Chemical Vapor Deposition Of Aluminum Research Articles

Structurization and High-Temperature Oxidation Resistance of U8A Steel with Ti–Cr–Al Multi-Component Diffusion Coatings

The phase and chemical composition, structure, and microhardness of multi-component coatings produced by tetanizing (titanium) and titanaluminizing (titanium–aluminum) chemical vapor deposition (CVD) of U8A chromium steel are examined. Both titanizing and titanaluminizing were carried out in powder mixtures of titanium, aluminum, inert additive, and activators at 1050°C for 4 h. It is demonstrated that using the proposed saturation methods results in the formation of multilayer coatings of: (i) chromium and titanium carbides after titanizing; (ii) chromium and titanium carbides; titanium, aluminum, chromium, and iron intermetallides after titanaluminizing. A high concentration of iron, chromium, titanium, and aluminum is discovered on the external surface of the titanaluminized coatings. Both Fe and Cr can be provided by a chromium layer based on chrome carbides. It is demonstrated that the microhardness of multilayer coatings based on chromium and titanium carbides is 16–31.5 GPa and that based on chromium and titanium carbides and intermetallides is 5.8–36 GPa. It is established that, at a temperature of 900°C, the hightemperature oxidation resistance of titanium–chromium–aluminum coatings on U8A steel exceeds that of titanium, titanium–chromium, and chromium coatings.

Amorphous alumina thin films deposited on titanium: Interfacial chemistry and thermal oxidation barrier properties

Ti/Al2O3 bilayer stacks are used as model systems to investigate the role of atomic layer deposition (ALD) and chemical vapor deposition (CVD) to prepare 30–180 nm thick amorphous alumina films as protective barriers for the medium temperature oxidation (500–600 °C) of titanium, which is employed in aeronautic applications. X‐ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), and X‐ray photoelectron spectroscopy (XPS) results show that the films produced from the direct liquid injection (DLI) CVD of aluminum tri‐isopropoxide (ATI) are poor oxygen barriers. The films processed using the ALD of trimethylaluminum (TMA) show good barrier properties but an extensive intermixing with Ti which subsequently oxidizes. In contrast, the films prepared from dimethyl aluminum isopropoxide (DMAI) by CVD are excellent oxygen barriers and show little intermixing with Ti. Overall, these measurements correlate the effect of the alumina coating thickness, morphology, and stoichiometry resulting from the preparation method to the oxidation barrier properties, and show that compact and stoichiometric amorphous alumina films offer superior barrier properties.

Investigation of the kinetics of the chemical vapor deposition of aluminum from dimethylethylamine alane: experiments and computations

AbstractExperiments and computations are performed for the metalorganic chemical vapor deposition (MOCVD) of aluminum (Al) from dimethylethylamine alane (DMEAA). The deposition rate as a function of the substrate temperature and the evolution of the deposition rate along the radius of the susceptor are experimentally determined, in a vertical, warm wall MOCVD reactor operating at 10 Torr, in the temperature range 139 °C‐240 °C. Following previously published mechanism for the decomposition of DMEAA, a predictive 3D model of the process is built, based on the mass, momentum, energy and species transport equations with the aim to simulate the process. Taking into account experimental results it is demonstrated that a volumetric and a surface reaction are responsible for the deposition of Al from DMEAA. For both reactions, first order Arrhenius kinetics are implemented and the kinetic parameters are determined through fitting to the experimental data. The results show satisfactory agreement between experiments and computations for almost the whole temperature range examined. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

UV Photoactivated Room Temperature CVD of Aluminum on Functionalized Self-Assembled Monolayers Adsorbed on Au

We have investigated the selective photoactivated room temperature chemical vapor deposition (CVD) of aluminum (Al) on functionalized self-assembled monolayers adsorbed on Au. The CVD precursor employed is trimethyl aluminum (TMA). Using a deuterium arc lamp we demonstrate that the rate of the Al film growth is approximately twice that observed for nonphotoactivated Al chemical vapor deposition (CVD) using TMA. At the wavelengths employed, the photolysis of TMA leads to the dissociation of the TMA dimer to its monomer followed by successive release of methyl groups to form (CH(3))(3-x)Al. The photogenerated (CH(3))(3-x)Al species react with -OH- and -COOH-terminated SAMs but not -CH(3)-terminated SAMs. Using these reactions we demonstrate that aluminum can be selectively deposited on -CH(3)/-COOH-patterned SAMs. The possible reaction mechanisms involved in the Al film growth are discussed. These results indicate that photoactivated CVD (laser CVD) processes are suitable for the deposition of stable films of metals and other materials on organic films.

