JPH0269692A - Spherical mirror analyzer of energy of charged particle beam - Google Patents

Abstract

PURPOSE: To secure the accurate angular convergence of charged particle beams under a constant dispersion and wide-width hole condition and a large scanning area on a tested surface by positioning a charged particle beam source and a detector having required shapes to prescribed positions symmetrically to each other with respect to the centers of concentric spherical electrodes. CONSTITUTION: A charged particle beam source 4 having the same shape of segment as that of an inner electrode 1 having a spherical shape concentric to a spherical outer electrode 3 and provided with a window 2 is provided on the inside of the electrode 1 and detecting means having the same shape as that of a power source 4 is provided symmetrically to the power source 4 with respect to the centers 0 of the electrodes 1 and 2. Secondary charged particle beams from point sources 1-c which are excited from an excited radiation generator 7 and outputted from the power source 4 respectively converge to the points a'-c' of a detector 5, because the beams of a gradient corresponding to the amount of delay of the potential applied across the electrodes 1 and 3 pass through the window. Therefore, the accurate angular convergence of the beams under a constant dispersion and wide-width hole condition and a large scanning area on a tested surface can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for analyzing the energy of a charged particle beam, and in particular to a spherical mirror analyzer for the energy of a charged particle beam.

The invention can be most advantageously used in the production of a novel electron spectrometer for investigating the surfaces of solid objects using optical, X-ray and Auger electron spectroscopy techniques, in particular raster spectroscopy.

The invention is also suitable for other energy analysis of charged particle beams in solid matter ion mass spectroscopy, for example by analyzing the energy of backscattered ions.

Currently, the development of solid-state physics requires improvements in its investigation methods. Electron spectroscopy involves increasing the sensitivity and precision in measuring the energy and angular distribution of secondary electrons and increasing the micro-scanning area of the test object through the use of an electron spectrometer in which the energy analyzer serves as the analytical element. It is generally necessary to

The rapid development of solid-state microelectronic wave manufacturing methods requires rapid and accurate quality control of the surface structures of wafers and integrated circuits at different manufacturing stages. One of the techniques used is the use of standing waves. This method is based on diffraction requires the manufacture of a new floor-hole energy analyzer.

[Prior art]

Conventional electrostatic spherical mirror energy analyzers include two spherical electrodes with a potential difference. The charged particle beam enters the reflective field of the mirror and exits from there to impinge on the inner spherical electrode.

Electrostatic bulb mirror circuits (Nucl, Ins.
trum, Meth, 1966, volume 42, 71
(See "More on a spherical capacitor as an analyzer" by H, Z, 5ar-E 1, pages 76 to 76) are known. Such a circuit configuration is a rare example of an electron-tip thread characterized by precise spatial focusing of the charged particle beam. The above published paper shows the following: That is, if the energy of the particle and the delayed potential of the electrostatic spherical mirror are related as (where q is the radius of the inner and outer spherical electrodes), then the point source can be Appears in the opposite direction.

This known circuit is unsatisfactory because the linear dispersion therein depends on the gradient of the charged particle beam being analyzed and the axial beam path is characterized by no dispersion. Thus, the above circuit is not suitable for use in energy analyzers with high energy resolution.

In addition, a display type analyzer (Rev, Sci, In5trun+, 1988
2015, Volume 59, 4th Edition, Page 545, by Hirochi Daimon, “
A novel display analyzer for the energy and angular dispersion of charged particles is known. This known analyzer is capable of performing precise angular focusing of electrostatic bulb mirrors as described in the above-mentioned published article by Sar-Ef.

Such analyzers have the disadvantage that the dispersion is highly dependent on the slope of the charged particle path, effectively limiting their energy resolution.

Moreover, to obtain good electro-optical properties of the analyzer, the inner sphere window through which the charged particle beam under test passes must meet stringent requirements. The use of conventional fine mesh windows defocuses widely divergent charged particle beams due to diffraction and lensing effects on the mesh that impair the resolution of the analyzer.

Keplatron-type analyzers for the energy of charged particle beams are also known (Nucl, Instrum, Me
Th.

