Method for determining the phase angle and/or the thickness of a contamination layer at an optical element and EUV lithography apparatus

摘要

A method and associated EUV lithography apparatus 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). The multilayer coating (16) is irradiated with EUV radiation, a photocurrent (IP) generated during the irradiation is measured, and the phase angle at the free interface (17) and/or the thickness (d) of the contamination layer (26) is determined on the basis of a predefined relationship between the phase angle and/or the thickness (d) and the measured photocurrent (IP). 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).

主权项

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.