A kHz and low debris capillary discharge EUV source

Summary form only given, as follows. We have developed xenon discharge plasma sources dedicated to EUV lithography and to EUV metrology. Few kA currents with fast rise time and short duration have been applied across xenon filled ceramics capillary (1 mm diameter and 10 mm length) to produce mostly EUV radiation in the wavelength range 10 to 16 nm. The radiative performances were studied by means of time resolved as well as time integrated spectroscopy and pinhole imaging measurements. The results demonstrated that the source produced intense flux of photons at 13.5 /spl plusmn/ 0.45 nm with an excellent conversion efficiency of electrical energy. This wavelength range is very well suited to EUV metrology and lithography applications. Consequently, optimization studies were undertaken to develop a source with the required specifications for metrology, (EUV reflectometry and EUV microscopy), or with the even more stringent specifications required by next generation EUV lithography. The source produces 0.3 Watt of EUV radiation in band, for a 2% bandwidth, at 13.5 nm. It can be operated repetitively at frequencies up to 300 Hz for hours with an EUV yield stability better than 0.6%. The shot to shot spatial position fluctuation of the source has been measured by pinhole imaging to be lower than 45 /spl mu/m. A high frequency regime of 1 kHz can be attained but only for short durations due to the switching element limitation. An important issue concerns the emission of debris. This was checked by examining the contamination of a silicon wafer placed 20 cm in front of the discharge in the vacuum tank. XPS, AES and RBS analysis showed that less than one monoatomic layer was deposited during a 1 million shot operation. Such a low contamination rate has been made possible by use of a special design for the electrode geometry.