Method for localizing defects on substrates
In a method for localizing defects on a substrate for EUV masks, a phase contrast optical unit having a phase mask is used for examining the substrate.
1. A method for localizing defects on substrates for producing optical components of a microlithographic EUV projection exposure apparatus, on substrates for EUV lithography masks or on EUV lithography masks, comprising the following steps:
provision steps for providing
a substrate to be examined,
an illumination device for illuminating the substrate to be examined with illumination radiation having a wavelength in the range of 100 nm to 300 nm,
a phase contrast optical unit for examining the substrate to be examined, and
a sensor device for detecting illumination radiation,
preparation steps for preparing the inspection of the substrate to be examined, and
examination steps for examining the substrate comprising
capturing at least one image of the substrate, and
analysis and/or aftertreatment steps,
wherein the phase contrast optical unit comprises a phase mask and a stop,
wherein the geometrical embodiment of the phase mask and that of the stop are adapted to one another,
wherein the sensor device is arranged in the beam path downstream of the phase mask, and
wherein the examination steps comprise detecting a phase shift, brought about by the substrate, of the illumination radiation by use of the sensor device.
2. The method as claimed in claim 1 , wherein the preparation steps comprise determining a positioning of the substrate in a coordinate system of the phase contrast optical unit, wherein predefined bearing points of a positioning device and/or measurement marks on the substrate serve as reference points.
3. The method as claimed in claim 1 , wherein the examination steps comprise predefining a region to be examined on the substrate wherein the region to be examined is predefined with an accuracy that is more precise than a diameter of a field of view of the phase contrast optical unit.
4. The method as claimed in claim 1 , wherein the substrate is displaced by use of a positioning device before the at least one image is recorded.
5. The method as claimed in claim 1 , wherein the examination steps comprise an image capture with recording of an image stack having at least one intrafocal image and at least one extrafocal image.
6. The method as claimed in claim 1 , wherein a single image of the substrate is captured for the purpose of examining the substrate.
7. The method as claimed in claim 1 , wherein the analysis and/or aftertreatment steps comprise determining a best focal position.
8. The method as claimed in claim 1 , wherein the analysis and/or aftertreatment steps comprise a two-stage method in which, in a first stage, a defect position is determined for each image of an image stack and in which, in a second stage, the defect positions of the images are adapted to a best focal position.
9. The method as claimed in claim 1 , wherein a position of the defect in a substrate coordinate system is determined with an accuracy of better than 100 nm.
10. The method as claimed in claim 1 , wherein the substrate has an absorber layer when the examination steps are carried out.
11. The method as claimed in claim 1 , wherein the analysis and/or aftertreatment steps comprise a reconstruction step for determining a phase image and a subsequent phase image evaluation.
12. A method for producing EUV lithography masks comprising the following steps:
providing a substrate for an EUV lithography mask,
inspecting the substrate in order to localize defects by using the method of claim 1 ,
structuring the substrate with a structure,
wherein the structure is chosen and/or aligned in such a way that defects on the substrate are covered by an absorber layer.
13. The method as claimed in claim 12 , wherein inspecting the substrate in order to localize defects is carried out after applying the absorber layer.
14. An apparatus for localizing defects on substrates and configured to perform the provision, preparation, and examination steps of claim 1 , the apparatus comprising
an illumination system for illuminating a substrate to be examined with illumination radiation having a wavelength in the range of 100 nm to 300 nm, and
a phase contrast optical unit for imaging the substrate to be examined,
wherein the phase contrast optical unit has a phase mask and a stop,
wherein the phase mask is adapted to a distribution of the illumination radiation in an entrance pupil of the phase contrast optical unit, and
wherein the geometrical embodiment of the phase mask and that of the stop are adapted to one another.
15. The apparatus of claim 14 , wherein the apparatus is configured to perform preparation steps that comprise determining a positioning of the substrate in a coordinate system of the phase contrast optical unit, wherein predefined bearing points of a positioning device and/or measurement marks on the substrate serve as reference points.
16. The apparatus of claim 14 , wherein the apparatus is configured to perform examination steps that comprise predefining a region to be examined on the substrate wherein the region to be examined is predefined with an accuracy that is more precise than a diameter of a field of view of the phase contrast optical unit.
17. The apparatus of claim 14 , wherein the substrate is displaced by use of a positioning device before the at least one image is recorded.
18. The apparatus of claim 14 , wherein the apparatus is configured to perform examination steps that comprise an image capture with recording of an image stack having at least one intrafocal image and at least one extrafocal image.
19. The apparatus of claim 14 , wherein the apparatus is configured to capture a single image of the substrate for the purpose of examining the substrate.
20. The apparatus of claim 14 , wherein the sensor device is arranged in the beam path downstream of the phase mask, and the apparatus is configured to detect a phase shift, brought about by the substrate, of the illumination radiation by use of the sensor device.