WO2016121226A1

WO2016121226A1 - Charged particle beam device and scanning electron microscope

Info

Publication number: WO2016121226A1
Application number: PCT/JP2015/084074
Authority: WO
Inventors: 和哉熊本; 定好松田
Original assignee: 松定プレシジョン株式会社
Priority date: 2015-01-30
Filing date: 2015-12-03
Publication date: 2016-08-04
Also published as: JP6204388B2; JP2016143514A; TW201721704A; TWI680488B

Abstract

[Problem] To achieve an improvement in the performance of a charged particle beam device. [Solution] This charged particle beam device is provided with: a charged particle source (11); an acceleration power supply (14) which is connected to the charged particle source (11), and which is provided in order to accelerate a charged particle beam (12) emitted from the charged particle source (11); and objective lenses which focus the charged particle beam (12) on a sample (23). The objective lenses include: a first objective lens (18) disposed at the side of the sample (23) on which the charged particle beam (12) is incident; and a second objective lens (26) disposed at the side of the sample (23) opposite to the side on which the charged particle beam (12) is incident. The device is provided with: a function for independently controlling the intensities of the first and second objective lenses (18, 26); a function for simultaneously controlling said intensities; a function for using only the first objective lens (18) to focus the charged particle beam (12) on the sample; a function for using only the second objective lens (26) to focus the charged particle beam (12) on the sample (23); and a function for simultaneously using the first objective lens (18) and the second objective lens (26) to focus the charged particle beam (12) on the sample , while enabling the aperture angle with which the charged particle beam (12) is incident on the sample (23) to be adjusted by the first objective lens (18).

Description

Charged particle beam apparatus and scanning electron microscope

The present invention relates to a charged particle beam apparatus and a scanning electron microscope. More specifically, the present invention relates to a charged particle beam apparatus and a scanning electron microscope that can improve performance.

Examples of the charged particle beam apparatus include a scanning electron microscope (hereinafter referred to as “SEM”), an EPMA (Electron Probe Micro Analyzer), an electron beam welding machine, an electron beam drawing apparatus, and an ion beam microscope. To do.

In the conventional SEM, the lens is devised to shorten the focus from the viewpoint of high resolution. In order to increase the resolution, it is necessary to increase B in the magnetic flux density distribution B (z) on the optical axis of the lens. In order to increase the resolution, it is necessary to reduce the lens thickness, that is, the z width of the B distribution.

Patent Document 1 listed below describes an SEM provided with two objective lenses (a first objective lens and a second objective lens) (hereinafter, a lens on the electron gun side with respect to a sample is used as a first objective lens). The objective lens on the opposite side of the electron gun from the sample is called the second objective lens). In particular, the second objective lens is used in a high-resolution observation mode during low acceleration with an acceleration voltage Vacc of 0.5 to 5 kV. The first objective lens is used in a normal observation mode at an acceleration voltage Vacc of 0.5 to 30 kV.

In the following Patent Document 1, the first objective lens and the second objective lens are not operated simultaneously. The first objective lens and the second objective lens are switched by mode switching means for each mode. Also, in the second embodiment (paragraph [0017]) of Patent Document 1 below, it is described that a part of the magnetic pole of the second objective lens is separated in terms of current potential through an electrical insulating portion. . A voltage Vdecel is applied to a part of the magnetic pole and the sample.

In the first embodiment (paragraphs [0010] to [0016]) of Patent Document 1 below, the secondary electron (or backscattered electron) detector is placed further on the electron gun side than the first objective lens. . Secondary electrons (or reflected electrons) generated in the sample portion pass through the first objective lens and enter the detector.

The following Patent Document 2 also discloses the configuration of the SEM. In the SEM of Patent Document 2, the objective lens is disposed on the opposite side of the electron gun from the sample. The secondary electrons are deflected by the electric field drawn from the secondary electron detector and captured by the secondary electron detector.

JP 2007-250223 A Japanese Patent Laid-Open No. 6-181041

An object of the present invention is to improve the performance of a charged particle beam apparatus and a scanning electron microscope.

In order to achieve the above object, according to one aspect of the present invention, a charged particle source, an acceleration power source connected to the charged particle source, provided to accelerate the charged particle beam emitted from the charged particle source, and the charged particle beam In the charged particle beam apparatus having an objective lens for focusing the sample on the sample, the objective lens has a first objective lens installed on the side where the charged particle beam is incident on the sample, and the charged particle beam on the sample. The charged particle beam device includes a first objective lens power source that varies an intensity of the first objective lens, and an intensity of the second objective lens. And a control device for controlling the first objective lens power source and the second objective lens power source. The control device includes the strength of the first objective lens and the second objective lens power source. Independent control of lens strength A function for simultaneously controlling, a function for focusing the charged particle beam on the sample only by the first objective lens, a function for focusing the charged particle beam on the sample only by the second objective lens, and a first objective The lens and the second objective lens are used at the same time, and the opening angle of the charged particle beam incident on the sample is varied by the first objective lens to focus on the sample.

