Integrated optical and charged particle inspection apparatus
An apparatus for inspecting a sample, is equipped with a charged particle column for producing a focused beam of charged particles to observe or modify the sample, and an optical microscope to observe a region of interest on the sample as is observed by the charged particle beam or vice versa. The apparatus is accommodated with a processing unit adapted and equipped to represent an image as generated with the column and an image as generated with the microscope. The unit is further adapted to perform an alignment procedure mutually correlating a region of interest in one of the images, wherein the alignment procedure involves detecting a change in the optical image as caused by the charged particle beam.
1. Method for correlating a charged particle microscope image and an optical image in an apparatus for inspecting a sample, said apparatus equipped with a charged particle column for producing a focused beam of charged particles to observe or modify the sample, and an optical microscope to simultaneously observe the same region of interest on the sample as is observed by the charged particle beam,
wherein the method involves detecting a change in the optical image caused by the charged particle beam, and
wherein the change in the optical image comprises a modification in luminescent or fluorescent light from the sample, or the generation of cathodoluminescence light by the charged particle beam falling on the sample.
2. Method according to claim 1 , wherein the correlation is performed on one area on one sample and is extrapolated to the correlation on another area or on another sample.
3. Method according to claim 1 , wherein the correlation parameters for different z-positions of a sample are stored, e.g. in the memory of a computer or processor, and retrieved when the sample is positioned on the corresponding z-position.
4. The alignment method of claim 1 , wherein the method of alignment is used to correlate images acquired by an independent electron and optical microscope.
5. Apparatus for inspecting a sample, provided with a charged particle microscope having a column for producing a focused beam of charged particles to observe or modify the sample, and an optical microscope to observe a region of interest on the sample as is observed by the charged particle beam or vice versa, the apparatus accommodated with a detection and processing unit is adapted and equipped for acquiring an image as generated with said charged particle and said optical microscope, the unit is further adapted for performing an image alignment procedure mutually correlating the image coordinate systems of said images,
wherein the apparatus is adapted for one of the group consisting of:
i) using a detection in the optical image of a modification in the luminescence or fluorescence as caused therein by the charged particle beam, for correlating said images, and
ii) using a detection in the optical image of the generation of cathodoluminescence light by the charged particle beam falling on the sample, for correlating said images.
6. The apparatus of claim 5 , wherein the position is calculated using the determination of the center of mass of the changes.
7. Apparatus of claim 5 , wherein the optical microscope and the charged particle microscope are arranged to simultaneously observe the same region of interest on the sample.
8. The apparatus of claim 5 , wherein said change is an increase or a decrease in brightness at the position of the charged particle beam.
9. The apparatus of claim 5 , wherein said change is a persistent effect, which is still detectable after the electron beam has been switched off.
10. The apparatus of claim 5 , wherein the adaptation is provided for correlating images acquired by an independent electron and optical microscope.
11. The apparatus of claim 5 , wherein said charged particle beam is scanned to form a pattern in the optical image.
12. The apparatus of claim 11 , wherein said pattern consists of at least two sub-patterns at the corners of the electron image.
13. The apparatus of claim 5 , wherein the procedure involves an automated recognition and interpretation of the change in the optical image caused by the electron beam.
14. The apparatus of claim 5 , wherein a position of the change in the optical image as caused by the electron beam is calculated with a precision that is better than the optical resolution.
15. The apparatus of claim 5 , wherein said change in the optical image as caused by the electron beam is used to calibrate the magnification of the optical image or the absolute dimensions in the image.
16. The apparatus of claim 5 , wherein the correlation is determined and stored by the processing unit while the sample is maintained in place in the apparatus.
17. The apparatus of claim 5 , wherein the apparatus is adapted for selecting a region of interest in either of the images of the two microscope systems for inspection of said area by the other system while the sample is maintained in place in the apparatus.