JPS626303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic spectrometer, for example for surface analysis of samples.

Conventionally, there have been two main types of electronic spectrometers used in surface analysis instrumentation. Thus, the first type of hemispherical analyzer (HSA) is primarily used in X-ray photoelectron spectroscopy (XPS), where the main radiation, i.e., X-rays, is distributed over a relatively large sample area, usually teeth
It is necessary to provide a device that is used to collide and release electrons from 0.1-1 cm ² , collects the released electrons from this relatively large area, and supplies the collected electrons to an analyzer. It was hot. For this purpose, an electron lens is used at a position between the sample under test and the analyzer in a mode that collimates the electrons emitted from the entire irradiation area and focuses them at the entrance of the analyzer. system was used.

The second type, the cylindrical Schiller analyzer (CMA), is conventionally used in Auger electron spectroscopy (AES), in particular in which the irradiation source, i.e. the electrons, is focused into a small area on the order of 1 μm ² or smaller sample. used in the field of application. In this application field, the geometry of the electron gun used as the primary radiation source allows the electrons emitted from a small radiation area to be collected over a large solid angle, typically 0.5 steradians, so that in its operating mode Maximum sensitivity allowed.

Although the HSA could not be used for high spatial resolution, it had the disadvantage of low sensitivity, since the input lens to the HSA is essentially a collimator, as mentioned above, and the small angle ,
For example, it was only useful for collecting electrons over half-angles smaller than 5°.

It is not impossible to use CMA for XPS applications in a similar manner, but its geometry also allows for the high acquisition efficiency of the system required for high spatial resolution AES in that mode. This is because it was impossible to obtain the maximum resolution while maintaining the maximum resolution.

In previous practice, electron spectrometers include a hemispherical analyzer and a sample positioned at the sample position such that electrons are emitted from it, as described for example in GB 1332207. an electron optical lens system having a plurality of components configured to receive electrons emitted from the sample and transmit the received electrons to an analyzer; and an analyzer to detect the analyzed electrons. and a drive device for applying an electrical potential to each of said components, such that electrons emitted from limited selected areas of the sample are focused by a lens system. An electronic spectrometer was used.

With the increasing demand for surface analysis instrumentation of samples sequentially by both XPS and high-resolution AES on the same instrument, there is a growing need for systems that can operate with maximum sensitivity in both modes. This requirement is fulfilled according to the invention by an electro-optical lens system having a mesh component at least two poles apart at the entrance to the lens system, which mesh component is located at the sample location. The drive device decelerates and refracts electrons passing between the mesh components in a first mode of operation, allowing collection of electrons from the selected area. applying a first set of potentials to the element such that the lens component receives electrons from an illuminated area many times larger than the selected area in a second mode of operation; The electro-optical lens system is constructed such that the electro-optic lens system further includes a device for switching the potential on the lens component to switch the spectrometer between different modes of operation without mechanical deformation of the lens component.

The electron lens system comprises an electron deflection device, and the drive device is satisfied in that the drive device is arranged to apply an electric potential to the deflection device so as to position the selected area at any desired position in the sample.

Particularly in the first mode, the electrons are collected over a large half-angle cone angle, e.g. 25-30°, e.g. magnification) is obtained.

Further, the electron lens system can include an electron deflection device, and the drive device is operative to apply an electric potential to the deflection device to position the selected area at any desired position in the sample within said relatively large area. It is possible.

More specifically, the drive device applies a potential, e.g. an oscillating potential, to a scanning lens for moving the selected area across the sample in a scanning motion to scan said relatively large area. ) equipment.

Furthermore, the detector can be provided with an averaging device that allows measurements of the average yield of energy from a selected energy or a relatively large examined area of the sample.

Thus, by operating switches that vary the potentials of different components of the lens, relatively large areas, typically
The collection efficiency of collecting electrons over 0.1−1 square cm is optimized to be:
Virtually aberration-free collection of electrons over a small area of 1 mm2 or less over a large half-angle cone angle, typically 25-30°, is optimized for AES. and/or collection efficiency i.e. AES or
Such that in XPS mode a small area is scanned across the sample to determine the average yield of electrons over the sample area under test.

