SU-8 is a negative tone proxy type resist which allows high aspect ratio for micro machining. SU-8 molds can be used for micro casting and embossing for making high aspect MEMS. A quick way to produce prototypes (Design -> Expose -> Prototype) is presently an important task in the micro fabrication. In this work we demonstrate the ability of multiple layer and binary structuring of SU-8 using maskless photolithography by the DWL66 device. As light source, we used a 30 mW He-Cd-Laser at 325 nm wavelength. The intensity is varied over 31 steps (grey levels) by an acousto-optical modulator (AOM) which provides the desired grey tone levels. By means of microlens arrays (MLA) we represent the achieved results by back side exposures. It can be shown that in addition to producing the curvature of the lenses by intensity modulation, the total height of lenses can be controlled by using supplementary attenuation. The total achieved height of micro lenses is approximately 65 μm resulting from a 100 μm thick SU-8 25 resist made by multiple coating method. Good chemical, mechanical and optical properties make SU-8 interesting for different applications as micro devices in micro-optics and micro-optoelectronics.

Over the last two decades, considerable research has been devoted to micro-optic and now nano-optical structures. Fabrication methods have become sufficiently mature to realize most concepts, but due to physics inherent in the process, geometry is distorted. Edges are rounded, sidewalls are sloped, surfaces are rough, and etching or deposition not uniform. Deviations from "perfect" geometry can dramatically affect optical behavior. In order to address the impact of the "non-perfect" nature of fabrication, numerical methods for modeling fabrication is discussed and quantified for various examples. As an example, comprehensive modeling of near-field nano-patterning is described. Numerical and experimental results are presented of three-dimensional photonic crystals fabricated in a contact mask aligner using a standard UV lamp as the source.

We present a new method that allows to fabricate structures with tightly controlled three-dimensional profiles in the 10 nm to 100 μm scale range. This consists of a sequence of lithographic steps such as Electron Beam (EB) or Focused Ion Beam (FIB) lithography, alternated with isotropic wet etching processes performed on a quartz substrate. Morphological characterization by SEM and AFM shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be realized. Quartz templates have been employed as complex system of micromirrors after metal coating of the patterned surface or used as stamps in nanoimprint, hot embossing or casting processes to shape complex plastic elements. Compared to other 3D micro and nanostructuring methods, in which a hard material is directly "sculptured" by energetic beams, our technique requires a much less intensive use of expensive lithographic equipments, for comparable volumes of structured material, resulting in dramatic increase of throughput. Refractive micro-optical elements have been fabricated and characterized in transmission and reflection modes with white and monochromatic light. The elements produce a distribution of sharp focal spots and lines in the three dimensional space, opening the route for applications of image reconstruction based on refractive optics.

Photonic crystals have received growing interest over the past decade on account of their excellent functionality to guiding and manipulating electromagnetic radiation and their diverse applications. Our approach to fabricate crystals is by a two step etching process in a semiconductor hetero-structure of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs) grown using molecular beam epitaxy (MBE). An array of holes was dry etched in Cl₂/Ar inductively coupled plasma. Etching selectivity between the mask and the substrate was 10:1.2 By using SF₆ in addition to the boron-tri-chloride (BCl₃) chemistry, the GaAs is etched selectively over the AlGaAs with selectivities over 5:1. Thus a robust two-step etching process has been developed based entirely on dry etching

In order to create high-performance integrated optical components based on polymers, such as on-chip spectrometers for lab-on-a-chip, significant process optimization is needed. Here is reported on the results of investigations concerning two aspects of processing of 40 μm thick coatings of the negative photoresist SU-8: 1) development of a process to remove the edge bead after spin coating, in order to reduce proximity effects in the exposure process, and 2) an investigation of parameters in the baking and exposure steps in order to optimize the lithographic resolution. Both aspects were investigated through design of experiment (DOE) and related statistical analysis. The first DOE investigated the significance of eight process parameters in solvent based edge bead removal (EBR), and involved 51 experiments. The optimized process based on the experimental series reduced the edge bead from approximately 30 μm to less than 1 μm, in effect eliminating it. The second DOE covered six parameters; two in the soft bake step, the exposure time, and three in the post-exposure bake. This DOE contained 64 experiments and resulted in significant resolution improvement. Because of the optimization the trench resolution was improved from a starting point of 6 μm to 2.5 μm, and the ridge resolution improved from 7 μm to 5 μm. As a final outcome the best procedure also results in crack-free films which do not delaminate.

