FR2634286A1 - ENERGY ANALYZER OF CHARGED PARTICLE BEAMS WITH REFLECTIVE SPHERES - Google Patents

Abstract

A spherical reflective type charged particle beam energy analyzer has a source of a charged particle beam, two concentric electrodes of spherical shape, connected to a stop voltage source, of which the inner electrode has windows for the passage of the charged particle beam, as well as a receiving device. According to the invention, the source 4 of the charged particle beam and the receiving device 5 have the shape of segments of a sphere, they are arranged symmetrically to each other with respect to the center of the spheres and at least one of them is arranged on the surface of the inner spherical electrode 1. The invention applies in particular to the creation of new electronic spectrometers intended for the analysis of solid bodies by methods of scanning spectrometry.

Description

The present invention relates to devices for analyzing energy

  beam of charged particles, and particularly relates to a charged particle energy analyzer of the spherical reflection type. The present invention can very effectively be used for the creation of new electron spectrometers for solid body surface analysis by methods such as ESCA or

  Auger spectroscopy and especially scanning spectroscopy.

  The invention can also find its application

  in other areas of energy analysis -

  charged particle beams, for example in the

  Ion mass spectrometry of the body surface

  by a method of ion energy analysis retro-

disseminated.

  At present, the development of physi-

  that the surface of solid bodies stimulates the perfection-

  methods for its study. In electron spectrometry

  tronic, problems arise in the foreground for increasing the sensitivity and accuracy of measurements of the energy and angular or directional distribution of secondary electrons, the increase of the microsonde area of the object to be studied,

  these goals being achieved by means of electron spectrometers

  whose analyzing element is an energy analyzer.

  ogy. The rapid development of the technology of the

  semiconductor microelectronics required the development of

  fast and accurate methods for quality control of the surface structures of pellets and semiconductor microcircuitry at different stages of manufacture. One of these methods is the

  ESCA spectroscopy based on the stationary wave

  X-rays. In this method, the intensity of the

  monochromatic X-rays and, consequently, the

  the site of the released photoelectrons, is very low, which has made it necessary to create a new energy analyzer of greater clarity, in order to reduce the analysis time from tens of hours to several minutes. An ordinary reflective electrostatic spherical energy analyzer is formed of two electrodes of

  spherical form between which a difference is

  potential. A charged particle beam enters and leaves the zone of the deflection field of the

  electrostatic mirror thus formed by crossing the elec-

inner spherical trode.

  We know a diagram of a spherical electrostatic mirror 'H.Z. Sar-El "More on the spherical condenser as an analyzer" -% ucl. Instrum. Meth 1966, Volume 42, pages 71-761, wherein a point source and its image are in the area of the inner spherical electrode at diametrically opposite points. This scheme

  represents in itself a very rare example of an opto-

  in which a focus is achieved

  very precise spatial pattern of a particle beam

  elderly. In the cited work, it is shown that if, between the kinetic energy E of the particles and the stopping potential V of the spherical electrostatic mirror, there is the relation: R qv 1

2), (1) -

E R

  R2 where q is the charge of the particles, R1 and R2 are the radii of the inner spherical electrodes and

  outside, we will have the image of the

  in a point diametrically opposed to the

  position of the latter without spherical aberration

America.

  The disadvantage of this scheme lies in the

  pendence of the linear dispersion of the inclination angle

  its trajectories of the charged particle beam to be analyzed. for an axial trajectory of the beam, the dispersion being zero. This makes the scheme considered inapplicable for the construction of energy analyzers

  possessing a high energy resolution.

  A display type analyzer is known

  (Hirochi Daimon, "New display-type analyzer for the ener-

  gy and the angular distribution of charged particles "-

  Rev. Sci. Instrum., 1988, Volume 59, No. 4, page 454) for measuring the energy and angular distribution in the case of photoelectrons emitted in a beam of 2-1 range. The work of the analyzer is based on the principle of a precise spatial focus for the

  spherical electrostatic mirror which has been proposed pre-

  previously in the Sar-El article.

  The disadvantage of this instrument lies in a

  very strong dependence on the dispersion of the angle of

  of the trajectories of the charged particles, this

  which limits very significantly its energy resolution.

  Similarly, to obtain satisfactory optoelectronic parameters of the analyzer, the windows of the inner sphere, through which the beam of charged particles to be analyzed, must meet very important requirements. Conventional windows are made of a thin metal grid and cause a defocus of a charged particle beam with high divergence because of the refraction and lens effects that appear in the cells of the grid,

  which in turn makes the analyzer's resolution worse.

