Tris(dimethylamido)aluminum(III): An overlooked atomic layer deposition precursor

Aluminum oxide and aluminum nitride-containing films were grown by atomic layer deposition (ALD) and plasma-enhanced atomic layer deposition (PE-ALD) by employing an under-utilized tris(dimethylamido)aluminum(III) precursor. This compound has not been reported as a precursor for ALD of alumina previously, and has only been reported as an AlN precursor for a thermal process using ammonia as a coreagent. Thermogravimetric analysis demonstrates its excellent volatility and thermal stability, both of which are ideal characteristics for an ALD precursor. Aluminum oxide films were deposited thermally using water as a coreagent. By x-ray photoelectron spectroscopy, the films appeared nearly pristine with only adventitious carbon on the surface accumulated postdeposition that was easily removed with 2 min of Ar+ sputtering. The rest of the films contained a very low 1.4% impurity of carbon. Aluminum nitride films were attempted using the same aluminum precursor with nitrogen plasma as a coreagent; they contained large amounts of oxygen due to ambient exposure, possible oxidation during characterization, or the presence of incidental oxygen during the deposition of AlN, which allowed the formation of an aluminum oxynitride. Though the composition was not stoichiometrically AlN, the films also contained ∼1% carbon impurities, which is an improvement over many other AlN films reported, particularly those using TMA as a precursor. This precursor shows great promise for the deposition of low-impurity or impurity-free aluminum nitride by PE-ALD

Self-seeding gallium oxide nanowire growth by pulsed chemical vapor deposition

A new heteroleptic gallium (III) alkyl amidinate [monoacetamidinatodiethylgallium(III), compound 1] was found to undergo self-seeding pulsed chemical vapor deposition (p-CVD) to gallium metal above temperatures of 450 °C. Below this temperature, the mono-layer formed on the surface of silica and alumina is unreactive to itself and H2O and O2 co-reactants. With no co-reactant above 450 °C gallium metal spheres (150-500 nm) was formed in a p-CVD experiment. With the addition of short H2O pulses produced interesting morphologies and gallium metal/gallium oxide structures resembling "ice cream cones" of varying sizes (2 produced micron long nanowires 2O as a co-reactant at 500 °C

Quantitative surface coverage calculations via solid-state NMR for thin film depositions: A case study for silica and a gallium amidinate

For the interrogation of precursor nucleation for vapor deposition processes like atomic layer deposition (ALD) and chemical vapor deposition (CVD), a modified method for quantitative analysis of surface coverage was undertaken via NMR. The initial chemisorption of a new gallium(III) alkyl amidinate compound was investigated on high-surface area silica. N,N′-Diisopropylacetamidinatediethylgallium(III) (2) was found to have excellent volatility with no decomposition during a ramped thermogravimetric analysis experiment. Stepped-isotherm experiments showed a 1 Torr vapor pressure at 64 C. Compound 2 was exposed to a pretreated high-surface area silica substrate at 100, 200, and 300 C and was found to exhibit stable, persistent chemisorbed surface species at all three temperatures. Substrates were analyzed by 29Si and 13C solid-state nuclear magnetic resonance spectroscopy (SS-NMR) and 1H high-resolution NMR. At 100 and 200 C the reactivity of compound 2 to geminal and lone hydroxyl surface sites varied slightly eliminating either one or both ethyl groups to produce an alkylated (or nonalkylated) gallium acetamidinate on the silica surface and producing fractional coverages of 0.087-0.088. At 300 C there was a larger degree of reactivity producing a minor amount of the same surface species as at 100 and 200 C but also producing additional chemisorbed products likely arising from the decomposition of the ligand framework but ultimately giving a fractional coverage of 0.232 on hydroxyl-terminated silica

Thermal study of an indium trisguanidinate as a possible indium nitride precursor

Tris-N,N,-dimethyl-N′,N″-diisopropylguanidinatoindium(III) has been investigated both as a chemical vapor deposition precursor and an atomic layer deposition precursor. Although deposition was satisfactory in both cases, each report showed some anomalies in the thermal stability of this compound, warrenting further investigation, which is reported herein. The compound was found to decompose to produce diisopropylcarbodiimide both by computational modeling and solution phase nuclear magnetic resonance characterization. The decomposition was shown to have an onset at approximately 120 °C and had a constant rate of decomposition from 150 to 180 °C. The ultimate decomposition product was suspected to be bisdimethylamido-N,N,-dimethyl-N′,N″-diisopropylguanidinato-indium(III), which appeared to be an intractable, nonvolatile polymer

Methylamines as Nitrogen Precursors in Chemical Vapor Deposition of Gallium Nitride

Chemical vapor deposition (CVD) is one of the most important techniques for depositing thin films of the group 13 nitrides (13-Ns), AlN, GaN, InN, and their alloys, for electronic device applications. The standard CVD chemistry for 13-Ns uses ammonia as the nitrogen precursor; however, this gives an inefficient CVD chemistry, forcing N/13 ratios of 100/1 or more. Here, we investigate the hypothesis that replacing the N-H bonds in ammonia with weaker N-C bonds in methylamines will permit better CVD chemistry, allowing lower CVD temperatures and an improved N/13 ratio. Quantum chemical computations show that while the methylamines have a more reactive gas-phase chemistry, ammonia has a more reactive surface chemistry. CVD experiments using methylamines failed to deposit a continuous film, while instead micrometer-sized gallium droplets were deposited. This study shows that the nitrogen surface chemistry is most likely more important to be considered than the gas-phase chemistry when searching for better nitrogen precursors for 13-N CVD