JP2009076422A - Aberration correcting lens for charged particle beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spherical aberration correction lens system which cancels spherical aberration of an axisymmetric lens having a great aberration coefficient, and an axisymmetric probe formation lens with no spherical aberration. <P>SOLUTION: A charged particle optical lens system is formed of quadrupole lenses of 4 stages, and three aperture electrodes. The aperture electrodes for inducing octopole lens action are arranged between the first and second stages, between the second and third stages, and between the third and fourth stages. Excitation control of the quadrupole lens is actuated to develop concave-convex-concave-convex lens action on an XZ plane, and convex-concave-convex-concave lens action on a YZ plane, and excitation intensity of the respective quadrupole lenses is adjusted so that a charged particle trajectory on the YZ plane intersects with an optical axis once between the quadrupole lenses of the second and third stages, the charged particle trajectories on the XZ plane and YZ plane intersect with an axis behind the quadrupole lens of the last stage so that the charged particle lens system satisfies an axisymmetric lens condition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aperture aberration correction lens and a spherical aberration correction lens for charged particle beams such as an electron beam and an ion beam.

  An axially symmetric electric field lens and magnetic field lens generally used in charged particle beam apparatuses cannot correct spherical aberration (which is synonymous with axial aberration of an axially asymmetric lens) and chromatic aberration, which are axial aberrations. Combining axially asymmetric multipole lenses such as quadrupole lenses, hexapole lenses, octupole lenses, and twelve-pole lenses composed of multiple electrodes or magnetic poles paired on the XY plane when the optical axis is the Z-axis In many literatures, it is already possible to correct spherical aberration and chromatic aberration.

The blurs ΔX (Zix) and ΔY (Ziy) corresponding to the deviation of the trajectory at the focal position due to the aperture aberration of the quadrupole lens used in the present invention are the beam opening angles on the XZ plane and the YZ plane, α, β and Then it is expressed as follows.
ΔX (Zix) ＝ C _A30 α ³ + C _A12 αβ ² (1)
ΔY (Ziy) ＝ C _A21 α ² β + C _A03 β ³ (2)
In the above formulas (1) and (2), C _A30 , C _A12 , C _A21 , and C _A03 are aperture aberration coefficients. Under the condition of Zix = Ziy, Mx = My where the magnifications Mx and My in the XZ plane and YZ plane are equal, the axial symmetry of the charged particle trajectory is obtained, and the values of the aperture aberration coefficients C _A12 and C _A21 are equal.

In an axially asymmetric optical system, optical axial symmetry is obtained by controlling individual lenses, and the condition of C _A30 = C _A12 (= C _A21 ) = C _A03 is satisfied by controlling the octupole lens action. The aperture aberration coefficient in this case is synonymous with the spherical aberration coefficient of the axially symmetric lens. If these three aperture aberration coefficients can generate a negative aberration coefficient by controlling the octupole lens action, the spherical aberration of the axially symmetric lens that can only have a positive value can be corrected.

  FIG. 1 shows an example of how to use an aberration correction lens for an axisymmetric lens that finely focuses a charged particle beam. The condenser lens 2 at the front stage of the correction lens system 1 and the objective lens 3 at the rear stage are independently an electric field type or magnetic field type axially symmetric lens incapable of correcting spherical aberration and chromatic aberration. 11 and 12 are orbits of charged particle beams on the XZ plane and the YZ plane. The trajectory characteristics that generate a negative aperture aberration coefficient to correct the spherical aberration of the axisymmetric lens in the latter stage are charged particle beam trajectories before and after loading the correction lens system with a magnification of | Mx | = | My | Is adjusted to take a far-focused orbit that does not change. Although the charged particle beam trajectory in the correction lens system is omitted, the charged particle beam trajectory in FIG. 2 corresponds to this.

  As a spherical aberration correction lens system for an axially symmetric lens, a previously proposed quadrupole / octupole correction lens system includes a four-stage quadrupole lens and a three-stage octupole lens (Non-Patent Document 1). . As a spherical aberration correction lens system arranged in front of the magnetic field type objective lens of the scanning transmission electron microscope, a four-stage magnetic field type quadrupole lens and a three-stage octupole lens are used to control the above three aperture aberration coefficients. A combined correction lens system has been studied. In the practical application system, in order to achieve strict alignment accuracy and excitation control between quadrupole lenses, a twelve-pole lens is used instead of a quadrupole lens, and the alignment and mechanical alignment are performed by excitation control of each individual twelve-pole lens. A quadrupole and octupole correction lens system is constructed by adjusting the mechanical and electromagnetic asymmetry.

