KEYWORDS: Optics manufacturing, Optical components, Optical lithography, Near field optics, Micro optics, Manufacturing, Chemical elements, Lithography, Electron beam lithography, Photomasks
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.
KEYWORDS: Beam shaping, Polarization, Optical components, Near field optics, Polarizers, Optical testing, Near field, Lithographic illumination, Silica, Binary data
Micro and nano optics enable the control of light for producing intensity distributions with given profiles, propagation properties and polarization states. The higher the requirements on the optical function, the more complicated will be its realizing with a single element surface or a single element class. Combinations of refractive and diffractive, both diffractive or sub-wavelength structures with each other give the ability to link the advantages of different element classes or different element functions for realizing the optical functionality. In the paper we discuss two different examples of combinations for DUV applications. In detail we present a diffractive - diffractive beam homogenizer with NA of 0.3 that show no zero order. A binary phase grating for polarization control combined with a beam shaping element will be presented. The polarized order of this grating shows an efficiency of about 90% with a degree of polarization better than 90%. Wave optical and rigorous design strategies and simulations as well as the optical measurements will be discussed for the given examples.
As lithographers push to extend optical lithography technologies to create smaller features with higher NA, especially immersion lithography, and lower k1 values, the polarization of the light in the illumination system becomes relevant. Nowadays the fabrication with electron-beam-lithography has the ability the produce diffractive structures for the DUV spectral range. We present binary phase gratings with polarization depended optical properties for 193nm designed with the rigorous coupled wave analysis (RCWA). The element function is based on a shift of the diffraction efficiencies between the first and the zero diffraction orders for different incident polarization angles. The properties of a 193nm polarizing phase grating will be discussed in detail. For TE-polarized light a zero order signal of less than 1% was measured. The efficiency for TE-polarized light in the first order is about 80%. For TM-polarized light the binary phase gratings achieve an efficiency of nearly 90% in the first and the zero order in transmission. The deflection angle of the first diffracted order can be varied between 14° and 40°.
The rigorous modelling as well as the fabrication technology and optical measurements will be discussed.
In the optimization process of DUV-illumination systems for inspection tools and lithographic devices, more and more an exact control of angular distribution and homogeneity of the illumination will be required. On the one hand, diffractive homogenizers enable homogeneous illumination of areas with almost arbitrary shape with a high numerical aperture. On the other hand, diffractive optical elements produce a zero order or so called “hot spot”. If the optical axis is within the illuminated area, this hot spot will decrease the homogeneity of illumination. The zero order is caused by profile aberrations and its intensity can be decreased by increasing the fabrication accuracy. But the higher the numerical aperture, the larger the ratio between zero order brightness and brightness of the surrounding homogenized area. I.e., in cases of high NA the zero order of a homogenizer cannot be reduced to the brightness of the surrounding area. We present a novel approach of beam homogenization using a combination of two serially arranged diffractive optical elements that produces an intensity distribution without hot spot. Such compact two-element homogenizers have been realized for wavelengths down to 193nm. A homogenizer for 193nm producing a homogeneously illuminated rectangle with 0.3 NA will be presented.
For future spacecrafts a lot of new UV or x-ray instruments are proposed. To enhance resolution and reduce scattering, new optical materials with optical surfaces with a roughness range of about 0.1 nm, i.e. supersmooth surfaces will be used to build the optics of the instruments. Some of the spacecrafts or instruments will be operated in the Low Earth Orbits (LEO's) of the Space Shuttle or the International Space Station. The natural and induced space environment can damage spacecraft and instrument materials. Since the LDEF-EURECA- and D2-experiments and the recovery of the Hubbel Space Telescope solar arrays it is well known that a large group fo materials degrade under space conditions. However very few data are available from inflight experiments especially on supersmooth materials. To fill the gap, the Surface Effects Sample Monitor SESAM has been developed. This space flight instrument was designed to expose test materials to the conditions of space during flight missions. Also included in the experiment is an online Atomic Oxygen (ATOX) Measurement Facility to monitor the impact of the ATOX on the exposed samples. The experiment was flown on four missions. The results show a degradation of supersmooth samples under space conditions which has to taken in account for the design of future UV or X-ray instruments.
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