Lens system with lens elements arranged in a gas-filled holder and photolithographic apparatus including such a system

摘要

A high-quality lens system (PL) is described, which system is rinsed with a gas having a low refractive index so as to reduce the influence of variations of ambient parameters on the optical behaviour. By adding a very small quantity of ozone to this gas, it is prevented that any deposit will be produced on the lens elements within the lens holder (PLH) as a result of decomposition of organic particles caused by UV radiation and precipitation of the decomposition products.