Abstract: A photolithography tool, e.g. for microelectronics production, having the stage units (both mask and substrate stage units) composed of two identical stage assemblies which are simultaneously driven with the programmed production motions. The acceleration time histories of the stage assemblies within the unit are identical but opposite in direction. Thus, the photolithography tool processes two substrates simultaneously while being free from objectionable dynamic loads and from shifts of its center of mass.