As an ultrafast laser has recently been developed, this leads to the innovative nanotechnology, the 3-D fabrication of the two-photon absorbed (TPA) photo-polymerization. The 3-D micro/nano structure by this method has a resolution of sub-hundred nm which is much smaller than the diffraction limit. Usually the 3-D polymer micro/nano structure by this method is made by stacking many of a unit polymer structure, so called 'voxel'. The size of the voxel is considered as the fabrication resolution. The size of a voxel, or the fabricating resolution is determined by several fabricating conditions such as the laser output power, the exposure time, the N.A. of the focusing lens, the types of polymerizing material, and the pulse-width. The voxel size due to power, exposure time and NA has been done by many research groups. Although the pulse-width is a very important condition for two-photon absorption, the study of influence on fabricating resolution by the pulse-width has not been done before. Therefore we studied the voxel size under the condition of increasing the pulse-width of the laser. To stretch the pulse-width, a single mode fiber (SMF) has been used. We demonstrated that the voxel lateral size decreased as pulse-width stretched to several picoseconds.

Functional prototypes produced via laser sintering already address the sub millimeter region with resolutions in the low micrometer range. The manufacturing process is very suitable for small scale, micro featured functional polymer parts because of its ability to generate complex and fine shaped geometries including undercuts and pores. The parts are built up layer by layer from three-dimensional data generated by CAD programs or by micro computer tomography as a copy of already existing parts. Up to now this field is dominated by polyamide, a semi-crystalline polymer. This thermoplastic material covers a wide range of applications but requirements concerning a high temperature resistance above 200 °C and tensile strengths above 50 N/mm² are not fulfilled despite glass fillings. A change in the sintering material can solve this issue. Investigations show that polyetheretherketone (PEEK) which is a high performance polymer with a melting temperature of 346°C can be used for laser sintering. Manufacturing small sized and micro featured parts with enhanced temperature and mechanical properties is possible using an adapted system technology. For minimum vertical outer features a value of about 250 &mgr;m was found, expanded outer features like walls show a width of 650 &mgr;m. A first low boundary for hole-diameters in the feeding 3D-data set was found. As a basic boundary for minimum geometrical features a core roughness average of about 23.3 &mgr;m could be measured.

The temporal coupling of femtosecond and nanosecond laser induces a remarkable increase in the processing efficiency 12 times more than that with an independent laser exposure. When femtosecond laser arrives before nanosecond laser, the dependence of the ablation efficiency on the time delay between the femtosecond and nanosecond laser pulses is very resemble to nanosecond laser traces. When femtosecond laser arrives after nanosecond laser, however, we observed an apparent delayed decaying component with a time constant of several hundreds of nanosecond in the ablation efficiency curve. Based on the current observation, we have explained the rather large enhancement in femtosecond laser ablation efficiency with synchronization between femtosecond and nanosecond laser in terms of silicon surface metallization due to the proceeding nanosecond laser. Such a progress in femtosecond laser micro processing makes it possible to maximize the processing speed and reduce the processing threshold energy. The current findings prominently reduce a various high order nonlinear effects which are frequently confronted when we focus high-power femtosecond laser pulses on the target under atmospheric conditions.

Arbitrarily complex 3-D polymeric structures with a resolution of under 100 nm are fabricated by two-photon absorption polymerization (TPAP) by an ultra-short pulsed laser. This method can be applied to many scientific and engineering fields such as micro/nano-optics, MEMS, microfluidic system, and so on. Many 3-D structures by TPA fabrication have been made. However the structures made with an acrylate-based prepolymer material have seriously structural problems, such as shrinkage, collapse, distortion, etc. These problems make the fabrication of a large and fine 3-D structure difficult. Using an epoxy-based material like SU-8, which is widely used in the conventional lithography, the problems above can be prevented. Although SU-8 is designed for the UV lithography, a two-photon absorbing dye and proton acid generator can make it a base prepolymer material for the two-photon absorption polymerization. We studied the size of voxel or the resolution of fabrication from the SU-8 structures under the various fabrication conditions such as the laser output power and the exposure time. We demonstrated 3-D micro/nano structures with SU-8 and compared them with same structure with SCR-500.

