Dimethylaluminum Isopropoxide Research Articles

A Process‐Structure Investigation of Aluminum Oxide and Oxycarbide Thin Films prepared by Direct Liquid Injection CVD of Dimethylaluminum Isopropoxide (DMAI)

AbstractWe present the direct liquid injection CVD of aluminum oxide and oxycarbide thin films using dimethylaluminum isopropoxide at high process temperature (500–700 °C) with the addition of O2 gas, and at low temperature (150–300 °C) with the addition of H2O vapor. Very smooth films with typical roughness values lower than 2 nm are obtained. The thin films are composed of an amorphous material. The composition evolves as a function of temperature from that of a partial hydroxide to a stoichiometric oxide at low deposition temperature (150–300 °C), and from that of a stoichiometric oxide to a mixture of an oxide with an (oxy) carbide at higher temperature (500–700 °C).

Alumina thin films prepared by direct liquid injection chemical vapor deposition of dimethylaluminum isopropoxide: a process‐structure investigation

AbstractThe development of a new process to obtain amorphous alumina thin films is presented. We show for the first time the direct liquid injection chemical vapor deposition (DLI CVD) of alumina thin films using dimethylaluminum isopropoxide (DMAI) precursor in two oxidizing atmospheres. At high process temperature (500‐700 °C), the film growth takes place in the presence of O2 whereas at low temperature (150‐300 °C) H2O vapor is used. The materials characteristics, such as the surface morphology and roughness (SEM and AFM), crystal structure (XRD), composition (EPMA) and chemistry (XPS) are discussed in detail. Very smooth films, with typical roughness values lower than 2.0 nm are obtained. The thin films are all composed of an amorphous material with varying composition. Supported by both EPMA and XPS results, film composition evolves from a partial oxyhydroxide to a stoichiometric oxide at low deposition temperature (150‐300 °C) in the presence of H2O. At higher growth temperature (500‐700 °C) in the presence of O2, the composition changes from that of a stoichiometric oxide to a mixture of an oxide with aluminum carbide. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Atomic Layer Deposition of TiOx/Al2O3 Bilayer Structures for Resistive Switching Memory Applications

The resistive switching (RS) properties of a thin Al2O3 layer and TiOx/Al2O3 bilayers integrated into TiN/metal oxide/Pt crossbar devices are investigated for future memristive device (ReRAM) applications. The oxide bilayer stack is realized in consecutive atomic layer deposition (ALD) processes at 300 °C without any post‐annealing step. Stoichiometric Al2O3 and oxygen‐deficient TiOx thin films are grown from dimethylaluminum isopropoxide [DMAI: (CH3)2AlOCH(CH3)2] and tetrakis‐dimethlyamido‐titanium [TDMAT: Ti(N(CH3)2)4], respectively, as the metal sources, and water as the oxygen source. High insulating characteristics are confirmed for as‐grown amorphous Al2O3 films with a dielectric permittivity of 8.0 and disruptive field strength of about 7 MV cm−1, whereas the oxygen‐deficient TiOx shows semiconducting behavior. The bipolar‐type RS characteristics of TiN/TiOx/Al2O3/Pt cells show a strong dependence on both oxide layer thicknesses. A stable OFF/ON state resistance ratio of about 105 is obtained for the bilayer structure of 5 nm TiOx and 3.7 nm Al2O3.

Characterization of plasma-enhanced atomic layer deposition of Al2O3 using dimethylaluminum isopropoxide

In this research, Al2O3 films were grown by remote plasma-enhanced atomic layer deposition using a nonpyrophoric precursor, dimethylaluminum isopropoxide (DMAI), and oxygen plasma. After optimization, the growth rate was determined to be ∼1.5 Å/cycle within a growth window of 25–220 °C; the higher growth rate than reported for thermal atomic layer deposition was ascribed to the higher reactivity of the plasma species compared with H2O and the adsorption of active oxygen at the surface, which was residual from the oxygen plasma exposure. Both effects enhance DMAI chemisorption and increase the saturation density. In addition, a longer oxygen plasma time was required at room temperature to complete the reaction and decrease the carbon contamination below the detection limit of x-ray photoemission spectroscopy. The properties of the subsequent Al2O3 films were measured for different temperatures. When deposited at 25 °C and 200 °C, the Al2O3 films demonstrated a single Al-O bonding state as measured by x-ray photoemission spectroscopy, a similar band gap of 6.8±0.2 eV as determined by energy loss spectroscopy, a similar index of refraction of 1.62±0.02 as determined by spectroscopic ellipsometry, and uniform growth with a similar surface roughness before and after growth as confirmed by atomic force microscopy. However, the room temperature deposited Al2O3 films had a lower mass density (2.7 g/cm3 compared with 3.0 g/cm3) and a higher atomic ratio of O to Al (2.1 compared with 1.6) as indicated by x-ray reflectivity and Rutherford backscattering spectroscopy, respectively.

