Development of a large displacement flexure based nano-precision XY positioning stage for vacuum environments

Choi, Yeong-jun
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Flexures are widely used in precision machines since they offer frictionless, particle-free, and low maintenance operation, and they provide extremely high resolution. Existing flexure-based translation stages usually have motion range to size ratios of less than 0.01 as compared 0.5 or higher in this research. It is believed that large motion flexure based XY stages can be a cost-effective solution for semiconductor applications, particularly the ones that operate in vacuum. The use of air bearings in vacuum leads to complicated designs making flexures attractive. Flexures also lead to less expensive designs as compared to magnetically-driven bearings. This dissertation presents a large displacement flexure based nano-precision XY positioning stage for vacuum-based semiconductor equipment. The weight support mechanism of the motion stage is made of links and flexure joints, and a linear motor is used as the actuator. This stage is not a dual servo stage, but it can provide large motion range of greater than 8” x 8” to support a substrate during semiconductor manufacturing. An over-constrained mechanism is used to incorporate symmetry to cancel out the effects of center shifting in large motion flexures. Advanced kinematic techniques such as screw system theory are used to achieve a good kinematic design. Dynamic models are developed for fully compliant machines to understand the dynamic behavior of the flexure based XY stage. A single axis motion stage actuated by a high-resolution linear motor with a laser interferometer providing real-time position feedback has been fabricated. Experiments are performed to characterize motion straightness, repeatability, dynamic response of the motion stage. This research is, to our knowledge, the first work for developing a macro motion stage that can support the weight of the stage and guide the motion by a mechanism based purely on flexure joints. A flexure-based XY stage can be potentially used to accurately place photomasks and wafers in an electron beam lithography machine, semiconductor steppers, wafer handling equipment, defect analysis machines in semiconductor industry, chip inspection tools, and coordinate measurement machines.