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4085. Deflection distortion in scanning electron-beam systems. (USA)
Classified
abstracts
4083-4090
e.g. Ar+ + F-,
the recombination rate is so slow that ambipolar diffusion is seen to dominate over ionic recombination under the conditions of the experiment, and it has only been possible to determine upper limits for al. The results indicate that for several rare gas/halide atomic ion reactions a, is at least one order of magnitude smaller than for those reactions involving molecular ions, in general accord with theoretical expectations. M Church and D Smith, J P/ZJJS D: Appl Phys, 11 (16), 1978,
beam transfer and evaluate the resulting beam quality without additional ray tracing. The specific device for which calculations are made employs a uniform electric field and a toroidal magnetic field. This analyzer is of special interest in our laboratory because it can be constructed with a very small stray magnetic field and in addition to its dispersive properties it also rotates the spin of a polarized electron beam. A Galejs and C E Kuyatt, J Vat Sci Technol, 15 (3), 1978, 865-867.
2199-2206. 33 4083. A neutral-particle analyser for plasma diagnostics. (GB) We describe an instrument which can be used to measure the neutralparticle flux from a plasma over the energy range 200 eV to 30 keV. This wide range makes the device especially useful for plasmas where
neutral injection heating may be employed. It has been used for measuring both the ion temperature and the high-energy spectrum due to the injection of high-power neutral beams into the DITE (Divertor Injection Tokamak Experiment) Tokamak. D D R Summers et al,JPhys E: SciZnstrum, 11(12), 1978,1183-l 190.
34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND
34 4084. Design of a variable-aperture projection and scanning system for electron beam. (USA) Results of design calculations of a variable-aperture projection and
scanning exposure system is presented. Use is made of newly developed aberration formulas for the focus deflection system, which can handle systems consisting of a set of focus and defection coils with superimposed fields and of deflection coils arranged in rotated angular positions, taking into account the finiteness of the object. The aberration of less than 0.2 pm and the incident angle less than 1 mrad with the normal, at the corners of a 5 x 5 mm deflection field, is expected for the 25 pm (maximum) square and 3 mrad semiangle probe, in the linear MOL deflector, with object to image distance of 100 mm, consisting of only an axially symmetric lens and five linear deflectors without dynamic corrections. (Japan) E Goto et al, J Vat Sci Technol, 15 (3), 1978, 883-886. 4085. Deflection
distortion
in scanning electron-beam
systems.
34 (USA)
A simple method for the measurement of deflection distortions in a scanning electron-beam system using a ‘Stripe Scan’ technique is described. This technique allows real-time measurements to be performed at high accuracy. Results obtained by this technique have been compared to those obtained by a laser interferometer measuring system and good agreements have been achieved. The effects on distortion of various factors in VSI, a vector scan electron-beam lithographic system, have been evaluated and the results will be described. T H P Chang and R Viswanathan, J Vuc Sci Technol, 15 (3), 1973, 878-882. 34 4086. Focusing of electron beams by laser-beam fields. (USA) Employing the paraxial electron-trajectory equation of a cylindrical
electron (beam) the theory of the focusing action of an enveloping annular laser beam is presented and discussed. Analogies between schemes employing laser-beam fields to focus electron beams and methods involving conventional ‘strong’ and ‘quadrupole’ focusing of electron beams are indicated. Some advantages and limitations of the suggested focusing method are pointed out. Also, some approximate numerical estimates regarding the parameters of a cylindrical electron beam and a (focusing) surrounding annular laser beam are obtained for a typical example. S Yadavalli, J Vuc Sci Technol, 15 (3), 1978, 868-871. 4087. Focusing and dispersing energy analyzer. (USA)
properties
of a stigmatic
34 crossed-field
The electron-optical properties of a stigmatic cross-field energy analyzer (double-focusing Wien filter) have been obtained from exact trajectory calculations. The results are given in the form of focusing and dispersing coefficients to the second order. These coefficients enable the device designer or potential user to calculate the total 326
34 4088. Systematic transformations of the asymptotic aberration coefficients of round electrostatic lenses (I). (USA) In previous work we formulated the third-order asymptotic aberration coefficients of round (axially symmetric) electrostatic lenses in a form independent of object and aperture positions, and expressions for the six quantities which are sufficient to specify completely the aberration properties of the lenses were derived in the form of integrals involving derivatives of the axial potential through the fourth order. Because actual calculations involved numerical differentiation of the axial potentials, integrations by parts were used to transform the integrals to two new forms with axial derivatives of lower degree. Many other forms of the aberration integrals can be obtained by further integrations by parts, but the transformations are laborious and it is not easy to predict the forms which are possible nor to determine the sequence of operations which will yield a desired result. However, using a method originally developed by Seman and extended by Hawkes, a completely genera1 formula has been derived from which all of the possible forms of the asymptotic integrals can be obtained simply. A few of these possible forms are derived and discussed. C E Kuyatt, J Vat Sci Technol, 15 (3), 1978, 861-864. 4089. Electrostatic einzel lenses with reduced spherical aberration use in field-emission guns. (USA)