Enhanced Doping Efficiency of Al-Doped ZnO by Atomic Layer Deposition Using Dimethylaluminum Isopropoxide as an Alternative Aluminum Precursor

Atomic layer deposition offers the unique opportunity to control, at the atomic level, the 3D distribution of dopants in highly uniform and conformal thin films. Here, it is demonstrated that the maximum doping efficiency of Al in ZnO can be improved from ∼10% to almost 60% using dimethylaluminum isopropoxide (DMAI, Al(CH3)2(OiPr)) as an alternative Al precursor instead of the conventionally used trimethylaluminum (TMA, Al(CH3)3). Due to the steric hindrance of the isopropoxyl ligand of the precursor, the Al atoms can be deposited more widely dispersed, which enables higher active-dopant densities and hence a higher conductivity of the Al-doped films.

Initial Reaction of Dimethylaluminum Isopropoxide with Hydrogen-Terminated Si (001) Surface Using Density Functional Theory

The initial reaction of dimethylaluminum isopropoxide (Al(CH3)2OC3H7, DMAI) with a fully hydrogen-terminated Si (001) surface for aluminum oxide thin-film growth was investigated using density functional theory. Al-C and Al-O bonds of the adsorbed DMAI were easily broken to produce unimethylaluminum isopropoxide (-AICH3OC3H7, UMAI) group and dimethylaluminum (-Al(CH3)2, DMA) group on the surface, and methane (CH4) and isopropoxide (HOC3H7) as a by-product, respectively, with low energy barriers in the range of 0.22-0.35 eV. UMAI and DMA groups further reacted with the surface to form aluminum isopropoxide (-AlOC3H7) and unimethylaluminum (-AICH3) groups on the surface, and CH4 and HOC3H7 as a by-product, respectively.

Non-stoichiometric AlOxFilms Prepared by Chemical Vapor Deposition Using Dimethylaluminum Isopropoxide as Single Precursor and Their Non-volatile Memory Characteristics

Dimethylaluminum isopropoxide (DMAI, <TEX>$(CH_3)_2AlO^iPr$</TEX>) as a single precursor, which contains one aluminum and one oxygen atom, has been adopted to deposit non-stoichiometric aluminum oxide (<TEX>$AlO_x$</TEX>) films by low pressure metal organic chemical vapor deposition without an additional oxygen source. The atomic concentration of Al and O in the deposited <TEX>$AlO_x$</TEX> film was measured to be Al:O = ~1:1.1 and any serious interfacial oxide layer between the film and Si substrate was not observed. Gaseous by-products monitored by quadruple mass spectrometry show that <TEX>${\beta}$</TEX>-hydrogen elimination mechanism is mainly contributed to the <TEX>$AlO_x$</TEX> CVD process of DMAI precursor. The current-voltage characteristics of the <TEX>$AlO_x$</TEX> film in Au/<TEX>$AlO_x$</TEX>/Ir metalinsulator-metal (MIM) capacitor structure show high ON/OFF ratio larger than <TEX>${\sim}10^6$</TEX> with SET and RESET voltages of 2.7 and 0.8 V, respectively. Impedance spectra indicate that the switching and memory phenomena are based on the bulk-based origins, presumably the formation and rupture of filaments.

