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During area-selective atomic layer deposition (ALD) based on growth inhibitors, nucleation eventually occurs as the metal precursor reacts with the surface through secondary pathways. We show that ALD of Al

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.

Small-molecule inhibitors are promising for achieving area-selective atomic layer deposition (ALD) due to their excellent compatibility with industrial processes. In this work, we report on growth inhibition during ALD of Al

AlOx was selectively deposited on top of SiCOH in 32 nm pitch Cu-SiCOH pattern to form a Fully Aligned Via (FAV) test structure. Selective deposition process performance and its integration into the 5nm BEOL FAV structure were evaluated. The selective AlOx deposition involves multistep process including surface treatment, selective Self-Aligned Molecules (SAM) bonding to inhibit Cu metal surface, and the selective growth of AlOx on top of SiCOH dielectric using Chemical vapor deposition process with various precursors and process conditions below 300°C. Thin selective AlOx of 4–6 nm thickness show excellent selectivity on SiCOH over Co capped Cu-SiCOH patterned structures with various spacing. The Via Chain electrical yields were measured on 32 nm pitch structures by AlOx selective deposition and are comparable to the established FAV process by Cu wet recess. This indicates that the Selective AlOx deposition process is highly selective on SiCOH dielectric surface without defect formation in the Co Capped Cu surfaces.

As the semiconductor industry progresses toward more complex multilayered devices with ever smaller features, accurately aligning these layers with respect to each other has become a bottleneck in the advancement to smaller transistor nodes. To avoid alignment issues, area-selective atomic layer deposition (ALD) can be employed to deposit material in a self-aligned fashion. Previously, we demonstrated area-selective ALD of SiO2 using three-step (i.e., ABC-type) ALD cycles comprising an acetylacetone (Hacac) dose (step A), a bis(diethylamino)silane precursor dose (step B), and an O2 plasma exposure (step C). In this work, the mechanisms of the removal and reapplication of the inhibitor molecules during area-selective ALD were studied, with the aim of enhancing the selectivity of the process. In situ infrared spectroscopy shows that the O2 plasma exposure does not completely remove the adsorbed Hacac species (i.e., acac adsorbates) at the end of the cycle. The persisting species were found to contain fragments of Hacac molecules, which hinder subsequent inhibitor adsorption in the next ALD cycle, and thereby contribute to a loss in selectivity. Alternatively, it was found that an H2 plasma is able to completely remove all acac species from the surface. An improvement in selectivity was achieved by using a four-step ALD cycle that includes an H2 plasma step, allowing the nucleation delay to be prolonged from 18 ± 2 to 30 ± 3 ALD cycles. As a result, 2.7 ± 0.3 nm SiO2 can be deposited with a selectivity of 0.9, whereas only 1.6 ± 0.2 nm can be achieved without the H2 plasma step. This work shows that the addition of a dedicated inhibitor removal step before the reapplication of the inhibitors can significantly improve the selectivity.

The semiconductor industry faces a tremendous challenge in the development of a transistor device with sub-10 nm complex features. Self-limiting atomic layer etching (ALE) is essential for enabling the manufacturing of complex transistor structures. In this study, we demonstrated a thermally driven ALE process for tungsten (W) using sequential exposures of O2 and WF6. Based on the insight gained from the previous study on TiO2 thermal ALE, we proposed that etching of W could proceed in two sequential reaction steps at 300 °C: (1) oxidation of metallic tungsten using O2 or O3 to form WO3(s) and (2) formation and removal of volatile WO2F2(g) during the reaction between WO3(s) and WF6(g). The O2/WF6 etch process was experimentally studied using a quartz crystal microbalance (QCM). We find that both the O2 and WF6 ALE half reactions are self-limiting, with an estimated steady-state etch rate of ∼6.3 A/cycle at 300 °C. We also find that etching of W proceeds readily at 300 °C, but not at temperatures lower tha...

Controlled thin film etching is essential for further development of sub-10 nm semiconductor devices. Vapor-phase thermal etching of oxides is appealing for achieving highly conformal etching of high aspect ratio features. We show that tungsten hexafluoride (WF6) can be used to selectively etch amorphous TiO2 films versus other oxides including Al2O3. Chemical vapor etching (CVE) of TiO2 by WF6 was studied with quartz crystal microbalance (QCM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and thermodynamic modeling. The XPS results show evidence for a WOxFy layer that forms on of the TiO2 films during the etch process, which may act as a surfactant layer to help enable fluorination of the TiO2. Direct CVE of TiO2 by WF6 is strongly temperature dependent, where etching proceeds readily at 220 °C, but not at T ≤ 170 °C. This is consistent with thermodynamic modeling showing that the etching rate is determined by the volatilization of metal fluoride and WF2O2 product species. We also ...

