Inspection device and inspection method for the optical examination of object surfaces, particularly of wafer surfaces
View Patent ↗An inspection device and a method of inspection, for optical examination of object surfaces, particularly wafer surfaces, wherein the object surface is illuminated by a first illumination device and a second illumination device, wherewith the light reflected and/or scattered from irregularities on the object surface is detected by means of a “scattered light detector” operating in the dark field of the first and second illumination devices, and wherewith the object surface is illuminated by a first illumination device and a second illumination device, wherewith the first illumination device has a laser for illuminating a measurement point on the object surface. The second illumination device is disposed (and oriented) to illuminate the same measurement point on the object surface but with a larger image spot, with the use of light of lower coherence and/or with less anisotropy than that of the laser.
1. An inspection device for optical examination of object surfaces, comprising: a first illumination device and a second illumination device, for illuminating the object surface, and further having a scattered light detector disposed in a dark field of the first and second illumination devices, which detector is employed to detect light reflected and/or scattered from irregularities in the object surface, wherewith the first illumination device comprises a laser for illuminating a measurement point on the object surface; wherein the second illumination device is disposed and oriented to illuminate the same measurement point on the object surface but with a larger image spot, with the use of light of lower coherence and with less anisotropy than that of the laser.
2. The inspection device according to claim 1 ; wherein the second illumination device is set up so as to emit unpolarized light.
3. An inspection device according to claim 2 ; wherein the second illumination device has at least one broadband light source.
4. The inspection device according to claim 3 ; wherein the second illumination device has a light density of 1-100 W/sq mm.
5. The inspection device according to claim 4 ; wherein the second illumination device has a plurality of light sources in symmetrical disposition around the image spot on the object from the illumination.
6. The inspection device according to claim 5 ; wherein the second illumination device has a plurality of light sources in a circular or partial circular disposition around the image spot.
7. The inspection device according to claim 6 ; wherein the second illumination device has one or more light-emitting diodes (LEDs).
8. The inspection device according to claim 7 ; comprising said control means which alternately control the first and second illumination devices.
9. The inspection device according to claim 8 ; wherein the first and second illumination devices have spectral ranges which mutually differ, and the scattered light detector has a dichroic beam splitter or a spectral filter.
10. The inspection device according to claim 1 wherein the second illumination device has at least one broadband light source.
11. The inspection device according to claim 1 wherein the second illumination device has a light density of 1-100 W/sq mm.
12. The inspection device according to claim 1 wherein the second illumination device has a plurality of light sources in symmetrical disposition around the image spot on the object from the illumination.
13. The inspection device according to claim 1 wherein the second illumination device has a plurality of light sources in a circular or partial circular disposition around the image spot.
14. The inspection device according to claim 1 wherein the second illumination device has one or more light-emitting diodes (LEDs).
15. The inspection device according to claim 1 comprising said control means which alternately control the first and second illumination devices.
16. The inspection device according to claim 1 wherein the first and second illumination devices have spectral ranges which mutually differ, and the scattered light detector has a dichroic beam splitter or a spectral filter.
17. The inspection device according to claim 1 , wherein the object is a wafer.
18. A method of inspection for optical examination of object surfaces comprising the steps of illuminating the object surface by a first illumination device and a second illumination device, wherewith the first illumination device illuminates a measurement point on the object surface by means of laser illumination, wherewith the light reflected and/or scattered from irregularities on the object surface is detected by means of a “scattered light detector” operating in a dark field of the first and second illumination devices; and illuminating with the second illumination device illuminates the same measurement point on the object surface as the laser beam, with a larger image spot, using light of lower coherence and lower anisotropy than that of the laser beam.
19. A method of inspection according to claim 18 ; wherein the first and second illumination devices are operated in alternation.
20. A method of inspection according to claim 19 wherein the first and second illumination devices are operated simultaneously but in different spectral ranges, wherewith the light emitted by the first and second illumination devices and reflected by the irregularities in the object surface is detected at spatially separate locations with the use of a dichroic beam splitter or a spectral filter.