DYNAMIC MOTION OF MASK MEMBRANE IN X-RAY STEPPER

This article presents a new analysis method and experimental results f or the deflection and vibration of x-ray masks, which are caused by th e squeeze effect of the gas film between a mask and a wafer in x-ray s teppers. The deflection and vibration occur when a mask-to-wafer gap s etting is executed or if the wafer vibrates in the mask direction duri ng stepping motion with a narrow gap. They are not only detrimental to the throughput, but may also damage the mask membrane. Lees' differen ce approximation method is applied to a compressible Reynolds' equatio n and the equation of motion for the mask membrane. The main results o f calculations and experiments, which showed good agreement with each other, are outlined below. (1) When the wafer approaches the mash: at a constant velocity, the mask deflection increases in proportion to th e velocity, and the mask deflection is larger for a smaller mask tensi le stress. (2) When the wafer vibrates in the mask direction, the ampl itude of the mask vibration increases with increasing the wafer freque ncy, and reaches a maximum value at a frequency that depends on the ga p size. The maximum amplitude of a tested mask becomes 4 times as larg e as the wafer amplitude. (3) For a high frequency and narrow gap, the mask vibrates while deflecting convexly in the direction opposite to that of the wafer. (C) 1996 American Vacuum Society.