A High-Precision, Magnetically Levitated Positioning Stage

High accuracy positioning stages with multiple degrees-of-freedom, or microsteppers, are ubiquitous in industrial manufacturing. These devices are used in probing and inspection systems, in the assembly of disk drive heads, and in semiconductor manufacturing. In semiconductor manufacturing, microsteppers are employed to accurately move silicon wafers in the photolithography process. To guarantee both speed and precision, microsteppers are usually composed of a lower stage, which actuates large high-speed movements, and an upper stage, which delivers short high-precision movements using piezoelectric actuators [1]. One such device, shown in Figure 1, delivers motion by means of mechanical contacts. Friction in mechanical contacts releases microscopic dust particles that limit the accuracy of the photolithographic process, thus reducing production throughput in semiconductor manufacturing [2]. For this reason, there is increasing interest in the semiconductor industry to replace mechanical microsteppers by magnetically levitated devices. Magnetically levitated microsteppers are an attractive alternative in other applications since their parts are not subject to mechanical wear and hence do not require extensive maintenance.