Eccentricity estimation with error modeling in dynamic wafer handling

Wafer-handling robots are used to transfer wafers in semiconductor manufacturing. Typically, a pick–measure–place method is used to transfer wafers accurately between stations. The measurement step is performed using an aligner, which is time-consuming. To increase the wafer transfer efficiency, it is desirable to speed up the measurement process or place it in parallel with other operations. Hence, optic sensors are installed at each station to estimate the wafer eccentricity on the fly. The eccentricity values are then used to control the robot to place the wafer directly onto another station accurately without using the aligner. In this paper, the kinematic model of a wafer-handling robot is developed. The errors in the kinematics model are analyzed. A model parameter identification method is proposed to obtain the parameters. A wafer eccentricity identification method is derived to calculate the eccentricity values on the fly. Experiments were performed to validate the proposed methods. The computed eccentricity errors are compared with those obtained by other researchers. The results demonstrated that the kinematics error modeling method can increase the wafer eccentricity identification accuracy. Hence, the developed methods can be applied to estimate the wafer eccentricity on the fly to reduce the wafer transfer cycle time and increase wafer-handling efficiency.