Methods and apparatus for inspection of articles, EUV lithography reticles, lithography apparatus and method of manufacturing devices
An EUV lithography reticle is inspected to detect contaminant particles. The inspection apparatus comprises illumination optics with primary radiation. An imaging optical system with plural branches is arranged to form and detect a plurality of images, each branch having an image sensor and forming its image with a different portion of radiation received from the illuminated article. A processor combines information from the detected images to report on the presence and location of contaminant particles. In one or more branches the primary radiation is filtered out, so that the detected image is formed using only secondary radiation emitted by contaminant material in response to the primary radiation. In a dark field imaging branch using the scattered primary radiation, a spatial filter blocks spatial frequency components associated with periodic features of the article under inspection, to allow detection of particles which cannot be detected by secondary radiation.
1. A method comprising:
directing primary radiation at one or more first wavelengths, from a radiation source, to interact with an article to produce secondary radiation, the secondary radiation being produced from the primary radiation interacting with non-fluorescent material of a contaminant particle on the article, the secondary radiation having one or more second wavelengths different than the one or more first wavelengths;
forming an image, with detection optics, of the article based on filtering out, using a filter, the primary radiation and transmitting, using the filter, the secondary radiation; and
detecting the image with an image sensor.
2. The method of claim 1 , further comprising:
detecting the presence and location of the contamination particles with a processing unit for processing of a signal from the imaging sensor.
3. The method of claim 1 , wherein the primary radiation is at a plurality of distinct first wavelengths, and
wherein the filter has a spectral response which includes a plurality of distinct stop bands corresponding to at least two of the distinct first wavelengths.
4. The method of claim 1 , comprising operating a plurality of branches in parallel, each branch forming an image of the illuminated article, detecting the image, and using secondary radiation of a different wavelength or wavelengths selected from the one or more second wavelengths.
5. The method of claim 4 , further comprising analyzing at least two images detected in different branches to detect the presence and location of the contamination particles.
6. The method of claim 5 , wherein the presence of the contamination particles is detected based on the location of image features detected in at least one of the images.
7. The method of claim 1 , wherein at least a portion of the filtered out primary radiation is diverted into a dark field imaging system having a spatial filter in an intermediate pupil plane to form and detect a dark field image of the article under inspection.
8. The method of claim 7 , wherein:
the spatial filter is arranged to block a selected spatial frequency component, and
the spatial frequency component is selected based on the article under inspection.
9. The method of claim 1 , wherein the first and second wavelengths are selected to detect contaminant particles of metal oxide material.
10. The method of claim 1 , wherein the first and second wavelengths are selected to detect contaminant particles of organic material.
11. The method of claim 1 , wherein the first and second wavelengths are selected to detect contaminant particles of non-noble metals.
12. A method of manufacturing a device, comprising:
inspecting an article for any contamination on the article, wherein the article is used to transfer a pattern from the article to the device,
wherein the inspecting comprises:
directing primary radiation at one or more first wavelengths from a radiation source, to interact with the article to produce secondary radiation, the secondary radiation being produced from the primary radiation interacting with non-fluorescent material of a contaminant particle on the article, the secondary radiation having one or more second wavelengths different than the one or more first wavelengths;
forming an image, with detection optics, of the article by filtering out, using a filter, the primary radiation and transmitting, using the filter, the secondary radiation; and
detecting the image with an image sensor.
13. An inspection apparatus for inspecting an article to detect and locate contaminant particles, the apparatus comprising:
a radiation source configured to generate primary radiation at one or more first wavelengths;
illumination optics arranged to receive the primary radiation and to illuminate at least a portion of the article with the primary radiation; and
an imaging optical system comprising:
detection optics arranged to form an image of the illuminated article, and
an image sensor arranged to detect the image of the illuminated article,
wherein the detection optics comprise a filter configured to remove the primary radiation from the detected image, so that the detected image is formed using secondary radiation at one or more second wavelengths different from the first wavelengths, said secondary radiation being produced from the primary radiation interacting with non-fluorescent material of the contaminant particles.
14. The apparatus of claim 13 , further comprising a processing unit for processing of a signal from the imaging sensor, thereby to detect the presence and location of the contamination particles.
15. The apparatus of claim 13 , wherein the radiation source is arranged to generate the primary radiation at a plurality of distinct first wavelengths, and
wherein the filter has a spectral response which includes a plurality of distinct stop bands corresponding to at least two of the distinct first wavelengths in the primary radiation.
16. The apparatus of claim 13 , wherein the imaging optical system comprises a plurality of branches operating in parallel, each branch forming and detecting an image from the secondary radiation at a different wavelength or wavelengths selected from the one or more second wavelengths.
17. The apparatus of claim 16 , comprising a processing unit arranged to process signals from at least two imaging sensors, each of the imaging sensors in a different branch, thereby to detect the presence and location of the contamination particles.
18. The apparatus of claim 13 , further comprising a dark field imaging optical system having a spatial filter in an intermediate pupil plane, thereby to form and detect a dark field image from at least a portion of the filtered out primary radiation.
19. The apparatus of claim 18 , wherein the spatial filter is a programmable spatial light modulator, said programmable spatial light modulator adjustable to block different spatial frequency components when inspecting different articles.
20. A lithographic apparatus comprising:
a support configured to support an article;
a support configured to support a substrate;
a projection optical system configured to transfer a pattern from the article to the substrate; and
an inspection apparatus configured to inspect an article to detect and locate contaminant particles, the apparatus comprising:
a radiation source configured to generate primary radiation at one or more first wavelengths;
illumination optics arranged to receive the primary radiation and to illuminate at least a portion of the article with the primary radiation;
an imaging optical system comprising:
detection optics arranged to form an image of the illuminated article, and
an image sensor arranged to detect the image of the illuminated article,
wherein the detection optics comprise a filter configured to remove the primary radiation from the detected image, so that the detected image is formed using secondary radiation at one or more second wavelengths different from the first wavelengths, said secondary radiation being produced from the primary radiation interacting with non-fluorescent material of the contaminant particles,
wherein the inspection apparatus is operable to inspect the article without removing said article from the lithographic apparatus.