Compact maglev stage system for nanometer-scale positioning

Abstract

Semiconductor manufacturing systems and ultra-precise machine tools now require nanometer-scale positioning accuracy. To improve positioning accuracy, it is efficient to support the top table with a noncontact guide system to prevent guide friction and heat transfer from the lower table or base. A magnetic levitation (maglev) stage can accomplish ultra-precise positioning accuracy with six-degrees-of-freedom (6DOF) control even in vacuum conditions. However, if the gravity of the levitated table is supported by the thrust of a linear motor, heat generation from the motor coil dramatically increases. In addition, a larger motor is required, which causes the moving mass to increase and the mechanical response to deteriorate. We aimed to develop a compact maglev stage for which the levitated mass is less than 1 kg and that is dramatically more lightweight than existing maglev stages. This compact feature was enabled by our newly proposed gravity compensation system with repellent force and a planar motor structure. The developed stage system also has long strokes, specifically 200 mm in the X and Y-directions on a horizontal plane. We designed a maglev stage with the following design concepts to create its compact structure: (1) Reduce top-table mass to minimize the motor dimensions and enable a light weight and high responsiveness. (2) Measure the top-table position from the base to eliminate positioning error and isolate vibrations of the coarse stage. (3) Install a motor in a symmetrical layout in view from the Z-axis to enable the same driving characteristics between the X and Y axes. The results of the performance evaluation showed that the developed maglev stage system with a compact structure with 0.81 kg levitated mass has ±10 nm positioning stability.