(A) study on the atomic layer deposition of Ti-Al-N thin films using plasmas

Abstract

Ferroelectric cell capacitors, using $PbZr_{1-x}Ti_xO_3$, have been normally fabricated by using multi-layers of noble metals and their oxide electrodes for ferroelectric random access memory (FRAM) devices with 0.25㎛ technology or under. Such multilayer structures, for example, Pt/IrOx/Ir/TiN/plugs, have been focused on in order to improve leakage current, ferroelectric properties, fatigue, and retention. Among them, the serious problem for volatile and nonvolatile capacitors is the oxidation of diffusion barrier because the high permittivity materials either need to be deposited at rather high temperatures of above 500℃ in oxidizing ambient, or require high post thermal-budget of more than 650℃ in order to improve chemical and electrical properties. Such barrier oxidation leads to a significant increase of the contact resistance as well as a severe degradation of capacitance properties. Therefore, the development of the diffusion barrier is absolutely essential. Until now, titanium nitride (TiN) is widely used as the diffusion barrier of oxygen. However, TiN is easily oxidized by ambient air at high temperatures (>500℃). Recently, ternary compounds of Ti-X-N films with superior oxidation resistance have been developed and investigated as an alternative to TiN. In this paper, we have investigated the Ti-Al-N films deposited by the plasma-enhanced atomic layer deposition (PEALD) using both metal-organic and chloride precursors. The advantages of the ALD and a plasma technique have been employed at the same time. Firstly, the electrical, structural, and morphological properties of Ti-Al-N films were investigated by the combination of Al and TiN steps using tetrakis dimethylamido titanium (TDMAT) and trimethylaluminum (TMA). Then, anti-oxidation properties of Ti-Al-N films were experimented and analyzed. The RMS is 0.332 nm with the thickness of 100 nm. Ti-Al-N films effectively prevent oxygen from incorporating into the films at 600℃ for 30 min in ambient $O...