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A sampler of diffraction and refraction optically variable image elements
Horáček, Miroslav ; Krátký, Stanislav ; Matějka, Milan ; Chlumská, Jana ; Meluzín, Petr ; Pirunčík, J. ; Aubrecht, I. ; Kotrlý, M. ; Kolařík, Vladimír
Diffraction and refraction optically variable image elements are basic building blocks of planar structures for advanced security of documents and valuables. A sampler formed by an array of 36 diffraction structures binary, tertiary, quaternary and blazed gratings (period range 400 nm 20,000 nm) represents a cross-section throughout technological steps mastering, galvanic replication and embossing. Electron-beam writing technology with Gaussian beam and electron energy of 100 keV, with very small forward scattering of high energy electrons and with the possibilities to create a linear grating with the minimal period of 100 nm, was used to create the master. An important advantage of high-resolution electron-beam lithography is its substantial flexibility in combining possible planar structures with significantly different parameters, such as very dense and relatively shallow structures together with deep structures (approx. 10 microns) with precise shapes (micro-lenses or Fresnel structures). For protection of documents and valuables, interesting results are induced with planar optical structures consisting of non-periodic arrangements, which are characterized by high robustness to counterfeiting and imitation. While the origination process is available for grating period down to 100 nm, the mass replication technology appears to be a bottleneck of the entire technological process. Measurement of topology and profiles of the structures by atomic forces microscope and documenting the quality of technological process of the three steps of replication of planar optically variable elements was performed for all 36 structure types of sampler.
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Silver micro drop structured twice around the earth
Meluzín, Petr ; Tryhuk, V. ; Horáček, Miroslav ; Knápek, Alexandr ; Krátký, Stanislav ; Matějka, Milan ; Kolařík, Vladimír
Planar micro structuring of thin metallic layers allows to achieve required surface properties of metallic layers covering bulk materials. Recently, the arrangement of micro holes or pillars placed around the primary spiral according to a phyllotactic model was presented. This deterministically aperiodic planar arrangement was used for benchmarking purposes of the e-beam writer patterning. This arrangement based on single primary spiral and a variety of derived secondary spirals has several interesting properties. One of them is a very low ratio between the area populated by individual micro elements and the length of the primary phyllotactic spiral. This paper presents analysis of the phyllotactic spiral length and the rising gradient at the spiral outer edge. The practical part of the presented work deals with the patterning of a thin silver layer deposited on the silicon or glass substrates using e-beam pattern generation, lithography techniques and related technologies. An interesting impact of the mentioned spiral properties on the e-beam writing strategies and the exposure ordering strategy are also discussed.
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Nanopatterning of Silicon Nitride Membranes
Matějka, Milan ; Krátký, Stanislav ; Řiháček, Tomáš ; Kolařík, Vladimír ; Chlumská, Jana ; Urbánek, Michal
Membranes are typically created by a thin silicon nitride (SIN) layer deposited on a silicon wafer. Both, top and bottom side of the wafer is covered by a thin layer of the silicon nitride. The principle of silicon nitride membranes preparation is based on the wet anisotropic etching of the bottom side of the silicon wafer with crystallographic orientation (100). While the basic procedure for the preparation of such membranes is well known, the nano patterning of thin membranes presents quite important challenges. This is partially due to the mechanical stress which is typically presented within such membranes. The resolution requirements of the membrane patterning have gradually increased. Advanced lithographic techniques and etching procedures had to be developed. This paper summarizes theoretical aspects, technological issues and achieved results. The application potential of silicon nitride membranes as a base for multifunctional micro system (MMS) is also\ndiscussed.
