Self-aligned split-gate flash memory cell and its contactless flash memory arrays

• US 6,525,369 B1
• Filed: 05/13/2002
• Issued: 02/25/2003
• Est. Priority Date: 05/13/2002
• Status: Expired due to Fees

• Current Assignee: Ching-Yuan Wu
• Original Assignee: Ching-Yuan Wu
• Inventors: Wu, Ching-Yuan
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): TRAN, LONG K
• Application Number:
  US10/142,878
• Time in Patent Office: 288 Days
• Field of Search: 257/314-323, 257/332, 257/346, 257/387, 257/388, 438/201, 438/211, 438/257, 438/262-266, 438/270, 438/271, 438/299, 438/585, 438/587, 438/588, 438/592, 438/594
• US Class Current: 257/315
• CPC Class Codes: H01L 29/42324 Gate electrodes for transistors with a floating gate
• CPC Class Codes: H10B 41/30 characterised by the memory core region
• CPC Class Codes: H10B 69/00 Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices

Abstract

A self-aligned split-gate flash memory cell of the present invention comprises a single-side dish-shaped floating-gate structure being formed on a first gate-dielectric layer with a first intergate-dielectric layer being formed on its top portion and a second intergate-dielectric layer being formed on its inner sidewall and tip portion; a planarized control/select-gate conductive layer being at least formed over a second gate-dielectric layer and the first/second intergate-dielectric layers; and a common-source diffusion region and a common-drain diffusion region being implanted by aligning to the planarized control/select-gate conductive layer. The self-aligned split-gate flash memory cells are configured into two contactless array architectures: a contactless NOR-type flash memory array and a contactless parallel common-source/drain conductive bit-lines flash memory array.

Claims

1. A self-aligned split-gate flash memory cell having a single-side dish-shaped floating gate structure, comprising:

a semiconductor substrate of a first conductivity type having an active region isolated by two parallel shallow-trench-isolation (STI) regions, wherein each of said two parallel STI regions is filled with a first raised field-oxide layer;

a cell region being formed on said semiconductor substrate and divided into three regions;

a common-source region, a gate region, and a common-drain region, wherein said gate region is located between said common-source region and said common-drain region;

said common-source region comprises a first sidewall dielectric spacer being formed over a sidewall of said gate region and on a portion of a first flat bed being formed by a shallow heavily-doped source diffusion region formed within a common-source diffusion region of a second conductivity type in said active region and two etched first raised field-oxide layers in said two parallel STI regions;

said common-drain region comprises a second sidewall dielectric spacer being formed over another sidewall of said gate region and on a portion of a second flat bed being formed by a shallow heavily-doped drain diffusion region formed within a common-drain diffusion region of said second conductivity type in said active region and two etched second raised field-oxide layers in said two parallel STI regions; and

said gate region comprises a single-side dish-shaped floating-gate structure being formed on a first gate-dielectric layer;

a first intergate-dielectric layer being formed over said single-side dish-shaped floating-gate structure;

a second intergate-dielectric layer being formed over an inner sidewall of said single-side dish-shaped floating-gate structure and its tip portion; and

a planarized control/select-gate conductive layer having a portion formed at least on a second gate-dielectric layer, said second intergate-dielectric layer, said first intergate-dielectric layer, and a portion of nearby said first/second raised field-oxide layers.

2. The self-aligned split-gate flash memory cell according to claim 1, wherein an implanted region of said first conductivity type comprising a shallow implant region for threshold-voltage adjustment and a deep implant region for forming a punch-through stop is formed in said semiconductor substrate under said second gate-dielectric layer.

3. The self-aligned split-gate flash memory cell according to claim 1, wherein said single-side dish-shaped floating-gate structure is formed by an isotropic dry etching process and said first intergate-dielectric layer is a thermal poly-oxide or nitrided thermal poly-oxide layer.

4. The self-aligned split-gate flash memory cell according to claim 1, wherein said single-side dish-shaped floating-gate structure is formed by an isotropic wet etching and said first intergate-dielectric layer is a thermal poly-oxide or nitrided thermal poly-oxide layer.

5. The self-aligned split-gate flash memory cell according to claim 1, wherein the gate length of said single-side dish-shaped floating-gate structure is defined by a sidewall dielectric spacer being formed over a portion of said planarized control/select-gate conductive layer to define an outer gate edge and another sidewall dielectric spacer being at least formed over a tip portion of said single-side dish-shaped floating-gate structure to define an inner floating-gate edge.

