JPS58158850A - Divergence magnetic field type charged particle microscope - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to charged particle microscopy (in which case the term is sometimes used to include spectroscopic microscopy).

Charged particles can be electrons or positive or negative ions, but for ease of description the invention will be described in relation to electrons.

In the case of electron microscopy, it is known that surface images can be obtained, for example, by irradiating a sample with ultraviolet light, which emits photoelectrons that can produce a magnified image of the sample surface. There are at least two effective methods for this; one method is to accelerate and focus the photoelectrons with an electron lens in the same manner as in conventional transmission electron microscopy. This is G.

Mollenstedt and F. Lenz, “Advances in Electronics.”
and Electronphysics)”, Part 1
8, pp. 251-329, 1963.

Another method does not use a focusing device, but uses a diverging magnetic field. The sample is placed within a strong magnetic field and irradiated with, for example, ultraviolet light or soft X-rays. Photoelectrons are emitted and each photoelectron travels in a spiral around the lines of magnetic flux. Therefore,
If the divergence of the magnetic flux lines means the divergence of the electron trajectories, the electrons can be bombarded with the screen, causing the emission of light beams and thus resulting in a magnified image of the sample surface. This is G, Beamson, H,Q.

Porter (Port, er) and D+W, Turner (T
urner) co-author, 6 Journal Op Physics (,r,phys,)”, E:8cientific
Instruments, Volume 13, Page 64~
p. 66, 1980 (below Beamson et al., 198
) and “Nature”
, Vol. 290, pp. 556-561, 1981.
(below referred to as Beamson et al., 1981), to which further reference is made.

In the case of this second type of microscope, the electron conserves relatively all its energy when it reaches the screen part,
The energy can therefore be analyzed by some suitable equipment in the range of low magnetic fields, so that the energy spectrum of the electrons can be measured or the images represent only part of the energy spectrum. Can be displayed on screen.

The energy spectrum thus obtained consists of a series of peaks that may or may not overlap depending on the incident radiation used. This spectrum carries information that can be inferred about the composition, properties and chemical structure inside the sample, as well as the composition, properties and chemical structure of the sample surface and of all atoms or molecules attached to or present on the sample surface. A sample is converted into a photon or an ion or a neutral particle (
atoms and molecules) or by irradiation with electrons.
Electrons emitted from a sample have an energy range depending on the nature of the radiation and the nature of the sample.

In some patent applications, for example, in the case of irradiation with photons of energy -5 to 40 electron volts, the emitted electrons have an energy in the range of 0 to about 5 electron volts or 4 electron volts, respectively.
It has an energy of up to o electron volts. Such emitted electrons are photoelectrons generated by ultraviolet irradiation. If the energy of the irradiating photon is greater than about 100 electron volts, the electron is an x-ray photoelectron. Ultraviolet (
Both photoelectrons excited by UV) and photoelectrons excited by X@If (UV) can carry chemical and other information.

Therefore, a diverging magnetic field type photoelectron microscope, when equipped with an electron energy analyzer, can enlarge the sample surface and indicate local changes in the chemical environment.

In the case of the type of divergent magnetic field electron microscope described above, virtually all the electrons emitted from the sample, regardless of the angle at which they are emitted, can pass through the 11 divergent magnetic field and be received by the analyzer. . This can produce relatively light images, but the spatial resolution of the images needs to be improved.

According to the invention, a divergent magnetic field generator, a device for positioning the sample and a device for irradiating the sample and causing charged particles to be released from the sample along the divergent flux lines of the magnetic field generator,
A device placed in a diverging magnetic flux line for receiving charged particles traveling along the magnetic flux line and forming an image from the charged particles, as well as a device disposed in a diverging magnetic flux line for receiving charged particles traveling along the magnetic flux line and for forming an image from the charged particles, and for reducing the magnetic flux at a value lower than a predetermined value for the purpose of improving the sharpness of the image. A diverging magnetic field charged particle microscope is obtained which consists of a device for selecting particles emitted from the sample with an energetic component along the line and removing them from the magnetic flux line upstream of the detection device.

The present invention provides a divergent magnetic field generator, a device for positioning a sample and a device for irradiating the sample and causing charged particles to be emitted from the sample along the divergent magnetic flux lines of the magnetic field generator and a predetermined value. There is also a method of operating a divergent magnetic field type charged particle microscope consisting of a device for selecting and removing from the magnetic flux line particles emitted from a sample that have an energy component along the magnetic flux line with a low value, this method , consisting in applying an electrical potential to the device for selecting and removing the particles such that the sharpness of the image of the sample is improved by removing the selected particles.

