L. Urbanski

Talbot lithography: Self-imaging of complex structures

The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings—and introduce the generalized Talbot imaging (GTI) where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet (EUV) reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He–Ne laser, and then demonstrated its potential as a nanolithography method using a compact table-top soft x-ray (EUV) 46.9nm laser source. These sources provide the high degree of coherence needed by diffraction-based imaging and are extendable to shorter wavelengths. They have recorded EUV GTI images up to the sixth Talbot plane, with consistent high quality good results, clearly demonstrating the ability of the GTI method to record high-resolution patterns at large distances.The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings—and introduce the generalized Talbot imaging (GTI) where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet (EUV) reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He–Ne laser, and then demonstrated its potential as a nanolithography method...

Defect-tolerant extreme ultraviolet nanoscale printing

We present a defect-free lithography method for printing periodic features with nanoscale resolution using coherent extreme ultraviolet light. This technique is based on the self-imaging effect known as the Talbot effect, which is produced when coherent light is diffracted by a periodic mask. We present a numerical simulation and an experimental verification of the method with a compact extreme ultraviolet laser. Furthermore, we explore the extent of defect tolerance by testing masks with different defect layouts. The experimental results are in good agreement with theoretical calculations.

Defect tolerant extreme ultraviolet lithography technique

A defect tolerant method of printing periodic structures with submicron resolution is presented. This technique is based on the self-imaging effect produced when a periodic semi-transparent mask is illuminated with coherent light. An analytical description of the effect, numerical simulations, and experimental evidence that is in good agreement with the theoretical analysis is presented. To explore the extent of defect tolerance, masks with different defect layouts were designed and tested.

Analysis of a scheme for de-magnified Talbot lithography

The authors describe a photolithographic scheme based on the replication of a periodic transparent mask in a photoresist utilizing the coherent self-imaging Talbot effect. A periodic two-dimensional diffractive structure (or Talbot mask) composed of unit tiles distributed in a square matrix was illuminated by a coherent extreme ultraviolet (EUV) beam from a table top EUV laser. The illumination beam was reflected in a spherical mirror and the Talbot mask was placed in the path of the convergent beam. At designed locations determined by the Talbot distance, reduced replicas of the mask were obtained and used to print the slightly de-magnified copies of the mask on the surface of a photoresist. Experimental results showing the de-magnification effect are in good agreement with the diffraction theory. The limits of the technique are discussed.

Hour-long continuous operation of a tabletop soft x-ray laser at 50-100 Hz repetition rate.

We report the uninterrupted operation of an 18.9 nm wavelength tabletop soft x-ray laser at 100 Hz repetition rate for extended periods of time. An average power of about 0.1 mW was obtained by irradiating a Mo target with pulses from a compact diode-pumped chirped pulse amplification Yb:YAG laser. Series of up to 1.8 x 10(5) consecutive laser pulses of ~1 µJ energy were generated by displacing the surface of a high shot-capacity rotating molybdenum target by ~2 µm between laser shots. As a proof-of-principle demonstration of the use of this compact ultrashort wavelength laser in applications requiring a high average power coherent beam, we lithographically printed an array of nanometer-scale features using coherent Talbot self-imaging.

Defect-free periodic structures using extreme ultraviolet Talbot lithography in a table-top system

A compact nanofabrication system that combines Talbot lithography and a table-top extreme ultraviolet laser is presented. The lithographic method based on the Talbot effect provides a robust and simple experimental setup that is capable to print periodic structures over millimeter square areas free of defects. Test structures were printed and transferred into metal layers showing a complete coherent extreme ultraviolet lithographic process in a table-top system.

New opportunities in interferometric lithography using extreme ultraviolet tabletop lasers

The development of tabletop extreme ultraviolet EUV lasers opens now the possibility to realize interferometric lithography systems at EUV wavelengths that easily fit on the top of an optical table. The high degree of spatial and temporal coherence and high brightness of the compact EUV laser sources make them a good option for interferometric applications. The combination of these novel sources with interferometric lithography setups brings to the laboratory environment capabilities that so far had been restricted exclusively to large synchrotron facilities.

Invited Article: Progress in coherent lithography using table-top extreme ultraviolet lasers

Compact (table top) lasers emitting at wavelengths below 50 nm had expanded the spectrum of applications in the extreme ultraviolet (EUV). Among them, the high-flux, highly coherent laser sources enabled lithographic approaches with distinctive characteristics. In this review, we will describe the implementation of a compact EUV lithography system capable of printing features with sub-50 nm resolution using Talbot imaging. This compact system is capable of producing consistent defect-free samples in a reliable and effective manner. Examples of different patterns and structures fabricated with this method will be presented.

Temporal Coherence and Spectral Linewidth of Neon-Like XUV Lasers Pumped in the Quasi-steady State Regime

We report recent experimental progress in the characterization of the temporal coherence and related spectral linewidth of plasma-based soft X-ray lasers (SXRL). New measurements were carried out with two types of SXRLs pumped in the quasi-steady state (QSS) regime, in a capillary-discharge plasma and in a laser-produced plasma. We describe the main results obtained from both experiments and compare them to dedicated numerical simulations. We discuss the results in the context of the possibility to achieve XUV lasers with pulse duration below 1 picosecond.

Spectral Linewidth Measurement of a Ne-Like Ar Capillary Discharge Soft X-Ray Laser

We report on the measurement of spectral linewidth of a Ne-like Ar table-top capillary discharge laser. The linewidth was measured as a function of the gain medium length. Due to inhomogeneous character of the linewidth, saturation re-broadening is expected. However no such behavior was observed while the amplifier length was extended beyond saturation. This situation is compared with a numerical model, identifying that even a small amount of collisional broadening effectively homogenizes the line profile.