Nanodot enhanced hybrid floating gate for non-volatile memory devices
A memory device and a method of making a memory device that includes a semiconductor channel, a tunnel dielectric layer located over the semiconductor channel, a floating gate located over the tunnel dielectric layer, the floating gate comprising a continuous layer of an electrically conductive material and at least one protrusion of an electrically conductive material facing the tunnel dielectric layer and electrically shorted to the continuous layer, a blocking dielectric region located over the floating gate, and a control gate located over the blocking dielectric layer.
1. A method of fabricating a memory device, comprising:
forming a tunnel dielectric layer over a semiconductor channel;
forming a floating gate over the tunnel dielectric layer, the floating gate comprising a continous layer of an electrically conductive material and at least one protrusion of an electrically conductive material facing the tunnel dielectric layer and electrically shorted to the continous layer;
forming a blocking dielectric region over the floating gate;
forming a control gate over the blocking dielectric layer; and
further comprising removing at least one nanodot located at least partially under corner regions of the continuous layer;
wherein the at least one protrusion comprises a plurality of protrusions; and
wherein the step of removing comprises:
forming a mask pattern over a stack comprising a tunnel dielectric layer, a plurality of nanodots, the continuous layer, a blocking dielectric layer and a control gate layer; and
etching portions of the stack that are exposed by the mask pattern to pattern the control gate layer into the control gate, pattern the blocking dielectric layer into the blocking dielectric region, pattern the continuous layer into a floating gate, and remove the nanodots which are located at least partially under the corner regions of the continuous layer and the nanodots which are completely exposed by the mask pattern.
2. The method of claim 1 , wherein forming the floating gate layer comprises:
depositing at least one nanodot over the tunnel dielectric layer to form the at least one protrusion; and
forming the continous layer over the at least one nanodot.
3. The method of claim 2 , wherein the continous layer is formed such that it electrically contacts the at least one nanodot.
4. The method of claim 2 , further comprising forming a dielectric layer over the nanodots prior to forming the continuous layer, wherein the dielectric layer allows direct electronic tunneling between the at least one protrusion and the continuous layer.
5. The method of claim 4 , wherein the dielectric layer comprises SiO 2 and is formed such that the continuous layer is separated from the at least one nanodot by less than 2 nm.
6. The method of claim 1 , further comprising:
forming a dielectric material over the nanodots such that the nanodots are completely embedded in the dielectric material; and
planarizing the dielectric material so that the nanodots are covered by less than 2 nm of dielectric material or exposed through the dielectric material prior to forming the continuous layer such that the continuous layer is located over the nanodots and dielectric material.
7. The method of claim 1 , wherein the at least one protrusion and the continuous layer are formed of the same material.
8. The method of claim 1 , wherein the at least one protrusion is formed of a first material and the continous layer is formed of a second material, different than the first material.
9. The method of claim 8 , wherein the at least one protrusion is formed of a metal material, and the continuous layer is formed of a different metal material or a highly-doped semiconductor material.
10. The method of claim 1 , wherein the memory device comprises a NAND device.