1960, vol. 6, p. 157 R.H., Ritchie J.
[Spherical Capacitors as High-Transmission Particle Spectrometers] by S. Sheka and R. D. Berknov), this analyzer is essentially formed by a field set up between two concentric spherical electrodes. It is an electrostatic mirror. The charged particle source is shaped as a disk and placed on the surface of the inner spherical electrode.

A charged particle beam emanating from this source is reflected by the electrostatic bulb field and focused onto a slit in the detection diaphragm to form a circuit image. This image is dependent on the energy of the particles due to the dispersion that characterizes known energy analyzers. Furthermore, this kepsitron analyzer has a very large acceptance angle.

However, the above analyzer suffers from the following factors: 1) inadequate focusing which considerably limits its resolving power (done only as a first approximation to the initial divergence of the beam), and 2) being placed in the mirror field. It is necessary to use a circular slit diaphragm as a detection means, and the disadvantages of distorting the working field and worsening the detection of charged particles, −
M was not satisfied.

An undesirable feature of all these known devices is the slow analysis speed due to the small micro-scanning area on the surface of the source, which is placed in front of the detector where the holes pass the charged particles escaping only from a defined area of the test object. This is due to the use of a detection diaphragm. Making the diaphragm hole larger increases the background and degrades the resolution of the analyzer.

[Problem to be solved by the invention]

The present invention consists in providing a spherical mirror analyzer of the energy of a charged particle beam that ensures accurate angular focusing and a larger scanning area of the surface under test under conditions of constant dispersion and wide aperture.

[Means to solve the problem]

According to the invention, said object comprises a charged particle beam source and two concentric spherical electrodes connected to a deceleration voltage source;
In a spherical mirror analyzer of the energy of a charged particle beam, the inner electrode has a window through which the beam of charged particles passes and is provided with detection means, the charged particle beam source and the detection means are spherical. by a spherical mirror analyzer characterized in that it is shaped as segments of a sphere arranged centrosymmetrically with respect to the center of the electrode, and that at least one of these segments is arranged on the surface of the inner spherical electrode. achieved.

According to the invention, it is to obtain an ideal angular focusing of a charged particle beam whose dispersion is independent of the slope of the beam path, a condition known as path equidispersity. Moreover, the image of the source representing a randomly shaped segment in any region of the energy spectrum is aberration-free and has a one-to-one magnitude on the diametrically opposite portion of the inner spherical electrode or its geometric extension. This has the advantage of providing certainty of the image.

This energy analyzer can thus considerably increase the resolving power at very large acceptance angles, provided that it provides an aberration-free image of the source or a larger section.

In one embodiment of the invention, the detection means comprises a detection diaphragm representing a segmented hole of the inner spherical electrode and a detector arranged behind said hole and forming a microchannel plate. This analyzer - for boat fishing, analyzes the energy of charged particles emanating from the surface of the specimen, which is a spherical segment placed in the geometrical extension of the inner sphere, in which all paths are homodispersive. , and the source image is aberration-free. Therefore, the solid angle surrounding the active area of the source and the charged particle beam under test can be increased several times if the high resolving power remains essentially unchanged. a sensing diaphragm arranged centrosymmetrically with respect to the source represents a segment hole in the inner sphere;
When accepting a microchannel plate whose surface is aligned with the inner sphere, a larger area of the test object is microscanned in the primary beam scanning mode, where high resolution is essentially unchanged.

In other embodiments of the invention, the detection means is also aligned with the diaphragm hole and comprises a position sensitive detector. For example, when the excitation is obtained from an x-ray tube, the use of the position-sensitive Nero detector is necessary when it is not possible to scan the surface of the specimen with a narrow focused beam. In this case, the X-rays are incident on the entire area of the source segment. Position detection detectors with microchannel plates provide information about the position of the desired quantity (element) at a given point on the test object for image reliability and are useful when performing microscanning analysis of the surface under test. It has the characteristic of increasing speed.

