Three-dimensional memory device including discrete memory elements and method of making the same
A method of forming a three-dimensional memory device includes forming an alternating stack of in-process composite layers and sacrificial material layers including a lower insulating layer, a sacrificial spacer layer including silicon nitride or a semiconductor material, and an upper insulating layer, forming a memory opening vertically extending through the vertical stack, forming a memory opening fill structure in the memory opening, the memory opening fill structure including an in-process memory film and a vertical semiconductor channel, forming backside trenches through the alternating stack, replacing the sacrificial material layers with electrically conductive layers by removing the sacrificial material layers to form backside recesses and by depositing an electrically conductive material in the backside recesses, and converting the in-process composite layers into composite insulating layers by removing the sacrificial spacer layers to form lateral cavities and by optionally depositing replacement dielectric material layers in the lateral cavities.
1. A method of forming a three-dimensional memory device, comprising:
forming an alternating stack of in-process composite layers and sacrificial material layers over a substrate, wherein each of the in-process composite layers comprises a lower insulating layer, a sacrificial spacer layer comprising silicon nitride or a semiconductor material, and an upper insulating layer;
forming a memory opening vertically extending through the vertical stack;
forming a memory opening fill structure in the memory opening, the memory opening fill structure comprising an in-process memory film and a vertical semiconductor channel;
forming backside trenches through the alternating stack;
performing a first selective isotropic etch process employing an etch chemistry that etches the sacrificial spacer layers of the alternating stack selectively to materials of the lower insulating layers, the upper insulating layers, and the sacrificial material layers of the alternating stack while sidewalls of the lower insulating layers, the upper insulating layers, and the sacrificial material layers of the alternating stack are exposed to the backside trenches to form lateral cavities in volumes from which the sacrificial spacer layers are exposed;
filling the lateral cavities with replacement dielectric layers having a different material composition than the sacrificial spacer layers to convert the in-process composite layers into composite insulating layers; and
replacing the sacrificial material layers with electrically conductive layers by removing the sacrificial material layers by performing a second selective isotropic etch process that etches the sacrificial material layers selectively to materials of the lower insulating layers, the upper insulating layers, and the replacement dielectric layers while sidewalls of the lower insulating layers, the upper insulating layers, and the replacement dielectric layers are exposed to the backside trenches to form backside recesses and by depositing an electrically conductive material in the backside recesses after formation of the composite insulating layers.
2. The method of claim 1 , further comprising:
depositing replacement dielectric material layers in the lateral cavities; and
separating the in-process memory film into a vertical stack of discrete charge storage elements through the lateral cavities after removing the sacrificial spacer layers and before the depositing replacement dielectric material layers.
3. The method of claim 2 , wherein the in-process composite layers are converted into the composite insulating layers prior to replacing the sacrificial material layers with the electrically conductive layers.
4. The method of claim 1 , wherein:
the in-process memory film comprises a layer stack of a blocking dielectric layer, a charge storage layer, and a tunneling dielectric layer; and
the method further comprises prior to performing the second selective isotropic etch process, performing a third isotropic etch process that thins each of the lower insulating layers and the upper insulating layers and etches cylindrical portions of the blocking dielectric layer exposed in the lateral cavities to form a vertical stack of discrete blocking dielectric portions around the charge storage layer.
5. The method of claim 4 , further comprising prior to performing the second selective isotropic etch process, performing a fourth isotropic etch process that etches portions of the cylindrical portions of the charge storage layer exposed in the lateral cavities selective to the tunneling dielectric layer, the lower insulating layers, and the upper insulating layers to form a vertical stack of discrete charge storage elements around the tunneling dielectric layer.
6. The method of claim 5 , wherein each of the replacement dielectric material layers is deposited directly on a respective outer cylindrical surface segment of the tunneling dielectric layer.
7. The method of claim 2 , wherein:
the replacement dielectric material layers are formed by a non-conformal anisotropic deposition process; and
at least one of the replacement dielectric material layers comprises a respective encapsulated cavity therein which laterally surround the memory opening fill structure.