According to another aspect of the present invention, a charged particle source, an acceleration power source provided to accelerate the charged particle beam emitted from the charged particle source, connected to the charged particle source, and the charged particle beam are focused on the sample. In a charged particle beam apparatus having an objective lens, the objective lens is opposite to a side on which a charged particle beam is incident on a sample and a first objective lens that is installed on the side on which the charged particle beam is incident on the sample. The charged particle beam device includes a first objective lens power source that varies the intensity of the first objective lens, and a second objective lens that varies the intensity of the second objective lens. Objective lens power source, and a first control device that controls the first objective lens power source and the second objective lens power source. The first control device includes the strength of the first objective lens and the second A function that controls the intensity of the objective lens independently The charged particle beam device has a two-stage deflecting member that scans the charged particle beam two-dimensionally, and the two-stage deflecting member includes an upper deflecting member and a lower deflecting member. A second deflection power source that varies the strength or voltage of the upper deflection member, a lower deflection power source that varies the strength or voltage of the lower deflection member, and a second that controls the upper deflection power source and the lower deflection power source. The upper deflection member and the lower deflection member are installed on the side from which the charged particle beam comes from the inside of the first objective lens, and the second control device includes an upper deflection power source and Vary the current ratio or voltage ratio of the lower deflection power supply.

According to still another aspect of the present invention, a charged particle source, an acceleration power source connected to the charged particle source provided to accelerate the charged particle beam emitted from the charged particle source, and the charged particle beam focused on the sample In the charged particle beam apparatus having the objective lens to be operated, the objective lens is provided on the side where the charged particle beam is incident on the sample. The charged particle beam device includes a first objective lens power source that varies the intensity of the first objective lens, and a second objective lens that varies the intensity of the second objective lens. 2 objective lens power supplies, and a first control device for controlling the first objective lens power supply and the second objective lens power supply, wherein the first control device determines the strength of the first objective lens and the second Independently controls the intensity of the objective lens The charged particle beam device has a two-stage deflection member that scans the charged particle beam two-dimensionally, and the two-stage deflection member includes an upper deflection member and a lower deflection member. The upper deflection power source for varying the strength or voltage of the upper deflection member, the lower deflection power source for varying the strength or voltage of the lower deflection member, and the upper deflection power source and the lower deflection power source. The upper deflection member and the lower deflection member are installed on the side from which the charged particle beam comes from the inside of the first objective lens, and the lower deflection members are respectively A plurality of coils having different numbers of turns, and the second control device controls one of the plurality of coils to be used.

Preferably, the deflection member is a deflection coil or a deflection electrode.

Preferably, when only the first objective lens power supply is used, the distance between the first objective lens and the measurement sample surface is made shorter than the distance between the second objective lens and the measurement sample surface, and the second objective lens power supply is used. When only the first objective lens is used, the distance between the second objective lens and the measurement sample surface is made shorter than the distance between the first objective lens and the measurement sample surface.

Preferably, the charged particle beam apparatus further includes a retarding power source for applying a negative potential to the sample and decelerating the charged particle beam.

Preferably, the charged particle beam device further includes a detector arranged so as not to block a trajectory through which the charged particle beam passes, and the detector is attached to a lower portion of the upper device that emits the charged particle beam toward the sample. It is done.

Preferably, the distance between the detector and the second objective lens is 10 mm to 200 mm.

Preferably, the detector is a semiconductor detector, a phosphor emission type detector, or a microchannel plate detector, and is disposed within 3 cm from the trajectory of the charged particle beam.

Preferably, the charged particle beam apparatus further includes a secondary electron detector having an electric field that attracts electrons, so that the electric field generated from the secondary electron detector attracts secondary electrons emitted from the sample by the charged particles. The secondary electron detector is arranged.

Preferably, the second objective lens has a charged particle beam accelerated with an acceleration power source of either −30 kV to −10 kV, from 0 mm when viewed from a position closest to the magnetic pole sample of the second objective lens. Focusing is possible at any height of 4.5 mm.

Preferably, the charged particle beam apparatus further includes an insulating plate disposed on the second objective lens, and a conductive sample stage disposed on the insulating plate, wherein the second objective lens and the conductive sample stage are provided. Is insulated.

Preferably, the conductive sample stage is shaped so as to move away from the insulating plate as it approaches the peripheral edge.

Preferably, the space between the insulating plate and the conductive sample stage is filled with an insulating material.

Preferably, the charged particle beam apparatus further includes a potential plate having an opening in the upper part of the conductive sample stage, and a ground potential, a positive potential, or a negative potential is applied to the potential plate.

Preferably, the opening of the potential plate has a circular shape or a mesh shape with a diameter of 2 mm to 20 mm.

