Study of Novel Hafnium-Based Hybrid Thin Films By Molecular Layer Deposition

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Molecular layer deposition (MLD) is a gas-phase reaction technique which relies on self-limiting surface reactions for growth of surface-bound polymers. Hybrid organic-inorganic materials usually possess properties distinct from both inorganic and organic components. MLD techniques can be used to deposit hybrid films with precisely defined composition and tunable properties that can be conformally deposited on high aspect ratio substrate. In this study, novel hybrid organic-inorganic hafnium based polymer films were successfully deposited using sequential exposures of a homoleptic tetrakis(dimethylamido)hafnium (TDMAH) complex and ethanolamine (EA) as the reactants by MLD. Hafnium nitrides and oxides have received much attention in the fields of microelectronics and lithium ion batteries, and thus are of interest as hybrid materials that may impart beneficial mechanical and chemical properties. To grow the Hf hybrid films, TDMAH and EA pulses were alternated with 120s of N2 purge. The processes were investigated as a function of temperature, precursor pulsing time and number of cycles. The results show that the self-limiting surface reactions possess a constant growth rate of ∼1.9 Å per cycle at 120 °C. Temperature-dependent growth characterization was performed for these hybrid materials. By increasing the temperature from 65 °C to 145 °C the growth rate decreases from ∼2.5 Å per cycle to ∼1.1 Å per cycle. The presence of expected C-N, C-O and -CH2 moieties in the MLD films were confirmed by Fourier transform infrared (FTIR) spectroscopy. Hafnium nitride and oxide bonds within hybrid thin films were identified by applying X-ray photoelectron spectroscopy (XPS). The results show that the deposited hafnium based organic-inorganic hybrid films contain both Hf – O and Hf – N bonds which enables flexibility, and thus have potential applications for both battery and microelectronics technologies.