Microstructure-related properties at 193 nm of MgF_(2) and GdF_(3) films deposited by a resistive-heating boat

摘要

MgF_(2) and GdF_(3) materials, used for a single-layer coating at 193 nm, are deposited by a resistive-heating boat at specific substrate temperatures. Optical characteristics (transmittance, refractive index, extinction coefficient, and optical loss) and microstructures (morphology and crystalline structure) are investigated and discussed. Furthermore, MgF_(2) is used as a low-index material, and GdF_(3) is used as a high-index material for multilayer coatings. Reflectance, stress, and the laser-induced damage threshold (LIDT) are studied. It is shown that MgF_(2) and GdF_(3) thin films, deposited on the substrate at a temperature of 300 deg C, obtain good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the stress mainly comes from MgF_(2), and the absorption comes from GdF_(3). Among those coatings, the sixteen-layer design, sub/(1.4L 0.6H)~(8)/air, shows the largest LIDT.