Residual gas analyser, projection exposure apparatus comprising a residual gas analyser and method of residual gas analysis

A projection exposure apparatus comprising:

• a vacuum housing;
• a radiation source for emitting very short-wave UV radiation arranged within the vacuum housing;
• a plurality of optical elements configured to guide radiation emitted along an exposure beam path of the projection exposure apparatus into an image plane;
• and
• a residual gas analyzer configured to analyze a residual gas in the projection exposure apparatus, the residual gas analyzer comprising:
• a mass spectrometer;
• and
• admission equipment configured to admit ionized constituents of the residual gas into the mass spectrometer from a vacuum environment, the admission equipment comprising an ion decelerator configured to provide an adjustable deceleration voltage to subject the ionized constituents to a selection according to kinetic energy prior to transfer into the mass spectrometer.