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Wafer-handling robots are widely used to transfer wafers in semiconductor manufacturing. To improve the wafer transfer efficiency, optic sensors are installed at each station to estimate the wafer eccentricity on the fly. However, due to nonideal factors such as light beam radius, robot motion error, and system nonlinearity and uncertainties, it is difficult to achieve high-accuracy eccentricity estimation to satisfy the demanding requirements in semiconductor manufacturing. To further improve the eccentricity estimation accuracy, the relationship among the robot kinematic error, sensor calibration error, and eccentricity identification error is analyzed. The analytic results show that both the error modeling method and the global data sampling method can greatly improve the wafer eccentricity estimation accuracy. The proposed eccentricity estimation techniques are verified by experiments performed on a wafer-handling robotic system. The results demonstrate that the developed methods can be used to improve the wafer-handling accuracy and reduce the wafer-handling cycle time in semiconductor manufacturing.
Cheng et al. (Thu,) studied this question.