In both embodiments of the spherical mirror analyzer of the energy of a charged particle beam, the windows on the surface of the inner electrode are arranged in a meridional plane that converges on the axis of symmetry passing through the center of the spherical segment of the source and image. Consists of slots. Such a window foil essentially prevents the diffraction effect of the charged particle beam in the meridional plane on the entrance to (or exit from) the retardation field, which greatly improves the angular focusing of the beam and reduces the spherical mirror energy. This has the advantage of increasing the resolution of the analyzer.

〔Example〕

A spherical mirror analyzer for the energy of charged particle beams (FIG. 1) consists of two spherical concentric electrodes, an inner electrode 1 having a radius R1 and provided with a window 2 positioned so as to pass through the particles. and a corresponding source (
an outer electrode 3 receiving a deceleration voltage from a source (not shown), a charged particle beam 4, a detection means 5 comprising a diaphragm 5' and a detector 6, and an excitation radiation generator 7 (
(electronic gun or X-green or ion unit). A charged particle beam source 4 representing a spherical segment with its center at point A is arranged on the surface of the inner sphere of the electrode 1 or on its geometrical extension, as shown in FIG. A diaphragm 5' representing a segment hole of the inner spherical electrode 1 with a center B is arranged centrosymmetrically with respect to the source 4. A charged particle detector 6 is installed behind the diaphragm 5'.

This spherical mirror energy analyzer has a source 4 installed at location B of the inner spherical electrode 1 of the analyzer, and a detection diaphragm 5' placed diametrically opposite the source 4 on a geometrical extension of the spherical surface of the inner electrode 1. A reverse circuit placed on the side may also be used. In the latter case, the detector 6 is also placed beyond the inner spherical electrode 1. With such a circuit configuration, the parameters of the energy analyzer remain essentially unchanged. In general, the holes in 'tA4 and the sensing diaphragm 5' are randomly shaped spherical segments, in particular round or square spherical segments or narrow strips.

In operation, this energy analyzer uses two properties of a spherical mirror with ideal focusing: energy equidispersity of the beam path and image certainty. For purposes of illustration, consider the passage of a charged particle beam characterizing an electron-optical relationship through an electrostatic spherical mirror with ideal angular focusing. FIG. 2 shows the path of a charged particle beam upon internal reflection from an electrostatic bulb mirror. Assume that the point source and image are located on the axis of symmetry at points A, B. Referring to the drawings, the coordinates X1, X2, α and α indicate the position of the entry and exit points on the surface of the inner spherical electrode 1 and the path gradient in the inner spherical electrode 1 with respect to the axis of symmetry. According to the law of conservation of energy and momentum,
The following formula is obtained.

Xl-α=α, -X2・・・・・・・・・・・・・・・
・・・・・・・・・＋21 In the above formula, ω−3” (2
S-1) sin2(X, -α) where S is the reflection periphery of the electrostatic bulb mirror, q and E are the charge and kinetic energy of the particle, and ■ is the reflected potential between the electrodes 1.3 of the mirror. .

Referring again to FIG. 2, the distance from the source and the image to the center of the sphere are respectively.

The linear value is expressed as a fraction of the radius of the inner spherical electrode 1. For ideal angular focusing, S=1. From formula (3), the following formula (
7) is obtained.

X=2 (X+-α)・・・・・・・・・・・・・・・
(7) When formula (7) is replaced with formula (2), α-α1 and 1. =1□=1 is obtained. For S=1, both paths of the chaotic path across the spherical region are tilted at the same angle α to the axis of symmetry, and aA and image B are symmetric about the spherical center. Consider the energy dispersion of a spherical mirror for conditions characterized by ideal angular focusing. In this case, the energy dispersion characterizes the image movement in the energy analyzer as the beam energy changes. Therefore, the following formula is obtained.

