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-be am writing machine (e-beam) is evaluated. The method is based on a mul tiple-exposure method that involves superimposing e-beam exposure patt erns with different main-field and sub-field sizes. The main-field and sub-field sizes are varied to eliminate main-field and sub-field stit ching on the chip. The stitched areas are overwritten with other expos ures and blurred out. When applied to the preparation of X-ray masks f or device fabrication, this method improves the e-beam writing pattern placement accuracy of the X-ray masks to 0.04 mum (3sigma). Both the field stitching accuracy and the uniformity of the exposed pattern wid th are also improved to 0.02 mum (3sigma).