THREE-DIMENSIONAL MEMORY DEVICE CONTAINING MULTI-LEVEL BRIDGE SUPPORT STRUCTURES AND METHODS FOR FORMING THE SAME
A semiconductor structure includes alternating stacks of insulating layers and electrically conductive layers which are located over a substrate and are laterally spaced apart among one another by first backside trenches and second backside trenches that are interlaced along a horizontal direction, first backside trench fill structures located in the first backside trenches, and second backside trench fill structures located in the second backside trenches. Each of the first backside trench fill structures includes a respective set of first backside bridge support structures comprising a first material, and each of the second backside trench fill structures includes a respective set of second backside bridge support structures comprising a second material that is different from the first material.
1 . A semiconductor structure, comprising:
alternating stacks of insulating layers and electrically conductive layers located over a substrate, wherein each of the alternating stacks laterally extends along a first horizontal direction, wherein the alternating stacks are laterally spaced apart from each other along a second horizontal direction by backside trenches that laterally extend along the first horizontal direction, and wherein the backside trenches comprise first backside trenches and second backside trenches that are interlaced along the second horizontal direction perpendicular to the first horizontal direction;
first backside trench fill structures located in the first backside trenches, wherein each of the first backside trench fill structures comprises a respective set of first backside bridge support structures comprising a first material; and
second backside trench fill structures located in the second backside trenches, wherein each of the second backside trench fill structures comprises a respective set of second backside bridge support structures comprising a second material having a different material composition than the sets of first backside bridge support structures.
2 . The semiconductor structure of claim 1 , wherein the sets of second backside bridge support structures comprise a dielectric material.
3 . The semiconductor structure of claim 2 , wherein the sets of first backside bridge support structures comprise a doped semiconductor material.
4 . The semiconductor structure of claim 3 , wherein the doped semiconductor material comprise boron-doped silicon including boron atoms at an atomic concentration greater than 1×10 18 /cm 3 .
5 . The semiconductor structure of claim 2 , wherein:
the sets of first backside bridge support structures are located at a first vertical spacing from the substrate; and
the sets of second backside bridge support structures are located at a second vertical spacing from the substrate that is different from the first vertical spacing.
6 . The semiconductor structure of claim 5 , wherein the second backside trenches do not include any material portion having a same material composition as the sets of first backside bridge support structures.
7 . The semiconductor structure of claim 1 , wherein:
each of the alternating stacks comprises, from bottom to top, a respective set of first insulating layers and first electrically conductive layers, a respective intermediate insulating cap layer, a respective set of additional insulating layers and additional electrically conductive layers, and a topmost insulating cap layer; and
each of the first backside bridge support structures has a respective top surface located within a horizontal plane including top surfaces of the intermediate insulating cap layers.
8 . The semiconductor structure of claim 7 , wherein each of the first backside bridge support structures has a respective bottom surface located above another horizontal plane including bottom surfaces of the intermediate insulating cap layers.
9 . The semiconductor structure of claim 7 , wherein each of the second backside bridge support structures has a respective top surface located within a horizontal plane including top surfaces of the topmost insulating cap layers.
10 . The semiconductor structure of claim 9 , wherein each of the second backside bridge support structures has a respective bottom surface located above an additional horizontal plane including bottom surface of the topmost insulating cap layers.
11 . The semiconductor structure of claim 1 , wherein:
each of the first backside trenches has a respective pair of lengthwise sidewalls that laterally extend along the first horizontal direction and vertically extends from the substrate at least to a horizontal plane including topmost surfaces of the alternating stacks; and
each of the first backside bridge support structures has a respective lateral dimension along the second horizontal direction that is greater than a maximum lateral spacing between the respective pair of lengthwise sidewalls.
12 . The semiconductor structure of claim 1 , wherein:
each of the second backside trenches has a respective pair of lengthwise sidewalls that laterally extend along the first horizontal direction and vertically extends from the substrate at least to a horizontal plane including topmost surfaces of the alternating stacks; and
each of the second backside bridge support structures has a respective lateral dimension along the second horizontal direction that is greater than a maximum lateral spacing between the respective pair of lengthwise sidewalls.
13 . The semiconductor structure of claim 1 , wherein each of the first backside trench fill structures further comprises a respective insulating spacer and a respective backside contact via structure that is laterally surrounded by the respective insulating spacer.
14 . The semiconductor structure of claim 13 , wherein each of the first backside bridge support structures further comprises a first bottom surface segment and a pair of first sidewall segments contacting a respective U-shaped dielectric semiconductor oxide liner, and second bottom surface segments and second sidewall segments that contact surfaces of intermediate insulating cap layers each interposed between an upper portion and a lower portion of a respective one of the alternating stacks.
15 . The semiconductor structure of claim 13 , wherein each of the first backside bridge support structures comprises a first top surface segment contacting a bottom surface of a respective one of the backside contact via structures, and second top surface segments contacting bottom surfaces of a respective one of the insulating spacers.
16 . A method of forming a semiconductor structure, comprising:
forming at least one vertically alternating sequence of continuous insulating layers and continuous sacrificial material layers;
forming lower-level backside trenches through the at least one vertically alternating sequence, wherein remaining portions of the at least one vertically alternating sequence comprise lower alternating stacks of insulating layers and sacrificial material layers;
forming first sacrificial trench fill structures in the lower-level backside trenches;
forming first backside bridge support structures in a first subset of the first sacrificial trench fill structures without forming any backside bridge support structures in a second subset of the first sacrificial trench fill structures;
forming an additional alternating sequence of additional continuous insulating layers and additional continuous sacrificial material layers; and
forming upper-level backside trenches through the additional vertically alternating sequence, wherein remaining portions of the additional vertically alternating sequence comprise upper alternating stacks of additional insulating layers and additional sacrificial material layers, and wherein a first subset of the upper-level backside trenches overlies the first subset of the lower-level backside trenches, and a second subset of the upper-level backside trenches overlies the second subset of the lower-level backside trenches.
17 . The method of claim 16 , wherein the step of forming the first backside bridge support structures comprises:
forming first discrete recesses in a first subset of the first sacrificial trench fill structures without forming any recess in a second subset of the first sacrificial trench fill structures;
forming first backside bridge support structures in the first discrete recesses by depositing and planarizing a first material.
18 . The method of claim 16 , wherein:
the first sacrificial trench fill structures comprise a semiconductor material; and
the step of forming the first backside bridge support structures comprises implanting dopants into exposed upper portions of a first subset of the first sacrificial trench fill structures without implanting dopants into a second subset of the first sacrificial trench fill structures.
19 . The method of claim 16 , further comprising:
forming second sacrificial trench fill structures in the upper-level backside trenches, wherein a first subset of the second sacrificial trench fill structures is formed in the first subset of the upper-level backside trenches and a second subset of the second sacrificial trench fill structures is formed in the second subset of the upper-level backside trenches;
forming second backside bridge support structures in the subset of the second sacrificial trench fill structures;
removing the second sacrificial trench fill structures and the first sacrificial trench fill structures after formation of the second backside bridge structures;
forming a backside insulating spacer within a first fraction of each contiguous volume formed by removal of the second sacrificial trench fill structures and the first sacrificial trench fill structures; and
forming a backside contact via structure within a second fraction of each of the contiguous volumes.
20 . The method of claim 16 , wherein:
the first backside bridge support structures comprise boron doped semiconductor structures that are formed at a first vertical spacing from the substrate; and
the second backside bridge support structures comprise dielectric structures that are formed at a second vertical spacing from the substrate that is different from the first vertical spacing.