The aim of this study was to establish a multi-center birth defects monitoring system to evaluate the prevalence and the serial occurrence of birth defects in Korea. Ten medical centers participated in this program. A trained nurse collected relevant records from delivery units and pediatric clinics in participating hospitals on a monthly basis. We observed 1,537 cases of birth defects among 86,622 deliveries, which included live births and stillbirths. The prevalence of birth defects was 1.8%, and the sex distribution of the birth defect cases was 55.2% male and 41.6% female. The highest proportion of birth defects was in the cardiovascular system (17.5%), followed by birth defects involving in the genitourinary system (15.6%). Chromosomal anomalies were detected 30.0 per 10,000 births. Of these chromosomal anomalies, Down syndrome was most frequently observed. This study led to an establishment of a multi-center active monitoring system for birth defects. To better understand the serial occurrence of birth defects in Korea, it is necessary to increase the number of participating hospitals and to launch on a nation-wide multi-center study.

T type megasonic waveguide was analyzed by finite element method (FEM), acoustic pressure measurements and particle removal efficiency for the single wafer cleaning application. Compared to conventional longitudinal waves, a transverse waves were generated in a T type waveguide. Not like longitudinal waves, transverse waves showed changes of direction and phase which increased the cleaning efficiency.

A near-field megasonic system for cleaning semiconductors was designed and fabricated. For the design of the near-field megasonic system, an impedance characteristic of a quartz megasonic waveguide with the piezoelectric actuator was analyzed using a finite element method (FEM). The analysis result showed that the anti-resonance frequency of the system was 982 kHz, which agreed well with the measured value of 988 kHz. The performance of the developed system was assessed by measuring acoustic pressures and comparing the maximim values of them with a conventional megasonic system. As a result, the maximim acoustic pressure of the developed system was decreased by 46.2% compared to the commercial system. Finally, the particle removal efficiency (PRE) test was performed and the obtained PRE was 90.8%. Theses results explain that the developed megasonic has an improved uniformity of the acoustic pressures, which can raise the energy efficiency of the system and lowering the consumption of chemical and ultra pure water (UPW).

When fabricating flat panel displays (FPDs), cleaning process is important in the preparation of next steps. A megasonic system for cleaning FPD which can remove smaller particles with lower power and lower consumptions of chemical and UPW was designed and manufactured. The anti-resonance frequency of the lead zirconate titanate (PZT) actuator was measured, and the value was 992 kHz. The impedance graph of the cleaning system was analyzed using commercial finite element method (FEM) analysis software Ansys, and the obtained value was 992 kHz. This agreed well with the measured value of 989 kHz. The performance of the developed system was evaluated by comparing the acoustic pressures with the conventional product. As a result, the acoustic pressures of the developed system were three times larger than that of the commercial system (conventional type: 13.9 kPa, the developed one: 43.1 kPa). In addtion, the PRE test was performed and the 83% particles were removed using 64% reduced power and 80% reduced chemical consumptions.

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