Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
1999-01-22
2001-01-23
Arroyo, Teresa M. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S492200, C250S492210, C250S397000
Reexamination Certificate
active
06177670
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of performing processing to form a cross section at a certain location on a semiconductor device, using a focused ion beam, for defect analysis or the like and of observing the cross section.
As LSIs (large-scale integrated circuits) and so on are fabricated with increasing device densities and in smaller size, techniques for processing and observing cross sections of the LSIs during development steps and fabrication steps with a focused ion beam device have been shown.
In particular, the position of a cross section to be processed is determined by the functions of a scanning ion microscope. Using the processed cross section as a plane, a rectangular hole is formed by maskless etching function. A desired cross-sectional portion is exposed, and then the sample is tilted to direct the cross-sectional portion in the direction of illumination of the ion beam. The processed cross section is observed again by the functions of the scanning ion microscope.
When the cross-sectional portion fabricated by the aforementioned method is observed by the functions of a scanning ion microscope, the ion current of the focused ion beam is set less than 5 pA to reduce the beam diameter. In this way, a high-resolution image is obtained. However, as the beam current decreases, the intensity of the secondary charged-particle signal also decreases, thus deteriorating the signal-to-noise ratio. Especially, the intensity of secondary ions is only approximately {fraction (1/10)} to {fraction (1/1000)} of the intensity of secondary electrons. Therefore, with scanning at an image refresh rate of a few or several seconds necessary for adjustment of the focus of the focused ion beam, the S/N is low. Image quality necessary for the work cannot be obtained. It has been difficult to finely adjust the voltage applied to the objective lens while watching the image of poor quality, to bring the focus of the focused ion beam onto the sample, and to obtain a high-resolution image of less than 10 nm. It is customary to slow the frame scanning rate as a method of improving the S/N. This method increases the time for which the secondary ion signal is accumulated to thereby improve the image quality. However, the image refresh rate is low. Therefore, skillfulness is necessary to adjust the focus of the focused ion beam while watching this image. It is not easy for everyone to make an adjustment.
SUMMARY OF THE INVENTION
The problem described above is solved by the present invention comprising first and second processing steps. In the first step, secondary electrons are detected by a secondary charged-particle detector. The focus of an ion optics is adjusted while observing a secondary electron image. In the second step, secondary ions are detected with the secondary charged-particle detector without readjusting the focus of the ion optics adjusted in the first step. A secondary ion image is observed. Thus, a focused high-resolution secondary ion image is obtained.
REFERENCES:
patent: 4933565 (1990-06-01), Yamaguchi et al.
patent: 5065034 (1991-11-01), Kawanami et al.
patent: 5739528 (1998-04-01), Kato
patent: 5824598 (1998-10-01), Yamaguchi et al.
Adams & Wilks
Arroyo Teresa M.
Seiko Instruments Inc.
Wells Nikita
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