Fabricating method of a flash memory cell
View Patent ↗A flash memory cell including a first conductive type substrate, a second conductive type well, a patterned film layer, a second conductive type doped region, a tunneling dielectric layer, a plurality of floating gates, an inter-gate dielectric layer and a plurality of control gates is provided. The floating gates are formed on the first conductive type substrate outside the patterned film layer. The floating gates have a thickness greater than the patterned film layer. Thus, the overlapping area between the floating gates and the control gates and hence the coupling ratio of the flash memory cell is increased.
1. A method of fabricating a flash memory cell, comprising the steps of:
providing a first conductive type substrate having a second conductive type well and a plurality of device isolation structures formed thereon, wherein the device isolation structures are disposed within the second conductive type well to define an active region on the first conductive type substrate;
forming a first conductive type doped region on the second conductive type well within the active region;
forming a patterned film layer over the first conductive type substrate, wherein the patterned film layer has a plurality of openings that exposes a portion of the first conductive type doped region within the active region;
forming a second conductive type doped region in the first conductive type substrate using the patterned film layer as a mask so that the second conductive doped region cuts off the first conductive type doped region;
forming a tunneling dielectric layer over the second conductive type doped region within the openings;
forming a plurality of floating gates inside the openings;
removing a portion of the patterned film layer so that the patterned film layer has a thickness smaller than that of the floating gate;
forming an inter-gate dielectric layer over the first conductive type substrate to cover the floating gates and the patterned film layer; and
forming a plurality of control gates over the inter-gate dielectric layer with each control gate stacked on top of each of the floating gates respectively.
2. The method of claim 1 , wherein the step of forming the floating gates comprises:
forming a first conductive layer over the first conductive type substrate; and
performing a chemical-mechanical polishing operation to remove the first conductive layer outside the openings.
3. The method of claim 2 , wherein there is an etching selectivity between the material constituting the first conductive layer and the material constituting the patterned film layer.
4. The method of claim 1 , wherein dopant concentrations of the second conductive type doped region and the second conductive type well are different.
5. The method of claim 1 , wherein the step of forming the control gate comprises:
forming a second conductive layer over the inter-gate dielectric layer; and
patterning the second conductive layer to form the control gates stacked on top of the floating gates.
6. The method of claim 1 , wherein the method of fabricating the flash memory cell further comprises forming conductive spacers on the sidewalls of the control gates and the floating gates.
7. The method of claim 6 , wherein the material constituting the conductive spacers comprises doped polysilicon.
8. The method of claim 1 , wherein the control gates formed over the inter-gate dielectric layer overlap with the upper surface and the sidewalls of the floating gate.
9. The method of claim 1 , wherein the method further comprises a step of forming a sacrificial layer over the first conductive type substrate to serve as an etching stop layer in the step for forming the patterned film layer before the step of forming the first conductive type doped region.
10. The method of claim 9 , wherein the material constituting the sacrificial layer comprises silicon nitride.
11. The method of claim 9 , wherein there is an etching selectivity between the material constituting the sacrificial layer and the material constituting the patterned film layer.
12. The method of claim 1 , wherein the material constituting the patterned film layer comprises silicon oxide.
13. The method of claim 1 , wherein step of forming the patterned film layer further comprises expanding the openings to expose a portion of the device isolation structures.
14. The method of claim 1 , wherein the material constituting the floating gate and the control gate comprises doped polysilicon.
15. The method of claim 1 , wherein the inter-gate dielectric layer comprises a silicon oxide layer or an oxide/nitride/oxide composite layer.
16. The method of claim 1 , wherein the material constituting the tunneling dielectric layer comprises silicon oxide.