Abstract
A high intensity laser beam focused onto a surface is a source of soft X-rays that is both simple and elegant. In the past the high peak power laser sources were limited in repetition rate and average power. Thus the laser produced plasma was not considered useful in applications where average power is important such as lithography. However, even single pulse, low average power, laser plasma soft X-ray sources have been used for lithography studies. 1-4 In this talk we describe advances in laser sources that may lead to laser plasma soft X-ray average power levels that are adequate for production X-ray lithography. Our work in this area was motivated by the recent advances in high peak and average power laser sources, particularly the slab geometry solid state laser devices. 5,6 We were also motivated by Grobman's pro7posal that synchrotron radiation could be used for production X-ray lithography. We were curious as to whether a laser plasma soft X-ray source could be competitive with the synchrotron source. Our study showed that a laser source of 100-W average powqr could produce soft X-rays at the same level as the synchrotron source proposed by Grobman.8 However, the laser source must provide high peak power pulses to drive the plasma efficiently. Using the slab geometry it is possible to construct a 100-W average power, high peak power Nd:Glass laser source. The laser source must meet a set of engineering criteria such as size, reliability and efficiency in addition to criteria required to efficiently drive the plasma such as high peak and average power, excellent spatial mode properties and proper wavelength. The design of the laser source must also reflect the application of the soft X-rays to lithography, microscopy or spectroscopy. We briefly describe the slab geometry laser concept and then proceed to consider the plasma properties. We conclude by comparing various laser sources for driving the plasma and compare the plasma soft X-ray source to a conventional rotating anode source.
