Euv light source contamination monitoring system

A system of an EUV light source, the system comprising:

• a first temperature sensor comprising an inserted portion that is inserted into a space surrounded by a plurality of vanes through a vane of the plurality of vanes;
• a signal processor configured to determine a decrease in a first temperature measured by the first temperature sensor;
• a heater attached to the plurality of vanes;
• and
• a process controller configured to activate the heater to perform a vane cleaning action based on the decrease in the first temperature.

A system of an EUV light source, comprising:

• a temperature sensor configured to determine a first temperature in a space surrounded by a plurality of vanes;
• a heater attached to the plurality of vanes;
• and
• a controller configured to perform operations comprising:
• performing a plurality of temperature measurements to determine a first temperature in the space as a function of time;
• determining a decrease of the first temperature vs. time;
• and
• activating the heater to perform a cleaning operation at a time when the first temperature has decreased below a first threshold temperature value.