Silex Microsystems handles a wide range of customized MEMS components. This speech will be describing Silex's MEMS foundry work model for providing customized solutions based on MEMS in a cost effective and well controlled manner. Factors for success are the capabilities to reformulate a customer product concept to manufacturing processes in the wafer fab, using standard process modules and production equipment. A well-controlled system increases the likelihood of a first batch success and enables fast ramp-up into volume production. The following success factors can be listed: strong enduring relationships with the customers; highly qualified well-experienced specialists working close with the customer; process solutions and building blocks ready to use out of a library; addressing manufacturing issues in the early design phase; in-house know how to meet demands for volume manufacturing; access to a wafer fab with high capacity, good organization, high availability of equipment, and short lead times; process development done in the manufacturing environment using production equipment for easy ramp-up to volume production. The article covers a method of working to address these factors: to have a long and enduring relationships with customers utilizing MEMS expertise and working close with customers, to translate their product ideas to MEMS components; to have stable process solutions for features such as Low ohmic vias, Spiked electrodes, Cantilevers, Silicon optical mirrors, Micro needles, etc, which can be used and modified for the customer needs; to use a structured development and design methodology in order to handle hundreds of process modules, and setting up standard run sheets. It is also very important to do real time process development in the manufacturing line. It minimizes the lead-time for the ramp-up of production; to have access to a state of the art Wafer Fab which is well organized, controlled and flexible, with high capacity and short lead-time for prototypes. It is crucial to have intimate control of processes, equipment, organization, production flow control and WIP. This has been addressed by using a fully computerized control and reporting system.

The fabrication of 3D high aspect ratio structures with positively sloped profiles has found extensive applications both in the front-end and in the back-end semiconductor manufacturing. Often, high etch rates are required and plasma etching processes with F-based chemistries need to be employed. However, plasma etching of silicon in F-based chemistries generally results in so-called "cusping" due to its isotropic nature. Of particular interest are the etch profiles with slope angles in the range of 50-80^o and without "cusping" at the top portion of etched structures. For 3D packaging applications, for example, even small cusping could degrade the step-coverage of diffusion barrier layer and metal seed layer and cause void formation in subsequent metal filling processes. At Oerlikon USA Inc., a proprietary process scheme has been developed to etch deep and positively sloped silicon structures (vias, trenches, etc.) at high etch rates while eliminating cusping with precise profile control. The new process scheme employs main plasma etch steps using gas mixtures and deposition pulse steps. And the deposition pulses intermittently punctuate the main etch steps. Using standard gases, such as SF₆ and C₄F₈, sloped Si trenches with slope angle of ~60^o are etched in both 6" and 8" wafers, at etch rates of ~7.0 (micron)m/min. Etch selectivity to photoresist mask materials exceeds 100:1. The process scheme and underlying mechanism will be presented in this work.

For the past few years we have been investigating the photophysical and photostructurable properties of Foturan, a photostructurable glass ceramic (PSGC) manufactured by Schott Glass Corp. In this paper, we discuss results on using Foturan as a MEMS and MOEMS substrate. Microfabrication in Foturan is possible through patterning by a pulsed UV laser, a subsequent heat treatment step, and chemical etching. In Foturan, the exposed areas undergo a selective phase change in which the native amorphous glass phase converts to a crystalline lithium silicate phase. The degree and type of crystallization are both sensitive functions of the irradiation and thermal processing procedures. Under high exposure dose, the crystallized areas etch up to 30 times faster than the unexposed material in HF, with the etch rate varying with irradiation dose. Because Foturan is transparent at visible through IR wavelengths, direct-write XYZ exposure with a pulsed laser can pattern complex 3-D structures within a sample. Devices made from Foturan may be glass, a glass-ceramic composite, or ceramic, with the final material composition depending on the irradiation and thermal processing procedures. Excellent aspect ratios (>30:1) have already been demonstrated in Foturan. Our interest is in making simple 3-D MEMS structures by implementing cost-effective manufacturing solutions that produce consistent results with a resolution on the order of ten microns.

Hydrolyzed silane primer solutions were made of an organosilane in glycolether diluted with a large amount of water with or without an acid as a catalyst. The newly developed primer compositions exhibited an extended shelf life of 3 months or more. The compositions were specially designed to accommodate ProTEK^TM. layer adhesion in the TALON Wrap. process. In this application, a spin-coatable polymeric material, ProTEK^TM., is applied as the protective coating to coat the top, edge, and underside rim of the wafer in preparation for backside etching. By applying an underlayer of primer and an overlayer of ProTEK^TM. coating to the top, edge and the bottom side rim of the wafer, an effective encapsulation of the wafer was achieved by using a custom-designed baffle. Each layer was applied by spin coating followed by baking at a wide temperature range. Thermal processing was followed by wet etching in KOH at an elevated temperature for . 10 hr. Post-etched wafers were rinsed with deionized (DI) water. Excellent edge profiles without "knife-edges" were obtained after etching the unprotected areas of the wafer. The process is fully automated because it is carried out in the TALON^TM automated wafer-processing tool. Intact films with no lifting or peeling were obtained during or after the KOH etch process/DI rinse for silicon substrates.

