Purging and contamination are two important issues that need to be treated in order to realize F 2 laser lithography system. For the purpose of developing gas-purging and chemically clean technologies, we designed and constructed an experimental set-up. It is used for the study of purging and out-gassing evaluation in order to obtain useful data for development of exposure system. Preliminary experiments showed that purging condition has a strong effect on the residual oxygen and water concentration in the final gas-replaced atmosphere. And we have found that the amount of out-gas depends on the surface finish method of the material used through analyses of impurity gas examination with or without laser irradiation.
The 1 57nm molecular fluorine laser is regarded as the next generation light source for semiconductor exposure technology in the vacuum ultraviolet (VUV) region. Research for high performance F2 laser optical materials is therefore indispensable. In this paper, we describe methods and results of evaluating optical materials used in the 157nm region. In order to evaluate F2 laser optical materials, we have developed an in-situ system, which measures the real-time transmittance at 157nm during laser irradiation and the transmittance in the vacuum ultraviolet (VLJV) region directly after laser irradiation to avoid airborne contamination. The system is purged with high purity nitrogen gas during irradiation to reduce laser light absorption and to keep contamination at a minimum. Due to F2 laser irradiation cleaning, the transmittance of uncoated calcium fluoride (CaF2) samples initially rapidly then gradually increased during 50 million pulses (Mpls). Thereafter the transmittance remained constant. In addition, durability test results of CaF2 substrates and coatings are also presented. Especially coating quality varied enormously between suppliers.
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