Fourier transform infrared studies of the aluminum chemical vapor deposition using aluminum boro-hydride trimethylamine

The chemical species exiting chamber after an aluminum chemical vapor deposition process using aluminum boro-hydride trimethylamine (ABHTMA) as a precursor were studied with a Fourier transform infrared spectroscope, which was installed in the exhaust line of the chamber. The variation in the absorption spectra of C–H, C–N, B–H, Al–H and Al–N stretching features and the morphology of the deposited films were investigated with varying temperatures using ABHTMA in two different states (normal and decomposed). The dissociation or recombination of ABHTMA in the gas phase and on the surface during deposition resulted in the change in B–H and Al–H peaks. With the information about the peaks, we could measure in real time the purity of ABHTMA and the degree of reaction in the gas phase as a function of deposition conditions.

Real-Time Evaluation of Aluminum Borohydride Trimethylamine for Aluminum Chemical Vapor Deposition

The chemical species in gas phase and on the surface of aluminum borohydride trimethylamine (ABHTMA) for aluminum chemical vapor deposition as a function of the hot-wall temperature and the chamber pressure were studied using two kinds of Fourier transform IR spectroscopes installed at the end of the chamber. The absorbance of Al–H, B–H, C–H, and C–N stretching features of ligands in ABHTMA in the gas phase and on the surface was sensitive to the variation of analysis conditions. The area ratio of integrated absorbance of Al–H and B–H stretching features located at the different position could estimate the dissociation rate of the ABHTMA, which was abruptly changed in the range of . With these results, the temperature dependence of the film composition and quality could be explained. Additionally, the stabilities of the chemical species were investigated using density functional theory calculations. The ABHTMA was found to be the most stable molecule when trimethylamine was rich and borane and alane were close in their concentrations. Borane-trimethylamine was also found to be produced in alane-poor conditions as a by-product.

Room-temperature Chemical Vapor Deposition of Aluminum and Aluminum Oxides on Alkanethiolate Self-Assembled Monolayers

We have investigated the reaction of trimethylaluminum (TMA) with −CH3, −OH, and −COOH terminated self-assembled monolayers (SAMs) adsorbed on Au, using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. TMA is a well-known atomic layer deposition precursor that is employed commercially to deposit compound semiconductors, alumina, and nitrides. We demonstrate that TMA can be employed to deposit both alumina and aluminum on SAMs at room temperature. TMA reacts with −OH and −COOH terminated SAMs to form a surface-bound dimethyl aluminum complex but does not react with −CH3 terminal groups. If deposition is performed in a nitrogen-purged glovebox, an alumina film is grown on −CH3, −OH and −COOH terminated SAMs. The alumina film can be removed from −CH3 terminated SAMs by rinsing with organic solvents. However if the base pressure of the deposition chamber is below 10-8 Torr, a metallic Al overlayer is selectively deposited on −OH and −COOH terminated SAMs, and no reaction is...

Vapor deposition of platinum alloyed nickel aluminide coatings

Platinum-doped NiAl coatings are widely used to increase the oxidation resistance of superalloys. These coatings are usually synthesized by a solid state reaction-diffusion process conducted at high temperature. It requires the chemical vapor deposition of aluminum on a nickel rich superalloy substrate that has been pre-coated with several microns of electrodeposited platinum. Here, we show that an electron beam directed vapor deposition (EB-DVD) technique can be used to deposit well bonded, structurally and chemically homogeneous NiAlPt bond coats of any composition onto superalloy substrates. The approach utilized a high voltage, rapid scan frequency electron beam to independently heat elemental nickel, aluminum and platinum melt pools to create three closely spaced vapor plumes. These vapor plumes were then entrained in an inert gas jet flow, which mixed and directed them to a substrate. By adjusting the electron beam current applied to each elemental source, homogeneous, dense, Pt alloyed β-phase NiAl coatings could be synthesized at substrate temperatures of 1050 °C. The width of the substrate–coating interdiffusion zone was controlled by the deposition temperature and time.