Preferably, the potential plate has a shape that is separated from the conductive sample stage at a place other than near the sample.

Preferably, the charged particle beam apparatus further includes moving means for moving the potential plate.

According to the present invention, it is possible to improve the performance of the charged particle beam apparatus and the scanning electron microscope.

It is a schematic sectional drawing explaining the structure of SEM in the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the case where a 1st objective lens is used and a reflected electron and a secondary electron are detected in the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the case where a 2nd objective lens is used for main focusing and a secondary electron is detected in the 1st Embodiment of this invention. It is a figure for demonstrating the lens part at the time of retarding in the 1st Embodiment of this invention, (a) The equipotential line at the time of retarding, (b) Magnetic flux on the optical axis of a 2nd objective lens It is a figure explaining the velocity of the charged particle at the time of density distribution B (z) and (c) retarding. It is a schematic sectional drawing explaining other structures of the insulation part and sample stand in the 1st Embodiment of this invention. 4A and 4B are diagrams for explaining adjustment of the opening angle α by the first objective lens according to the first embodiment of the present invention, in which (a) simulation data 3 (Vacc = −1 kV), (b) simulation data 4 (Vacc = -10 kV, Vdecel = -9 kV), and (c) Simulation data 5 (Vacc = -10 kV, Vdecel = -9 kV, using the first objective lens). It is a figure for demonstrating adjusting the intersection of deflection | deviation by intensity ratio adjustment of the upper and lower deflection coils of a deflection coil in the 1st Embodiment of this invention. In the 2nd Embodiment of this invention, it is a schematic sectional drawing explaining the simple case without a 1st objective lens. It is sectional drawing which shows an example of the apparatus structure of SEM which concerns on the 4th Embodiment of this invention.

Next, an embodiment of the present invention will be described with reference to the drawings. It should be noted that the following drawings are schematic and dimensions and aspect ratios are different from actual ones.

Further, the embodiments of the present invention described below exemplify apparatuses and methods for realizing the technical idea of the present invention. The technical idea of the present invention does not specify the material, shape, structure, arrangement, etc. of the component parts as follows. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

[First embodiment]

With reference to FIG. 1, a schematic configuration of the SEM according to the first embodiment of the present invention will be described.

The SEM includes an electron source (charged particle source) 11, an acceleration power source 14, a condenser lens 15, an objective lens diaphragm 16, a two-stage deflection coil 17,

objective lenses

18 and 26, and a detector 20. Electron beam apparatus. The acceleration power source 14 accelerates a primary electron beam (charged particle beam) 12 emitted from the electron source 11. The condenser lens 15 focuses the accelerated primary electron beam 12. The objective lens stop 16 removes unnecessary portions of the primary electron beam 12. The two-stage deflection coil 17 scans the primary electron beam 12 on the sample 23 two-dimensionally. The

objective lenses

18 and 26 focus the primary electron beam 12 on the sample 23. The detector 20 detects the signal electrons 21 (secondary electrons 21a and reflected electrons 21b) emitted from the sample 23.

The SEM includes a first objective lens power source 41, a second objective lens power source 42, and a control device 45 as a control unit of the electromagnetic lens. The first objective lens power supply 41 varies the intensity of the first objective lens 18. The second objective lens power source 42 varies the intensity of the second objective lens 26. The control device 45 controls the first objective lens power source 41 and the second objective lens power source 42.

The control device 45 can control the intensity of the first objective lens 18 and the intensity of the second objective lens 26 independently. The control device 45 can control both lenses simultaneously. Further, although not shown in the figure, each power source can be adjusted by being connected to the control device 45.

As the electron source 11, a thermionic emission type (thermionic source type) or a field emission type (Schottky type or cold cathode type) can be used. In the first embodiment, a crystal electron source such as thermionic emission type LaB6 or a tungsten filament is used for the electron source 11. For example, an acceleration voltage of −0.5 kV to −30 kV is applied between the electron source 11 and the anode plate (ground potential). A negative potential is applied to the Wehnelt electrode 13 more than the potential of the electron source 11. Thereby, the amount of the primary electron beam 12 generated from the electron source 11 is controlled. A crossover diameter that is the first minimum diameter of the primary electron beam 12 is formed immediately in front of the electron source 11. This minimum diameter is called the electron source size So.

Accelerated primary electron beam 12 is focused by condenser lens 15. Thereby, the size So of the electron source is reduced. The reduction ratio and the current applied to the sample 23 (hereinafter referred to as probe current) are adjusted by the condenser lens 15. The objective lens aperture 16 removes unnecessary orbital electrons. Depending on the hole diameter of the objective lens aperture 16, the opening angle α of the beam incident on the sample 23 and the probe current are adjusted.

