Corey P. Fucetola

Low-cost interference lithography

The authors report demonstration of a low-cost (∼1000 USD) interference lithography system based on a Lloyd’s mirror interferometer that is capable of ∼300nm pitch patterning. The components include only a 405nm GaN diode-laser module, a machinist’s block, a chrome-coated silicon mirror, substrate, and double-sided carbon scanning electron microscopy (SEM) tape. The laser and the machinist’s block were assembled in a linear configuration, and to complete the system, the mirror and substrate were taped to perpendicular surfaces of the machinist’s block. Approximately 50 silicon substrates were prepared, exposed, and developed, after which some were inspected in a SEM. The associated laser spectrum was also measured, enabling calculation of the laser’s fringe visibility as it varied along the substrate surface. To compare the exposed resist pattern to the fringe visibility, the authors measured the first order diffraction efficiency as a function of position along the grating surface. Their measurements ind...

Development of a simple, compact, low-cost interference lithography system

Interference lithography (IL) has proven itself to be an enabling technology for nanofabrication. Within IL, issues of spatial phase distortion, fringe stability, and substrate development have been explored and addressed. However, IL tools are still unnecessarily expensive, large, and complex. To address these issues, the authors previously built a simple IL tool that used a blue laser diode to produce ∼300 nm pitch structures. The resulting patterned areas (∼mm2) were limited by both the temporal and spatial coherence of the laser. Here, the authors report on the advancement of their low-cost interference lithography tool that makes use of newly available blue laser diodes and a simplified spatial filter to print larger-area (∼cm2) patterns. With this configuration, the authors have designed and implemented a small-footprint (∼0.2 m2) Lloyd’s mirror IL tool that can be assembled for less than ∼6000 USD.

Coherent diffraction lithography: Periodic patterns via mask-based interference lithography

Periodic structures, such as gratings and grids, are required in a variety of applications including spectroscopy, photonic and phononic devices, and as substrates for basic studies in materials science. Interference lithography readily forms periodic patterns in photoresist, but conventional approaches, using a Lloyd’s mirror or Mach–Zehnder configuration, suffer from a number of shortcomings including difficulty in aligning patterns with respect to pre-existing structures on a substrate and difficulty in precisely repeating a given spatial period. Coherent diffraction lithography (CDL), a mask-based approach, utilizes the well-known Talbot effect to accurately replicate the one- or two-dimentional pattern on a mask by reimaging the mask pattern in photoresist. Moreover, with appropriate alignment marks on the mask, one can align the replicated pattern relative to pre-existing patterns on the substrate. The authors describe the design, construction, and utilization of a dedicated CDL apparatus that permits replication, at a well-defined mask-substrate gap, of the periodic structure of a phase mask. The system also incorporates interferometric-spatial-phase imaging for aligning the replicated pattern relative to fixed fiducials on a substrate. They obtained high quality replications of a mask pattern, consisting of a 600 nm period grating, from the 1st to the 52nd plane of reimaging, i.e., from 1.55 to 40.16 μm.

3D fabrication by stacking prepatterned, rigidly held membranes

The authors describe an approach to fabricating high resolution, complex 3D structures based on the stacking of thin membranes that have been patterned in advance. The membranes are attached to a rigid frame by means of tethers that are strong enough to permit normal handling but can be cleaved after bonding. The tether shape was designed using finite-element analysis to enable clean cleavage at a specific location so that fragments are avoided that would interfere with the bonding of subsequent layers. The authors used 12 × 12 mm SiNx membranes, 350 nm thick, patterned with a square array of holes at 600 nm pitch and demonstrate the stacking of three layers.

3D nanostructures by stacking pre-patterned fluid-supported single-crystal Si membranes

The fabrication of complex three-dimensional (3D) structures at sub-100 nm resolution presents a difficult challenge. 3D photonic crystals that contain waveguides, resonant cavities, filters or other devices, and require deep-sub-100 nm dimensional control, are a particular example of this challenge. Multilayer 3D structures can be formed by stacking and bonding thin membranes that have been patterned in advance. This approach enables the full panoply of 2D planar-fabrication techniques to be employed. Membranes containing patterns that are not perfectly regular will exhibit in-plane distortion unless their intrinsic stress is zero. To minimize the effects of intrinsic stress we float individual membranes on the surface of a liquid. Thin single-crystal Si membranes on an oxide substrate are first patterned and then removed by etching the oxide in hydrofluoric acid. The freed Si membranes readily float on the liquid surface, aided by the hydrophobic nature of H-terminated Si. The authors describe methods for cleaning, patterning, manipulating, bonding and stacking such freely floating membranes.The fabrication of complex three-dimensional (3D) structures at sub-100 nm resolution presents a difficult challenge. 3D photonic crystals that contain waveguides, resonant cavities, filters or other devices, and require deep-sub-100 nm dimensional control, are a particular example of this challenge. Multilayer 3D structures can be formed by stacking and bonding thin membranes that have been patterned in advance. This approach enables the full panoply of 2D planar-fabrication techniques to be employed. Membranes containing patterns that are not perfectly regular will exhibit in-plane distortion unless their intrinsic stress is zero. To minimize the effects of intrinsic stress we float individual membranes on the surface of a liquid. Thin single-crystal Si membranes on an oxide substrate are first patterned and then removed by etching the oxide in hydrofluoric acid. The freed Si membranes readily float on the liquid surface, aided by the hydrophobic nature of H-terminated Si. The authors describe methods f...

Porous Materials for Ion-Electrospray Spacecraft Microengines

AbstractPorous materials are essential for ion-electrospray propulsion systems (iEPS). These are miniaturized devices designed to provide mobility to small satellites after they have been launched ...