Trench vertical NAND and method of making thereof

1. A method of making a monolithic three dimensional NAND string, comprising:

providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate;

etching the stack to form at least one trench in the stack;

forming a blocking dielectric over a side wall of the at least one trench;

forming a charge storage layer over the blocking dielectric in the at least one trench;

forming a tunnel dielectric over the charge storage layer in the at least one trench; and forming a semiconductor channel over the tunnel dielectric in the at least one trench;

wherein:

etching the stack to form the at least one trench comprises etching the stack to form a plurality of trenches extending in a first direction;

the plurality of trenches are separated by a plurality of rails extending in the first direction;

each of the plurality of rails is located between two adjacent trenches; each of the plurality of rails comprises the stacked alternating first material layers and second material layers; and

the semiconductor channel extends continuously over an upper surface of the plurality of rails and over a bottom surface and side walls of the plurality of trenches; and

further comprising:

etching the semiconductor channel to form a plurality of strips extending in a second direction which is substantially perpendicular to the first direction;

filling the plurality of trenches with a sacrificial material after the step of forming the semiconductor channel and before the step of etching which forms the plurality of strips;

forming a mask comprising a plurality of strips extending in the second direction over the sacrificial layer; and

etching the sacrificial material using the mask to form a plurality of sacrificial strips, wherein the step of etching to form the plurality of strips comprises etching the semiconductor channel using at least one of the mask and the sacrificial strips to form the plurality of strips; and

removing the mask and the sacrificial strips.

2. A method of making a monolithic three dimensional NAND string, comprising:

providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate;

etching the stack to form at least one trench in the stack;

forming a blocking dielectric over a side wall of the at least one trench;

forming a charge storage layer over the blocking dielectric in the at least one trench;

forming a tunnel dielectric over the charge storage layer in the at least one trench; and forming a semiconductor channel over the tunnel dielectric in the at least one trench;

wherein:

etching the stack to form the at least one trench comprises etching the stack to form a plurality of trenches extending in a first direction;

the plurality of trenches are separated by a plurality of rails extending in the first direction;

each of the plurality of rails is located between two adjacent trenches;

each of the plurality of rails comprises the stacked alternating first material layers and second material layers; and

the semiconductor channel extends continuously over an upper surface of the plurality of rails and over a bottom surface and side walls of the plurality of trenches; and

further comprising:

etching the tunnel dielectric and the semiconductor channel to form a plurality of strips extending in a second direction which is substantially perpendicular to the first direction;

filling the plurality of trenches with a sacrificial material after the step of forming the semiconductor channel and before the step of etching which forms the plurality of strips;

forming a mask comprising a plurality of strips extending in the second direction over the sacrificial layer; and

etching the sacrificial material using the mask to form a plurality of sacrificial strips, wherein the step of etching to form the plurality of strips comprises etching the tunnel dielectric and the semiconductor channel using at least one of the mask and the sacrificial strips to form the plurality of strips; and

removing the mask and the sacrificial strips.

3. A method of making a monolithic three dimensional NAND string, comprising:

providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate;

etching the stack to form at least one trench in the stack;

forming a blocking dielectric over a side wall of the at least one trench;

forming a charge storage layer over the blocking dielectric in the at least one trench;

forming a tunnel dielectric over the charge storage layer in the at least one trench; and forming a semiconductor channel over the tunnel dielectric in the at least one trench;

wherein:

etching the stack to form the at least one trench comprises etching the stack to form a plurality of trenches extending in a first direction;

the plurality of trenches are separated by a plurality of rails extending in the first direction;

each of the plurality of rails is located between two adjacent trenches; each of the plurality of rails comprises the stacked alternating first material layers and second material layers; and

the semiconductor channel extends continuously over an upper surface of the plurality of rails and over a bottom surface and side walls of the plurality of trenches; and

further comprising:

etching the charge storage laver, the tunnel dielectric and the semiconductor channel to form a plurality of strips extending in a second direction which is substantially perpendicular to the first direction;

filling the plurality of trenches with a sacrificial material after the step of forming the semiconductor channel and before the step of etching which forms the plurality of strips;

forming a mask comprising a plurality of strips extending in the second direction over the sacrificial layer; and

etching the sacrificial material using the mask to form a plurality of sacrificial strips, wherein the step of etching to form the plurality of strips comprises etching the charge storage layer, the tunnel dielectric and the semiconductor channel using at least one of the mask and the sacrificial strips to form the plurality of strips; and

removing the mask and the sacrificial strips; further comprising:

filling the plurality of trenches with a sacrificial material after the step of forming the semiconductor channel and before the step of etching which forms the plurality of strips;

forming a mask comprising a plurality of strips extending in the second direction over the sacrificial layer; and

etching the sacrificial material using the mask to form a plurality of sacrificial strips, wherein the step of etching to form the plurality of strips comprises etching the charge storage layer, the tunnel dielectric and the semiconductor channel using at least one of the mask and the sacrificial strips to form the plurality of strips; and

removing the mask and the sacrificial strips.

4. A method of making a monolithic three dimensional NAND string, comprising:

providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate;

etching the stack to form at least one trench in the stack;

forming a blocking dielectric over a side wall of the at least one trench;

forming a charge storage layer over the blocking dielectric in the at least one trench;

forming a tunnel dielectric over the charge storage layer in the at least one trench; and forming a semiconductor channel over the tunnel dielectric in the at least one trench;

wherein:

etching the stack to form the at least one trench comprises etching the stack to form a plurality of trenches extending in a first direction;

the plurality of trenches are separated by a plurality of rails extending in the first direction;

each of the plurality of rails is located between two adjacent trenches; each of the plurality of rails comprises the stacked alternating first material layers and second material layers; and

the semiconductor channel extends continuously over an upper surface of the plurality of rails and over a bottom surface and side walls of the plurality of trenches; and

further comprising:

etching the charge storage laver, the tunnel dielectric and the semiconductor channel to form a plurality of strips extending in a second direction which is substantially perpendicular to the first direction;

forming a plurality of bit lines extending in the second direction and electrically contacting the channel region in each of the plurality of strips;

forming a plurality of source lines extending in the first direction above or below the plurality of strips and electrically contacting the semiconductor channel in each of the plurality of strips;

etching a plurality of slit trenches in each respective one of the plurality of rails, the slit trenches cutting at least a first one of the first material layers and the second material lavers in each of the plurality of rails; and

filling the plurality of the slit trenches with an insulating material;

wherein:

the first material layers comprise electrically conductive control gate layers and select gate layers, and the second material layers comprise electrically insulating layers; and

the plurality of slit trenches are formed through at least one of an upper or lower select gate layer in each respective one of the plurality of rails, such that the plurality of slit trenches do not extend through the control gate layers.

5. The method of claim 4 , wherein:

the plurality of slit trenches are etched and filled with the insulating material prior to the step of forming the blocking dielectric; and

the plurality of strips extend continuously over the upper surface of the plurality of rails containing the slit trenches filled with the insulating material and over a bottom surface and side walls of the plurality of trenches.

6. The method of claim 4 , wherein:

the plurality of slit trenches are etched and filled with the insulating material after to the step of forming the semiconductor channel such that the plurality of slit trenches extend through the plurality of strips at the upper surface of the plurality of rails; and

the plurality of strips contain a discontinuity comprising a respective one of the plurality of slit trenches filled with the insulating material over an upper surface of the plurality of rails.

7. The method of claim 6 , wherein each of the plurality of bit lines contacts adjacent portions of the semiconductor channel separated by a respective one of the plurality of slit trenches filled with the insulating material to form a conductive bridge between the adjacent portions of the semiconductor channel.