Arrangement and process for adjusting imaging systems

• US 4,486,664 A
• Filed: 07/26/1982
• Issued: 12/04/1984
• Est. Priority Date: 07/31/1981
• Status: Expired due to Fees

• Current Assignee: Finnigan Corporation (Thermo Fisher Scientific Incorporated)
• Original Assignee: Hermann Wollnik
• Inventors: Wollnik, Hermann
• Primary Examiner(s): Anderson, Bruce C.
• Application Number:
  US06/401,614
• Time in Patent Office: 862 Days
• Field of Search: 250/292, 250/296, 250/396 R, 250/396 ML, 313/361
• US Class Current: 250/396.00R
• CPC Class Codes: G21K 1/087 by electrical means
• CPC Class Codes: H01J 37/1471 for centering, aligning or positioning of ray or beam
• CPC Class Codes: H01J 49/061 Ion deflecting means, e.g. ion gates

Abstract

An arrangement and a process for adjusting imaging systems for bundles of charged particles, or for adjusting spectrometers for bundles of charged particles, are indicated, in which arrangement and process electric and/or magnetic correcting elements are used, which possess, in every case, a large number of electrodes and/or current conductors, which are arranged, symmetrically or asymmetrically, around the optical axis of the particle bundle, these electrodes being at potentials such that the resulting potentials V (r, Φ) at an azimuth angle (Φ) to a cylindrical surface at a radius (r) around an optical axis (Z) can be represented as the sum of V₁ and V₂, or, as the case may be, these current conductors carrying currents such that the magnitudes of the resulting currents I (r, Φ) at the azimuth angle (Φ), as defined above, can be represented as the sum of I₁ and I₂. The expressions V₁, V₂ and I₁, I₂ can, in their turn, be represented as sums, their addends being, respectively, of the type V₁ =V_1k sinkΦ, V₂ =V_2k coskΦ, and I₁ =I_1k sinkΦ and I₂ =I_2k coskΦ, where k=1, 2, . . . P, with P representing the order of the multipole. The potentials and/or the currents are utilized, in this manner, to obtain superpositions of electric and/or magnetic dipoles, quadrupoles, hexapoles, etc.

Claims

1. Arrangement for adjusting an imaging system for bundles of charged particles, or for adjusting a spectrometer for bundles of charged particles, by means of one or more electrostatic correcting elements, characterised in that each of these correcting elements possesses a large number (N) of electrodes, which are arranged, symmetrically or asymmetrically, around the optical axis (Z) of the particle bundle, and are at potentials such that the resulting potential (V(r,Φ

)) at an azimuth angle (Φ

) relative to a cylindrical surface at a specified radius (r) around a straight optical axis (Z) or, as the case may be, relative to a corresponding toroidal surface around a curved axis, can be represented as the sum of

space="preserve" listing-type="equation">V.sub.1 =V.sub.11 sin Φ

+V.sub.12 sin 2Φ

+V.sub.13 sin 3Φ

+V.sub.14 sin 4Φ

+V.sub.15 sin 5Φ

+V.sub.16 sin 6Φ

and

space="preserve" listing-type="equation">V.sub.2 =V.sub.21 cos Φ

+V.sub.22 cos 2Φ

+V.sub.23 cos 3Φ

+V.sub.24 cos Φ

+V.sub.24 cos 4Φ

+V.sub.25 cos 5Φ

+V.sub.26 cos 6Φ

it being possible to set the coefficients V_1k and V_2k, as desired, by selecting values for k from k=1 to 6, so that the potentials represent a superposition of an electric dipole, of a quadrupole, of a hexapole, of an octapole, of a decapole, and/or of a duodecapole, the orientation and strength of each individual multipole, relative to the angle Φ

=0, being in every case adjustable as desired.

2. Arrangement according to claim 1, characterised in that N electrodes are arranged parallel to the optical axis, and at a preset radial distance (R) around this axis, at angular intervals which are given, in each case, by

3. Arrangement according to claims 1 or 2, characterised in that all the electrodes extend parallel to the optical axis (Z), and at different distances therefrom, so that their periphery forms a rectangle, with the optical axis (Z) passing through its central point.

7. Arrangement according to claims 1 or 4, characterised in that the sine functions and cosine functions are replaced by other orthogonal functions.

8. Arrangement according to any one of claims 1 to 7, characterised in that both electrodes and current conductors are provided, the electrodes for producing electrical multipole fields, and the conductors for producing magnetic multipole fields.

9. Arrangement according to any one of claims 1 to 8, characterised in that only some of the coefficients V_1k, V_2k and i_1k, i_2k are specified in advance, by prescribing values for k from k=1 to 6, for example only the coefficients V₁₁, V₂₁ and i₁₁, i₂₁, while the remaining coefficients are zero, or the terms corresponding to them are disregarded.

10. Arrangement according to any one of claims 1 to 9, characterised in that the coefficients V_1k, V_2k and i_1k, i_2k, in which k=1 to 6, are defined by preset potentials or currents, a network of resistors, diodes and/or transistors being provided to apportion these potentials and currents to the individual electrodes or current conductors, in accordance with the function (Φ

, Φ

_M) describing their deflection effects in terms of azimuth angle.