This allows a single device to have two
XPS and high resolution with maximum efficiency, although previously only possible by using two analytical systems.
It becomes possible to test samples using AES. Furthermore, the scanned area can be kept constant no matter how much electron energy passes through the analyzer.

Additional requirements of the system enable scanning techniques combined with one mode of operation of the entrance lens system to collect electrons from small areas on the order of less than 1 square mm in XPS.

Next, the present invention will be explained using illustrated embodiments.

The electron lens structure (assembly) shown in FIG. 1 includes a first or aberration compensation lens group CL and a second or zoom lens group ZL arranged in this order along an electron path. The first lens has components 1a and 1b, which together constitute a partially transparent conductive mesh, whose shape is preferably concave towards the sample and which, for example, have a partially spherical surface; The center of the curved surface is located between the center of the sample 4 and the component 1a.

The lens assembly is enclosed within a vacuum chamber (not shown), and component 1a of the lens assembly
is, for example, held at the same potential as that of the sample and the vacuum chamber. This potential is hereinafter referred to as ground potential. Component 1b, which is placed at the same or different potential than component 1a, is electrically and mechanically connected to component 1c. The first lens group CL further includes component 1.
d and 1e.

All these components 1c, 1d, 1e have a suitable cylindrical shape that is axially symmetrical about a common central axis, which is also the component 1a.
It also includes the center of the curved surface 1b.

The first lens group CL is further provided with an electron deflection device, in particular a plate assembly P, which is an electromagnetic or electrostatic lens. The deflection plate assembly advantageously includes two pairs of opposing plates P1P1', P2, P2' as shown in FIG. These are collectively referred to as a deflection device P.

Between the first and second lenses an aperture plate 3a is provided in the cylinder 3a, which aperture plate limits the spread of the beam. This opening may be axisymmetric or non-axisymmetric.

The second lens ZL has components 2a, 2b and 2c, all of which are axially symmetrical about a common axis of components 1c, 1d and 1e, all of which generally have different potentials. Component 1e can be constructed integrally with components 1e and 1a, this integral component forming a part common to the components of the first and second lenses.

The component 2c is, for example, a peripheral plate 5 located at the entrance of an electronic energy analyzer, which will be described later.
has a potential equal to An aperture plate 2d is provided at the end of the component 2c.

The first or aberration compensation lens group CL has three operating modes. In the first operating mode, the potentials applied to the lens components 1a-1e are as follows. That is, a magnified image of electrons emitted from a small selected area of the sample in FIG. 1, e.g. C or D in FIG. , is determined by the potential applied to the deflection device P. For example, when no potential is applied to the deflection device, the selected area is coaxial with each lens component (at position C in FIG. 1) and the emitted electrons follow the trajectory shown by the dashed line in FIG. When a suitable non-zero potential is applied to the deflection device, the selected area assumes a non-coaxial position as shown at D in Figure 1, and the emitted electrons follow a trajectory as shown by the solid line in Figure 1. Follow. In this mode of operation, the lens components 1a, 1b serve to decelerate and refract the electrons towards the axis. Further components 1c, 1d, 1e serve to focus the beam at or near the plane of plate 3a, and deflection devices serve to direct the focused beam axially through an aperture in plate 3a. The linear magnification of the image of plate 3a is usually between 3 and 20, preferably between 5 and 20, which is referred to herein as high magnification.

When a sample is properly irradiated, electrons are emitted in a wide range of directions. Only the electrons that enter the lens group CL within a limited cone angle are
Focused. The remainder hits the lens component and is absorbed.

Two pairs of opposing plates P1P in Figure 1
2 of a deflection device such as 1', P2P2' (Fig. 1).
The stage allows the electrons emitted from the off-axis area of the sample, as shown in D in FIG. must be taken at the plate 3a.
The first deflection stage changes the inclination angle of each trajectory bundle of electrons received from the off-axis area with respect to the lens axis. Meanwhile, the second deflection stage modifies the trajectory bundle to be coaxial with each lens component. The two deflection stages create a dog leg shaped path shown in solid line in FIG. By varying the strength of the deflection, the selected area D can be moved either towards or away from the axial area.

