Three-dimensional memory device with a dielectric isolation spacer and methods of forming the same
An alternating stack of insulating layers and sacrificial material layers is formed over a substrate. Memory stack structures extending through the alternating stack are formed. A backside trench is formed through the alternating stack. The sacrificial material layers are replaced with electrically conductive layers. An insulating spacer and the backside contact via structure are formed within the backside trench. A dielectric isolation trench is formed by removing a peripheral portion of an upper region of the backside contact via structure and an upper portion of the insulating spacer. A dielectric isolation spacer is formed in the dielectric isolation trench to prevent an electrical short between an upper portion of the backside contact via structure and the electrically conductive layers.
1. A three-dimensional memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
memory stack structures extending through the alternating stack, wherein each of the memory stack structures comprises a memory film and a vertical semiconductor channel;
a backside contact via structure having a pair of lengthwise sidewalls that laterally extend along a first horizontal direction and vertically extending through each layer within the alternating stack and contacting the substrate;
an insulating spacer laterally surrounding the backside contact via structure and vertically extending from the substrate to a height below a topmost electrically conductive layer within the alternating stack; and
a dielectric isolation spacer laterally surrounding an upper portion of the backside contact via structure, contacting a top surface of the insulating spacer, and contacting a sidewall of the topmost electrically conductive layer within the alternating stack.
2. The three-dimensional memory device of claim 1 , wherein:
the insulating spacer has a first lateral thickness; and
the dielectric isolation spacer has a second lateral thickness that is greater than the first lateral thickness.
3. The three-dimensional memory device of claim 1 , wherein the backside contact via structure comprises:
a metallic barrier liner comprising a metallic barrier material; and
a conductive fill material portion that is laterally surrounded by the metallic barrier liner and contacting an inner sidewall of the dielectric isolation spacer.
4. The three-dimensional memory device of claim 3 , wherein a topmost surface of the metallic barrier liner contacts a bottom surface of the dielectric isolation spacer.
5. The three-dimensional memory device of claim 1 , wherein an inner sidewall of the dielectric isolation spacer is laterally offset inward with respect to a top edge of an inner sidewall of the insulating spacer.
6. The three-dimensional memory device of claim 1 , wherein an outer sidewall of the dielectric isolation spacer is laterally offset outward with respect to a top edge of an outer sidewall of the insulating spacer.
7. The three-dimensional memory device of claim 1 , wherein a top surface of the backside contact via structure is within a same horizontal plane as a top surface of the dielectric isolation spacer.
8. The three-dimensional memory device of claim 1 , wherein the backside contact via structure comprises:
an upper sidewall in contact with an inner sidewall of the dielectric isolation spacer;
a lower sidewall in contact within an inner sidewall of the insulating spacer; and
a non-vertical surface connecting the upper sidewall and the lower sidewall and contacting a bottom surface of the dielectric isolation spacer.
9. The three-dimensional memory device of claim 1 , further comprising a dielectric isolation structure that laterally extends along the first horizontal direction, vertically extends through at least the topmost electrically conductive layer within the alternating stack, and is laterally spaced from the dielectric isolation spacer.
10. The three-dimensional memory device of claim 9 , wherein the dielectric isolation structure and the dielectric isolation spacer comprise a same dielectric material, and contact a respective sidewall of the topmost electrically conductive layer within the alternating stack.
11. The three-dimensional memory device of claim 9 , wherein:
the dielectric isolation structure is located between two adjacent rows of the memory stack structures; and
the dielectric isolation spacer is located between one row of the memory stack structures and the adjacent backside contact via structure.
12. The three-dimensional memory device of claim 9 , further comprising a contact-level dielectric layer that overlies the alternating stack, wherein a top surface of the dielectric isolation spacer and a top surface of the dielectric isolation structure are located within a horizontal plane including a top surface of the contact-level dielectric layer.
13. The three-dimensional memory device of claim 1 , wherein:
the substrate comprises a semiconductor material layer embedding a source region that contacts a bottom surface of the backside contact via structure and a bottom surface of the insulating spacer;
the alternating stack comprises a terrace region in which each electrically conductive layer other than the topmost electrically conductive layer within the alternating stack laterally extends farther than any overlying electrically conductive layer within the alternating stack;
the terrace region includes stepped surfaces of the alternating stack that continuously extend from a bottommost layer within the alternating stack to a topmost layer within the alternating stack; and
support pillar structures extend through the stepped surfaces and through a retro-stepped dielectric material portion that overlies the stepped surfaces.
14. A method of forming a three-dimensional memory device, comprising:
forming an alternating stack of insulating layers and sacrificial material layers over a substrate;
forming memory stack structures extending through the alternating stack, wherein each of the memory stack structures comprises a memory film and a vertical semiconductor channel;
forming a backside trench having a pair of lengthwise sidewalls that laterally extend along a first horizontal direction through the alternating stack;
replacing the sacrificial material layers with electrically conductive layers by sequentially providing an isotropic etchant for etching the sacrificial material layers and a precursor for deposition of a conductive material into the backside trench;
forming an insulating spacer and a backside contact via structure within the backside trench;
forming a dielectric isolation trench by removing a peripheral portion of an upper region of the backside contact via structure and an upper portion of the insulating spacer; and
forming a dielectric isolation spacer in the dielectric isolation trench.
15. The method of claim 14 , wherein the dielectric isolation trench is formed by:
forming a patterned photoresist layer over the alternating stack, the insulating spacer, and the backside contact via structure, wherein the patterned photoresist layer includes a moat-shaped opening that overlies a periphery of a top surface of the backside contact via structure and without exposing a center portion of the top surface of the backside contact via structure; and
performing an anisotropic etch process that anisotropically etches unmasked portions of the backside contact via structure that are not masked by the photoresist layer.
16. The method of claim 15 , wherein the anisotropic etch process etches through at least a topmost electrically conductive layer of the electrically conducive layers underneath the moat-shaped opening.
17. The method of claim 15 , wherein:
the patterned photoresist layer includes a memory-region isolation opening that overlies a region located between two rows of memory stack structures that are arranged along the first horizontal direction; and
the anisotropic etch process forms a memory-region isolation trench underneath the memory-region isolation opening through the at least a topmost electrically conductive layer of the electrically conducive layers.
18. The method of claim 14 , further comprising forming a contact-level dielectric layer over the alternating stack after formation of the memory stack structures, wherein the backside trench is formed through the contact-level dielectric layer.
19. The method of claim 18 , further comprising
forming a source region by implanting electrical dopants into a portion of the substrate that underlies the backside trench;
conformally depositing an insulating material layer on the source region and over sidewalls of the backside trench; and
anisotropically etching the insulating material layer, wherein a remaining tubular portion of the insulating material layer constitutes the insulating spacer.