Dense homogeneous fluoride films for DUV elements and method of preparing same

摘要

The invention is directed to optical elements that are coated with dense homogeneous fluoride films and to a method of making such coated elements. The coatings materials are a high (“H”) refractive index fluoride material and a low (“L”) refractive index material that are co-evaporated to form a coating layer of a L-H coating material (a co-deposited coating of L and H materials). Lanthanide metal fluorides (for example, neodymium, lanthanum, dysprosium, yttrium and gadolinium, and combinations thereof) are preferred metal fluorides for use as the high refractive index materials with lanthanum fluoride (LaF₃) and gadolinium fluoride (GdF₃) being particularly preferred. Aluminum fluoride (AlF₃) and alkaline earth metal fluorides (fluorides of calcium, magnesium, barium and strontium) are the preferred low refractive index materials, with magnesium fluoride (MgF₂) being a preferred alkaline earth metal fluoride.