  As a measure for improving the structure of a correction lens that is complicated and requires strict alignment accuracy, a correction lens (Non-Patent Document 2) that includes a quadrupole lens and an aperture electrode disclosed in Patent Document 1 can be used. FIG. 2 shows an example of simulation calculation of charged particle beam trajectories and aperture aberrations in the XZ plane and YZ plane in this case. Q1 to Q4 are electric field type quadrupole lenses, and A1 to A3 are aperture electrodes. Electrode diameter of quadrupole lens φ8mm, length 14mm, aperture diameter of quadrupole lens and aperture electrode φ6.989mm, aperture electrode thickness 2mm, distance between end surface of quadrupole lens and aperture electrode 4mm It is.

In the electric field type quadrupole lens, when VQ [V] is applied to the electrode on the XZ plane, −VQ [V] is applied to the electrode on the YZ plane. When the acceleration voltage is Va [V], the excitation intensity of the quadrupole lens is expressed as VQ / Va, and the excitation intensity of the aperture electrode is expressed as VA / Va. In the example of the simulation calculation result in Fig. 2, in order to correct the spherical aberration coefficient Cs = 56 mm of the axisymmetric objective lens, C _A30 = C _A12 (= C _A21 ) = C _A03 = -56mm. 11 is a charged particle beam orbit of the XZ plane, and 12 is a charged particle beam orbit of the YZ plane. 21 is a potential distribution corresponding to the excitation polarity of the quadrupole lens, and 31, 32, and 33 are octupole potential distributions expressed by exciting A1, A2, and A3, respectively. Reference numerals 41, 42, and 43 are axisymmetric potential distributions generated by exciting A1, A2, and A3, respectively. The excitation intensity on the XZ plane of the four-stage quadrupole lens is +0.05745, −0.057265, +0.057265, −0.05745, and the excitation intensity on the YZ plane is −0.05745, +0.057265, −0.057265, +0.05745. The excitation intensity of the aperture electrode is −0.300, +0.125, and −0.300.

In the method of using a correction lens system as shown in Fig. 1, by increasing the number of steps of the quadrupole lens, the excitation intensity of each quadrupole lens can be lowered, and the strict alignment accuracy between the multistage quadrupole lenses can be relaxed. Although the magnification of the correction lens system shown in FIG. 1 is | Mx | = | My | = 1, the magnification of the entire optical system is approximately | M | = b / a. Therefore, it is not possible to use the correction lens system to increase the reduction magnification. In addition, when the spherical aberration coefficient of the axisymmetric lens is very large, an octupole lens or a correction lens system that takes a far-focus type charged particle trajectory as shown in FIG. The excitation intensity of the aperture electrode becomes very strong, and its practicality is low except for charged particle devices with a low acceleration voltage. Further, the chromatic aberration of the system in which the correction lens system having the magnification | Mx | = | My | = 1 and the axisymmetric lens is combined is a value obtained by adding the chromatic aberration of the correction lens system to the chromatic aberration of the objective lens.
Japanese Patent Application No. 2007-042273 MGR Thomson, Optik, 34, 528-534 (1972) S. Okayama and H. Kawakatsu, A new correction lens, Journal of Physics E, 15, 580-586 (1982)

  In a charged particle optical system, when a charged particle beam emitted from an electron source or an ion source is reduced by a charged particle lens, it is important to obtain a fine charged particle probe by increasing the reduction ratio in the entire optical system. It is. Also, in the realization of a correction lens system that is arranged in front of an axially symmetric objective lens having a large positive spherical aberration coefficient and generates a negative spherical aberration coefficient, a correction lens system and an axially symmetric lens as shown in FIG. In this relationship, the correction lens system does not contribute to a large reduction ratio. In addition, the beam off-axis distance in the correction lens system is increased, the excitation intensity of the quadrupole lens is high, and it is difficult to use as a correction lens system that generates a large negative aperture aberration. In SEMs, electron beam lithography systems, focused ion beam systems, etc. that form fine charged particle probes, the entire optical system is effectively reduced by a lens system that constitutes a charged particle beam emitted from a charged particle source. It is important to optimize the correction of aberrations. For this purpose, as shown in FIG. 3, a correction lens system capable of canceling the spherical aberration of the axially symmetric lens under the condition that the magnification of the correction lens system is | Mx | = | My | ≠ 1 is required.

