Flash memory and methods of fabricating the same
View Patent ↗Flash memory and methods of fabricating the same are disclosed. An illustrated example flash memory includes a first source formed within a semiconductor substrate; an epitaxial layer formed on an upper surface of the semiconductor substrate; an opening formed within the epitaxial layer to expose the first source; a floating gate device formed inside the opening; and a select gate device formed on the epitaxial layer at a distance from the floating gate device.
1. A flash memory comprising:
a first source in a semiconductor substrate;
an epitaxial layer on an upper surface of the semiconductor substrate;
an opening in the epitaxial layer to expose the first source;
a floating gate device inside the opening comprising:
a tunneling oxide layer along side and bottom walls of the opening;
floating gates on the tunneling oxide layer between the side walls and the bottom wall of the opening;
a dielectric layer on the floating gates and on the tunneling oxide layer between the floating gates; and
a control gate on the dielectric layer; and
a select gate device on the epitaxial layer at a distance from the floating gate device, wherein the select gate device has a select gate having a height substantially identical with a height of the control gate.
2. A flash memory as defined in claim 1 , wherein the tunneling oxide layer is thicker on the bottom wall of the opening than on the side walls of the opening.
3. A flash memory as defined in claim 1 , wherein the bottom wall of the opening is etched to a predetermined depth into the first source.
4. A flash memory as defined in claim 1 , wherein the select gate device comprises:
a gate dielectric on the epitaxial layer;
select gates on the gate dielectric adjacent a first drain; and
a second source and a second drain in the epitaxial layer on a side of the select gate opposite the first drain.
5. A flash memory as defined in claim 1 , wherein the select gate device comprises a number of select gates and the floating gate device comprises a number of floating gates, and the number of select gates is identical to the number of floating gates.
6. A flash memory as defined in claim 1 , wherein the floating gates are separate from one another, on opposite side walls.
7. A flash memory as defined in claim 1 , wherein the dielectric layer comprises an oxide-nitride-oxide (ONO) layer.
8. A flash memory as defined in claim 1 , wherein the first source comprises n-type impurities.
9. A flash memory as defined in claim 1 , wherein the semiconductor substrate comprises a p-type silicon substrate.
10. A flash memory as defined in claim 1 , wherein the epitaxial layer comprises silicon.
11. A flash memory as defined in claim 1 , wherein the epitaxial layer comprises an appropriate concentration of p-type impurities to avoid a punch through effect.
12. A flash memory as defined in claim 1 , wherein the first source has a higher doping concentration than the epitaxial layer.
13. A flash memory as defined in claim 1 , wherein the side walls of the opening comprise an appropriate concentration of impurity ions to adjust the initial threshold voltage of the flash memory.
14. A flash memory as defined in claim 1 , wherein the floating gates comprise doped polysilicon.
15. A flash memory as defined in claim 1 , further comprising spacers on sidewalls of the control gate and the select gate.
16. A flash memory as defined in claim 1 , further comprising a silicide layer on the on the control gate, the select gate, and an exposed upper surface of the epitaxial layer.
17. A flash memory as defined in claim 16 , further comprising a dielectric layer on the floating gate device, the select gate device, and the silicide layer.
18. A flash memory as defined in claim 17 , further comprising contact holes in the dielectric layer to die silicide layer on the exposed upper surface of the epitaxial layer.