High trap density and long retention time from self-assembled amorphous Si nanocluster floating gate nonvolatile memory

Abstract

The memory performance of floating gate nonvolatile memory based on amorphous Si (a-Si) nanoclusters self-assembled during low-temperature oxidation is investigated. A 2 nm thick a-Si layer was grown on a top of a 5.6 nm thick thermal oxide tunneling layer by ultrahigh vacuum ion beam sputter deposition and subsequently oxidized by annealing in flowing N-2/O-2 (9:1) environment for 0-540 s at 900 degrees C. After oxidation, a 14 nm thick Al2O3 control oxide layer was grown by atomic layer deposition. The authors find that the a-Si layer breaks up upon oxidation, self-assembling into a dense array of < 3 nm sized a-Si nanoclusters separated by thermal oxide after 180 s. This combination of discrete Si nanoclusters separated by thermal oxide and modest thermal budget enabled by the use of amorphous cluster enables achieving a trap density in the excess of 10(13) cm(-2) and a retention time of > 1000 s at at 150 degrees C. (c) 2006 American Institute of Physics.