Patent ID: 11874608
Assignee: ASML NETHERLANDS B.V.
Field: Optics (Instruments)
Classification: CPC G  H | IPC G  H

Claim 18:
19. A method of decreasing a partial pressure of hydrogen radicals in a region in a vessel in an EUV source having a reflective optical element in the vessel, the reflective optical element having a primary focus, an intermediate focus, and an optical axis, the region being positioned between the primary focus and the intermediate focus, the method comprising the steps of:
introducing an active gas in the region to participate in a reaction with the hydrogen radicals in which the hydrogen radicals are consumed; and
exhausting the active gas and products of the reaction from the vessel using an exhaust outlet at an exhaust position located between the primary focus and the intermediate focus,
introducing the active gas being performed using an inlet at an inlet position between the exhaust position and the intermediate focus.