Three Dimensional Nonvolatile Memory Cell Structure with Upper Body Connection

• US 20150131381A1
• Filed: 11/04/2014
• Published: 05/14/2015
• Est. Priority Date: 11/08/2013
• Status: Active Grant

• Current Assignee: Mosaid Technologies Incorporated (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Original Assignee: MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management)
• Inventors: Rhie, Hyoung Seub
• Granted Patent: US 9,236,394 B2
• Time in Patent Office: Days
• US Class Current: 365/185.17
• CPC Class Codes: G11C 16/0408 comprising cells containing floating gate transistors G11C16/0483, G11C16/0491 take precedence
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/14 Circuits for erasing electrically, e.g. erase voltage switching circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: H01L 29/7926 Vertical transistors, i.e. transistors having source and drain not in the same horizontal plane
• CPC Class Codes: H10B 41/27 the channels comprising vertical portions, e.g. U-shaped channels
• CPC Class Codes: H10B 41/35 with a cell select transistor, e.g. NAND
• CPC Class Codes: H10B 43/27 the channels comprising vertical portions, e.g. U-shaped channels
• CPC Class Codes: H10B 43/35 with cell select transistors, e.g. NAND

Abstract

A three-dimensional integrated circuit non-volatile memory array includes a memory array of vertical channel NAND flash strings connected between a substrate source line and upper layer connection lines which each include n-type drain regions and p-type body line contact regions alternately disposed on each side of undoped or lightly doped string body regions so that each NAND flash string includes a vertical string body portion connected to a horizontal string body portion formed from the string body regions of the upper body connection lines.

Claims

1. A non-volatile memory device, comprising:

a substrate comprising a source line region of a first conductivity type formed at a surface of the substrate; and

a NAND flash memory array formed over the substrate comprising a plurality of NAND flash strings, each comprising a vertical channel string body connected between the source line region and an upper semiconductor layer which extends parallel to the surface of the substrate, where the upper semiconductor layer comprises;

a horizontal string body region connected to each vertical channel string body,

a drain region of the first conductivity type connected to each horizontal string body region, and

a body line contact region of a second, opposite conductivity type connected to each horizontal string body region.

2. The non-volatile memory device of claim 1, where the source line region comprises a heavily doped N+ source line region formed in the substrate.

3. The non-volatile memory device of claim 1, where each NAND flash string comprises a plurality of series-connected transistors formed along a corresponding vertical channel string body between the source line region and the upper semiconductor layer, comprising an upper select gate transistor, a lower select gate transistor, and a plurality of memory cell transistors formed between the upper and lower select gate transistors.

4. The non-volatile memory device of claim 3, where upper select gate transistor comprises a string select transistor formed adjacent to a corresponding horizontal string body region that is connected to the vertical channel string body, thereby defining horizontal and vertical string body portions for the NAND flash string.

5. The non-volatile memory device of claim 1, where the NAND flash memory array comprises a plurality of upper semiconductor layer strips running in a bit line direction which are electrically isolated from one another in a word line direction, each upper semiconductor layer strip electrically connecting a shared bit line through one or more drain regions in said upper semiconductor layer strip to NAND flash strings from different word lines.

6. The non-volatile memory device of claim 5, where the plurality of upper semiconductor layer strips electrically connect a shared body line through body line contact regions in said upper semiconductor layer strips to NAND flash strings sharing one or more common word lines.

7. The non-volatile memory device of claim 1, where the upper semiconductor layer comprises alternating first and second connection strips running in the bit line direction and formed in a continuous semiconductor layer,

where each first connection strip is formed over a column of NAND flash strings and comprises a horizontal string body region connected to each underlying NAND flash string, and a drain region connected to each horizontal string body region for electrically connecting a bit line through said drain region and horizontal string body region to said underlying NAND flash string;

and

where each second connection strip is formed adjacent to a corresponding first connection strip and comprises a body line contact region connected to each horizontal string body region in the corresponding first connection strip for electrically connecting a body line through said body line contact region and each connected horizontal string body region to said underlying NAND flash string.

8. The non-volatile memory device of claim 7, where the upper semiconductor layer comprises a plurality of first connection strips formed over a corresponding plurality of NAND flash string columns running in a bit line direction, and a plurality of second connection strips formed between the plurality of first connection strips for electrically connecting one or more shared body line conductors through body line contact regions formed in each second connection strip to the plurality of NAND flash strings.

9. The non-volatile memory device of claim 1, where the drain region comprises an n+ doped region formed in the upper semiconductor layer to be laterally offset from the vertical channel string body, and where the body line contact region comprises a p+ doped region formed in the upper semiconductor layer to be laterally offset from the vertical channel string body.