By providing additional deflection plates in a plane perpendicular to that shown in FIG. 1, selected areas can be moved in a direction perpendicular to the plane of FIG. The further provided deflection plates are plates P1 and P as shown in FIG.
1' and two plates P3P3' in the same row,
and two opposing plates P4, P4' on the same level as P2, P2'. According to a further embodiment of the invention shown in FIG. 3, another deflection plate can be provided intermediate P1, P1' and P2, P2' in one stage and beyond them in the other stage.

The shape, position and potential of the components of the lens group CL in the first operating mode are such that the lens group reduces spherical aberrations and other aberrations and allows the electrons emitted from the sample to It is such that it is received at a large half-angle cone angle and focused at a small size point at or near the opening in plate 3a. Aberrations caused by collecting electrons over a wide angle are at least partially overcome by the use of a partially transparent conductive mesh of suitable shape and the application of a suitable electrical potential thereto. The required shapes and potentials of those meshes and other components of the aberration-compensating lens in a given application can be determined as follows: This can be determined by performing computer calculations of the electron trajectories through the lens and selecting the shape and potential that give the final image with minimal aberrations.
Alternatively, the desired shape and potential of the mesh and other lens components can be determined by making experimental measurements of final image aberrations for different shapes and potentials.

All lenses consisting only of cylindrically symmetrical components that do not pass through the axis usually have large aberrations that cannot be reduced to zero, whereas meshes have the potential to reduce some of the aberrations to zero. be.
Additionally, the use of concave meshes with a deceleration field between them allows for wide ranges (e.g. ±30
The electrons emitted over
It is focused into a nearly parallel beam that is more easily processed by subsequent lenses.

While maintaining the conditions for aberration compensation, the lens group CL
By changing the potential of each component of plate 3
The driving energy of the electrons reaching the aperture at a can be varied. The focusing effect of the lens is maintained by applying an electric potential to component 1d that corresponds to the change in kinetic energy. The possible range of values for the ratio of the kinetic energy of the focused electrons in the aperture in the plate 3a to the kinetic energy of the same electrons that are being emitted from the sample is usually 1/50 to 1/50.
It is 1/2.

The location of the selected area (such as D in FIG. 1) from which electrons are received in the first mode of operation is the plate P1, P in FIG.
1', P2, P2'. When the entire area of the sample is thus continuously irradiated, this first mode of operation:
The emitted electrons are received from a limited area with adjustable positioning over a large half-angle cone angle, so that each limited portion of the sample can be examined in turn. On the other hand, if a certain localized area of the sample is irradiated, then the first mode of operation may cause the deflection device to suitably move in synchronism with the irradiation device, provided that the irradiation area is probably scanned in a raster motion. The area from which electrons are received with high efficiency is driven to coincide or nearly coincide with the area being irradiated, increasing the yield of electrons received.

In the second mode of operation of the aberration compensation lens CL, the potential applied to the lens component is
The same as in the mode, but with the oscillatory potential as
A selected area, such as D in FIG. 1, feeds the deflection device so that a predetermined area larger than D but smaller than the continuously illuminated area of the sample is scanned. The number of electrons emitted during one complete scan time of a given area, received by the analyzer, and then received by the detection system is averaged over the scan time to detect electrons of a selected energy or energies. The yield obtained corresponds to the average electron emission capacity of the sample over a given area for electrons of said energy. By varying the amplitude and average value of the oscillating potential applied to the deflection device, the positions of the boundaries of a given area and its center, as well as the positions of the boundaries and centers, can be determined with respect to the initial energies of the emitted, received and detected electrons. may be provided to be unrelated.
The waveform of the oscillating potential, for example a sine wave or a sawtooth wave,
It is suitably selected such that the detection yield of electrons corresponds to a uniform, or if necessary non-uniform, average value of the electron emission capacity over a given area.

