M. Michman

Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds

Abstract HfO 2 films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 A) nearly stoichiometric monoclinic HfO 2 . The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO 2 films varied between 2 × 10 6 and 4.5 × 10 6 V cm −1 . C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10 11 and 6 × 10 11 cm t−2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V FB values were between −0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V 2 over a wide range.

Thin films of metal oxides on silicon by chemical vapor deposition with organometallic compounds. I

Abstract Thin films of TiO2, ZrO2 and HfO2 have been deposited on single crystals of (111) silicon, by chemical vapor deposition (CVD) of the respective organometallic compounds. The thin films of TiO2 have the anatase structure while ZrO2 and HfO2 are monoclinic. All films are easily etched by 5% HF solution, while films of TiO2 are also etched by 70% H2SO4. The indices of refraction of the thin films are 2.05–2.26 for TiO2, 1.94 for ZrO2 and 2.02 for HfO2. All the oxide films show good MOS C-V characteristics, the flatband voltages having values near zero. The bias-temperature (B-T) tests on C-V curves in the case of HfO2 show high stability.

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

Abstract ZrO 2 films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO 2 , were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10 6 and 2.0 × 10 6 V cm −1 . Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0−6.0) × 10 11 cm −2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between −0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V 2 dependence for negative bias and an I ∝ V 2.6 to I ∝ V 3.4 dependence for positive bias.

Alkylation reactions with organometallic compounds : I. the reaction of methyltris(triphenylphosphine)rhodium with diphenylacetylene☆

Abstract The reaction of diphenylacetylene with (Ph3P)3RhCH3 was studied in order to clarify the role of the organometallic compound as an alkylating reagent. Trans-α-methylstilbene was the main product of addition to the alkyne. The reaction is mostly an insertion process as concluded from studies with D2O. It was compared with the reaction of diphenylacetylene with the systems (Ph3P)3RhBr/CH3MgBr, and RhBr3·3H2O/CH3MgBr. With the first system mainly trans-α-methylstilbene was formed. In this reaction however, (Ph3P)3RhCH3 is shown not to be an active intermediate. With the second system, cis-addition was observed with a high degree of stereospecificity cis-α-methylstilbene being the main product. Condensation of diphenylacetylene to products like 1,2,3-triphenylnaphthalene, 1,2,3,4-tetraphenylbutadiene and 1,2,3,4-tetraphenylcyclopentadiene was also observed.

Palladium-catalyzed cross-methylation of aryl triflates by intramolecularly stabilized dialkyl-aluminum, -gallium and -indium reagents

Abstract Several phenyl and naphthyl triflates undergo catalytic cross-methylation with the monomeric and dimeric dimethyl-aluminum, -gallium and -indium complexes 1a , 1b , 1c , 3a , 3b and 3c in the presence of either PdCl 2 (PPh 3 ) 2 , Pd(PPh 3 ) 4 or Pd(binap)(OAc) 2 . 4-Bromophenyl triflate reacts selectively via the triflate function. Structural features of the substrate and the methylating agent, as well as the nature and quality of the palladium catalyst have a considerable influence on the cross-coupling process.

Alkylation reactions with organometallic compounds : II. The reaction of diphenylacetylene with palladium compounds of the type L2PdCl2 and CH3MgBr

Abstract α,α′-Dimethylstilbene is obtained in the reaction of diphenylacetylene with CH 3 MgBr and L 2 PdCl 2 (L = benzonitrile or norbornadiene), in 65% yield based on the alkyne. Stilbene and α-methylstilbene form as side products (~25%). No reaction takes place when phosphines or arsines are present as L in L 2 PdCl 2 . The addition of strong nucleophiles like Ph 3 P, Ph 2 PCH 2 CH 2 PPh 2 or (PhO) 3 P to a cold mixture (−70°) of (C 6 H 5 CN) 2 PdCl 2 and CH 3 MgBr yields the corresponding L 2 Pd(CH 3 ) 2 , indicating the presence of methyl-palladium components in the reaction reagent and offering thereby a convenient synthesis of these compounds.

Alkylation reactions with organometallic reagents : III. The effect of oxygen on alkylation reactions with cobalt(I) compounds

Abstract Methylmagnesium bromide reacts with diphenylacetylene in the presence of cobalt(I) and cobalt(II) complexes. Oxygen is shown to have a significant effect on the reaction. Under argon the alkyne is consumed either by formation of cyclisation products or by addition across the triple bond to yield stilbene derivatives and 1,2-diphenylpropene (by mono-alkylation of the triple bond). Under oxygen the consumption of the alkyne through condensation tends to be blocked while the yield of addition reactions to the triple bond increases and includes the formation of 2,3-diphenylbut-2-ene (by dialkylation of the alkyne). The same effect to a smaller extent is observed when CH3Co(Ph3P)3 reacts with PhCCPh. An attempt to rationalize the oxygen effect is presented.

Cleavage and rearrangement of phosphorus-carbon and phosphine-metal bonds in alkyltris(tertiary phosphine)cobalt compounds

Abstract Complexes of the type L3CoCH3 have been prepared in which L = Ph3P, P2PCH3, PhP(CH3)2, Ph2PGe(CH3)3, Ph2PSn(CH3)3, Ph3As, and R = CH3, Ph, and (CH3)3Si. Decomposition of these complexes under mild conditions in several solvents has been studied. Among the identified products are benzene, toluene, biphenyl, and rearranged phosphines, such as Ph3P from [Ph2PCH3]3CoCH3 or Ph2PCH3 from [Ph2PGe(CH3)3]3CoCH3.

Selective hydrogenation of the CC-triple bond in PhCCPh by tris(triphenylphosphine)cobalt activated NaBH4; deuterium tracing experiments

Abstract Sodium borohydride does not on its own react with diphenylacetylene, but becomes an active hydrogenation agent in the presence of (Ph 3 P) 3 CoCl. Unlike systems involving other catalysts, e.g. cobalt halides in ethanol, this is a selective reagent for hydrogenation in which an alkyne is selectively hydrogenated to cis and trans alkenes. The role of NaBH 4 in this hydrogenation and isomerization has been studied by deuterium labelling. A brief comparison is made with other active catalysts in this system like (Ph 3 P) 3 CoBH 4 .

Reactions of methyltris(triarylphosphine)cobalt : III. Aldol condensation catalysed by methyltris(triphenylphosphine)cobalt, (Ph3P)3CoCH3☆

Abstract Methyltris(triphenylphosphine)cobalt catalyses the aldol condensation of acetone and ethyl methyl ketone. From acetone mesityl oxide is obtained in ∼70% yield, while from ethyl methyl ketone 3-methyl-2-heptene-5-one and 3-methyl-3-heptene-5-one are formed in equal amounts in a total yield of about 100%. The latter products are known to be those of base-catalysed aldol condensation. The corresponding aldols are also observed in small quantities. The reactions mostly take place in the absence of solvent.