  The problem to be solved is to form an aperture aberration correction lens system that exhibits an axisymmetric reduction lens action (| Mx | = | My | <1) by setting the number of stages of the quadrupole lens and the excitation control. Optimizing the arrangement and excitation conditions of quadrupole or dodecapole lenses, aperture electrodes or octupole lenses, and adjusting the off-axis distance of the charged particle beam trajectories on the XZ and YZ planes, effectively increasing the negative Adjust the excitation control of the quadrupole lens or twelve-pole lens so as to form a charged particle beam trajectory that can generate spherical aberration, and the spherical surface of the axially symmetric lens placed in the latter stage by the excitation control of the aperture electrode or octupole lens It is to correct the aberration. In addition, by realizing an aperture aberration correction lens system that exhibits an axially symmetric reduction lens action, it can be easily used as an axially symmetric objective lens with zero spherical aberration.

  It is composed of a four-stage quadrupole lens and an aperture electrode that induces three octupole lens actions. The aperture electrode is arranged between the first and second quadrupole lenses, between the second and third stages, and In the charged particle optical lens arranged between the third and fourth stages, the quadrupole lens is excited so that the Z-axis is the optical axis and the concave / convex lens action is produced on the XZ plane and the convex / concave concave / convex lens action is produced on the YZ plane. Controlling the polarity, the charged particle trajectory on the YZ plane intersects the optical axis near the entrance of the second quadrupole lens, and the charged particle trajectory on the XZ plane and YZ plane after the fourth quadrupole lens. The aperture aberration coefficient can be controlled by adjusting the excitation intensity of each quadrupole lens and aperture electrode so as to intersect the optical axis.

  The aperture electrode can be replaced with an octupole lens. It is composed of a four-stage quadrupole lens and a three-stage octupole lens. The octupole lens is arranged between the first and second quadrupole lenses, between the second and third stages, and the third stage. In the charged particle optical lens arranged between the 4th stage, the excitation polarity of the quadrupole lens is controlled so that the convex / concave / concave lens action is developed on the XZ plane and the convex / concave / concave lens action is developed on the YZ plane, and the YZ plane is charged. Only the particle trajectory intersects the optical axis near the octupole lens placed between the first and second quadrupole lenses, and the charged particle trajectories on the XZ and YZ surfaces after the fourth quadrupole lens. The aperture aberration coefficient can be controlled by adjusting the excitation intensity of each quadrupole lens and octupole lens so as to intersect the optical axis.

  Instead of a quadrupole lens requiring high-precision electrode alignment, axial alignment between multistage lenses and correction of electrode asymmetry are possible, and a twelve-pole lens that excites the quadrupole lens action can be used. When a twelve-pole lens is used, the octupole lens action due to the interaction between the quadrupole lens and the aperture electrode cannot be used. Therefore, an octupole lens is required to control the aperture aberration. Therefore, in a four-stage dodecapole lens and a three-stage octupole lens configuration, the octupole lens is between the first and second twelve-pole lenses, between the second and third stages, and In the charged particle optical lens placed between the 3rd and 4th stages, the excitation polarity of the twelve-pole lens is controlled so that the concave / convex lens action on the XZ plane and the convex / concave concave lens action on the YZ plane are controlled. The charged particle trajectory of the plane intersects the optical axis near the octupole lens placed between the first and second quadrupole lenses, and the XZ and YZ planes after the fourth quadrupole lens. The aperture aberration coefficient can be controlled by adjusting the excitation intensity of each dodecapole lens and octupole lens so that the charged particle trajectory intersects the optical axis.

  Aperture aberration coefficient by adjusting the off-axis distance between the XZ plane and the YZ plane and adjusting the excitation of the aperture electrode or octupole lens so that the excitation intensity of the quadrupole lens and dodecapole lens constituting the correction lens system can be lowered. In order to expand the control range, the excitation intensity of each lens can be reduced by increasing the number of quadrupole lenses or twelve-pole lenses used. Can be generated. Therefore, it is composed of a six-stage quadrupole lens and three or four aperture electrodes for inducing the action of the octupole lens. The aperture electrode is provided between the second and third quadrupole lenses and the third stage. In the charged particle optical lens arranged immediately after the quadrupole lens and / or immediately before the fourth-stage quadrupole lens and between the fourth-stage and fifth-stage quadrupole lenses, The excitation polarity of the quadrupole lens is controlled so that the concave / convex / concave / convex lens action on the surface and the convex / concave / concave / convex lens action on the YZ plane are produced, and the charged particle trajectories on the YZ plane are the second and third quadrupoles. By adjusting the excitation intensity of each quadrupole lens and aperture electrode so that the charged particle trajectory on the XZ plane and YZ plane crosses the optical axis after the sixth stage quadrupole lens. The aperture aberration coefficient can be controlled.