10. The non-volatile memory device of claim 3, where the upper select gate transistor has a first channel portion that runs parallel to the surface of the substrate and a second channel portion that runs perpendicular to the surface of the substrate.

11. The non-volatile memory device of claim 10, where the upper select gate transistor comprises a gate electrode that is located between the first channel portion of the upper select gate transistor and the surface of the substrate.

12. A NAND Flash memory cell array formed on a substrate comprising a plurality of semiconductor string bodies running in a direction perpendicular to a surface of the substrate, where each semiconductor string body is connected between an n-type source region formed in the substrate and an upper semiconductor layer formed over the substrate, where each upper semiconductor layer comprises:

a horizontal string body region connected to and formed over an associated semiconductor string body,

an n-type conductivity region connected through each horizontal string body region to the associated semiconductor string body, and

a p-type conductivity region connected through each horizontal string body region to the associated semiconductor string body,

where the n-type conductivity region and p-type conductivity region are each laterally offset from the associated semiconductor string body.

13. The NAND Flash memory cell array of claim 12, further comprising an upper select gate formed at an upper end of each semiconductor string body, each of said upper select gates controlling a first channel portion formed in the horizontal string body region that runs parallel to the surface of the substrate and a second channel portion formed in the semiconductor string body that runs perpendicular to the surface of the substrate.

14. The NAND Flash memory cell array of claim 13, where the upper select gate is located between the first channel portion and the surface of the substrate.

15. The NAND Flash memory cell array of claim 13, wherein each upper select gate is positioned upon application of a first voltage to induce n-type conductivity in the first and second channel portions to electrically connect the first channel portion to an associated n-type conductivity region in the upper semiconductor layer.

16. The NAND Flash memory cell array of claim 13, wherein each upper select gate is positioned upon application of a second voltage to induce p-type conductivity in the first and second channel portions to electrically connect the first channel portion to an associated p-type conductivity region in the upper semiconductor layer.

17. The NAND Flash memory cell array of claim 12, where each n-type conductivity region is electrically connected to a first conductive line, and where each p-type conductivity connective region is electrically connected to a second conductive line.

18. The NAND Flash memory cell array of claim 17, wherein said first conductive line comprises a bit line for transferring data bits to or from one or more semiconductor string bodies, and wherein said second conductive line comprises a body line for transferring a positive voltage to one or more semiconductor string bodies.

19. A method for reading an addressed memory cell transistor from a plurality of NAND flash strings, each comprising a vertical channel string body in which a plurality of series-connected transistors are formed between a substrate source line region and an upper semiconductor layer, the plurality of series-connected transistors comprising an upper select gate transistor, a lower select gate transistor, and a plurality of memory cell transistors formed between the upper and lower select gate transistors, comprising:

applying a bit line read voltage to a bit line conductor which is connected through an n-type string drain region formed in the upper semiconductor layer to a selected flash string on which the addressed memory cell transistor is formed;

applying a body voltage to a body line conductor which is connected through a p-type string region formed in the upper semiconductor layer to the selected flash string on which the addressed memory cell transistor is formed; and

applying a read gate voltage to the addressed memory cell transistor while otherwise applying a positive gate voltage to the other series-connected transistors formed on the selected flash string, thereby reading a value from the addressed memory cell transistor that is transferred through the n-type string drain region formed in the upper semiconductor layer and to the bit line conductor under control of the upper select gate transistor for the selected flash string.

20. The method of claim 19, where applying the positive gate voltage to the other series-connected transistors comprises applying the positive gate voltage to an upper select gate formed at an upper end of the selected flash string to control a first channel portion of a horizontal string body region formed in the upper semiconductor layer and a second channel portion of a vertical string body formed in the selected flash string.

21. A method for erasing an erase block of NAND flash strings, each comprising a vertical channel string body in which a plurality of series-connected transistors are formed between a substrate source line region and an upper semiconductor layer, the plurality of series-connected transistors comprising an upper select gate transistor, a lower select gate transistor, and a plurality of memory cell transistors formed between the upper and lower select gate transistors, comprising:

applying a large positive erase voltage to a body line conductor which is connected through p-type string regions formed in the upper semiconductor layer to the erase block of NAND flash strings, thereby charging the vertical channel string bodies in the erase block of NAND flash strings;

applying a smaller erase gate voltage to the plurality of series-connected transistors formed on the erase block of NAND flash strings; and

floating the substrate source line and one or more bit line conductors which are connected through an n-type string drain regions formed in the upper semiconductor layer to the erase block of NAND flash strings.