Three-dimensional memory device containing a capped insulating source line core and method of making the same
In-process source-level material layers including a source-level sacrificial layer are formed over a substrate, and an alternating stack of insulating layers and spacer material layers and memory stack structures are formed over the in-process source-level layers. A backside trench is formed through the alternating stack, and a source cavity is formed by removing the source-level sacrificial layer employing an etchant provided through the backside trench. A source contact layer including a doped semiconductor material is formed on vertical semiconductor channels of the memory stack structures within the source cavity. The source contact layer includes an unfilled cavity, which is subsequently filled with a silicon nitride liner, a silicon oxide fill material and a semiconductor cap. A semiconductor oxide structure can be formed by filling voids in the silicon oxide fill material by oxidizing the semiconductor cap into a thermal semiconductor oxide material portion.
1. A three-dimensional memory device comprising:
source-level material layers located over a substrate and comprising a source contact layer including a doped semiconductor material;
an alternating stack of insulating layers and electrically conductive layers located over the source-level material layers; and
a memory stack structure extending through the alternating stack and comprising a memory film and a vertical semiconductor channel,
wherein:
a sidewall of the vertical semiconductor channel contacts a respective surface of the source contact layer;
the source contact layer includes at least one cavity that is filled at least partly with an insulating core;
the insulating core comprises a silicon nitride liner that contacts an inner surface of the source contact layer and a portion of a semiconductor oxide structure;
the source-level material layers comprise a lower source-level material layer including an additional doped semiconductor material, having a same type of doping as the source contact layer, and contacting a bottom surface of the source contact layer;
the semiconductor oxide structure comprises a silicon oxide structure; and
the semiconductor oxide structure contacts a horizontal surface of the lower source-level material layer and sidewalls of the source contact layer.
2. The three-dimensional memory device of claim 1 , further comprising a dielectric wall structure laterally extending along a first horizontal direction and vertically extending through each layer within the alternating stack and contacting the semiconductor oxide structure.
3. The three-dimensional memory device of claim 2 , wherein the semiconductor oxide structure comprises:
a horizontal semiconductor oxide portion underlying a bottom surface of the dielectric wall structure and consisting essentially of thermal semiconductor oxide; and
a pair of vertical semiconductor oxide portions vertically protruding upward from edges of the horizontal semiconductor oxide portion, contacting bottom portions of lengthwise sidewalls of the dielectric wall structure, and comprising a thermal semiconductor oxide material portion and a semiconductor oxide portion including at least 10 parts per million of hydrogen atoms and at least 3 parts per million of carbon atoms.
4. The three-dimensional memory device of claim 3 , wherein a laterally extending silicon oxide fill material portion of the semiconductor oxide structure laterally encircles a bottom portion of the memory stack structure.
5. The three-dimensional memory device of claim 3 , wherein:
the pair of vertical semiconductor oxide portions have a greater lateral thickness than the horizontal semiconductor oxide portion; and
the source-level material layers comprise an upper source-level material layer, wherein the pair of vertical semiconductor oxide portions has a lesser lateral thickness on a sidewall of the upper source-level material layer than on a sidewall of the source contact layer.
6. The three-dimensional memory device of claim 1 , wherein a portion of the cavity is filled with a polycrystalline semiconductor fill material portion that is embedded within the semiconductor oxide structure.
7. The three-dimensional memory device of claim 1 , wherein:
the vertical semiconductor channel extends below a horizontal plane including an interface between the source contact layer and the lower source-level material layer;
the vertical semiconductor channel contacts a dielectric material stack; and
the dielectric material stack is embedded within a combination of the vertical semiconductor channel, the lower source-level material layer, and the source contact layer, and comprises a same dielectric material stack as the memory film.
8. The three-dimensional memory device of claim 1 , wherein the silicon nitride liner comprises a cylindrical portion that encircles the memory stack structure and is laterally spaced from an outer cylindrical sidewall of the vertical semiconductor channel by a uniform lateral distance.
9. The three-dimensional memory device of claim 1 , wherein the semiconductor oxide structure directly contacts the source contact layer above a first horizontal plane including a top surface of the silicon nitride liner and below a second horizontal plane including a bottom surface of the silicon nitride liner, and is laterally spaced from the source contact layer by the silicon nitride liner between the first horizontal plane and the second horizontal plane.
10. The three-dimensional memory device of claim 1 , wherein the at least one cavity comprises a void that is free of a solid state material and is filled with vacuum or a gas phase material.