Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/44—Energy spectrometers, e.g. alpha-, beta-spectrometers
  • H01J49/46—Static spectrometers
  • H01J49/48—Static spectrometers using electrostatic analysers, e.g. cylindrical sector, Wien filter
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
  • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/244—Detection characterized by the detecting means
  • H01J2237/24485—Energy spectrometers

Definitions

• This invention relates to charged particle energy analysers.
• charged particle spectrometers are commercially available with multichannel capabilities, the range of energies they can detect is typically only about 1 % of a useful Auger spectrum (eg 50eV to 2050eV).
• Preferred embodiments of the present invention aim to provide electron energy analysers or spectrometers whose prime feature is the ability to detect electrons with a large range of energies, in parallel.
• the main purpose envisaged is for the energy analysis of electrons scattered from a sample.
• the electrons may be generated by photons, electrons or other ionising radiation.
• the scattered electrons include secondary, back-scattered, Auger, loss and photoelectrons, with energies between about lOeV and 3000eV.
• preferred embodiments of the present invention may collect a full useful Auger spectrum in one process, and therefore operate approximately 100 times faster than existing spectrometers.
• a charged particle energy analyser comprising: a. field means for creating a substantially hyperbolic field defined with reference to an x-axis and a y-axis, each of which axes is at a substantially constant potential; b. entry means for admitting charged particles into said field; and c. detecting means arranged substantially along said x-axis, for detecting electrons deflected by said field.
• said field is at least partly electrostatic.
• Said field may be at least partly magnetic.
• said entry means is arranged to admit charged particles into said field, at a region along said x-axis.
• said charged particles are electrons.
• said field is defined by the equations:
• V Vi a "n ⁇ n sin(n0) (0 ⁇ ⁇ ⁇ ⁇ r/n)
• V ⁇ is the potential of the line of equipotential whose closest point to the origin of the x,y axes is a distance a from it
• n 2 ⁇ k
• k is in the range 0 to 0.4.
• k 0.1, 0.2, 0.3 or 0.4.
• a charged particle energy analyser as above may include means for causing emission of said charged particles.
• Figure 1 illustrates a hyperbolic electrostatic field
• Figure 4 illustrates focussing of electrons originating from a point outside a field, such that first order focussing occurs at 21.51 ° ⁇ 24.78°;
• Figure 5 illustrates one example of a substantially hyperbolic field within an analyser, by way of an elevation which shows an x-y view;
• Figure 6 is a plan view of a detector and entrance aperture
• Figure 7 shows essential elements of one example of a substantially hyperbolic field analyser, and also shows some examples of electron trajectories
• Figure 8 shows energy dispersion (energy versus position) in one example of a hyperbolic field analyser
• Figure 9 shows energy resolution (energy versus energy resolution) in one example of a hyperbolic field analyser
• Figure 10 illustrates a prototype analyser with electron column and sample shown, in which a hyperbolic field is approximated with a small number of electrodes; and Figure 11 shows a silver Auger spectrum obtained using the prototype analyser of Figure 10.
• Figure 1 illustrates a two-dimensional hyperbolic electrostatic field defined with reference to an x-axis and a y-axis, each of which axes is at a substantially constant potential - typically zero potential.
• a field is used in preferred embodiments of the invention, examples of which are given below, to disperse electrons according to their energies.
• the potential distribution, which determines the field, is given by the following equations (in cylindrical polar form):
• V V j a "n r 11 sin(n0) (0 ⁇ ⁇ ⁇ ⁇ r/n)
• V 0 ( ⁇ r/n ⁇ 0 ⁇ 2 r)
• Equations for calculating the trajectories of electrons in such fields are well known and in fact a full quadrupole electrostatic field has long been used in a variety of applications involving the transport and dispersion of charged particles. Examples include 'strong' electrostatic lenses, beam deflectors and single channel energy analysers. Nevertheless, certain properties of the field of Figure 1 , which represents only a quarter of a full quadrupole electrostatic field as traditionally used in the past in other applications, are central to the preferred embodiments of the present invention described below, and have not previously been recognised or exploited. These relate to the focussing of beams of electrons having angular divergence or width in a way which is independent, or nearly so, of the energy of the electrons.
• the length L is again proportional to the square root of the energy of the electrons.
• the hyperbolic electrostatic field is created by applying appropriate voltages to electrodes E 0 to E 10 arranged orthogonally in the x-y plane. In the z direction, the electrodes continue for some distance until the field in the centre is undistorted. It may be noted that the x and y potential gradients (E 0 to E 10 ) are linear. This is only one of many possible ways of creating the field.