  A charged particle beam energy analyzer of the "kepplertron" type is known (R. H. Ritchie, I. S. Cheka, R. D. Birkhoff "The Spherical Condenser as High Transmission Particle Spectrometer" - Nucl.

  1960, volume 6, page 157), which represents in itself a half

2U34286

  Electrostatic wave formed of a field applied between two concentric electrodes of spherical shape. Source

  of charged particles has a disk shape and is dis-

  placed on the surface of the inner spherical electrode.

  The charged particle beam coming out of the source!

  undergoes reflection on the spherical electrostatic field

  and is focused on the slot of a receiving diaphragm, forming an annular image whose position,

  because of the dispersion of the energy analyzer

  depends on the energy of the particles. The "Kepplertron"

has considerable clarity.

  The disadvantages of this instrument are as follows: firstly, unsatisfactory focusing properties 'the focusing is only carried out in first approximation, according to the angle of the initial divergence of the beam', which substantially limits the resolution; need to use, for detection, an annular slot diaphragm which is in the field of the mirror field, which causes the deformation of the field of work and makes difficult the

  detection of charged particles.

  All the devices mentioned have a disadvantage

  common cause which results in a low speed of

  analysis because of a scanning surface (micro-

  probing) which is due to the presence of a reception diaphragm which is placed upstream of the detector, this diaphragm having an opening allowing only the particles leaving a limited region of the sample to be studied to pass through. . The increase in the opening of the diaphragm causes the application of the bottom and the empire

the resolution of the instrument.

  The object of the invention is to create a charged particle beam energy analyzer of the spherical type at I

  reflection, which would make it possible to focus

  precise beam distance with constant dispersion

  and high clarity, as well as an effective scanning surface

flood of the sample to be studied.

  The problem solved is solved by the fact that, in a reflective spherical type charged particle beam energy analyzer I, comprising a charged particle beam source, two concentric spherical electrodes connected to a source of

  stopping voltage, the inner electrode having

  to let the particle beam through

  as well as a reception device, according to the inven-

  tion. the source of charged particle beams and the receiving device have a segmental shape

  spheres, which are arranged symmetrically

  port in the center of the spherical electrodes and at least one

  segments is located on the surface of the spherical electrode

interior.

  The proposed invention makes it possible to

  perfect spatial separation of the particle beam

  loaded under conditions of independence of the

  the angle of inclination of the trajectories in the beam (the isodispersion of the trajectories). In addition, the image of the source in the form of an arbitrarily shaped segment in any area of the energy spectrum is not distorted by

  aberrations and is transferred on a scale equal to the

  at a diametrically opposite point of the spherical electrode.

  interior or its geometric continuation (authentically

ticity of the image).

  Thus, the energy analyzer according to the invention makes it possible to substantially increase the resolution in the

  conditions for increased clarity of the analyzer and

  presence of aberration of the image of large portions

area of the source.

  In one of the versions of execution of the structure according to the invention, the receiving device is formed of a receiving diaphragm, which has the shape of a segment orifice in the inner spherical electrode, and a detector which is placed downstream of this orifice and which represents a microchannel plate. The proposed energy analseur performs an energy analysis of the beam of

  charged particles coming out of the surface of a sample

  ion having, in the general case, a shape of sphere segment and which is on the geometric continuation

  of the inner spherical surface under conditions of

  dispersion of all trajectories and absence of deformation by aberration of the image of the source. This allows, without decreasing the high energy resolution, to increase many times the size of the charged particle beam and the useful surface of the source. Of

  more. if the receiving diaphragm is symmetrically

  at the source in relation to the center of the spheres

  the shape of a segmented aperture in the inner sphere

  re and if we place at this location a microchannel plate by confusing its surface with the surface of the inner sphere, we will, during a scanning regime of

  initial beam, a microsound of a large surface area

  of the sample to be studied without losing any of the

  high resolution reached in this analizer.

  In another version of the structure according to

  the invention, the receiving device, also confron-

  from the orifice of the diaphragm, represents a position-sensitive detector. The use of a position-sensitive detector is necessary in the case of narrow beam scanning of the sample surface

  is impossible. For example, this is just for the exci-

  by X-ray tube. In this case, the X-ray

  the area of the segmented area of the source. The detection

  position-sensitive driver used here, executed based on

  a microchannel plate, thanks to the authenticity of the image

  ge, gives information on the position of the energy

  for example, the information on the chemical element to be detected), at the determined point of the sample in this way, an increase in speed is achieved.

  microsonde analysis of the surface to be studied.

