Design of imaging system for EUVL

Manufacturing for large-scaled integrated circuit requires a large exposure area and high throughput. According to the SLA road map, 16 GbitDRAM requires exposure area of 26 mm x 44 mm for a 0.1-mu m generation. In order to determine these feasibility, we designed an imaging optics which is based on three aspherical-mirror optics for EUVL. This designed optics is very compact one, and the optics can achieve a resolution of less than 0.1 mu m and an ring field of 26 mm x 1.0 mm on a wafer. In assembling the demagnifying optical system, various adjustment errors such as decenter, tilt and despace affect one another in an intricate way and degrade the system performance in a complicated manner. It is therefore important in practice to adjust the system as a whole rather than trying to optimize the effects of individual adjustment mirrors on the resolution by fulfilling respective tolerances. Another important factor affecting the system performance is surface figure error of aspherical mirrors. The surface figure error of aspherical mirror is estimated by calculation of ray tracing method We obtained the tolerance of the figure errors of M1, M2, and M3 to be 0.66 nm, 0.75 nm, and 0.90 nm for replicating 0.1-mu m-pattern, respectively. It is found that these values are twice or three times larger than the values obtained from Marechal criteria.