Dimethylaluminum Hydride Research Articles

Effects of carbon impurity in ALD-Al2O3 film on HAXPES spectrum and electrical properties of Al2O3/AlGaN/GaN MIS structure

In this study, the effects of carbon impurity in the atomic layer deposited-Al2O3 film on the hard X-ray photoelectron spectroscopy (HAXPES) spectra and the electrical properties of metal–insulator–semiconductor (MIS) structure were measured. The carbon concentration in the Al2O3 film was adjusted by varying the deposition conditions (precursor: trimethylaluminum, Al(CH3)3, or dimethylaluminum hydride, Al(CH3)2H, oxidant, and deposition temperature) in the atomic layer deposition process. The HAXPES measurements revealed the correlation between full width at half maximum (FWHM) of Al 1 s and O 1 s spectra and the carbon concentration in the Al2O3 film. Furthermore, the negative charges in the Al2O3 film could change the FWHM, attributed to the carbon impurity. The correlation between the carbon concentration and the electrical characteristics of the Al2O3/AlGaN/GaN MIS structure was analyzed. The interface state density and the effective charge density were dependent on the carbon concentration in the Al2O3 film.

Bias stress and humidity exposure of amorphous InGaZnO thin-film transistors with atomic layer deposited Al2O3 passivation using dimethylaluminum hydride at 200 °C

Highly reliable amorphous InGaZnO (a-IGZO) (In:Ga:Zn:O = 2:2:1:7) thin-film transistors (TFTs) were fabricated with 25 nm-thick Al2O3 passivation deposited by atomic layer deposition (ALD) using dimethylaluminum hydride (DMAH). Al2O3 passivation deposited at various temperatures was studied to determine its effect on TFT behavior following gate bias stress and humidity exposure. The Al2O3-passivated a-IGZO TFTs demonstrated an on-off current ratio (Ion/Ioff) of ~108 and linear mobility (µ) of 9 to 13 cm2 V−1 s−1. An optimum ALD temperature of 200 °C was demonstrated to result in Al2O3-passivated a-IGZO TFTs with very small on-voltage shifts of 0.3 V and −2.7 V against positive bias stress and negative bias illumination stress (NBIS) after 10 000 s of stress time. Furthermore, negligible degradation was observed after humidity exposure. The results of x-ray photoelectron spectroscopic analysis of the O 1s spectra showed the highest peak area ratio for metal–oxygen (M–O) bonding and lowest metal–oxygen vacancy (M–Vo) bonding, relating to the least amount of trap sites both in the bulk region of a-IGZO and near the interface of Al2O3/a-IGZO, for the device passivated at 200 °C. It was also found that at a low deposition temperature (⩽100 °C), low-density Al2O3 was formed with high carbon contamination and hydrogen while at a high deposition temperature (⩾300 °C), high hydrogen concentration was also present in high-density Al2O3. The hydrogen incorporation from Al2O3 passivation to a-IGZO channel creates bulk defects and trap sites as well as in the interface of a-IGZO and SiO2 gate insulator. At 200 °C, high quality Al2O3 passivation was achieved with high density and reduced impurities leading to improved device reliability. These results can be applied to long term sustained device operations which are reliable against different stresses.

Influence of carbon impurities and oxygen vacancies in Al2O3 film on Al2O3/GaN MOS capacitor characteristics

Effects of carbon impurities and oxygen vacancies in Al2O3 film on the characteristics of Al2O3/GaN MOS capacitors were studied using the different atomic layer deposition (ALD) precursor and high-pressure water vapor annealing (HPWVA). Trimethyl aluminum (TMA: Al(CH3)3) and dimethyl aluminum hydride (DMAH: Al(CH3)2H) were used as ALD precursors to control the carbon impurities. On the other hand, oxygen vacancies in Al2O3 film were suppressed using the HPWVA. The DMAH precursor reduced the concentration of carbon impurities in the ALD Al2O3 film. It was found that the interface trap density (Dit) was mainly affected by the carbon impurities rather than the oxygen vacancies at the Al2O3/GaN interface. On the other hand, voltage stress induced flat band voltage (VFB) shift was attributed to both the carbon impurities and the oxygen vacancies.

Dimethylaluminum hydride for atomic layer deposition of Al2O3 passivation for amorphous InGaZnO thin-film transistors

Atomic layer deposition (ALD) of Al2O3 using dimethylaluminum hydride (DMAH) was demonstrated as an effective passivation for amorphous InGaZnO thin-film transistors (TFTs). Compared with the most commonly used precursor, trimethylaluminum, TFTs fabricated with DMAH showed improved stability, resulting from the lower amount of oxygen vacancies, and hence fewer trap sites, as shown by X-ray photoelectron spectroscopy (XPS) depth profiling analysis. We found that prolonged plasma exposure during ALD can eliminate the hump phenomenon, which is only present for DMAH. The higher Al2O3 deposition rate when using DMAH is in line with the requirements of emerging techniques, such as spatial ALD, for improving fabrication throughput.

