Hirokazu Chiba

Cation-controlled assembly of Na+-linked lacunary α-Keggin tungstosilicates

Two novel salts of lacunary tungstosilicates with guanidinium and alkali metal cations, (CH6N3)7Na[SiW11O39]·(CH3)2CO·8H2O (1) and (CH6N3)K6Na[SiW11O39]·11.5H2O (2), have been synthesized and their crystal structures have been determined by synchrotron X-ray diffraction. In both crystals, the Na+ cations link the lacunary Keggin-type tungstosilicate anions into linear structures. The neighboring [SiW11O39]8− anions are related by two-fold screw and translational operations in compounds 1 and 2, respectively. Second harmonic generation was observed for compound 1.

Development of Novel Silicon Precursors for Low-Temperature CVD/ALD Processes

Si-TBES (2) and Si-TBAS (4), novel CVD/ALD precursors bearing a diazasilacyclopentene framework, were synthesized. Thermal analyses revealed that both of them are highly volatile, and their decomposition temperatures were lower than those of comparable silicon precursors, Si(OEt)4 (TEOS) and SiH(NMe2)3 (TDMAS). Deposition properties of SiO2 thin films were investigated by a thermal CVD apparatus. The deposition rates of SiO2 thin films using these new precursors were higher than that of TDMAS. Deposition rate dependency on oxygen partial pressure indicates the high reactivity of the diazasilacyclopentene framework towards oxygen contributes to the high growth rates. Details of the SiO2 thin films were evaluated by XPS, AFM, and SIMS. While Si-TBAS can form conformal SiO2 thin films efficiently, Si-TBES can provide a film with low carbon and nitrogen contamination.

A new 19-metal-atom cluster [(Me2PhP)10Au12Ag7(NO3)9] with a nearly staggered–staggered M5 ring configuration

New mixed metal clusters with M19 metal frameworks have been synthesized by NaBH4 reduction of Au(NO3)(PMe2Ph) together with AgNO3 in ethanol. Single crystal X-ray diffraction has revealed Au12Ag7 and Au17Ag2 metal skeletons for these clusters, which are best described in terms of bicapped pentagonal antiprismatic cages with a staggered-staggered M(5) ring configuration. These clusters connect the missing link between M13 icosahedral and M25 biicosahedral clusters providing a view of the cluster growth process. A TEM image of this cluster has been observed, which has clearly demonstrated single-sized nano-particles of less than 1.0 nm.

Characterization of Ru thin films from a novel CVD/atomic layer deposition precursor “Rudense” for capping layer of Cu interconnects

The authors have succeeded in development of a novel Ru precursor, Ru(EtCp)(η5-CH2C(Me)CHC(Me)O) [Rudense], for CVD and atomic layer deposition (ALD) processes under nonoxidative condition. Rudense has sufficient vapor pressure and good thermal stability (decomposition temperature = ca. 230 °C). Ru thin films were grown on Pt, Ru, Si, and SiO2 substrates using Rudense and NH3 as Ru precursor and reactant, respectively. Rudense gave the conformal, low-impurity (<1021 atoms/cc), and low-resistivity (16 μΩ cm) Ru thin films. Moreover, Rudense showed substrate selectivity; therefore, Rudense will be a candidate for area-selective CVD and ALD precursor for Ru capping layers of Cu interconnects.

Effect of incubation time on preparation of continuous and flat Ru films

Ru films were deposited from Ru(C7H11)(C7H9)–O2 and Ru(C7H11)2–O2 systems on SiO2 (native oxide)/(001)Si, HfSiON/SiON/(001)Si, and HfO2/SiON/(001)Si substrates by pulsed metal organic chemical vapor deposition. Ru deposition was hardly observed at 210 °C at the early stage of the deposition, i.e., incubation time, and this time depended on the source systems and the kinds of the substrates as well as the deposition temperature. After this incubation time, the deposition amount almost linearly increased with the deposition time. This slope, i.e., the deposition rate after the incubation time, was hardly independent of the kinds of substrates. This slope changed by the source systems. The minimum deposition amount to get films with the apparent resistivity below 100 μΩ cm and its average surface roughness depended on the kinds of the substrates, the source systems and the deposition temperature. More importantly, the shorter incubation time of the film deposition resulted in the thinner continuous films wit...

Diversity in the packing modes of mesogenic diphenylpyrimidines with two chiral centres in their crystal structures: the role of interactions between the pyrimidine rings

Various different crystal structures were found for four mesogenic diphenylpyrimidines with two chiral centres and these have been compared with the previously determined crystal structure of 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-{4-[(S)-2-fluoro-2-methyldecanoyloxy]phenyl}pyrimidine (1) which shows an isotropic mesophase. 2-{4-[(S)-2-Fluoro-2-methyldecanoyloxy]phenyl}-5-{4-[(R)-2-fluorohexyloxy]phenyl}pyrimidine (2) and 2-{4-[(R)-2-fluorohexyloxy]biphenyl-4′-yl}-5-[(S)-2-fluoro-2-methyldecanoyloxy]pyrimidine (3), which are isomers of 1 with different N positions, have a structure comprising L-shaped molecules with the chains associated between layers (MHPOBC-type) and a polar structure of stacked monolayers of parallel molecules, respectively. Two diastereomers, 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-{4-[(R)-2-butyloxypropanoyloxy]phenyl}pyrimidine (4) and 2-{4-[(S)-2-fluorohexyloxy]phenyl}-5-{4-[(R)-2-butyloxypropanoyloxy]phenyl}pyrimidine (5) with the same core as 1 but a different chain, have similar structures with crossed core moieties. It is concluded that electrostatic or dipole–dipole interactions between pyrimidine rings, maximizing the overlap of the core moieties, and the bulkiness of the chains are competing tendencies which produce the diversity of the crystal structures. In striking contrast to 1, chiral interactions are not dominant in these crystals, confirming the uniqueness of the crystal structure of 1.