  For the first as the second version of the structure of the energy analyzer of charged particle beams of the spherical reflection type, the windows in the surface of the inner electrode have the shape of a multitude of longitudinal slots which lie in southern planes intersecting on the axis of symmetry passing through the centers of the sphere segments of the source and the image. Thanks to such a system of

  windows, the refractive effect of the beams of parti-

  loaded into the southern planes at the entrance to

  the stop (or exit) field is removed. In con-

  sequence, the spatial focus of the beam is improved.

  and the resolution of the energy analyzer of the type

  spherical reflection is increased.

  The intention will be better understood and other goals, details and benefits of it will appear better

  in the light of the following explanatory description

  of an embodiment given solely by way of example

  non-limiting, with reference to the non-limiting drawings

  FIG. 1 shows a charged particle beam energy analyzer of the reflective spherical type according to the invention; FIG. 2 shows the trajectories during an internal reflection of the charged particle beam on the spherical electrostatic mirror;

  - Figure 3 illustrates the authenticity property

  city of the image in the spherical mirror; - Figure 4 shows a version of the structure

  of the particle beam energy analyzer char-

  spherical reflection type according to the invention; and FIG. 5 schematically shows a version of the structure of the spherical reflection analyzer according to the invention. The charged particle beam energy analyzer I of the spherical reflection type that can be seen

  in FIG. i comprises two spherical electrodes concentrating

  the inner electrode of a R-line possesses

  2 of particle passing windows 2 and the outer electrode 3 of a radius PR to which is applied a shutdown voltage from a suitable night (not shown, a source 4 of the charged particle beam, a receiving device 5, consisting of a diaphragm 5 'and a detector 6, and a generator 7 exciting the radiation electron gun or X-ray or ion.The source 4 of the charged particle beam has the form of a sphere segment whose center is at A and which is arranged on the surface of the sphere

  inside of the electrode 1 _ its geometric continuation

  3. The diaphragm 5 ', in the form of a segmented aperture in the inner spherical electrode before the center B, is arranged symmetrically with the source 4 with respect to the center of the spheres. Downstream of the diaphragm 5 'is placed

  the charged particle detector 6.

  One can also conceive a diagram which is the inverse of the energy analyzer of the spherical type with reflection: the source 4 is then placed at the point B in

  the area of the inner spherical electrode 1 of the

  lyser of energy, while the receiving diaphragm 'is at the point diametrically opposed to the source

  4 and the geometric continuation of the spherical surface

  1.In the latter case, the detection of

  6 is also located outside the spherical electrode.

  1. The parameters of the energy analyzer

  They stay the same. Source 4 and the orifice of the dia-

  In the general case, the 5 'reception

  as arbitrary configuration sphere segments

  milking, including sphere segments that are round

  or quadrangular, or narrow bands.

  The operation of the energy analyzer pro-

  posited is based on the two properties of a spherical mirror

  than with perfect focus: the energy isodispersion

  trajectories and the authenticity of the image. To meet

  If these properties are clearer, we will examine the main opto-electric laws of charged particles passing through a spherical electrostatic mirror in a perfect spatial focusing regime. FIG. 2 represents a diagram showing the shape of the trajectories in the case of an internal reflection of a particle on

  the electrostatic mirror. It is assumed that a source

  and its image are arranged on the axis of symmetry at points A and B. The positions of the entry and exit points of the trajectory are determined on the surface of

  the inner spheroidal electrode and the inclination

  sound of the trajectory with respect to the axis of symmetry

  in the area of the inner spherical electrode 1 to the

  yen angular coordinates xl, x2, A and the

  laws of conservation of energy and the moment of quan-

  moment of motion determine the following relations: xl - Q <O \ 1 -x 2 (2) x X 2 nx sin2 (xl - i) sin-- = (3) 2 2 V wO o AZ s52 - (25 - 1 ) sin2 (x -i), (4) $: qV. 1

2E RR

  o S is the reflection parameter of the electrical mirror

spherical trostatic;

  q and E are the charge and the kinetic energy of the

  ticles; 1G L is the stopping potential applied between

electrodes 1 and 3 of the mirror.