This paper presents the trends for the years to come for the different MEMS markets. Consumer applications have really started to push the MEMS business in 2005. Many different devices are involved, like pressure sensors (altimeters), microphones, accelerometers, gyroscopes . . . One of the most significant consequences is that all the Top 50 semiconductor companies are now looking at these MEMS applications as possible growth areas. Another result of the growth of the MEMS market is the strong growth of the foundries and contract manufacturers. We have seen growth of more than 35% in 2005 compared to 2004 and we expect similar growth in the next 3 years. We will review the next MEMS applications which have currently a high growth: Si microphones, microdisplays (for RPTV, portable projectors or automotive HUDs), gyroscopes and micro-fuel cells. In the longer term, micro-source of energy could also become an important MEMS market. In term of milestones, the following points can be highlighted: -In 2005 market, the MEMS market is 5.1 B$ worldwide and very fragmented in terms of companies and products. -In 2010, it will be a 9.7 B$ market worldwide. MEMS foundries and contract manufacturers will account for at least 8 % of the world market with several being public companies. More than 50% of today's systems companies who have integrated fabs will be using external manufacturers. Several large integrated companies will have created independent MEMS spin-offs and IC manufacturers will be deeply involved in MEMS manufacturing. -In 2015, it will be an 18 B$ market worldwide with no longer systems manufacturers with internal fabs. And we forecast that 50% of the total market will be in the hands of semiconductor manufacturers.

We report fabrication technology for micro fluidic filter device with fine and high aspect ratio filtration gap using single-mask and CMOS compatible process flow. Advantage of Si based Microfabrication platform technology has been fully exploited by adopting manufacture-able process flow. A novel approach of combining silicon deep reactive ion etch (RIE) capability with subsequent gap-fill engineering enabled achieve wide range of filtration gaps of deep sub-micron size with high aspect ratios of >200. This approach eliminated the need to use high-end lithography techniques in order to achieve deep sub-micron gaps after pattern transfer. Si deep RIE etch process was optimized by applying dual passivation technique which enabled to realize sub-micron gap pillar-type filter structures and large reaction chambers simultaneously using single-mask process. Wide range of filtration gap sizes demonstrated in this work offer versatile applications for fine cell trapping such as protozoa and bacteria. Fluid injection channels for the device were realized through wafer backside Si wet etch processing to complete the filter device chip fabrication.

Thin film fabrication processes for MEMS are characterized by a variety of different process technologies and materials. Unlike in microelectronics the MEMS fabrication process is in most cases application specific and therefore integral part of the application design. Discovering the correct combination of process steps, materials and process parameters usually requires many expensive and time consuming experiments. This paper presents a new software system that supports the MEMS device and process designers in managing their process knowledge and in verifying their fabrication processes in virtual fabrication environment, thus reducing the number of real world experiments to a minimum.

Replication technologies have been recommended as an alternative means of high volume manufacturing of the polymer optical components with low-cost. We demonstrated replication technology as a means of implementing polymer-based MOEMS. To achieve this, a polymer optical bench with embedded electric circuits was designed to integrate the functional planar-lightwave-circuit (PLC)-type optical waveguide devices; the designed packaging structures were realized using a novel fabrication process that incorporated the UV imprint technique. In addition, the detail fabrication steps of the UV imprint process were investigated. The optical bench has v-grooves for the fiber ribbon and the alignment pits for opoelectronic interconnection. The plastic mold for imprinting the designed optical bench was made of UV-transparent perfluorinated polymer material. The designed optical bench was configured on the electric-circuitpatterned silicon substrate. Flip-chip bonded polymer optical waveguide device showed not only a good electric contact but also a coupling loss of 0.9 dB at a wavelength of 1.5 ?m. It was concluded that replication technology has versatile application capabilities in manufacturing next generation optical interconnect systems.

We present the fabrication of a kind of hexagonal and triangular cavity mold, which can cast Polymethyl Methacrylate (PMMA) resonators and couplers. The mold is designed on (111) silicon wafer according to its crystal structure and anisotropic etching properties in the etchant of ethylene diamine, pyrocatechol, and water (EDP/EPW), forming sidewalls by six {110} crystal surfaces, which are perpendicular to the (111) plane and constitute precise hexagons and triangles. The RIE-ICP etching is used to define the depth of the triangle and hexagonal cavities, and the following EDP etching smoothes the sidewalls of cavities. Only high temperature EDP etching is proved to be able to get smooth sidewalls. Before etching, the wafer is aligned to the right crystal orientation by pre-etched marks. The etched results of different geometrical cavities are analyzed and discussed based on the crystal structure.