In this second mode of operation, the shape and amplitude of the oscillating potential applied to the deflection device may be selected to provide a detector electron yield commensurate with the average electron emission power over the illuminated area fraction of the sample. .

In the third operating mode of the aberration compensation lens CL, different potential sets are applied to the lens components 1a to 1e.
and a zero potential is applied to the deflection device,
An image of electrons emitted from the entire irradiated area of the sample (including areas C and D in FIG. 11) is focused at or near the opening in plate 3a. In this mode, components 1a~
1d are typically placed at substantially the same potential, and components 1d, 1e serve to slow down the electrons and focus the electron beam at or near the aperture. The ratio of the kinetic energy of the focused electrons to the kinetic energy of the same electrons being emitted from the sample is typically 1/30 to 1/10. In this mode of operation, the linear magnification (magnification) of the image in the plate 3a is approximately uniform or smaller, typically 3/2 to 1/2, over which the emitted electrons cover the irradiated area of the sample. The half-angle of the cone received from each part of the cone typically ranges from 10° to 1°. The lens thus acts as a collimator.

The potentials for the lens components and the deflection devices are generated by a drive circuit which does not form part of the invention, but has a switching device which is capable of varying the potentials applied to different lens components. The first lens group CL can be switched between its different operating modes by appropriate operation of the switching device of the drive circuit without the need for mechanical deformation of the lens components.

a second or zoom lens ZL receives the electronic image at or near the aperture in plate 3a;
A focused image is formed at or near the aperture in plate 5, which forms the entrance to the electronic energy analyzer. Component 2a is component 1e of lens group CL and plate 3
The potential is the same as that in a. component 2d
typically has a potential equal or approximately equal to that of plate 5. The reduction ratio, ie the ratio of the kinetic energy of the received electrons in plate 3a to the kinetic energy of the same electrons in plate 5, is typically between 5 and 1/5. The focusing action of the lens is maintained over its range by applying an electric potential to component 2b that corresponds to the reduction ratio.

The combined system of lens groups CL and ZL normally operates in one of two modes. One of these two modes is called FAS (Fixed Analyzer Transmission). In this mode, when emitted from the sump, the emitted electrons to be investigated, which have an initial kinetic energy Ei, are focused by the lens assembly at the plate 5, as described above, and are passed through the analyzer. A certain predetermined kinetic energy Ea is introduced. Therefore, the potential applied to the lens component produces a focusing effect as already described, and at the same time Ei
such that it gives the required kinetic energy change from to Ea. If a range of possible energies Ei of the emitted electrons is to be scanned, the potentials supplied to the lens components are synchronously and suitably adjusted to maintain the focusing situation and bring the electron kinetic energy at the plate 5 to the value Ea. must be maintained.

The second mode of the combination of lenses CL and ZL is FRR
Mode (Fixed Retarding Mode)
Ratio)). In this mode, the emitted electron to be investigated with initial kinetic energy Ei is
As already mentioned, it is focused at plate 5, where it is brought to a kinetic energy Ea which is a constant predetermined fraction 1/R of Ei. The potential applied to the lens component and the analyzer element produces a focusing effect as described above, and at the same time provides the required ratio of E and Ea, causing electrons of energy Ea to pass through the analyzer. When attempting to scan the range of possible energy Ei of emitted electrons, the potentials applied to the lens component and analyzer element must be synchronously adjusted to maintain the focusing condition, ratio R, and analyzer passage condition. It won't happen.

Lens group in FAT or FRR mode without installing lens ZL between lens group CL and analyzer
It is also possible to run CL. However, in that case, the range of energies Ea that the received and focused electrons have at the entrance of the analyzer is reduced, and therefore the range of electron energy resolution that the analyzer can operate with is reduced.