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Structural Colors of Self-Similar Nano Patterns
Meluzín, Petr ; Horáček, Miroslav ; Krátký, Stanislav ; Kolařík, Vladimír
E-beam lithography is a flexible technology for various diffraction gratings origination. The e-beam patterning typically allows for the creation of optical diffraction gratings in the first diffraction order. However, the very high resolution enables also the patterning of structures providing the zero-order diffraction. Recently, we presented a work on the structural colors of metallic layers covering both regular-line structures and CGH (computer generated hologram) structures. This work presents a study dealing with zero-order diffraction structures with self-similar properties. The practical part of the work is focused on two aspects: design parameters and technological issues. Variations in design parameters include the tone of the structure (positive or negative),\nthe density of filling, the filling factor, and the depth of the structures. The achieved gamut of colors may by primarily extended by the proper selection of metal deposition technology and its parameters, and further by the proper selection of the metal and the thickness of its layer, these are the technological issues.
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Phyllotactic Model Linking Nano and Macro World
Horáček, Miroslav ; Meluzín, Petr ; Krátký, Stanislav ; Urbánek, Michal ; Bok, Jan ; Kolařík, Vladimír
Recently, the arrangement of diffraction primitives according to a phyllotactic model was presented. This arrangement was used to benchmarking purposes of the e-beam writer nano patterning. The phyllotactic arrangement has several interesting properties. One of them is related with the coherence between the nanoor microscopic domain of individual optical primitives and the properties of visually perceived images crated by these structures in the macro domain. This paper presents theoretical analysis of the phyllotactic arrangement in the referred context. Different approaches enabling the creation of diffractive optically variable images are proposed. The practical part of the presented work deals with the nano patterning of such structures using two different types of the e-beam pattern generators. One of them is a system with a variable shaped beam of electrons, while the other one is a system with a Gaussian-shaped beam. E-beam writing strategies and the use of inherent spiral patterns for exposure ordering and partitioning are also discussed.
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Large-area gray-scale structures in e-beam writer versus area current homogeneity and deflection uniformity
Kolařík, Vladimír ; Horáček, Miroslav ; Matějka, Milan ; Krátký, Stanislav ; Bok, Jan
The high stability and good current homogeneity in the spot of the e-beam writer is crucial to the exposure quality, particularly in the case of large-area structures when gray-scale lithography is used. Even though the deflection field distortion is calibrated regularly and beam focus and beam astigmatism is dynamically corrected over the entire deflection field,\nwe can observe disturbances in the exposed relief for both nowadays types of e-beam writers, the shaped e-beam writing system and the Gaussian e-beam writing system. A stable and homogeneous angular current density distribution in the spot is important especially in the case of shaped e-beam lithography systems. A non-homogeneity of the spot over deflection field is seen alongside the field boundaries of both lithography systems.
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Some Other Gratings: Benchmarks for Large-Area E-Beam Nanopatterning
Meluzín, Petr ; Horáček, Miroslav ; Urbánek, Michal ; Bok, Jan ; Krátký, Stanislav ; Matějka, Milan ; Chlumská, Jana ; Kolařík, Vladimír
E-beam lithography is a flexible technology for diffraction gratings origination. Nevertheless, requirements of the high optical quality of large area diffractive structures imply various severe challenges to e-beam delineating processes. This paper summarizes the e-beam process parameters that influence the quality of large area grating structures. Next, we propose some new methods to prepare diffraction gratings that were found to be useful for testing and benchmarking purposes. Those methods include single line gratings, labyrinth structures, fractional structures, tiling patterns, quasi regular filling structures and forked line structures. Various samples were prepared with the standard and newly developed e-beam patterning processes using both e-beam writers available: one with the Gaussian beam at 100 keV and another one with the shaped beam at 15 keV. Some of the results are presented further in this paper, their variants and parameters are discussed as well as their usefulness as benchmarking e-beam patterns for large area optical structures, elements and devices.
