Black and white fused silica: modified sol-gel process combined with moth-eye structuring for highly absorbing and diffuse reflecting SiO2 glass.

Diffuse reflecting (white) and highly absorbing (black) fused silica based materials are presented, which combine volume modified substrates and surfaces equipped with anti-reflective moth-eye-structures. For diffuse reflection, micrometer sized cavities are created in bulk fused silica during a sol-gel process. In contrast, carbon black particles are added to get the highly absorbing material. The moth-eye-structures are prepared by block copolymer micelle nanolithography (BCML), followed by a reactive-ion-etching (RIE) step. The moth-eye-structures drastically reduce the specular reflectance on both diffuse reflecting and highly absorbing samples across a wide spectral range from 250 nm to 2500 nm and for varying incidence angles. The adjustment of the height of the moth-eye-structures allows us to select the spectral position of the specular reflectance minimum, which measures less than 0.1%. Diffuse Lambertian-like scattering and absorbance appear nearly uniform across the selected spectral range, showing a slight decrease with increasing wavelength.

Pulse compression grating fabrication by diffractive proximity photolithography.

We report about a newly devised throughput-scalable fabrication method for high-quality periodic submicron structures. The process is demonstrated for optical transmission gratings in fused silica with a period of 800 nm (1250 lines/mm) to be used in laser pulse compression. The technology is based on an innovative advancement of i-line proximity photolithography performed in a mask aligner. The aerial image is encoded in a rigorously optimized electron-beam-written three-level phase mask which is illuminated by an adapted multipole configuration of incidence angles. In comparison to conventional proximity lithography, the process enables a significantly higher resolution while maintaining a good depth of focus--in contrast to lithography based on direct Talbot-imaging. Details about the grating fabrication process and characterization of fabricated pulse compression grating wafers are presented. The gratings show a diffraction efficiency of 97% at a wavelength of 1030 nm and a wavefront error comparable to gratings fabricated by electron-beam lithography.

Ultra-high aspect ratio replaceable AFM tips using deformation-suppressed focused ion beam milling.

Fabrication of ultra-high aspect ratio exchangeable and customizable tips for atomic force microscopy (AFM) using lateral focused ion beam (FIB) milling is presented. While on-axis FIB milling does allow high aspect ratio (HAR) AFM tips to be defined, lateral milling gives far better flexibility in terms of defining the shape and size of the tip. Due to beam-induced deformation, it has so far not been possible to define HAR structures using lateral FIB milling. In this work we obtain aspect ratios of up to 45, with tip diameters down to 9 nm, by a deformation-suppressing writing strategy. Several FIB milling strategies for obtaining sharper tips are discussed. Finally, assembly of the HAR tips on a custom-designed probe as well as the first AFM scanning is shown.

Advanced mask aligner lithography: fabrication of periodic patterns using pinhole array mask and Talbot effect.

The Talbot effect is utilized for micro-fabrication of periodic microstructures via proximity lithography in a mask aligner. A novel illumination system, referred to as MO Exposure Optics, allows to control the effective source shape and accordingly the angular spectrum of the illumination light. Pinhole array photomasks are employed to generate periodic high-resolution diffraction patterns by means of self-imaging. They create a demagnified image of the effective source geometry in their diffraction pattern which is printed to photoresist. The proposed method comprises high flexibility and sub-micron resolution at large proximity gaps. Various periodic structures have been generated and are presented.

Advanced mask aligner lithography: new illumination system.

A new illumination system for mask aligner lithography is presented. The illumination system uses two subsequent microlens-based Köhler integrators. The second Köhler integrator is located in the Fourier plane of the first. The new illumination system uncouples the illumination light from the light source and provides excellent uniformity of the light irradiance and the angular spectrum. Spatial filtering allows to freely shape the angular spectrum to minimize diffraction effects in contact and proximity lithography. Telecentric illumination and ability to precisely control the illumination light allows to introduce resolution enhancement technologies (RET) like customized illumination, optical proximity correction (OPC) and source-mask optimization (SMO) in mask aligner lithography.

Highly efficient three-level blazed grating in the resonance domain.

We designed, fabricated, and characterized three-level transmission gratings in the resonance domain with reduced shadowing losses based on a three-wave interference mechanism. A new technological approach allows for fabrication of homogeneous and large area multilevel gratings without spurious artifacts. To our knowledge, the measured efficiency of 86% exhibits the largest value yet reported for a multilevel transmission grating in the resonance domain close to normal incidence.