The primary electron beam 12 that has passed through the objective lens stop 16 passes through the first objective lens 18 after passing through the scanning two-stage deflection coil 17. The general-purpose SEM focuses the primary electron beam 12 on the sample 23 using the first objective lens 18. The SEM of FIG. 1 can be used in this way.

In FIG. 1, the configuration from the electron source 11 to the first objective lens 18 constitutes an upper device that emits the primary electron beam 12 toward the sample 23. Further, the lower device is constituted by the potential plate 22 and members disposed below the potential plate 22. The sample 23 is held in the lower device. The upper device has a hole 18c through which the charged particle beam that passes through the upper device is finally emitted. In the first embodiment, the hole 18 c exists in the first objective lens 18. The detector 20 is attached below the hole 18c. The detector 20 also has an opening through which the primary electron beam 12 passes. The detector 20 is attached to the lower part of the first objective lens 18 so that the hole 18c and the opening overlap each other. A plurality of detectors 20 may be attached to the lower part of the first objective lens 18. The plurality of detectors 20 are attached such that the detection part of the detector 20 is as small as possible except for the hole 18c of the upper device, while preventing the path of the primary electron beam 12 from being blocked.

FIG. 2 shows an example in which the first objective lens 18 is used to focus the primary electron beam 12 on the sample 23. In particular, a thick sample 23 is observed by this method.

On the other hand, when the second objective lens 26 is mainly used, the primary electron beam 12 that has passed through the first objective lens 18 is reduced and focused by the second objective lens 26. Since the second objective lens 26 has a stronger magnetic field distribution toward the sample 23 (see FIG. 4B), a low aberration lens is realized. The first objective lens 18 is used to control the opening angle α and adjust the reduction ratio, lens shape, and depth of focus so that an easy-to-view image is obtained. That is, the first objective lens 18 is used to optimize each of these control values. In addition, when the primary electron beam 12 cannot be focused only by the second objective lens 26, assistance for focusing the primary electron beam 12 by the first objective lens 18 can be performed.

Referring to FIG. 3, the operation when no retarding is performed will be described.

When the retarding is not performed, the potential plate 22 in FIG. 1 may be removed. The sample 23 is preferably installed as close to the second objective lens 26 as possible. More specifically, the sample 23 is preferably placed close to the upper part of the second objective lens 26 so that the distance from the upper part (upper surface) of the second objective lens 26 is 5 mm or less.

The primary electron beam 12 scans the sample 23 with energy accelerated by the acceleration power source 14. At that time, the secondary electrons 21a are wound around the magnetic flux by the magnetic field of the second objective lens 26 and rise while spiraling. When the secondary electrons 21a move away from the surface of the sample 23, the magnetic flux density rapidly decreases, so that the secondary electrons 21a are swung away from the swirl and diverge. Captured by 19. That is, the secondary electron detector 19 is arranged such that the electric field generated from the secondary electron detector 19 attracts secondary electrons emitted from the sample by the charged particles. In this way, the number of secondary electrons 21a entering the secondary electron detector 19 can be increased.

Next, an outline of the case of retarding will be described with reference to FIG. In FIG. 4, (a) shows the equipotential lines at the time of retarding, (b) shows the magnetic flux density distribution B (z) on the optical axis of the second objective lens, and (c) shows the charge at the time of retarding. It shows the velocity of the particles.

As shown in FIG. 4B, the magnetic flux density on the optical axis of the second objective lens 26 has a stronger distribution as it is closer to the sample, so the objective lens becomes a low aberration lens. When a negative potential is applied to the sample 23, the primary electron beam 12 is decelerated as it approaches the sample 23 (see FIG. 4C). Since the primary electron beam 12 is more susceptible to the influence of the magnetic field as the speed is lower, it can be said that the second objective lens 26 becomes a stronger lens closer to the sample 23. Therefore, when a negative potential is applied to the sample 23, the second objective lens 26 becomes a lens with further low aberration.

Also, the signal electrons 21 are accelerated by the electric field generated by the retarding voltage of the sample 23, are amplified, and enter the detector 20. Therefore, the detector 20 has high sensitivity. With such a configuration, a high-resolution electron beam apparatus can be realized.

Further, the distance between the first objective lens 18 and the second objective lens 26 is set to 10 mm to 200 mm. More preferably, the thickness is 30 mm to 50 mm. When the distance between the first objective lens 18 and the second objective lens 26 is shorter than 10 mm, the reflected electrons 21b can be detected by the detector 20 placed immediately below the first objective lens 18. However, the secondary electrons 21 a are easily drawn into the first objective lens 18 during the retarding. By separating the distance between the first objective lens 18 and the second objective lens 10 by 10 mm or more, the secondary electrons 21 a are easily detected by the detector 20. In addition, when there is a gap of about 30 mm between the first objective lens 18 and the second objective lens 26, the sample 23 can be easily put in and out.

Next, the configuration of each part will be described in detail. First, the shape of the second objective lens 26 will be described with reference to FIG.

