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Thin films of Al2O3 are deposited using in situ ultraviolet (UV) light enhanced atomic layer deposition (ALD) with trimethylaluminum and H2O and compared to those deposited using traditional thermal ALD at low temperatures of 45 and 80 °C. Coexposing the UV light with the H2O pulse enhanced the growth-per-cycle and refractive index. Metal/insulator/metal devices using the in situ UV enhanced Al2O3 films demonstrated a reduction in leakage current at ±1 MV/cm by nearly an order of magnitude at a deposition temperature of 45 °C as compared to standard thermal ALD films as well as thermal ALD films that received a postdeposition (in vacuo) UV exposure. In addition, capacitance–voltage behavior of UV enhanced Al2O3 showed a dramatic reduction in capacitance–voltage hysteresis. Taken together, these electrical results suggest that in situ UV enhanced ALD of Al2O3 results in a reduced density of electrically active defects that likely arise from incorporated H and potentially other organic impurities left by incomplete surface reactions. This proof-of-concept approach could enable low temperature fabrication of metal/insulator/metal and other devices in temperature-sensitive applications such as flexible electronics.

The mechanism for growth initiation on the nongrowth surface during area-selective atomic layer deposition (ALD) processes is not well understood. In this study, we examine the ALD of ZrO2 on a SiO2 surface functionalized with alkylated-aminosilane inhibitors delivered from the vapor phase. ZrO2 films were deposited by ALD using tetrakis(ethylmethylamino)zirconium(IV) with H2O as the coreactant. In situ surface infrared spectroscopy shows that aminosilane inhibitors react with almost all the surface —SiOH groups on the SiO2 surface by forming Si—O—Si bonds. In situ four-wavelength ellipsometry shows that no ZrO2 growth occurs on the functionalized SiO2 during the first few ALD cycles, but growth eventually initiates after a few ALD cycles. We speculate that after repeated exposure of the functionalized SiO2 surface to Zr precursors, in the absence of surface —SiOH groups, growth initiates due to either reaction of the precursors with strained Si—O—Si bonds or through a strongly physisorbed state. These reaction pathways are usually not relevant in ALD reactions on the unprotected —SiOH-terminated SiO2 surface due to a higher activation energy barrier, but become relevant on the passivated surface as a result of repeated precursor exposure. Thus, this study highlights the importance of steric blocking of these higher activation energy barrier reaction pathways.

The authors have investigated the surface reaction mechanisms during the atomic layer deposition (ALD) of ZrO2 from tetrakis(ethylmethylamino)zirconium (TEMAZ) with H2O, C2H5OH, and H2O-C2H5OH mixture as the oxygen sources. The ligand-exchange reactions were characterized using in situ attenuated total reflection Fourier transform infrared spectroscopy, and the film growth was recorded using in situ four-wavelength ellipsometry. In the H2O-based ALD process, as expected, surface –OH groups were the reactive sites for TEMAZ, and a growth per cycle (GPC) of ∼1.1 A was obtained at 200 °C. Contrary to previous reports, no film growth was observed for the C2H5OH-based ALD process. During the TEMAZ half-cycle, the –OC2H5-terminated surface obtained after the C2H5OH half-cycle simply underwent ligand exchange without any addition of Zr to the surface, most likely forming Zr[N(CH3)(C2H5)]4 – x[OC2H5]x (1 ≤ x ≤ 3) as the byproduct. Film growth was observed during the ALD of ZrO2 using an H2O-C2H5OH mixture as the oxygen source. The addition of C2H5OH reduced the surface hydroxyl coverage by forming surface ethoxide sites, which did not contribute to film growth. This in turn led to a lower GPC, ∼0.6 A, compared to the TEMAZ/H2O ALD process.The authors have investigated the surface reaction mechanisms during the atomic layer deposition (ALD) of ZrO2 from tetrakis(ethylmethylamino)zirconium (TEMAZ) with H2O, C2H5OH, and H2O-C2H5OH mixture as the oxygen sources. The ligand-exchange reactions were characterized using in situ attenuated total reflection Fourier transform infrared spectroscopy, and the film growth was recorded using in situ four-wavelength ellipsometry. In the H2O-based ALD process, as expected, surface –OH groups were the reactive sites for TEMAZ, and a growth per cycle (GPC) of ∼1.1 A was obtained at 200 °C. Contrary to previous reports, no film growth was observed for the C2H5OH-based ALD process. During the TEMAZ half-cycle, the –OC2H5-terminated surface obtained after the C2H5OH half-cycle simply underwent ligand exchange without any addition of Zr to the surface, most likely forming Zr[N(CH3)(C2H5)]4 – x[OC2H5]x (1 ≤ x ≤ 3) as the byproduct. Film growth was observed during the ALD of ZrO2 using an H2O-C2H5OH mixture as the ...

