Two processes that lower the emission energy of an electric-discharge KrF laser

Abstract

Results are reported of an experimental investigation of the processes that lower the emission energy of an electric-discharge excimer KrF laser operating on mixtures containing F2 and NF3. The existence is demonstrated of two processes, reversible and irreversible, that lower the KrF-laser emission energy as the number of excitation pulses is increased (without continuous replenishment of the mixture) and as the pulse repetition frequency is increased. The irreversible process is connected with the decrease of the concentration of initial halogen-containing gas in the mixture as a result of interaction between the halogen atoms and the chamber material. The reversible process is due to the long reduction time of the halogen-containing molecule (~ 1 sec for F2) and influences the laser emission energy only at pulse repetition frequencies that exceed the reciprocal time of reduction of these molecules. If complex halogen-containing molecules (NF3, SF6, ...) are used, the pulse-repetition regime is realized because of the radicals that are produced. The use of such molecules, however, affects adversely the service life of the excimer gas mixture.