Initiation of atomic layer deposition of metal oxides on polymer substrates by water plasma pretreatment

The role of surface hydroxyl content in atomic layer deposition (ALD) of aluminum oxide (AO) on polymers is demonstrated by performing an atomic layer deposition of AO onto a variety of polymer types, before and after pretreatment in a plasma struck in water vapor. The treatment and deposition reactions are performed in situ in a high vacuum chamber that is interfaced to an x-ray photoelectron spectrometer to prevent adventitious exposure to atmospheric contaminants. X-ray photoelectron spectroscopy is used to follow the surface chemistries of the polymers, including theformation of surface hydroxyls and subsequent growth of AO by ALD. Using dimethyl aluminum isopropoxide and water as reactants, ALD is obtained for water-plasma-treated poly(styrene) (PS), poly(propylene) (PP), poly(vinyl alcohol) (PVA), and poly(ethylene naphthalate) (PEN). For PS, PP, and PEN, initial growth rates of AO on the native (untreated) polymers are at least an order of magnitude lower than on the same polymer surface following the plasma treatment. By contrast, native PVA is shown to initiate ALD of AO as a result of the presence of intrinsic surface hydroxyls that are derived from the repeat unit of this polymer.

ALD and MOCVD of Ga2O3 Thin Films Using the New Ga Precursor Dimethylgallium Isopropoxide, Me2GaOiPr

AbstractThin films of gallium oxide (Ga2O3) are prepared by using a new gallium precursor, dimethylgallium isopropoxide (DMGIP), employing both atomic layer deposition (ALD) and metal‐organic (MO)CVD. The gallium precursor DMGIP, a gallium analogue of dimethylaluminum isopropoxide (DMAIP) that has been successfully used for MOCVD and ALD of aluminum oxide, is likewise a non‐pyrophoric liquid at room temperature with a reasonably high vapor pressure. Using water as the oxygen source, DMGIP shows an ALD temperature window in the range 280–300 °C with a growth rate of ∼0.3 Å per cycle. On the other hand, using oxygen as the reactant gas in the MOCVD of Ga2O3, films are grown in the temperature range 450–625°C with the apparent activation energy of 225.5 kJ mol−1. This study shows that DMGIP can be utilized as a new source for the preparation of Ga2O3 thin films.

Deposition of alumina from dimethylaluminum isopropoxide

Results from an investigation of chemical vapor deposition of aluminum oxide from dimethylaluminum isopropoxide as a function of deposition temperature at a total pressure of 1.5 mTorr are reported. An effective activation energy for this process was determined to be 85 kJ/mol. Deposited films were shown to be oxygen-rich compared to Al 2O 3, with higher deposition temperatures resulting in films closer to stoichiometric alumina. Carbon content of the films increased from approximately 1 to 8 at.% at substrate temperatures of 417 and 659 °C, respectively.

Metal-organic chemical vapor deposition of aluminum oxide thin films via pyrolysis of dimethylaluminum isopropoxide

Metal-organic chemical vapor deposited aluminum oxide films were produced via pyrolysis of dimethylaluminum isopropoxide in a high vacuum reaction chamber in the 417–659 °C temperature range. Deposited films contained aluminum, oxygen, and carbon, and the carbon-to-aluminum ratio increased with increased deposition temperature. Aluminum-carbon bonding was observed in films deposited at 659 °C by x-ray photoelectron spectroscopy, but not in films deposited at 417 °C. The apparent activation energy in the surface reaction controlled regime was 91 kJ/mol. The O/Al and C/Al ratios in the deposited films were greater and less than, respectively, the ratios predicted by the stoichiometry of the precursor. Flux analysis of the deposition process suggested that the observed film stoichiometries could be explained by the participation of oxygen-containing background gases present in the reactor at its base pressure.

Carbon incorporation in chemical vapor deposited aluminum oxide films

We report results from an investigation into the nature and extent of carbon incorporation into aluminum oxide thin films deposited from the pyrolysis of dimethylaluminum isopropoxide via high-vacuum chemical vapor deposition. The chemical nature and distribution of carbon in films deposited in the 417–659 °C temperature range were investigated through X-ray photoelectron spectroscopy and Auger electron spectroscopy. Carbon composition increased with increasing deposition temperature, up to approximately 8 at.% at 659 °C. Carbon in films deposited at 477 °C was bonded only to oxygen or carbon, but films deposited above 538 °C also contained metal carbide-like bonding. Carbon content in films deposited on hydrogen-terminated Si (100) substrates increased toward the film–substrate interface, but no silicon–carbon bonding was observed.

