JP2002501285A - Charged particle energy analyzer - Google Patents

Abstract

(57) Abstract The electron energy analyzer has an electron column 10 for exciting a sample 11 on a sample holder 12. Excitation of sample 11 causes electrons to be emitted, some of which enter the analyzer through aperture 13. Here, the electrons are exposed to a substantially hyperbolic field defined with respect to the x and y axes. Each axis is substantially located at a constant potential is approximated by a small number of electrodes E ₁ to E _6. The electrons are deflected by the substantially hyperbolic field and strike the detector 14. The detector 14 is positioned substantially along the x-axis and includes, for example, a microchannel plate and a phosphor screen, around which electrons are focused. Electrodes E _{1 to} E ₅ are located in a plane inclined with respect to the overall axis of the analyzer (ie, the x-axis parallel to detector 14), and electrode E ₆ is similarly inclined. But in the opposite direction. A key feature of electron energy analyzers is their ability to detect together electrons with a large range of energies.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a charged particle energy analyzer. Although charged particle spectrometers with multi-channel capability are commercially available, the energy range that these charged particle spectrometers can detect is typically about 1% of the effective Auger spectrum (eg, 50 eV to 2050 eV). Not just.

A preferred embodiment of the present invention aims to provide an electron energy analyzer or spectrometer whose main feature is the ability to detect a wide range of energies in parallel. The main purpose sought from this detection is for the energy analysis of the electrons scattered from the sample.

[0002] Electrons can be generated by photons, electrons, or other ionizing radiation. Scattered electrons include secondary electrons, backscattered electrons, Auger electrons, lost electrons, and photoelectrons having an energy of about 10 eV to 3000 eV. In terms of collection efficiency (solid angle acceptance) compared to existing spectrometers, the preferred embodiment of the present invention can collect a very effective Auger spectrum in a single process, thus
It can operate about 100 times faster than existing spectrometers.

According to one embodiment of the present invention, a charged particle energy analyzer comprises: a) field means for creating a substantially hyperbolic field defined with respect to an x-axis and a y-axis, wherein each of the axes is substantially Field means being at a substantially constant potential; b) entry means for introducing charged particles into the field; c) being arranged substantially along the x-axis so as to deflect electrons deflected by the field. And detecting means for detecting.

[0004] Preferably, the field is at least partially electrostatic. The field may be at least partially magnetic. Preferably, the entry means is arranged to accommodate charged particles in the field in a region along the x-axis. Preferably, said charged particles are electrons.

[0005] Preferably, the field is defined by the following equation: ^{_{That, V = V 1 a -n r}} n sin (nθ) (0 ≦ θ ≦ π / n) V = 0 (π / n <θ <2π) where, _{V 1} is, x, to the origin of the y-axis Is the potential of the equipotential line at a distance a from the origin, and n = 2 ± k, where k is in the range of 0 to 0.4.

Preferably, k = 0.1, 0.2, 0.3 or 0.4. The above charged particle energy analyzer may include means for effecting the emission of the charged particles.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention and to show how embodiments of the present invention may be implemented, reference is now made to the accompanying drawings. FIG. 1 shows a two-dimensional hyperbolic electrostatic field defined with respect to the x and y axes, each axis being at a substantially constant potential (typically zero potential). Such fields are used in a preferred embodiment of the present invention to disperse electrons corresponding to their energy, examples of which are given below.

The potential distribution that determines the field is given by the following equation (in the form of a cylindrical pole): V = V ₁ a ⁻ⁿ r ⁿ sin (nθ) (0 ≦ θ ≦ π / n) V = 0 (π / n <θ <2π) In the case of a hyperbolic field, n = 2 and V ₁ are the potentials of the equipotential line, and the point of the potential closest to the origin of the axis is the distance from the origin. is there.

