JPH01319240A - Secondary electron detector - Google Patents

Abstract

PURPOSE:To symmetrically form the collecting electric field with respect to an optical axis by forming a scintillator in a ring shape centering the optical axis. CONSTITUTION:A ring-shaped scintillator 2 is covered by a shield cover 3 to form a secondary electron detector 1, it is arranged so that its center matches with an optical axis 12. When the scintillator 2 is set to a high potential and the shield cover 3 is set to the earth potential in this constitution, the collecting electric field 14 formed by the secondary electron detector 1 is made symmetrical with respect to the optical axis 12. The escape of an electron beam, the occurrence of astigmatism, and the drift of a visual field can be prevented when the secondary electron detector is in operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a secondary electron detector used in a scanning electron microscope or the like.

[Prior Art] Various methods of detecting secondary electrons have been proposed in a scanning electron microscope, and one of the known methods is the configuration shown in FIG. 3. In FIG. 3, the secondary electron detector 1
consists of a scintillator 2 and a shield cover 3 that covers it, and forms a collecting electric field for secondary electron detection.
Usually, a high voltage of about 10 kV is applied to the scintillator 2, and the shield cover 3 is set to ground potential. In addition,
The scintillator 2 is constructed by applying fluorescent paint to a light guide made of glass or plastic, and then forming an aluminum pack on top of the light guide.

Further, the sample 4 is inserted between the pole pieces e and 70 that constitute the objective lens 5. In the above configuration, the incident electrons 8 are deflected by the scanning coil 8 to raster scan the surface of the sample 4. As a result, secondary electrons are emitted from the sample 4, and some of the electrons pass through the sample and become transmitted electrons 10. The secondary electrons emitted from the sample 4 draw a spiral trajectory as shown at 11 due to the nearby magnetic field and the electric field collected by the secondary electron detector 1, and are captured by the secondary electron detector 1. A light spot generated by the collision of secondary electrons in the scintillator 2 is guided by a light guide to a photomultiplier (not shown), converted into an electrical signal, and used as a brightness signal for a display device.

[Problems to be Solved by the Invention] In the structure shown in FIG. 3, the structure of the secondary electron detector 1 is simple and the overall cost is low; (same as the orbit), the collected electric field is asymmetrical with respect to the optical axis 12, as shown by 13 in Figure 4, and the electron beam escapes and the astigmatism occurs. This had an adverse effect on the generation of electron beams, and also had an adverse effect on narrowing down the electron beam. Furthermore, in FIG. 3, the secondary electron detector 1 is deactivated to detect the transmitted electrons 10, and an electron microscope image is displayed based on this, but due to the asymmetrical collecting electric field, There has also been a problem in that the field of view of the scanned image is shifted depending on whether the secondary electron detector 1 is activated or not.

The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to provide a secondary electron detector in which a collected electric field is formed symmetrically with respect to an optical axis.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a secondary electron detector in which a high voltage for collecting secondary electrons is applied to the scintillator, in which the scintillator is exposed to light. It is characterized by being formed into a ring shape centered on the shaft.

[Function] In the present invention, since the scintillator is formed in a ring shape centered on the optical axis, the collected electric field formed by applying a high voltage to the scintillator becomes symmetrical with respect to the optical axis, and secondary electron detection This prevents the electron beam from escaping, causing astigmatism, and shifting the field of view during device operation.

[Example] Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of one embodiment of a secondary electron detector according to the present invention, FIG. 1 a is a plan view, and FIG. FIG.

In FIG. 1, the secondary electron detector 1 is formed by covering a ring-shaped scintillator 2 with a shield cover 3, and the secondary electron detector 1 is arranged such that its center coincides with the optical axis 12. It is located in In such a configuration, if the scintillator 2 is set to a potential of about 10 kV and the shield cover 3 is set to ground potential, the collected electric field formed by the secondary electron detector 1 will be directed to the optical axis 12 as shown at 14 in Figure 1. It is easy to understand that it is symmetrical. The secondary electrons emitted from the sample travel in a spiral trajectory and collide with the scintillator 2 of the secondary electron detector 1, causing the phosphor to emit light, as shown in FIG. 3.