We have previously demonstrated that two-photon induced polymerization allows fabrication of complex threedimensional structures such as photonic crystals and micromachines with a spatial resolution around 120 nm. In this report, we show the resolution improvement till 65 nm. Experimentally, 780-nm femtosecond laser pulses were focused into a photopolymerizable resin by a high numerical aperture objective lens. The resin is polymerized by means of radical initiation. In the radical polymerization, oxygen molecules dissolved in the resin inhibit the polymerization reactions by scavenging the radicals that initiate the polymerization. At controlled laser pulse energy, the radicals can survive and initiate polymerization only at the region where exposure energy is larger than the polymerization threshold, leading to a sub-diffraction-limited spatial resolution. In order to further improve the fabrication accuracy, we introduced a radical quencher into the resin, and at an optimized concentration the lateral spatial resolution was improved to 100 nm. Moreover, we fabricated a suspended fiber connected between two anchors by controlling the exposure dose within the fiber. After removing the unsolidified resin by ethanol and drying, a 65-nm width fiber was obtained, suggesting a possible spatial resolution of similar dimension. The size less than 1/10 of the excitation wavelength could satisfy requirements of many photonic and optoelectronic devices.

Vector diffraction theory was applied to study computationally the effect of two and three-zone annular multi-phase plates (AMPs) on the three-dimensional point-spread-function (PSF). The two- and four-dimensional solutions spaces associated with a two- and three-zone AMP, respectively, were discretized and the PSF was calculated using the Wolf diffraction integrals for each unique combination of zone radius and relative phase. Conditions are identified in which a three-zone AMP generates an intensity distribution that is super-resolved by 19% in the axial direction with minimal change in the transverse distribution and sufficiently small axial side-lobes that this intensity pattern could be used for advanced photolithographic techniques, such as multi-photon three-dimensional microfabrication.

Miniaturized, single mode polymer dye lasers are realized by means of grey scale electron beam lithography (EBL) in functionalized SU-8 2000 resist, doped with Rhodamine 6G laser dye. These devices offer the possibility of easy integration of single mode laser sources in polymer based lab-on-a-chip microsystems. The demonstrated laser device consists of a planar waveguide with a 1st-order distributed feedback grating (DFB) surface corrugation, which forms an optical resonator. When optically pumped at 532 nm, single mode lasing is obtained in the wavelength range 570 nm - 630 nm, determined by the grating period. Our results demonstrate the feasibility of fabricating advanced nano-structured active optical components in a rapid prototyping process.

Soft x-ray zone plate microscopy has proven to be a valuable imaging technique for nanoscale studies. It complements nano-analytic techniques such as electron and scanning probe microscopies, and offers a unique set of capabilities including high spatial resolution, natural elemental/chemical and magnetic sensitivities, large permissible sample thickness, and a myriad of in-situ sample environments. In this paper, a new zone plate fabrication technique based on overlaying complementary, semi-dense patterns is described. The new technique permits zone plates with sub-20 nm zones, which are extremely challenging for conventional fabrication processes, to be fabricated. With the new technique, zone plates of 15 nm outermost zone width were successfully fabricated for the first time, yielding a spatial resolution better than 15 nm. Zone plates of 10 nm outer zones, as well as 3-D zone plate structures, which cannot be fabricated using conventional zone plate fabrication processes, are anticipated with the overlay technique.

Planar chirality can lead to interesting polarization effects whose interpretation has invoked possible violation of reciprocity and time reversality. We show that a quasi-two-dimensional array consisting of gold nanoparticles with no symmetry plane and having sub-wavelength periodicity and thickness exhibits giant specific rotation (~10⁴ °/mm) at normal incidence. The rotation is the same for light incident on the front and back sides of the sample. Such reciprocity manifests three-dimensionality of the structure arising from the asymmetry of light-plasmon coupling at the air-metal and substrate-metal interfaces of the structure. The structures thus enable nanoscale polarization control but violate no symmetry principle.

We have developed a fabrication method for hollow anti-resonant reflecting waveguides (ARROW) on planar silicon substrates. Our fabrication technique is a bottom-up process making use of a sacrificial core material which is removed in an acid etch, leaving a hollow channel. This method is compatible with standard silicon processing steps, enabling the production of integrated devices. Using different core materials, we have build hollow ARROW waveguides with different core geometries, and have also demonstrated the fabrication of solid-core waveguides to interface with the hollow ARROWs. By optimizing the layer structure and fabrication process, we can reduce the optical loss of these waveguides to below 0.33/cm for liquid-filled waveguides and 2.4/cm for air-core waveguides.