Further, the present invention includes a method of operating a charged particle microscope that generates a diverging magnetic flux line, irradiates a sample, and releases charged particles from the sample into the magnetic flux line, the method comprising: Selected particles that have an energy component along the magnetic flux line at a value lower than the value are removed by applying an electrostatic potential to the sample such that removing this selected particle improves the sharpness of the image of the sample. It's more than that.

The invention and the theory on which it is based will now be described in detail with reference to the accompanying drawings.

Figure 1 shows that photoelectrons emitted from sample S are
We will explain in detail how to generate this.

It is observed that a typical electron travels from a strong magnetic field B(1) to a weak magnetic field B(2), and the magnetic flux lines become parallel again so that they are constant again. In the tuft of the true solenoid, the magnetic flux lines still diverged. However, if the magnetic field is shaped by suitable means, then it can be substantially constant, which is advantageous for all energy analysis devices.

Figure 2 details what happens to photoelectrons emitted from a given point on the sample. When electrons are emitted from the sample, those that did not initially travel along the magnetic flux lines travel in cyclotron orbits around the magnetic flux lines, and the axial component of this motion (i.e., along the magnetic flux lines) is , depends on the angle between the emission line and the magnetic flux line. Furthermore, the point on the sample where the electron appeared has a circle or diameter of uncertainty of 4Rmax.
within the "circle of confusion", where 2RmaX is the maximum diameter of the electron trajectory in the plane of the sample. This is because the electrons emitted from the sample travel at a distance of 21 from the emission point depending on the emission angle.
This is because the magnetic flux can be distributed on the magnetic flux line up to Rmax.

Next, regarding each electron, it is well known that the orbital moment of the electron is conserved as well as its total energy. As electrons travel from a region of strong magnetic field to a region of weak magnetic field, they are subjected to a force that uses energy transverse to the magnetic flux lines to increase their axial or longitudinal velocity. Therefore, following Beamson et al. (1980, 1981)
See ).

B(2) ”'=Etotal cyc B(1)
(1) E = final energy amount of the forward motion Etotal = total electron energy amount "'cyc" energy amount at the start of cyclotron motion B (2) /B (1) = magnetic field ratio (Fig. 1) Therefore, high The ratio of magnetic field to low magnetic field is high (e.g. B
(1)/B (2))100 ), the electrons eventually travel almost parallel to the magnetic flux lines. Orbital moment is conserved only if the variation of the magnetic field in the axial direction is adiabatic, i.e. the magnetic field experienced by the electron changes very little during one cycle of the helix as the electron progresses along the helix. I have to admit that I don't. If the adiabatic conditions are not satisfied, aberrations may occur.

With reference to Figure 1, the cyclotron radius is: where B = magnetic field strength, "'total'" the total energy of the electron, R = radius of the electron orbit (or cyclotron radius), m = mass of electron, e - amount of charge of electron, θ - emission angle of photoelectron with respect to magnetic field direction.

Therefore, if the photoelectrons have the same total energy, the larger the emission angle, the larger the cyclotron radius. Maximum cyclotron radius, Rmax
, occurs when the emission angle is 90°. The larger the value of Rmax, the smaller the spatial resolution becomes. Beamson et al. (1980, 1981) considered this problem and predicted the approximate final resolution or minimum "circle of confusion" d.

Due to this derivative, all electrons emitted over a solid angle of 180° in the direction of travel are expected to be collected. If one chooses to collect all the electrons traveling down the magnetic flux line from a given point on the sample, this collection is done by collecting a constant number of electrons emerging from a circle of uncertainty or a circle of confusion with a diameter of 4R. Also includes. If we assume that the angle of appearance of the electrons extends over the range 0 to 90°, there is a significantly sharper distribution of intensities across the resolved points (see Figure 2), which is contributes to the resulting intensity distribution.

