| 摘要 |
A method is described of protecting a surface of a mirror located in a chamber exposed to extreme ultra violet (EUV) radiation. The EUV radiation is generated from a plasma, which emits both EUV radiation and electrically charged particles. Organic molecules are supplied to the chamber, which interact with the EUV radiation to form a coating of carbonaceous deposits on the mirror surface. The charged particles emitted from the plasma impact the deposits, causing the deposits to be sputtered from the mirror surface. By controlling at least one of the rate of deposition of deposits on the mirror surface and the rate of removal of the deposits from the mirror surface, the thickness of the coating can be actively controlled both to prevent impact of the charged particles directly on to the mirror surface and to minimise the loss of reflectivity of the mirror surface due to the formation of the coating. The method is also suitable for protecting the surface of a window used to transmit EUV radiation from the chamber.
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