Radiation studies of the tin-doped microscopic droplet laser plasma light source specific to EUV lithography.

摘要

Extreme ultraviolet lithography (EUVL) is being developed worldwide as the next generation technology to be inserted around 2009 for mass production of IC chips with feature sizes 35 nm. One major challenge to its implementation is the development of a 13.5 nm EUV source of radiation that meets the requirements of current roadmap designs of the source of illumination in commercial EUVL scanners. The light source must be debris-free, in a free-space environment with the EUV optics that must provide sufficient, narrow spectral band EUV power to print 100 wafers/hr. To meet this need, extensive studies on emission from a laser plasma source utilizing tin-doped droplet target were conducted. Presented in this work are the many optical techniques, including spectroscopy, radiometry, and imaging, that were employed to characterize and optimize emission from the source.; State-of-the-art spectrographs were employed to observe the source's spectrum under various laser irradiation conditions. Comparing the experimental spectra to those from theory, has allowed the determination of the Sn ion stages that emit useful EUV. The experimental results also demonstrated a prediction of Collisional-Radiative Equilibrium model. Moreover, an extensive spectral measurement from 1 nm to 30 nm, which covers nearly the region of the electromagnetic spectrum defined as EUV, was accomplished.; Absolutely calibrated metrology was employed with the Flying Circus instrument from which the source's conversion efficiency (CE)---from laser to the useful EUV energy---was characterized under various laser irradiation conditions. Hydrodynamic simulations and the CRE model predicted the condition at which optimum conversion could be attained. The condition was demonstrated experimentally, with the highest CE to be slightly above 2%, which is the highest value among all EUV source contenders. The CE was studied for its dependence on laser intensity, laser wavelength, irradiation geometry, and so on. For better understanding, experimental observations are compared to simulations.; Through a novel approach, the plasma size was characterized by recording images of the plasma around 13.5 nm. The size, approximately 100 micrometer, is safely within the EUV scanner's etendue limit. Finally, the notion of irradiating the target with multiple laser beams was explored to improve the plasma expansion and the CE.