11. Arrangement according to any one of claims 1 to 9, characterised in that the potentials of the individual electrodes, or the currents in the individual current conductors, can be set by means of one or more process computers, in particular by means of a large number of digital/analog converters operating in parallel, or by means of one or more digital/analog converters and analog multiplexers with an appropriate number of outputs and short-term analog memory devices.

12. Arrangement according to any one of claims 1 to 11, characterised in that the magnitudes of the coefficients V_1k, V_2k and i_1k, i_2k, in which k=1 to 6, or the magnitudes of the potentials of all the electrodes, and of the currents in all the current conductors, belonging, in each case, to the correcting elements, as well as the magnitudes of the potentials and currents in other components which are employed, in the particle spectrometer or imaging system, for deflecting or focussing purposes, can be adjusted by one or more process computers, the adjustment being effected as a function of the particle-current distribution in the image plane, or in an intermediate image plane, or as a function of the particle-current signals in the final target or targets, or in intermediate targets, when the particle bundle is modified in a defined manner by one or more correcting elements, to the zero-th, 1st, 2nd, 3rd, 4th or 5th approximation, that is to say, when it is deflected or focussed, and/or has aberrations of the 2nd, 3rd, 4th and 5th orders impressed on it, additional deflecting capacitors, or short deflecting magnets, with flux lines perpendicular to the optical axis (Z), and/or beam-twisting magnet coils, with flux lines running parallel to the optical axis, being provided in addition to the controlled correcting elements.

4. Arrangement for adjusting an imaging system for bundles of charged particles, or for adjusting a spectrometer for bundles of charged particles, by means of one or more magnetic correcting elements, characterised in that each of these correcting elements possesses a large number (N) of conductors, through which current flows, and which are arranged, symmetrically or asymmetrically, around the optical axis (Z) of the particle bundle, and through which electric currents which are, in general, dissimilar, flow, these currents giving rise to a magnetic flux density (B) which can also be obtained by means of conductors which are arranged parallel to the optical axis (Z), at a uniform radial distance (R) therefrom, and through which currents flow, of magnitudes such that the current density (i) can be represented, as a function of the azimuth angle (Φ

) relative, in the case of a straight optical axis (Z), to this cylindrical surface, or relative, in the case of a curved optical axis, to this toroidal surface, by the sum of

space="preserve" listing-type="equation">i.sub.1 =i.sub.11 sin Φ

+i.sub.12 sin 2Φ

+i.sub.13 sin 3Φ

=i.sub.14 sin 4Φ

+i.sub.15 sin 5Φ

+i.sub.16 sin 6Φ

and

space="preserve" listing-type="equation">i.sub.2 =i.sub.21 cos Φ

+i.sub.22 cos 2Φ

+i.sub.23 cos 3Φ

+i.sub.24 cos 4Φ

+i.sub.25 cos 5Φ

+i.sub.26 cos 6Φ

,

it being possible to set the coefficients i_1k and i_2k, as desired, by selecting values for k from k=1 to 6, so that the currents produce a superposition of a magnetic dipole, of a quadrupole, of a hexapole, of an octapole, of a decapole, and/or of a duodecapole, the orientation, relative to the angle Φ

=0, and the strength of each individual multipole being in every case adjustable as desired.

5. Arrangement according to claim 4, characterised in that N current conductors are arranged parallel to the optical axis (Z), and at a preset radial distance (R) around this axis, at angular intervals which are given, in each case, by

6. Arrangement according to claim 4, characterised in that all the current conductors extend parallel to the optical axis, but at different distances therefrom, so that their periphery forms a rectangle, with the optical axis (Z) passing through its central point.

13. Process for adjusting an imaging system for bundles of charged particles, or for adjusting a spectrometer for bundles of charged particles, this process employing one or more electrostatic correcting elements, characterised in that (N) electrodes are used for each correcting element, these electrodes being arranged, symmetrically or asymmetrically, around the optical axis of the particle bundle, and being maintained at potentials such that the resulting potential V(r,Φ

) at the azimuth angle (Φ

) relative to a cylindrical surface at a specified radius (r) around a straight optical axis (Z), or, as the case may be, relative to a corresponding toroidal surface around a curved optical axis, can be represented as the sum of

space="preserve" listing-type="equation">V.sub.1 =V.sub.11 sin Φ

+V.sub.12 sin 2Φ

+V.sub.13 sin 3Φ

+V.sub.14 sin 4Φ

+V.sub.15 sin 5Φ

+V.sub.16 sin 6Φ

and

space="preserve" listing-type="equation">V.sub.2 =V.sub.21 cos Φ

+V.sub.22 cos 2Φ

+V.sub.23 cos 3Φ

+V.sub.24 cos 4Φ

+V.sub.25 cos 5Φ

+V.sub.26 cos 6Φ

it being possible to set the coefficients V_1k and V_2k, as desired, by selecting values for k from k=1 to k=6, so that the potentials represent a superposition of an electric dipole, of a quadrupole, of a hexapole, of an octapole, of a decapole, and/or of a duodecapole, the orientation, relative to the angle Φ

=0, and the strength of each individual multipole, being in every case adjustable as desired.