Chemical vapor deposition of aluminum from methylpyrrolidine alane complex

Chemical vapor deposition of aluminum from a recently developed precursor, methylpyrrolidine alane complex, has been studied. Aluminum films deposited on conducting surfaces (titanium nitride, copper, gold), but not on insulating surfaces (silicon, silicon dioxide, glass) at low substrate temperatures, showing deposition selectivity, while the deposition selectivity was lost at high substrate temperatures (> 210 °C). Al deposition rates on TiN and Cu were very close, but much higher than on Au. Deposition rates on all conducting substrates increased with the temperature and reached maximum at ∼180 °C. Al films deposited on as-sputtered TiN or Cu have no preferred orientations. Al–Au alloys and intermetallics were observed in the films deposited on Au. Surface morphology observation revealed that the film growth on TiN or Cu is different from that on Au. The surface roughness of Al films increased with the deposition time or the film thickness.

NiAl bond coats made by a directed vapor deposition approach

Intermetallic, nickel aluminide alloys are widely used as bond coat materials in thermal barrier coating systems applied to nickel base super alloy components. They are usually synthesized by a solid-state reaction–diffusion heat treatment following the chemical vapor deposition of aluminum on the nickel rich substrate. Here, an electron beam directed vapor deposition (EB-DVD) technique is used to simultaneously evaporate nickel and aluminum and then reactively deposit NiAl bond coats that are structurally and chemically homogeneous and well bonded to the superalloy substrate. The approach utilizes individual nickel and aluminum sources placed within a rarefied helium gas jet with flow conditions that promote vapor phase intermixing. By adjusting the electron beam current applied to each elemental source, we show that the coating layer composition can be precisely controlled. Fully dense, homogeneous, β-phase NiAl coating layers with a relatively sharp compositional interface with the substrate have been deposited. The extent of the substrate interdiffusion zone is controlled by the deposition conditions.

Underlayer work function effect on nucleation and film morphology of chemical vapor deposited aluminum

The dependence of early stage of dimethylaluminum hydride (DMAH)-sourced aluminum chemical vapor deposition on underlayer material was investigated. Identical process conditions were used to deposit the aluminum on TiN, TaN and Ti-W surfaces. Surface coverage and particle densities of aluminum deposited on TiN were much greater than those deposited on Ti-W or TaN. Work function measurements performed on the three metal surfaces suggest that the difference in nucleation rate on TiN compared to TaN and Ti-W is due its increased ability to donate electrons to the DMAH decomposition process.

The Surface Reaction Mechanism on Al(111)

Abstract A surface reaction mechanism in the aluminum chemical vapor deposition (Al-CVD) method using dimethylaluminum hydride (DMAH) as the material gas has been studied using quantum chemical methods. Density functional theory (DFT) and a cluster model were used to calculate the potential energies and the structures of adsorbates and transition states of surface reactions. We have obtained the result that the hydrogen molecule and trimethylaluminum (TMA) are easily produced, while methane cannot be formed as a reaction product of Al-CVD because of the large barrier height, although the latter reaction path is thermodynamically accessible.

Density functional study on the adsorption of DMAH on hydrogen terminated Si(111) surfaces

We have studied theoretically the initial process of aluminum chemical vapor deposition using dimethylaluminum hydride as a source gas. In particular, the reaction mechanism of selective deposition on hydrogen terminated Si(111) surfaces is investigated based on quantum chemical calculations using density functional theory. In addition to an experimentally suggested reaction model that produces a methane molecule, we have found that (1) there is a path that produces a hydrogen molecule; and (2) rather high activation energies are needed for these reactions, the epitaxial growth of aluminum on the hydrogen terminated silicon surface.