The magnetic pole forming the second objective lens 26 includes a central magnetic pole 26a whose central axis coincides with the ideal optical axis of the primary electron beam 12, an upper magnetic pole 26b, a cylindrical side magnetic pole 26c, and a lower magnetic pole 26d. . The center magnetic pole 26a has a shape with a smaller diameter at the top. The upper part of the center magnetic pole 26a has, for example, a one-stage or two-stage truncated cone shape. The lower part of the center magnetic pole 26a has a cylindrical shape. There is no through hole in the central axis below the central magnetic pole 26a. The upper magnetic pole 26b has a disk shape in which the side close to the center of gravity of the central magnetic pole 26a is thinned toward the center. An opening having an opening diameter d is open at the center of the upper magnetic pole 26b. The tip diameter D of the central magnetic pole 26a is larger than 6 mm and smaller than 14 mm. The relationship between the opening diameter d and the tip diameter D is dD ≧ 4 mm.

Next, specific examples of magnetic poles are shown. The upper surfaces on the sample side of both the center magnetic pole 26a and the upper magnetic pole 26b have the same height. The lower outer diameter of the center magnetic pole 26a is 60 mm. A thin outer diameter is not preferable because it causes a decrease in magnetic permeability.

When the center magnetic pole 26a is D = 8 mm, the opening diameter d of the upper magnetic pole 26b is preferably 12 mm to 32 mm. More preferably, the opening diameter d is 14 mm to 24 mm. As the aperture diameter d increases, the magnetic flux density distribution on the optical axis becomes gentler and wider, and the AT (ampere turn: number of coil turns N [T] and current I [A] necessary for focusing the primary electron beam 12 is increased. Product) can be reduced. However, when the relationship between the opening diameter d and the tip diameter D is d> 4D, the aberration coefficient increases. Here, the opening diameter d of the upper magnetic pole 26b is 20 mm, and the outer diameter of the side magnetic pole 26c is 150 mm. A through hole may be provided at the center of the central magnetic pole 26a.

Here, for example, when the primary electron beam 12 is focused on the sample 23 having a thickness of 5 mm even at a high acceleration voltage of 30 kV, the tip diameter D is preferably larger than 6 mm and smaller than 14 mm. If D is too small, the magnetic pole is saturated and the primary electron beam 12 is not focused. On the other hand, when D is increased, performance is deteriorated. On the other hand, if the difference in size between d and D is smaller than 4 mm, the magnetic poles are too close to be saturated and the primary electron beam 12 is not focused. Further, when the distance between the first objective lens 18 and the second objective lens 26 is 10 mm or less, workability is deteriorated. When this distance is longer than 200 mm, the opening angle α becomes too large. In this case, in order to optimize the aberration, the first objective lens 18 needs to be adjusted to reduce α, and the operability is deteriorated.

Also, for example, when the acceleration voltage is 5 kV or less and the sample 23 is thin, the tip diameter D may be 6 mm or less. However, for example, when the acceleration voltage is 5 kV, if D is 2 mm, d is 5 mm, the thickness of the sample 23 is 5 mm, and only the second objective lens 26 is used, the magnetic pole is saturated and the primary electron beam 12 does not converge. However, if the sample 23 is limited to a thin one, the performance of the lens can be further improved.

As a method for applying a potential to the sample 23, a part of the magnetic poles of the second objective lens 26 is sandwiched between the electrically insulating portions and part of the magnetic poles are lifted from the ground potential, and a retarding voltage is applied to the sample 23 and a part of the magnetic poles. Can also be given. However, in this case, if a non-magnetic material is sandwiched in the magnetic circuit, the magnetic lens becomes weak. Further, when the retarding voltage is increased, discharge occurs. If the electrical insulating part is thickened, there is a problem that the magnetic lens becomes weaker.

As shown in FIG. 1, it is desirable to place a seal portion 26f (for example, copper, aluminum, or monel) made of a nonmagnetic material between the upper magnetic pole 26b and the central magnetic pole 26a. The seal part 26f makes the space between the upper magnetic pole 26b and the central magnetic pole 26a vacuum-tight with an O-ring or brazing. In the second objective lens 26, the vacuum side and the atmosphere side are hermetically separated by the upper magnetic pole 26b, the seal portion 26f, and the central magnetic pole 26a. Although not shown in the drawing, the upper magnetic pole 26b and the vacuum vessel are coupled so as to be airtight by an O-ring. In this way, the second objective lens 26 can be exposed to the atmosphere except for the vacuum side surface. Therefore, it becomes easy to cool the second objective lens 26.

It is possible to put the second objective lens 26 in the vacuum vessel, but the degree of vacuum becomes worse. This is because if the coil part 26e is on the vacuum side, it becomes a gas emission source. Further, if the vacuum side and the atmosphere side are not hermetically separated in this way, the gas will pass through the place where the second objective lens 26 and the insulating plate 25 are in contact with each other when evacuation is performed. There's a problem.

