Structure and Method of Manufacturing a Stacked Memory Array for Junction-Free Cell Transistors
A three-dimensional NAND memory device and an associated method for manufacturing this device are provided. The three-dimensional NAND memory device includes a source contact electrically isolated from a conductive gate material. The source contact also electrically connects a conductive source line to a first silicon strip and a second silicon strip through the conductive gate material.
1 . A memory device comprising:
a substrate silicon;
a first stack of strings comprising:
a first dielectric layer deposited on the substrate silicon;
a first silicon strip deposited on the first dielectric layer;
a second dielectric layer deposited on the first silicon strip;
a second silicon strip deposited on the second dielectric layer; and
a third dielectric layer deposited on the second silicon strip;
a second stack of strings comprising:
a fourth dielectric layer deposited on the substrate silicon;
a third silicon strip deposited on the fourth dielectric layer;
a fifth dielectric layer deposited on the third silicon strip;
a fourth silicon strip deposited on the fifth dielectric layer; and
a sixth dielectric layer deposited on the fourth silicon strip;
an isolating cover coating the first stack of strings and the second stack of strings;
a conductive gate material covering the isolating cover;
a conductive source line; and
a source contact electrically isolated from the conductive gate material, and the source contact also electrically connecting the conductive source line to the first silicon strip and the second silicon strip through the conductive gate material.
2 . The memory device of claim 1 , wherein a first part of the source contact is electrically isolated from the conductive gate material by the isolating cover and a second part of the source contact is electrically isolated from the conductive gate material by a sidewall nonconductive layer.
3 . The memory device of claim 1 , wherein the first dielectric layer comprises a first type of material, and wherein the third dielectric layer comprises a second type of dielectric material.
4 . The memory device of claim 1 , wherein the isolating cover is a multi-layered gate dielectric and comprises a tunnel dielectric, a charge storage layer, and a coupling dielectric.
5 . The memory device of claim 1 , further comprising:
a ground select line at one end of the first stack of strings; and
a first string select line island at the other end of the first stack of strings.
6 . The memory device of claim 5 , further comprising:
a second string select line island, different than the first string select line island, and
wherein the ground select line is also at one end of the second stack of strings, and the second string select line island is at the other end of the second stack of strings.
7 . A method comprising:
manufacturing a through hole in a stack of alternating layers of semiconductor layers and dielectric layers, the stack of alternating layers of semiconductor and dielectric layers fabricated on a substrate silicon, the through hole extending from a topmost layer to a lowest semiconductor layer of the alternating layers;
filling the through hole with a contact material;
removing portions of the stack of alternating layers of semiconductor and dielectric layers, forming a first stack of strings, and a second stack of strings, the first stack of strings comprising the contact material;
depositing an isolating layer on exposed portions of the first stack of strings, the second stack of strings, and the substrate silicon;
depositing a gate material on the isolating layer;
depositing an interlayer dielectric on the gate material;
etching a contact hole through the interlayer dielectric, the gate material and the isolating layer to an upper portion of the contact material;
depositing a side wall spacer comprising nonconductive material on sidewalls and bottom of the contact hole;
etching the side wall spacer on the bottom of the contact hole, exposing the upper portion of the contact material; and
filling the contact hole with a conductive material.
8 . The method of claim 7 , wherein the topmost layer comprises a type of dielectric material.
9 . The method of claim 7 , wherein the isolating layer is a gate dielectric layer and comprises a tunnel dielectric, a charge storage layer, and a coupling dielectric.
10 . The method of claim 7 , wherein the contact material comprises a n-doped polycrystalline silicon, and the conductive material comprises n-doped polycrystalline silicon.
11 . The method of claim 7 , wherein the contact material comprises a n-doped polycrystalline silicon, and the conductive material comprises a metal plug.
12 . The method of claim 7 , wherein the manufacturing of the through hole occurs prior to the removing the portions of the stack of alternating layers.
13 . The method of claim 7 , wherein the manufacturing of the through hole occurs after the removing the portions of the stack of alternating layers.
14 . A three-dimensional NAND memory array comprising:
a chip substrate; and
a source contact that at least partially overlaps, relative to a direction perpendicular to the chip substrate, with a gate layer in the three-dimensional NAND memory array to which a gate of a ground select transistor is connected, and
wherein a stack of strings in the three-dimensional NAND memory array is stacked upwards from the chip substrate.
15 . The memory array of claim 14 , wherein the source contact entirely overlaps, relative to the direction perpendicular to the chip substrate, with the gate layer.
16 . The memory array of claim 14 , wherein the source contact only partially overlaps, relative to a direction perpendicular to the chip substrate, the gate layer.
17 . The memory array of claim 14 , wherein the source contact passes through the gate layer but is electrically isolated from the gate layer by a dielectric layer surrounding the source contact.
18 . The memory array of claim 14 , wherein the source contact electrically contacts at least one string of the memory array.
19 . The memory array of claim 18 , wherein the source contact is electrically screened from a neighboring string of the at least one string by the gate material of the gate layer.
20 . The memory array of claim 14 , wherein a plurality of strings in the memory array are arranged in an even/odd layout, source contacts of even strings are formed as individual contacts located between adjacent even strings, and source contacts of odd strings are formed as individual contacts located between adjacent odd strings.
21 . The memory array of claim 14 , wherein the source contact comprises a lower portion and an upper portion, the lower portion being disposed between the lowest and highest portions of the stack of strings and electrically isolated from a gate material by a gate dielectric layer, and the upper portion being disposed between the lower portion and a source line and electrically isolated from the gate material by a sidewall dielectric.