MEMORY DEVICE INCLUDING A GERMANIUM-CONTAINING SOURCE STRUCTURE AND METHODS FOR FORMING THE SAME
A memory device includes a semiconductor source line layer containing silicon and electrical dopants, an alternating stack of insulating layers and electrically conductive layers located over the semiconductor source line layer, a memory opening vertically extending through the alternating stack, and a memory opening fill structure located in the memory opening. The memory opening fill structure includes a memory film, a vertical semiconductor channel including silicon that is laterally surrounded by the memory film, and a silicon-germanium structure contacting an end portion of the vertical semiconductor channel and contacting the semiconductor source line.
1 . A memory device, comprising:
a semiconductor source line layer comprising silicon and electrical dopants;
an alternating stack of insulating layers and electrically conductive layers located over the semiconductor source line;
a memory opening vertically extending through the alternating stack; and
a memory opening fill structure located in the memory opening and comprising a memory film, a vertical semiconductor channel comprising silicon that is laterally surrounded by the memory film, and a silicon-germanium structure contacting an end portion of the vertical semiconductor channel and contacting the semiconductor source line.
2 . The memory device of claim 1 , wherein the memory opening fill structure further comprises a dielectric core that is laterally surrounded by the vertical semiconductor channel and the silicon-germanium structure.
3 . The memory device of claim 2 , wherein the silicon-germanium structure comprises a cylindrical silicon-germanium portion that laterally surrounds the dielectric core.
4 . The memory device of claim 3 , wherein the silicon-germanium structure further comprises a planar portion contacting an end surface of the dielectric core.
5 . The memory device of claim 1 , wherein the silicon-germanium structure is in direct contact with a sidewall of a bottommost insulating layer within the alternating stack, and does not directly contact any other insulating layer within the alternating stack except the bottommost insulating layer.
6 . The memory device of claim 1 , wherein the silicon-germanium structure is not in direct contact with any of the insulating layers in the alternating stack.
7 . The memory device of claim 1 , wherein the silicon-germanium structure comprises a cylindrical outer sidewall that is in direct contact with the memory film.
8 . The memory device of claim 1 , wherein:
the vertical semiconductor channel comprises a doped polysilicon layer of a first conductivity type;
the semiconductor source line layer comprises a doped polysilicon layer of a second conductivity type opposite to the first conductivity type; and
the silicon-germanium structure comprises a doped silicon-germanium compound semiconductor material of the second conductivity type.
9 . The memory device of claim 1 , wherein the memory opening fill structure comprises a dielectric tube comprising a dielectric metal oxide material in contact with a cylindrical outer sidewall of the silicon-germanium structure.
10 . The memory device of claim 9 , wherein the dielectric tube comprises a first annular surface in contact with an annular end surface of the memory film and a second annular surface in contact with the semiconductor source line layer.
11 . The memory device of claim 9 , wherein the dielectric tube comprises a first annular surface in contact with an annular end surface of the memory film and a second annular surface in contact with an annular surface of the silicon-germanium structure.
12 . The memory device of claim 1 , wherein the semiconductor source line layer contacts a bottom surface of a bottommost insulating layer of the insulating layers of the alternating stack, and contacts a cylindrical surface segment of an opening in the bottommost insulating layer.
13 . The memory device of claim 1 , wherein the semiconductor source line layer comprises a surface portion that is free of germanium.
14 . The memory device of claim 1 , wherein the silicon-germanium structure has a vertical compositional gradient such that an atomic concentration of germanium in the silicon-germanium structure increases with a vertical distance from the vertical semiconductor channel.
15 . The memory device of claim 1 , wherein the vertical semiconductor channel is free of germanium.
16 . A method of forming a memory device, comprising:
forming an alternating stack of insulating layers and spacer material layers over a carrier substrate, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers;
forming a memory opening through the alternating stack;
forming a memory opening fill structure in the memory opening, wherein the memory opening fill structure comprises a memory film and a vertical semiconductor channel;
removing the carrier substrate;
removing an end portion of the memory film to physically expose an end portion of the vertical semiconductor channel;
forming a tubular cavity by vertically recessing the end portion of the vertical semiconductor channel, wherein the tubular cavity is formed within a volume of the memory opening and is laterally spaced from a cylindrical sidewall of the memory opening by a lateral offset distance;
depositing a germanium-containing material in the tubular cavity;
forming a silicon-germanium structure including a silicon-germanium material by interdiffusing the germanium-containing material with a silicon-containing material in the end portion of the vertical semiconductor channel; and
forming a semiconductor source line layer on the silicon-germanium structure.
17 . The method of claim 16 , further comprising removing a portion of the germanium-containing material that does not form the silicon-germanium material by performing an etch back process that etches the germanium-containing material at a higher etch rate than the silicon-germanium material.
18 . The method of claim 16 , wherein the silicon-germanium material of the silicon-germanium structure has a variable atomic percentage of germanium that increases with a vertical distance from the vertical semiconductor channel.
19 . The method of claim 16 , wherein:
the vertical semiconductor channel is free of germanium prior to deposition of the germanium-containing material; and
the semiconductor source line layer comprises a surface portion that is free of germanium.
20 . The method of claim 16 , further comprising:
vertically recessing an end portion of the memory film, wherein an additional tubular cavity is formed in a volume from which the end portion of the memory film is removed; and
forming a dielectric tube comprising a dielectric metal oxide in the additional tubular cavity.