JPH0581875B2 - - Google Patents

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 by using an electron spectrometer in which the energy analyzer serves as the analytical element. It is generally necessary to increase the

The rapid development of manufacturing methods for solid-state microelectronic technology requires rapid and accurate quality control of wafer and integrated circuit surface structures at different manufacturing stages. One of the techniques used is diffractive X-ray photoelectron spectroscopy, which is based on the use of standing waves. In such a method, the single color X used
The line strength, and hence the density of the ejected photoelectrons, is so small that it requires the fabrication of new wide-hole energy analyzers to reduce the analysis time from tens of hours to a few minutes.

[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, exits from there and penetrates the inner spherical electrode.

Electrostatic spherical mirror circuit in which the point source and image are seen at diametrically opposite locations on the inner spherical electrode (HZ Sar-El, Analyzer, Nucl. Instrument. Meth., 1966, Vol. 42, pp. 71-76) A mower on a spherical capacitor (see "Mower on a spherical capacitor") is known. Such a circuit configuration is a rare example of an electro-optical system characterized by precise spatial focusing of a charged particle beam.
The above published paper shows the following:
That is, the energy of the particle and the delay voltage V of the electrostatic bulb mirror are qV/E=2(1-R ₁ /R ₂ )...(1) (In the above formula, q is the charge of the particle and R ₁ , R ₂ are the radii of the inner and outer spherical electrodes), the point source is reflected at diametrically opposite locations without spherical aberration.

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.

Also, a disk plate analyzer (Rev.Sci.Instrum., 1988,
59, 4th edition, p. 545, ``A Novel Display Type Analyzer for the Energy and Angular Dispersion of Charged Particles'' by Hirochi Daimon) 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-El.

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 degrade the resolution of the analyzer.

In addition, a Keplatron-type analyzer for the energy of charged particle beams is known (Nucl.Instrum.
Meth., 1960, vol. 6, p. 157 R.H. Richie,
The analyzer is essentially an electrostatic mirror formed by a field set up between two concentric spherical electrodes (see ``Spherical Capacitors as High-Transmission Particle Spectrometers'' by JS Sieca and RD Berknov). be. 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 an electrostatic bulb field and focused onto a slit in a detection diaphragm to form an image of the circuit. This image is dependent on the energy of the particles due to the dispersion that characterizes known energy analyzers. Furthermore, this Keplaton type analyzer has a very large acceptance angle.

However, the above analyzer is not suitable for the following factors:
(1) inadequate focusing which considerably limits its resolution (which is done only as a first approximation to the initial divergence angle of the beam); and (2) the use of a circular slit diaphragm placed in the mirror field as a detection means. This has generally been unsatisfactory due to the disadvantages of distorting the working field and impairing the detection of charged particles.

An undesirable feature of all these known devices is that the analysis speed is slow due to the small micro-scanning area on the surface of the source, which means that the hole is placed in front of the detector which allows the charged particles to escape only from a defined area of the test object. This is due to the use of a detection diaphragm. Enlarging the diaphragm hole 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 decelerated electron source, the inner electrode defining a window adapted to pass the beam of charged particles. In a spherical mirror analyzer of the energy of a charged particle beam, the charged particle beam source and the detection means are shaped as segments of a sphere arranged centrosymmetrically about the center of the spherical electrode. and at least one of these segments
This is achieved by means of a spherical mirror analyzer, characterized in that the spherical mirror is located on the surface of an inner spherical electrode.

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 significantly 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 segment hole of the inner spherical electrode;
a detector located behind the hole and forming a microchannel plate. This analyzer is
Generally, the energy of charged particles emanating from the surface of a test object, which is a spherical segment placed in the geometric extension of the inner sphere, is analyzed, with all paths being equidispersive and the source image being It has no aberrations. Therefore, if the high resolving power remains essentially unchanged, the working area of the source and the solid angle surrounding the charged particle beam under test can be increased several times. In the primary beam scanning mode, where the high resolving power is essentially unchanged, if the detection diaphragm arranged centrosymmetrically with respect to the source represents a segment hole in the inner sphere and receives a microchannel plate whose surface is aligned with the inner sphere,
A larger area of the test object is microscanned.