The spectrometer shown schematically in FIG. 4 includes a lens assembly 1, an electronic energy hemispherical analyzer 6 with an outer plate 5 at its entrance, an electronic detector 7 located at the exit of the analyzer, an amplifier 8 and a display device. 9. The display device 9 is preferably a cathode ray tube connected to a detector via an amplifier, so that the CRT display is intensity modulated or deflection modulated by the output signal from the detector. or display device 9
is an X-Y recorder, whose Y input measurement is connected to the detector via an amplifier, and the X input measurement is scanned in synchronization with the drive device to scan the energy Ei of the emitted electrons received and detected. . The detector 7 has or is connected to a device for measuring the average number of electrons received during one or more scans of the sample. The illustrated analyzer is an electrostatic hemispherical deflection analyzer, but it may be of other electrostatic or electromagnetic types.

A drive 10 is connected to the lens for applying an appropriate potential, and a skin generator 11 applies an appropriate time-varying waveform to the plate to scan the selected area D on the sample as required. is connected to deflection plate assembly D. The scan generator 11 can be controlled by a drive circuit 10 such that the deflection device can be made variable in synchronism with the drive to scan the energy Ei of the emitted electrons received and detected. Alternatively, the scan generator is the deflection plates 9a and 9b of the cathode ray device 9.
may be connected to scan the display as desired in synchronization with the scan of the lens deflection plate.

When carrying out an analysis using a spectrometer with a hemispherical analyzer or a cylindrical cylindrical energy analyzer (CMA), as in the spectrometers described above, a large area is examined by scanning a beam that is finely focused on the sample. It has been found that, in some cases, the outer part of the area to be scanned is often not focused and scanned by analyzers that are conventionally powered by a magnifying lens. Both types of spectrometers can only scan an area of a few 100 μm without going out of focus or without significant loss of intensity. This is because the Auger electron emission area of the sample, which is the area where the illumination beam impinges, is not completely on the lens axis. However, as mentioned above, the use of a lens deflection system returns the electron trajectory from such an off-axis radiation area onto the lens axis and synchronizes the lens and illumination beam with respect to the sample. A high yield of electrons is obtained as a focused beam at the entrance of the analyzer.

Although this example refers to a hemispherical analyzer, the hemispherical concept is
It does not have to be 180 degrees, but may be a part of a complete sphere that is not 180 degrees, for example, 120 degrees to 180 degrees.

[Brief explanation of the drawing]

1 is a schematic cross-sectional view showing the wide acceptance angle electron lens assembly forming the spectrometer portion of the present invention, with the axial beam path of the electrons shown in dashed lines and the deflected electron beam shown in solid lines; FIG. a cross-sectional schematic diagram on an enlarged scale showing a portion of the lens assembly of the lens assembly together with the arrangement of the deflection plates;
FIG. 3 is a schematic cross-sectional view showing another embodiment of the deflection plate in a lens assembly corresponding to that of FIG. 2; FIG. FIG. CL...First or aberration compensation lens group, ZL...Second or zoom lens group, 1a to 1e...Lens components, 4...Sample.

Claims (1)

