprise a plurality of vertically spaced apart floating gates or a plurality of vertically spaced apart dielectric charge storage segments.
11. The array of claim 9 , wherein:
the semiconductor channel of the at least one NAND string has a pillar shape; and
the entire pillar-shaped semiconductor channel of the at least one NAND string extends substantially perpendicularly to the major surface of the substrate.
12. The array of claim 11 , further comprising one of a source or drain electrode which contacts the pillar-shaped semiconductor channel of the at least one NAND string from above, and another one of a source or drain electrode which contacts the pillar-shaped semiconductor channel of the at least one NAND string from below.
13. The array of claim 9 , wherein:
the semiconductor channel of the at least one NAND string 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.
14. The array of claim 13 , further comprising one of a source or drain electrode which contacts the first wing portion of the semiconductor channel of the at least one NAND string from above, another one of a source or drain electrode which contacts the second wing portion of the semiconductor channel of the at least one NAND string from above, and a body contact electrode which contacts the connecting portion of the semiconductor channel of the at least one NAND string from below.
15. The array of claim 9 , wherein:
at least a portion of the blocking dielectric layer of the at least one NAND string has a clam shape which surrounds a respective control gate electrode of the at least one NAND string; and
the plurality of spaced apart charge storage segments of the at least one NAND string comprise silicon nitride segments or a composite segments comprising metal silicide nanoparticles embedded in a silicon nitride matrix.
16. The array of claim 9 , wherein the air gap is surrounded by an insulating layer which is located between the tunnel dielectric layer and the blocking dielectric layer.