A method for generating complementary mask data for an EPL stencil mask using a commercial pattern operation tool

Electron-beam projection lithography (EPL) using stencil mask is one of the most promising candidates for next-generation lithography. However, the practical use of a stencil mask for fabricating ULSIs needs proximity effect correction (PEC) as well as complementary data to be prepared in order to solve the "doughnut pattern problem". We have developed a method for generating complementary data by using a pattern operation tool for design-rule checking and phase-shift-mask generation. The advantages of using these commercial DA tools are high processing speed as a result of maintenance of a hierarchical data structure, high reliability, and flexibility to allow the generation rules to be changed. Since beam blur, which varies according to pattern density in a sub-field, has to be estimated in PEC, sub-field division has to be performed prior to PEC. In the developed method, sub-field division is performed after the complementary-data generation. Sub-field division makes the chip data almost flatten and enlarge the output data volume. If the sub-field division is performed prior to complementary decomposition, complementary-data generation cannot take advantage of high-speed processing resulting from the maintenance of a hierarchical data structure. We applied this method for metal layer data of a 14x14-mm test chip that includes 300 million figures in flat form. For the complementary-data generation by the developed method CPU time was about 20 minutes using a 500-MHz PC with a 256-Mbyte memory. Maintenance of the hierarchical data structure made the volume of output GDSII data compact. The method can equalize the aperture densities of two complementary masks in a Coulomb-interaction range that is smaller than a sub-field. Although sub-field division using a DRC tool expands the output data volume in GDSII format, sub-field division using EB pattern data generator reduces output data in realistic size.