Methods for fabricating flash memory devices
View Patent ↗Methods for fabricating a flash memory device are provided. A method comprises forming a plurality of gate stacks overlying a substrate. Each gate stack comprises a charge trapping layer and a control gate. The control gate is a first distance from the substrate. Adjacent gate stacks are a second distance apart. A cell spacer material layer is deposited and is etched to form a spacer about sidewalls of each gate stack. A source/drain impurity doped region is formed adjacent a first gate stack and a last gate stack. The first distance and the second distance are such that, when a voltage is applied to a gate stack during a READ operation, a fringing field is created between the control gate of the gate stack and the substrate and is sufficient to invert a portion of the substrate between the gate stack and an adjacent gate stack.
1. A method for fabricating a flash memory device, the method comprising the steps of:
providing a silicon substrate;
forming a plurality of gate stacks overlying said silicon substrate, wherein each of said plurality of gate stacks comprises a charge trapping layer and a control gate overlying said charge trapping layer, wherein said control gate is a first distance from said silicon substrate and wherein each gate stack of said plurality of gate stacks is a second distance from an adjacent gate stack;
depositing a cell spacer material layer overlying said plurality of gate stacks;
etching said cell spacer material layer to form a cell spacer about sidewalls of each of said plurality of gate stacks; and
forming a first impurity doped region adjacent a first gate stack in said plurality of gate stacks and a second impurity doped region adjacent a last gate stack in said plurality of gate stacks,
wherein, said first distance and said second distance are such that, when a voltage is applied to a selected gate stack of said plurality of gate stacks during a READ operation, a fringing field is created between said control gate of said selected gate stack and said silicon substrate and is sufficient to invert a portion of said silicon substrate between said selected gate stack and an adjacent gate stack.
2. The method of claim 1 , wherein the step of depositing a cell spacer material layer comprises the step of depositing a high dielectric constant material layer.
3. The method of claim 1 , wherein the step of forming a plurality of gate stacks overlying said silicon substrate comprises the steps of:
forming overlying said silicon substrate a charge trapping stack comprising a charge trapping layer overlying a first oxide layer;
depositing a high dielectric constant material overlying said charge trapping stack;
depositing a polysilicon layer overlying said high dielectric constant material;
forming a patterned hard mask overlying said polysilicon layer; and
etching said polysilicon layer to form a plurality of control gates overlying said charge trapping stack.
4. The method of claim 3 , further comprising the step of etching said high dielectric constant material using said cell spacers as a mask.
5. The method of claim 3 , further comprising the steps of:
conformally depositing a silicon oxide layer overlying said plurality of control gates after the step of etching said polysilicon layer to form a plurality of control gates and before the step of depositing said cell spacer material layer;
after the step of etching said cell spacer material layer, anisotropically etching said silicon oxide layer to expose a portion of each gate stack of said plurality of control gates and to form sidewall spacers about said sidewalls of each gate stack of said plurality of gate stacks; and
etching said high dielectric constant material using said cell spacers and said sidewall spacers as a mask.
6. The method of claim 3 , further comprising the steps of:
before the step of depositing a cell spacer material layer and after the step of etching said polysilicon layer, removing exposed portions of said high dielectric constant material; and
removing exposed portions of said charge trapping layer to expose portions of said first oxide layer that do not underlie said control gates and to form said plurality of gate stacks.
7. The method of claim 6 , further comprising the step of depositing a second oxide layer overlying said plurality of gates stacks and said exposed portions of said first oxide layer, wherein said step of depositing a second oxide layer is performed before the step of depositing a cell spacer material layer and after the step of removing portions of said charge trapping layer.
8. The method of claim 7 , further comprising the step of etching said second oxide layer to form sidewall spacers about sidewalls of each of said plurality of gates stacks, the step of etching said second oxide layer performed before the step of forming said first and second impurity doped regions and after the step of etching said cell spacer material layer.
9. The method of claim 1 , further comprising the steps of:
after the step of forming a first impurity doped region and a second impurity doped region, depositing an insulating layer overlying the plurality of gate stacks and the first and second impurity doped regions;
etching a via through said insulating layer to said first impurity doped region; and
forming a conductive contact within said via, wherein said conductive contact is in electrical contact with said first impurity doped region.
