Programming Speed Enhancement by NH[sub 3] Plasma Nitridation of Tunneling Oxide for Ge Nanocrystals Memory

Abstract

The characteristics of Ge nanocrystals charge-storage memory stacks with NH 3 plasma surface treatment of the tunneling oxide layer have been studied in this paper. The tunneling silicon oxide ͑TO͒ surface was nitrided by NH 3 plasma treatment, which appears to modify the bonding type of the substrate surface and enhance the nucleation sites for Ge nanocrystals. The chemical bonding depth profile of the Si x Ge 1−x /TO layers and the Ge nanocrystals structure were examined by X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. The trap charge densities were estimated to be as high as 9.1 ϫ 10 12 cm −2 from hysteresis loop for Ϯ10 V sweep. The nitrided interface ͑oxynitride͒ between the trapping layer and the tunneling silicon oxide has a bandgap lower than the silicon oxide, which causes an asymmetric tunneling barrier under programming and erasing conditions. An effective thinner barrier under programming bias results in enhanced programming speed due to improved carrier injection efficiency. It was also observed that the nitrided interface reduces Ge diffusion into the TO layer, which is known to result in degradation of the properties of Ge nanocrystal-based memory devices.