Reduction of periodic oscillations in a source plasma chamber

摘要: In laser-produced plasma (LPP) extreme ultraviolet (EUV) systems, pressure waves and other impulsive disturbances originating from bubble emitting EUV light are created which affect flight of incoming droplets. These slow the migration subsequent droplets to bubble. Because slowed, laser beam does not directly hit droplet at a primary focus point. This causes resulting level generated be lower than expected is manifested as periodic oscillation in LPP system. An iterative learning controller (ILC) used reduce oscillations when operating system burst mode or continuous mode. The ILC, on rising edge each burst, uses an error signal collected during completed input control update for next burst.