34 for
Focusing properties and aberration coefficients are calculated for electrostatic einzel lenses suitable for use as preaccelerator lenses in field-emission electron guns. Various lens shapes are analysed and asymmetric designs with conical central electrodes are found to have reduced spherical aberration. A lens shape with optimized geometry is found to have a spherical aberration coefficient of less than six times the working distance from the lens to the focal point. This lens has a bored conical central electrode located close to a thin first electrode. Calculations indicate that a field-emission gun using such a lens should be able to provide a 0.24 PA beam from a 1100 A effective source size into an emission half-angle of 2.4 x 10e2 rad. At lower emission angles the source size would be limited by chromatic rather than spherical aberration. G H N Riddle, J Vat Sci Technol, 15 (3), 1978, 857-860. 34 4090. Averaging of electron-beam aberrations. (USA) The design of the imaging and deflection components in an electron probe is directly related to the resolution required in the target plane. The resolution has an especially strong effect on the design when the probe is to be scanned over a large area. The theoretical models of such systems commonly calculate the properties of single trajectories through the column, and from these properties the worst-case aberrations are inferred. But such calculations, though more convenient than direct measurement, are often misleading. In most applications, the average properties of an electron beam have more physical meaning than the relatively few electrons with worst-case trajectories. The calculation of single electron trajectories can be applied to the actual electron-optical system by modelling the actual illumination of the electron beam and averaging over this illumination to get certain specific properties of the beam. The illumination is described by probability distributions over the beam parameters; these distributions are related to the electron source through the optical transfer functions of the column. Intervening apertures also affect the boundary conditions of the distributions. This method can be applied to a shaped electron probe. The dislocation and blurring of the shaped spot can be calculated from the single electron trajectories in the final imaging and deflection system by taking into account the correlation of the various aberrations. Changes in beam energy or lens excitation cause beam dislocation and blurring different from what has usually been reported. J L Mauer, J Vat Sci Technol, 15 (3), 1978, 853-856.
abstracts
4083-4090
e.g. Ar+ + F-,
the recombination rate is so slow that ambipolar diffusion is seen to dominate over ionic recombination under the conditions of the experiment, and it has only been possible to determine upper limits for al. The results indicate that for several rare gas/halide atomic ion reactions a, is at least one order of magnitude smaller than for those reactions involving molecular ions, in general accord with theoretical expectations. M Church and D Smith, J P/ZJJS D: Appl Phys, 11 (16), 1978,
beam transfer and evaluate the resulting beam quality without additional ray tracing. The specific device for which calculations are made employs a uniform electric field and a toroidal magnetic field. This analyzer is of special interest in our laboratory because it can be constructed with a very small stray magnetic field and in addition to its dispersive properties it also rotates the spin of a polarized electron beam. A Galejs and C E Kuyatt, J Vat Sci Technol, 15 (3), 1978, 865-867.
2199-2206. 33 4083. A neutral-particle analyser for plasma diagnostics. (GB) We describe an instrument which can be used to measure the neutralparticle flux from a plasma over the energy range 200 eV to 30 keV. This wide range makes the device especially useful for plasmas where
neutral injection heating may be employed. It has been used for measuring both the ion temperature and the high-energy spectrum due to the injection of high-power neutral beams into the DITE (Divertor Injection Tokamak Experiment) Tokamak. D D R Summers et al,JPhys E: SciZnstrum, 11(12), 1978,1183-l 190.
34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND
34 4084. Design of a variable-aperture projection and scanning system for electron beam. (USA) Results of design calculations of a variable-aperture projection and
scanning exposure system is presented. Use is made of newly developed aberration formulas for the focus deflection system, which can handle systems consisting of a set of focus and defection coils with superimposed fields and of deflection coils arranged in rotated angular positions, taking into account the finiteness of the object. The aberration of less than 0.2 pm and the incident angle less than 1 mrad with the normal, at the corners of a 5 x 5 mm deflection field, is expected for the 25 pm (maximum) square and 3 mrad semiangle probe, in the linear MOL deflector, with object to image distance of 100 mm, consisting of only an axially symmetric lens and five linear deflectors without dynamic corrections. (Japan) E Goto et al, J Vat Sci Technol, 15 (3), 1978, 883-886. 4085. Deflection
distortion
in scanning electron-beam
systems.