14. Process according to claim 13, characterised in that N electrodes are used, parallel to the optical axis, and at a preset radius (R) around this axis, at angular intervals which are given, in each case, by

15. Process according to claims 13 or 14, characterised in that all the electrodes are arranged parallel to the optical axis (Z), but are not located at a uniform distance therefrom, so that their periphery forms a rectangle, with the optical axis (Z) passing through its central point.

19. Process according to claims 13 or 16, characterised in that the sine functions and cosine functions can be replaced by other orthogonal functions.

20. Process according to any one of claims 13 to 19, characterised in that both electrodes and current conductors are used, the electrodes for producing electrical multipole fields, and the conductors for producing magnetic multipole fields.

21. Process according to any one of claims 13 to 20, characterised in that only some of the coefficients V_1k, V_2k and i_1k, i_2k are specified in advance, by prescribing values for k from k=1 to 6, for example only the coefficients V₁₁, V₂₁ and i₁₁, i₂₁, while the remaining coefficients are made equal to zero, or the terms corresponding to them are disregarded.

22. Process according to any one of claims 13 to 21, characterised in that the coefficients V_1k, V_2k and i_1k, i_2k, in which k=1 to 6, are defined by preset potentials or currents, a network of resistors, diodes and/or transistors being used to apportion these potentials and currents to the individual electrodes or current conductors, in accordance with the function (Φ

,Φ

_M) describing their deflection effects in terms of azimuth angle.

23. Process according to any one of claims 13 to 22, characterised in that the potentials of the individual electrodes, or the currents in the individual current conductors, are set by means of one or more process computers, for example by means of a large number of digital/analog converters operating in parallel, or by means of one or more digital/analog converters and analog multiplexers with an appropriate number of outputs and short-term analog memory devices.

24. Process according to any one of claims 13 to 23, characterised in that the magnitudes of the coefficients V_1k, V_2k and i_1k, i_2k, in which k=1 to 6, or the magnitudes of the potentials of all the electrodes, and of the currents in all the current conductors, belonging, in each case, to the correcting elements, as well as the magnitudes of the potentials and currents in other components which are employed in the particle spectrometer, for deflecting or focussing purposes, are adjusted by one or more process computers, the adjustment being effected as a function of the particle-current distribution in the image plane, or in an intermediate image plane, or as a function of the particle-current signals in the final target or targets, or in intermediate targets, when the particle bundle is modified in a defined manner by one or more correcting elements, to the zero-th, 1st, 2nd, 3rd, 4th or 5th approximation, that is to say, when it is deflected or focussed, and/or has aberrations of the 2nd, 3rd, 4th and 5th orders impressed on it, additional deflecting capacitors, or short deflecting magnets, with flux lines perpendicular to the optical axis, and/or beam-twisting magnet coils, with flux lines running parallel to the optical axis, being employed in addition to the controlled correcting elements.

16. Process for adjusting an imaging system for bundles of charged particles, or for adjusting a spectrometer for bundles of charged particles, in which process one or more magnetic correcting elements are used, characterised in that a large number (N) of conductors are used for each magnetic correcting element, through which conductor current flows, and which are arranged, symmetrically or asymmetrically, around the optical axis of the particle bundle, and through which electric currents which are, in general, dissimilar, flow, these currents giving rise to a magnetic flux density (B) which can also be obtained by means of conductors which are arranged parallel to the optical axis (Z), at a uniform distance (R) therefrom, and through which currents flow, of magnitudes such that the current density (i) can be represented, as a function of the azimuth angle (Φ

) relative, in the case of a straight optical axis, to this cylindrical surface, or relative, in the case of a curved optical axis, to this toroidal surface, as the sum of

space="preserve" listing-type="equation">i.sub.1 =i.sub.11 sin Φ

+i.sub.12 sin 2Φ

+i.sub.13 sin 3Φ

+i.sub.14 sin 4Φ

+i.sub.15 sin 5Φ

+i.sub.16 sin 6Φ

and

space="preserve" listing-type="equation">i.sub.2 =i.sub.21 cos Φ

+i.sub.22 cos 2Φ

+i.sub.23 cos 3Φ

+i.sub.24 cos 4Φ

+i.sub.25 cos 5Φ

+i.sub.26 cos 6Φ

,

it being possible to set the coefficients i_1k and i_2k, as desired, by selecting values for k from k=1 to 6, so that the currents produce a superposition of a magnetic dipole, of a quadrupole, of a hexapole, of an octapole, of a decapole, and/or of a duodecapole, the orientation, relative to the angle Φ

=0, and the strength of each individual multipole being in every case adjustable as desired.

17. Process according to claim 16, characterised in that N current conductors are arranged parallel to the optical axis (Z), and at a preset radial distance (R) around this axis, at angular intervals which are given, in each case, by

18. Process according to claims 16 or 17, characterised in that all the current conductors are arranged parallel to the optical axis, but are not located at a uniform distance therefrom, so that their periphery forms a rectangle, with the optical axis (Z) passing through its central point.