Correcting method for mechanical vibration in electron-beam lithography system

In electron beam lithography (EBL), mechanical vibration is an important factor degrading positioning accuracy. We propose a new method to correct for mechanical vibration to improve this accuracy and investigate the effectiveness of this method in a nanometer EBL system. First, the natural frequencies and modes were investigated by experimental modal analysis. The analysis clarified that the beam positioning error in each natural frequency is identified by the vibration amplitude of each natural mode. So, the real-time correction is performed in the following way. Mechanical vibration is sensed with accelerometer at the top of the electron optical column. Then a correction signal is produced by filtering the natural frequencies from the vibration signal, and then, by adjusting the gain and phase of the through signal. Lastly, the correction signal is sent to the deflector. In experiments, to evaluate the effectiveness, we exposed patterns under the constant mechanical excitation. With the vibration amplitude 130 nm at the top of the column, the pattern positioning error was reduced from 60 nm to within 10 nm by the correction. These results indicate that this correction method is a valuable means of improving the positioning accuracy.