Toward the Improvement of the Microstructure of Chemical Vapor Deposited Aluminum on Silicon Carbide

This paper presents results on the chemical vapor deposition of aluminum on silicon carbide starting from triisobutylaluminum. The deposited films show important systematic trends in surface roughness and porosity. Considering literature information on the deposition of aluminum on silicon, pretreatments of the deposition surface with hydrofluoric acid and/or titanium tetrachloride have been tested. They lead to films with a smoother morphology and stronger adhesion with the substrate than in the case of an untreated surface. Different heteroelements are observed at the interface under these conditions. A short thermal activation of the nucleation process following these pretreatments does not unambiguously improve the characteristics of the aluminum films. The obtained results can be considered for the modification of surface characteristics of silicon carbide particles which are used in discontinuously reinforcement aluminum composite materials with the aim to improve their mechanical properties and corrosion resistance as well as their fabrication process. © 2001 The Electrochemical Society. All rights reserved.

Aluminum chemical vapor deposition reaction of dimethylaluminum hydride on TiN studied by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry

To understand the nucleation mechanisms of aluminum film during chemical vapor deposition (CVD), the reactions of dimethylaluminum hydride (DMAH) with oxidized TiN and Si surfaces were studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was observed that DMAH exposure reduced the native oxide on the TiN surface, resulting in a clean TiN surface. The reduction of the native oxide and the deposition of Al on the TiN surface were enhanced with increasing DMAH dose. In contrast with the reaction on the TiN surface, no reduction of native oxide by DMAH exposure was observed on the Si surface except at the uppermost surface level analyzed by TOF-SIMS. The amount of Al deposited on the oxidized Si surface was less than that on the oxidized TiN surface under the same experimental conditions and was largely independent of the amount of DMAH dose over the studied range. The reduction of native oxide and the appearance of a clean TiN surface are thought to be important in accounting for the nucleation mechanism and the improved surface morphology of Al film deposited on TiN surfaces using the CVD process.

Elementary Surface Reaction Simulation of Aluminum Chemical Vapor Deposition from Dimethylaluminumhydride Based on Ab Initio Calculations: Theoretical Process Optimization Procedure (2)

This work demonstrates how to develop a qualitative surface reaction model to an elementary surface reaction simulation of deposition for the quantitative examination of model validity. Chemical vapor deposition of Al (Al-CVD) from dimethylaluminumhydride (DMAH) is examined as an example of this method. The surface reaction model of DMAH was deduced from ab initio cluster model calculations and experimental measurements of reaction products. Rate constants of all the elementary reactions were estimated for an elementary reaction model. Transition-state theory enabled the calculation of rate constants using the activation energies obtained from ab initio calculations. Entropy terms, however, were estimated by using an empirical method to reduce the computational effort. This approach minimized the ab initio calculations required to form a reaction data set. Simulated deposition profiles were compared with experimental data for Al-CVD in a tube reactor. Good agreement between the results of simulations and experiments indicate the possibility of constructing surface-reaction data sets for CVD process simulations based on ab initio quantum-chemical calculations.

Quantum chemical study of aluminum CVD reaction for titanium nitride (111) surface with terminal fluorine

Reaction mechanisms and interface structures in aluminum (Al) chemical vapor deposition (CVD) have been investigated in terms of the surface termination models for TiN by ab initio quantum chemical approach. The B3LYP density functional calculations and coupled-cluster calculations were carried out by using the local structural models in order to investigate reaction mechanisms, and we found Al can be deposited on F-terminated TiN (111) surface via the substitution of hydrogen for terminal fluorine. Energetics of the reaction processes has also been discussed by the local density approximation (LDA) with the periodic boundary models. The result that total reaction enthalpy is exothermic has been obtained for the local structural models calculations and the periodic boundary calculations. In particular, a series of reactions by the successive attack of AlH3 proceed with no energy barrier for the periodic models.

