JPS637656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charged particle energy analyzer that combines a low-pass filter and a high-pass filter. Here, a low-pass filter is a device that selectively reflects only charged particles with energy lower than a certain energy value, and a high-pass filter transmits only charged particles with energy higher than a certain energy value. This is a device that allows you to A low-pass filter consists of a reflective surface and a grid extending parallel to the reflective surface in front of the reflective surface, and the reflective surface is charged with the same polarity as the charged particles to be analyzed with respect to the grid. If the potential difference between the grid and the reflective surface is V, among the charged particles, those with energy greater than (V) eV (V electron volts) are incident on the reflective surface and absorbed, and charged particles with energy less than (V) eV is taken out. A high-pass filter is a double grid stretched in parallel.The grid on the incident side of the charged particle is used as a reference, and the subsequent grid is charged to the same polarity as the charged particle, and the potential difference between the two is reduced to V.
Then, charged particles of (V)eV or more will be transmitted through both grids, and particles with energy lower than (V)eV will be reflected to the incident side. Therefore, by combining a high-pass filter and a low-pass filter, particles having energy within an arbitrarily set narrow energy range are selected and extracted.

A conventionally proposed charged particle energy analyzer constructed using the above-mentioned low-pass filter and high-pass filter has a structure as shown in FIG. M is a spherical reflective surface having a center of curvature at point O, and a grid G1 is arranged concentrically in front of M, and both constitute a low-pass filter. There are double spherical grids G2 and G3 with the center of curvature at the O point on the opposite side of the O point when viewed from M, and the G
2 and G3 constitute a high pass filter. Grids G1 and G2 are kept at the same potential, and G
Appropriate voltages are applied between 1 and M and between G2 and G3, respectively. If the emission point of charged particles is placed at point S near point O, charged particles with energy below a certain level V1 will be reflected by M and once focused near point O, then diverge and go to grid G2, which is a high-pass filter. G3
This is detected because particles incident on the grid G3 with an energy below a certain energy V2 are reflected, and only particles with an energy between V1 and V2 pass through the grid G3. With this configuration, the charged particles between the extracted energies V1 and V2 are divergent and do not form an image of the charged particle radiation source.
It is not possible to observe an image of a sample using emitted electrons with a certain energy.
In addition, as a practical matter, the S point is surrounded by a low-pass filter and a high-pass filter, and it is not possible to set the sample there.Specifically, there is a sample excitation part on the side, and the sample is emitted from the sample. The charged particles are guided to point S by an electron optical system and emitted from point S toward M (Special Publication No. 51-2396), so the device configuration is complicated, and the center of curvature point O is in between. Since a low-pass filter and a high-pass filter are arranged on both sides, the device becomes large.

The present invention aims to eliminate the drawbacks of the previously proposed devices described above, and to provide a charged particle energy analyzer that is capable of observing images of a sample with a simple and compact configuration and has excellent performance. . The present invention will be explained below with reference to Examples.

FIG. 2 shows an embodiment of the invention. A1, A2
are an entrance port and an exit port for charged particles, and since this device has a symmetrical structure, either one may be used as the entrance port.
M is a reflective surface, which is an ellipsoid of revolution with focal points at the centers of A1 and A2. The entire device is surrounded by an outer wall W shaped like a double-headed cone. A grid G1 is provided in front of the reflective surface M in parallel with the reflective surface. This reflective surface M and grid G1 constitute a low-pass filter. The double heads of the outer wall are provided with grids G2, G3 and G4, G5, respectively. The grids G2 and G3 are concentric spherical surfaces whose center of curvature is the center of the aperture A1. Similarly, the grids G4 and G5 are concentric spherical surfaces with the center of curvature at the center of the aperture A2. GR is a guard ring for preventing disturbance of the electric field at the edges between the reflective surface M and the grid G1, between the grids G2 and G3, and between the grids G4 and G5.

The potentials and effects applied to each part will be described with the aperture A1 as the entrance aperture for charged particles and A2 as the exit aperture. The grid G2 and the double heads of the outer wall from opening A1 to grid G2 are at the same potential and are at the same potential as the charged particle source, generally at ground potential. Grid G3 has a polarity that reflects charged particles and changes its potential.
Let it be Va. When the energy of an incident charged particle is expressed in electron volts and is V, particles where V is smaller than Va are repelled by G3, and only charged particles with energy such that V>Va pass through grid G3.
The grids G1, G3, G4 and the outer wall W between these grids are all at the same potential. Therefore, the entire space surrounded by these parts has the same potential. The charged particles that have passed through the grid G3 travel straight through the above-mentioned space and are incident on the surface of the grid G1. A potential is applied to the reflective surface M in a direction that repels charged particles, and the potential is V1, and V1>Va. Then, among the charged particles that have entered between the grid G1 and the reflective surface M, only those with V<V1 are reflected, and the particles with V>V1 collide with the reflective surface M and lose their charge. The charged particles reflected by M travel straight toward the center of the aperture A2. This is because the reflective surface M is an ellipse with focal points at A1 and A2. A potential V2 is applied to the grid G5 in a direction to repel charged particles.
Therefore, particles that have passed through grid G4 and have energy smaller than V2 are reflected by grid G5, and particles that are larger than V2 pass through grid G5 and are focused at the center of aperture A2. Therefore, if a detector is placed at A2, only particles with energy between V2 and V1 will be detected. Third
The figure is a graph showing the relationship between the potentials applied to each grid and the reflective surface, and the performance of a filter composed of grids G2, G3, G4, G5, reflective surface M, and grid G1.

