Erik H. Anderson

Holographic lithography with thick photoresist

Gratings with periods as fine as 199 nm and height‐to‐width ratios ∼5:1 have been produced directly in photoresist by holographic lithography using a technique that reduces ‘‘orthogonal standing wave’’ problems. The technique uses a single layer of photoresist to attenuate the ‘‘orthogonal standing wave,’’ as well as record the grating pattern. The technique is tolerant of process variations and produces structures suitable for further processing steps such as liftoff and etching.

Achromatic holographic configuration for 100-nm-period lithography.

For the fabrication of large-area, spatially coherent gratings with periods of 100 nm or less, a grating interferometer is preferred over a conventional holographic configuration because of the limited coherence of available sources. Using a configuration that employs two matched fused silica phase gratings and an ArF excimer laser, we obtain high-quality 100-nm gratings in polymethyl methacrylate. We analyze the conditions for achieving high-contrast fringes with such an achromatic holographic configuration and show that the depth of focus depends only on the spatial coherence of the source. We also describe a highly accurate method for calculating the diffraction efficiency of the phase gratings as a function of polarization, incidence angle, and grating structure.

Fabrication by tri-level electron beam lithography of X-ray masks with 50nm linewidth, and replication by X-ray nanolithography

Abstract A process has been developed to produce x-ray nanolithography masks containing fine linewidth patterns generated by scanning-electron-beam lithography. This technology allows researchers to combine the high resolution, arbitrary-pattern-generation capability of electron-beam lithography with the parallel replication, high contrast, and large process-latitude of x-ray nanolithography. A tri-level structure was used which consisted of PMMA as the electron-sensitive material, titanium as the middle, masking layer, and polymide as the buffer layer on top of a gold plating base. After electron-beam exposure and development, the pattern is transfered to the Ti layer by CCl 2 F 2 RIE, and then a polyimide mold is produced by O 2 RIE. Gold is then electroplated into this mold to form the x-ray absorber. X-ray masks with 100nm-period gratings and electronic device patterns of ≈ 100nm linewidths were fabricated by this process and replicated.

Fabrication of 100 nm-period gratings using achromatic holographic lithography

Abstract We have fabricated large area, 100nm-period gratings using achromatic holographic lithography. Previously, we reported fabrication of relatively small area gratings with periods of 270nm and 125nm using an achromatic configuration that incorporated feedback to stabilize the fringes during exposure. In the present scheme, the need for a feedback system has been eliminated by physically clamping together the configuration, thereby achieving mechanical stability. Back reflection from the substrate was eliminated using an anti-reflective coating between the resist (PMMA) and the substrate, resulting in grating lines of high contrast. The area of the grating (currently ≈ 1 cm2) is limited only by the size of the fused silica optical flats that contain the beam splitter and recombiner gratings.

Planar Techniques for Fabricating X-Ray Diffraction Gratings and Zone Plates

Planar techniques employed in fabricating Fresnel zone plates and diffraction gratings are reviewed briefly, with emphasis on recent developments.

Transmission x-ray diffraction grating alignment using a photoelastic modulator

We have developed a high-resolution alignment technique which utilizes the partial polarization property of fine period transmission gratings. It is especially useful when the grating period is sufficiently small so that there are no visible diffracted orders. This technique uses a photoelastic modulator (PEM) to produce an intensity signal that is proportional to the sine of twice the angle between the grating lines and the PEM crystal axis. The experimentally demonstrated resolution of this technique on 200-nm period gold transmission gratings is better than 1 sec of arc. This technique was developed to align x-ray transmission gratings for spectroscopy and interferometry applications.

The SEMATECH high-NA actinic reticle review project (SHARP) EUV mask-imaging microscope

The SEMATECH High Numerical Aperture Actinic Reticle Review Project (SHARP) is a newly commissioned, synchrotron-based extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP offers several major advances including objective lenses with 4xNA values from 0.25 to 0.625, flexible, lossless coherence control through a Fourier-synthesis illuminator, a rotating azimuthal plane of incidence up to ±25°, illumination central ray angles from 6 to 10°, and a continuously tunable, EUV illumination wavelength. SHARP is now being used to study programmed and native mask defects, defect repairs, mask architecture, optical proximity correction, and the influence of mask substrate roughness on imaging. SHARP has the ability to emulate a variety of current and future lithography tool numerical apertures, and illumination properties. Here, we present various performance studies and examples where SHARP’s unique capabilities are used in EUV mask research.