Measurement of Optical Properties of Refractive Materials at Actinic Wavelength
Publication Date: 2002-Aug-06
The IP.com Prior Art Database
The optical properties of refractive material used for DUV lithography have been historically measured at visible wavelengths and scaled to calculate the property at the actinic wavelength. These properties have included index of refraction homogeneity, densification and stress induced birefringence. Recently, phenomena have been discovered that do not scale linearly with wavelength. Two examples are intrinsic birefringence in Calcium Fluoride and the photo refractive effect in irradiated fused silica. We describe here methods of measuring material for these sorts of effects at the actinic wavelength in order to test those scaling laws. With this data, we can better predict the performance of lithographic objectives at wavelength.