Recent development work on the EUV electric capillary discharge source been has focused on two areas: increasing EUV power generation and minimizing debris deposition on plasma facing optics. To achieve high-power operation, a pulser capable of driving the source up to 1.7 kHz and a new high-power lamp have been integrated. An EUV flux of 9 W into p-sr and a 2 percent bandwidth has been generated in burst mode at 1000 Hz. Three additional parametric studies are discussed. The first compares the EUV power generation and spectral output for three different capillary materials. The second study compares the source efficiency for 3 mm and 6 mm length capillaries. And the third parametric study measures the EUV output stability over a one million pulse run. The second focus area has been to increase mirror reflectance lifetimes through the further development of the gas curtain debris mitigation approach. A new gas curtain laboratory has been built with more than a 10x increase in flow capability and a 10x reduction in chamber background pressure. Measurements of the gas curtain efficiency have demonstrated a reduction in particulate deposition rate of at least a factor of eighty.
Progress continues on the development of the EUV Electric Capillary Discharge Source. Over the past year we have studied the high average power operational characteristics, used interferometry to measure the in-capillary electron density, and further reduced the debris deposition rate on plasma facing optics. A pulser capable of driving the source at up to 1 kHz was acquired and preliminary testing is in progress. EUV flux and spectral emission measurements were made for pure xenon and xenon-helium mixtures using a new electrode designed to prevent debris from depositing on multilayer optics. Finally, through improvements in capillary and electrode design and material properties coupled with the assistance of mitigation approaches, we have been able to significantly reduce the amount of debris generated by the source thereby increasing the reflectance lifetime of plasma-facing optics.
We report on the development of an electric capillary discharge source that radiates with comparable efficiency at both 13.5 nm and 11.4 nm, two wavelengths of interest for EUV lithography. The discharge source is comprised of a low- pressure, xenon-filled, small diameter capillary tube with electrodes attached to both ends. A high-voltage electric pulse applied across the capillary tube generates an intense plasma that radiates in the EUV. This source is capable of producing 7 mJ/steradian per pulse in a 0.3 nm bandwidth centered at 13.4 nm. In this paper we will address three significant issues related to the successful development of this source: minimization of debris generation, thermal management, and imaging quality.
An intense pulsed capillary discharge source operating at 13.5 nm and 11.4 nm, suitable for use in conjunction with Mo:Si or Mo:Be coated optics, has produced an average power of approximately 1.4W within a 0.3 nm emission bandwidth from the end of the capillary when operated at a repetition rate of 100 Hz. The source is comprised of a small capillary discharge tube filled with xenon gas at low pressure to which electrodes are attached at each end. When a voltage is applied across the tube, an electrical current is generated for short periods within the capillary that produces highly ionized xenon ions radiating in the EUV. Issues associated with plasma bore erosion are currently being addressed from the standpoint of developing such a source for operation at repetition rates of greater than 1 kHz.