Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Patent
1985-12-06
1987-04-14
Anderson, Bruce C.
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
250396R, 250397, H01J 37244
Patent
active
046581367
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a secondary electron detecting apparatus and, more particularly, to a secondary electron detecting apparatus which is suitable for use in a scanning electron microscope.
BACKGROUND ART
In recent years, the resolution of the scanning electron microscope has been so improved that it has been frequently used at low acceleration voltages, especially for observation of semiconductors so as to avoid damaging the semiconductor with an electron beam.
In the ordinary secondary electron detecting apparatus used in the scanning electron microscope, the secondary electrons emitted from a sample are detected by means of a secondary electron detector through an objective lens magnetic field for focusing the electron beam which irradiates and bombards the sample. A photoelectron multiplication type detector is generally used as the secondary electron detector. This is because that detector has a high detection sensitivity. Since a high voltage for attracting the secondary electrons is applied to the front end of the secondary electron detector, however, it obstructs deflection of the electron beam with the consequent disadvantage that the electron beam is misaligned.
This problem is solved by positioning the secondary electron detector apart from the electron beam. However, this positioning raises another problem that the secondary electrons cannot be efficiently detected.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a secondary electron detecting apparatus which can detect the secondary electrons from a sample efficiently without interfering with the deflection of an electron beam.
According to the present invention, there is provided a secondary electron detecting apparatus comprising: means for generating an electron beam and for irradiating a sample with said electron beam--for generating secondary electrons from said sample at the side of said sample, which is irradiated by said electron beam, with respect to said sample; means for generating an electric field for deflecting said electron beam and said secondary electrons in a first direction; means for generating a magnetic field for deflecting said electron beam in a second direction opposite to said first direction to deflect said secondary electrons in said first direction and to reduce the deflection of said electron beam in said first direction substantially to zero; and means for detecting the secondary electrons which are deflected in said first direction.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic longitudinal section showing a secondary electron detecting apparatus according to one embodiment of the present invention;
FIG. 2 is a top plan view showing the electron beam misalignment correcting means of FIG. 1;
FIG. 3 is a section taken along line A--A of FIG. 2;
FIG. 4 is a perspective view showing the electrodes shown in FIGS. 2 and 3; and
FIG. 5 is a perspective view showing the coil shown in FIGS. 2 and 3.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIG. 1, a low acceleration electron beam 2 generated by an electron beam generator 1 is focused on a sample 4 by a magnetic field type electronic lens 3. When the sample 4 is irradiated with or bombarded by the electron beam 2, information signals characterizing the sample 4 such as secondary electrons, reflected electrons or X-rays are emitted from the sample 4. Of these information signals, the secondary electrons generated at the side of the sample 4, which is irradiated by the electron beam, with reference to the sample 4 are caused to pass through the lens magnetic field of the objective lens 3 while swirling along the axis of the electron beam 2. The secondary electrons thus having passed are detected by means of a photoelectron multiplication type secondary electron detector 5. The output signal of the secondary electron detector 5 is introduced as a brightness modulated signal into a cathode ray tube (not-shown).
A deflector 6 deflects the electron beam 2 in two dimensions so that the samp
REFERENCES:
patent: 3474245 (1969-10-01), Kimura et al.
patent: 3717761 (1973-02-01), Koike et al.
patent: 4442355 (1984-04-01), Tamura et al.
Kuroda Katsuhiro
Nakaizumi Yasushi
Ohtaka Tadashi
Anderson Bruce C.
Berman Jack I.
Hitachi , Ltd.
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