Nikon sets out immersion schedule
It has been decided to move ArF immersion lithography to the development stage with a view to productisation. A "product introduction schedule" is given:
* Later half of 2004: Completion of engineering evaluation model of ArF immersion lithography and start of user evaluations. Development will be on the basis of Nikon’s currently marketed ArF exposure tool NSR-S307E, with a projection lens NA of 0.85.
* 2005: Completion of pre-production model based on successor of NSR-S307E, with an NA of 0.92.
* 2006: Sales of mass-produced model with an NA greater than 1.0.
Higher numerical aperture (NA) lenses mean better resolution. NA is limited to less than 1 in air. Liquids such as water, with a refractive index greater than 1, open the road to NAs greater than 1. In an immersion lithography exposure system using an ArF laser as the light source, de-ionized (DI) water with a refractive index of 1.44 is introduced between the projection lens and the wafer.
Although immersion has been used for a long time to boost resolution in microscopes, only in recent years has serious research started for applications to lithography exposure tools.