Plasma etching is an enabling technology in nano optic, nanoelectronic devices, nano electro mechanical systems (NEMS) and nanoresolution templates for nano imprint lithography (NIL). With shrinkage, one must overcome significant challenges to meet the stringent profile and CD goals necessary for nanoscale applications. Using the example of Si nanoimprint template fabrication, we show how ion/sidewall/mask interactions can dominate feature profile evolution at the nanoscale and what to look for successful pattern transfer. Gas chopping or multiplexed etching, generally used for deep silicon etching, is often avoided at the nanoscale due to unacceptable undercut and sidewall scalloping. We demonstrate a multiplexed etching process in silicon with sub-5 nm amplitude scallops which is well suited for NEMS and nano optics applications and which reduces the deleterious role of ion/sidewall/mask interactions at the nanoscale.

Fueled by the need for better performing optics, glass optics are now replacing plastic optics in many industrial and consumer electronic devices. One of these devices is the mobile phone camera. The optical sub-assembly in a mobile phone includes several micro lenses that are spherical and/or aspherical in shape and require form tolerances in the submicron range. These micro glass lenses are mass produced by a replication process known as glass press molding. The process entails the compression of a glass gob between two precise optical quality molds at an elevated temperature, usually near the transition temperature of the glass material. The elevated forces and temperatures required in the glass molding process limits the materials of the molds to very tough materials such as tungsten carbide or silicon carbide. These materials can withstand large pressing forces at high temperatures without any significant deformation. These materials offer great mechanical properties for glass press molding but they are also a challenge to machine to submicron accuracy. The work in this paper discusses a deterministic micro grinding manufacturing process referred to as wheel normal grinding, which is utilized to produce these optical quality molds. Wheel normal grinding is more accurate and more deterministic than most other grinding techniques and can produce molds to the form and finish tolerances required for optical molding. This method relies on the ability to recognize and compensate for grinding wheel wear and machine repeatable errors. Results will be presented to illustrate the accuracy of this micro grinding technique.

In this paper we will discuss the use of the crossbeam ZEISS XB1540 applied to photonic structures and to obtain nano-imprinting templates. Some 1D Photonic Crystals (PhC) on silica based optical waveguides are shown as well as the realization of 3D optical structures curved directly on silica and used subsequently as a master for imprinting. Focused ion beam lithography (FIB) is a technique for direct writing of patterns; it means is substantially slow, but its versatility and the combination with other "faster" techniques make it an interesting method to produce prototypes and special devices. The resolution and the perturbation of the samples are perfectly compatible with the photonic applications. In fact, the contamination due to the gallium ion implantation as well as the roughness of the vertical and horizontal surface doesn't affect the performance of the devices shown in this paper.

The literature on high brightness LED's shows that patterning the top surface of LED's with photonic crystals is being used to create the most intense LED light sources. The best example is that you can now buy projection displays that are illuminated by LED's with Photonic Crystals. The experimental and model data, reviewed in this article, shows that patterning delivers value through improved beam shaping and light extraction using carefully optimized photonic crystals. The data also suggests that in the future, patterning in combination with sub micron device layers and strategically placed mirrors can produce extraction efficiencies of greater than 80%. In addition, patterning can improve current spreading and reduce epitaxy defects. The long term goal is to develop a LED that can be used with minimal additional packaging to focus the light or extract heat. The solution to low cost patterning for Photonic Crystals 100 nm features is to use imprint. The imprint patterning process is implemented in a module that consists of a clean and coat tool, an imprint tool and an etch tool. Cleaning is essential because imprint is a contact technology and particles will lead to process defects and mold damage. There are 2 companies that are developing production tools for LED applications; Molecular Imprints (MII) and Obducat. There are 2 companies that are supporting research tools, and expect to develop production systems in response to customer order, EV Group and Nanonex. The principal difference between imprint suppliers are the different strategies used to conform the mold to the substrate, and the state of system development. To date MII has published the most complete process performance data on an automated production tool. The cost of patterning is less than 0.5 cent per device. First the value of increased LED output will be described, followed by a discussion of the different patterning solutions for improving output, then the different solutions for creating the patterning will be described and finally the costs are estimated.

We demonstrate wafer-scale fabrication of integrated polymer optics, comprising nm to mm features, by combined nanoimprint and photolithography (CNP). Active and passive polymer optical components are integrated: Distributed feed-back (DFB) polymer dye lasers and polymer waveguides. The laser devices are defined in SU-8 resist, doped with Rhodamine 6G laser dye, shaped as planar slab waveguides on a Si/SiO₂ substrate, and with a 1st-order DFB surface corrugation forming the laser resonator. In the CNP process, a combined UV mask and nanoimprint stamp is embossed into the resist, which is softened by heating, and UV exposed. Hereby the mm to (micron)m sized features are defined by the UV exposure through the metal mask, while nm-scale features are formed by mechanical deformation (nanoimprinting). The UV exposed (and imprinted) SU-8 is crosslinked by a post-exposure bake, before the stamp and substrate are separated, and the un-exposed resist is dissolved. Polymer waveguides are added to the system by an additional UV lithography step in a film of un-doped SU-8, which is spincoated on top of the lasers and substrate. When optically pumped at 532 nm, lasing is obtained in the wavelength range 559 nm - 600 nm, determined by the grating period. Our results, where 20 laser devices are defined across a 10 cm diameter wafer substrate, demonstrate the feasibility of CNP for wafer-scale fabrication of advanced nano-structured active and passive polymer optical components.

