발간논문

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Si∥SiO₂ structure was prepared by using Silicon Direct Bonding(SDB) of a bare Si wafer to the oxidized Si wafer. Linear annealing method was applied to the SOI formation instead of conventional furnace annealing. IR images and a cross-sectional SEM image showed nearly perfect bonding interface. The bonding strength was measured by crack-opening method and tensile test method. The results showed that the bonding strength increased with increasing the annealing temperature. By tensile test, interface oxide of a bonded pair was split into two parts. One part was left on the surface of the Si wafer where the oxide had grown up, while the other part was separated from the wafer and attached strongly to the other Si wafer. From this result, Linear annealing method was considered to be applicable to the SOI fabrication.

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In this study we investigated the formation of denuded zone and bulk microdefects by three-step-annealing in a Czochralski grown silicon wafer. Three-step-annealing was performed in a sequence of high temperature (900-1100℃), low temperature (600-800℃) and medium temperature (850-950℃) respectively. Oxygen concentration profiles by outdiffusion in the 1st step annealing were calculated using error-function-solutions to Fick`s 2nd law. Based on these results, denuded zone width were determined after the 2nd and the 3rd step annealing. The calculated values of denuded zone width were correlated well with the measured ones. The denuded zone width was found out to be proportional to the square root of denudation time (the 1st step annealing time). Morphological changes of bulk microdefects were observed according to changes of the 3rd step annealing time. Finally the effect of pre-oxidation on the changes of denuded zone width is also discussed.

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In order to investigate relationship between characteristics of pore texture such as porosity, diameter and shape factors and reduction behaviors of ferric oxide pellets, pore texture of pellets reduced with H₂ and CO gas at 700-900℃ were analysed with image analysis system. Reduction rate of H₂ gas was faster than that of CO gas. It was confirmed that reduction behaviors with H₂ gas could be analysed by the intermediate model, but that one with CO gas could be analysed by the unreacted core model. Porosity of pellets in the Fe₂O₃→Fe₃O₄ reduction stage was increased, but that of the Fe₃O₄→FeO and FeO→Fe was gradually decreased. In each reduction stage, porosity was decreased in the temperature range from 700℃ to 900℃, and this decrease of porosity was greater in the reduction by H₂ gas than that by CO gas. Mean diameter of pore was increased with proceeding of the reduction stage and was the biggest in the Fe₃O₄→FeO stage. In each reduction stage, porosity was decreased with the increase of temperature. Shape of pores such as roundness, aspect ratio and fullness ratio was rapidly worsened in the Fe₂O₃→Fe₃O₄ stage, but gradually improved in the reduction stage from magnetite to metal iron.

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This study was to investigate the effects of extrusion condition (extrusion temperature, extrusion ratio, dies angle, initial Ti thickness) on the fabrication of Ti-Cu clad material for high conductivity and high corrosion resistance, using indirect extrusion method in which there is no friction between container and billet. The range of extrusion temperature, extrusion ratio, directs angle and initial Ti thickness were changed front 700℃ to 900℃, from 9.5 to 38.0, from 20° to 50°, and from 1.8 ㎜ to 4.8 ㎜ , respectively. Extrusion pressure decreased with increasing extrusion temperature owing to the reduction of flow stress. However. increment of extrusion temperature resulted in the drawback of lubricant effect between dies and billet. Extrusion pressure increased with increasing extrusion ratio and initial Ti thickness. Extrusion pressure was also affected by dies angle. Namely, extrusion pressure was raised with smaller dies angle because the friction between billet and dies increased with decrease in dies angle. The thickness of interface layer between Ti and Cu increased with increasing extrusion temperature. The interface layer composed of hard intermetallic phases which may act a reducer of bonding strength depending upon its thickness.

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