High-precision compliant mechanism for lens XY micro-adjustment

The high resolution of lithography lenses has led to a requirement for high-precision lens-adjusting compensators. This paper presents the design, analysis, and testing of a high-precision two-degrees-of-freedom compliant mechanism to be used for lens XY micro-adjustment. The monolithic mechanism, which is based on a 1RR-2RRR configuration, uses flexure hinges to connect the movable inner ring with the fixed outer ring. The apparatus is driven using two piezoelectric actuators, and the lens terminal displacement is fed back in real time using two capacitive sensors. This paper describes the principle of the mechanism. Simulations and experiments are then performed to evaluate the system. The results show that the strokes along both the x-axis and the y-axis exceed ±25 µm. The accuracy of the proposed mechanism is better than ±7 nm. The root-mean-square induced figure error is better than 0.051 nm. The coupling z and tip/tilt rigid motions are less than 50 nm and 220 mas, respectively. The first natural frequency of the mechanism is 212 Hz. These results indicate that the mechanism has advantages that include high accuracy, low coupling errors, high rigidity, and compactness and that it will act as an efficient compensator for lithography lenses.