Novel insight into the mechanisms that govern nucleation during tungsten atomic layer deposition is presented through a detailed analysis using density functional theory. Using the calculated energetics, the authors suggest the most probable series of reactions that lead to monolayer formation on desired growth surfaces, Si(100) and W(110), during sequential doses of WF 6 and SiH 4. From this analysis, they conclude that a relatively high-energy barrier exists for initial nucleation of WF 6 on a silicon substrate; therefore, the system is limited to physical adsorption and is only capable of accessing nucleation pathways once the reaction barrier is energetically accessible. During early doses of WF 6, the initial silicon surface acts as the reductant. Results from this half-reaction provide support for the noncoalesced growth of initial W layers since nucleation is shown to require a 2:1 ratio of silicon to WF 6. In addition, the release of H 2 is significantly favored over HF production leading to the formation of fluorine-contaminated silicon sites; etching of these sites is heavily supported by the absence of fluorine observed in experimentally deposited films as well as the high volatility of silicon-subfluorides. In the second half-reaction, SiH 4 plays the multipurpose role of stripping fluorine atoms from W, displacing any adsorbed hydrogen atoms, and depositing a silicon-hydride layer. Saturation of the previously formed W layer with silicon-hydrides is a crucial step in depositing the consecutive layer since these surface species act as the reductants in the succeeding dose of WF 6. The SiH 4 half-reaction reaches a limit when all fluorine atoms are removed as silicon-subfluorides (SiF xH y) and tungsten sites are terminated with silicon-hydrides. The WF 6 dose reaches a limit in early doses when the reductant, i.e., the surface, becomes blocked due to the formation of a planar network of fluorine-containing tungsten intermediates and in later cycles when the reductant, i.e., adsorbed silicon-hydrides, is etched entirely from the surface. Overall, the calculated energetics indicate that WF xH y, SiF x, and H 2 molecules are the most probable by-products released during the ALD process. Results from this work contribute significantly to the fundamental understanding of atomic layer growth of tungsten using silicon species as reducing agents and may be used as a template for analyzing novel ALD processes.

Molecular layer deposition (MLD) of “metalcones,” including alucone, zincone, titanicone, and others, involves self-limiting half-reactions between organic and organometallic (or metal-halide) reactants. Studies have typically focused on metal precursors reacting with ethylene glycol or glycerol to form the films' polymeric O-M-O-(CHx)y-O-M-O repeat units. The authors report new MLD materials that incorporate tertiary amine groups into the organic linkage. Specifically, reacting triethanolamine (TEA) with either trimethylaluminum or titanium tetrachloride produces TEA-alucone (Al-TEA) and TEA-titanicone (Ti-TEA), respectively, and the amine group leads to unique physical and optical properties. Fourier-transform infrared (FTIR) analysis confirms that the films have prominent C-H, C-N, and M-O-C peaks, consistent with the expected bond structure. When exposed to vapors, including water, alcohol, or ammonia, the Ti-TEA films changed their visible color within minutes and increased physical thickness by >35%. The Al-TEA showed significantly less response. X-ray photoelectron spectroscopy and FTIR suggest that HCl generated during MLD coordinates to the amine forming a quaternary ammonium salt that readily binds adsorbates via hydrogen bonding. The visible color change is reversible, and ellipsometry confirms that the color change results from vapor absorption. The unique absorptive and color-changing properties of the TEA-metalcone films point to new possible applications for MLD materials in filtration, chemical absorption, and multifunctional chemical separations/sensing device systems.