Dimethylgallium Isopropoxide as a New Volatile Source for ALD and MOCVD of Ga2O3

Dimethylgallium isopropoxide, Me2GaOiPr, is a gallium analogue of the volatile aluminum source dimethylaluminum isopropoxide, Me2AlOiPr, which was recently commercialized as a precursor for Al2O3. It is a liquid at room temperature and has a reasonably high vapor pressure, high enough for atomic layer deposition and/or metal organic chemical vapor deposition. We employed this precursor in the atomic layer deposition (ALD) and metalorganic chemical vapor deposition (MOCVD) of Ga2O3 thin films. Our ALD process, in which water was used as the oxygen source, showed an apparent ALD temperature window between 300 and 325ºC with a growth rate of ~1.5 Aå/cycle. The MOCVD was performed in the temperature range 450-625ºC with oxygen as the reacting gas. The Ga2O3 films deposited in both processes were found to be stoichiometric and amorphous.

Atomic Layer Deposition of Undoped and Al-Doped ZnO Thin Films Usingthe Zn Alkoxide Precursor Methylzinc Isopropoxide

Undoped and Al-doped ZnO thin films have been prepared by atomic layer deposition (ALD) using the Zn precursor methylzinc isopropoxide [MZI, (CH3)Zn(OCH(CH3)2)] with water (H2O). Dimethylaluminum isopropoxide (DMAI) was used as an Al precursor. The self-limiting ALD process via alternate surface reactions of MZI and H2O was confirmed by thickness measurements of the ZnO films with varying MZI supply time and numbers of MZI-H2O ALD cycles. Under optimal reaction conditions, the growth rate of the ZnO films was 1.9 to approximately 2.0 A/cycle in the substrate temperature range of 160 to approximately 200 degrees C and the maximum growth rate reached about 2.58 A/cycle at 240 degrees C. Room temperature photoluminescence (PL) measurements revealed a strong free excitonic peak at 3.27 eV with almost negligible deep level emission. Resistivities of ZnO films were measured to be 5 x 10(-3) to approximately 3.2 x 10(-3) omega cm depending on the substrate temperature. By Al-doping, the resistivity was minimized to approximately 1.35 x 10(-4) cm.

Adsorption Reactions of Dimethylaluminum Isopropoxide and Water on the H/Si(100)-2 × 1 Surface: Initial Reactions for Atomic Layer Deposition of Al2O3

The surface reaction pathways of dimethylaluminum isopropoxide (DMAI) and water with the H/Si(100)-2 x 1 surface were theoretically investigated with SIMOMM:MP2/6-31G(d). The oxygen atom in DMAI stabilizes an initial complex, facilitating the approach of DMAI to the surface. The methane loss reaction, propane loss reaction, methylation, hydrogen loss reaction, and ring closing reaction channels of the DMAI-surface reactions were identified. Among these, the methane loss reaction depositing -Al(CH3)OCH(CH3)2 was found to be the major channel due to low barrier height and large exothermicity. The ring closing reaction is kinetically the second most accessible channel, even though it is not thermodynamically favorable. On the basis of these theoretical results, recent experimental data were reinterpreted such that the experimentally observed peaks of CH4 and CH(CH3)2OH are in fact the products of these two channels. The propane loss reaction is kinetically the third most probable channel. It produces the surface Si-O bond, which is a reaction unique to DMAI as compared to trimethylaluminum. In summary, the oxygen substitution not only affects the basic nature of the existing potential energy surfaces but also opens new possibilities.