Material and process studies in the integration of plasma-promoted chemical-vapor deposition of aluminum with benzocyclobutene low-dielectric constant polymer

The integration of low-temperature plasma-promoted chemical-vapor deposition (PPCVD) of aluminum, using dimethylethylamine-alane (DMEAA) as the source precursor, with benzocyclobutene (BCB) low-k polymers has been investigated to explore the feasibility of BCB-based Al metallization for sub-quarter-micron integrated circuitry. The study examined the thermal, chemical, and structural compatibility of PPCVD Al interconnects with the BCB polymer, including the feasibility of barrierless aluminum–BCB multilevel metallization stacks. Studies were conducted on a range of BCB surfaces, consisting of untreated (UNT), reactive-ion etched (RIE), and SiO2-capped BCB (SiO2–BCB) surfaces. The purpose was to mimic the actual BCB surfaces encountered during damascene processing. Each BCB surface was treated with argon or hydrogen plasma prior to aluminum processing to ensure reduction in the barrier to aluminum formation, leading potentially to enhanced Al nucleation mechanisms. In all cases, the direct deposition of Al on BCB films via PPCVD was successfully demonstrated, with the RIE-BCB substrate providing the best Al nucleation characteristics. Compositional analyses of the Al films indicated that carbon and nitrogen contaminants, which could have resulted from the dissociation reaction of the DMEAA molecule, were below the detection limits of the techniques used. Alternatively, oxygen inclusion was highly dependent on the chemical state and type of plasma treatment of the BCB surface, with only the PPCVD Al on plasma pretreated RIE BCB exhibiting bulk oxygen levels below the detection limits of x-ray photoelectron spectroscopy. Oxygen incorporation in the PPCVD Al films on UNT BCB and SiO2–BCB could be attributed to the diffusion of oxygen through intergranular voids upon air exposure, resulting in increased Al film resistivity. In all cases, the study indicated that an appropriate diffusion barrier/adhesion promoter is required to ensure viable BCB integration in Al metallization schemes.

New molecular compound precursor for aluminum chemical vapor deposition

A new type of precursor for aluminum chemical vapor deposition (Al-CVD) has been developed by mixing dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA). The new precursor has proven itself to be effective for Al-CVD, where a good selectivity between the Si and the SiO 2 mask, a 3.0 μΩ cm resistivity and a pure Al film with low C and O contamination levels (under 100 ppm) were achieved. Quadrupole mass and infrared absorption analysis have shown that the precursor contains a new molecular compound, consisting of a DMAH monomer and a TMA monomer. The mixture has lower viscosity than DMAH and can be easily bubbled for a stable precursor vapor supply.

Superiority of DMAH to DMEAA for al CVD technology

The superiority of dimethylaluminumhydride [(CH 3) 2AlH, DMAH] to dimethylethylaminealane [AlH 3N(CH 3) 2(C 2H 5), DMEAA] has been investigated from the view point of aluminum chemical vapor deposition (Al CVD) technology in ULSI manufacturing. Both DMAH and DMEAA have the same filling capability such as surface morphology and step coverage. For deposition reproducibility, the smaller activation energy is more suitable for manufacturing. The activation energy of Al deposition is found to be 0.38 [eV] for DMAH and 0.74 [eV] for DMEAA. These results mean the reproducibility of Al thickness using DMAH is superior to that using DMEAA. For safe storage and precise precursor delivery, the precursor should be chemically stable. From the results of measuring the pressure increase in vessel, it has shown that DMAH has superior chemical stability to DMEAA. Manufacturing apparatus such as Al CVD cluster module requires the deposition selectivity that is defined as Al deposition only on the desired areas of wafer surface and not on any parts of cluster module. Using DMAH, Al is deposited on barrier metal surface of silicon wafer, while Al is not deposited on the sealed anodic oxidized aluminum or the synthetic quartz. DMAH has shown excellent selectivity in comparison with DMEAA. Therefore, DMAH is superior to DMEAA as a precursor for the Al CVD technology in ULSI manufacturing.