High coupling memory cell
View Patent ↗A first dielectric layer is formed over a substrate. A single layer first conductive layer that acts as a floating gate is formed over the first dielectric layer. A trough is formed in the first conductive layer to increase the capacitive coupling of the floating gate with a control gate. An intergate dielectric layer is formed over the floating gate layer. A second conductive layer is formed over the second dielectric layer to act as a control gate.
1. A method for fabricating a memory cell, the method comprising:
forming a tunnel dielectric over a substrate;
forming a single layer floating gate over the tunnel dielectric;
performing shallow trench isolation to form isolation trenches in the substrate that extend through the tunnel dielectric and floating gate, the isolation trenches comprising dielectric material each having a lower portion and an upper portion wherein the upper portion extends above the substrate and into the floating gate such that the floating gate extends along each upper portion;
forming a trough in the floating gate to create a concave shape on top of the floating gate, wherein the trough has first and second sidewalls such that the first and second sidewalls are substantially aligned with edges of the tunnel dielectric;
narrowing the upper portions of the isolation material such that uppermost edges of the upper portions are narrower than edges of the lower portions of the isolation material in the tunnel dielectric and substrate;
forming an intergate dielectric over the floating gate; and
forming a control gate over the intergate dielectric wherein the control gate is composed of a polysilicon/silicide/metal structure.
2. The method of claim 1 wherein the floating gate is a doped polysilicon floating gate.
3. The method of claim 1 wherein narrowing the upper portions comprises creating a substantially concave shape on each side of the upper portions into which the floating gate is formed upwards along the upper portion.
4. The method of claim 1 wherein the tunnel dielectric is an oxide.
5. The method of claim 1 wherein the intergate dielectric comprises an oxide-nitride-oxide composite.
6. The method of claim 1 wherein the intergate dielectric comprises a nitride-oxide composite.
7. The method of claim 1 wherein the control gate comprises a doped polysilicon.
8. The method of claim 1 wherein performing shallow trench isolation comprises:
patterning the floating gate layer to produce exposed areas that are susceptible to etching; and
removing a portion of the exposed areas of the floating gate layer.