Improved process control of photomask fabrication in e-beam lithography

In mask-making process with e-beam lithography, the process stabilization can be evaluated by looking at the fluctuation of critical dimension (CD) uniformity, mean to target(MTT), and defect controllability. Among them, the capability of CD uniformity and mean to target depends strongly on the acceleration voltage of an exposure machine. Generally, a high acceleration voltage has advantages on dose latitude, pattern fidelity and CD linearity due to its small forward scattering range. Therefore, those merits using a high acceleration voltage can provide a higher yield for production photomask. In this paper, we have examined the CD uniformity and the MTT capability for production photomask fabrication in order to compare the process stabilization between 50 keV and 10 keV. By choosing a 50 keV exposure, significant improvements can be made in CD uniformity and MTT capability.