10. A method for fabricating a flash memory device, the method comprising the steps of:
providing a silicon substrate;
forming a plurality of memory cells overlying said silicon substrate;
depositing a high dielectric constant material layer as a cell spacer material layer overlying said plurality of memory cells and between each memory cell of said plurality of memory cells;
etching said cell spacer material layer with an etch chemistry to expose a surface of each memory cell of said plurality of memory cells and to form a cell spacer about each memory cell of said plurality of memory cells, wherein said etching is terminated before said etch chemistry etches through said cell spacer material layer between said memory cells to an underlying material layer; and
forming a source/drain impurity doped region adjacent a first memory cell in said plurality of memory cells and a source/drain impurity doped region adjacent a last memory cell in said plurality of memory cells, wherein said cell spacers serve as a mask to prevent formation of said source/drain impurity doped regions between adjacent memory cells of said plurality of memory cells.
11. The method of claim 10 , wherein the step of forming a plurality of memory cells comprises the steps of:
forming overlying said silicon substrate a charge trapping stack comprising a charge trapping layer overlying an oxide layer;
depositing a high dielectric constant material overlying said charge trapping stack;
depositing a polysilicon layer overlying said high dielectric constant material;
forming a patterned mask overlying said polysilicon layer; and
etching said polysilicon layer to form a plurality of control gates overlying said charge trapping stack.
12. The method of claim 11 , wherein the step of forming a plurality of memory cells further comprises the steps of:
etching exposed portions of said high dielectric constant material; and
etching exposed portions of said charge trapping stack.
13. The method of claim 12 , further comprising the step of forming a sidewall spacer about each of said plurality of memory cells before the step of forming said source/drain impurity doped regions.
14. The method of claim 11 , further comprising the step of etching said high dielectric constant material using said cell spacers as a mask, the step of etching said high dielectric constant material performed before the step of forming said source/drain impurity doped regions.
15. The method of claim 11 , further comprising the step of forming a sidewall spacer about each of said control gates of said plurality of control gates before the step of forming said source/drain impurity doped regions.
16. The method of claim 15 , further comprising the step of etching said high dielectric constant material using said cell spacers and said sidewall spacers as a mask, the step of etching said high dielectric constant material performed before the step of forming said source/drain impurity doped regions.
17. The method of claim 10 , wherein the step of forming a plurality of memory cells comprise the steps of:
forming a tunnel oxide layer overlying said substrate; and
forming a floating gate layer overlying said oxide layer.
18. A method for fabricating a flash memory device, the method comprising the steps of:
providing a silicon substrate;
depositing a charge trapping stack comprising a charge trapping layer overlying said silicon substrate;
depositing a layer of control gate material overlying said charge trapping stack;
selectively etching said layer of control gate material to form a plurality of control gates overlying said charge trapping layer, wherein each of said plurality of control gates is a first distance from an adjacent control gate;
conformally depositing a high dielectric constant material layer as a cell spacer material layer overlying said plurality of control gates to a thickness that is no less than said first distance;
etching said cell spacer material layer to form a cell spacer about each control gate of said plurality of control gates; and
forming a source/drain impurity doped region within said substrate adjacent a first end of said plurality of control gates and a source/drain impurity doped region within said substrate adjacent a second end of said plurality of control gates.
19. The method of claim 18 , further comprising the step of depositing a high-dielectric constant material overlying said charge trapping layer, wherein the step of depositing a high-dielectric constant material is performed before the step of depositing a layer of control gate material.
20. The method of claim 19 , further comprising etching said high-dielectric constant material after the step of etching said cell spacer material layer.
21. The method of claim 18 , further comprising the step of depositing an oxide layer overlying said plurality of control gates before the step of depositing said cell spacer material layer.
22. The method of claim 21 , further comprising the step of etching said oxide layer after the step of etching said cell spacer material layer and before the step of forming said source/drain impurity doped regions.
23. The method of claim 18 , further comprising the step of etching exposed portions of said charge trapping layer that do not underlie said control gates of said column of control gates.
24. The method of claim 23 , further comprising the step of globally depositing an oxide layer before the step of depositing said cell spacer material layer and after the step of etching portions of said charge trapping layer.
25. The method of claim 24 , further comprising the step of etching said oxide layer after the step of etching said cell spacer material layer and before the step of forming said source/drain impurity doped regions.