  It is composed of a 6-stage quadrupole lens and a 3-stage or 4-stage octupole lens. The octupole lens is placed between the second and third quadrupole lenses and immediately after the third stage quadrupole lens. Or, in a charged particle optical lens disposed immediately before the fourth-stage quadrupole lens and between the fourth-stage and fifth-stage quadrupole lenses, the concave / convex concave / convex lens on the XZ plane with the Z axis as the optical axis The excitation polarity of the quadrupole lens is controlled so that the convex / concave / concave / convex lens action appears on the YZ plane, and the charged particle trajectory on the YZ plane is the optical axis between the second and third quadrupole lenses. The aperture aberration coefficient is controlled by adjusting the excitation intensity of each quadrupole lens and octupole lens so that the charged particle trajectories of the XZ plane and YZ plane intersect the optical axis after the 6th stage quadrupole lens. can do.

  Consists of a 6-stage dodecapole lens and a 3-stage or 4-stage octupole lens. The octupole lens is arranged between the 2nd and 3rd stage 12-pole lenses and between the 3rd stage 12-pole lenses. In the charged particle optical lens immediately after and / or immediately before the fourth stage of the twelve-pole lens and between the fourth and fifth stage of the twelve-pole lens, the Z axis is the optical axis and the XZ plane is used. The excitation polarity of the twelve-pole lens is controlled so that the concave-convex concave-convex lens action and the convex-concave convex-concave convex-concave lens action are exhibited on the YZ plane, and the charged particle trajectory on the YZ plane is the second and third quadrupole lenses. The excitation intensity of each dodecapole lens is adjusted so that the charged particle trajectories of the XZ plane and the YZ plane cross the optical axis after the sixth stage quadrupole lens. The aperture aberration coefficient can be controlled by adjusting the excitation intensity of the pole lens.

In the present invention, the number of steps of the quadrupole lens or twelve-pole lens for controlling the charged particle beam trajectory on the XZ plane and the YZ plane is set to four, so that the concave / convex lens action is on the XZ plane and the convex / concave concave lens action is on the YZ plane. In addition, by controlling the excitation polarity of the quadrupole lens or the twelve-pole lens so that the concave / convex / concave / concave lens action is generated on the XZ plane and the convex / concave / concave / concave lens action is expressed on the YZ plane, In the case of Y, the charged particle trajectory on the YZ plane intersects the optical axis between the first and second quadrupole lenses, and in the case of six, the optical axis intersects between the second and third quadrupole lenses. In the case of four stages, the charged particle beam on the YZ plane is between the third and fourth stage quadrupole lenses, and in the case of six stages, between the fourth and fifth stage quadrupole lenses. The excitation intensity of the quadrupole lens is adjusted so that the off-axis distance of the orbit is larger than the off-axis distance of the orbit on the XZ plane. Here, an aperture electrode for inducing an octupole lens action or an octupole lens is disposed between the quadrupole lens or the dodecapole lens, respectively, so that C _A30 and C _A03 are effectively controlled. In the case of a quadrupole lens or a twelve-pole lens having four stages, it is between the second and third stages. In the case of a quadrupole lens or a six-pole lens having six stages, the third and fourth stages. A CA12 (= CA21) is effectively controlled by arranging an aperture electrode or octupole lens in the X-axis and adjusting the excitation intensity so that the off-axis distances of the charged particle trajectories on the XZ and YZ planes are the same. Therefore, the control range of all aperture aberration coefficients can be expanded. The number of aperture electrodes or octupole lenses arranged between the third and fourth stages in the case of six stages can be selected in accordance with the value of C _A12 (= C _A21 ) to be controlled. This is the reason why the description of the six-stage quadrupole lens or the twelve-pole lens has been made with three or four aperture electrodes, or three or four octupole lenses.

