Choi Aerim1,Il-Kwon Oh1
Ajou University1
With the miniaturization of electronic devices, high-k dielectric materials replacing SiO<sub>2</sub> are being intensively studied to improve leakage current characteristics. Understanding the surface reactions and chemistry of precursor molecules during atomic layer deposition (ALD) has played an essential role. Chemical precursors and reactants contribute significantly to ALD thin film properties. So far, various Zr precursors for ZrO<sub>2</sub> thin films have been studied for the ALD process. Among them, the widely used precursor type is the heteroleptic precursor because the structure can improve the vapor pressure and tune the Lewis acidity of the precursor. However, the surface reaction of heteroleptic precursor molecules requires more attention to understand because the reaction pathway is different for each ligand exchange reaction.<br/>In this study, we used a commercially used CpZr(N(CH<sub>3</sub>)<sub>2</sub>)<sub>3</sub> precursor for the high-k layer of dynamic random access memory (DRAM) by providing low impurities and good conformability with other reactants in H<sub>2</sub>O and O<sub>2</sub> plasma. The surface reaction mechanism regarding the ZrO<sub>2</sub> growth and its dependence on impurity incorporation has been elucidated based on the results of quantum chemistry calculations. In addition, chemical composition, surface roughness and microstructural analysis by electron microscopy and X-ray techniques were introduced. The correlation between experimental observations and theoretical calculations was studied using density functional theory (DFT) ; 1) 1<sup>st</sup> half reaction in a cycle : When CpZr(N(CH<sub>3</sub>)<sub>2</sub>)<sub>3</sub> precursor reacting with OH groups on the substrate surface, it is highly likely to react with 2 -N(CH<sub>3</sub>)<sub>2</sub> out of 4 ligands, 2) 2<sup>nd</sup> half reaction in a cycle: showed that the reaction pathway of Zr–Cp ligand exchange ligands is less favorable than that of Zr–N(CH<sub>3</sub>)<sub>2</sub>. In addition, defects and impurities appearing because the reaction between Cp ligands and H<sub>2</sub>O molecules is less effective than alkylamide ligands degrade device performance. In contrast, we used O<sub>2</sub> plasma to dramatically remove all ligands, improving the leakage current and dielectric properties of ZrO<sub>2</sub> thin films. We believe that these findings on the surface reaction of heteroleptic ALD precursors will be helpful for future miniature semiconductor devices.