Moza M. Al-Rabban

Laser plasma EUVL sources: progress and challenges

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.

EUV spectroscopy of mass-limited Sn-doped laser micro-plasmas

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.

High-efficiency tin-based EUV sources

We have previously proposed the use of mass-limited, tin-containing laser plasma sources for EUV lithography applications. Here we report advances in measurements of the spectral output, conversion efficiency, and debris emission from these sources. We also report progress in the use of repeller field debris inhibition techniques for this source.

Dynamics of Mass-Limited Laser Plasma Targets as Sources for Extreme Ultraviolet Lithography

The droplet laser plasma source has many attractive features as a continuous, almost debris-free source for extreme ultraviolet (EUV) and X-ray radiation applications. In a combined experimental and theoretical study, we are analyzing the interaction physics between the laser light and microscopic spherical liquid droplet targets over a range of conditions.

EUV generation from lithium laser plasma for lithography

Hydrogen-like line emission from lithium has long been considered a candidate for EUV light source for lithography. We have completed the evaluation of the potential of lithium as a laser-plasma source, both theoretically and experimentally. Theoretical calculations show optimum intensity region for lithium for attaining high conversion is close to 5.0 x 1011 W/cm2, with plasma temperature near 50 eV. Experimental studies compare directly, the conversion efficiency and optimum irradiation conditions for both planar tin and lithium solid targets. Best conversion efficiency found in this study is 2% for lithium, while CE measured is better than 4% for tin target at identical experimental conditions.

Spectroscopic studies of the Sn-based droplet laser plasma EUV source

We have previously reported encouraging results with a new type of laser plasma source. As a radiation source at 13.5nm spectral band, tin has several advantages over xenon, not the least of which is the number of ion species within the plasma that contribute to the in-band emission. In this paper we report results from spectroscopic measurements of the laser plasma emission from 12 - 19nm from this target, together with hydrodynamic code simulations of the source, towards developing a suitable laser plasma source for EUV lithography.

Characterization of the Tin-doped droplet laser plasma EUVL sources for HVM

Tin-doped droplet target has been integrated with several lasers including high power high repetition rate lasers and demonstrated high conversion efficiencies for all the lasers. This implies the EUV source power is linearly increasing as the laser frequency goes higher. The target exhibit very low out-of-band radiation and debris emission. The drawback of increasing the repetition rate of the target and the laser will be limited. The total amount of tin consumed for a EUVL source system is also small enough to be operated for a long term without large effort for recycling of the target materials. We address and demonstrate in this paper the primary issues associated with long-term high power EUV sources for high volume manufacturing (HVM) using tin-doped droplet target.

Radiation transport modeling for Xe and Sn-doped droplet laser-plasma sources

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.

Efficient 13.5 nm EUV generation from a laser plasma

We describe a source of 13.5 nm radiation, based on multi-kHz laser-plasmas created from tin-bearing micro-droplets that has a high probability of satisfying the requirements for EUVL, the next generation lithography for computer chip fabrication.

Dynamics of mass-limited laser plasma targets as sources for EUVL

Summary form only given. We report a detailed experimental and theoretical study of the plasma and radiation dynamics of droplet targets. For the first time the interaction region is investigated using separate optical probing techniques, revealing the symmetry and temporal evolution of the plasma expansion. This is compared with the predictions of hydrodynamic code calculations of the evolution of the electron density and temperature profiles. Details of the ionization state of the plasma are investigated spectroscopically, using a high-resolution flat field spectrograph and a new transmission grating spectrograph. Correspondence of the line emission with predicted line intensities from an atomic physics code is made to acquire a detailed understanding of the ionization dynamics in the plasma. These advances can now be extended to other laser interaction conditions with limited mass targets. This could lead to the development of a laser-plasma sources that are even more effective than current sources.