| 摘要 |
The invention relates to a method for determining the phase angle at a free interface (17) of an optical element (13) provided with a multilayer coating (16) that reflects EUV radiation and/or for determining the thickness (d) of a contamination layer (26) formed on the multilayer coating (16), comprising: irradiating the multilayer coating (16) with EUV radiation, measuring a photocurrent (lP) generated during the irradiation, and determining the phase angle at the free interface (17) and/or the thickness (d) of the contamination layer (26) on the basis of a predefined relationship between the phase angle and/or the thickness (d) and the measured photocurrent (lP), wherein the measured photocurrent (Ip) is generated from the entire wavelength and angle- of-incidence distribution of the EUV radiation impinging on the multilayer coating (16). The invention also relates to an EUV lithography apparatus, comprising: at least one optical element (13) having a substrate (15) and a multilayer coating (16) that reflects EUV radiation, wherein the optical element (13) is in contact with a charge amplifier (20) for deriving a photocurrent (lP) generated during the irradiation with EUV radiation, and a measuring device for measuring the photocurrent (Ip) on the basis of an output voltage (VP) supplied by the charge amplifier (20), wherein the measuring device is connected to a pulsed EUV light source (5) of the EUV lithography apparatus (1 ) in order to read out the output voltage (VP) supplied by the charge amplifier (20) synchronously with the pulses (P) of the EUV light source (5). |
