Laser welding by means of multi-kilowatt solid state lasers can be considerably improved if the focused welding spot is embedded in a pre-heating spot generated e.g. by an additional laser. To improve the compactness of the optical system, the same functionality can be effectively achieved by means of diffractive diffusers. Because such a diffractive optical solution may suffer from the presence of speckles, a comprehensive characterization of the laser source is performed. The paper includes the design, the compensation of the difference in the intensity levels, the fabrication and the optical performances of the fabricated DOEs. We furthermore present the functionality of the DOEs in the welding process.

We report the fabrication of periodic structures with a critical dimension of 90 nm on a fused silica substrate by i-line (λ=365  nm) proximity mask-aligner lithography. This realization results from the combination of the improvements of the optical system in the mask aligner (known as MO exposure optics), short-period phase-mask optimization, and the implementation of self-aligned double patterning (SADP). A 350 nm period grating is transferred into a sacrificial polymer layer and coated with an aluminum layer. The removal of the metal initially present on the horizontal surfaces and on top of the polymer grating leaves a 175 nm period grating on the wafer, which can be used as a wire grid polarizer. A computation of the efficiency is performed from the measured profile and confirms the deep-blue visible to infra-red operation range.

Modern optical applications have special demands on the lithographic fabrication technologies. This relates to the lateral shape of the structures as well as to their three dimensional surface profile. On the other hand optical nano-structures are often periodic which allows for the use of dedicated lithographic exposure principles. The paper briefly reviews actual developments in the field of optical nano-structure generation. Special emphasis will be given to two technologies: electron-beam lithography based on a flexible cell-projection method and the actual developments in diffractive mask aligner lithography. Both offer a cost effective fabrication alternative for high resolution structures or three-dimensional optical surface profiles.

Mask-aligner (MA) lithography is a well-known method for the fabrication of micrometer sized structures on a substrate with a diameter up to 300 mm. In spite of a theoretical resolution below 200 nm, the minimum printable feature sized remained above 1μm due to diffraction effects and limit its utilization to advanced packaging, or MEMS fabrication. Recently, developments in the illumination system and mechanical parts (known as AMALTIH for Advanced MA LITHography) as well as mask design, have permitted to used diffractive based photo-mask, and then reach the resolution limit mentioned above. This opens the possibility to fabricate smaller structures, usually accessible only by ebeam lithography. We propose here to demonstrate a fast and robust fabrication method of large area plasmonic absorber structures based on 2D sub-micrometric (350 nm period) nano-needles in a transparent polymer on a glass substrate and coated with a 50 nm thick gold layer. The interaction of the incoming light with metallic structured surface leads to the small total reflections of the 0th order below 5 %, over a large spectral band (460-660 nm) and a large set of incidence angles with TE and TM polarizations. Those results demonstrate that our fabrication process is a step toward the implementation of plasmonic based effect structures for a wide range of application.

Diffractive mask-aligner lithography allows printing sub-micrometer resolution structures by using non-contact mode. For such a purpose, binary diffraction gratings are used as masks and are designed to transmit solely the +/- 1st diffraction orders. The high resolution interferogram is realized by the overlapping and the interference of the propagating beams. By applying the techniques known as Self-Aligned Double Patterning (SADP), it's possible to decrease the period of the fabricated grating (350 nm) by a factor of two, and thus reaching the 90nm structure width. As application, metallic gratings have been fabricated operating as wire grid polarizer (WGP).

Diffractive mask-aligner lithography allows printing structures that have a sub-micrometer resolution by using non-contact mode. For such a purpose, masks are often designed to operate with monochromatic linearly polarized light, which is obtained by placing a spectral filter and a polarizer in the beam path. We propose here a mask design that includes a wire-grid polarizer (WGP) on the top side of a photo-mask and a diffractive element on the bottom one to print a 350 nm period grating by using a classical mask-aligner in proximity exposure mode. Linearly polarizing locally an unpolarized incident beam is only possible by using a WGP on the top side of the mask. This configuration opens the possibility to use different linear polarization orientation on a single mask and allows to print high resolution structures with different orientation within one exposure.

Diffractive mask-aligner lithography is capable to print structures that have a sub-500-nanometer resolution by using non-contact mode. This requires the use of specially designed phase-masks and dedicated illumination conditions in the Mask-Aligner to obtain the optimal exposure conditions, a spectral filter and a polarizer needs to be placed in the beam path. We introduce here mask designs that includes a polarizer on the top side of a photo-mask and a diffractive element on the bottom one. This enables printing of high resolution structures of arbitrary orientation by using a classical mask-aligner in proximity exposure mode.

This Letter, describes a fabrication method based on a high refractive index binary phase mask combined with a suitable illumination setup, which produces a close to normal incidence illumination, to fabricate sub-micrometer diffraction gratings. The method uses the i-line (365 nm) of a mercury lamp spectrum in a mask-aligner in proximity mode, to avoid any contact between the mask and the wafer, which is normally used to produce high resolution structures. The transfer of the structure in a fused silica wafer demonstrates that mask-aligner lithography can produce high aspect ratio sub-wavelength structures without resorting to any contact between mask and wafer.

