Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
2006-01-31
2006-01-31
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S306000, C250S310000, C250S398000, C250S3960ML, C250S491100, C250S492100, C250S492200
Reexamination Certificate
active
06992289
ABSTRACT:
Method for performing focusing in a particle-optical device with the aid of astigmatism in the particle beam.In a particle-optical device such as an electron microscope it is advantageous to perform the process of focusing automatically. In accordance with the invention, the electron beam which is to be focused is deliberately made astigmatic to a certain degree. With this astigmatic beam, two images of a specimen are made at two different settings of the objective, after which in each of the images the direction of the astigmatic smearing is determined—for example, with the aid of a two-dimensional Fourier transform (FFT). The directions of the astigmatic smearing are perpendicular to each other if, in the transition from a first setting of the objective to a second one, the point of optimum focus is passed. Through a process of interpolation (which process may be iterative) between these two settings, the point of optimum focus can now be determined. Possible anisotropy in the specimen itself can be eliminated by making two images at both of the settings of the objective and by subtracting the FFTs thereof from each other.
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K.H. Ong, J C.H. Phang and J.T.L. Thong, “A Robust Focusing and Astigmatism Correction Method for the Scanning Electron Microscope,” Scanning, vol. 19, (1997) pp. 553-563.
Ogasawara Munehiro et al, “Automatic Focusing and Astigmatism Correction Method Based on Fourier Transform of Scanning Electron Microscope Images,”Appl. Phys., Publication Board, Japanese Journal of Applied Physics, vol. 38 (1999) pp 957-960.
Maes Willem Hendrik
Sterken Hendrikus Petrus Maria
Vucht Robertus Johannes Michael
FEI Company
Scheinberg Michael O.
Wells Nikita
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