A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

The difference in reflow characteristics between electroplated and sputtered Cu films during high-temperature high-pressure treatment was confirmed, and the basis for this difference was analyzed. Using test element groups containing a number of via holes, it was found that electroplated Cu films had much superior embedding characteristics compared with sputtered Cu films. This was confirmed by measurements of the stress–strain curves of these Cu films, which indicated that the strength at high temperature of the electroplated films was lower than that of sputtered films. Identification of lattice defects and analysis of the microstructure of these films were carried out by positron lifetime measurements and transmission electron microscopy, respectively. The results showed that a large quantity of vacancy clusters was present in the electroplated Cu films, and this increased to a maximum after isochronal annealing at 300°C. From the results, it was shown that Cu atoms in electroplated films with a large number of vacancy clusters diffuse rapidly at around 300°C, and this rapid diffusion contributes greatly to softening of the film and a promotion in reflow behavior. This study revealed that the reflow behavior of Cu films strongly depends on the presence of vacancy clusters within it.     

Hydrogen storage and thermal conductivity properties of Mg-based materials with different structures

Mg-based hydrogen storage materials can be very promising candidates for stationary energy storage application due to the high energy density and low cost of Mg. Hydrogen storage kinetics and thermal conductivity are two important factors for the material development for this kind of application. Here we studied several types of Mg-based materials with different structure-micrometer scale Mg powders, Mg nanoparticles, single crystal Mg, nanocrystalline Mg₅₀Co₅₀ BCC alloy and Mg thin film samples. It seems the Mg materials with good kinetics usually are the ones with nanostructure and tend to show poor thermal conductivity due to electron/phonon scattering resulting from more interfaces and boundaries in nanomaterials. Based on this work, good crystallinity Mg phase incorporated in carbon nano framework could be one promising option for energy storage.     

Studies of characteristics and design of superconducting fault current limiter with adjustable trigger current level in current limiting operation

Superconducting fault current limiters (SCFCLs) are expected to improve not only reliability but also stability of power systems. To introduce an SCFCL in a power system, various specifications such as trigger current level, impedance in current limiting operation, recovery time, and so on are necessary. Fault analyses point out that accuracy of the trigger current level is necessary. Therefore, an SCFCL of a transformer type with adjustable trigger current level was proposed and manufactured. Using the trial SCFCL, adjustability of the trigger current level was confirmed. It is found that the SCFCL has good limiting and recovery characteristics. In this paper, characteristics of the SCFCL are considered from a design point of view. Most of the specifications necessary for design depend on the characteristics in current limiting operation. Therefore, the characteristics of the SCFCL in current limiting operation are discussed. It is shown that this kind of SCFCL has good property for easy design, and its design principle is summarized. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 30–38, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10054     

Malignant tumors of the kidney, brain, and soft tissues in children and young adults with the tuberous sclerosis complex

BACKGROUND: The tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation, and benign tumors of the brain, heart, skin, and kidney. Malignant tumors also can occur in patients with tuberous sclerosis, particularly in the kidney, although they occur less frequently than benign tumors. The types of malignancy that occur in TSC have not been characterized fully. METHODS: Clinical and pathologic features of 8 malignant tumors from 6 TSC patients ranging in age from 22 months to 21 years are reviewed. Six tumors were renal, one was from the inguinal region, and one was from the brain. The tumors were analyzed for loss of heterozygosity (LOH) in the chromosomal regions of the TSC1, TSC2, and VHL genes. RESULTS: Three patients (ages 7, 8, and 20 years) had renal cell carcinomas (RCCs). Two of these patients had multifocal RCCs. All three patients with RCC also had prominent multifocal dysplasia of renal cyst epithelium. Two patients (ages 20 and 21 years) had malignant angiomyolipomas (1 renal and 1 inguinal). One patient (age 22 months) had a Grade 4 giant cell astrocytoma (glioblastoma multiforme). LOH in the region of the TSC2 gene was found, either in the malignant tumor or in benign tumors, in all five patients whose DNA could be analyzed. CONCLUSIONS: Children with TSC, as well as adults with the disease, are at risk for developing malignant tumors. Two types of renal malignancy occur in TSC: RCC, which appears to arise from dysplastic renal cyst epithelial cells, and malignant angiomyolipoma. Tumors cytologically similar to malignant angiomyolipomas also may occur at extrarenal sites. LOH analyses suggest that the majority of patients with TSC who develop malignant tumors have germline TSC2, rather than TSC1, gene mutations.     

The corrosion behaviour of iron in hydrogen chloride gas and gas mixtures of hydrogen chloride and oxygen at high temperatures

Catastrophic corrosion of iron by oxychlorination in hydrogen chloride gas containing 0–75 vol. % oxygen at 300–800°C has been investigated mainly by means of measurements of weight loss and the amount of sublimates. In pure hydrogen chloride gas, the corrosion behaviour was determined by the formation and sublimation of ferrous chloride. Addition of oxygen to hydrogen chloride gas greatly accelerated corrosion of iron due to the formation and sublimation of a low melting point volatile ferric chloride by oxychlorination reactions.     

A Kinetic Model of Degradation of Phenol in Water by Direct Contact of Gas Nonpulsed Corona Discharge

Reaction byproducts from degradation of aqueous phenol by contact of gas d.c. corona discharge with treated water were analyzed by liquid chromatography. According to the retention time, three byproducts, pyrocatechol, hydroquinone, 1,4‐benzoquinone, were identified. Also, acetic acid was detected as a final relatively stable byproduct by gas chromatography. A simple reaction model in which relevant elementary reactions are assumed to be first order was proposed to correlate the practical behavior of degradation processes.     

Porous Ceramic Filters Produced by Hot Isostatic Pressing

Porous TiO₂ ceramics were produced by capsule-free hot isostatic pressing (HIPing) and were evaluated by measuring gas permeability and pore size distribution. In comparison to conventionally sintered TiO₂, the HIPed TiO₂ has a higher permeability and narrower pore size distribution. The differences are caused by the effects of high-pressure gas during sintering.