Dynamic wafer handling process in semiconductor manufacturing

In semiconductor manufacturing, wafers are transferred using wafer handling robots. 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 wafer transfer efficiency, it is desirable to speed up the measurement or place it in parallel with other operations. Hence two 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. A sensor position calibration is proposed to identify the sensor positions. A wafer eccentricity identification method is then derived. Experiments were performed to validate the proposed methods. The computed wafer eccentricity values are compared with those measured using an aliger. The results demonstrated that the developed methods can be applied to estimate the wafer eccentricity on-the-fly, thus reduce the wafer transfer cycle time and increase productivity.