An improved PBS process for the e-beam photomask lithography

An improved PBS process has been developed and tested for the photomask production. Significant improvements in CD uniformity (3 sigma < 40 nn over 6'' plates) and CD mean-to-target control (< 30 nn) have been achieved through a specially treated puddle development. A low-temperature bake (95 degrees C; 30 minutes) was utilized for better linearity while the resolution was 0.5 mu m for the regular process and as low as 0.35 mu m for the ghosting process. Defect densities on production plates have been greatly improved to a level lower than our normal production process. The new process is not limited by any specific type of processor, therefore it can be implemented into current production lines easily. It is expected that this new process will meet advanced specs for 256M DRAM (with 0.25 mu m design rule) and extend the life of the PBS production line for another 3-4 years.