X-Ray Mask Pattern Accuracy Improvement by Superimposing Multiple Exposures Using Different Field Sizes

A method to improve the accuracy of patterns written by an electron-beam writing machine (e-beam) is evaluated. The method is based on a multiple-exposure method that involves superimposing e-beam exposure patterns with different main-field and sub-field sizes. The main-field and sub-field sizes are varied to eliminate main-field and sub-field stitching on the chip. The stitched areas are overwritten with other exposures and blurred out. When applied to the preparation of X-ray masks for device fabrication, this method improves the e-beam writing pattern placement accuracy of the X-ray masks to 0.04 µm (3σ). Both the field stitching accuracy and the uniformity of the exposed pattern width are also improved to 0.02 µm (3σ).