THREE-DIMENSIONAL MEMORY DEVICE INCLUDING BACKSIDE SEMICONDUCTOR SOURCE STRUCTURE AND METHODS FOR FORMING THE SAME
A semiconductor structure includes an alternating stack of insulating layers and electrically conductive layers located on a semiconductor layer, a memory opening vertically extending through the alternating stack and the semiconductor layer, a memory opening fill structure located in the memory opening and containing a memory film and a vertical semiconductor channel, and a backside semiconductor source structure including a doped semiconductor material. The backside semiconductor source structure may be polycrystalline or single crystalline.
1 . A semiconductor structure, comprising:
an alternating stack of insulating layers and electrically conductive layers located on a planar semiconductor layer comprising a first semiconductor material and laterally extending along a horizontal direction;
a memory opening vertically extending through the alternating stack;
a memory opening fill structure located in the memory opening and comprising a memory film and a vertical semiconductor channel that includes a second semiconductor material; and
a backside semiconductor source structure comprising a third semiconductor material and contacting the vertical semiconductor channel and the planar semiconductor layer.
2 . The semiconductor structure of claim 1 , wherein:
a horizontal interface is present between the backside semiconductor source structure and the planar semiconductor layer;
the vertical semiconductor channel has a doping of a first conductivity type; and
the first semiconductor material of the planar semiconductor layer comprises a doped polycrystalline semiconductor material having a doping of a second conductivity type that is an opposite of the first conductivity type.
3 . The semiconductor structure of claim 1 , wherein the backside semiconductor source structure comprises:
a planar portion in contact with the planar semiconductor layer and having a backside surface that is spaced from the first horizontal plane by a uniform vertical spacing; and
a cap portion in contact with the vertical semiconductor channel and having an areal overlap with the memory opening fill structure and vertically protruding farther from the alternating stack than a distal surface of the planar portion.
4 . The semiconductor structure of claim 3 , wherein the cap portion protrudes farther outward from a horizontal plane including an interface between the planar semiconductor layer and the alternating stack than the planar portion.
5 . The semiconductor structure of claim 3 , wherein the backside semiconductor source structure contacts an entirety of a non-vertical end surface of the memory film.
6 . The semiconductor structure of claim 3 , wherein the backside semiconductor source structure is in contact with a non-vertical end surface of the vertical semiconductor channel.
7 . The semiconductor structure of claim 3 , wherein the backside semiconductor source structure is in contact with an end portion of an outer sidewall of the vertical semiconductor channel.
8 . The semiconductor structure of claim 3 , wherein:
the memory opening fill structure further comprises a dielectric core that is laterally surrounded by the vertical semiconductor channel;
the dielectric core comprises an end portion that protrudes farther away from the alternating stack than a first horizontal plane including the horizontal interface between the planar semiconductor layer and the backside semiconductor source structure; and
the backside semiconductor source structure is in contact with the dielectric core.
9 . The semiconductor structure of claim 8 , wherein the backside semiconductor source structure is in contact with an end portion of an inner sidewall of the memory film.
10 . The semiconductor structure of claim 8 , wherein the backside semiconductor source structure is in contact with an end portion of an outer sidewall of the memory film.
11 . The semiconductor structure of claim 8 , wherein the backside semiconductor source structure comprises:
a first vertical sidewall in contact with the vertical semiconductor channel; and
a second vertical sidewall in contact with the planar semiconductor layer and laterally offset outward from the first vertical sidewall.
12 . A method of forming a semiconductor structure, comprising:
forming an etch stop material layer over a carrier substrate;
forming a planar semiconductor layer over the etch stop material layer;
forming an alternating stack of insulating layers and spacer material layers over the planar semiconductor layer, 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 the etch stop material layer and an end portion of the memory film to expose an end portion of the vertical semiconductor channel and a backside surface of the planar semiconductor layer; and
growing a backside semiconductor source structure from physically exposed surfaces of the vertical semiconductor channel and the planar semiconductor layer.
13 . The method of claim 12 , wherein the step of growing the backside semiconductor source structure comprises selective lateral growth of the backside semiconductor source structure using physically exposed surfaces of the vertical semiconductor channel and the planar semiconductor layer as a seed.
14 . The method of claim 12 , wherein the selective lateral growth comprises a chemical vapor deposition process employing a semiconductor precursor gas containing a plurality of atoms of a semiconductor element per molecule at a temperature of 500 degrees Celsius or less.
15 . The method of claim 43 , wherein the semiconductor precursor gas comprises a gas selected from Si 2 H 6 , Si 3 H 8 , Si 4 H 10 , SiH(SiH 3 )3, or Si(SiH 3 ) 4 .
16 . The method of claim 12 , wherein the step of removing the etch stop material layer and the end portion of the memory film comprises:
removing the etch stop material layer without physically exposing any portion of the vertical semiconductor channel; and
physically exposing an end surface of the vertical semiconductor channel by removing the end portion of the memory film selective to the vertical semiconductor channel.
17 . The method of claim 16 , wherein the backside semiconductor source structure is deposited directly on an end surface of the vertical semiconductor channel that is not vertical.
18 . The method of claim 16 , further comprising removing a planar horizontal end portion of the vertical semiconductor channel after the step of physically exposing to form an annular surface of the vertical semiconductor channel, wherein the backside semiconductor source structure is formed on the annular surface of the vertical semiconductor channel.
19 . The method of claim 18 , wherein an annular portion of the planar semiconductor layer is collaterally removed during removal of the planar horizontal end portion of the vertical semiconductor channel to form a recessed contoured sidewall of the planar semiconductor layer, and the backside semiconductor source structure is formed on the recessed contoured sidewall of the planar semiconductor layer.
20 . The method of claim 12 , wherein the step of removing the etch stop material layer and the end portion of the memory film comprises:
physically exposing an end surface of the vertical semiconductor channel by removing the end portion of the memory film selective to the vertical semiconductor channel; and
removing the etch stop material layer by performing an etch process that etches the etch stop material layer selective to the vertical semiconductor channel and the planar semiconductor layer.