Damage free megasonic resonance cleaning for the 45nm design rule

Scatter bar (SB) breakage presents a mounting confrontation for final cleaning of masks. While the industry is strongly dependent on megasonic (MS) energy, MS is hazardous to scatter bars which approach the size of particles which must be removed. The difference in energy needed to remove small particles and the energy needed to remove small features represents a subtle and shrinking domain. Here we observe cleaning effects when the plate is inverted. This gives us a look that at affects which might otherwise remain hidden. We provide evidence of plate resonance effects and constructive interference from internal reflection. We assess the ability to clean a plate without direct exposure to the MS beam. We adapt a MS bath qualification method for use on spinning plates and use it to assay cavitation activity and uniformity for Upright and Inverted spinning plates. Cavitation activity is recorded in the spalling on a metallic film, which allows quantitation by optical reflectance measurements. Value to both cleaning and SB breakage are assessed.