Patterning Accuracy Estimation of Electron Beam Direct-Writing System EX-8D.

Self-diagnosis functions related to patterning accuracy are important techniques for developing, improving and maintaining electron beam exposure systems. An evaluation method of beam position deviation has been developed to reduce fluctuation of patterning accuracy. High-frequency beam position deviation was detected by scanning the beam on a W mark with subsequent fast fourier transform analysis. A magnetic field compensator has been developed to reduce low-frequency beam position deviations induced by ambient magnetic field changes. The beam position deviations of high- and low-frequency have been restricted to about 17 nm (3σ). A mark stand, which carries a height-changeable mechanism, was developed to calibrate the beam deflection accuracy depending on the Z direction. By applying the above diagnostic function, a main frame stitching accuracy of 32 nm has been achieved with short turnaround time.