34 (USA)
A simple method for the measurement of deflection distortions in a scanning electron-beam system using a ‘Stripe Scan’ technique is described. This technique allows real-time measurements to be performed at high accuracy. Results obtained by this technique have been compared to those obtained by a laser interferometer measuring system and good agreements have been achieved. The effects on distortion of various factors in VSI, a vector scan electron-beam lithographic system, have been evaluated and the results will be described. T H P Chang and R Viswanathan, J Vuc Sci Technol, 15 (3), 1973, 878-882. 34 4086. Focusing of electron beams by laser-beam fields. (USA) Employing the paraxial electron-trajectory equation of a cylindrical
electron (beam) the theory of the focusing action of an enveloping annular laser beam is presented and discussed. Analogies between schemes employing laser-beam fields to focus electron beams and methods involving conventional ‘strong’ and ‘quadrupole’ focusing of electron beams are indicated. Some advantages and limitations of the suggested focusing method are pointed out. Also, some approximate numerical estimates regarding the parameters of a cylindrical electron beam and a (focusing) surrounding annular laser beam are obtained for a typical example. S Yadavalli, J Vuc Sci Technol, 15 (3), 1978, 868-871. 4087. Focusing and dispersing energy analyzer. (USA)
properties
of a stigmatic
34 crossed-field
The electron-optical properties of a stigmatic cross-field energy analyzer (double-focusing Wien filter) have been obtained from exact trajectory calculations. The results are given in the form of focusing and dispersing coefficients to the second order. These coefficients enable the device designer or potential user to calculate the total 326
34 4088. Systematic transformations of the asymptotic aberration coefficients of round electrostatic lenses (I). (USA) In previous work we formulated the third-order asymptotic aberration coefficients of round (axially symmetric) electrostatic lenses in a form independent of object and aperture positions, and expressions for the six quantities which are sufficient to specify completely the aberration properties of the lenses were derived in the form of integrals involving derivatives of the axial potential through the fourth order. Because actual calculations involved numerical differentiation of the axial potentials, integrations by parts were used to transform the integrals to two new forms with axial derivatives of lower degree. Many other forms of the aberration integrals can be obtained by further integrations by parts, but the transformations are laborious and it is not easy to predict the forms which are possible nor to determine the sequence of operations which will yield a desired result. However, using a method originally developed by Seman and extended by Hawkes, a completely genera1 formula has been derived from which all of the possible forms of the asymptotic integrals can be obtained simply. A few of these possible forms are derived and discussed. C E Kuyatt, J Vat Sci Technol, 15 (3), 1978, 861-864. 4089. Electrostatic einzel lenses with reduced spherical aberration use in field-emission guns. (USA)
34 for
Focusing properties and aberration coefficients are calculated for electrostatic einzel lenses suitable for use as preaccelerator lenses in field-emission electron guns. Various lens shapes are analysed and asymmetric designs with conical central electrodes are found to have reduced spherical aberration. A lens shape with optimized geometry is found to have a spherical aberration coefficient of less than six times the working distance from the lens to the focal point. This lens has a bored conical central electrode located close to a thin first electrode. Calculations indicate that a field-emission gun using such a lens should be able to provide a 0.24 PA beam from a 1100 A effective source size into an emission half-angle of 2.4 x 10e2 rad. At lower emission angles the source size would be limited by chromatic rather than spherical aberration. G H N Riddle, J Vat Sci Technol, 15 (3), 1978, 857-860. 34 4090. Averaging of electron-beam aberrations. (USA) The design of the imaging and deflection components in an electron probe is directly related to the resolution required in the target plane. The resolution has an especially strong effect on the design when the probe is to be scanned over a large area. The theoretical models of such systems commonly calculate the properties of single trajectories through the column, and from these properties the worst-case aberrations are inferred. But such calculations, though more convenient than direct measurement, are often misleading. In most applications, the average properties of an electron beam have more physical meaning than the relatively few electrons with worst-case trajectories. The calculation of single electron trajectories can be applied to the actual electron-optical system by modelling the actual illumination of the electron beam and averaging over this illumination to get certain specific properties of the beam. The illumination is described by probability distributions over the beam parameters; these distributions are related to the electron source through the optical transfer functions of the column. Intervening apertures also affect the boundary conditions of the distributions. This method can be applied to a shaped electron probe. The dislocation and blurring of the shaped spot can be calculated from the single electron trajectories in the final imaging and deflection system by taking into account the correlation of the various aberrations. Changes in beam energy or lens excitation cause beam dislocation and blurring different from what has usually been reported. J L Mauer, J Vat Sci Technol, 15 (3), 1978, 853-856.