Reactivity of Yttrium Carboxylates Toward Alkylaluminum Hydrides

Yttrocene-carboxylate complex [Cp*2Y(OOCAr(Me))] (Cp*=C5Me5, Ar(Me) =C6H2Me3-2,4,6) was synthesized as a spectroscopically versatile model system for investigating the reactivity of alkylaluminum hydrides towards rare-earth-metal carboxylates. Equimolar reactions with bis-neosilylaluminum hydride and dimethylaluminum hydride gave adduct complexes of the general formula [Cp*2Y(μ-OOCAr(Me))(μ-H)AlR2] (R=CH2SiMe3, Me). The use of an excess of the respective aluminum hydride led to the formation of product mixtures, from which the yttrium-aluminum-hydride complex [{Cp*2Y(μ-H)AlMe2(μ-H)AlMe2(μ-CH3)}2] could be isolated, which features a 12-membered-ring structure. The adduct complexes [Cp*2Y(μ-OOCAr(Me))(μ-H)AlR2] display identical (1)J(Y,H) coupling constants of 24.5 Hz for the bridging hydrido ligands and similar (89)Y NMR shifts of δ=-88.1 ppm (R=CH2SiMe3) and δ=-86.3 ppm (R=Me) in the (89)Y DEPT45 NMR experiments.

Preparation of Al-doped hydrogenated nanocrystalline cubic silicon carbide by VHF-PECVD for heterojunction emitter of n-type crystalline silicon solar cells

Al-doped p-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) thin films were successfully deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) using dimethylaluminum hydride (DMAH) as an Al source. A high dark conductivity of 6.88×10−4S/cm was obtained for a 27nm-thick film under high H2/MMS and plasma power conditions. We applied this optimized film to a heterojunction emitter of n-type c-Si solar cells. The solar cell showed high fill factor of 0.756. The internal quantum efficiency in the short wavelength region was improved to 0.87 with decreasing the thickness of a buffer layer.

Metal-organic chemical vapor deposition of aluminium oxynitride from propylamine–dimethylaluminium hydride and oxygen: growth mode dependence and performance optimization

AlOxNy thin films have been successfully obtained by new metal-organic chemical vapor deposition (MOCVD) chemistry using propylamine–dimethylaluminium hydride (DMAH) mixture and O2 as precursor and oxidant, respectively. Attention has been paid to investigate the MOCVD behavior of this new precursor as a function of the process parameters in the MOCVD of AlOxNy films. A new growth mode based on atomic layer deposition (ALD) mechanism has been carried out to optimize the MOCVD process. Compared to the normal mode, suppressed interface growth and improved electrical properties have been observed for ALD-mode-derived samples. Electrical measurements based on post-deposition annealing (PDA) and forming gas annealing (FGA) processed samples have indicated that better electrical performance are achieved in FGA-derived AlOxNy films. Based on analysis and observations, it can be concluded that ALD-mode-derived AlOxNy films grown by ALD MOCVD chemistry demonstrate potential application as high-k candidates in future nano-devices taking advantage of the improved physical and electrical performance.

Hydroalumination of bis(alkynyl)germanes and -silanes: Generation of a chelating Lewis-acid and observation of a dismutation reaction

Treatment of diphenyl-di(phenylethynyl)germane with two equivalents of di(tert-butyl)aluminum hydride afforded the corresponding dialkenyl derivative, Ph2Ge[C(AltBu2)C(H)–Ph]2 (1) by dual hydroalumination. The aluminum atoms of 1 are attached to the carbon atoms in α-position to germanium. They are coordinatively unsaturated and are able to act as chelating Lewis-acids and to coordinate donors such as chloride or bromide anions in a chelating manner (2, 3). The analogous reaction of the corresponding silicon-centered dialkyne with two equivalents of dimethylaluminum hydride gave a mixture of unknown compounds. Interestingly, equimolar quantities of the hydride and the dialkyne resulted in dismutation and the formation of the unprecedented compound MeAl[C(CH–Ph)–SiPh2–CC–Ph]2 (4). Compound 4 has two alkenyl groups bonded to the central aluminum atom and a terminal alkynyl group attached to each silicon atom. An attempt to reduce the remaining triple bonds by reaction with di(tert-butyl)aluminum hydride resulted in cleavage and isolation of the monoalkenyl compound tBu2Al–C[C(H)–Ph]–SiPh2–CC–Ph (5). The molecular structure of 5 showed a close interaction between the α-carbon atom of the triple bond and the coordinatively unsaturated aluminum atom.

