Krypton fluoride excimer laser for advanced microlithography

The excimer-laser-based stepper is now expected to play a significant role in the manufacturing of ULSI devices requiring sub-0.4-mum design rule features. They will be used in a mix-and-match strategy along with high NA i-line steppers for critical layers in the production of 64-Mbit dynamic random access memory (DRAM) generation of IC devices. This is supported by the present availability of a number of production worthy high-NA, wide-field excimer stepper models, along with the recent introduction of several process worthy and moderate cost, positive tone deep-UV photoresists. The excimer laser for the stepper, since its introduction in 1987, has evolved from a laboratory instrument to fully production worthy fab-line equipment. The status of such a laser is discussed. We will discuss the operating theory and the design features of an excimer laser; in particular, the discharge chamber, spectral narrowing module, and the wavemeter. Some of the latest technical innovations incorporated into the laser that reduce maintenance intervals and increase reliability are also presented. Finally we will present and discuss the performance specifications of a current production lithography excimer laser.