Methods and apparatus for use with extreme ultraviolet light having contamination protection

A method of contamination protection for use in an extreme ultraviolet (EUV) actinic mask inspection system or an EUV lithographic system, comprising:

• flowing a low pressure gas in a duct having A) a first end opening and a second end opening and B) an intermediate opening disposed intermediate the first end opening the second end opening;
• and
• projecting EUV light through the duct, the EUV light A) traveling from the second end opening then through the first end opening to an optical element or B) traveling from the optical component, then through the first end opening to the second end opening, the gas having a high transmission of EUV light.

A method of contamination protection for use in an extreme ultraviolet (EUV) actinic mask inspection system or an EUV lithographic system, comprising:

• maintaining a voltage difference between a first portion of a duct and a second portion of the duct with a grounded insulative portion disposed between the first portion and the second portion, the duct having A) a first end opening and a second end opening, the first portion and second portion both being disposed between the first end opening and the second end opening;
• and
• projecting EUV light through the duct, the EUV light 1) traveling from the second end opening then through the first end opening to an optical element or 2) traveling from the optical component, then through the first end opening to the second end opening, the gas having a high transmission of EUV light.