Affiliations: FOM-lnstitute for Plasma Physics Rijnhuizen, Edisonbaan 14, 3439 MN Nienwegein, The Netherlands | SERC Rutherford Appleton Laboratory, Chilton Didcot, Oxon OX11 0QX, United Kingdom
Note: [] Permanent address: Department of Physics, University of Essex, Wivenhoe Park, Colchester CO4 35Q. United Kingdom.
Note: [] On leave from Instituto di Fisica Atomica e Moleculare, CNF, Pisa, Italy.
Abstract: In order to develop a high-intensity laser plasma x-ray source appropriate for industrial application of x-ray lithography, experiments have been carried out using a high-repetition-rate (up to 40 Hz) excimer laser (249 nm, 300 mJ) with a power density of 2 × 1013 W/ cm2 in the laser focus. In this study emphasis is given to remedying specific problems inherent in operating the laser plasma x-ray source at high repetition rates and in its prolonged operation. Two different methods of minimizing the production of target debris are investigated. First, the use of helium as a quenching gas results in a reduction of the amount of atomic debris particles by more than two orders of magnitude with negligible x-ray absorption. Second, a tape target as opposed to a solid target reduces the production of larger debris particles by a further factor of 100. Remaining debris is stopped by an aluminized plastic or beryllium filter used to avoid exposure of the resist by plasma ultraviolet radiation. The x-ray source has been used to image x-ray transmission mask structures down to 0.3 μm onto general purpose x-ray photo-resist. Results have been analyzed with SEM. The x-ray emission spectrum of the repetitive laser plasmas created from an iron target has been recorded and the conversion efficiency of the laser light into x-rays that contribute to exposure of the resist was measured to be 0.3% over 2π sr.