The correction lens system according to the present invention differs from the far-focus type correction lens system with a magnification of | Mx | = | My | = 1, and actively uses the correction lens system as a reduction lens and has a spherical surface of an axisymmetric objective lens. A feature is that a large negative aperture aberration coefficient can be generated and controlled to correct the aberration. As a result, as shown in Fig. 2, a far-focus correction with a magnification of | Mx | = | My | = 1 Compared with the excitation intensity of the lens system and the correction lens system with a magnification of | Mx | = | My | close to 1, the distance between the charged particle orbits of the XZ and YZ surfaces can be reduced, thereby controlling the charged particle beam trajectory. The excitation intensity of the pole lens, the dodecapole lens, and the octupole lens or aperture electrode that controls the aperture aberration coefficient can be reduced. Therefore, it is possible to provide a correction lens system in which the spherical aberration correction coefficient of the axially symmetric objective lens is large and the aperture aberration coefficient that has been difficult to realize so far exceeds −10000 mm. As a result, taking advantage of the ability to generate a large negative aperture aberration coefficient, spherical aberration can be corrected and used even when the magnification of the axially symmetric objective lens placed downstream of the correction lens system is M _O <1. A correction optical system having a large range can be provided.

For example, the spherical aberration coefficient of an axially symmetric objective lens is C _S = 1000 mm, the magnification of the correction lens system placed in the front stage where the magnification is M _O = 0.5 is | Mx | = | My | = 0.3, and the axial chromatic aberration is
When C _CX = C _CY = C mm, the spherical aberration of the axisymmetric objective lens can be reduced to zero by controlling the excitation intensity of the aperture electrode or octupole lens, and the aperture aberration of the correction lens system can be reduced to C _A30 = By adjusting C _A12 (= C _A21 ) = C _A03 = −C _S / M _O ⁴ = −16000 mm, an axially symmetric objective lens having zero spherical aberration can be realized. Here, the total magnification of the charged particle optical system is | M _TOTAL | = | Mx | × M _O = 0.15, and the axial chromatic aberration coefficient of the correction lens affecting the objective lens is also reduced to C × M _O ² = 0.25 C be able to. By realizing a correction lens system capable of generating such a large negative aperture aberration coefficient, the charged particle beam is reduced by the charged particle beam optical lens, and the spherical surface in various charged beam devices used by focusing on a fine probe. The field of application can be expanded as an aberration correction technique.

In the present invention, a four-stage or six-stage quadrupole lens or a dodecapole lens for suppressing the off-axis distance of the charged particle beam trajectory on the XZ plane and the YZ plane in the correction lens, and an octupole for correcting aperture aberration. In a charged particle optical lens system composed of three or four aperture electrodes or octupole lenses for exciting a lens action, the excitation polarity of a quadrupole lens or a dodecapole lens , Convex / concave concave / convex lens action, convex / concave / concave / concave lens action on the YZ surface, or convex / concave / concave / concave / concave lens action is controlled, and aperture aperture coefficient C _A30 , C _A12 (= C _A21 ) In order to control _CA03 effectively, the quadrupole lens or the twelve-pole lens has four stages, the second and third stages, and the sixth stage has the third and fourth stages. Between the opening electrode or eight In the vicinity of the position where the octupole lens action is exhibited, the optical axis is once crossed, and in the case of 4 stages, between the 3rd and 4th stages, and in the case of 6 stages, the 4th stage. Between the fifth stage, the off-axis distance of the charged particle trajectory on the YZ plane is made larger than the off-axis distance of the XZ-plane trajectory, and the XZ plane at the rear stage of the correction lens satisfying the axisymmetric lens condition, By adjusting the excitation intensity of each quadrupole lens or twelve-pole lens so as to focus at the same position on the YZ plane, and adjusting the excitation intensity of the aperture electrode, C _A30 , C _A12 , C _A21 , C _A03 The aperture aberration coefficient can be controlled efficiently.

  In a correction lens system composed of six stages of quadrupole lenses or twelve-pole lenses, the geometric structure and excitation intensity of the second and third stages of quadrupole lenses or twelve-pole lenses, and four stages By making the excitation intensity the same or similar to the geometric structure of the quadrupole lens or the twelve-pole lens of the fifth stage and the fifth stage, the structure can be made symmetric at the center position of the correction lens. Assembling can be simplified. It is also possible to reduce the number of control power supplies for the quadrupole lens or the dodecapole lens. Further, the correction lens system on the incident side and the exit side of the charged particle beam with respect to the center position of the correction lens system has a two-body structure, and a two-stage axial deflector and astigmatism corrector are inserted near the intermediate position. As a result, it is possible to accurately align the entire six-stage correction lens system.