We propose a fabrication method to realize tapered defects in three-dimensional photonic crystals. This process utilizes a combination of electron-beam lithography and ultraviolet interference lithography to create embedded defects within the photonic crystal lattice. We exploit the natural scattering profile of the electron beam within the thick resist film to create conical defects, where the angle of the cone can be tuned by adjusting the electron beam's accelerating voltage. The process begins by exposing a dot with e-beam, which generates a latent cone structure. This is followed by an exposure to an interference pattern formed by four coherent UV laser beam, which generates a 3D lattice surrounding the defects. Upon post-exposure bake, the areas that have received greater than threshold dose are crosslinked, yielding after developer treatment a 3D polymer photonic crystal with conical embedded defect. Subsequently, this structure is used as a template for backfilling with silicon via chemical vapor deposition. Further processing with standard silicon micormachining places the structure at the end of a cantilever that can be used in an instrument similar to an atomic force microscope or scanning probe microscope. We anticipate that these structures will find applications in multifunctional nanoprobe microscopy, because photonic-crystal defects can confine optical modes to smaller regions, with low propagation loss, than is possible with conventional tapered-fiber NSOM tips.

We report here on an effort to design and fabricate a polarization splitter that utilizes form-birefringence to disperse an input beam as a function of polarization content as well as wavelength spectrum. Our approach is unique in the polarization beam splitting geometry and the potential for tailoring the polarized beams' phase fronts to correct aberrations or add focusing power. A first cut design could be realized with a chirped duty cycle grating at a single etch depth. However, this approach presents a considerable fabrication obstacle since etch depths are a strong function of feature size, or grating period. We fabricated a period of 1.0 micron form-birefringent component, with a nominal depth of 1.7 microns, in GaAs using a CAIBE system with a 2-inch ion beam source diameter. The gas flows, ion energy, and sample temperature were all optimized to yield the desired etch profile.

The Step and Flash Imprint Lithography (S-FIL^TM) process is a step and repeat nano-imprint lithography (NIL) technique based on UV curable low viscosity liquids.^1,2,3Investigation by this group and others has shown that the resolution of replication by imprint lithography is limited only by the size of the structures that can be created on the template (mold). S-FIL uses field-to-field drop dispensing of UV curable liquids for step and repeat patterning. This approach allows for micro and nano-fabrication of devices with widely varying pattern densities and complicated structures. Wire grid polarizers and micro lenses are two examples for optical components that can be formed using SFIL technology. Step and Flash Imprint Lithography Reverse (S-FIL/R) tone has been used to form resist patterns for a number of different device types ^1,4,6. The authors have employed S-FIL/R and dry develop techniques to form resist patterns with 100 nm period useful for the fabrication of wire grid polarizers. S-FIL/R has a number of advantages over interference lithography techniques for the fabrication of sub 200 nm period grating structures including but no limited to pattern repeatability, vibration insensitivity, high aspect ratio feature formation, greater extendibility and high resolution. The authors have devised imprint and dry etching processes for resist and substrate patterning to form Al based wire grid polarizers with 100 nm pitch. The fabrication processes and resulting devises will be described. While S-FIL is useful for in the formation of resist patterned wafers, it is also capable of forming devices by functional material patterning. Polymer micro lenses are a good examples of functional material devices useful for a number of applications including CMOS and CCD cameras. The fact that lens geometry is defined by the template and requires no post imprint processing provides a strong advantage over current lens formation approaches. Recent results and the state of current micro lens fabrication by S-FIL is described.

UV-NanoImprint Lithography (NIL) is a fast and low cost method, which becomes an increasingly important instrument for fabrication of μ-TAS and telecommunication devices. The key elements of UV-NIL are transparent molds and low viscosity resists. Two different transparent mold materials, allowing UV curing through the stamp, were developed: rigid quartz or flexible PDMS. Typical resist viscosities are in a range of <100mPas, ensuring fast and successful filling of the stamp cavities. UV-curing is carried out at a wavelength of 350-450 nm.

A dual grating reflector is a scheme for wavelength stabilization of laser diodes. The fabrication of a dual grating reflector involves the fabrication of a grating coupler on the p-side of a laser diode and a feedback grating on the n-side of the same device. The basic theory of the dual grating reflector is presented, along with the methods used to determine the required tolerances for near optimum performance. The fabrication processes used to obtain the required tolerances needed for a dual grating reflector are presented.

