METHOD OF CLEANING OPTICAL SURFACES OF AN IRRADIATION UNIT IN A TWO-STEP PROCESS

摘要

The present invention provides a method of cleaning optical surfaces in an irradiation unit in order to remove contaminations deposited on said optical surfaces. The method includes a cleaning step in which a first gas or gas mixture is brought into contact with said optical surfaces thereby forming a volatile compound with a first portion of said contaminations. In an operation pause of the irradiation unit prior to the cleaning step, a pretreatment step is performed, in which a second gas or gas mixture is brought into contact with said optical surfaces. Said second gas or gas mixture is selected to react with a second portion of said contaminations different from said first portion to form a reaction product, which is able to form a volatile compound with said first gas or gas mixture.