Metal–organic frameworks (MOFs) are chemically functionalized micro- and mesoporous materials with high surface areas and are attractive for multiple applications including filtration, gas storage, and catalysis. Postsynthetic modification (PSM), via solution or vapor-based techniques, is a way to impart additional complexity and functionality into these materials. There is a desire to shift toward vapor-phase methods in order to ensure more controlled modification and more efficient reagent and solvent removal from the modified MOF material. In this work we explore how the metal precursors titanium tetrachloride (TiCl4) and trimethylaluminum (TMA), commonly used in atomic layer deposition, react with UiO-66-NH2 MOF. Using in situ quartz crystal microbalance (QCM) and Fourier transform infrared spectroscopy (FTIR) at 150 and 250 °C, we find that the ALD precursors react with μ3-OH hydroxyl and μ3-O bridging oxygen groups on Zr6 nodes, as well as oxygen from carboxylate linker groups. The reactions occur p...

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.

Substrate-dependent nucleation during CVD has been heavily studied, and several strategies for selective growth are known. Compared to CVD, atomic layer deposition generally allows more precise control over surface reactions, but to date, the most successful selective-area deposition processes are based on CVD and not ALD mechanisms. Most ALD processes have an inherent substrate bias during nucleation, leading to problems in process development. Better understanding of this native substrate bias can be used to promote and enhance selective-area ALD. We have studied nucleation of ALD metals and dielectrics to promote native substrate bias and improve selectivity. Tungsten ALD using WF6/SiH4 onto SiO2 proceeds when surface Si-H (from SiH4) begins to form, allowing WF6 reduction to W and elimination of SiF4. We hypothesized that the introduction of a H2 or H-plasma exposure into the ALD sequence may help remove Si from the SiO2, which could extend the nucleation delay on SiO2, while not affecting W growth on Si. Using ellipsometry, XPS, high resolution SEM and in-situ quadrupole mass spectrometry we find that a H2 exposure during W ALD on ex-situ prepared SiO2 decreased the rate of W nucleation compared to growth without the H2 step, effectively increasing the selectivity window. Also, using XPS in-situ FTIR, we explored how various oxide ALD precursors react with different surfaces. For example, doing TiO2 ALD using TiCl4 with titanium isopropoxide as the oxygen source (instead of water), we find that eliminating water slows the substrate oxidation in areas where TiO2 deposition is not desired, thereby promoting the nucleation delay to as much as 200 ALD cycles at 170°C, resulting in a maximum selectivity thickness, ts,max ≈ 2–3 nm. We will discuss other details of initial reactions obtained from in–situ infrared spectroscopy, quartz crystal microbalance, TEM, SEM, ellipsometry and other tools to better understand and improve “inherent” substrate selective ALD of metals and metal oxides.

Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

Area-selective thin film deposition is expected to be important in achieving sub-10 nm semiconductor devices, enabling feature patterning, alignment to underlying structures, and edge definition. Atomic layer deposition (ALD) offers advantages over common chemical vapor deposition methods, such as precise thickness control and excellent conformality. Furthermore, several ALD processes show inherent propensity for substrate-dependent nucleation. For example, tungsten ALD using SiH4 (or Si2H6) and WF6 is more energetically favorable on Si than on SiO2, but selectivity is often lost after several ALD cycles. We show that modifying the W ALD process chemistry can decrease the W nucleation rate on SiO2, thereby expanding the ALD “selectivity window”. Specifically, we find that adding H2 during the WF6 dose step helps passivate SiO2 against W nucleation without modifying W growth on silicon. Surface characterization confirms that H2 promotes fluorine passivation of SiO2, likely through surface reactions with HF...

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 ...

The semiconductor industry faces a tremendous challenge in the development of a transistor device with sub-10 nm complex features. Self-limiting atomic layer etching (ALE) is essential for enabling the manufacturing of complex transistor structures. In this study, we demonstrated a thermally driven ALE process for tungsten (W) using sequential exposures of O

Thin ∼ 20 nm conformal poly(3,4-ehylenedioxythiophene) (PEDOT) films are incorporated in highly conductive mesoporous indium tin oxide (m-ITO) by oxidative molecular layer deposition (oMLD). These three-dimensional catalytic/conductive networks are successfully employed as Pt-free cathodes for dye-sensitized solar cells (DSSCs) with open circuit voltage equivalent to Pt cathode devices. Thin and conformal PEDOT films on m-ITO by oMLD create high surface area and efficient electron transport paths to promote productive reduction reaction on the PEDOT film. Because of these two synergetic effects, PEDOT-coated m-ITO by oMLD shows power conversion efficiency, 7.18%, comparable to 7.26% of Pt, and higher than that of planar PEDOT coatings, which is 4.85%. Thus, PEDOT-coated m-ITO is an exceptional opportunity to compete with Pt catalysts for low-cost energy conversion devices.