Preparation of Al2O3Thin Films by Atomic Layer Deposition Using Dimethylaluminum Isopropoxide and Water and Their Reaction Mechanisms

Al 2 O 3 thin films were grown on H-terminated Si(001) substrates using dimethylaluminum isopropoxide [DMAI: (CH 3 ) 2 AlOCH(CH 3 ) 2 ], as a new Al precursor, and water by atomic layer deposition (ALD). The self-limiting ALD process by alternate surface reactions of DMAI and H 2 O was confirmed from measured thicknesses of the aluminum oxide films as functions of the DMAI pulse time and the number of DMAI-H 2 O cycles. Under optimal reaction conditions, a growth rate of ∼1.06 A per ALD cycle was achieved at the substrate temperature of 150 °C. From a mass spectrometric study of the DMAI-D 2 O ALD process, it was determined that the overall binary reaction for the deposition of Al 2 O 3 [2 (CH 3 ) 2 AlOCH(CH 3 ) 2 + 3 H 2 O → Al 2 O 3 + 4 CH 4 + 2 HOCH(CH 3 ) 2 ] can be separated into the following two half-reactions: (A) AIO H * + (CH 3 ) 2 AlO C H(CH 3 ) 2 → Al-O - Al(O C H(CH 3 ) 2 ]* + CH 4 ∩ (B) Al[O C H(CH 3 ) 2 ]* + H 2 O → AlO H * + HO C H(CH 3 ) 2 ∩ where the asterisks designate the surface species. Growth of stoichiometric Al 2 O 3 thin films with carbon incorporation less than 1.5 atomic % was confirmed by depth profiling Auger electron spectroscopy. Atomic force microscopy images show atomically flat and uniform surfaces. X-ray photoelectron spectroscopy and cross-sectional high resolution transmission electron microscopy of an Al 2 O 3 film indicate that there is no distinguishable interfacial Si oxide layer except that a very thin layer of aluminum silicate may have been formed between the Al 2 O 3 film and the Si substrate. C-V measurements of an Al 2 O 3 film showed capacitance values comparable to previously reported values.

Thermal decomposition of dimethylaluminum isopropoxide on Si(1 0 0)

The thermal decomposition of dimethylaluminum isopropoxide dimer, [(CH3)2Al(OiC3H7)]2, on Si(100) is investigated by line-of-sight temperature programmed desorption (LOS-TPD), line-of-sight isothermal reaction spectroscopy (LOS-IRS), and Auger electron spectroscopy (AES). [(CH3)2Al(OiC3H7)]2 does not decompose upon adsorption on Si(100) held at 100K or during subsequent LOS-TPD. AES indicates that film growth starts when the precursor is dosed with the substrate at ∼650K. LOS-IRS shows that the monomer, [(CH3)2Al(OiC3H7)]2, is an intermediate in the process of the dimer decomposition to aluminum-containing films, and that further decompositions occur via breaking the CAl and OC bonds.

Atomic layer deposition of Al2O3 thin films using dimethylaluminum isopropoxide and water

Dimethylaluminum isopropoxide (DMAI), (CH3)2AlOCH(CH3)2, a precursor originally developed for the metalorganic chemical vapor deposition of alumina, was adopted as a new precursor for growing aluminum oxide thin films on HF-treated Si(001) substrates by atomic layer deposition (ALD). This precursor is stable for a prolonged period of storage time under inert atmosphere (such as in nitrogen or argon) and does not react vigorously in air, and therefore is easy to handle and safe, without causing hazards. The self-limiting ALD process by alternate surface reactions of DMAI and H2O was confirmed by thicknesses of the grown aluminum oxide films measured as functions of the DMAI pulse time and the number of DMAI-H2O cycles. A maximum growth rate of ∼1.06 Å/cycle was achieved in the substrate temperature range ∼120–150 °C. Growth of stoichiometric Al2O3 thin films without appreciable carbon incorporation was verified by Rutherford backscattering spectrometry. Atomic force microscopy images showed atomically flat and uniform surfaces. In particular, a cross-sectional high-resolution transmission electron microscopy image of an Al2O3 film shows that there is no distinguishable interfacial oxide layer between the Al2O3 film and the Si substrate. These results prove the validity of DMAI as a new ALD source for aluminum oxide.

Chemical vapor deposition of Al 2O 3 films using highly volatile single sources

Amorphous Al 2O 3 films were grown on Si(100) and Si(111) substrates by low-pressure chemical vapor deposition in the temperature range of 250–600°C using dimethylaluminum isopropoxide, dimethylaluminum tert-butoxide, and diethylaluminum isopropoxide as single sources. All these sources vaporize readily at room temperature under reduced pressure. The films were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Auger depth profiling analysis of the samples indicates no appreciable carbon incorporation in the films.