8. The method of claim 2 , wherein:
the lower insulating layers and the upper insulating layers comprise a respective silicon oxide material; and
each of the replacement dielectric material layers comprises a dielectric material having a lower dielectric constant than the silicon oxide materials of the lower insulating layers and the upper insulating layers.
9. The method of claim 8 , wherein the sacrificial material layers comprise silicon nitride and the sacrificial spacer layers comprise the semiconductor material.
10. The method of claim 8 , wherein the sacrificial spacer layers comprise the silicon nitride, and the sacrificial material layers comprise a silicon nitride material which has a different etch rate than the silicon nitride of the sacrificial spacer layers.
11. A method of forming a three-dimensional memory device, comprising:
forming an alternating stack of in-process composite layers and sacrificial material layers over a substrate, wherein each of the in-process composite layers comprises a lower insulating layer, a sacrificial spacer layer, and an upper insulating layer, wherein the sacrificial material layers comprise silicon nitride, and the sacrificial spacer layers comprise a semiconductor material or silicon nitride which has a different etch rate than the silicon nitride of the sacrificial material layers;
forming a memory opening vertically extending through the vertical stack;
forming a memory opening fill structure in the memory opening, the memory opening fill structure comprising an in-process memory film and a vertical semiconductor channel;
forming backside trenches through the alternating stack;
performing a first selective isotropic etch process employing an etch chemistry that etches the sacrificial spacer layers of the alternating stack selectively to materials of the lower insulating layers, the upper insulating layers, and the sacrificial material layers of the alternating stack while sidewalls of the lower insulating layers, the upper insulating layers, and the sacrificial material layers of the alternating stack are exposed to the backside trenches to form lateral cavities in volumes from which the sacrificial spacer layers are exposed;
filling the lateral cavities with replacement dielectric layers having a different material composition than the sacrificial spacer layers to convert the in-process composite layers into composite insulating layers; and
and
replacing the sacrificial material layers with electrically conductive layers by removing the sacrificial material layers by performing a second selective isotropic etch process that etches the sacrificial material layers selectively to materials of the lower insulating layers, the upper insulating layers, and the replacement dielectric layers while sidewalls of the lower insulating layers, the upper insulating layers, and the replacement dielectric layers are exposed to the backside trenches to form backside recesses and by depositing an electrically conductive material in the backside recesses after converting the in-process composite layers into the composite insulating layers.
12. The method of claim 11 , further comprising:
separating the in-process memory film into a vertical stack of discrete charge storage elements through the lateral cavities after the removing the sacrificial spacer layers and before the depositing replacement dielectric material layers.
13. The method of claim 12 , wherein:
the lower insulating layers and the upper insulating layers comprise a respective silicon oxide material; and
each of the replacement dielectric material layers comprises a dielectric material having a lower dielectric constant than the silicon oxide materials of the lower insulating layers and the upper insulating layers.
14. The method of claim 11 , wherein:
the in-process memory film comprises a layer stack of a blocking dielectric layer, a charge storage layer, and a tunneling dielectric layer.
15. The method of claim 14 , further comprising, prior to performing the second selective isotropic etch process:
performing a third isotropic etch process that thins each of the lower insulating layers and the upper insulating layers and etches cylindrical portions of the blocking dielectric layer exposed in the lateral cavities to form a vertical stack of discrete blocking dielectric portions around the charge storage layer; and
performing a fourth isotropic etch process that etches portions of the cylindrical portions of the charge storage layer exposed in the lateral cavities selective to the tunneling dielectric layer, the lower insulating layers, and the upper insulating layers to form a vertical stack of discrete charge storage elements around the tunneling dielectric layer.
16. The method of claim 12 , wherein:
the replacement dielectric material layers are formed by a non-conformal anisotropic deposition process; and
at least one of the replacement dielectric material layers comprises a respective encapsulated cavity therein which laterally surround the memory opening fill structure.