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Exposure Time Comparison between E-beam Writer with Gaussian Beam and Variable Shaped Beam
Horáček, Miroslav ; Krátký, Stanislav ; Urbánek, Michal ; Kolařík, Vladimír ; Meluzín, Petr ; Matějka, Milan ; Chlumská, Jana
One of the main goals in e-beam lithography is to increase exposure speed to achieve higher throughput. There are basically two types of electron-beam writers, shaped beam lithography systems and Gaussian beam lithography systems. The exposure time of both e-beam writers consist in essence of beam-on time, deflection system stabilization time and stage movement time. Exposure time testing was carried out on two types of patterns. There were completely filled in areas, binary period gratings (ratio 1:1 between exposed and unexposed areas), and multileveled structures (computer generated holograms). Exposures data was prepared according to standard technology (PMMA resist, exposure dose, non-alcoholic based developer) for both systems. The result of experiment shows that variable shaped beam system has advantage in multileveled structures while the Gaussian beam system is more suitable for gratings type of pattern. It was proved that combination of both systems has its use to increase exposures throughput.
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Interferometrický odměřovací systém pro elektronový litograf
Řeřucha, Šimon ; Šarbort, Martin ; Lazar, Josef ; Číp, Ondřej
Spolehlivost zápisu rozsáhlých struktur pomocí elektronového litografu je do velké míry závislá na přesném řízení polohy posuvného stolku se substrátem. Typicky je pro tuto úlohu využíváno optického odměřování pomocí laserových interferometrů, které poskytuje požadovanou úroveň přesnosti. Této přesnosti dosahuje za cenu využití složité optické sestavy, která díky nárokům na přesnost a robustnost v důsledku představuje netriviální navýšení ceny elektronového litografu jako výsledného produktu. V rámci spolupráce jsme se zaměřili na návrh a ověření optimalizovaného měřicího systému, který poskytne srovnatelnou přesnost a zároveň bude robustnější a cenově efektivnější. Jádrem optimalizace je v zásadě přesun zpracování interferenčního signálu z optické oblasti do oblasti výpočetní. V našem případě se jedná zejména o využití alternativní interferometrické detekční techniky, která využívá kontinuálně frekvenčně modulovaný laserový zdroj v kombinaci se zjednodušeným optickým systém. Výstupem optické soustavy je v obou případech dvojice fázových signálů, které v kvadraturní formě reprezentují hodnotu interferenční fáze. Požadavky na odměřovací systém jsou následující: nejistota měření menší než 2,5 nm, rozsah měření 100 mm, odezva systému 10 kHz. Navíc je vyžadováno využití jiné než viditelné vlnové délky z důvodů interference se scintilátory litografu. Pro účely ověření metody je použita optická sestava. Jako zdroj je využit kompaktní laserový modul RIO Orion (Rio Redfern Integrated Optics Inc.), založený na stabilizované DFB diodě, frekvenčně modulovaný změnou čerpacího proudu. Výstup z interferometrické sestavy je snímán dvěma detekčními systémy: jedním je standardní homodynní detekce, druhým je nová testovaná metoda. Toto uspořádání umožňuje srovnat vyhodnocení různými detekčními technikami a přitom, díky sdílené optické trase, eliminovat vnější vlivy, které mohou mít na přesné vyhodnocení výrazný vliv.
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Measurement of current density distribution in shaped e-beam writers
Horáček, Miroslav ; Bok, Jan ; Kolařík, Vladimír ; Urbánek, Michal ; Matějka, Milan ; Krátký, Stanislav
The ZrO W(100) Schottky cathode is used in our e-beam writing system working with a rectangular-shaped electron beam. The homogeneous angular current density distribution is crucial for quality of exposures of the shaped beam lithography systems. Two basic types of the angular emission distribution can be observed in dependence on the microscopic final end form shape of the emitter tip, with bright centre and more common dark centre. The stable operation of the cathode thus stable end form shape requires a delicate balance of parameters inside the gun which however can slightly change during cathode life time. This implies the necessity of analysing and periodical monitoring the current density distribution in e-beam. Four methods enabling this measurement are presented.
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