The equation for calculating the trajectory of electrons in such a field is well known, and in fact, a complete quadrupole electrostatic field or the like is long in various applications involving the transfer and dispersion of charged particles. Has been used. Examples include "strong" electrostatic lenses, beam deflectors, single channel energy analyzers, and the like.

However, certain characteristics of the field of FIG. 1 (in FIG. 1, only one quarter of a full quadrupole electrostatic field, as used in previous applications for tubes). (Not shown) are central to the preferred embodiment of the present invention, and these features have not heretofore been recognized or exploited. These features relate to focusing an electron beam having an angular divergence or width in a manner independent of or close to the energy of the electrons.

As explained below, an important feature of the preferred embodiment of the present invention is the angle at which electrons are emitted into the hyperbolic field. 2 to 4 show the principle for explaining this.

As shown in FIG. 2, electrons emanating from the origin of the axis at an angle α = 24.78 ° with respect to the x-axis, or substantially at a deceleration field having an initial flight trajectory at this angle, Focusing is performed on the x-axis at the distance L. The length L is proportional to the square root of the electron energy.

As shown in FIG. 3, the parallel electron beam entering the deceleration field at the origin of the axis with an initial flight trajectory having an angle α = 21.51 ° with respect to the x-axis, or substantially at this origin, Focusing on the x-axis at a distance L from. The length L is again proportional to the square root of the electron energy.

As shown in FIG. 4, the field emanates from a point outside the field at a right angle distance d from the x-axis, and has a field near the origin of the axis at an angle α = 21.51 ° to α = 24.78 °. Will be focused on a point near the x-axis.
The focus positions of the different energy electrons depend on α, Δα, x ₀ , d and the energy extremes E _max , E _min of the electrons.

In all three cases of FIGS. 2-4, the focus depends only slightly on the motion component in the z-direction. The third arrangement described with reference to FIG. 4 provides the basis for a practical analyzer. This is because the arrangement takes into account the point source at a finite distance from the entrance to the analyzer. The first two cases in FIGS. 2 and 3 are actually the extreme values (d = 0 and d = ∞) of the third arrangement in FIG.

One example of an electron energy analyzer using such a hyperbolic electrostatic field is shown in FIG.
Shown in A hyperbolic electrostatic field is created by applying an appropriate voltage to the electrodes E ₀ -E ₁₀ arranged orthogonally to the xy plane. The electrodes continue for a distance in the z-direction until the central field is no longer deflected. x, (from _{E 0} to _{E 10)} y potential gradient should be noted that it is linear, that.

This is just one of many ways to create a field. Entrance aperture is centered at x ₀ (in the x-z plane) is placed on the x axis. Because it is on the equipotential surface and in the region of the weakest electric field, the entrance aperture does not distort the field. This means that the energy resolution resulting from the hyperbolic field geometry can be achieved. The size and shape of the entrance aperture will determine the solid angle acceptance of the analyzer. The distance x ₀ from the origin is significantly smaller than the average dispersion length (ie, the distance between the entrance aperture and the center of the detector area).

As shown in FIG. 6, electron detectors are also arranged along the x-axis in the xz plane. The detector can analyze the electrons landing at various locations in front of it upon arrival. This detector consists of a microchannel plate (to amplify the signal) followed by a fluorescent screen.

The light pattern on the screen can be measured using a photodiode array or CCD connected directly to the screen, or connected to the screen via a fiber optic bundle, or a conventional optical lens Can also be measured. FIG. 6 is a schematic plan view of the detector and the entrance aperture, showing the energy dependence of the site where electrons are detected.

