Excimer laser for 157-nm lithography

Optical deep UV (DUV) lithography is aiming to reach feature sizes of below 100 nm. The likely choice of the exposure wavelength will be 157 nm, which is emitted by the F₂ excimer laser. Experience with this laser type in a variety of applications has been gained at Lambda Physik for the past 20 years. A major breakthrough in performance, in particular laser efficiency and durability, was achieved with the introduction of our metal ceramic laser tube in 1996. In this paper, we report on the progress in the development of the F₂ laser light source. A major advance in narrowing the bandwidth of a 10W laser is the achievement of output spectral width of about 1 pm. With a newly developed NovaTube based F₂ discharge chamber we show more than 19 million pulses gas lifetime without any additional gas actions. The laser achieves up to 1 kHz repetition rate. Energy stability sigma is 1 percent, dose energy stability 0.5 percent. The performance characteristics as temporal and spatial beam profile and the suitability the laser for microlithography are discussed. Typical lifetimes of the key components and a projection of the present and future cost of operation are presented.