Patent ID: 9618387
Date: 2017-04-11
CPC Classifications: B82Y,G01B,G01J,G01N,G03F,G21K

Claim:
1. An extreme ultraviolet (EUV) lithography apparatus, comprising: at least one optical element, having a substrate and a multilayer coating that reflects EUV radiation, and an electrical contact with the optical element, to derive a photocurrent generated in response to irradiation of the optical element with the EUV radiation, a charge amplifier in contact with the optical element and configured to supply an output voltage in accordance with the photocurrent, a measuring device configured to measure the photocurrent in accordance with the output voltage supplied by the charge amplifier, a pulsed EUV light source, and an evaluation device, configured to determine a phase angle at a free interface of the optical element and/or a thickness of a contamination layer formed on the multilayer coating in accordance with a predefined relationship between the phase angle and/or the thickness and the measured photocurrent, wherein the measured photocurrent is generated from an entire wavelength and angle-of-incidence distribution of the EUV radiation impinging on the multilayer coating.