In other embodiments of the invention, the detection means is also aligned with the diaphragm hole and comprises a position sensitive detector. For example, if the excitation is obtained from an X-ray tube,
The use of such position sensitive detectors 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. A position-sensitive detector with a microchannel plate provides information about the position of the desired quantity (element) at a given point on the test object for image reliability and speed when performing a microscanning analysis of the surface under test. It has the characteristic of increasing

In both embodiments of the spherical mirror analyzer of the energy of a charged particle beam, the window on the surface of the inner electrode has multiple longitudinal directions arranged in a meridional plane that focuses on the axis of symmetry passing through the center of the spherical segment of the source and image. Consists of slots. Such a window system 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 a charged particle beam (FIG. 1) comprises two spherical concentric electrodes, namely a window 2 having a radius R ₁ and positioned so as to avoid passing through the particles. inner electrode 1 with radius
an outer electrode 3 having a voltage R ₂ and receiving a deceleration voltage from a corresponding source (not shown), a charged particle beam 4, a detection means 5 consisting of a tire flam 5' and a detector 6; radiation generator 7 (electron gun, X-ray 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, detector 6
is also arranged beyond the inner spherical electrode 1. With such a circuit configuration, the parameters of the energy analyzer remain essentially unchanged. Generally, the holes in the source 4 and detection diaphragm 5' are randomly shaped spherical segments, particularly 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 X ₁ , X ₂ , α and α ₁ 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 operating quantity, the following formula can be obtained.

X ₁ −α＝α ₁ −X ₂ ...(2) sinX/2=sin ² (X ₁ −α)/2√ω ...(3) In the above formula, ω=S ² −(2S−1) sin ² (X ₁ − α) = qV/2E
・1/1-R ₁ /R ₂ ...(4) However, S is the reflection parameter of the electrostatic spherical mirror, q and E are the charge and kinetic energy of the particle, and V is the distance between the mirror's electrodes 1 and 3. It is a reflected potential.

Referring again to Figure 2, the distance from the source and the image to the center of the sphere are respectively 1 ₁ = sin (X ₁ - α)/sin α ... (5) 1 ₂ = sin (X ₁ - α) / sin α ₁ ...(6).

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

X = 2 (X ₁ - α) ... (7) When formula (7) is replaced by formula (2), α = α ₁ and 1 ₁ = 1 ₂ with reference to formulas (5) and (6) =1 is obtained. For S=1, both branches of the disordered path across the spherical region are tilted at the same angle α to the axis of symmetry, and source A 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 D characterizes the image movement in the energy analyzer as the beam energy changes. Therefore, the following formula is obtained.

Δ1=D(ΔE/E)...(8) In this case, the dispersion along the axis of symmetry is the differentiation of equation (6) with respect to energy. That is, D=21 ² cosα/√1−1 ² sin ² α (9) From equation (9), when 1<1, the dispersion largely depends on the path gradient angle α. However, as 1 increases, the function D(α) essentially becomes a step function. In the case of 1→1, the D(α) curve becomes twice the height. Therefore, if the source 4 and its image are present at the surface of the inner spherical electrode 1, then for ideal angular focusing (i.e. S=1), the energy dispersion of the spherical mirror is at a maximum and (radius of the inner spherical electrode 1 ), which is independent of the angle at which the particles escape from the source 4 (a property known as the homodispersity of the path of a spherical mirror). For ideal angular focusing, the increment factor is equal to one. Thus, a source 4 representing randomly shaped spherical segments arranged on the surface of the inner spherical electrode 1 or a geometric extension thereof
The image is centrally symmetrically projected on the diametrically opposite portion of the electrode 1 with a one-to-one size (image certainty).

