NAND MEMORY CELL STRING HAVING A STACKED SELECT GATE STRUCTURE AND PROCESS FOR FOR FORMING SAME

• US 20170018555A1
• Filed: 09/27/2016
• Published: 01/19/2017
• Est. Priority Date: 06/22/2009
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Kwan, Ming Sang, Fang, Shenqing, Suh, Youseok, Van Buskirk, Michael A.
• Granted Patent: US 10,038,004 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 16/16 for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: H01L 23/528 Geometry or layout of the interconnection structure H01L27/0207 takes precedence; algorithms G06F30/00
• CPC Class Codes: H01L 29/04 characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes characterised by physical imperfections H01L29/30
• CPC Class Codes: H01L 29/16 including, apart from doping materials or other impurities, only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 29/513 the variation being perpendicular to the channel plane
• CPC Class Codes: H01L 29/518 the insulating material containing nitrogen, e.g. nitride, oxynitride, nitrogen-doped material
• 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
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

A memory string is disclosed including a plurality of core cells serially connected between a source select gate and a drain select gate along a channel. Each core cell includes a wordline separated from the channel by a stack of layers including a charge trapping layer. At least one of the source and drain select gates is a stacked select gate with a plurality of components, including a first component adjacent to the plurality of core cells and a second component separated from the core cells by the first component. The first component includes a wordline separated from the channel by a stack of layers including a charge trapping layer, and a distance between the wordline of the first component and the wordline of a first core cell in the plurality of core cells is substantially the same as distances between each wordline in the plurality of word core cells.

Claims

1. A memory string, comprising:

a plurality of core cells serially connected between a source select gate and a drain select gate along a channel, each core cell including an internal wordline separated from the channel by a stack of layers including a charge trapping layer;

wherein at least one of the source and drain select gates is a stacked select gate comprising a plurality of components, including a first component adjacent to the plurality of core cells and a second component separated from the plurality of core cells by the first component, and the first component comprises a first gate separated from the channel by a stack of layers including a charge trapping layer; and

wherein a distance between the first gate of the first component and the internal wordline of a first core cell in the plurality of core cells is substantially the same as distances between each internal wordline in the plurality of word core cells.

2. The memory string of claim 1 wherein the second component of the stacked select gate comprises a second gate separated from the channel by a single layer gate dielectric.

3. The memory string of claim 2 wherein the first gate of the first component and the second gate of the second component comprise a same size.

4. The memory string of claim 2 wherein the first gate of the first component and the second gate of the second component comprise a different size.

5. The memory string of claim 1 wherein the stacked select gate is a triple stacked select gate further comprising a third component separated from the plurality of core cells by the first component and the second component.

6. The memory string of claim 1 wherein the stack of layers in the first component has the same stoichiometric composition and thicknesses as the stack of layers in each core cell in the plurality of core cells.

7. The memory string of claim 6 wherein the stack of layers in the first component and in each core cell comprises an oxide-nitride-oxide (ONO) stack.

8. The memory string of claim 1 wherein the memory string is a NAND memory string wherein each of the plurality of core cells comprises an oxide-nitride-oxide (ONO) memory transistor separated from the ONO memory transistors in an adjacent core cell by source-drain junctions.

9. The memory string of claim 1 wherein the memory string comprises a vertical NAND memory string, wherein the channel comprises a polysilicon cylinder extending vertically from source in a substrate to a drain overlying the substrate, and wherein the internal wordlines of the plurality of core cells are formed by alternating conducting and dielectric layers overlying the substrate and through which the channel extends.

10. The memory string of claim 1 wherein the first gate of the first component is configured to be biased during an erase operation with an erase voltage to have a same bias environment as the internal wordlines of the plurality of core cells to provide erasure threshold voltage uniformity.

11. The memory string of claim 10 wherein the first gate and the internal wordlines are configured to be biased during with a same erase voltage during an erase operation.

12. A memory string, comprising:

a plurality of core cells serially connected between a source select gate and a drain select gate along a channel, each core cell including an internal wordline separated from the channel by a first stack of layers including a charge trapping layer comprising a nitride;

at least one of the source and drain select gates is a stacked select gate comprising a plurality of components, including a first component adjacent to the plurality of core cells and a second component separated from the plurality of core cells by the first component; and

wherein the first component comprises a first gate separated from the channel by a second stack of layers having the same stoichiometric composition and thicknesses as the first stack of layers, and the second component comprises a second gate separated from the channel by a gate dielectric not including a charge trapping layer.

13. The memory string of claim 12 wherein a distance between the first gate of the first component and the internal wordline of a first core cell in the plurality of core cells is substantially the same as distances between each internal wordline in the plurality of word core cells.

14. The memory string of claim 12 wherein the first gate of the first component and the second gate of the second component comprise a same size.

15. The memory string of claim 12 wherein the first gate of the first component and the second gate of the second component comprise a different size.

16. The memory string of claim 12 wherein the stacked select gate is a triple stacked select gate further comprising a third component separated from the plurality of core cells by the first component and the second component.

17. The memory string of claim 12 wherein the charge trapping layer is a bilayer charge trapping layer comprising a substantially trap-free, oxygen-rich first nitride layer overlying the channel, and a trap-dense, oxygen-lean second nitride layer overlying the first nitride layer.

18. A memory string, comprising:

a plurality of core cells serially connected between a source select gate and a drain select gate along a channel, each core cell including an internal wordline separated from the channel by a first oxide-nitride-oxide (ONO) stack including a charge trapping layer comprising a nitride;

at least one of the source and drain select gates is a stacked select gate comprising a plurality of components, including a first component adjacent to the plurality of core cells and a second component separated from the plurality of core cells by the first component;

wherein the first component comprises a first gate separated from the channel by a second ONO stack having the same stoichiometric composition and thicknesses as the first ONO stack, and the second component comprises a second gate separated from the channel by a gate dielectric not including a charge trapping layer; and

wherein the channel comprises a polysilicon cylinder extending vertically from source in a substrate to a drain overlying the substrate, and wherein the internal wordlines of the plurality of core cells are formed by alternating conducting and dielectric layers overlying the substrate and through which the channel extends.

19. The memory string of claim 18 wherein the first gate of the first component and the second gate of the second component comprise a same size.

20. The memory string of claim 18 wherein the first gate of the first component and the second gate of the second component comprise a different size.