Methods of forming sidewall gates
A method of forming sidewall gates for vertical transistors includes depositing a gate dielectric layer over polysilicon channel structures, and depositing a gate polysilicon layer over the gate dielectric. The gate polysilicon layer is then etched back to form separated gate electrodes. Filler portions are then formed between gate electrodes, which are then etched from the top down while their sides are protected.
1. A method of forming a three dimensional memory array comprising:
forming a plurality of vertical polysilicon structures;
subsequently depositing a dielectric layer on sidewalls of the plurality of vertical polysilicon structures;
subsequently depositing a polysilicon gate layer on the dielectric layer on sidewalls of the plurality of vertical polysilicon structures;
subsequently etching back the polysilicon gate layer to form separate polysilicon gate electrodes;
subsequently forming filler portions between the polysilicon gate electrodes, the filler portions covering sides of the polysilicon gate electrodes and exposing tops of the polysilicon gate electrodes;
subsequently etching the polysilicon gate electrodes from the exposed tops downwards while the filler portions cover sides of the polysilicon gate electrodes;
wherein the plurality of vertical polysilicon structures are formed on a plurality of global bit lines that extend horizontally along a first direction; and
wherein a barrier layer is formed between the plurality of global bit lines and the vertical polysilicon structures.
2. The method of claim 1 wherein the plurality of vertical polysilicon structures form channels of vertical transistors controlled by the polysilicon gate electrodes.
3. The method of claim 1 wherein the polysilicon gate electrodes extend horizontally in a second direction that is perpendicular to the first direction.
4. The method of claim 1 wherein forming filler portions includes etching back a filler material to expose tops of the polysilicon gate electrodes.
5. The method of claim 1 wherein the filler portions are formed of Silicon Dioxide.
6. The method of claim 1 wherein the filler portions are formed of a resist material.
7. The method of claim 1 wherein the polysilicon gate electrodes are etched from the exposed tops downwards using a wet etch.
8. The method of claim 7 wherein the wet etch is selective to the polysilicon gate electrodes over the filler portions.
9. The method of claim 1 further comprising subsequently forming vertical bit lines extending up from the vertical polysilicon structures and controlling current in the vertical bit lines by biasing the polysilicon gate electrodes.
10. A method of forming a vertical transistor comprising:
forming a vertical polysilicon structure;
subsequently depositing a dielectric layer on sidewalls of the vertical polysilicon structure;
subsequently depositing a polysilicon gate layer on the dielectric layer on sidewalls of the vertical polysilicon structure;
subsequently etching back the polysilicon gate layer to form separate polysilicon gate electrodes;
subsequently forming filler portions covering sides of the polysilicon gate electrodes and exposing tops of the polysilicon gate electrodes;
subsequently etching the polysilicon gate electrodes from the exposed tops downwards while the filler portions cover sides of the polysilicon gate electrodes; and
subsequently forming vertical bit lines extending up from the vertical polysilicon structures.
11. The method of claim 10 wherein the vertical polysilicon structure forms a channel of a vertical transistor that is controlled by the polysilicon gate electrodes on either side.
12. The method of claim 10 wherein the vertical polysilicon structure is formed on a global bit line that extends horizontally along a first direction.
13. The method of claim 12 wherein the polysilicon gate electrodes extend horizontally in a second direction that is perpendicular to the first direction.
14. The method of claim 13 wherein a barrier layer is formed between the global bit line and the vertical polysilicon structure.
15. The method of claim 10 wherein forming filler portions includes etching back a filler material to expose tops of the polysilicon gate electrodes.
16. The method of claim 10 wherein the filler portions are formed of Silicon Dioxide.
17. The method of claim 10 wherein the filler portions are formed of a resist material.
18. The method of claim 10 wherein the polysilicon gate electrodes are etched from the exposed tops downwards using a wet etch.
19. The method of claim 10 further comprising subsequently controlling current in the vertical bit lines by biasing the polysilicon gate electrodes.