Patent ID: 8598552
Filing Date: 2013-12-03
Classification: G03F,H05G

Abstract:
1. A method of positioning an optical element to optimize power output from an extreme ultraviolet (EUV) light source comprising: (a) measuring with a sensor a metric of a proxy function having an extremum correlated to maximum EUV generation, the metric resulting from a focal setpoint of the EUV light source relative to a target material, the focal setpoint based on a current position of the optical element along an axis; (b) removing by a computing device DC bias from the metric; (c) extracting by the computing device a gradient of the bias-removed metric with respect to the position of the optical element; (d) determining by the computing device an average gradient for the metric gradient; (e) estimating by the computing device based on the average gradient a current position setpoint for the optical element along the axis; (f) augmenting the estimated current position setpoint with a dither signal to obtain a target setpoint; and (g) outputting by the computing device a control signal for adjusting an actuator to change the position of the optical element along the axis from the current position setpoint to the target setpoint.