In this case, the dispersion along the axis of symmetry is the differentiation of equation (6) with respect to energy. That is, from equation (9), in the case of 1 x 1, the dispersion largely depends on the path gradient α. However, as ■ increases, the function D(α) essentially becomes a step function. For l-1, the D(α) curve has steps twice the height. Therefore, if the source 4 and its image are present at the surface of the inner spherical electrode, the ideal angular focusing (
5 = 1), the energy dispersion of the spherical mirror is maximum (equal to twice the radius of the inner spherical electrode 1) and the angle at which particles escape from the source 4 (known as the homodispersity of the path of the spherical mirror) characteristics). For ideal angular focusing, the incremental factor is constant. Therefore, the image of 'tA4, which represents the randomly shaped spherical segments arranged on the surface of the inner spherical electrode l or its geometric extension, is centrally symmetrical in a one-to-one size on the diametrically opposite part of the electrode 1. imaged (certainty of image).

FIG. 3 shows the image reliability characteristics of a spherical mirror according to the invention. Referring to the figure, a concentration of a spatial beam of charged particles occurs whose energy corresponds to the matching energy for the ideal angular focusing of a spherical mirror. As a result, images of points aa, b, and C are formed at centrally symmetrical points a' and b'C', and these images have no aberration. In this case, ab=a'b
' and bc=d'c'.

The spherical mirror analyzer of the energy of a charged particle beam, which is the object of the present invention, operates as follows. A delay potential ■ is applied between electrodes 1 and 3. The source 4, excited by the primary beam from the generator 7, emits charged particles at different angles α to the axis of symmetry, and these particles are guided through the window 2 into the electrostatic spherical field. If condition (1) is satisfied, all the charged particles emitted from the source 4 are reflected by the electrostatic field and enter the segment hole of the diaphragm 5', regardless of the gradient α,
There, it is detected by the detector 6. FIG. 1 shows only one of the charged particle beams emitted by the surface of source 4. FIG. This beam is reflected from the mirror and ideally focused on the central symmetry point of the window of the detection means 5.

For a given value of the delay potential V, particles with a kinetic energy E corresponding to equation (1) are focused into the hole in the detection diaphragm 5'. 2R for all routes regardless of slope α.

Due to the linear energy dispersion, particles with other energy values are not focused on the holes in the diaphragm 5', but are dispersed, and a small amount of them enters the holes in the diaphragm 5'. By varying the delay potential V, the total kinetic energy spectrum in the analyzed charged particle beam can be recorded in each part.

The operation of the present energy analyzer will be explained by way of example with reference to the circuit shown in FIG. The detector 6 has an inner spherical electrode 1 on the outer surface.
A microchannel plate representing a spherical segment fitted into a hole in a diaphragm 5' so as to be aligned with the surface of the diaphragm 5'. The illustrated embodiment uses properties such as beam path codispersity and image certainty in mirrors that are characterized by ideal focusing.

The operation of the energy analyzer is essentially as follows.

1. Scanning mode. As shown in FIG. 4, an excitation microprobe representing a thin beam of electrons, ions or photons from a generator 7 scans the entire segment surface of the source 4 line by line. The secondary electrons reach a spherical mirror which is adjusted for ideal focusing of electrons with a set kinetic energy that corresponds, for example, to the Auger transition of the atoms of the chemical element to be sought.

Due to the image certainty properties characterizing this spherical mirror, a focused beam of secondary electrons with a set vibrational energy scans the surface of the microchannel plate 6 synchronously with the movement of the microprobe over the surface of the segment 4. . The centrosymmetric image reproduces the scanning area of the source 4. At each point in time, recording is carried out only locally on the microchannel plate 6, ie on the part where the secondary electron beam is focused at the time of assertion.

The signal output from the microchannel plate 6 is amplified and used to adjust the intensity of the electron beam with a video signal processing structure that performs beam scanning in synchronization with the movement of the microprobe on the surface of the segment 4. . The image formed on the screen of this video signal processing structure shows the distribution of the secondary electron sources with a set energy over the scanning area of the segment.

2.Stationary mode. The generator 7 emits a wide beam of radiation (electrons, ions, photons) that excites secondary electrons. This beam is used to uniformly illuminate segment 4. Adjust the spherical mirror to ideal focusing of secondary electrons with a set kinetic energy (eg, the energy of an Auger transition, or the differential energy of an excitation quantum and an internal atomic level coupling energy).