  FIG. 4 shows an embodiment of a correction lens system comprising a four-stage quadrupole lens and three aperture electrodes according to the present invention. Q1 to Q4 are electric field type quadrupole lenses, and A1 to A3 are aperture electrodes. The potential distribution, charged particle beam trajectory, and correction characteristics of the correction lens system are obtained from highly accurate simulation calculations. The excitation intensity of the quadrupole lenses Q1 to Q4 is +0.04300, -0.04050, +0.04570, -0.014646 on the XZ plane, and -0.04300, +0.04050, -0.04570, +0.014646 of the opposite polarity on the YZ plane. It is. The excitation intensity of the aperture electrodes A1 to A3 for obtaining the aperture aberration coefficient CA30 = CA12 = CA21 = CA03 = −554 mm is −0.161877, +0.097013, and −0.135262. 11 is a charged particle beam orbit of the XZ plane, and 12 is a charged particle beam orbit of the YZ plane. 21 is a potential distribution corresponding to the excitation polarity of the quadrupole lens, and 31, 32, and 33 are octupole potential distributions expressed by exciting A1, A2, and A3, respectively. Reference numerals 41, 42, and 43 are axisymmetric potential distributions generated by exciting A1, A2, and A3, respectively. In the drawing, the control power source for exciting the quadrupole lens and the aperture electrode is omitted.

FIG. 5 shows an embodiment in which a large negative aperture aberration coefficient is generated in the correction lens system according to the present invention. Q1 to Q6 are electric field type quadrupole lenses, and A1 to A4 are aperture electrodes. The excitation intensity of the quadrupole lenses of Q1 to Q6 has the opposite polarity on the + Z2 plane, +0.02900, −0.01233, −0.01233, +0.014291, +0.014291, −0.020014 on the XZ plane. Aperture aberration coefficients C _A30 = C _A12 = C _A21 = C _A03 = −26000 mm, the excitation intensity of the aperture electrodes A1 to A4 is −0.1388, +0.2318, +0.2318, −0.146847 . 11 is a charged particle beam orbit of the XZ plane, and 12 is a charged particle beam orbit of the YZ plane. 21 and 22 are potential distributions corresponding to the excitation polarity of the quadrupole lens by the correction lens on the incident side and the emission side with respect to the center position of the correction lens system, and 31, 32, 33, and 34 are A1, A2, and A3, respectively. , Octupole potential distribution expressed by exciting A4. Reference numerals 41, 42, 43, and 44 are axially symmetric potential distributions generated by exciting A1, A2, A3, and A4, respectively. Note that the control power source for exciting the quadrupole lens and the aperture electrode is omitted.

In FIG. 5, since the electric field type quadrupole lens and the aperture electrode constituting the correction lens have the same geometric dimensions and a symmetrical structure at the center of the correction lens, the excitation intensity of the quadrupole lens is set to V _Q2 = V _Q3 , V _Q4 = V _Q5 , and V _A2 = V _A3 in setting the excitation intensity of the aperture electrode. If there is an error in the geometric dimensions, the above relational expression will not hold, so it is obvious that the excitation intensity of each quadrupole lens and aperture electrode must be finely adjusted. For, simplification is possible.

FIG. 6 shows another embodiment of the correction lens system according to the present invention. The structure is the same as the embodiment of FIG. Compared to the embodiment of FIG. 5, an axisymmetric objective lens for forming a probe with zero spherical aberration that achieves an aperture aberration coefficient C _A30 = C _A12 (= C _A21 ) = C _A03 = 0 mm with weak aperture electrode excitation intensity An aberration correction lens system can be used. The excitation intensities of the quadrupole lenses Q1 to Q6 are +0.02900, −0.013365, −0.013365, +0.015437, +0.015437, −0.022102 on the XZ plane, and have opposite polarities on the YZ plane. Aperture aberration coefficient | C _A30 | = | C _A12 | = | C _A21 | = | C _A03 | <0.01 The excitation intensity of the aperture electrodes A1 to A4 to obtain 0.01 mm is −0.017291, +0.017144, +0 00.0144 and -0.018530, excluding the excitation of the first quadrupole lens, and realizing the excitation intensity of the remaining five quadrupole lenses and the four aperture electrodes at 2% or less of the acceleration voltage of the charged particle beam Can do. Here, the control power source for exciting the quadrupole lens and the aperture electrode is omitted.

