Methods of forming and operating NAND memory with side-tunneling
View Patent ↗A string of nonvolatile memory cells are formed with control gates extending between floating gates, control gates and floating gates separated by tunnel dielectric layers. Electron tunneling between control gates and floating gates is used for programming. A process for forming a memory array forms odd numbered floating gates from a first layer and even numbered floating gates from a second layer.
1. A method of forming a NAND flash memory array comprising: forming a first gate dielectric layer that includes a blocking layer to block electron tunneling through the first gate dielectric layer;
forming a first floating gate layer over the first gate dielectric layer; patterning the first gate dielectric layer and the first floating gate layer in the same pattern to leave first floating gate portions and openings between first floating gate portions;
forming a second gate dielectric layer within the openings, the second gate dielectric layer including a blocking layer to block electron tunneling through the second gate dielectric layer; forming a second floating gate portions over the second gate dielectric layer within the openings;
etching the first and second floating gate portions so that first and second floating gate portions have an inverted-T shape in cross section;
and forming control gates that extend between neighboring floating gate portions.
2. The method of claim 1 wherein the blocking layer includes Silicon Nitride.
3. The method of claim 1 further comprising forming word lines that overlie the control gates and connect control gates in the word line direction.
4. The method of claim 1 wherein etching the first and second floating gate portions is performed using masking portions that are defined by sidewall spacers.
5. The method of claim 1 further comprising forming a tunnel dielectric layer between the control gates and the first and second floating gate portions.