  It can be seen in Figure 2 that the distance of the source and the distance of the image from the center of the spheres are equal to: sin'x i - O s

1 sin i-

42 = 1 -

  sin 1 The linear quantities can be expressed in fractions of the radius of the inner spherical electrode 1. In the perfect spatial focusing regime, we have S: 1. From the formula 3. we can deduce: x = 2'xid By substitution of 7 to 2, we obtain t and based on equations 5 and 6. we obtain

  In the regime where S = 1, the two branches of labor

  arbitrary jectory, outside the spherical field, are inclined with respect to the axis of measurement at the same angle t, the source A and the image B being symmetrical

  to each other in relation to the center of the spheres. The dis-

  Persion of the energy of the spherical mirror in regime of

  Perfect spatial focus can be written as follows.

  The energy dispersion D characterizes the value of the

  placement of the image in the energy analyzer for a variation of the energy of the beam: A t D * PE (8 i1

  In this case, the expression of the

  persion along the axis of symmetry is obtained by different

  ferentiation of the expression (6) with respect to the energy 2 cos X, D = 2i2 cosX 92

2 2

  - - sin It follows from formula (9) that for> <1, the dispersion strongly depends on the angle of inclination of

  the trajectory i but with the growth of, the

  lure of the curve D v approaches a stepped shape and for) - 1, the curve D t presents a step of a height equal to 2. In this way, if the source 4 and its image are located on the surface of the electrode

  spherical interior 1, we have, under conditions of

  spatial distribution (S = 1), an energy dispersion

  than the spherical mirror which is maximum, equal to the radius

  double of the inner spherical electrode 1 and

  during step of the exit angle of the particle of the source 4 (property of isodispersion of the trajectories in a spherical mirror). Under perfect spatial focusing conditions, the magnification coefficient is equal to 1, ie the image of the source 4, in the form of a sphere segment of arbitrary shape, disposed at the surface of the inner spherical electrode 1 or the geometric continuation thereof,

  is transferred, life-size, symmetrically

  port in the center of the spheres, on the diametrically

  opposite to the source of this electrode 1 (authentic image

  than). Figure 3 illustrates the property of authenticity

  of the image: the three-dimensional beams, whose parti-

  cules move with energy corresponding to the energy

  on which the spherical electrostatic mirror is

  to achieve a perfect spatial focus,

  converge by forming images without aberration of the

  these points a, b and c at points that are

  arranged "in relation to the center of the spheres, a ',

  b ', c' and, under these conditions, ab = a'b ', bc = b'c'.

  The charged particle beam energy analyzer of the bending spherical type functions as

  follows. A shutdown potential V is applied between the electri-

  trodes 1 and 3. Source 4 excited by an initial beam

  tial provided by a generator 7, emits charged particles at different angles to the axis of symmetry, which,

  windows 2, arrive in the zone of the elec-

  spherical trostatic. If the condition is fulfilled, all the charged particles discharged from the source 4, independently of the angle of inclination 9, after having been reflected by the field, meet at the orifice in the segment of the diaphragm 5 'and after their passage. by

  this hole, they are recorded by the detector 6.

  Figure 1 shows only one beam of a multi-

  study of charged particle beams emitted by the surface of the source 4, this beam shown, after being reflected on the mirror, is focused in a perfect manner at a point of the window of the symmetrical receiving device 5 compared to the center of

  spheres. With a determined stopping potential V, on the ori-

  receiving diaphragm 5 'are focused on the

  particles of a kinetic energy E determined for its

  to satisfy the relation (1). Thanks to the energy dispersion

  whereas linear giving 2R1 for all the trajectories, independently of the angle t, the particles of other energies do not focus on the orifice of the diaphragm 5 ', dissipate and pass through the orifice of the diaphragm only in an insignificant amount. By changing the stopping po- tential V, one records sequentially, zone

  per zone, the whole spectrum of kinetic energies of the

  particle of charged particles to be analyzed.

  As an example illustrating how the analysis works 1

  of energy proposed, one serefèreau diagram shown in Figure 4.

  The detector 6 is in the form of a microchannel plate in

  sphere segment in the orifice of the diaphragm

  5 'so that its outer surface coincides with the surface of the inner spherical electrode 1. In this case, the isodispersion properties are used for the analysis.

  trajectories and authenticity of the image in a half

perfect focus.

The instrument works as follows.

