Advanced Lithography Excimer System: Absolute Wavelength Adjustment, Five Watt Average Power

ABSTRACT A commercial Lambda 248 L excimer system has been equipped with a newly developed wavemeter. The self- controlling laser system can be stabilized at a pre­ selected wavelength in the range of 248.180 to 248.580 nm with an absolute accuracy of ± 0.001 nm. Due to the deep-UV stepper optics the wavelength can be adjusted absolutely to comply with different optics. The modified 248 L-system can be operated at an average power of up to 5 W. Experimental results are presented. 1. INTRODUCTION Optical microlithographyl using 248 nm excimer lasers is going to become the next equipment generation for 16 Mbit DRAMS. The technical requirements for the excimer laser source are special laser beam specifications and additionally a design which fits into the production environment of wafer fabrication facilities.The self-controlling Lambda 248 L-system2 controls the intensity (pulse energy), the wavelength and the narrow linewidth of the laser radiation. In order to make operation of the Lambda 248 L-systems as easy as possible, an automatic wavelength calibration system has been developed. The wavemeter is based on a Fabry- Perot-etalon generated fringe system which is calibrated by means of a wavelength standard of a natural line. This calibration allows to select the excimer wavelength automatically, which gives a required focal plane for a specified optics.Additionally, experiments have been performed to enhance the throughput of excimer steppers. Enhancing the pulse energy or the rep.-rate resulted in a higher average power of up to 5 W.2. WAVEMETERThe Lambda 248 L can be tuned within 248.180 to 248.580 nm (Figure 1). For the required absolute calibration a natural line within this range is used. Those natural lines are known with an accuracy better than 0.001 nm.