Two optical devices with nano-scale subwavelength structures have been fabricated by using nanoimprint lithography (NIL). (1) Wire grid polarizer (WGP) is one of key optical components for projection displays with liquid crystal micro-display. Although WGP with 140 nm pitch is commercially available now, it still poses a problem with low extinction ratio (ER) for blue color. Since the ER can be increased by reducing the pitch, fabrication of a WGP with 100 nm pitch was attempted by NIL. We successfully developed thermal nanoimprint and aluminum dry etching processes. Fabricated WGPs showed twice higher ER than 140 nm pitch one. (2) Photonic crystal (PC) structures on LED have been known to enhance the light extraction significantly. Although e-beam lithography has been used for the proof of principle, it is far from real production method. We applied thermal NIL to fabricate PC structures in p-GaN layer of green LED. To identify the PC effect, two structures were fabricated and compared. One structure makes the green light of 525 nm wavelength fall within the photonic band gap (PBG) while the other puts it outside of PBG. The former structure showed 9-fold increment of photoluminescence compared to LED without PC structures, while the latter showed only 6-fold increment

Engineering of both the polarization state and the operating frequency band can be accomplished by nanoengineering the morphology of a complex substance such that it is both anisotropic as well as periodic and/or structurally chiral. Three examples show that sculptured-thin-film technology provides opportunities for polarization engineering in specific spectral regimes through nanoengineered morphology.

In the past two decades, photonic crystals (PhCs) have received rapidly increasing attentions for their unique properties of confining, directing and manipulating the propagation of electromagnetic waves. Since the lattice constant is usually comparable to the operating wavelength, advanced lithography techniques are borrowed from integrated circuits (ICs) fabrication to pattern PhCs. For many applications working in visible or near infrared light, however, fabrication of PhCs is difficult unless E-beam system or high-end stepper is employed. In this paper, we present a new lithography method, Chemical Lithography (ChemLith), for the fabrication of planar PhCs. The concept is based on the fact that most of the commonly used photoresists change their solubility upon an acid-catalyzed chemical reaction. In photolithography, photo acid generator (PAG) is mixed in the resist formula, and the acid is generated by photon-initiated reactions. Using photons sets the fundamental limit on the feature size for photolithography. To overcome this limit, we propose to physically introduce the catalyzing acid (proton source) to the desired position on the resist surface. Using a prefabricated template, we have implemented this concept for patterning of planar PhCs. In this work, we have tested different acids as well as commercially available resist systems. We will show some of the experiment results, and discuss potential issues of the proposed method for further development.

As the development of extreme ultraviolet (EUV) lithography progresses, interest grows in the extension of traditional optical components to the EUV regime. The strong absorption of EUV by most materials and its extremely short wavelength, however, makes it very difficult to implement many components that are commonplace in the longer wavelength regimes. One such component is the diffractive optical element used, for example, in illumination systems to efficiently generate modified pupil fills. Here we demonstrate the fabrication and characterization of EUV binary phase-only computer-generated holograms allowing arbitrary far-field diffraction patterns to be generated.

We demonstrate deposition of periodic tungsten nanoripple on different substrate using a single 400nm femtosecond laser beam at room temperature. The laser beam generated by frequency doubling the output from mode-locked 80MHz Ti: sapphire oscillator was applied in a laser-induced chemical vapor deposition configuration, in which tungsten hexacarbonyl was used as precursor. The deposition strongly depended on laser polarization. With linearly polarized light, periodic ripple structure with willow-leaf shape was formed inside the exposure area. The ripple orientation was found parallel to the laser polarization direction. Affects of laser power and exposure time on ripple formation were investigated. By translating the substrate with respective to the laser beam, longitudinal or transverse grating structure was observed. The period of this grating structure is about 150nm on sapphire, and the orientation is parallel to laser polarization. Simply by programming the translation of the substrate, large area patterns and other patterns such as circle and characters were formed. Similar ripple and grating structures observed on all the substrates we investigated, including insulators, semiconductors and metals, implies that ripple formation might be a universal phenomenon. Considering the simplicity of this process and material flexibility of laser CVD, this technique may provide a novel costeffective patterning method to produce periodic subwavelength nanostructures of a wide range of materials on many substrates.