Integration of metal–organic frameworks (MOFs) on textiles shows promise for enabling facile deployment and expanding MOF applications. While MOFs deposited on flat substrates can show relatively smooth surface texture, most previous reports of MOFs integrated on fibers show poor conformality with many individual crystal domains. Here we report a new low-temperature (

Metal-organic frameworks (MOFs) are chemically functionalized micro- and mesoporous materials with high surface areas and are attractive for multiple applications including filtration, gas storage, and catalysis. Postsynthetic modification (PSM), via solution or vapor-based techniques, is a way to impart additional complexity and functionality into these materials. There is a desire to shift toward vapor-phase methods in order to ensure more controlled modification and more efficient reagent and solvent removal from the modified MOF material. In this work we explore how the metal precursors titanium tetrachloride (TiCl

Patterned, chemically reactive poly(methyl)methacrylate can act as a chemical “sponge” via Lewis acid/base adduct formation with metal-organic reactants commonly used in atomic layer deposition. Extended reactant exposures saturate the reactant within the polymer, and subsequent oxidation removes the polymer and converts the saturated reactant to a metal oxide film that precisely mimics the lateral dimensions of the original polymer. Resulting oxide thickness scales with the starting polymer thickness. Regions without polymer are coated with less than 1 nm of metal oxide. Repeatable nanoscale features are formed simultaneously and uniformly across a 150 mm diameter silicon wafer.

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.

Rapid room-temperature synthesis of metal-organic frameworks (MOFs) is highly desired for industrial implementation and commercialization. Here we find that a (Zn,Cu) hydroxy double salt (HDS) intermediate formed in situ from ZnO particles or thin films enables rapid growth (1 min) of HKUST-1 (Cu3(BTC)2) at room temperature. The space-time-yield reaches3 × 10(4) kg·m(-3)·d(-1), at least 1 order of magnitude greater than any prior report. The high anion exchange rate of (Zn,Cu) hydroxy nitrate HDS drives the ultrafast MOF formation. Similarly, we obtained Cu-BDC, ZIF-8, and IRMOF-3 structures from HDSs, demonstrating synthetic generality. Using ZnO thin films deposited via atomic layer deposition, MOF patterns are obtained on pre-patterned surfaces, and dense HKUST-1 coatings are grown onto various form factors, including polymer spheres, silicon wafers, and fibers. Breakthrough tests show that the MOF-functionalized fibers have high adsorption capacity for toxic gases. This rapid synthesis route is also promising for new MOF-based composite materials and applications.

Area-selective thin film deposition is expected to be important for advanced sub-10 nanometer semiconductor devices, enabling feature patterning, alignment to underlying structures, and edge definition. Several atomic layer deposition (ALD) processes show inherent propensity for substrate-dependent nucleation. This includes tungsten ALD (W-ALD) which is more energetically favorable on Si than on SiO2. However, the selectivity is often lost after several ALD cycles. We investigated the causes of tungsten nucleation on SiO2 and other "non-growth" surfaces during the WF6/SiH4 W-ALD process to determine how to expand the "selectivity window." We propose that hydroxyls, generated during the piranha clean, act as nucleation sites for non-selective deposition and show that by excluding the piranha clean or heating the samples, following the piranha clean, extends the tungsten selectivity window. We also assessed how the W-ALD precursors interact with different oxide substrates though individual WF6 and SiH4 pre-exposures prior to W-ALD deposition. We conclude that repeated SiH4 pre-exposures reduce the tungsten nucleation delay, which is attributed to SiH4 adsorption on hydroxyl sites. In addition, oxide surfaces were repeatedly exposed to WF6, which appears to form metal fluoride species. We attribute the different tungsten nucleation delay on Al2O3 and TiO2 to the formation of nonvolatile and volatile metal fluoride species, respectively. Through this study, we have increased the understanding of ALD nucleation and substrate selectivity, which are pivotal to improving the selectivity window for W-ALD and other 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.

While metal-organic frameworks (MOFs) show great potential for gas adsorption and storage, their powder form limits deployment opportunities. Integration of MOFs on polymeric fibrous scaffolds will enable new applications in gas adsorption, membrane separation, catalysis, and toxic gas sensing. Here, we demonstrate a new synthesis route for growing MOFs on fibrous materials that achieves high MOF loadings, large surface areas and high adsorptive capacities. We find that a nanoscale coating of Al2O3 formed by atomic layer deposition (ALD) on the surface of nonwoven fiber mats facilitates nucleation of MOFs on the fibers throughout the mat. Functionality of MOFs is fully maintained after integration, and MOF crystals are well attached to the fibers. Breakthrough tests for HKUST-1 MOFs [Cu3(BTC)2] on ALD-coated polypropylene fibers reveal NH3 dynamic loadings up to 5.93 0.20 mol/kg (MOF+fiber). Most importantly, this synthetic approach is generally applicable to a wide range of polymer fibers (e. g., PP, PET, cotton) and MOFs (e.g., HKUST-1, MOF-74, and UiO-66).