Patent ID: 8382301

Claim:
A projection exposure apparatus for EUV lithography wherein a radiation exposure operation is conducted, the projection exposure apparatus comprising: a main housing that encloses an interior space into which contaminating substances are outgassed during said operation; said main housing including three interconnected housing parts in said interior space of said main housing; a first one of said housing parts including a first interior space; a second one of said housing parts including a second interior space; and, a third housing part including a third interior space; said first housing part enclosing a light source in said first interior space; said second housing part enclosing an illumination system in said second interior space; said third housing part enclosing a projection optics system in said third interior space; at least one optical element arranged in one of said housing parts and said one optical element having an optical surface; a vacuum generating unit that generates a vacuum in the interior space of said one housing part of said main housing so as to cause the contaminating substances therein to be at a first partial pressure; a vacuum housing that is arranged in the interior space of said one housing part so as to be independent thereof; said vacuum housing enclosing at least said optical surface of said optical element so as to leave a first opening communicating with said interior space of said main housing or into the interior space of another one of said housing parts; a light source that directs light onto said optical surface during the radiation exposure operation to form a beam of exposure light traveling along a beam path from said optical surface within said vacuum housing through said first opening into said interior space of said main housing or into the interior space of another one of said housing parts; and, a contamination reduction unit associated with said vacuum housing and, during the radiation exposure operation, reducing the partial pressure of the contaminating substances at least in proximity to said optical surface to a second partial pressure of the contaminating substances less than said first partial pressure in the interior space of said one housing part; said contamination reduction unit further comprising a purge unit that purges at least a partial region of said vacuum housing with an inert gas; and, a second opening in said vacuum housing defining a suction unit for generating a flow of purge gas from the inside of said vacuum housing to the interior space of said one housing part.