We have previously produced antiresonant reflecting optical waveguides (ARROWs) with hollow cores that can guide light through liquid or gas media. In order to utilize these structures in sophisticated sensing applications, we have improved our initial designs and fabrication methods to increase yield, lower waveguide transmission loss, and incorporate structural features into the waveguides themselves. Yields have been increased by optimizing PECVD film conformality leading to greater sidewall strength for hollow waveguides. Sensing applications require interfacing hollow waveguides with solid waveguides on the surface of a substrate to direct light on and off a chip and into and out of a test medium. Previous interfaces required light transferring from solid to hollow waveguides to pass through the antiresonant layers, with measured transmission efficiencies of about 30%. By removing the ARROW layers at the interfaces, transmission efficiencies at these interfaces can be improved to greater than 95%. We also demonstrate the fabrication of micropore structures on the hollow waveguides to be used for chemical sensing. A fabrication method has been developed that allows for removal of the thick top oxide and nitride ARROW layers leaving only a thin nitride membrane directly over the hollow core allowing controlled access to test media.

A fabrication process for PFCB waveguide air-trench bends with scanning electron microscope (SEM)-based electron beam lithography (EBL) and autoalignment has been developed and high efficiency air-trench bends (97.2% for TE polarization and 96.2% for TM polarization) have been demonstrated. We have successfully developed a high aspect ratio (18:1) anisotropic PFCB etch using a CO/O₂ etch chemistry in an inductively coupled plasma reactive ion etcher (ICP RIE) for PFCB waveguide air-trench splitter fabrication. The fabricated splitters show a 90.1% overall efficiency and ~ 85-to-15 (85:15) splitting ratio for 950 nm wide splitter trench, which closely matches 2D-FDTD simulation results. Using air-trench bends, an ultracompact PFCB arrayed waveguide grating (AWG) 8 x 8 wavelength demultiplexer for Wavelength Division Multiplexing (WDM) application had been designed. Compared to a conventional AWG in the same material system, the air-trench bend AWG reduces the area required by a factor of 20. Compact ring resonators using these splitters and bends has been designed and fabrication and improvements are currently underway.

Laser micromachining by ablation is an established technique for the production of 2.5D and 3D features in a wide variety of materials. Mask projection techniques using excimer lasers have been used to fabricate microstructures on large panels where diamond turning and reflow techniques have reached their limits. We have developed 3D structuring tools based upon UV laser ablation of polymers to create large arrays of repeating micro-optical features. Synchronization of laser pulses with workpiece movement allows layer-by-layer growth of deep structures with outstanding repeatability. Here, we show recent developments in laser structuring with the combination of half-tone and binary mask techniques. Significant improvements in surface quality are demonstrated for a limited range of structures.

Many manufacturing techniques have been developed and implemented to fabricate a wide range of micro-optical products. The challenges of the micro-optics business are diverse and tend to resist a widely accepted manufacturing process such as has been implemented for CMOS fabrication. Many of the challenges that have been addressed with various solutions include optical waveband of operation from DUV through LWIR, material systems, cost of manufacturing for the intended application space, feature sizes based on device functionality, and fabrication technology based on the manufacturing volume. Some of the technologies to be discussed include device patterning by e-beam lithography, optical lithography, direct CNC machining and micro-polishing, and plastic replication.

Considerable effort has gone into the development of techniques for three-dimensional fabrication. A particularly promising class of techniques for creating 3D structures relies upon the use of multiphoton absorption. In multiphoton absorption polymerization (MAP), 3D structures are created on a point-by-point basis by hardening a prepolymer resin with a tightly focused laser beam. While MAP offers the capability of creating arbitrarily complex 3D structures with feature sizes on the order of 100 nm, it is inherently a serial technique. In order to scale this technique up for mass production of microstructures, it will be necessary to develop a means for parallelizing the creation of structures on the wafer scale. One promising avenue for attaining this goal is the use of soft lithography, in the form of microtransfer molding (&mgr;TM). However, in the past &mgr;TM has been limited to the reproduction of "2.5D" structures, i.e. those without closed loops. We have developed a new technique called membrane-assisted microtransfer molding (MA-&mgr;TM) that can circumvent the closed-loop issue, allowing for the replication of truly 3D structures.

The prospect of an inexpensive organic laser which can dynamically alter its lasing wavelength is desirable for a number of display and communication technologies. In this effort, real-time tuning of the lasing wavelength is accomplished through the use of colloidal crystals to provide the required reflectivity in an external resonator cavity design in which a gain medium is sandwiched between a dielectric stack and colloidal crystal. Optical pumping of the gain medium lead to a lasing peak that corresponded to the stop band of the photonic crystal. By varying the compressive strain placed on the colloidal crystal, the lasing could be tuned across the photoluminescent spectrum of the gain material. Repeated straining of the assembly did not appear to alter its proclivity to lase when photo-excited or introduce hysteresis in the lasing wavelength strain relationship. The fast response of the crystal to compressive strain could lead to pulsed organic lasers operating at kHz modulation frequencies.