The secondary electron beams escaping from different parts of the segment 4 are focused onto the surface of a position sensitive detector, thus forming a centrosymmetric image of the exposed area of the segment 4. The background signal and the true signal generated by unfocused secondary electrons with other energy values are input into the amplifier/collector device of the recording means to suppress the noise and the secondary electrons with a set energy in the exposed area of segment 4 Obtain location data characterizing the distribution of sources.

In both modes, the area to be exposed is not limited by the present energy analyzer due to the image certainty properties that characterize the spherical mirror. This region may constitute a considerable portion of the surface of the inner spherical electrode 1, which exceeds the scanning region of a known electronic spectrometer by about twice as wide. When the diameter of the inner spherical electrode 1 is sufficiently large compared to the size of the source 4, the source 4
The detector 6 has a disk shape, and the surface of the detector 6 may be flat. In this case, convergence and dispersion values are essentially unaffected.

FIG. 5 schematically shows another embodiment of a spherical mirror energy analyzer, in which the aperture window 2 of the inner spherical electrode 1 has a plurality of holes arranged in a meridional plane converging on the axis of symmetry. Consists of longitudinal slots.

This energy analyzer also comprises a system of circular conductors at a potential to protect the area of action of the field.

The illustrated energy analyzer operates in the same manner as described above.

The edge bounds of the separate slots are two-dimensional bounds that are independent of the angle of the poles. Thus, on the path through the aperture window 2, the beam path is not refracted in the meridian plane and the convergence of the widely divergent beam is not distorted. These slots should be narrow enough so that disturbances at the surface of the inner spherical electrode 1 are minimal.

The gap between the slots should be small so that the transparency of the hole window is not compromised.

〔Effect of the invention〕

The present invention can be used in the production of a novel electron spectrometer for investigating the surfaces of solid objects using optical, X-ray and Auger electron spectroscopy techniques, in particular Rusk spectroscopy.

[Brief explanation of the drawing]

1 is a schematic diagram of a spherical mirror analyzer for the energy of a charged particle beam according to the invention; FIG. 2 is a diagram showing the path of a charged particle beam upon internal reflection from an electrostatic spherical mirror according to the invention; FIG. 3 FIG. 4 is a diagram showing the characteristics of the image certainty in a spherical mirror according to the invention; FIG. 4 is a diagram of an embodiment of a spherical mirror analyzer for the energy of a charged particle beam according to the invention; FIG. FIG. 3 is a schematic diagram of another embodiment of an analyzer. 1...Inner electrode, 2...Window, 3...Outer electrode, 4
...Charged particle beam source, 5...Detection means, 5'...
-Diaphragm, 6...Detector, 7...Exciting radiation generator, R3...Radius of the inner electrode 1, R2...Radius of the outer electrode 3. F million, 3 FIG, 4

Claims (1)

[Claims] 1. Comprising a charged particle beam source (4) and two concentric spherical electrodes (1, 3) connected to a decelerating voltage source, the inner electrode (1) directing the beam of charged particles. In a spherical mirror analyzer of the energy of a charged particle beam having a window adapted to pass therethrough and comprising detection means (5), the charged particle beam source (4) and the detection means (5) Charging characterized in that it is shaped as segments of a sphere arranged centrosymmetrically with respect to the center of the spherical electrode, and that at least one of these segments is arranged on the surface of the inner spherical electrode (1). Spherical mirror analyzer of particle beam energy. 2. A claim characterized in that the detection means (5) are formed with a detection diaphragm (5') representing a segment hole of the inner spherical electrode (1) and a detector (6) consisting of a microchannel plate. A spherical mirror analyzer for the energy of a charged particle beam according to item 1. 3. A spherical mirror analyzer of the energy of a charged particle beam according to claim 1, characterized in that the detection means (5) are essentially position-sensitive detectors. 4. according to claim 1, 2 or 3, characterized in that the window (2) on the surface of the inner electrode (1) consists of a plurality of longitudinal slots arranged in a meridional plane converging on the axis of symmetry. Spherical mirror analyzer of the energy of charged particle beams.