6. A contactless NOR-type self-aligned split-gate flash memory array, comprising:

a semiconductor substrate of a first conductivity type having a plurality of active regions and a plurality of parallel shallow-trench-isolation (STI) regions formed alternately, wherein each of the plurality of parallel STI regions is filled with a first raised field-oxide layer;

a plurality of common-source regions and a plurality of virtual-gate regions being formed alternately and transversely to the plurality of parallel STI regions, wherein each of the plurality of virtual-gate regions includes a pair of self-aligned split-gate regions being located in each side portion and a common-drain region being located between the pair of self-aligned split-gate regions;

each of the plurality of common-source regions comprises a pair of first sidewall dielectric spacers being formed over each sidewall of nearby said virtual-gate regions and on a portion of a first flat bed being alternately formed by an etched first raised field-oxide layer in said parallel STI region and a shallow heavily-doped source diffusion region formed within a common-source diffusion region of a second conductivity type in said active region;

a common-source conductive bus line being formed over said first flat bed between the pair of first sidewall dielectric spacers; and

a first planarized thick-oxide layer being formed over said common-source conductive bus line;

said common-drain region comprises a pair of second sidewall dielectric spacers being formed over each sidewall of nearby self-aligned split-gate regions and on a portion of a second flat bed being alternately formed by an etched second raised field-oxide layer in said parallel STI region and a shallow heavily-doped drain diffusion region formed within a common-drain diffusion region of said second conductivity type in said active region;

a plurality of planarized common-drain conductive islands being at least formed over said shallow heavily-doped drain diffusion regions formed within said common-drain diffusion regions between the pair of second sidewall dielectric spacers;

each of the pair of self-aligned split-gate regions comprises a single-side dish-shaped floating-gate structure being alternately formed on a first gate-dielectric layer in said active region with a first intergate-dielectric layer being formed on its top and a second intergate-dielectric layer being formed over its inner sidewall and tip portion; and

an elongated planarized control/select-gate conductive layer acted as a word line being formed over a surface alternately formed by a second gate-dielectric layer and said first/second intergate-dielectric layers in said active region and said first/second raised field-oxide layers in said parallel STI region; and

a plurality of first interconnect-metal layer integrated with the plurality of planarized common-drain conductive islands being simultaneously patterned and etched to form a plurality of bit lines transversely to the plurality of common-source conductive bus lines by using a plurality of hard masking layers, wherein each of the plurality of hard masking layers comprises a masking dielectric layer being aligned above said active region and two sidewall dielectric spacers being formed over each sidewall of said masking dielectric layer.

7. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said common-source conductive bus line comprises preferably a doped polycrystalline-silicon layer being further implanted with a high dose of doping impurities to act as a dopant diffusion source for forming a shallow heavily-doped source diffusion region of said second conductivity type within said common-source diffusion region.

8. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said common-source conductive bus line is preferably a polycide structure having a tungsten-silicide (WSi₂) layer formed over a heavily-implanted polycrystalline-silicon layer or a tungsten (W) layer lined with a barrier-metal layer such as a titanium-nitride (TiN) or tantalum-nitride (TaN) layer.

9. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said planarized common-drain conductive island is preferably made of a composite conductive layer structure such as a heavily-doped polycrystalline-silicon plug being capped with a metal-silicide layer, a tungsten plug lined with a barrier-metal layer, or a tungsten plug formed within a heavily-doped thin polycrystalline-silicon layer.

10. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said single-side dish-shaped floating-gate structure is preferably formed by an isotropic dry etching process and said first intergate dielectric layer is a thermal poly-oxide or nitrided thermal poly-oxide layer.

11. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said single-side dish-shaped floating-gate structure is preferably formed by an isotropic wet etching and said first intergate dielectric layer is preferably a thermal poly-oxide or nitrided thermal poly-oxide layer.

12. A contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein each gate length of said single-side dish-shaped floating-gate structures is preferably defined by a sidewall dielectric spacer being formed over a portion of said elongated control/select-gate conductive layer to define an outer gate edge and another sidewall dielectric spacer being at least formed over a tip portion of said single-side dish-shaped floating-gate structure to define an inner floating-gate edge.

