Patterning accuracy improvement of the electron beam direct writing system EX‐8D

To improve patterning accuracy, a feedback compensation technique for the magnetic field was applied to EX‐8D. The beam position deviation induced by low‐frequency ambient magnetic field changes and 50 Hz magnetic interference has been minimized by using a feedback system for the interference source signals. As the result of the feedback technique and magnetic shielding applied to EX‐8D, the subfield position deviation measured on written patterns has been improved to be 22 nm as a 3σ value without room shielding. The main deflection calibration method was also improved by utilizing an axially displaceable mark together with a fixed‐height mark. On the fixed mark, the main deflection coefficients were determined with no concern to height sensor outputs. Height‐dependent coefficients were then calibrated by evaluating the field size for various heights using the axially displaceable mark. The calibration accuracy was estimated to be 9.7 nm at the main field edge. It was also confirmed that height‐dependent...