• An entrance aperture is placed on the x-axis (in the x-z plane) centred at X Q . Because this is on an equipotential surface, and in the region of weakest electric field, the entrance aperture does not distort the field.
• the size and shape of the entrance aperture determines the solid angle acceptance of the analyser.
• the distance of X Q from the origin is very much smaller than the average dispersion length - i.e. the distance between the entrance aperture and the middle of the detector area.
• an electron detector is also placed along the x- axis in the x-z plane.
• the detector is able to resolve simultaneously the arrival of electrons landing in different locations on its front face.
• This may consist of a microchannel plate (to amplify the signal) followed by a phosphor screen.
• the light pattern on the screen may be measured using a photodiode array or CCD, either coupled directly to the screen, coupled via a fibre optic bundle or using a conventional optical lens.
• Figure 6 is a schematic diagram of a plan view of the detector and entrance aperture showing the energy dependence of the location at which electrons are detected.
• the value of is chosen to make the locus of focal points as near as possible to the detector face so as to maximise the energy resolution of the analyser.
• the solid angle acceptance in this case is —0.05 % of the full 2 ⁇ steradians emitted from the surface of a sample. Both ⁇ and ⁇ can be increased in order to collect more signal but, as with any analyser, this will affect the energy resolution achievable.
• Figure 8 illustrates energy dispersion (energy versus position) in a hyperbolic field analyser having an arrangement as shown in Figure 4 and parameters according to Table 1.
• Figure 9 shows the theoretical energy resolution (energy versus energy resolution) in a hyperbolic field analyser having an arrangement as shown in
• Figure 10 illustrates a prototype analyser with an electron column 10 to excite a sample 11 on a suitable sample holder 12. Excitation of the sample 11 causes electrons to be emitted, and some of the electrons enter the analyser through an aperture 13, where they are subjected to a substantially hyperbolic field which is approximated with a small number of electrodes E j to E 6 . In a manner as described above, die electrons are deflected by the substantially hyperbolic field to impinge upon a detector 14 comprising, for example, a microchannel plate and phosphor screen, in the vicinity of which they are focussed.
• a detector 14 comprising, for example, a microchannel plate and phosphor screen
• the electrodes ⁇ to E 5 are arranged in a plane which is inclined to the general axis of the analyser (i.e. the axis parallel to the detector 14), and the electrode E 6 is similarly inclined, but in an opposite direction.
• Figure 11 shows a silver Auger spectrum obtained using the prototype analyser of Figure 10.
• the acquisition time was 2 seconds and the primary electron beam lOnA, 5000eV.
• Figure 11 only part of the spectrum is shown, although a full Auger spectrum from 50eV to 2050eV was collected in parallel, in the 2 second period. Substantially faster collection times are possible, using the same principle.
• the illustrated analysers are two-dimensional, to give a linear detection area, they may be rotated by up to 2 ⁇ about their axis or any line which goes through the point source, to give a rotationally symmetrical version in which a spectrum may be collected on a disk, cylinder or other shaped collector or detector.
• the electrostatic field may be replaced or supplemented by a magnetic field.
• Alternative embodiments of the invention may receive, deflect and detect other charged particles (e.g. ions, positrons), or electrons with much higher or lower energy than in Auger spectroscopy.
• other charged particles e.g. ions, positrons
• electrons with much higher or lower energy than in Auger spectroscopy.
• the x, y and z axes can have any absolute orientation in space, and are not necessarily as shown in the Figures.
• detector includes both a single detector and a set or array of detectors.
• the invention is not restricted to die details of the foregoing embodiment(s).
• the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
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• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
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• Analysing Materials By The Use Of Radiation (AREA)
• Electron Tubes For Measurement (AREA)

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• 1998
  • 1998-01-12 GB GBGB9800488.0A patent/GB9800488D0/en not_active Ceased
• 1999
  • 1999-01-12 AU AU19755/99A patent/AU1975599A/en not_active Abandoned
  • 1999-01-12 JP JP2000527963A patent/JP2002501285A/ja active Pending
  • 1999-01-12 WO PCT/GB1999/000009 patent/WO1999035668A2/en not_active Application Discontinuation
  • 1999-01-12 EP EP99900537A patent/EP1051735A2/de not_active Withdrawn

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