Three-dimensional memory device with straddling drain select electrode lines and method of making thereof
An alternating stack of insulating layers and spacer material layers is formed over a substrate. The spacer material layers are formed as, or are replaced with, electrically conductive layers. An insulating cap layer is formed over the alternating stack. After formation of memory stack structures through each layer of the alternating stack and the insulating cap layer, a line trench straddling a neighboring pair of rows of the memory stack is formed. Sidewalls of the line trench include a sidewall of each memory stack structure within the neighboring pair of rows of the memory stack structures. A drain select gate dielectric and a drain select electrode line are formed within the line trench. The drain select electrode line controls flow of electrical current through an upper portion of a vertical semiconductor channel within each memory stack structure below the drain regions to activate or deactivate the neighboring rows.
1. A three-dimensional memory device comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
an insulating cap layer overlying the alternating stack;
memory stack structures arranged in rows that laterally extend along a first horizontal direction and extending through each layer of the alternating stack and the insulating cap layer, wherein each of the memory stack structures comprises a memory film and a vertical semiconductor channel laterally surrounded by the memory film;
a line trench straddling a neighboring pair of rows of the memory stack structures and extending along the first horizontal direction, wherein sidewalls of the line trench comprise a sidewall of each memory stack structure within the neighboring pair of rows of the memory stack structures; and
a drain select electrode line located within the line trench;
wherein:
a bottom surface of the line trench is located above a first horizontal plane including a bottom surface of the insulating cap layer; and
a top surface of the drain select electrode line is located below a second horizontal plane including a top surface of the insulating cap layer.
2. The three-dimensional memory device of claim 1 , wherein:
each vertical semiconductor channel contacts a bottom surface of a respective drain region; and
each drain region contacts a respective memory film.
3. The three-dimensional memory device of claim 2 , further comprising a drain select gate dielectric contacting at least one of the sidewalls of the line trench and a bottom surface of the line trench, wherein the drain select electrode line contacts the drain select gate dielectric.
4. The three-dimensional memory device of claim 3 , wherein the vertical semiconductor channel comprises an L-shaped doped region having a doping of an opposite conductivity type from a conductivity type of the drain regions and contacting a sidewall and a bottom surface of the drain select gate dielectric.
5. The three-dimensional memory device of claim 4 , wherein the L-shaped doped region has a greater concentration of electrical dopants than portions of the vertical semiconductor channels that extend through the alternating stack and having a same conductivity type as the L-shaped doped region.
6. The three-dimensional memory device of claim 3 , further comprising a contact level dielectric layer that contacts an entire top surface of the drain select electrode line.
7. The three-dimensional memory device of claim 6 , wherein the contact level dielectric layer contacts a top surface and a sidewall surface of each of the drain regions, and wherein the contact level dielectric layer contacts a top surface of the drain select gate dielectric.
8. The three-dimensional memory device of claim 6 , wherein the drain select gate dielectric contacts each of the drain regions.
9. The three-dimensional memory device of claim 6 , wherein the contact level dielectric layer contacts a sidewall of each of the vertical semiconductor channels.
10. The three-dimensional memory device of claim 1 , wherein:
each of the memory stack structures has a circular horizontal cross sectional shape below the bottom surface of the line trench; and
each of the memory stack structures has a semi-circular horizontal cross sectional shape above the bottom surface of the line trench.
11. The three-dimensional memory device of claim 1 , wherein:
the three-dimensional memory device comprises a monolithic three-dimensional NAND memory device;
the electrically conductive layers comprise, or are electrically connected to, a respective word line of the monolithic three-dimensional NAND memory device;
the substrate comprises a silicon substrate;
the monolithic three-dimensional NAND memory device comprises an array of monolithic three-dimensional NAND strings over the silicon substrate;
at least one memory cell in a first device level of the array of monolithic three-dimensional NAND strings is located over another memory cell in a second device level of the array of monolithic three-dimensional NAND strings;
the silicon substrate contains an integrated circuit comprising a driver circuit for the memory device located thereon;
the array of monolithic three-dimensional NAND strings comprises:
a plurality of semiconductor channels, wherein at least one end portion of each of the plurality of semiconductor channels extends substantially perpendicular to a top surface of the substrate and comprises a respective one of the vertical semiconductor channels, and
a plurality of charge storage elements embodied as portions of the memory films, each charge storage element located adjacent to a respective one of the plurality of semiconductor channels.
12. A three-dimensional memory device comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
an insulating cap layer overlying the alternating stack;
memory stack structures arranged in rows that laterally extend along a first horizontal direction and extending through each layer of the alternating stack and the insulating cap layer, wherein each of the memory stack structures comprises a memory film and a vertical semiconductor channel laterally surrounded by the memory film;
a line trench straddling a neighboring pair of rows of the memory stack structures and extending along the first horizontal direction, wherein sidewalls of the line trench comprise a sidewall of each memory stack structure within the neighboring pair of rows of the memory stack structures; and
a drain select electrode line located within the line trench;
wherein:
each vertical semiconductor channel contacts a bottom surface of a respective drain region;
each drain region contacts a respective memory film;
a drain select gate dielectric contacting at least one of the sidewalls of the line trench and a bottom surface of the line trench, wherein the drain select electrode line contacts the drain select gate dielectric; and
the vertical semiconductor channel comprises an L-shaped doped region having a doping of an opposite conductivity type from a conductivity type of the drain regions and contacting a sidewall and a bottom surface of the drain select gate dielectric.