Present status of excimer laser exposure apparatus

One of the most important technical driving forces for IC manufacturing is lithography. IC manufacturing equipment is required to work in sever full-time operation, such as 24 hours a day and 7 days a week. KrF laser, however, has established its status, and has proven the applicability of excimer laser itself. The transition from super high pressure mercury lamp (i-line:365nm) to KrF laser was a natural trend, because the resolution is improved proportionally with shorter wavelength. Practical resolution is now said to attain half the wavelength, using high NA optics and imaging tricks, such as phase shifting masks, oblique illumination, etc. At present, 130nm resolution is pursued using a KrF laser and a projection lens whose NA is nearly 0.7. ArF laser lithography is also under extensive development. In the initial stage, it has proven 120nm resolution with an NA 0.6 projection lens, and now aims at 100nm resolution of 4G-bit DRAM as the next generation. The light source development always comes first in lithography, and F2 laser technology is now paid much attention.