An ultraprecision stage for alignment of wafers in advanced microlithography

We present an ultraprecision stage specially designed to align wafers for the microlithography of integrated circuit patterns of sub-0.3 μm design rules. The whole stage mechanism is composed of two individually operating xyθ-stages: a global stage to provide initial coarse alignment of wafers in stepping mode; and a micro stage to produce fine controlability in nanometer range. The global stage is configured with three linear motors kinematically linked to produce xyθ-motions without resorting to precision guideways. The micro stage corrects positional errors in the global stage by activating three piezoelectric microactuators housed in an elastic flexure. These two stages are simultaneously controlled as a dual servo system, because the main emphasis is given to achieving an overall positioning reproducibility of 20 nanometers in xyθ-motions in aligning wafers of 200-mm size.