Helen C. Aspinall

Some recent developments in the MOCVD and ALD of high-κ dielectric oxides

A range of high-permittivity (κ) dielectric oxides are currently being investigated as alternatives to SiO2 as the dielectric insulating layer in sub-0.1 μm CMOS technology. Metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are promising techniques for the deposition of these high-κ dielectric oxides. Some recent developments in precursors for the MOCVD and ALD of ZrO2, HfO2, Zr- and Hf-silicate and the rare earth oxides M2O3 (M = Pr, La, Gd, Nd) are discussed.

Three component synthesis of homoallylic amines. Efficient catalysis by lanthanum triflate/benzoic acid

Abstract Lanthanum triflate–benzoic acid catalyses the in situ formation and allylation of various imines from aldehydes and an aromatic amine.

Thermal stability of neodymium aluminates high-κ dielectric deposited by liquid injection MOCVD using single-source heterometallic alkoxide precursors

Thin films of neodymium aluminate (NdAlOx) have been deposited by liquid injection metalorganic chemical vapor deposition (MOCVD) using the bimetallic alkoxide precursor [NdAl(OPri)6(PriOH)]2. The effects of high-temperature postdeposition annealing on NdAlOx thin films are reported. The as-deposited thin films are amorphous in nature. X-ray diffraction (XRD) and medium energy ion scattering (MEIS) show, respectively, no crystallization or interdiffusion of metal ions into the substrate after annealing at 950°C. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the thin films exhibited good electrical integrity following annealing. The dielectric permittivity (κ) of the annealed NdAlOx was 12, and a density of interface states at flatband (Dit) of 4.01 × 1011 cm-2 eV-1 was measured. The deposited NdAlOx thin films are shown to be able to endure high-temperature stress and capable of maintaining excellent dielectric properties.

Permittivity enhancement of hafnium dioxide high-κ films by cerium doping

The effect of cerium doping on the dielectric properties of hafnium dioxide is reported. Thin films of cerium-doped hafnium oxide Cex–Hf1−xO2 (x=0.10,0.17,0.34) have been grown by liquid injection atomic layer deposition. After annealing at 900 °C, all films were transformed from an amorphous state into a stabilized cubic or tetragonal phase. As-deposited films of Ce0.1–Hf0.9O2 showed low hysteresis voltages and negligible flat band voltage shifts. After annealing to form the crystalline cubic or tetragonal phase, the relative permittivity (κ) increased from 25 to 32 at 100 kHz with leakage current densities at ±1 MV cm−1 of ∼1.58×10−5 A cm−2.The effect of cerium doping on the dielectric properties of hafnium dioxide is reported. Thin films of cerium-doped hafnium oxide Cex–Hf1−xO2 (x=0.10,0.17,0.34) have been grown by liquid injection atomic layer deposition. After annealing at 900 °C, all films were transformed from an amorphous state into a stabilized cubic or tetragonal phase. As-deposited films of Ce0.1–Hf0.9O2 showed low hysteresis voltages and negligible flat band voltage shifts. After annealing to form the crystalline cubic or tetragonal phase, the relative permittivity (κ) increased from 25 to 32 at 100 kHz with leakage current densities at ±1 MV cm−1 of ∼1.58×10−5 A cm−2.

Catalytic, asymmetric cyanohydrin synthesis mediated by lanthanide(III) chloride pybox complexes

Abstract Complexes formed between lanthanide trichlorides and 2,6-bis( substituted -2-oxazolin-2-yl)pyridine (pybox) ligands are effective catalysts for the enantioselective addition of trimethylsilylcyanide (TMSCN) to a range of aldehydes.

Ytterbium triflate catalysed allylation of aldehydes: An unusual benzoic acid induced acceleration

Abstract Addition of one equivalent of benzoic acid greatly enhances the efficiency of our ytterbium triflate catalyzed allylation of aldehydes with allyltributyltin in acetonitrile. Crucial modifications to reaction conditions result in a dramatically increased rate at remarkably low catalyst loading.

Ytterbium trifluoromethanesulfonate [Yb(OTf)3] as a novel catalyst for the allylation of aldehydes

Abstract Ytterbium triflate has been found to be an excellent Lewis acid catalyst for the reaction of aldehydes with allyltributylstannane.

Lanthanum triflate-catalysed allylation of aldehydes: crucial activation by benzoic acid

Abstract Lanthanum triflate in combination with benzoic acid catalyses the allylation of aldehydes at low catalyst loading, without the need to activate the catalyst in advance.

Ce(IV) complexes with donor-functionalized alkoxide ligands: improved precursors for chemical vapor deposition of CeO2.

Thin films of ceria (CeO(2)) have many applications, and their synthesis by liquid-injection MOCVD (metal-organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO(2). New complexes were synthesized by alcohol exchange reactions with [Ce(OBu(t))(4)]. [Ce(mmp)(4)] and [Ce(dmap)(4)] were both found to be excellent precursors for liquid-injection MOCVD of CeO(2), depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350-600 °C for [Ce(mmp)(4)]; 300-600 °C for [Ce(dmap)(4)]). [Ce(mmp)(4)] is also an excellent precursor for liquid-injection ALD of CeO(2) using H(2)O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)(4)] has lower thermal stability than [Ce(mmp)(4)] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD.

An improved Williamson etherification of hindered alcohols promoted by 15-crown-5 and sodium hydride

Abstract 15-crown-5 greatly facilitates Williamson ether synthesis when sodium hydride base is used in THF solvent. This mild yet versatile procedure has been employed in the synthesis of new homochiral polyether ligands and bis-allylic ethers which are inaccessible by conventional methods.