Nanocrystal Memory Cell Integration in a Stand-Alone 16-Mb nor Flash Device

We report on the full process integration of nanocrystal (NC) memory cells in a stand-alone 16-Mb NOR Flash device. The Si NCs are deposited by chemical vapor deposition on a thin tunnel oxide, whose surface is treated with a low thermal budget process, which increases NC density and minimizes oxide degradation. The device fabrication has been obtained by means of conventional Flash technology, which is integrated with the CMOS periphery with high- and low-voltage transistors and charge pump capacitors. The memory program and erase threshold voltage distributions are well separated and narrow. The voltage distribution widths are related to NC sizes and dispersion, and bigger NCs can induce a cell reliability weakness. An endurance issue is also related to the use of an oxide/nitride/oxide dielectric which acts as a charge trapping layer, causing a shift in the program/erase window and a distribution broadening during cycling.