Arrangement for monitoring the energy radiated by an EUV radiation source
View Patent ↗The invention is directed to an arrangement for monitoring the energy radiated by an EUV radiation source with respect to energy variations acting in an illumination beam path, wherein the radiation source has a plasma column emitting extreme ultraviolet radiation. The arrangement includes an energy monitoring unit, and a detection beam path. The detection beam path is separate from the illumination beam path and is arranged with the energy monitoring unit for detecting pulse energy, so that the illumination beam path is not impaired by the energy measurement. The detection beam path is matched to the illumination beam path with respect to bundle extension and optical losses.
1. An arrangement for monitoring the energy radiated by an EUV radiation source with respect to energy variations acting in an illumination beam path, wherein the radiation source has a plasma column emitting extreme ultraviolet radiation, comprising:
an energy monitoring unit;
a detection beam path which is separate from the illumination beam path being arranged with said energy monitoring unit for detecting pulse energy, so that the illumination beam path is not impaired by the energy measurement; and
wherein the detection beam path is matched to the illumination beam path with respect to bundle extension and optical losses.
2. The arrangement according to claim 1 , wherein the detection beam path is arranged opposite to the illumination beam path with respect to the plasma column.
3. The arrangement according to claim 1 , wherein the illumination beam path comprises a first collector optics having a given aperture and the detection beam path having an etendue that is matched to the given aperture of the first collector optics by a diaphragm with a defined aperture.
4. The arrangement according to claim 3 , wherein the aperture of the diaphragm is adjustable.
5. The arrangement according to claim 3 , wherein all filters required in the illumination beam path are arranged in the detection beam path in an equivalent manner.
6. The arrangement according to claim 5 , wherein the same debris filters are present in the illumination beam path and detection beam path.
7. The arrangement according to claim 5 , wherein the same spectral filters are present in the illumination beam path and detection beam path.
8. The arrangement according to claim 1 , wherein the energy monitoring unit has an energy detector, which is arranged with its light-sensitive surface completely within the detection beam path having a light bundle that is transmitted by a reflection optics and a second detector whose light-sensitive surface is only partially illuminated by a border area of the light bundle of the detection beam path, so that variations in the position of the light bundle due to fluctuations in the spatial distribution of the emitted EUV radiation are quantifiable.
9. The arrangement according to claim 8 , wherein a substantial central portion of the light bundle is deflected to the energy detector by a plane mirror, and the energy detector is arranged along the bent optical axis of the light bundle emanating from the reflection optics.
10. The arrangement according to claim 9 , wherein the plane mirror is a multilayer mirror which deflects the light bundle orthogonal to the axis of the reflection optics.
11. The arrangement according to claim 9 , wherein the plane mirror is a metal mirror with grazing incidence.
12. The arrangement according to claim 1 , wherein the energy monitoring unit comprises a position-sensitive receiver having different segments for simultaneous detection of the total pulse energy and variations in the spatial distribution of the emitted EUV radiation, wherein the total pulse energy is determined by summing and changes in the spatial distribution is determined by centroid calculation from different segments of said position-sensitive receiver.
13. The arrangement according to claim 12 , wherein the position-sensitive receiver is a quadrant diode.