Patent ID: 6395657
Filing Date: 2002-05-28
Classification: C30B,G02B,G03F,Y10S

Abstract:
A fluoride crystalline optical lithography lens element blank, said fluoride crystalline optical element blank comprising a plurality of crystalline subgrains, each of said subgrains having a crystalline subgrain structure, said fluoride crystalline blank including at least a first subgrain structure and a second subgrain structure, said second subgrain structure adjacent and abutting said first subgrain structure at a first defect boundary formed by a plurality of dislocation defects, said boundary dislocation defects having an adjacent first subgrain-second subgrain boundary angle, said first subgrain-second subgrain boundary angle less than two minutes, said crystalline optical element blank having an impurity level less than 1 ppm Pb by weight, less than 0.5 ppm Ce by weight, less than 2 ppm Na by weight and less than 2 ppm K by weight, said blank having a 157 nm absorption coefficient less than 0.0022/cm base 10 absorption coefficient and a 193 nm absorption coefficient less than 0.00043/cm base 10 absorption coefficient, said blank having an optical homogeneity less than 2 ppm and an average birefringence less than 2 nm/cm RMS with a maximum birefringence less than 5 nm/cm.