As can be inferred from the embodiments of FIGS. 4 and 5, the correction lens system according to the present invention is also applied to a charged particle optical lens including a five-stage quadrupole lens and three aperture electrodes for inducing the action of an octupole lens. Can be built. FIG. 7 shows one example. In an embodiment in which aperture electrodes are arranged between the first and second quadrupole lenses, between the second and third stages, and between the third and fourth quadrupole lenses, the Z axis is As the axis, the excitation polarity of the quadrupole lens is controlled so that the concave and convex lens action on the XZ plane and the convex and concave lens action on the YZ plane are expressed, and the charged particle trajectories on the YZ plane are the first and second stages. Excitation intensity of each quadrupole lens and aperture electrode so that the charged particle trajectories of the XZ plane and YZ plane cross the optical axis after the fifth stage quadrupole lens. The aperture aberration coefficient can be controlled by adjusting the angle. The excitation intensity of the quadrupole lenses Q1 to Q5 is +0.03500, −0.03242, +0.02226, +0.02226, −0.020906 on the XZ plane, and has a reverse polarity on the YZ plane. The excitation intensity of the aperture electrodes A1 to A3 for obtaining the aperture aberration coefficient C _A30 = C _A12 = C _A21 = C _A03 = −17000 mm is −0.3340, +0.2300, and −0.1330. This embodiment corresponds to replacing the roles of Q2, A1, Q3, A2, and A3 in FIG. 5 with A1, Q2, and A2 in the embodiment of FIG.

  Magnetic field type quadrupole lenses can be used instead of the electric field type quadrupole lenses Q1 to Q6 in FIGS. However, in the case of a magnetic field type quadrupole lens, this corresponds to the case where the magnetic pole of the quadrupole lens is arranged at a position rotated 45 degrees on the XY plane with respect to the electric field type electrode.

  4, 5, 6, and 7, an electric field type or magnetic field type dodecapole lens capable of correcting an asymmetry and an axis alignment function instead of the electric field type quadrupole lenses Q1 to Q6, and A1 By using an octupole lens instead of the aperture electrode of ~ A4, a similar correction lens can be realized.

  As described above, the octupole lens can be used in place of the aperture electrodes A1 to A4 in the embodiments of FIGS. 4, 5, 6, and 7. Since the octupole lens action can also induce the octupole lens action by the excitation control of individual poles of the electric field type or magnetic field type dodecagon lens, the twelve pole elements can be used instead of the aperture electrodes of A1 to A4. A similar correction lens can also be realized by using a lens.

  4, 5, 6, and 7 can be used as an objective lens for forming a spherical aberration correcting lens system or a probe having zero spherical aberration in an electron beam microanalyzer and an electron beam drawing apparatus. In addition, a high performance can be achieved by using a focused ion beam apparatus using an axially symmetric electric field lens having a large aberration coefficient as compared with a magnetic lens. In particular, in the embodiment shown in FIG. 5, the excitation intensity of the quadrupole lens is 2.9% or less of the acceleration voltage value, and the excitation intensity of the aperture electrode is 23.2% or less. Therefore, in the electron beam apparatus up to about 200 KV acceleration voltage. Can contribute to higher performance.

Use of Axisymmetric Objective Lens and Aberration Correction Lens (Prior Art) Spherical aberration correction lens with four-stage quadrupole lens and three aperture electrodes (prior art) Use of aberration correction lens for axisymmetric objective lens as reduction lens Aperture aberration correction lens using a four-stage quadrupole lens and three aperture electrodes (Example 1) Aperture aberration correction lens using a six-stage quadrupole lens and four aperture electrodes (Example 2) Objective lens with zero spherical aberration by a six-stage quadrupole lens and four aperture electrodes (Example 3) Spherical Aberration Correction Lens (Embodiment 4) with a 5-stage quadrupole lens and three aperture electrodes

Explanation of symbols

1 Aberration correction lens system for charged particle beam
2 Axisymmetric condenser lens
3 Axisymmetric objective lens
11 XZ-plane charged particle beam trajectory
12 YZ-plane charged particle beam trajectory
13 Crossing position of charged particle beam orbit
21,22 Quadrupole potential distribution
31, 32, 33, 34 Octupole potential distribution
41, 42, 43, 44 On-axis potential distribution
Q1, Q2, Q3, Q4, Q5, Q6 Electric field type quadrupole lens
A1, A2, A3, A4 Aperture electrode

Claims (6)