Metalorganic Chemical Vapor Deposition of Al2O3 Thin Films from Dimethylaluminumhydride and O2

Metalorganic chemical vapor deposition (MOCVD) of Al2O3 thin films using dimethylaluminumhydride (DMAH) and O2 as precursor and oxidant, has respectively been performed on Si substrate. Compared with some reported results, Al2O3 films with low carbon content and suppressed interfacial layer using this new chemistry can be obtained at a low deposition temperature. Growth kinetics study indicates that these kinetic behaviors follow the Langmuir–Hinshelwood mechanism. Process optimization suggests that high-quality Al2O3 films with low carbon content and high refractive index, as well as the suppressed interfacial layer thickness of 0.2 nm, can be deposited at the substrate temperature of 300 °C and oxygen partial pressure of 1.6 Torr. On the basis of our investigation, it can be concluded that the MOCVD-derived Al2O3 films on Si grown by the new CVD chemistry show reasonable properties as promising candidates for high-k gate dielectrics.

Investigation on GaAs surface treated with dimethylaluminumhydride

The reduction and removal of surface native oxides from as-degreased and HCl-treated GaAs substrates using dimethylaluminumhydride (DMAH) have been studied by x-ray photoelectron spectroscopy. It is revealed that higher oxide states are more easily removed from the GaAs surface after exposure to DMAH at 300 °C. Complete consumption of native oxides on HCl-treated GaAs surface has been realized with 10 s DMAH exposure. In addition, the metallization of the Al–O bonding with increase of DMAH exposure confirms the reduction of native oxides on GaAs.

Reactions of Terminal Alkynes with a Bulky Dialkylaluminum Hydride: Hydroalumination versus Deprotonation

In recent investigations we found an easy access to dialkyl(alkynyl)aluminum compounds by the deprotonation of phenylethyne with di(tert-butyl)- and dimethylaluminum hydride with evolution of molecular hydrogen. In contrast, the reactions of the bulky hydride R2Al−H [R = CH(SiMe3)2] with different alkynes R−C≡C−H (R = CMe3, SiMe3, C6H5, H) yielded vinylic aluminum compounds, R2Al−CH═CH−R′, by hydroalumination. Due to the effective steric shielding of the bulky alkyl substituents, the products were monomeric even in the solid state, with the alkenyl groups bonded to coordinatively unsaturated, tricoordinated aluminum atoms. Quantum-chemical calculations verified that there was no interaction between the π-electrons of the C═C bond and the vacant p-orbital at the coordinatively unsaturated aluminum atoms.

C−H Bond Activation by Hyperconjugation with Al−C Bonds and by Chelating Coordination of the Hydride Ion

On treating di(tert-butyl)butadiyne with dimethylaluminum hydride under different reaction conditions two unprecedented organoelement compounds, containing cationic carbon atoms stable in solution at room temperature, were obtained. A vinyl cation (2) in which the cationic carbon atom is part of a C=C double bond was produced from 3 equiv of the hydride, whereas a large excess of the hydride yielded an aliphatic carbocation (3) by complete hydroalumination of all C-C multiple bonds. Each compound is zwitterionic with the hydride counterion effectively coordinated in a chelating manner by two strongly Lewis acidic aluminum atoms. In agreement with quantum-chemical calculations the C-H bond activation and the stabilization of the cationic species are further supported by a strong hyperconjugation with Al-C single bonds. This considerably diminishes the effective positive charge at the respective cationic carbon atoms.

Optimization of Al-CVD process based on elementary reaction simulation and experimental verification: From the growth rate to the surface morphology

We propose a method to reduce the surface roughness of Al film in the chemical vapor deposition (CVD) using dimethyl-aluminum-hydride (DMAH) as the precursor. An elementary reaction simulation was executed not only to predict the deposition rate but also to predict the coverage of the film by surface adsorbates. It was assumed that high surface coverage is essential in order to deposit smooth films because the adsorbates protect the surface from oxidation which causes discontinuous growth of crystal grains. According to this principle, the condition, that realizes both high surface coverage and high deposition rate at the same time by using the elementary reaction simulation, was sought. A nozzle inlet was used instead of a conventional showerhead. This drastically improved the surface morphology, showing the effectiveness of this theoretical optimization procedure.

HeI Photoelectron Spectroscopy of Trialkylaluminum and Dialkylaluminum Hydride Compounds and Their Oligomers

The HeI photoelectron spectra of trimethylaluminum, triethylaluminum, dimethylaluminum, and diethylaluminum hydrides were recorded as a function of temperature. From the spectra observed at different temperatures the spectra of the pure monomers and the trimethylaluminum, dimethylaluminum, and diethylaluminum hydride dimers and some of the bands related to the dimethylaluminum hydride trimer have been obtained. The spectra were interpreted with the aid of ab initio quantum chemical calculations, including Hartree−Fock/Koopmans, outer valence Green's function, and equation of motion coupled-cluster ionization energy calculations. The vertical ionization energies predicted by the latter two methods are in excellent agreement with the experimental values. Furthermore, the association capability of these compounds, the effects of the substituents, and the degree of association on the electronic structure are also discussed.