The coil portion 26e can be set to a coil current of 6000AT, for example. When the coil generates heat and becomes high temperature, the coating of the winding may melt and cause a short circuit. Since the second objective lens 26 can be exposed to the atmosphere, the cooling efficiency is increased. For example, when the base of the lower surface of the second objective lens 26 is made of aluminum, the base can be used as a heat sink. Then, the second objective lens 26 can be cooled by an air cooling fan or water cooling. By performing hermetic separation in this way, the second objective lens 26 with strong excitation can be obtained.

Referring to FIG. 1, the retarding unit will be described.

The insulating plate 25 is placed on the second objective lens 26. The insulating plate 25 is, for example, a polyimide film or a polyester film having a thickness of about 0.1 mm to 0.5 mm. Then, a non-magnetic conductive sample stage 24 is placed thereon. The sample table 24 is, for example, an aluminum plate having a bottom surface of 250 μm, and is processed into a curved shape that is separated from the insulating plate 25 as the peripheral edge approaches the peripheral edge. The sample table 24 may be further filled with an insulating material 31 in a gap between the curved surface portion and the insulating plate 25. In this way, the withstand voltage between the second objective lens 26 and the sample stage 24 is increased, and it can be used stably. The planar shape of the sample stage 24 is circular, but may be any planar shape such as an ellipse or a rectangle.

The sample 23 is placed on the sample table 24. The sample stage 24 is connected to a retarding power source 27 in order to give a retarding voltage. The power source 27 is a power source whose output that can be applied from 0 V to −30 kV, for example, is variable. The sample stage 24 is connected to a sample stage stage plate 29 made of an insulator so that the position can be moved from outside the vacuum. Thereby, the position of the sample 23 can be changed. The sample stage stage plate 29 is connected to an XY stage (not shown) and can be moved from outside the vacuum.

A conductive plate having a circular opening (hereinafter referred to as potential plate 22) is disposed on the sample 23. The potential plate 22 is installed perpendicular to the optical axis of the second objective lens 26. The potential plate 22 is disposed so as to be insulated from the sample 23. The potential plate 22 is connected to a potential plate power source 28. The potential plate power supply 28 is a power supply whose output is variable, for example, from 0 V and −10 kV to +10 kV. The diameter of the circular opening of the potential plate 22 may be about 2 mm to 20 mm. More preferably, the diameter of the opening may be 4 mm to 12 mm. Alternatively, the portion of the potential plate 22 through which the primary electron beam 12 or the signal electrons 21 pass may be formed into a conductive mesh shape. The mesh portion of the mesh is preferably made thin so that electrons can easily pass therethrough so that the aperture ratio is increased. The potential plate 22 is connected to an XYZ stage (not shown) so that the position can be moved from outside the vacuum for adjusting the central axis.

The periphery of the sample stage 24 has a thickness on the potential plate 22 side. For example, when the potential plate 22 is flat, the potential plate 22 is close to the sample table 24 at the periphery of the sample table 24. Then, it becomes easy to discharge. Since the potential plate 22 has a shape away from the conductive sample stage 24 at a place other than the vicinity of the sample 23, the withstand voltage with respect to the sample stage 24 can be increased.

The potential plate 22 is arranged so as not to be discharged by separating the sample 23 from a distance of about 1 mm to 15 mm. However, it should be arranged so that it is not too far apart. The purpose is to overlap the deceleration electric field at a position where the magnetic field generated by the second objective lens 26 is strong. If the potential plate 22 is placed far from the sample 23, or if the potential plate 22 is not present, the primary electron beam 12 is decelerated before being focused by the second objective lens 26, thereby reducing the aberration. The effect of doing is reduced.

This will be described with reference to FIG. 4 (FIG. 4 is an explanatory diagram corresponding to simulation data 4 described later). FIG. 4A is a diagram for explaining equipotential lines during retarding.

If the opening of the potential plate 22 is too large and the distance between the sample 23 and the potential plate 22 is too close, the equipotential lines are distributed far beyond the opening of the potential plate 22 toward the electron gun. In this case, the primary electrons may be decelerated before reaching the potential plate 22. As the opening diameter of the potential plate 22 is smaller, there is an effect of reducing the leakage of the electric field. However, it is necessary to prevent the signal electrons 21 from being absorbed by the potential plate 22. Therefore, it is possible to adjust the potential difference between the sample 23 and the potential plate 22 within a range in which no discharge occurs, to adjust the distance between the sample 23 and the potential plate 22, and to appropriately select the opening diameter of the potential plate 22. It becomes important.

