Multi-tier three-dimensional memory device with dielectric support pillars and methods for making the same
A multi-tier three-dimensional memory array includes multiple alternating stacks of insulating layers and electrically conductive layers that are vertically stacked. Memory stack structures including memory films and semiconductor channels extend through the alternating stacks. The alternating stacks are formed as alternating stacks of insulating layers and sacrificial material layers, and are subsequently modified by replacing the sacrificial material layers with electrically conductive layers. Structural support during replacement of the sacrificial material layers with the electrically conductive layers is provided by the memory stack structures and dielectric support pillar structures. The dielectric support pillar structures may be formed only for a first-tier structure including a first-tier alternating stack of first insulating layers and first spacer material layers, or may vertically extend over multiple tiers. The dielectric support pillar structures may be formed before or after formation of stepped surfaces in the alternating stack.
1. A three-dimensional semiconductor device, comprising:
a first-tier alternating stack of first insulating layers and first electrically conductive layers located over a substrate;
a second-tier alternating stack of second insulating layers and second electrically conductive layers located over the first-tier alternating stack;
a memory array region including memory stack structures that vertically extend through each layer of the first-tier alternating stack and the second-tier alternating stack;
a staircase region including first stepped surfaces of the first-tier alternating stack and second stepped surfaces of the second-tier alternating stack; and
dielectric support pillar structures consisting essentially of at least one dielectric material and located within the staircase region, wherein one of the dielectric support pillar structures extends through all layers of the first-tier alternating stack and at least a bottommost layer of the second-tier alternating stack, and has a greater lateral extent at a level of a topmost layer of the first-tier alternating stack than at a level of the bottommost layer of the second-tier alternating stack and wherein bottom surfaces of the dielectric support pillar structures are located within a first horizontal plane, and bottom portions of the memory stack structures contact a source contact layer having a top surface that underlies the first horizontal plane.
2. The three-dimensional semiconductor device of claim 1 , wherein the one of the dielectric support pillar structures comprises:
a first straight sidewall that extends through all layers of the first-tier alternating stack and into a layer underlying the first-tier alternating stack;
an annular horizontal surface contacting a bottom surface of the bottommost layer of the second-tier alternating stack and overlying the first straight sidewall; and
a second straight sidewall that extends through at least the bottommost layer of the second-tier alternating stack.
3. The three-dimensional semiconductor device of claim 2 , wherein a retro-stepped dielectric material portion continuously extends from a surface of a bottommost insulating layer within the first-tier alternating stack to a surface of a topmost insulating layer within the second-tier alternating stack, has a homogeneous composition throughout, and has a top surface located at, or overlies, a topmost surface of the second-tier alternating stack.
4. The three-dimensional semiconductor device of claim 1 , wherein the dielectric support pillar structures have different heights that decrease with a lateral distance from the memory array region.
5. The three-dimensional semiconductor device of claim 1 , wherein the dielectric support pillar structures have top surfaces located within a same horizontal plane.
6. The three-dimensional semiconductor device of claim 1 , further comprising a retro-stepped dielectric material portion overlying the first stepped surfaces and the second stepped surfaces.
7. The three-dimensional semiconductor device of claim 6 , wherein each of the dielectric support pillar structures includes a top surface that contacts a surface of the retro-stepped dielectric material portion.
8. The three-dimensional semiconductor device of claim 7 , wherein another one of the dielectric support pillar structures extends through a subset of layers of the first-tier alternating stack, does not contact the second-tier alternating stack, and underlies and contacts the retro-stepped dielectric material portion.
9. The three-dimensional semiconductor device of claim 6 , further comprising:
first word line contact via structures extending through the retro-stepped dielectric material portion and contacting a respective one of the first electrically conductive layers; and
second word line contact via structures extending through the retro-stepped dielectric material portion and contacting a respective one of the second electrically conductive layers.
10. The three-dimensional semiconductor device of claim 6 , wherein each of the dielectric support pillar structures has a top surface within a same horizontal plane that includes a top surface of the retro-stepped dielectric material portion.
11. The three-dimensional semiconductor device of claim 1 , wherein each of the memory stack structures comprises a respective memory film and a respective vertical semiconductor channel.
12. The three-dimensional semiconductor device of claim 1 , further comprising an insulating cap layer located between the first-tier alternating stack and the second-tier alternating stack, wherein each of the memory stack structures and the one of the dielectric support pillar structures has a greater lateral extent at a level of the insulating cap layer than at a level of a topmost layer within the first-tier alternating stack, and than at a level of a bottommost layer within the second-tier alternating stack.
13. A three-dimensional semiconductor device, comprising:
a first-tier alternating stack of first insulating layers and first electrically conductive layers located over a semiconductor substrate;
a second-tier alternating stack of second insulating layers and second electrically conductive layers located over the first-tier alternating stack;
a memory array region including memory stack structures that vertically extend through each layer of the first-tier alternating stack and the second-tier alternating stack;
a staircase region including first stepped surfaces of the first-tier alternating stack and second stepped surfaces of the second-tier alternating stack;
support pillar structures located within the staircase region; and
a dielectric material contacting bottom portions of the support pillar structures and separating the support pillar structures from the semiconductor substrate, wherein the dielectric material is not continuous between bottom portions of adjacent support pillar structures located within the staircase region.