  1. In scanning mode, a microprobe of exci-

  tation, as shown in Figure 4, as a narrow beam. (electronic, ionic, photon, generator 7 performs the scan of the surface of the segment, which is the source 4, by browsing, line by

  line, all its surface. Secondary electrons arrive

  wind in the spherical electrostatic mirror, set for a perfect spatial focusing regime of the electrons

  having the predetermined kinetic energy, corresponding to

  for example, to a definite Auger transition

  atoms of a certain chemical element. Thanks to the

  authenticity of the image transferred by the spherical mirror in synchronism with the movement of the probe

  on the surface of segment 4, the focus of the

  secondary trons of a determined kinetic energy scans the surface of the microchannel plate 6, forming an image symmetrical with respect to the center of the spheres of the swept area of the source 4. At each given instant, it is activated for recording of the portion of the microchannel plate 6 on which there is, at this moment,

  the focus of the secondary electron beam. The signal

  raised on the microchannel plate 6 is amplified and is

* used for the modulation of the beam intensity

  of a video control device, in which the scanning of the cathode ray beam is synchronized with the

  scanning by the microprobe of the surface of segment 4.

  On the screen of the video control device is formed an image reflecting the distribution of sources of secondary electrons of a predetermined energy on the surface

scanned from segment 4.

  2. In static mode, the generator 7 sends a wide beam, exciting the radiation of secondary electrons (electrons, ions, photons) which illuminates

  the surface of the segment 4. The spherical mirror

  that is set for a perfect focusing regime

  secondary electrons with a predetermined kinetic energy

  completed 'for example an energy of the Auger transition

  or energy representing in itself the difference between

  the energies of the quantum of excitation and

  atomic and internal level), electron beam

  Secondary trons emerging from different zones of segment 4 are focused on the surface of a position-sensitive detector and create a symmetrical image with respect to the center of the spheres of the analyzed surface of segment 4. Accompanied by a crack whose origin consists of the unfocused electrons of other energies, the signal

  useful is in the collector and ampli-

  registration, where the substance is rejected and the information

  the position is key, characterizing the distribution of secondary electron sources of a predetermined energy on the analyzed surface of segment 4. In both regimes, thanks to

  authenticity of the image of the spherical mirror, the dimensions

  the surface exposed to exciting irradiation are not limited, the exposed surface may

  of a large part of the surface of the spherical electrode

  1 and be superior, of two orders, to the surface being probed in known electron spectrometers. With a diameter of the inner spherical electrode 1 sufficiently large compared to the size of the source 4, the latter may represent a disc, in which case the surface of the detector 6 may also be flat, which will hardly be 2c34286 I5 influence neither on the quality of the focus nor on

the value of the dispersion.

  FIG. 5 shows a reflective spherical-type energy analyzer scheme, in which the diaphragm aperture windows 2 which are practiced in the inner spherical electrode 1 are in the form of a multitude of longitudinal slots which are arranged in southern planes intersecting on

the axis of symmetry.

  The energy analyzer also has a

  annular conductor system 8 to which

  electrical potentials for the protection of the

  work area of the field. The operation of the analy-

  is similar to the versions described above.

  above. The edge field of an insulated slot is bidimensional, it does not depend on the polar angle, thanks to

  what the trajectories, crossing the opening window,

  ture 2, do not undergo any refraction in the southern planes and the focus of a wide beam does not get worse. The slots must be sufficiently narrow so that the disturbances of the field on the surface of the inner spherical electrode 1 are minimal, the intervals between the slots must be small so that the opening window 2 does not lose its properties of

transmission.

  The present invention can be used for the creation of new electronic spectrometers for studying the surface of solid bodies by

  spectroscopy methods such as ESCA and Auger,

everything from scanning spectroscopy.

Claims (4)

R E V E N D I C A T I D N S   1. Particle beam energy analyzer   charged with a spherical reflection shape, of the type   a source of charged particle beams, two concentric electrodes of spherical shape, connected to a source of stopping voltage, including the inner electrode   has windows for the passage of the beam of   charged particles, as well as a receiving device,   characterized in that the source 4) of the beam of   charged particles and the receiving device 5; have shapes of segments of the sphere, which are arranged symmetrically to each other with respect to the center of   spheres and in that at least one of them is available   on the surface of the inner spherical electrode.   2. Analyzer according to claim 1.   characterized in that the receiving device (5 ') is formed of a receiving diaphragm' 5 'in the form of a segment orifice in the electrode   spherical interior (1) and a detector (6j represented smelling a microchannel plate.   3. Analyzer according to claim 1, characterized   in that the receiving device (5) represents   a position sensitive detector.   4. Analyzer according to any one of the   in which the windows 2 on the surface of the inner electrode (1) are in the form of a multitude of longitudinal slots which lie in southern planes intersecting on the axis of symmetry.