4B is a diagram for explaining the magnetic flux density distribution B (z) on the optical axis of the second objective lens 26. FIG. The vertical axis is B (z), the horizontal axis is coordinates, and the surface of the second objective lens 26 is the origin (−0). It is shown that B (z) increases rapidly as the distance from the second objective lens 26 increases.

(C) of FIG. 4 is a figure explaining the speed of the charged particle at the time of retarding. It is shown that the velocity of the charged particle beam is decelerating immediately before the sample.

By placing the potential plate 22 near the sample 23, the velocity of the primary electrons does not change so much until near the potential plate 22. The speed of the primary electrons decreases as the distance from the potential plate 22 approaches the sample 23, and the primary electrons are easily affected by the magnetic field. Since the magnetic field generated by the second objective lens 26 is stronger as it is closer to the sample 23, both effects are combined, and the closer to the sample 23, the stronger the lens and the smaller the aberration.

If the retarding voltage can be brought close to the accelerating voltage while increasing the accelerating voltage as much as possible, the irradiation electron energy can be reduced and the depth at which the electrons enter the sample 23 can be reduced. This enables high-resolution observation of the surface shape of the sample. Furthermore, since the aberration can be reduced, an SEM with high resolution and low acceleration can be realized.

In the first embodiment, the breakdown voltage between the sample 23 and the potential plate 22 can be easily increased. The distance between the first objective lens 18 and the second objective lens 26 can be a distance of 10 mm to 200 mm. Therefore, for example, in the case of the flat sample 23, if the distance between the sample 23 and the potential plate 22 is about 5 mm, a potential difference of about 10 kV can be applied to the sample 23 and the potential plate 22 relatively easily. In the case of the sample 23 having a sharp portion, it is necessary to appropriately select the distance and the opening diameter so as not to discharge.

Fig. 5 shows examples of different sample arrangements. As shown in FIG. 5, a cylindrical discharge prevention electrode 30 having a cylindrical shape whose upper surface is R-processed may be installed around the sample 23 on the sample stage 24 to make it difficult to discharge. The cylindrical discharge preventing electrode 30 is also useful for smoothing equipotential lines on the sample and alleviating the deviation of the focusing point due to the rattling of the sample 23.

As the detector 20 in the first embodiment, a semiconductor detector 20, a microchannel plate detector 20 (MCP), or a phosphorescent-type Robinson detector 20 is used. At least one of these is arranged directly below the first objective lens 18. The secondary electron detector 19 is arranged so that the electric field is applied above the sample 23 so as to collect the secondary electrons 21a.

The semiconductor detector 20, the MCP detector 20, or the Robinson detector 20 is in contact with the sample side of the first objective lens 18 and is disposed within 3 cm from the optical axis. More preferably, a detector 20 is used in which the center of the detection unit is placed on the optical axis and an opening through which primary electrons pass is provided at the center. The reason why it is set within 3 cm from the optical axis is that when retarding, signal electrons travel close to the optical axis.

The primary electron beam 12 is obtained by subtracting the retarding voltage Vdecel from the acceleration voltage used for acceleration by the acceleration power supply 14 (Vacc), that is, energy obtained by applying an electronic charge to − (Vacc−Vdecel) [V]. 23 is scanned. At that time, signal electrons 21 are emitted from the sample 23. Depending on the values of the acceleration voltage and the retarding voltage, the way of being affected by electrons differs. The reflected electrons 21 b are subjected to a rotating force by the magnetic field of the second objective lens 26 and at the same time are accelerated due to the electric field between the sample 23 and the potential plate 22. For this reason, the spread of the radiation angle of the reflected electrons 21b is narrowed, and the reflected electrons 21b are easily incident on the detector 20. The secondary electrons 21 a are also subjected to a rotating force by the magnetic field of the second objective lens 26, and at the same time are accelerated due to the electric field between the sample 23 and the potential plate 22, It is incident on the detector 20 below. Since both the secondary electrons 21a and the reflected electrons 21b are accelerated and the energy is amplified and enters the detector 20, the signal becomes large.

In general-purpose SEM, it is usual to focus electrons with a lens such as the first objective lens 18. The first objective lens 18 is usually designed to have a higher resolution as the sample 23 is closer to the first objective lens 18. However, the semiconductor detector 20 or the like has a thickness, and the sample 23 needs to be separated from the first objective lens 18 by the thickness. If the sample 23 is too close to the first objective lens 18, the secondary electrons 21 a will not easily enter the secondary electron detector 19 outside the first objective lens 18. Therefore, in the general-purpose SEM, a thin semiconductor detector 20 that is disposed at a position immediately below the first objective lens 18 and has an opening through which primary electrons pass is used. The sample 23 is placed with a slight gap so as not to hit the detector 20. Therefore, the sample 23 and the first objective lens 18 are slightly separated from each other, and it is difficult to improve the performance.

