Patent ID: 7671347
Filing Date: 2010-03-02
Classification: G03F

Abstract:
1. A method to clean one or more optical elements of an apparatus, the apparatus being configured to project a beam of radiation onto a target portion of a substrate and comprising a plurality of optical elements arranged in a sequence in a path of the radiation beam, wherein the method comprises cleaning a second optical element of the sequence, which receives a second radiation dose during operation of the apparatus, utilizing a cumulatively shorter cleaning period than a first optical element of the sequence, which receives a first radiation dose during operation of the apparatus, the second radiation dose being lower than the first radiation dose, wherein the cleaning comprises (i) detecting a radiation loss of radiation passing one or more of the optical elements and automatically starting a cleaning cycle to clean at least one of the optical elements in the case a detected radiation loss reaches a certain amount of radiation loss, or (ii) detecting contamination of at least one of the optical elements and automatically starting a cleaning cycle to clean at least one of the optical elements when the contamination reaches a certain amount of contamination.