Non-volatile memory cell with self aligned floating and erase gates, and method of making same
View Patent ↗A memory device, and method of making the same, in which a trench is formed into a substrate of semiconductor material. The source region is formed under the trench, and the channel region between the source and drain regions includes a first portion that extends substantially along a sidewall of the trench and a second portion that extends substantially along the surface of the substrate. The floating gate is disposed in the trench, and is insulated from the channel region first portion for controlling its conductivity. The control gate is disposed over and insulated from the channel region second portion, for controlling its conductivity. The erase gate is disposed at least partially over and insulated from the floating gate. The erase gate includes a notch, and the floating gate includes an edge that directly faces and is insulated from the notch.
1. An electrically programmable and erasable memory device comprising:
a substrate of semiconductor material having a first conductivity type and a surface;
a trench formed into the surface of the substrate;
first and second spaced-apart regions formed in the substrate and having a second conductivity type, with a channel region in the substrate there between, wherein the first region is formed under the trench, and the channel region includes a first portion that extends substantially along a sidewall of the trench and a second portion that extends substantially along the surface of the substrate;
an electrically conductive floating gate at least partially disposed in the trench adjacent to and insulated from the channel region first portion for controlling a conductivity of the channel region first portion;
an electrically conductive control gate disposed over and insulated from the channel region second portion for controlling a conductivity of the channel region second portion;
an electrically conductive erase gate disposed adjacent to and insulated from the floating gate; and
a block of conductive material having at least a lower portion thereof disposed in the trench that is electrically connected to the first region and is adjacent to and insulated from the floating gate.
2. The device of claim 1 , wherein there is no vertical overlap between the control gate and the floating gate.
3. The device of claim 1 , wherein the erase gate is disposed adjacent to the floating gate and insulated there from with insulation material having a thickness that permits Fowler-Nordheim tunneling.
4. The device of claim 1 , wherein the erase gate includes a notch and the floating gate includes an edge that directly faces and is insulated from the notch.
5. The device of claim 4 , wherein the erase gate includes an upper portion having a first width and lower portion having a second width less than the first width.
6. The device of claim 5 , wherein the notch is formed where the first and second portions of the erase gate meet.
7. The device of claim 5 , wherein the erase gate lower portion at least partially extends into the trench.
8. The device of claim 4 , further comprising:
a third region formed in the substrate and having a second conductivity type, with a second channel region in the substrate between the first and third regions, wherein the second channel region includes a first portion that extends substantially along a sidewall of the trench and a second portion that extends substantially along the surface of the substrate;
a second electrically conductive floating gate at least partially disposed in the trench adjacent to and insulated from the second channel region first portion for controlling a conductivity of the second channel region first portion; and
an electrically conductive control gate disposed over and insulated from the second channel region second portion for controlling a conductivity of the second channel region second portion;
wherein the erase gate includes a second notch and the second floating gate includes an edge that directly faces and is insulated from the second notch.