Three-dimensional memory device having stressed vertical semiconductor channels and method of making the same
Three-dimensional memory devices include structures that induce a vertical tensile stress in vertical semiconductor channels to enhance charge carrier mobility. Vertical tensile stress may be induced by a laterally compressive stress applied by stressor pillar structure. The stressor pillar structures can include a stressor material such as a dielectric metal oxide material, silicon nitride, thermal silicon oxide or a semiconductor material having a greater lattice constant than that of the channel. Vertical tensile stress may be induced by a compressive stress applied by electrically conductive layers that laterally surround the vertical semiconductor channel, or by a stress memorization technique that captures a compressive stress from sacrificial material layers. Vertical tensile stress can be generated by a source-level pinning layer that prevents vertical expansion of the vertical semiconductor channel. Vertical tensile stress can be induced by using a layer stack including polysilicon and a silicon-germanium alloy for the vertical semiconductor channel.
1. A three-dimensional memory device comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
a memory stack structure vertically extending through the alternating stack, wherein the memory stack structure comprises a memory film that contains a vertical stack of memory elements located at levels of the electrically conductive layers, and a vertical semiconductor channel that contacts the memory film;
a source contact layer underlying the alternating stack and laterally surrounding, and contacting a sidewall of, the vertical semiconductor channel; and
a dielectric fill material layer underlying the source contact layer and including a dielectric fill material having a Young's modulus that is less than 70% of a Young's modulus of a material of the source contact layer.
2. The three-dimensional memory device of claim 1 , wherein the vertical semiconductor channel is under a vertical tensile stress.
3. The three-dimensional memory device of claim 2 , wherein the electrically conductive layers comprise a compressive-stress-generating material that applies a lateral compressive stress to the vertical semiconductor channel.
4. The three-dimensional memory device of claim 1 , wherein the dielectric fill material layer comprises a material selected from undoped silicate glass, a doped silicate glass, or organosilicate glass.
5. The three-dimensional memory device of claim 4 , wherein the source contact layer comprises a doped semiconductor material having an atomic dopant concentration in a range from 5.0×10 19 /cm 3 to 2.0×10 21 /cm 3 .
6. The three-dimensional memory device of claim 5 , further comprising a lower source-level semiconductor layer comprising another doped semiconductor material, contacting a bottom surface of the source contact layer, and contacting a top surface of the dielectric fill material layer.
7. The three-dimensional memory device of claim 6 , wherein:
the memory film comprises a first layer stack including a charge storage layer and a tunneling dielectric layer; and
an annular layer stack laterally surrounds the vertical semiconductor channel, is laterally surrounded by the lower source-level semiconductor layer, and contacts the source contact layer and the dielectric fill material layer, wherein the annular layer stack comprises a material layer having a same composition and a same thickness as the charge storage layer and another material layer having a same composition and a same thickness as the tunneling dielectric layer.
8. The three-dimensional memory device of claim 1 , wherein:
the memory stack structure comprises a vertical NAND string;
the alternating stack comprises a terrace region in which each electrically conductive layer other than a 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
the electrically conductive layers comprise word lines for the vertical NAND string.