In order to improve the resolution of the instrument, it is necessary to reduce the diameter of the tail of the intensity distribution curve, ie 4 RfflaX. This is done by removing electrons with large emission angles, ie electrons with a high transverse velocity component for a given amount of energy. The intensity distribution curve shown in FIG. 2 is recognized. It turns out that by decreasing the diameter of the tail of this intensity distribution curve, the diameter d of the circle of confusion pushes up the "cusp" part of the distribution curve, thus improving the resolution of the instrument. This can be done by an electrostatic deceleration device that only passes electrons that have a relatively large longitudinal (i.e. axial) velocity component relative to the predetermined total amount of energy e2 of electrons. The effect of such a potential blocking layer is shown in FIG. Electrons with an insufficient amount of longitudinal kinetic energy to overcome this potential blocking layer in the RM are returned and possibly returned to the sample. The number of electrons returned is 1. It is the one with the largest lateral energy and therefore the largest cyclotron radius, so its separation improves the spatial resolution of the image. Electrons returning to the sample have the added benefit of reducing charge formation on non-conducting samples.

The speed reduction device schematically shown in FIG. 3 is an electrostatic speed reduction screen RM.
However, other devices can be used, such as those that electrostatically bias the sample.

Deceleration, which limits the emission angle (for a given amount of total photoelectron energy) accepted by the instrument, results in an increase in resolution, but also a decrease in the number of photoelectrons collected.

However, this is not too critical since in normal mode the microscope actually collects a solid angle of 2π5 teraa in the direction of travel (in the case of gases a solid angle of 4π5 teraa can be collected with a suitable current collector). This is significantly higher than in conventional instruments, so that acceptable imaging magnifications can be obtained despite the fact that some electrons are repelled.

With reference to FIG. 3, electrons of a certain energy appearing at an angle θ, are repelled by the electrostatic moderation grating, and electrons appearing at an angle θ2 with a certain energy pass through the screen RM. Substituting θ, -90' and θ2=100 gives 1
, the solid angles collected in the direction of travel are 2π5te, respectively.
rad and o, 1π5 terad, which represents collection of about 63 times the total photoelectron flux assuming isotropic emission of photoelectrons.

A decrease of 0 is the orbital radius times sin θ, or 0.1
Also associated with a reduction to 7×Rmax. This does not necessarily mean that the minimum stereoscopic resolution is improved by a factor of 6. This is because a weight factor must be introduced into the corresponding equation. Nevertheless, the final resolution is improved.

An implementation of a photoelectron microscope with a spectroscopic analysis device of the type outlined above is shown in FIG.

FIG. 4 schematically shows a photoelectron microscope in which the sample S is mounted on a support Sc and placed in a high-field solenoid HFS of the superconducting type;
At that time, this solenoid P is connected to the liquid helium cooling device Li.
It has He. The irradiation device IM is provided to irradiate the sample. The solenoid HFS has a high magnetic field adjacent to the sample, and the electrostatic retarder RM is equipped, in the vicinity of the sample in the form of a grid, and held at a suitable electrostatic potential to remove unwanted electrons. Ru. An accelerator A in the form of a grid held at an electrostatic potential is present beyond the retarder RM, this electrostatic potential in this case allowing the photoelectrons to recover their previous energy and thus downstream of the accelerator A in the low-field region. Let the energy be analyzed accurately within the body.

After expansion of the magnetic field, the electrons enter this low field range LMF, which is essentially a constant magnetic field range. An electron energy analyzer EE is equipped within this range.

In this case, an electrostatic moderation grating device is shown although other energy analysis devices can be used provided that it preserves imaging properties. It is also recognized that the electrostatically retarded magnetic field type of analyzer produces an integrated energy spectrum. Other analysis devices include the Trochoir monochromator described by Beamson et al. (1980).

As pointed out in FIG. 5, yet another suitable analysis device EE
consists of a pair of opposing Wien type filters arranged one behind the other along the axis of the measuring instrument, and a member A having an opening at the center between them. It has an additional magnetic field transverse to the instrument axis, and an electric field transverse to the axis of the instrument but perpendicular to the additional magnetic field. The directions of the magnetic and electric fields in the second filter W2 of the pair of filters are opposite to the directions of the respective magnetic and electric fields in the first filter W.

As illustrated by the embodiment of FIG. 5, the magnetic fields MF1 and MF2 of the filters W1 and W2, respectively, are oriented in the vertical direction, unlike the electric fields EF1 and EE2.
are directions coming from and entering the plane of FIG. 5, respectively. The magnitude of the transverse magnetic field is the desired amount of energy E.

electrons pass through the two filters without changing direction, and the length of the filters in the vertical direction and the spacing between the filters are such that #1 has the same amount of energy (Eo + ΔE
and E. -ΔE) are returned to their initial direction after passing through a pair of filters in such a way that spatial imaging is maintained. greater than or less than the desired passband of energy (i.e., Eo+
greater than ΔE or E. An electron with an energy content of less than -28) undergoes a fairly sufficient lateral deflection to impact it and be removed by the apertured plate. Therefore, only electrons in the desired passband of energy 2ΔE form an image when passing through the two Wlen filters.

