| Lithography is the key equipment of semiconductor manufacture.and Wafer stage system is one of the most important system of lithography. Its moving accuracy impacts directly on the resolution of lithography, but it is influenced by the motor constant, gain balance matrix and the force ripple of linear motor.Motor constant is the conversion factor between the force and the current. Gain balance matrix is the conversion matrix between the force of logical axis and the force of physical axis. Motor constant and gain balance matrix are impacted by the actual motor load Because actual motor load is different from theoretical motor load, it is needed to calibrate and update motor constant and gain balance matrix periodically. As a result of slot effect and end effect, the stationarity and moving accuracy of the wafer stage are reduced. it is needed to compensate the force ripple of the linear motor.Calibration methods for motor constant of the linear motor and the plannar motor, gain balance matrix of the plannar motor are studied on the basis of analysing the wafer stage structure,driving mode,control theory and inspection technology. And on the method for reduction motor ripple force is also studied. The actual motor load is calculated according to transfer function curve derived from the mathematical model of wafer stage and the relationship between motor constant and actual motor mass is established. Coefficients are defined to describe the crosstalk between different axes and their calculation methods are presented. A calibration method for gain balance matrix is also proposed. This paper puts forward a method of establishing a list table between position and force to degree force ripple of linear motor, and explains how to establish the list table in detail.The experiment results show that accuracy of wafer stage and the synchronization performance of wafer stage and reticle stage are improved obviously after calibration of the motor constants and compensation of the ripple force. |
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