Incidentally, the scintillator 2 may be a light guide made of glass or the like coated with fluorescent paint and an aluminum back formed on the light guide, as in conventional scintillators.

Another embodiment is shown in FIG. 2, in which the secondary electron detector is configured to be thinner. As shown in FIG. A substantially circular opening through which the electrons 8 pass is provided. Then, aluminum is vapor-deposited except for the contact surface with the plug 28 to prevent light leakage and to allow high voltage to be applied by the high-voltage conductive plate 21. The scintillator 20 and the high voltage conductive plate 21 are sandwiched between insulating plates 23 and 24,
Furthermore, it is covered with a ground plate 26.2θ. Insulating plate 23.24
The convex portion is fitted into the concave portion of the plug 28. Figure 2 shows how these parts are assembled. In Figure 2, the axis of the secondary electron detector is optical axis 1.
2, a high voltage of about 10 kV is applied to the scintillator 20 through a high voltage lead wire 22, and the earth plate 26 is brought to earth potential through an earth lead wire 27. Further, the ground plate 26 is connected to the ground plate 26 by conductive bolts and nuts, and is set to the ground potential. In such a configuration, light generated when secondary electrons collide with the scintillator 20 is transmitted through the plug 28,
The light is guided through an optical fiber 28 to a photomultiplier tube (not shown).

In the configuration shown in Figure 1, the fluorescent paint must be applied uniformly to the rod-shaped light guide and an aluminum back must be formed, so a certain diameter is required, and the shield cover 3 shown as D in Figure 1 requires a certain diameter. The diameter of the secondary electron detector 1 will be approximately 10 mm, and the overall thickness of the secondary electron detector 1 will be larger, so it cannot be used if such a space cannot be secured. However, the configuration shown in Fig. 2 According to the invention, the scintillator 20 can be made thinner, and by selecting an insulating material or depending on the applied voltage, the insulating plate 23.2 can be made thinner.
Since the thickness of the secondary electron detector can be made thinner, the thickness of the entire secondary electron detector can be reduced to about 5 mm.

[Effects of the Invention] As is clear from the above description, according to the present invention, the scintillator is ring-shaped and arranged so that the center of the scintillator coincides with the optical axis, so that the collected electric field of the secondary electron detector is It is formed symmetrically with respect to the optical axis, and does not have any adverse effects such as generation of astigmatism on incident electrons. Also, the second
As shown in the figure, by making the scintillator into a plate shape, a thin secondary electron detector can be constructed, so that it can also be used in a scanning electron microscope with a narrow space. Furthermore, since the configuration shown in FIG. 2 uses optical fibers, the light guide section is flexible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of one embodiment of a secondary electron detector according to the present invention, FIG. 2 is a diagram showing the configuration of another embodiment, and FIG. 3 is an example of a conventional secondary electron detector. FIG. 4 is a diagram showing the state of the collected electric field in the secondary electron detector of FIG. 3. 1...Secondary electron detector, 2...Scintillator, 3...
...Shield cover, 4...Sample, 5...Objective lens, 8.7...Pole piece, 8...Scanning coil,
20... scintillator, 21... high voltage conduction plate, 22
...High voltage Riet wire, 23, 24...Insulation plate, 2
5, 2El... Earth plate, 27... Earth lead wire, 28... Plug, 29... Optical fiber. Applicant JEOL Ltd. Agent Patent Attorney Hideo Sugai (4 others) Figure 1 Figure 2 (a) Figure 2 Cause 3 Figure 4

Claims (2)

[Claims] (1) A secondary electron detector in which a high voltage for collecting secondary electrons is applied to a scintillator, characterized in that the scintillator is formed in a ring shape centered on the optical axis. . (2) The secondary electron detector according to claim 1, wherein the scintillator of the secondary electron detector has a plate shape with an opening for passing incident electrons.