Strictly speaking, the critical energy of particles reflected by each filter changes depending on the incident angle θ when they enter the filter. In Figure 4, P1 and P2 are grids or reflective surfaces, and the potential of P1 is set to O, P
The potential of 2 is V, and the energy of the incident charged particle is
Let V′ be the angle of incidence and θ. Particles are P1 and P2
Since it is the component of the velocity of motion in the direction of the electric field that is affected by the electric field between V
V′cosθ. When θ is small, cosθ=1−θ ² /
2, the term θ ² can be ignored and the reflection condition is VV'.
Furthermore, even if the term θ ² cannot be ignored, as long as θ is constant, the energy selection threshold will not vary.

FIG. 5 shows a cross section near the opening A1 in FIG. 2 along a plane perpendicular to the plane of the drawing. S is the sample and X is the X-ray source. The sample S is excited by the X-rays and emits photoelectrons. The energy of these photoelectrons is analyzed by the action described above. Scanning of the energy value is performed by setting the grids G1, G3, and G4 to the same potential, and changing the potential of the grid G1, etc. while keeping the potential difference between the reflecting surface M1 and the grid G1, etc. of the grid G5 constant. Of the photoelectrons emitted from the sample S, only those that fall within a certain energy range are focused on the aperture A2 to form an image of the sample using these photoelectrons. Particles that have passed through grid G1 have an extremely low velocity, but if you simply want to detect the energy-selected particles and measure the energy spectrum of the particles emitted from the sample, there is a gap between grid G5 and aperture A2. There is no need to provide an acceleration grid. In this case, the charged particles are attracted and accelerated by the potential of the detector placed at position A2. When observing an image of a sample with specific energy particles, an accelerating grid is placed between G5 and aperture A2 concentrically with G5, and the particle image formed on the surface of aperture A2 is further magnified using an electron optical system. The image is then projected onto a fluorescent surface, photographic film, image pickup tube, etc. Note that the method for exciting the sample is not limited to the type shown in FIG. 4, but may be arbitrary, and charged particles emitted from the sample may be made to enter the aperture A1 via the electron optical system.

It is preferable to make the distance between A1 and A2 as close as possible within a range that accommodates the sample excitation system and the charged particle detection system, and the closer the distance between A1 and A2, the smaller the difference in the above-mentioned θ at each point on the reflecting surface. Further, in the above embodiment, the reflecting surface M is a spheroidal surface, but when the distance between A1 and A2 is smaller than the distance from A1 and A2 to the reflecting surface, the center of curvature of the reflecting surface is at the midpoint between A1 and A2. A spherical surface with .

Charged particle energy analyzers using energy filters are expected to have higher sensitivity than electrostatic hemispherical energy analyzers because they can handle charged particles incident within a wider solid angle. However, as mentioned above, the previously proposed device introduces the charged particles to be analyzed into the energy analyzer using an electron optical system. Since the solid angle of introduction is limited and the electron optical system generally has different energy transmission characteristics for particles, it has the disadvantage of allowing particles with biased energy to pass through, and cannot fully demonstrate its original characteristics.

Since the present invention has the above-described configuration and has an entrance aperture and an exit aperture for charged particles at two conjugate points on the concave reflective surface, the charged particles emitted from the sample can be made to directly enter the energy analysis system. In addition, since the sample, sample excitation system, and charged particle detection system can be placed outside the energy analysis system, there are no foreign substances in the energy analysis system that block the charged particle beam flux, and the charged particles emitted from the sample within a wide solid angle can be detected. Since it can be handled without loss, it has higher sensitivity than the previously proposed device, and the size of the device is half that of the existing device (because the energy analysis system is only on one side of the center of curvature of the reflecting surface). Since the analyzed charged particles are focused, the present invention has the advantage that it can be used both for simply detecting charged particles and for accelerating them and guiding them to a re-imaging system for mapping.

[Brief explanation of the drawing]

Fig. 1 is a schematic side view of an already proposed device, Fig. 2 is a horizontal sectional view of an embodiment of the device of the present invention, Fig. 3 is a graph showing the relationship between potentials applied to each grid and reflective surface and filter characteristics, and Fig. 4 is a graph showing filter characteristics. The figure is an enlarged view of the particle reflection section, and FIG. 5 is a vertical sectional view of the vicinity of the opening A1 in FIG. 2. M... Reflective surface, G1-G5... Grid, A1, A
2...Charged particle entrance or exit aperture.

Claims (1)

[Claims] 1. Openings for the entrance and exit of charged particles are provided at two conjugate points arranged in a direction perpendicular to the center line of the concave reflective surface, and a grid is provided in front of the reflective surface in parallel with the same surface. , constitutes a low pass filter together with the concave reflective surface, and two grids are concentrically stretched between one of the two apertures and the reflective surface with the center of the aperture as the center of curvature. A charged particle energy analyzer characterized in that a high pass filter is configured.