JPH0214663B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage measuring device, and more particularly to a voltage measuring device that irradiates a sample with an electron beam, extracts secondary electrons from the sample, and measures the voltage of the sample.

The voltage of the sample is measured by irradiating the sample with an electron beam and measuring secondary electrons emitted from the sample using an energy analyzer. This is the energy distribution of secondary electrons, that is, the secondary electron energy distribution curve between the velocity of secondary electrons flying out of the sample and the number of secondary electrons at that velocity. As a result, only the secondary electrons with a faster ejection velocity will eject from the sample surface due to the force of preventing ejection, and will shift to the right. Conversely, if the voltage of the sample is positive, the above distribution curve will become This takes advantage of the shift to the left. Various devices have been proposed as voltage measuring devices using energy analyzers for secondary electrons.

As one of these voltage measuring devices, a sample 3 is placed inside a dome-shaped anode 2 made of a hemispherical metal plate as well as a grid group 1 having grids _G1 to _G3 made of a plurality of hemispherical meshes, as shown in the first figure. A through hole 4 is provided above the dome-shaped anode 2.
By irradiating the sample 3 with the electron beam 5 through the dome-shaped anode, secondary electrons 5a emitted from the sample are captured by the dome-shaped anode, and the voltage v is taken out through the amplification circuit 6 to measure the voltage of the sample 3. What has been done is known.

Furthermore, as shown in FIG. 2, another voltage measuring device using a scintillator and a photomultiplier tube is known. The gist of this device is to irradiate an electron beam 5 onto a sample 3 placed in a grid group 1 having grids G ₁ to _{G 3} consisting of a plurality of hemispherical meshes, and detect the emitted secondary electrons 5a. Detected at 7. The detection means has a fluorescent film 7b at the rear of an aluminum film 7a with a thickness of about 1000 Å to which a high voltage of about 10 kV is applied, and the secondary electrons transmitted through the aluminum film 7a cause the fluorescent film to emit light. Light from the membrane 8
is added to the photomultiplier tube 9, and the output from the photomultiplier tube 9 is measured to know the voltage v of the sample.

In the configuration as described above, an integrated circuit (IC) or the like is used as the sample 3 in the case shown in the first diagram, and in particular, an integrated circuit (IC) is used as the sample 3.
In the case of a MOSIC, applying a high-energy electron beam will destroy the IC, making it impossible to apply a large electron beam.Furthermore, since the IC is composed of a thin pattern of about 2μ, increasing the current will reduce the beam diameter. As the electron beam becomes larger, it becomes necessary to reduce the beam diameter and the electron beam current in order to increase the resolution, which lowers the sensitivity to secondary electrons. In order to obtain a predetermined measurement voltage by performing multi-stage amplification, the amplification circuit 6 itself has the disadvantage of being affected by noise, etc., which deteriorates the S/N ratio.

Furthermore, in the case of the conventional example shown in FIG. 2, the S/N ratio is better than that in the configuration shown in FIG. It has the disadvantage that it becomes smaller. This phenomenon naturally occurs because the detection means is placed at a position where it can capture only a small portion of the secondary electrons radially emitted from the sample 3. As a result, even the configuration shown in FIG. 2 has the disadvantage that the S/N ratio becomes small.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide a voltage measurement device that improves voltage measurement accuracy by improving the capture rate of secondary electrons and improving S/N.

The feature of the present invention is that a disc-shaped microchannel plate is provided in parallel to cover the hemispherical grid, and a large number of secondary electrons captured in this microchannel plate are multiplied and extracted as a voltage signal. This is a voltage measuring device.

Embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 3 is a principle diagram showing the electrode structure of the energy analyzer of the present invention. Sample 3 consists of a first grid G ₁ consisting of a hemispherical mesh, a second grid G ₂ ,
V _{1 , −V 2 , V 1 , −V 2 ,}
A voltage indicated by V ₃ is applied, and a large-area microchannel plate 11 is disposed above the semicircular third grid G ₃ , and this microchannel plate consists of a substrate 11a and an anode portion 11b, which are It is formed into a disk shape and has a central hole 11c in the center through which the electron beam 5 irradiating the sample 3 passes, and the measurement voltage v is taken out from this microchannel plate 11. The first grid is a grid for extracting secondary electrons ejected from the sample 3, and a voltage of several hundred volts is applied to it. A negative voltage is applied to the second grid _G2 so as to prevent secondary electrons having a speed lower than a predetermined speed from passing therethrough. The third grid _G3 is a hemispherical mesh metal that further accelerates the secondary electrons that have passed through the second grid _G2 and also serves as an electric field shield effect together with the shield 12 provided close to the upper surface of the anode 11b. When the sample 3 is irradiated with an electron beam through the center hole 11c, secondary electrons having an energy distribution curve a as shown in FIG. 4 are emitted from the sample. In Figure 4, the horizontal axis represents the ejection velocity (S) of secondary electrons, and the vertical axis represents the number of emitted secondary electrons. Figure 4 shows the distribution curve when no voltage is applied to sample 3. The secondary electron jumping-out speed S, at which the number of secondary electrons reaches a peak value P, changes depending on the voltage applied to the sample 3. For example, when a negative voltage is applied to the sample, the secondary electron jumping-out speed S reaches the peak value P.
is shifted to the right in FIG. Therefore, the peak value P
In other words, the speed at which secondary electrons jump out gives 2
The voltage of the sample can be found by finding the energy (eV) of the secondary electron. For this purpose, the ejection velocity of the secondary electrons, that is, the energy spectrum may be analyzed.

Therefore, in the present invention, the secondary electrons 5a are collected using microchannel plates as shown in FIG. 5A and B, and the secondary electrons are amplified by the microchannel plate to increase the sensitivity. This is how it was done. FIGS. 5A and 5B show a plan view and a cross-sectional view of one embodiment of the microchannel plate used in the present invention. The microchannel plate formed on a disk is composed of a substrate 11a and an anode electrode 11b, A large number of narrow holes 11d are drilled, and secondary electrons jump into the holes and are repeatedly reflected, thereby emitting the secondary electrons one after another within the inner walls of the holes and multiplying them. A center hole 11c is made in the center of the disk-shaped substrate and the anode to allow the beam to pass therethrough.

FIG. 6 shows another embodiment of the microchannel plate used in the present invention, in which the electrodes G ₄ , G ₅
is connected to chrome metal deposited with a thin film on both ends of the substrate 11a, and the substrate is made of a material made of thin tubes bundled together and finished in a disk shape, and the inner wall of the tube has a secondary electron emitting layer. It is coated with a semi-conducting material. Now electrodes G ₄ , G ₅ and anode 1
1b with a predetermined potential (anode is approximately 1kV)
When is applied, the substrate 11a becomes excited, and low-speed, low-energy secondary electrons ejected from the sample enter the tube and collide with the inner wall to induce secondary electrons, and the induced secondary electrons further collide with the inner wall. This phenomenon is repeated until a huge number of electrons are ejected from many tubes.

Since the present invention uses the energy analyzer and microchannel plate as described above, by controlling the voltage of the second grid _G2 , the secondary electrons have a speed that passes through the decelerating electric field due to the negative voltage applied to the second grid. That is, by measuring the secondary electrons within the shaded area to the right of the boundary line Q corresponding to the second grid _G2 in Fig. 4, it is determined that the secondary electrons having a velocity higher than the second grid voltage are in the microchannel. Since the secondary electrons are multiplied by jumping into the substrate hole of the plate or inside the tube, the capture rate of secondary electrons is improved and the amplifier 6 is not required, so the energy spectrum can be adjusted with high S/N and at high speed. It has the characteristic that the voltage of the sample can be obtained quickly and accurately.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a conventional voltage measuring device for secondary electrons generated when a sample is irradiated with an electron beam using a hemispherical metal anode, and Figure 2 is a schematic diagram showing another conventional example of a voltage measuring device. Figure 3 is a schematic diagram of an embodiment of a device for measuring the voltage of secondary electrons generated when a sample is irradiated with an electron beam using the microchannel plate of the present invention, and Figure 4 is a schematic diagram of the number of emitted secondary electrons. FIG. 5A and B are a plan view and side sectional view of a microchannel plate used in the present invention, and FIG. 6 is a microchannel plate used in the present invention. FIG. 3 is a partially sectional side view showing the relationship between other embodiments and electrical wiring; DESCRIPTION OF SYMBOLS 1...Grid group, 2...Anode, 3...Sample, 4...Through hole, 5...Electron beam, 6...Amplification circuit, 7...Detection means, 9...Photomultiplier tube, 1
1...Microchannel plate.

Claims (1)

[Claims] 1. A voltage for measuring the voltage of the sample by irradiating an electron beam onto a sample arranged in a plurality of concentrically arranged hemispherical grids and extracting secondary electrons from the sample. A voltage measuring device comprising: a disk-shaped microchannel plate arranged substantially parallel to the sample surface on the grid and having an electron beam hole in the center.