3-dimensional NOR memory array architecture and methods for fabrication thereof
A method addresses low cost, low resistance metal interconnects and mechanical stability in a high aspect ratio structure. According to the various implementations disclosed herein, a replacement metal process, which defers the need for a metal etching step in the fabrication process until after all patterned photoresist is no longer present. Under this process, the conductive sublayers may be both thick and numerous. The present invention also provides for a strut structure which facilitates etching steps on high aspect ratio structures, which enhances mechanical stability in a high aspect ratio memory stack.
1. A memory structure, comprising:
a semiconductor substrate having a planar surface, the semiconductor substrate having circuitry formed therein and thereon;
a first dielectric layer;
a first plurality of conductors electrically connected to the circuitry extending along a first direction substantially parallel to the planar surface, the conductors being accessible through the dielectric layer by a plurality of conductive plugs formed in vias to contact the conductors, the conductive plugs formed rows each extending along a second direction substantially parallel to the planar surface and substantially perpendicular to the first direction; and
a first stack of active strips and a second stack of active strips formed over dielectric layer and separated by a predetermined distance along the first direction, wherein each stack of active strips comprises two or more active strips provided one on top of another on two or more isolated planes and being substantially aligned lengthwise with each other along the second direction, and wherein each active strip comprises a first semiconductor layer of a first conductivity type provided between a second semiconductor layer and a third semiconductor layer each of a second conductivity type;
a storage layer;
a strut system connecting the first and second stacks of active strip; and
a second plurality of conductors each extending lengthwise along a third direction that is substantially perpendicular to the planar surface, each conductor being within a group of the conductors that are provided between the first stack of active strips and the second stack of active strips and separated from each stack of active strips by the storage layer, thereby forming in each active strip at least one NOR string, each NOR string including a plurality of storage transistors that are formed out of the first, the second and the third semiconductor layers of the active strip and their adjacent the storage layer and the conductors within the group, wherein selected ones of the second plurality of conductors being connected by the conductive plugs to the first plurality of conductors.
2. The memory structure of claim 1 , further comprising a third plurality of conductors electrically connected to the circuitry extending along the first direction, the conductors of the third direction being provided above the memory structure and being connected to the conductors of the second plurality that are not electrically connected to the first plurality of conductors through the conductive plugs.
3. The memory structure of claim 1 , wherein struts including extensions that extend along the third direction through substantially the height of the stacks of active strips.
4. The memory structure of claim 1 , further comprising a metallic layer contacting one of the second and the third semiconductor layer.
5. The memory structure of claim 1 , wherein the metallic layer is provided in cavities or recesses that result from the removal of all or part of a sacrificial layer.
6. The memory structure of claim 4 , wherein the sacrificial layer comprises one or more of: silicon oxide, boron doped silicon oxide, phosphorus doped silicon oxide, boron phosphorus doped silicon oxide, silicon nitride, silicon carbide, silicon carbon nitride, silicon carbon oxygen hydrogen, germanium, and any combinations thereof.
7. The memory structure of claim 5 , wherein the sacrificial layer is porous.
8. The memory structure of claim 4 , wherein the metallic layer further includes two or more sublayers where a first sublayer is disposed adjacent to and in electrical contact with a second sublayer, and the first sublayer surrounds the second sublayer on three or more sides.
9. The memory structure of claim 8 , wherein the thickness of the second sublayer is at least 1.5× the thickness of the first sublayer.
10. The memory structure of claim 4 , wherein the metallic layer comprises one or more of: titanium, titanium nitride, tungsten nitride, tungsten, titanium tungsten, tantalum, tantalum nitride, cobalt, chrome, molybdenum, niobium, and any alloys thereof.
11. The memory structure of claim 4 , wherein the metallic layer is deposited by atomic layer deposition.
12. The method of claim 1 , wherein the storage layer in the memory structure comprises first and second types of storage material provided at different locations in the memory structure, the first and second types of storage material having different characteristics.
13. The method of claim 12 , wherein the first and second types of storage material comprise, respectively, first and second tunnel dielectric layers, the first tunnel dielectric layer being thicker than the second tunnel dielectric layer.
14. The memory structure of claim 12 , wherein the first tunnel dielectric layer has a thickness of 5 nm or more.
15. The memory structure of claim 12 , wherein the second tunnel dielectric layer has a thickness of 3 nm or less.
16. The memory structure of claim 12 , wherein the storage layer comprises an oxide-nitride-oxide material.
17. The memory structure of claim 1 , wherein the storage layer in the memory structure comprises first and second types of storage material provided at different locations in the memory structure, the first and second types of storage material having different characteristics.
18. The memory structure of claim 17 , wherein the first and second types of storage material comprise, respectively, first and second tunnel dielectric layers, the first tunnel dielectric layer being thicker than the second tunnel dielectric layer.
19. The memory structure of claim 17 , wherein the first tunnel dielectric layer has a thickness of 5 nm or more.
20. The memory structure of claim 17 , wherein the second tunnel dielectric layer has a thickness of 3 nm or less.
21. The memory structure of claim 17 , wherein the storage layer comprises an oxide-nitride-oxide material.