CaF2(Calcium fluoride) lens materials are required for the most important component of the ArF laser lithography stepper for the reason of its excellent transparency in DUV region and excellent laser durability as compared with quartz. Last year we reported to succeed in growing both <111> and <100> crystals, which had 210m diameter and 150mm length by the Czochralski (CZ) method with high productivity1). The obtained CaF2 crystal had low stress birefringence by way of the optimized annealing process. Although, for the higher NA system, larger CaF2 single crystals are required for the lens materials having the high quality and high productivity.
To meet the above mentioned demands, we made efforts to produce and succeeded the first in the world ultra-large (φ300mm over) and high quality CaF2 single crystal by the CZ method with high productivity. The crystal had very low stress birefringence, good transparency in DUV region and good homogeneity. It was also easy to control the orientation of the crystal by the selection of seed crystal.
CaF2 (Calcium fluoride) lens materials are required for the composition of F2 laser lithography stepper. Recently, it is reported that both <111> crystal and <100> crystal are necessary for the lens blanks, which can resolve the intrinsic birefringence of CaF2. Although CaF2 single crystal has been produced by Bridgman method, some problems are pointed out on the optical properties and production yield especially on <100> crystal with large diameter. So it is worried that the amount of the supply of CaF2 will be short when F2 stepper will start on a large scale. To resolve the above mentioned problems, we tried to grow a large CaF2 single crystal by Czochralski (CZ) technique, because we expected that CZ technique could provide higher productivity and higher quality which mean lower residual stress than conventional method. CZ technique can also easily control the growing crystal axis by the selection of seed crystal. Consequently we succeeded in growth both <111> and <100> direction single crystal which has 210mm diameter and 150mm length. The obtained crystal is a single crystal over a whole boule and it shows high transparency in vacuum ultraviolet region. Moreover it shows very low birefringence value and good homogeneity after annealing process. We hope our challenge should prompt the development of F2 lithography.
Perylene- and phthalocyanine- pigment molecules were systematically modified and consequences were studied for their solid state properties. Thin films (1 - 150 nm) were prepared by physical vapor deposition. Intermolecular interactions were probed by optical measurements in absorption and emission. Atomic force microscopy served to analyze the morphology of films. Different interactions among the molecules and with the substrate surfaces allowed to prepare either crystalline or amorphous films. Crystalline films of perylene pigments were typically characterized by strong chromophore coupling leading to a characteristic splitting, well- defined shifts of the optical absorption bands and emission mainly from excimer species whereas the chromophore coupling in amorphous films was suppressed sufficiently to provide a significantly increased optical emission yield from uncoupled monomer states. Temperature-dependent optical emission experiments are presented which allow a detailed discussion of monomer vs. excimer emission. Decoupling of the chromophores could be obtained by appropriate chemical substitutions at the aromatic core system of phthalocyanines and perylene pigments that led to strong deviations from planarity. This was achieved by the introduction of bulky substituents in the bay position of the aromatic perylene core and by changes in the coordination number of the central group in phthalocyanines. The strategy led to a strongly enhanced optical emission for both classes of materials. This could be obtained, however, either in an amorphous arrangement of the molecules or under conservation of crystallinity, both offering alternative advantages.
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