TY - JOUR
AU - Fukuda, Tsuguo
AB - CaF 2 (Calcium fluoride) lens materials are required for the composition of F 2 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 CaF 2 . Although CaF 2 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 CaF 2 will be short when F 2 stepper will start on a large scale. To resolve the above mentioned problems, we tried to grow a large CaF 2 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 F 2 lithography.
TI - Properties of large CaF 2 crystals grown by CZ method for lens materials
JF - Proceedings of SPIE
DO - 10.1117/12.556614
DA - 2004-05-28
UR - https://www.deepdyve.com/lp/spie/properties-of-large-caf-2-crystals-grown-by-cz-method-for-lens-W08lcwHMy2
SP - 1886
EP - 1893
VL - 5377
IS - 1
DP - DeepDyve
ER -