Yaw compensation for an electron‐beam lithography system

Recent experience with the wayless planar stage designed by IBM shows that accurate e‐beam lithography is possible in the Write‐on‐the‐Fly^TM mode with varying stage yaw. The metrology equations necessary to compensate for yaw and axial misalignment of the interferometers with respect to the laser beam are introduced for plane mirror interferometers of the double‐beam type. Geometric equations are derived for various errors of setup of the column, lasers, and interferometers, and for relative positioning errors of the distance and yaw interferometers. The rotation of beam electron deflections and the required yaw‐induced electron‐beam offset are updated within 10 μs using digital signal processors. The offsets for each coordinate sufficient for Write‐on‐the‐Fly lithography are constants to be determined by calibration in terms of the form: const×sin(yaw), const×(interferometer reading)×sin(yaw), and (interferometer reading+const) ×[1−cos(yaw)]. The optimum choice of the definition of the zero point of yaw and the effect of this choice on both the form of the metrology equations and the calibration procedures are discussed.