The lateral oxidation of epitaxially grown Al_xGa_1-xAs layers is investigated in an open-chamber system based on a conventional horizontal tube furnace, and in a closed-chamber system. The oxidation is selective and depends on the Al content, process temperature, and process time. The process is characterized as a function of these parameters. The closed chamber system provides faster oxidation with superior control, repeatability and uniformity of the oxidation extent as compared to the open-chamber system. Based on these investigations of the oxidation reaction, we propose a unique method for realizing 3D photonic crystals in GaAs/AlGaAs-based material.

A novel manufacturing technique has been developed to make a stochastic antireflective structure into polymer substrates. This paper discusses the production method, test results, and applications for a new antireflective structure, PlasmAR. This capability has enhanced antireflective properties over visible wavelengths when compared with conventional single and multilayer antireflective coatings on polymers.

Three dimensions photonic crystals represent one of the most important building blocks towards the achievement of a full optics communication technology. Although several methods have been demonstrated to prepare 3D photon crystals, 3D photonic crystals still represent a challenge to a fabrication point of view. It is highly desirable that the fabrication of these 3D structures involves simple technologies. In this paper, a novel method has been developed to fabricate 3D photonic crystals structure. The process of multi deep X-ray lithography is: Firstly, the cube or cuboid of resist sample is shaped by lathe. Then, the microstructures are patterned by three times deep X-ray lithograph through three surfaces that are vertically each other. After development, the 3D PC structure is obtained. The 3D photonic crystals structures are fabricated to demonstrate this method. The result shows that this method can avoid many problems caused by tilt X-ray lithography and the lattice layer is enough to meet the requirement of 3D photonic crystals. It is simple and effective to realize the 3D photonic crystals structure by using multi deep X-ray lithography. And various 3D photonic crystals types and lattice defects can be achieved by using this method.

Extreme ultraviolet lithography (EUVL) is the most likely next generation lithography technique which uses radiation near 13.4 nm wavelength. At this short wavelength, most materials readily absorb the radiation, making refractive lens optical systems unusable. We demonstrate a novel method for fabrication of highly efficient optics for extreme ultraviolet (EUV) radiation using focused ion beam (FIB). These optics are based on Fresnel zone plates, similar to those used for x-ray microscopy, but with a geometry to improve the efficiency for EUV radiation. A typical zone plate has concentric rings with a radially decreasing feature size such that the path of light through every second zone to the focus differs by one optical wavelength following the Bragg's Law. An optic with a net efficiency of 21% can be achieved for 13.4 nm radiation using the standard zone plate design with 86 nm thick zones made from Mo and mounted on a 50 nm silicon nitride membrane. Further improvement in the efficiency can be achieved by fabricating blazed zone plates, which can have a net efficiency of 40% when fabricated on a 50 nm silicon nitride membrane. These lenses are cheap to manufacture and easy to align for imaging since it is a single optic. The preliminary data will be presented on the fabrication of both standard and blazed zone plates optimized for EUV radiation.

This paper describes the fabrication of several diverse examples of molding tools designed for high volume production of plastic and glass optical components. The examples shown demonstrate a wide combination of surface shapes and structures all with nanometer level accuracy. The tungsten carbide molding tools were produced using grinding and magnetorheological finishing (MRF), new raster fabrication, and micro-milling. Mold tools were fabricated to produce a glass free-form surface, (profile accuracy of less than 200nm in PV, surface roughness of less than Ra5nm), a radial arrangement of 188-microlens, a microscopic pin (3um in diameter, 100um in height), and a molding tool for DOE with little optical loss. The molding of glass optics requires mold materials which can be used at high temperatures. In addition to tungsten carbide this paper describes molds fabricated from nano-structural sintered material or ceramic with partially stabilized molecular structure.

This paper demonstrates a new tolerancing technique that allows the prediction of microlens optical performance based on metrology measurements taken during the fabrication process. A method for tolerancing microlenses to ensure operating performance using the optical design code ZEMAX^(R) is presented. Parameters able to be measured by available metrology tools are assigned tolerances. The goal of the tolerance analysis is to assess the sensitivity of a microlens design to changes in the shape of the lens surface with regard to specific optical performance criteria related to the intended application. Two designs are presented with the tolerance analysis results. In the first design, the radius of curvature and conic constant are varied for an aspheric lens, and the change in the spot size is determined. For the second design, fiber-coupling efficiency is tabulated for a biconic lens. In each case, a metric can be produced showing the ability of the design to meet performance goals within the specified tolerances. A fabrication technician can then use this tolerancing metric with appropriate metrology data to determine if the device will yield acceptable performance. The metric can also determine if a design is overly sensitive to expected tolerances, thereby allowing the optical designer to evaluate the design from a manufacturing perspective.