Deep-UV lithography using high-efficiency phase mask has been developed to print 100 nm period grating on sol-gel based thin layer. High efficiency phase mask has been designed to produce a high-contrast interferogram (periodic fringes) under water immersion conditions for 244 nm laser. The demonstration has been applied to a new developed immersion-compatible sol-gel layer. A sol-gel photoresist prepared from zirconium alkoxides caped with methacrylic acids was developed to achieve 50 nm resolution in a single step exposure. The nanostructures can be thermally annealed into ZrO(2). Such route considerably simplifies the process for elaborating nanopatterned surfaces of transition metal oxides, and opens new routes for integrating materials of interest for applications in the field of photocatalysis, photovoltaic, optics, photonics or microelectronics.

A method is demonstrated for writing long grating phase masks, which can be used for patterning large-area (square meter size) submicron-period gratings. The method consist of illuminating a small area transmission grating phase mask by a continous wave transverse-electric-polarized collimated laser beam under the -1st order Littrow mounting to define a high-contrast interferogram composed of fringes. By sliding a long photoresist-coated substrate under this small area phase mask, gratings of arbitrary length may be written, with grating lines oriented in the scan direction. The patterning of uninterrupted gratings with lengths exceeding 300 mm is demonstrated. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3549254]

An optimized achromatic high-efficiency monolithic phase mask is presented whose principle was demonstrated and described in reference [1]. The mask comprises three submicron period diffraction gratings at a single substrate side that create a purely single spatial frequency interferogram of large period. The optical scheme is that of an integrated Mach-Zehnder interferometer where all light circulation functions are performed by diffraction gratings. The paper describes the operation principle of the phase mask, the fabrication process, and its utilization in a write-on-the-fly scheme for the writing of a long, 2 μm-period grating.

Cette these presente un banc d'ecriture de reseaux de diffraction de grande surface dont la periode peut varier de 100 nm a plusieurs micrometres. Le principe est base sur l'ecriture au vol qui permet d'ecrire des longs reseaux en balayant continument un substrat recouvert de resine photosensible sous un interferogramme de petite dimension cree par un masque de phase. Deux types de masques ont ete fabriques. Le premier, pouvant etre decrit comme un interferometre de type Mach-Zehnder monolithique, presente l'interet d'ecrire des reseaux de grandes periodes sans limite superieure. Il est compose de trois reseaux de diffraction, ecrits sur la meme face d'un substrat epais grâce a destechniques standards de lithographie (e-beam, gravure RIE) accessibles lors d'un echange a l'UEF aJoensuu. A la longueur d'onde 442 nm, ce masque a permis d'ecrire un reseau de periode de 2 µmde grande dimension a l'aide d'une nappe de lumiere divergente. Le second type de masque est monolithique en materiau haut indice. Il est utilise en immersion a la longueur d'onde de 244 nm; des reseaux de periode de 100 nm ont ete ecrits. La structure capable de supprimer l'ordre zero transmis a ete modelisee et les masques ont ete fabriques par trois partenaires europeens du reseau d'excellence NEMO. La gravure du LuAG a egalement ete etudiee en vue de fabriquer un masque de phase pour la longueur d'onde 193 nm. Afin d'ecrire des reseaux larges et homogenes, une etude des differentes techniques d'elargissement de faisceau a ete realisee en vue de disposer d'une ligne de lumiere avec un profil d'intensite homogene dit top-hat , et une methode de fabrication d'un long masque de phase a ete developpee

The interferogram of a high index phase mask of 200 nm period under normal incidence of a collimated beam at 244 nm wavelength with substantially suppressed zeroth order produces a 100 nm period grating in a resist film under immersion. The paper describes the phase mask design, its fabrication, the effect of electron-beam lithographic stitching errors and optical assessment of the fabricated sub-cutoff grating.

A new type of achromatic phase mask is presented which creates an interferogram of single spatial frequency regardless of the ratio between the interferogram period and the exposure wavelength. The functional demonstration of this monolithic phase mask was made in the case of a long grating of period as large as 2 mu m by mean of an exposure beam at 442 nm wavelength, i.e., more than four times smaller. The monolithic element performs one first splitting function exerted by a central transmission grating of period Lambda(1) which diffracts the incoming beam in two diffracted beams in the substrate which are then reflected to the backside of the substrate. The element performs a second diffractive function by means of two identical side-grating of period Lambda(2) placed at either side of the first grating. This function is the redirection of the two said beams under the monolith substrate at an angle which creates an interferogram of the desired period

A monolithic double-grating phase mask comprising three short-pitch grating sections of spatial frequencies k(1) and k(2) collocated at one side of a substrate produces a large-period interferogram without higher harmonics to print in a photoresist film a latent grating of small spatial frequency equal to twice k(2)-k(1). When incorporated in a write-on-the-fly scheme, the elements permit the fabrication of unlimitedly long gratings.

Whereas microelectronic lithography is heading to the 32 nm node and discussing immersion and double-patterning strategies, there is much which can be done with the 45 nm node in microoptics for white light processing. For instance, one of the most demanding applications in terms of achievable period is the LCD lossless polarizer, which can transmit the TM polarization and reflect the TE polarizaton evenly all through the visible spectrum - provided that a 1D metal grad of 100 nm period can be fabricated. The manufacture of such polarizing panels cannot resort to the step & repeat cameras of microelectronics since the substrates are too large, too thin, too wavy and full of contaminants. There is therefore a need for specific fabrication techniques. It is one of these techniques that a subgroup of partners belonging to two of the Networks of Excellence of the European Community, NEMO and ePIXnet, have decided to explore together.

Zeroth transmitted order suppression in a phasemask of wavelength scale period is achieved by making the binary corrugation in a high index layer deposited on a transparent substrate. The produced single spatial frequency interferogram can also be created in the presence of an immersion liquid.