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The development of a source bright enough for EUVL, possessing the required long-term stability within a reasonable cost, is forcing plasma physicists to address issues associated with dense plasmas that have up until now received scant attention. With both discharge plasmas and laser plasmas, addressing these issues has stimulated many new ideas and concepts for source design and measures associated with them. Although these new developments are currently directed toward satisfying the needs of next-generation lithography (NGL), it is likely they will also open new fields of application in the years ahead. Early on in the development of EUVL sources, when the required source power (2π sr, 2% bandwidth) was ∼10 W, we speculated that the so-called debris problem would be the most difficult to overcome. It was for this reason that we proposed the notion of the mass-limited target for the laser plasma source. In this scenario, the material supplied to the source should consist only of a mass sufficient to provide the minimum required number of atomic radiators.

The 13 nm emission that results from laser plasmas created from tin targets, results from a milliard of transitions occurring in many ions of tin (Sn6+-Sn13+). Understanding the energy manifolds within these multiple states will further our ability to manipulate energy into the narrow emission band demanded by EUV Lithography. A combined experimental theoretical program is underway to measure and interpret the detailed EUV emission spectra from laser plasmas suitable for EUVL, particularly mass-limited droplet laser plasmas. We employ high resolution spectroscopy in the 2 - 60 nm wavelength regions to characterize the emission from the plasma. This is interpreted with the aid of combined hydrodynamic/ radiation transport computer models. The results of this study will have impact on the in-band EUV conversion efficiency, estimation of the out-of-band short-wavelength emission, and in the development of electron temperature plasma diagnostics.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Detailed understanding of the complex UTA emission from Xe and Sn laser plasmas is imperative to the development of efficient 13.5 nm sources for EUVL. We are developing a comprehensive theoretical modeling approach to these sources, utilizing state-of-the-art hydrodynamic and radiation transport plasma codes. These models are specifically applied to Xe and Sn-doped microscopic droplet targets laser-plasmas irradiated with nanosecond laser pulses. The plasma expansion models are compared to experimental determinations of the plasma electron density distributions. The output of the radiation transport code is used to interpret details of the spectral emission measured from these plasmas over a broad range of parameters.

A high repetition-rate laser plasma source, possessing distinct radiation and particle emission characteristics, is now a principal candidate light source for the next generation of technology for the fabrication of computer chips. For these sources to satisfy this critical need they will need to meet unprecedented levels of performance, stability and lifetime. We review here some of the principal diagnostics of the EUV radiation that are now being utilized in the metrology, spectroscopy and imaging of these sources.

The most pressing technical issue for the success of EUV lithography is the provision of a high repetition-rate source having sufficient brightness, lifetime, and with sufficiently low off-band heating and particulate emissions characteristics to be technically and economically viable. We review current laser plasma approaches and achievements, with the objective of projecting future progress and identifying possible limitations and issues requiring further investigation.

One of the key leverage factors in determining the viability of laser-plasma sources for EUVL is the conversion efficiency of laser light to EUV emission in the 13-nm region. We describe experiments and theoretical calculations on a mass-limited laser target design using tin that offers high conversion efficiency.

As a mass limited target the water droplet laser plasma source has been shown to have many attractive features as a continuous, almost debris-free source for extreme ultraviolet (EUV) and X-ray applications. Through a dual experimental and theoretical study, we analyze the interaction physics between the laser light and the target. The hydrodynamic laser plasma simulation code, Medusa103 is used to model the electron density distribution for comparison to electron density distributions obtained through Abel inversion of plasma interferograms. In addition, flat field EUV spectra are compared to synthetic spectra calculated with the atomic physics code RATION.

The droplet laser plasma source has previously been shown to have many attractive features as a continuous, almost debris-free source for EUV and x-ray applications. In a combined experimental and theoretical study, we analyze the interaction physics between the laser light and the target over a range of conditions.