Electrical characterization of metal-oxide-semiconductor memory devices with high-density self-assembled tungsten nanodots

Tungsten nanodots (W-NDs) with an ultrahigh density of 1 × 10 ¹³/cm² and a small size of around of 1.5-2 nm were successfully formed by self-assembled nanodot deposition (SAND). A metal-oxide-semiconductor (MOS) memory device was also fabricated with a W-ND layer placed between tunneling SiO₂ and block SiO₂. Using this device, the effects of annealing on the capacitance characteristics were investigated in detail. After 900 °C post deposition annealing (PDA), an extremely large memory window of about 9.2V was obtained, indicating that the device is a strong contender for future nonvolatile memory (NVM) applications. The program/erase speed and retention characteristics were also evaluated. The oxidation of tungsten by oxygen from the cosputtered silicon oxide was confirmed by X-ray photoelectron spectroscopy (XPS) measurement. It is considered to degrade the retention characteristics of MOS memory devices.