Three-dimensional memory device and methods of making the same using replacement drain select gate electrodes
A method of forming a three-dimensional memory device includes forming an alternating stack of insulating layers and sacrificial material layers over a substrate, forming a patterned template structure around memory openings in a drain-select-level above the alternating stack, forming drain-select-level isolation structures in trenches in the patterned template structure, forming memory stack structures in the memory openings extending through the alternating stack, where each of the memory stack structures includes a memory film and a vertical semiconductor channel, replacing the sacrificial material layers with word lines, and separately replacing the patterned template structure with a drain select gate electrode.
1. A three-dimensional memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
drain-select-level electrically conductive strips located over the alternating stack, wherein each of the drain-select-level electrically conductive strips comprises a combination of at least one metallic material portion and a doped semiconductor spacer;
a drain-select-level isolation structure located between a neighboring pair of drain-select-level electrically conductive strips;
memory stack structures comprising a memory film and a vertical semiconductor channel vertically extending through the alternating stack and a respective one of the drain-select-level electrically conductive strips; and
drain regions located on top of a respective one of the memory stack structures;
wherein each doped semiconductor spacer contacts convex vertical surfaces of a respective subset of the memory stack structures.
2. A three-dimensional memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
drain-select-level electrically conductive strips located over the alternating stack, wherein each of the drain-select-level electrically conductive strips comprises a combination of at least one metallic material portion and a doped semiconductor spacer;
a drain-select-level isolation structure located between a neighboring pair of drain-select-level electrically conductive strips;
memory stack structures comprising a memory film and a vertical semiconductor channel vertically extending through the alternating stack and a respective one of the drain-select-level electrically conductive strips; and
drain regions located on top of a respective one of the memory stack structures;
wherein:
the drain-select-level isolation structure generally extends along a first horizontal direction; and
the drain-select-level isolation structure includes a pair of laterally alternating sequences of planar vertical sidewall segments and concave vertical sidewall segments that alternate along the first horizontal direction.
3. The three-dimensional memory device of claim 2 , wherein each of the concave vertical sidewall segments is laterally spaced from a respective most proximal one of the memory stack structures by a uniform lateral spacing.
4. A method of forming a three-dimensional memory device, comprising:
forming an alternating stack of insulating layers and spacer material layers over a substrate, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers;
forming a sacrificial matrix layer over the alternating stack;
forming sacrificial pillar structures through the sacrificial matrix layer and the alternating stack;
replacing at least the sacrificial matrix layer with a combination of a patterned template structure, doped semiconductor spacers contacting sidewalls of the patterned template structure, and an insulating cap layer;
replacing the sacrificial pillar structures with memory opening fill structures comprising a memory film and a vertical semiconductor channel;
forming drain-select-level cavities by removing an entirety of each of the patterned template structure selective to materials of the doped semiconductor spacers and the insulating cap layer; and
depositing at least one electrically conductive material within volumes of the drain-select-level cavities to form drain-select-level electrically conductive strips comprising a combination of a respective portion of the at least one deposited electrically conductive material and a respective pair of doped semiconductor spacers.
5. The method of claim 4 , wherein:
inner rows of the memory stack structures contact the patterned template structure and do not contact any of the doped semiconductor spacers; and
outer rows of the memory stack structures contact the patterned template structure and a respective one of the doped semiconductor spacers.
6. The method of claim 4 , further comprising removing horizontal portions of the insulating cap layer, wherein remaining portions of the insulating cap layer comprise a drain-select-level isolation structure contacting a pair of doped semiconductor spacers among the doped semiconductor spacers.
7. The method of claim 4 , wherein the patterned template structure is formed by:
forming recess regions surrounded by remaining portions of the sacrificial matrix layer by etching regions of the sacrificial matrix layer selective to the sacrificial pillar structures;
depositing a template material within the recess regions; and
planarizing the template material.
8. The method of claim 7 , wherein the doped semiconductor spacers are formed by:
removing the remaining portions of the sacrificial matrix layer after formation of the patterned template structure;
depositing a conformal doped semiconductor material liner over the patterned template structure and on physically exposed surfaces of the sacrificial pillar structures; and
anisotropically etching horizontal portions of the conformal doped semiconductor material liner, wherein remaining vertical portions of the conformal doped semiconductor material liner constitute the doped semiconductor spacers.
9. The method of claim 7 , wherein:
the template material portions comprise a dielectric material different from materials of the insulating layers and the insulating cap layer;
the sacrificial pillar structures comprise a sacrificial semiconductor material.
10. The material of claim 7 , wherein the sidewalls of the doped semiconductor spacers include convex vertical sidewall segments that are laterally spaced from a most proximal one of sidewalls of the sacrificial pillar structures by a same uniform lateral spacing.
11. The method of claim 7 , wherein the recess regions are formed by:
forming a photoresist layer including openings therein over the sacrificial matrix layer; and
anisotropically etching unmasked regions of the sacrificial matrix layer employing an etch chemistry that is selective to a material of the sacrificial pillar structures,
wherein:
a first subset of the sacrificial pillar structures protrudes within the recess regions; and
a second subset of the sacrificial pillar structures contacts the remaining portions of the sacrificial material layer and has sidewalls that are physically exposed to a respective one of the recess regions.
12. The method of claim 4 , wherein:
each memory opening fill structure comprises a memory stack structure and a drain region overlying the memory stack structure, and
the entirety of each of the patterned template structure is removed employing a wet etch process that removes the patterned template structure selective to materials of the drain regions and memory films within the memory stack structures.