Some parameters for typical configurations suitable for detecting Auger excited electrons are shown in Table 1 below, and some examples of electron trajectories are also shown in FIG. Table 1 ┏━━━━━━━━┯━━━━━━━┓ ┃ α │ 24.55 ° ┃ ┠────────┼───────┨ ┃ Δα │ 1 ° ┃ ┠────────┼───────┨ ┃ β│ 10 ° ┃ ┠────────┼───────┨ ┃ d│ 8mm ┃ ────────┼───────┨ ┃ x ₀ │ 1.2 mm ┃ ┠────────┼───────┨ ┃ E _min │ 50 eV ┃ ┠ _{────────┼───────┨ ┃ E max │2050eV ┃ ┠────────┼───────┨ ┃} V max │2400V ┃ ┗━━ ━━━━━━┷━━━━━━━┛

For this arrangement, the value of α is chosen to create a focal position as close as possible to the detector plane in order to maximize the energy resolution of the analyzer. The solid angle acceptance in this case is about 0.05% of full 2π steradian emanating from the surface of the sample.
It is. Both Δα and β can be increased to collect more signal, but, as with any analyzer, this will work to achieve energy resolution.

FIG. 8 shows the energy dispersion (energy vs. position) in a hyperbolic field analyzer having the arrangement as shown in FIG. 4 and the parameters according to Table 1.

FIG. 9 shows the theoretical energy resolution (energy vs. energy resolution) in a hyperbolic field analyzer having an arrangement as shown in FIG. 4 and a parameter tp according to Table 1. This resolution is suitable for detecting and quantifying the chemical composition of the sample surface.

FIG. 10 shows that a prototype analyzer having an electron column 10 excites a sample 11 on a suitable sample holder 12. Excitation of the sample 11 causes electrons to be emitted, causing some electrons to enter the analyzer through the aperture 13 where the electrons are reduced to a small number of substantially hyperbolic numbers close to the electrodes E ₁ -E _6. Exposed to the field. In the manner described above,
The electrons are deflected by a substantially hyperbolic field, in which the electrons are focused, for example a detector 1 consisting of a microchannel plate and a phosphor screen.
Collision on 4

As can be seen in FIG. 10, the electrodes E ₁ -E ₅ are arranged in a plane inclined with respect to the total axis of the analyzer (ie, the axis parallel to the detector 14). Yes,
The electrode E ₆ is also inclined similarly, the direction is the opposite direction.

FIG. 11 shows a silver Auger spectrum obtained using the prototype analyzer of FIG. In this example, the acquisition time was 2 seconds and the primary electron beam was 10 nA, 5000 eV. Although only a small portion of the spectrum is shown in FIG. 11, the entire Auger spectrum from 50 eV to 2050 eV is collected in two seconds in parallel. Using the same principle, it is possible to make the collection time even faster.

[0027] Modifications to the above embodiment of the present invention are possible. By slightly distorting the field or having n slightly different from 2 (n in the above equation), the field will not be a true hyperbola, but the analyzer will work very well. Can be made. Therefore,
The value n can be replaced by n ± k, where k is, for example, k = 0, 0.1, 0.2, 0.3 or 0.4.

Although the analyzers shown here are two-dimensional and provide a linear detection zone, these analyzers may have 2π around their own axis or around a line passing through a point source. Can be rotated to obtain a rotatable symmetric version, in which case the spectrum can be collected on a disk, on a cylinder, or on another form of collector or detector. A magnetic field may be used or added instead of the electrostatic field.

In another embodiment of the present invention, other charged particles (eg, ions, positrons) and electrons that have significantly higher or lower energies than in Auger spectroscopy are accepted or deflected. , Can be detected.

It should be understood that in the above embodiment, the x, y, and z axes can each have a unique orientation in space, and are not necessarily as shown.

As used herein, the term “detector” means both a single detector and a detector set or detector array.

As used herein, the verb “include” has the usual meaning in a dictionary and refers to inclusion that is not entirely exclusive. That is, the use of the word "comprising" (or words derived therefrom) to include one or more features does not exclude the possibility of including further features. That's what it means.

Attention should be paid here to all papers / documents submitted concurrently with or before this specification in connection with the present application, and to all papers / papers disclosed in this specification. . The contents of all these papers and documents are incorporated herein by reference. .

