The implementation of a Laser Produced Plasma Extreme Ultra-Violet (LPP EUV) source requires a high-power laser focused onto a target. In order to minimize the required laser input power the target material must have a high conversion efficiency to 13.5 nanometer radiation. Ideally, a pulsed laser is used and the target should be delivered in small uniform volumes to a point in space at high repetition rates. The small volumes minimize the amount of debris, the high repetition rates enable higher power systems and the free space delivery alleviates thermal issues and allows large collection angles. It has been demonstrated that lithium and tin have very high conversion efficiencies and system solutions exist to use these materials. In this paper we describe the requirements and performance of a liquid metal micro-droplet target generator capable of dispensing both lithium and tin. Finally it is shown that the current generator performance is sufficient to support stable source operation.
Extensive testing of fused silica has been completed over the past few years by several researchers. A generalized model has been proposed that describes both the compaction that occurs at high peak intensities and the rarefaction that occurs at lower peak intensities. An exposure setup has been constructed to help verify these damage models and to determine the fitting parameters for various types and processing of fused silica. This setup simultaneously exposes samples to two sets of intensities, each set with a different integrated-square pulse width. To make these tests relevant to the microlithography community, the energy densities chosen for these tests span the range found in the projection optics of a 193nm excimer laser-based microlithography tool (50μj/cm2 - 400μj/cm2 ). The samples have been exposed for 40 billion pulses with wavefront measurements made periodically with both 633nm interferometry and 193mn interferometry. This large number of pulses represents the equivalent of several years worth of lens exposure. Data for several fused silica samples will be presented and comparisons will be made to the proposed damage model. According to the obtained parameters, optical performance will be estimated during long term laser exposure on the projection optics. We take into consideration actual light intensity on each lens element for several illumination conditions. We will discuss the difference of the impact on optical performance between different fused silica materials, illumination conditions, reticle transmission, pulse durations, number of pulses, and so on.
Extensive testing of the laser damage behavior of fused silica has been performed over the past few years by several researchers. The results have shown that compaction and rarefaction / expansion of the material can occur. The actually observed process depends on the used energy density and laser pulse number at constant pulse length. In order to check the influence of the different laser parameters in more detail, an experimental set up has been constructed that allows us to investigate not only the influence of the energy density and laser pulse number but also the effect of the integrated square pulse width on the laser damage behavior. An optical delay line is used to create a longer integrated pulse width than the natural laser pulse width. To make these tests relevant to the microlithography community, the integrated energy densities chosen for these tests span the range typically found in the projection optics of a 193-nm excimer laser-based microlithography tool. The samples are exposed to several billions of pulses with wavefront measurements made periodically.
Excimer laser light sources for photolithography are subject to a cycle of ever-tightening precision requirements, dictated by the design-rule shrinks planned into the industry roadmap. But pulse-to-pulse stability of the center wavelength of the emitted light is limited by the presence of vibration in key components and structures. This paper covers the application of Active Vibration Control (AVC) technology to an excimer laser to mitigate the effects unwanted vibration, and enable compliance with anticipated future stability specifications. The laser system is described, from a structural-dynamics point of view. A systematic approach to vibration diagnostics is presented, with experimental results to support key conclusions regarding the types and sources of vibrations. Next, analytical assessment of active control performance is discussed, followed by breadboard-type implementation results showing reductions of > 30% in a key stability performance metric.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.