[Claims] 1. A hemispherical analyzer;
Electron optics having a device for irradiating a sample placed at a sample position so that electrons are emitted therefrom, and a plurality of components for receiving electrons emitted from the sample and transmitting the received electrons to an analyzer. a lens system, a detector connected to the analyzer to detect the analyzed electrons, and a drive device for applying an electrical potential to each of said components, in which case a limited selected area of the sample is In an electron spectrometer, the electron optical lens system comprises at least two mutually spaced mesh components at the entrance to the lens system. , the mesh components are configured to be concave toward the sample position, and the drive device decelerates and refracts electrons passing between the mesh components in a first mode of operation. applying a first set of potentials to said element to enable collection of electrons from a selected area and receiving electrons from an illuminated area many times larger than the selected area in a second mode of operation; the electro-optical lens system is configured to apply a second set of potentials to the lens component, and the electro-optical lens system is further configured to switch the potential to the lens component to switch the spectrometer between different modes of operation without mechanical deformation of the lens component. An electronic spectrometer characterized by having: 2. The electron lens system has an electron deflection device, and the drive device is configured to apply an electric potential to the deflection device so as to position the selected area at any desired position in the sample. The electronic spectrometer according to item 1. 3. An electronic spectrometer according to claim 2, wherein the drive device comprises a scanning device that applies a time-varying potential to the deflection device to move selected areas across the sample during a scanning operation. 4. configured to focus electrons of a selected energy or energy band in an analyzer and to be operative to change the selected energy or energy band of the focused electrons by changing the potential at the lens component. An electronic spectrometer according to claim 3. 5. The lens scanning device is configured and operative to supply an oscillating potential to the deflection device to enable continuous scanning of the sample and to accept electrons from an area larger than said selected area. In this case, an area larger than said selected area can be kept substantially constant as the initial energy of the electrons received by the analyzer upon emission from the sample is varied. An electronic spectrometer according to scope 3. 6. Claim 3, wherein the device for irradiating the sample irradiates only a selected area of the sample or a limited area including the selected area, and scans the sample in synchronization with a scanning device. Electronic spectrometer as described in section. 7. An electronic spectrometer according to claim 6, wherein the irradiation device irradiates the entire area of the sample scanned by the lens at any time. 8. A display system is connected to the detector such that the display is modulated in intensity or polarization by the output of the detector, and further provided with a device for scanning the display in synchronization with a lens scanning device. An electronic spectrometer according to range 6. 9. Claim 5 in which the amplitude of the scanning device is variable in order to move outward or inward the boundary of the area of the sample to be scanned in a selected area to change the size of the scanned area. Electronic spectrometer described. 10. Claim 5, further comprising a device for averaging the signal from the detector over the entire area scanned during one or more scanning cycles.
Electronic spectrometer as described in section. 11. An electronic spectrometer according to claim 1, wherein the second set of potentials is such that the lens acts as a collimator and at the same time accepts electrons from said larger area. 12 A hemispherical analyzer, a device that irradiates the sample placed at the sample position so that electrons are emitted from the analyzer, and a device that receives the electrons emitted from the sample and sends the received electrons to the analyzer. an electron optical lens system having a plurality of components, a detector connected to an analyzer to detect the analyzed electrons, and a drive device for applying an electric potential to each of said components; In an electron spectrometer in which electrons emitted from a limited, selected area of the sample are focused by a lens system, the electron optical lens system:
at least two spaced apart mesh components at the entrance to the lens system, the mesh components being concave towards the sample location, and the lens components having at least The drive device has an electron deflection member in two deflection stages, the drive device having a lens scanning device, and in a first mode of operation, decelerating and refracting electrons passing between the mesh components in the selected area. of electrons from
A potential is applied to said component to enable acquisition over a wide angle and a highly linear magnification or multiplication, and in a second mode of operation the scanning device scans an area of the sample many times larger than the selected area. the lens system is configured to move the selected area in a continuous and repeated motion over a period of time, and the lens system further includes a device for averaging the signal at the detector for each scan. An electronic spectrometer characterized by: 13 Hemispherical analyzer and
Electron optics having a device for irradiating a sample placed at a sample position so that electrons are emitted therefrom, and a plurality of components for receiving electrons emitted from the sample and transmitting the received electrons to an analyzer. a lens system, a detector connected to the analyzer to detect the analyzed electrons, and a drive device for applying an electrical potential to each of said components, in which case a limited selected area of the sample is In an electron spectrometer in which electrons emitted from a , the mesh component is configured concavely toward the sample position, and further the electro-optical lens system has at least two stages of electron deflection devices in the lens system, and the drive device includes a first stage of electron deflection devices. In one mode of operation, a potential is applied that slows down and refracts the electrons passing between the mesh components, allowing collection of electrons from the selected area over a wide angle and with high linearity. , applying the same potential to said element and applying the same potential to the lens components except for the deflection device in a second mode of operation, but applying an oscillatory potential to the deflection device to accept electrons from an area larger than said selected area. and in a third mode the initial energy of the electrons received by the analyzer emitted from the sample in an area larger than the selected area can be varied and held substantially constant; The spectrometer is configured to apply different potential sets to the lens component to accept electrons from an entire illumination area many times larger, and to switch the spectrometer between different modes without mechanical modification of the lens component. An electronic spectrometer characterized by being provided with a switching device that switches the potential to a lens component.