3D memory having crystalline silicon NAND string channel
Disclosed herein are 3D NAND memory devices having vertical NAND strings with a crystalline silicon channel and techniques for fabricating the same. The NAND string channel may be a single crystal of silicon or have a few large grains of polysilicon. The single crystal may have a (100) orientation with respect to a tunnel oxide of the 3D NAND string. When the channel region comprises grains of polysilicon, predominantly all of the silicon channel is part of a grain of polysilicon having the (100) orientation. The (100) orientation may be favorable for high carrier mobility. Techniques using metal induced crystallization (MIC) for forming the NAND strings having a crystalline silicon channel are also disclosed.
1. A three-dimensional (3D) non-volatile storage device, comprising:
a plurality of horizontal layers of material above a substrate; and
a plurality of vertically oriented NAND strings in the horizontal layers, each of the vertically oriented NAND strings comprising:
a tunnel oxide layer, wherein the tunnel oxide layer has a hollow cylindrical shape that extends vertically with respect to the plurality of horizontal layers of material, the hollow cylindrical shape having an inner surface; and
a channel region that comprises crystalline silicon, wherein the crystalline silicon has a hollow cylindrical shape, wherein the tunnel oxide layer completely surrounds the crystalline silicon, wherein the crystalline silicon has predominantly a (100) orientation with respect to the inner surface of the tunnel oxide layer.
2. The three-dimensional (3D) non-volatile storage device of claim 1 , wherein the channel region is single crystal of silicon having a (100) orientation with respect to the inner surface of the tunnel oxide layer.
3. The three-dimensional (3D) non-volatile storage device of claim 1 , wherein the channel region comprises grains of polysilicon with predominantly all of the channel region being part of grains of polysilicon having a (100) orientation with respect to the inner surface of the tunnel oxide layer.
4. The three-dimensional (3D) non-volatile storage device of claim 1 , wherein the channel region comprises large grains of polysilicon with most of the channel region being part of large grains having a (100) orientation with respect to the inner surface of the tunnel oxide layer, wherein a large grain extends at least 300 nanometers in a direction parallel to the vertically oriented NAND strings.
5. The three-dimensional (3D) non-volatile storage device of claim 1 , wherein the crystalline silicon of the channel region comprises a metal dopant.
6. The three-dimensional (3D) non-volatile storage device of claim 5 , wherein the metal dopant is aluminum.
7. A three-dimensional (3D) non-volatile storage device, comprising:
a plurality of conductive layers above a substrate;
a plurality of dielectric layers alternating with the plurality of conductive layers above the substrate; and
a plurality of NAND strings, each of the NAND strings comprising:
a tunnel oxide layer, wherein the tunnel oxide layer has a hollow cylindrical shape that extends vertically with respect to the plurality of conductive layers, the hollow cylindrical shape having an inner surface; and
a channel region that comprises crystalline silicon, wherein the crystalline silicon has a hollow cylindrical shape having an inner surface and an outer surface, wherein the outer surface is in direct physical contact with the inner surface of the tunnel oxide layer, wherein the tunnel oxide layer completely surrounds the crystalline silicon, wherein the crystalline silicon comprises one or more crystal lattice structures, wherein predominantly all of the one or more crystal lattice structures have a (100) plane that is oriented parallel to the outer surface of the crystalline silicon.
8. The three-dimensional (3D) non-volatile storage device of claim 7 , wherein predominantly all of the one or more crystal lattice structures have a (100) plane that is oriented parallel to the inner surface of the crystalline silicon.
9. The three-dimensional (3D) non-volatile storage device of claim 7 , wherein the channel region comprises grains of polysilicon with predominantly all of the channel region being part of grains of polysilicon having a (100) plane that is oriented parallel to the outer surface of the crystalline silicon.
10. The three-dimensional (3D) non-volatile storage device of claim 7 , wherein the channel region comprises large grains of polysilicon with most of the channel region being part of large grains having a (100) plane that is oriented parallel to the outer surface of the crystalline silicon, wherein a large grain extends at least 300 nanometers in a direction parallel to the NAND strings.
11. The three-dimensional (3D) non-volatile storage device of claim 7 , wherein the crystalline silicon of the channel region comprises a metal dopant.
12. The three-dimensional (3D) non-volatile storage device of claim 11 , wherein the metal dopant is aluminum.
13. The three-dimensional (3D) non-volatile storage device of claim 7 , further comprises a core filler dielectric inside of the crystalline silicon.
14. A method of forming a three-dimensional (3D) non-volatile storage device, comprising:
forming a plurality of horizontal layers of material above a substrate; and
forming a plurality of vertically oriented NAND strings in the horizontal layers, wherein forming each of the vertically oriented NAND strings comprises:
forming a tunnel oxide layer, wherein the tunnel oxide layer has a hollow cylindrical shape that extends vertically with respect to the plurality of horizontal layers of material, the hollow cylindrical shape having an inner surface; and
forming a channel region that comprises crystalline silicon, wherein the crystalline silicon has a hollow cylindrical shape, wherein the tunnel oxide layer completely surrounds the crystalline silicon, wherein the crystalline silicon has predominantly a (100) orientation with respect to the inner surface of the tunnel oxide layer.