A SERVO GUIDED X-Y-THETA STAGE FOR ELECTRON-BEAM LITHOGRAPHY

This paper describes a high precision X-Y-theta stage for use inside the variable axis immersion lens of IBM's EL3 + direct write e-beam lithography systems. X-Y stages typically use some form of rail and bearing combination to provide guidance along the X and Y axes. The planar stage presented in this paper has no X or Y guide rails or bearings, instead both guidance and positioning are provided by the simultaneous operation of three mechanical drives controlled by closed-loop velocity, position, and theta servos. The control requirements, architecture, and performance of the servo electronics is discussed. The design and materials constraints imposed by having to operate inside a magnetic lens are discussed and stage performance data is presented. Servo guided stages eliminate the need for precise alignment of guide rails and bearings, while the kinematic nature of the design results in low sensitivity to temperature variations and reduces the need for extreme mechanical tolerances.