CHARACTERISTICS OF SEALED PARTS UNDER INTERNAL PRESSURE IN SUPER HIGH PRESSURE MERCURY DISCHARGE LAMPS

Super high pressure mercury discharge lamps have been used as a UV light source in photolithography exposure processes such as patterning LCDs, PCBs and semiconductors. It is well known that burst of the lamps during operation is a major problem. Rupture initiation has been found empirically in the sealed parts of lamps and an internal pressure is assumed as a dominant factor for the rupture in the sealed parts. Thus, the characteristics of rupture and improvement methods for the sealed parts under internal pressure have been investigated. Static water pressure tests were carried out in order to investigate the rupture pressure of the sealed parts. In addition, photoelasticity was employed to observe the stress distribution of the sealed parts. Finite-element method (FEM) calculations were done to obtain the maximum principal stress sigma(1) distribution of the sealed parts under internal pressure. From the results, it was found that the rupture pressure of sealed parts was increased as debonded length between the foils and quartz was decreased. In addition, it was observed that the rupture of the sealed parts occurred at about 4 MPa internal pressure and a stress concentration exists near the end of molybdenum foil and quartz glass. The trends of the numerical results were in good agreement with that of the experimental ones.