  It is composed of a four-stage quadrupole lens and three aperture electrodes for inducing the action of an octupole lens. The aperture electrodes are arranged between the first and second quadrupole lenses, between the second and third stages, and In the charged particle optical lens arranged between the third and fourth stages, the quadrupole lens is excited so that the Z-axis is the optical axis and the concave / convex lens action is produced on the XZ plane and the convex / concave concave / convex lens action is produced on the YZ plane. Controlling the polarity, the charged particle trajectory on the YZ plane intersects the optical axis near the entrance of the second quadrupole lens, and the charged particle trajectory on the XZ plane and YZ plane after the fourth quadrupole lens. An aperture aberration correction lens, wherein the aperture aberration coefficient is controlled by adjusting the excitation intensity of each quadrupole lens and aperture electrode so as to intersect the optical axis.   It is composed of a four-stage quadrupole lens and a three-stage octupole lens. The octupole lens is arranged between the first and second quadrupole lenses, between the second and third stages, and the third stage. In the charged particle optical lens placed between the 4th stage, the excitation polarity of the quadrupole lens is controlled so that the concave / convex lens action on the XZ plane and the convex / concave concave lens action on the YZ plane are expressed with the Z axis as the optical axis. And only the charged particle trajectory on the YZ plane intersects the optical axis near the octupole lens arranged between the first and second quadrupole lenses, and the XZ plane after the fourth quadrupole lens. An aperture aberration correction lens, wherein the aperture aberration coefficient is controlled by adjusting the excitation intensity of each quadrupole lens and octupole lens so that the charged particle trajectory on the YZ plane intersects the optical axis.   In the charged particle optical lens in which the quadrupole lens in claim 2 is replaced with a twelve-pole lens, the concave / convex concave / convex lens action is expressed on the XZ plane and the convex / concave concave / convex lens action is expressed on the YZ plane with the Z axis as the optical axis. Controls the excitation polarity of the twelve-pole lens, and the charged particle trajectory on the YZ plane intersects the optical axis near the octupole lens arranged between the first and second twelve-pole lenses, and has four stages. The aperture aberration coefficient is adjusted by adjusting the excitation intensity of each dodecapole lens and adjusting the excitation intensity of the octupole lens so that the charged particle trajectories on the XZ and YZ planes intersect the optical axis after the twelve-pole lens of the eye. An aperture aberration correction lens characterized by controlling the aperture.   It consists of a 6-stage quadrupole lens and 3 or 4 aperture electrodes that induce the action of an octupole lens. The aperture electrode is placed between the second and third quadrupole lenses and the third quadrupole element. In a charged particle optical lens arranged immediately after the lens and immediately before the fourth-stage quadrupole lens and between the fourth-stage and fifth-stage quadrupole lenses, the Z axis is the optical axis, and the XZ plane is used. The excitation polarity of the quadrupole lens is controlled so that the concave / convex / concave / convex lens action and the convex / concave / concave / convex lens action are expressed on the YZ plane, and the charged particle trajectories on the YZ plane are the second and third quadrupole lenses. Aperture aberration by adjusting the excitation intensity of each quadrupole lens and aperture electrode so that the charged particle trajectories on the XZ plane and YZ plane intersect the optical axis after the sixth stage quadrupole lens. An aperture aberration correction lens characterized by controlling a coefficient.   It is composed of a 6-stage quadrupole lens and a 3-stage or 4-stage octupole lens. The octupole lens is placed between the second and third quadrupole lenses and immediately after the third stage quadrupole lens. Or, in a charged particle optical lens disposed immediately before the fourth-stage quadrupole lens and between the fourth-stage and fifth-stage quadrupole lenses, the concave / convex concave / convex lens on the XZ plane with the Z axis as the optical axis The excitation polarity of the quadrupole lens is controlled so that the convex / concave / concave / convex lens action appears on the YZ plane, and the charged particle trajectory on the YZ plane is the optical axis between the second and third quadrupole lenses. The aperture aberration coefficient is controlled by adjusting the excitation intensity of each quadrupole lens and octupole lens so that the charged particle trajectories of the XZ plane and YZ plane intersect the optical axis after the 6th stage quadrupole lens. An aperture aberration correction lens.   In the charged particle optical lens in which the quadrupole lens in claim 5 is replaced with a twelve-pole lens, with the Z axis as the optical axis, the concave / convex concave / convex lens action on the XZ plane and the concave / convex concave / convex lens action on the YZ plane are exhibited. In this way, the excitation polarity of the twelve-pole lens is controlled, and the charged particle trajectory on the YZ plane intersects the optical axis between the second and third stage twelve-pole lenses, and the sixth stage twelve-pole element Aperture aberration correction characterized by controlling the aperture aberration coefficient by adjusting the excitation intensity of each dodecapole lens and octupole lens so that the charged particle trajectories on the XZ plane and YZ plane intersect the optical axis after the lens lens.

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