Paper TF-TuM12
Atomic Layer Deposition of Zinc Hybrid Films from Diethyl Zinc and Ethylene Glycol

Tuesday, October 21, 2008, 11:40 am, Room 302

Atomic/molecular layer deposition of organic-inorganic hybrid materials could significantly expand the range of materials available in thin film applications. However, the detailed mechanisms associated with the integration of organic materials into the ALD process scheme need to be more fully understood. In this study, zinc hybrid films were formed by atomic layer deposition using alternative dosing of diethyl zinc (DEZ) and ethylene glycol (EG). The process was characterized using in-situ quartz crystal microbalance (QCM), as well as a range of external characterization tools and results were compared directly to the ZnO ALD process (DEZ/H2O) performed under similar reaction conditions. Consistent with literature results, during the ZnO ALD process at 120degree C, the mass uptake during the DEZ exposure is ~130 ng/cm2 per cycle, with a small mass loss during H2O exposure. The QCM results confirmed the self-limiting surface adsorption during both reaction steps of ZnO ALD. When H2O is replaced with ethylene glycol in the process sequence at 120 degree C, the mass uptake during the DEZ pulse is reduced significantly to ~19 ng/cm2 , and the positive mass uptake of ~ 4 ng/cm2 is observed during the EG pulse in the steady-state deposition of Zn hybrid. The reduced mass uptake during DEZ exposure is likely due to the lower density of reaction sites resulting from: (i) the twice reaction of EG with surface bonded –O-Zn-C2H5 ligands; (ii) steric hindrance of bulky EG molecules and its related surface bonded ligands; (iii) the possible dehydration reaction between the surface bonded EG ligands. Self-limiting adsorption of DEZ and EG, which is consistent with a typical ALD process, was confirmed by QCM. The process steps of Zn hybrid can continue for several hundred cycles with consistent and repeatable mass uptake. The growth rate per cycle of the hybrid material decreases as the deposition temperature increases. Infrared analysis of as-formed Zn hybrid films shows modes consistent with EG and Zn-O bonds. Upon exposure to laboratory air, the resulting hybrid films readily undergo hydrolysis, resulting in films consisting of ZnO and hydroxide with significant carbon content, as evidenced by FTIR and XPS analysis. AFM shows the films are uniform, and TEM analysis indicates that hydrolysis process results in conformal and porous layers. Further results of in-situ characterization and post-deposition analysis of the zinc hybrid materials will be presented.