Molecular Layer Deposition of Hybrid Organic‐Inorganic Polymer Films using Diethylzinc and Ethylene Glycol

The molecular layer deposition (MLD) of a hybrid organic-inorganic polymer based on zinc is demonstrated using sequential exposures of diethyl zinc (DEZ, Zn(CH2CH3)2) and ethylene glycol (EG, HOCH2CH2OH). This polymer is representative of a class of zinc alkoxide polymers with an approximate formula of (� ZnORO� )n that can be called ''zincones''. The film growth and surface chemistry during zincone MLD is studied using in-situ Fourier transform infrared (FTIR) measurements. The absorbance of the infrared features of the zincone film increase progressively versus the number of MLD cycles. The FTIR spectra after the DEZ and EG exposures are consistent with the gain and loss of absorbance from CH, OH, CO, and ZnO stretching vibrations. FTIR studies also confirm the self-limiting nature of the surface reactions and monitor the temperature dependence of the film growth. Transmission electron microscope (TEM) images of ZrO2 nanoparticles show very conformal zincone films and determine that the growth rate varies from 4.0 A u per MLD cycle at 908C to 0.25 A u per MLD cycle at 1708C. Quartz crystal microbalance (QCM) and X-ray reflectivity (XRR) measurements show linear zincone growth versus the number of MLD cycles. XRR studies on silicon wafers are consistent with a growth rate of 0.7 A u per MLD cycle at 1308C. The higher growth rate on the ZrO2 nanoparticles is attributed to the lower gas conductance and possible CVD reactions in the ZrO2 nanoparticles. The reaction mechanism for zincone MLD is dependent on temperature. At higher temperatures, there is evidence for ''double'' reactions of EG because no free hydroxyl groups are observed in the FTIR spectrum after the EG exposures. The zincone film can grow in the absence of free hydroxyl groups if DEZ can diffuse into the zincone film and react during the subsequent EG exposure. The zincone films initially adsorb H2O upon exposure to air and then are very stable with time.