13. The contactless NOR-type self-aligned split-gate flash memory array according to claim 6, wherein said elongated planarized control/select-gate conductive layer is preferably made of doped polycrystalline-silicon and is preferably capped with a tungsten-silicide (WSi₂) layer.

14. A contactless parallel common-source/drain conductive bit-lines flash memory array, comprising:

a semiconductor substrate of a first conductivity type having a plurality of active regions and a plurality of parallel STI regions formed alternately, wherein each of the plurality of parallel STI regions is filled with a first raised field-oxide layer;

a plurality of common-source regions and a plurality of virtual-gate regions being formed alternately and transversely to the plurality of parallel STI regions, wherein each of the plurality of virtual-gate regions includes a pair of self-aligned split-gate regions being located in each side portion and a common-drain region being located between the pair of self-aligned split-gate regions;

each of the plurality of common-source regions comprises a pair of first sidewall dielectric spacers being formed over each sidewall of nearby said virtual-gate regions and on a portion of a first flat bed being alternately formed by an etched first raised field-oxide layer in said parallel STI region and a shallow heavily-doped source diffusion region formed within a common-source diffusion region of a second conductivity type in said active region;

a common-source conductive bus line being formed over said first flat bed between the pair of first sidewall dielectric spacers; and

a first planarized thick-oxide layer being formed over said common-source conductive bus line;

said common-drain region comprises a pair of second sidewall dielectric spacers being formed over each sidewall of nearby said self-aligned split-gate regions and on a portion of a second flat bed being alternately formed by an etched second raised field-oxide layer in said parallel STI region and a shallow heavily-doped drain diffusion region formed within a common-drain diffusion region of said second conductivity type in said active region;

a common-drain conductive bus line being formed over said second flat bed between the pair of second sidewall dielectric spacers; and

a second planarized thick-oxide layer being formed over said common-drain conductive bus line;

each of the pair of self-aligned split-gate regions comprises a single-side dish-shaped floating-gate structure being alternately formed on a first gate-dielectric layer in each of said active regions with a first intergate-dielectric layer being formed on its top and a second intergate-dielectric layer being formed over its inner sidewall and tip portion; and

a planarized control/select-gate conductive island being at least formed alternately over a second gate-dielectric layer and the first/second intergate-dielectric layers in said active region and a portion of said first/second raised field-oxide layers in said parallel STI region; and

a plurality of first interconnect-metal layers integrated with the plurality of planarized control/select-gate conductive islands being simultaneously patterned and etched to form a plurality of word lines transversely to the plurality of common-source/drain conductive bus lines by using a plurality of hard masking layers, wherein each of the plurality of hard masking layers comprises a masking dielectric layer being aligned above said active region and two sidewall dielectric spacers being formed over each sidewall of said masking dielectric layer.

15. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein said common-source/drain conductive bus line comprises preferably a doped polycrystalline-silicon layer being further implanted with a high dose of doping impurities to act as a dopant diffusion source for forming a shallow heavily-doped diffusion region of said second conductivity type within said common source/drain diffusion region.

16. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein said common-source/drain conductive bus line is preferably a polycide layer having a tungsten-silicide (WSi₂) layer formed over a heavily-implanted polycrystalline-silicon layer or a tungsten-layer lined with a barrier-metal layer such as a titanium-nitride (TiN) or tantalum-nitride (TaN) layer.

17. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein said single-side dish-shaped floating-gate structure is preferably formed by an isotropic dry-etching process and said first intergate-dielectric layer is a thermal poly-oxide or nitrided thermal poly-oxide layer.

18. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein said single-side dish-shaped floating-gate structure is preferably formed by an isotropic wet-etching process and said first intergate dielectric layer is preferably a thermal poly-oxide or nitrided thermal poly-oxide layer.

19. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein each gate length of said single-side dish-shaped floating-gate structures is preferably defined by a sidewall dielectric spacer being formed over a portion of said planarized control/select-gate conductive islands to define an outer gate edge and another sidewall dielectric spacer being at least formed over a tip portion of said single-side dish-shaped floating-gate structure to define an inner floating-gate edge.

20. The contactless parallel common-source/drain bit-lines flash memory array according to claim 14, wherein said planarized control/select-gate conductive island is preferably made of doped polycrystalline-silicon and is silicided with a refractory-metal silicide layer such as a titanium-silicide (TiSi₂) or cobalt-silicide (CoSi₂) layer.