Infrared, femtosecond laser pulses are ideal for the fabrication of 3D structures in transparent media. Due to the low absorption cross-section, 2 or more photons are necessary for absorption. This multi-photon effect limits the affected volume to the focal area allowing for sharp features on the order of the wavelength of light. One possible multi-photon reaction is the photo-destruction (ablation, decomposition, etc.) or photo-polymerization of materials. Using these techniques, 3D photonic components can be realized. A photonic band gap template has been created with a monodisperse polystyrene (PS) spheres (diameter ~ 624 nm). We have used ultrafast laser pulses to remove spheres (introduce defined defects) at the surface to gain a fuller understanding of the laser-material interaction. To optimally focus inside the bulk, an index matching material must be infiltrated. By using a photosensitive material, two-photon polymerization can be used to harden the material surrounding the spheres and insert defects inside the bulk. With proper placement of defects, 3D photonic components, i.e., waveguides, splitters, and filters, can be created.

Interest in three-dimensional (3D) metal photonic crystals (MPCs) has grown considerably given their potential applications in optics and photonics. Yet, experimental studies of such materials remain few because of the difficulties associated with fabricating 3D micron- and sub-micron-scale metallic structures. We report a route to MPCs based on metallization of 3D polymeric photonic crystals fabricated by multi-photon direct laser writing. Polymeric photonic crystals (PCs) having simple-cubic symmetry with periodicities varying from 1.6 to 3.2 microns were created using a cross-linkable acrylate pre-polymer. The resulting dielectric PCs were metallized by electroless deposition of silver. Analysis of the metallized structures in cross-section by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy shows that silver deposited conformally onto the entire micro-porous lattice. The dielectric and metallized PCs were characterized by Fourier transform infrared (FTIR) spectroscopy in the (001) direction. The polymer photonic crystals exhibit a stop band resulting in circa 60% reflectance centered at 3.2 to 6.4 microns, depending upon the lattice period, with a full-width at half-maximum (FWHM) of 500 nm. Interestingly, FTIR spectra of the metallized PCs show widened stop bands of nearly 6 microns FWHM, while the center wavelengths were red shifted and ranged from 6 to 7 microns. The appreciable broadening of the stop band due to the presence of the deposited silver is a result consistent with previously reported theoretical and experimental data for all-metallic 3D PCs. Thus, the approach described here appears suitable for fabricating 3D MPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.

We study the application of two-photon absorption of near infrared femtosecond laser pulses and nonlinear maskless femtosecond laser lithography for the fabrication of dielectric and metallic SPP-structures, being used for localization, guiding, and manipulation of SPPs on a subwavelength scale. Resolutions down to 100 nm are already achievable. Characterization of these structures is performed by detection of the plasmon leakage radiation. Nonlinear lithography allows the fabrication of dielectric waveguides, splitters, and couplers directly on metal surfaces, e. g. by two-photon polymerization. The dielectric structures on metal films are demonstrated to be very efficient for the excitation of SPPs. Using these structures, excitation and focusing of the resulting plasmon field can be achieved. Results on the fabrication and characterization of metallic SPP-structures and components on dielectric substrates fabricated by nonlinear femtosecond laser lithography will be presented and discussed.

Patterning of SiO₂ materials like fused silica, crystalline quartz, or SiO₂-thin films by laser ablation is very challenging based on their high transparency in the whole spectral range from the deep UV to the near IR. Therefore laser microfabrication of UV-optical elements, e.g. silica micro lenses is rather difficult. In those cases where only a shallow surface relief on a silica slab is required, like for instance in the case of phase gratings, a new approach provides a flexible solution. The novel fabrication process consists of three steps. First, a silicon suboxide coating (SiO_x with x < 2) with a predefined thickness is deposited on a fused silica substrate. Second, utilizing its strong UV-absorption, this coating is removed in defined areas by excimer laser ablation at 193 nm or 248 nm leading to the desired phase pattern in form of a binary depth profile. Third, by applying a thermal annealing process, the remaining SiO_x-coating is oxidized to UV-transparent SiO₂. This results in a SiO₂-surface relief element with excellent UV-transmission. The precisely defined interface between substrate and layer allows for ablation with exact depth control and perfect optical surface quality. Various irradiation concepts for the fabrication of low line density gratings (period ~ 10 microns) and high line density gratings (period < 1 micron) are demonstrated. The fabricated phase masks can be used in various laser applications like fabrication of Bragg gratings in optical fibers or micro- and nano-patterning by high power laser ablation.

