SYSTEM FOR CLEANING AT LEAST ONE INTERNAL SPACE OF OBJECTIVE LENS WITH GAS

摘要

PROBLEM TO BE SOLVED: To provide a system for cleaning at least one internal space of an objective lens with gas that enables an inert gas to be used for cleaning, and at the same time, can prevent the refractive index of the lens from being changed. SOLUTION: This system cleans at least one internal space of an objective lens, particularly, an exposing and projecting objective lens for semiconductor lithography. The cleaning is performed by mixing at least two kinds of inert gases with each other so that the refractive index of the lens resulting from the mixing may become almost coincident with at least the refractive index of air.