After the electrons have left the analysis device EE, they are further converted into a form in which images can advantageously be recorded. The apparatus of FIG. 4 for doing this is a pair of electron multiplier channel plates (EMPs) followed by a phosphor. The resulting light image can then be photographed or studied by a TV camera C.

[Brief explanation of the drawing]

The accompanying drawings illustrate a diverging magnetic field type charged particle microscope according to the present invention, and FIG. Figure 2 is a diagram showing the intensity distribution of electrons emitted from a source at one point on the sample; Figure 6 is a diagram showing the intensity distribution of electrons emitted from a source at one point on the sample; Figure 4 is a schematic diagram showing the path of electrons.
A schematic diagram showing the path of electrons through opposed Wien type filters, and FIG. 5 is a diagram showing another suitable analysis device for the case of FIG. HFS...Divergent magnetic field generator, S...Sample, S'C
...sample support device, IM...irradiation device, RM...
・Device for selecting and removing charged particles, A... Accelerator, EE... Particle energy analysis device

Claims (1)

[Claims] 1. A diverging magnetic field generator (HFS), a device (SC) for arranging the sample (S), and a device for irradiating the sample and releasing it from the sample along the divergent magnetic flux line of the magnetic field generator. In a divergent magnetic field charged particle microscope consisting of a device (IM) for moving charged particles, and a device placed on the divergent magnetic flux line to detect the charged particles traveling along the divergent magnetic flux line to form an image, With the aim of improving the sharpness of the image, a device (RM ) A diverging magnetic field type charged particle microscope. 2. The charged particle microscope according to claim 1, wherein the device for selecting and removing particles is followed by a device (A) for accelerating particles not removed in the magnetic flux line. 3. The charged particle microscope according to claim 1 or 2, wherein the charged particle microscope is disposed in a path of particles not removed by the particle energy analyzer (EE). 4. Charged particle microscope according to claim 3, wherein the device for selecting and removing particles is located in the particle path between the sample and the detection device. 5. Charge according to any one of claims 1 to 6, wherein the device for selecting and removing particles comprises a device for raising the particles selected for return to the sample. particle microscope. 6. Charge according to any one of claims 1 to 4, wherein the device for selecting and removing particles comprises a charged particle deceleration device located adjacent to a magnetic field generator. particle microscope. 5. Charged particle microscope according to claim 4, wherein the Z deceleration device is a screen IJ (RM) arranged in the path of the ejected particles and arranged to be electrostatically chargeable. 81. Charged particle microscope according to claim 4, comprising a device for electrostatically biasing the sample relative to its surroundings to suppress selected particles. 9 a divergent magnetic field generator (HFS), a device (SC) for positioning the sample (s) and a device (SC) for irradiating the sample and causing charged particles to be emitted from the sample along the divergent magnetic flux line of the magnetic field generator ( IM), as well as a device placed in a divergent magnetic flux line that detects charged particles traveling along the divergent magnetic flux line to form an image, during a band of reduced magnetic field strength. Charged particles entering along a magnetic flux line are received into a spectrometer analyzer consisting of a pair of opposing Wien-type filters placed one behind the other along the magnetic flux line, each filter having a a transverse additional magnetic field and an electric field transverse to the passageway and perpendicular to the magnetic field of the filter, where the direction of the additional magnetic field and electric field of one filter is different from that of the other filter, respectively. A diverging magnetic field charged particle microscope characterized in that the directions of the additional magnetic and electric fields are opposite. 10. The charged particle microscope according to claim 9, wherein the filter has the effect of passing electrons of a selected energy through the pair of filters without changing direction. 11. The axial length of the filters and the spacing between the filters are such that particles of substantially the same energy can emerge from a pair of filters along the same direction as the particles enter the filters. , a charged particle microscope according to claim 8 or 9. 12. The filter is operable to cause particles with energies outside the selected energy band W-band to be deflected from the path of particles in the selected energy band;
A charged particle microscope according to claim 8, 9, or 10.