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.

Density functional study on the reactivity of oxidized aluminum surfaces: effects of adsorbed metallic atoms (Au, Cu, Ti, V)

Theoretical studies on the possibility of restoring the reactivity of an oxidized Al surface by the adsorption of a metallic atom, such as Au, Cu, Ti, V or Al, have been carried out. We studied: (i) the population distributions; (ii) the energy levels of the highest occupied molecular orbital (HOMO); (iii) the softness and the local softness; and (iv) the adsorption energy and structure of AlH 3. The latter is a model for dimethylaluminum hydride, which is used as a source gas for chemical vapor deposition (CVD). The indicators of reactivity (i–iv) were calculated for three systems: (a) a clean Al surface, (b) an oxidized Al surface, and (c) an oxidized Al surface adsorbing a metallic atom, using density functional theory (B3P86/Lanl2DZ) with a cluster model for the Al surface. It was found that the adsorption of these metallic atoms can restore the reactivity of the oxidized surface.

Infrared spectroscopic study of dimethylaluminum-hydride adsorption on oxidized, hydrogen-terminated, and reconstructed Si surfaces

Adsorption and decomposition of dimethylaluminum-hydride (DMAH) on various Si(111) and Si(100) surfaces [chemically oxidized, hydrogen-terminated, reconstructed (7×7) and (2×1)] have been investigated at 90 K with a multiple reflection infrared (IR) attenuated total reflection (ATR) method. On the chemically oxidized Si(111) surface, IR absorption due to DMAH increased linearly with DMAH exposure, indicating that DMAH was merely condensed on the surface. Upon DMAH exposure to the hydrogen-terminated Si(111) surface, the stretch band of the surface monohydride (Si–H) diminished immediately, revealing that DMAH reacts with the terminated hydrogens. In contrast, DMAH exposure to the hydrogen terminated Si(100) surface leads to a slight intensity decrease in the bands due to surface hydrides (Si–Hx:x=1–3). On the reconstructed Si surfaces [Si(100)(2×1) and Si(111)(7×7)], IR bands due to DMAH could not be observed during the early stage of DMAH exposure, suggesting that the reactivity of DMAH with the reconstr...

Examination of Surface Elementary Reaction Model for Chemical Vapor Deposition of Al Using In Situ Infrared Reflection Absorption Spectroscopy: Teoretical Optimization Procedure (3)

This work provides experimental evidence for the validity of the elementary reaction model of dimethyl-aluminum-hydride (DMAH) on the aluminum surface which the authors developed using a combination of experiments and quantum chemical calculations. Surface adsorbates on an aluminum film were analyzed with in situ infrared reflection absorption spectroscopy (IRAS) during chemical vapor deposition (CVD). Peaks of –CH3 and C–Al–C structures were observed, which was in accordance with the reaction model. The absence of an Al–H peak also supported the model. In order to examine the validity of the model quantitatively, the authors observed the dependence of the absorbance peak area on the surface temperature. This dependence was roughly in agreement with the corresponding results of elementary reaction simulations based on the reaction model.

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.

New Carbaalanes − (AlMe)8(CCH2Me)5(C≡C−Me) and the THF Adduct (AlMe)8(CCH2Me)5H·2THF

The hydroalumination of Me2Al−C≡C−Me with a large excess of Me2AlH afforded the arachno-carbaalane (AlMe)8(CCH2Me)5H (4) by the release of AlMe3. 4 is almost insoluble in noncoordinating solvents and could not be purified by recrystallization. On an attempt to recrystallize 4 from a THF solution, the adduct (AlMe)8(CCH2Me)5H·2THF (5) was isolated as the first stable ether adduct of a carbaalane. Crystal structure determination revealed a cube of eight aluminium atoms, five faces of which are bridged by C−CH2Me groups. The sixth face is µ2-bridged by a hydrogen atom, and two opposite aluminium atoms of this face are coordinated by one THF ligand each. When the excess of dimethylaluminium hydride was reduced and the starting compounds were employed in a 1:2.1 molar ratio, an incomplete hydroalumination reaction led to the formation of the carbaalane (AlMe)8(CCH2Me)5(µ-C≡C−Me) (6), in which the bridging hydrogen atom of 4 is replaced by an alkynido group. 27Al NMR spectroscopic data of all the characterized carbaalanes are reported and supplemented by 27Al NMR chemical shift calculations.