발간논문

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Centerline macrosegregation is one of the most significant problems in continuous casting on stainless steel slabs. Numerical model have been developed in order to decrease centerline macrosegregation during continuous casting of STS 420J2 stainless steel slab. Extra cooling zone and extra cooling water quantity are determined by iterative coupled analysis of heat transfer and segregation. Segregation ratio is decreased by the intensive cooling at the extra cooling zone above the solid fraction of the slab center 0.7, so called thermal soft reduction (TSR). The experimental results show good agreements with numerical results.

keyword : Thermal Soft Reduction, Centerline macrosegregation, Solidification, Stainless 420J2

The interfacial reactions of the Cu(100 nm)/Ta(50 nm)/Si structures and their relationship with the microstructure of Ta diffusion barriers are investigated. The Ta films were deposited on Si (100) substrates at various bias voltages ranging from 0 to -200 V. The Ta diffusion barrier which was deposited at the substrate bias voltages of -50 V and -125 V prevented Cu-Si interaction up to 600℃ in flowing purified H₂ for 60 min, whereas the Ta layer with a columnar structure which was deposited at zero bias voltage degraded at 400℃. It was found that a slight resistivity increase of the Cu/Ta(-50 V or -125 V)/Si structures at 650℃ seemed to be due to a Cu agglomeration. To confirm the thermal stability of the Ta diffusion barrier deposited at the substrate bias voltage, a SiO₂ capping layer was used as a suppressor and was deposited on the Cu/Ta(-125 V)/Si structure. As a result, the Cu/Ta(-125 V)/Si structures were stable up to 650℃ without the Cu-Si interaction. Two different reactions of the Cu/Ta(0 V)/Si and the Cu/Ta(-50 V or -125 V)/Si structures concerning the thermal stability were discussed on the basis of the experimental results.

keyword : Tantalum, Diffusion barrier, Ion beam deposition, Resistivity, Substrate bias voltage, Thermal stability