Synthesis, Structure and Thermal Properties of Volatile Indium and Gallium Triazenides

Indium and gallium nitride are important semi-conductor materials with desirable properties for high-frequency and power electronics. We have previously demonstrated high-quality ALD grown InN and GaN using the hexacoordinated 1,3-diisopropyltriazenide In(III) and Ga(III) precursors. Herein we report the structural and thermal properties their analogues employing combinations of isopropyl, sec-butyl and tert-butyltriazenide alkyl groups on the exocyclic nitrogen of the triazenide ligand. The new triazenide compounds were all found to be volatile (80-120 degrees C, 0.5 mbar) and showed very good thermal stability (200 and 300 degrees C). These new triazenide analogues provide a set of precursors whose thermal properties are determined and can be accordingly tailored by strategic choice of exocyclic nitrogen alkyl substituents

Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition

Amidinate and guanidinate ligands have been used extensively to produce volatile and thermally stable precursors for atomic layer deposition. The triazenide ligand is relatively unexplored as an alternative ligand system. Herein, we present six new Al(III) complexes bearing three sets of a 1,3-dialkyltriazenide ligand. These complexes volatilize quantitatively in a single step with onset volatilization temperatures of similar to 150 degrees C and 1 Torr vapor pressures of similar to 134 degrees C. Differential scanning calorimetry revealed that these Al(III) complexes exhibited exothermic events that overlapped with the temperatures of their mass loss events in thermogravimetric analysis. Using quantum chemical density functional theory computations, we found a decomposition pathway that transforms the relatively large hexacoordinated Al(III) precursor into a smaller dicoordinated complex. The pathway relies on previously unexplored interligand proton migrations. These new Al(III) triazenides provide a series of alternative precursors with unique thermal properties that could be highly advantageous for vapor deposition processes of Al containing materials

Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition

Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga-N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 degrees C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 degrees C were epitaxial on 4H-SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes

Synthesis, Structure and Thermal Properties of Volatile Indium and Gallium Triazenides

Indium and gallium nitride are important semi-conductor materials with desirable properties for high-frequency and power electronics. We have previously demonstrated high-quality ALD grown InN and GaN using the hexacoordinated 1,3-diisopropyltriazenide In(III) and Ga(III) precursors. Herein we report the structural and thermal properties their analogues employing combinations of isopropyl, sec-butyl and tert-butyltriazenide alkyl groups on the exocyclic nitrogen of the triazenide ligand. The new triazenide compounds were all found to be volatile (80-120 degrees C, 0.5 mbar) and showed very good thermal stability (200 and 300 degrees C). These new triazenide analogues provide a set of precursors whose thermal properties are determined and can be accordingly tailored by strategic choice of exocyclic nitrogen alkyl substituents.Funding Agencies|Swedish foundation for Strategic Research [SSF-RMA 15-0018]; Knut and Alice Wallenberg foundation [KAW 2013.0049]</p

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

Deposition Study of Indium Trisguanidinate as a Possible Indium Nitride Precursor

A time-resolved chemical vapor deposition process for indium nitride (InN) is reported using tris-N,N-dimethyl-N’,N”-diisopropylguanidinatoindium(III) (1) and ammonia plasma at 200 °C. The deposition was self-limiting with respect to the pulse time of 1, indicative of a surface-controlled deposition chemistry. The films were confirmed to be InN by X-ray photoelectron spectroscopy (XPS) and film thicknesses of 10 nm were measured by X-ray reflectivity (XRR), corresponding to a deposition rate of 0.1 nm/cycle. Grazing incidence X-ray diffraction (GIXRD) showed a hexagonal polycrystalline film with a preferred (002) orientation. Morphology studies suggest an island growth mode. The poor thermal stability of 1, previously discussed in the literature, prevented full characterization of the deposition process and the deposition of thicker films. It is concluded that while 1 can act as an In precursor for InN, its poor thermal stability prevents its practical use. </p

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 use 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 shows 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, instead micrometer sized gallium droplets were deposited. This study shows that the nitrogen surface chemistry is most likely more important to consider than the gas phase chemistry when searching for better nitrogen precursors for 13-N CVD

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. <i>N</i>,<i>N</i>′-Diisopropylacetamidinatediethylgallium­(III) (<b>2</b>) 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 <b>2</b> 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 <b>2</b> 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

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