We have produced aluminum wire grids with 33 nm periodicity using a thin film of a self-assembling cylinder forming diblock copolymer as a template. These grids, supported on fused quartz wafers, function as transmission polarizers for visible and near-ultraviolet lights and are a thin design, compared to commercially available polarization prisms. Their polarization efficiency is measured to be near 50% in the visible. Quantitative comparison with a new theoretical analysis of such wire grids indicates that they should perform well into the far UV. This analysis also explains a reversal in polarization direction at short wavelengths which we observe in our specimens. This is an expanded version of a previous paper.¹

Micro- and nano-sized periodic structures are important components for wavelength dispersion, conversion, signal processing and modulation of optical signals. Thus, many micromachining technologies for the micro- and nano-sized patterns have been recently studied. Especially, nano-imprinting lithography has been rapidly developed as an attractive, low-cost alternative to photolithography and other lithographic techniques. Meanwhile, newly optimized materials for the specific nano-imprinting process have been continually required. Recently, the functionally modified inorganic-organic hybrid materials were found to have a highly efficient thermal curability, a high optical transparency in the visible and near infrared wavelength regions, and excellent mechanical and thermal properties once fully cured. In this study, we could successfully fabricate the micro- and nano-sized periodic structures by thermal nanoimprinting process using our original functionally modified hybrid materials. The fabricated structures exhibited the excellent uniformity and surface smoothness through a large imprinted area. In addition, the optical transparency is more than 90% within visible and near infrared wavelength regions. These nano-imprinted periodic structures showed the highly thermal durability without any structural changes for 2 hours at 300°C, which is much better than commercially available organic imprinting materials. Thus, these nano-imprinted sub-wavelength periodic structures using our original hybrid materials have great potentials for several applications to micro- and nano-photonic devices.

The interaction of light with a sub-wavelength period grating can be approximated by a uniform medium with an effective refractive index. The effective index is a function of the grating structure, the indices of its composite materials and the polarization of light. In this paper we report on the design, fabrication and testing of CD, DVD polarization selective hologram gratings based upon this principle. We first describe the design, fabrication and testing of a one-layer structure. We then consider the design, fabrication and testing of a two-layer structure. We show, how the two-layer structure produces similar performance however has the lower aspect ratio. The two-layer structure is also shown to be less sensitive to off design wavelength and incident angle. Both gratings have been designed to function with the wavelengths of CD, and DVD.

The broad development of the micro- and nano-technologies in the past few years increased the need of techniques capable of fabricating sub-micron structures with arbitrary surface profiles. Out of the several fabrication approaches (HEBS lithography, laser writing, etc.) the electron beam writing stands out as the one capable of the highest resolution, superior alignment accuracy and very small surface roughness. These characteristics make the technique greatly applicable in the fields of photonics and micro-opto-electro-mechanical-systems (MOEMS). Here we describe the specificity of fabricating 3D diffractive micro- and nano-optical elements using Leica EBPG 5000+ electron beam system. Parameters like speed of writing, dose accumulation, pattern writing specifics, etc. affect greatly the electronbeam resist properties and the desired 3D profile. We present data that can be used to better understand the different dependencies and therefore achieve better profile and surface roughness management. The results can be useful in future developments in the areas of integrated photonic circuits and MOEMS.

We proposed a method, which is the first to our knowledge, to realize the phase-shift patterns of the near-field lithography in the optical far field. The key component of the optical Fourier system was a phase-only diffractive optical element which generated a diffracted light field of a semi-phase-only complex-valued function. The achieved feature size was beyond the diffraction limit. The advantages of the proposed method included the capability to generate the complicated patterns, spatial parallelism, and low cost.

Using a simplified fabrication process, we present the experimental verification of the performance of a 3-D photonic crystal optical transmission filter. Inherent to this unique fabrication approach to the realization of narrow line width, highly efficient optical transmission filters, is the ability to spatially vary the transmission characteristics across the filter aperture. This differentiates this type of filter from conventional dielectric based space variant optical transmission filters which require additional processing at intermediate steps within the dielectric film deposition process. The multilayer stack consists of alternating high and low refractive index dielectric material grown on either side of a high index dielectric spacer layer, which produces a narrow transmission notch in the center of a large stop band. The nano-structuring of a square lattice array of holes and subsequent etching of the pattern through a dielectric stack provides the ability to spatially vary the location of the narrow transmission peak within the wide stop band based off of variation of the hole diameter or lattice constant of the array.

This paper discusses the precise pressing technology for the fabrication of diffractive optical elements (DOEs). The new established fabrication process allows mass production of DOEs in high homogeneous optical glasses. Our precise pressing process guarantees a very constant quality over the complete production chain. Glass DOEs made by SCHOTT AG are planar optical phase elements with highly accurate shape and efficiency. The blazed profile of the diffractive optical elements was approximated by a stepped profile with up to sixteen phase levels. The highest measured diffraction efficiency for sixteen level gratings was 95%.