Most semi-conductor process stepper uses a dual stage control
to achieve both large stroke and high precision motion. The
fine-stage of the stepper compensates for the resolution of the
coarse stage servo. In this design, the stepper fine-stage is to
adjust the semi-conductor wafer position and orientation to a
close to 10nm positioning accuracy with a 10m motion stroke. The
stage uses a three sets of piezo-electric actuator to adjust the
x, y positioning and q orientation. The servo controller
positions and orients the stage to meet the specification. A
multi-variable system identification process indicates that
there is a serious coupling among the system dynamics in
different degrees of freedom. In addition, the actuators possess
a non-linear hysteresis effect. A decoupling controller design
based upon the linear-quadratic gaussian design is modified to
overcome the actuators'' hysteresis. The experimental results
show that the resultant control achieves a satisfactory
performance.