Investigation of a novel discharge EUV source for microlithography

摘要

A plasma discharge could be an inexpensive and efficient EUV source for microlithography, if issues of brightness, lifetime, debris, repetition rate, and stability can be resolved. A novel discharge EUV source (international patent pending) is being investigated that may offer an economical solution to these issues. The novel EUV discharge seeks to efficiently assemble a hot, dense, uniform, axially stable plasma with magnetic pressure and inductive current drive, employing resonant theta-pinch-type compression of plasma confined in a magnetic mirror. This resonantly compressed mirror plasma (RCMP) source would be continuously driven by a radio frequency oscillator, to obtain an EUV conversion efficiency greater than that of sources in which the plasma is discarded after each radiation burst. An analytic calculation indicates the novel RCMP source could provide 115 W of 13.45-nm radiation in 3.3 mm~2sr etendue to an intermediate focus. Numerical modeling of RCMP dynamics has been performed with MHRDR-EUVL, a magnetohydrodynamic (MHD) numerical simulation with atomic and radiation physics. The numerical simulation demonstrates the efficacy of resonant magneto-acoustic heating. An experiment is being developed to test the new concept. A 50-kW, 3-MHz rf generator is connected to a water-cooled coil in vacuum. Time-resolved spectroscopy will be used to characterize the EUV source.