All features disclosed in this specification (including the claims, the abstract, and the drawings) and / or all steps of the methods or processes disclosed therein may be combined in any combination. Combinations can be made, provided that combinations that are mutually exclusive among at least these features and steps are excluded.

Each feature disclosed in this specification (including the claims, the abstract, and the drawings) is, unless explicitly stated otherwise, equivalent, equivalent, or similar feature serving alternatives. Can be replaced. Thus, unless expressly stated otherwise, each feature disclosed herein is only an example of a series of equivalent and similar features.

The present invention is not limited to the detailed description of the embodiments described above. The present invention is directed to the novel features disclosed herein, including the appended claims, abstract, and drawings, or novel combinations of these features, or the method or process steps disclosed therein. Or new combinations thereof.

[Brief description of the drawings]

FIG. 1 shows a hyperbolic electrostatic field.

FIG. 2 illustrates focusing of electrons originating from the origin such that primary focusing occurs at α = 24.78 °.

FIG. 3 shows focusing of a parallel electron beam such that primary focusing occurs at α = 21.51 °.

FIG. 4 shows the focusing of electrons emanating from a point outside the field such that primary focusing occurs at 21.51 ° ≦ α ≦ 24.78 °.

FIG. 5 shows one example of a substantially hyperbolic field in the analyzer by an elevation view showing an xy perspective.

FIG. 6 is a plan view of a detector and an entrance aperture.

FIG. 7 shows the essential elements of one example of a substantially hyperbolic field analyzer, and shows some examples of electron trajectories.

FIG. 8 shows energy dispersion (energy distribution) in one example of a hyperbolic field analyzer.
-Versus-position).

FIG. 9 shows the energy resolution (energy-to-energy resolution) in one example of a hyperbolic field analyzer.

FIG. 10 is a prototype analyzer showing an electron column and a sample, where the hyperbolic field is approximated with a small number of electrodes.

FIG. 11 shows a silver Auger spectrum obtained using the prototype analyzer of FIG.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE , KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW 15 (72) Inventor El Gomaty, Mohammed, Mocharle, UK Wyo 13 P.Y. Yoke, Osboldwick, W. Wiedel Road 23 (72) Inventor, Jacka, Marcus, UK 01 01 Dee D. Yoke Heslington Department of Physics F term (reference) 5C038 KK06 KK13

Claims (9)

[Claims] 1. A charged particle energy analyzer comprising: a) field means for creating a substantially hyperbolic field defined with respect to an x-axis and a y-axis, wherein each of the axes has a substantially constant potential. B) entry means for introducing charged particles into the field; c) detection means disposed substantially along the x-axis and detecting electrons deflected by the field. And a charged particle energy analyzer comprising: 2. The charged particle energy analyzer according to claim 1, wherein
A charged particle energy analyzer wherein the field is at least partially electrostatic. 3. A charged particle energy analyzer according to claim 1, wherein said field is at least partially magnetic. 4. A charged particle energy analyzer according to claim 1, wherein said entry means is arranged to place charged particles in said field in a region along said x-axis. A charged particle energy analyzer, comprising: 5. A charged particle energy analyzer according to claim 1, wherein said charged particles are electrons. 6. A charged particle energy analyzer according to claim 1, wherein said field is represented by the following equation: V = V ₁ a ⁻ⁿ r ⁿ sin (nθ) (0 ≦ θ ≦ π / n) V = 0 (π / n <θ <2π), where V ₁ is the potential of an equipotential line whose closest point to the origin of the x, y axis is a distance a from the origin. A charged particle energy analyzer, wherein n = 2 ± k, and k is in the range of 0 to 0.4. 7. The charged particle energy analyzer according to claim 6, wherein
A charged particle energy analyzer, wherein k = 0.1, 0.2, 0.3 or 0.4. 8. A charged particle energy analyzer according to claim 1, further comprising means for causing the emission of said charged particles. 9. A charged particle energy analyzer as described and described below with substantial reference to FIG. 1 of the accompanying drawings and any of FIGS. [0001]