FIG. 3 shows the image reliability characteristics of a spherical mirror according to the invention. Referring to the drawing,
A concentration of a spatial beam of charged particles occurs whose energy corresponds to the matching energy for the ideal angular focusing of the spherical mirror. As a result, the central symmetry points a′, b′,
Images of point sources a, b, and c are formed at c', and these images are free of aberrations. 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 delayed potential V is applied between electrodes 1 and 3. Generator 7
A source 4, excited by a primary beam from , 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. Figure 1 is source 4
shows only one of several charged particle beams emitted by the surface of the . 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 retardation potential V, particles with a kinetic energy E corresponding to equation (1) are focused into the hole in the detection diaphragm 5'. Due to the linear energy dispersion, which is 2R ₁ for all paths, regardless of the gradient α, particles with other energy values are not focused into the holes in the diaphragm 5', but are dispersed, and a small amount of them enter the diaphragm 5'.
enter the hole. 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 is a microchannel plate representing a spherical segment fitted into a hole in the diaphragm 5' so that its outer surface is aligned with the surface of the inner spherical electrode 1. 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.
An excitation microprobe representing a thin beam (electrons, ions or photons) from the source 4 scans the entire segment surface of the source 4 line by line. The secondary electrons reach a spherical mirror which is adjusted for ideal angular focusing of the electrons with a set kinetic energy that corresponds, for example, to a certain Augier transition of the atoms of the chemical element to be sought. Due to the characteristic of image-reliable movement that characterizes this spherical mirror, a focused beam of secondary electrons with a set kinetic energy moves over the surface of the microchannel plate 6 in synchronization with the movement of the microprobe over the surface of the segment 4. scan. The centrosymmetric image reproduces the scanning area of the source 4. At each point in time, recording is performed only locally on the microchannel plate 6, ie in the area where the secondary electron beam is focused at the time of determination. 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. The spherical mirror is tuned for ideal focusing of secondary electrons with a set kinetic energy (eg, the energy of a certain Augier transition, or the differential energy between the excitation quantum and the binding energy at the internal atomic level). 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 generated by unfocused secondary electrons with other energy values and the true signal are input into the amplifier/collector device of the recording means to suppress the background 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 relative to the size of the source 4, the source 4 may be disk-shaped 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 edges of the separate slots are two-dimensional planes 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 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 aperture window is not compromised.

〔Effect of the invention〕

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

[Brief explanation of drawings]

FIG. 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 charged particle beam path upon internal reflection from a static spherical mirror according to the invention; FIG. Figure 4 shows the characteristics of the image certainty in a spherical mirror according to the invention; Figure 4 is an illustration of an embodiment of the spherical mirror analyzer for the energy of a charged particle beam according to the invention; Figure 5
The figure is a schematic diagram of another embodiment of a spherical mirror energy analyzer according to the invention. 1...Inner electrode, 2...Window, 3...Outer electrode,
4...Charged particle beam source, 5...Detection means, 5'
... diaphragm, 6 ... detector, 7 ... excitation radiation generator, R ₁ ... radius of inner electrode 1, R ₂ ...
Radius of outer electrode 3.

Claims (1)

[Claims] 1. Comprising a charged particle beam source 4 and two concentric spherical electrodes 1, 3 connected to a deceleration voltage source, the inner electrode 1 passing the charged particle beam. In a spherical mirror analyzer of the energy of a charged particle beam, which has a window and is also equipped with a detection means 5, the charged particle beam source 4 and the detection means 5 are arranged centrosymmetrically with respect to the center of the spherical electrode. A spherical mirror analyzer of the energy of a charged particle beam, characterized in that it is shaped as spherical segments and that at least one of these segments is arranged on the surface of an inner spherical electrode 1. 2. The energy of the charged particle beam according to claim 1, characterized in that the detection means 5 is 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. spherical mirror analyzer. 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. Energy of a charged particle beam 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.