In the first embodiment, when the second objective lens 26 is used as a main lens, the sample 23 can be placed close to the second objective lens 26. Then, the distance between the first objective lens 18 and the second objective lens 26 can be increased. For example, if the distance is 30 mm, the MCP detector 20 having a thickness of about 10 mm can be placed immediately below the first objective lens 18. Naturally, a Robinson type detector 20 or a semiconductor detector 20 can also be provided. There is also a method in which a reflecting plate is placed, the signal electrons 21 are applied to the reflecting plate, and electrons generated or reflected therefrom are detected by a second secondary electron detector. Various signal electron detectors 20 having the same function can be installed.

Next, the opening angle α related to the performance of the lens optical system will be described.

The beam diameter when the primary electron beam 12 hits the sample 23 is called the probe diameter. The following formula is used as a formula for evaluating the probe diameter. In the following formula, the number following “^” is a power index.

[Equation 1] Probe diameter Dprobe = sqrt [Dg ^ 2 + Ds ^ 2 + Dc ^ 2 + Dd ^ 2] [nm]

[Equation 2] Reduced diameter of light source Dg = M1, M2, M3, So = M, So [nm]

[Equation 3] Spherical aberration Ds = 0.5 Cs · α 3 [nm]

[Equation 4] Chromatic aberration Dc = 0.5 Cc · α · ΔV / Vi [nm]

[Equation 5] Diffraction aberration: Dd = 0.75 × 1.22 × Lambda / α [nm]

Here, the size of the electron source is So, the reduction ratio of the first-stage condenser lens 15a is M1, the reduction ratio of the second-stage condenser lens 15b is M2, and the first objective lens 18 and the second objective lens 26 are formed. The reduction ratio of the lens is M3, the total reduction ratio M = M1 × M2 × M3, the spherical aberration coefficient is Cs, the chromatic aberration coefficient is Cc, the opening angle of the primary electron beam 12 on the sample surface is α, and the irradiation voltage (primary electrons are the sample) Is a voltage corresponding to the energy spread of the primary electron beam 12, ΔV, and the electron wavelength is Lambda.

An example of SEM performance using a thermionic emission electron source will be described using simulation data. The first objective lens 18 in FIG. 1 is an out-lens type.

The case where the primary electron beam 12 is focused by the first objective lens 18 is shown. This corresponds to a general purpose SEM.

Suppose that ΔV of the primary electron beam 12 is 1 V and the size So of the electron source is 10 μm. It is assumed that M1 × M2 = 0.00282. An objective lens aperture 16 having a hole diameter of 30 microns is placed to remove unnecessary orbital electrons. The opening angle α of the beam incident on the sample 23 and the probe current can be adjusted by the hole diameter of the objective lens aperture 16. WD is 6 mm and acceleration voltage Vacc = −30 kV (Vi = 30 kV). When calculating simulation,

(Simulation data 1)

Dprobe = 4.4 nm, Dg = 1.59, Ds = 3.81, Dc = 0.916, Dd = 1.25,

Cs = 54.5 mm, Cc = 10.6 mm, α = 5.19 mrad, M3 = 0.0575.

Next, a case where the primary electron beam 12 is focused by the second objective lens 26 will be described.

In the configuration of FIG. 1, the distance between the second objective lens 26 and the first objective lens 18 is 40 mm. The second objective lens 26 has D = 8 mm and d = 20 mm, and the hole diameter of the objective lens aperture 16 is 21.8 microns in order to adjust α. At this time, the condenser lens 15 is weakened and adjusted so that the probe current amount does not change compared to the case of the general-purpose SEM. Other conditions are the same. When simulating the performance at the position of Z = -4mm,

(Simulation data 2)

Dprobe = 1.44 nm, Dg = 0.828, Ds = 0.657, Dc = 0.503, Dd = 0.729,

Cs = 1.87 mm, Cc = 3.391 mm, α = 8.89 mrad, M3 = 0.0249.

As described above, it can be seen that the use of the second objective lens 26 significantly improves the performance of the SEM.

Also, Dg is smaller when focusing with the second objective lens 26 than when focusing with the first objective lens 18. This indicates that when the probe diameters are made equal, the condenser lens 15 can be weakened compared to when focusing with the first objective lens 18. Therefore, it can be seen that the probe current can be increased by using the second objective lens 26 as compared with the general-purpose SEM.

Next, a case where the second objective lens 26 is used without using the first objective lens 18 and the acceleration voltage Vacc is set to −1 kV (Vi = 1 kV) (retarding voltage is set to 0 V) will be described. The condenser lens 15 is adjusted so that the probe current does not change (however, the trajectory and beam amount from the electron gun are the same as when −30 kV). Other conditions are the same. The following is the simulation data.

(Simulation data 3)

The result is shown in FIG.

Dprobe = 15.6 nm, Dg = 0.828, Ds = 0.657, Dc = 15.1, Dd = 3.99,

Cs = 1.87 mm, Cc = 3.39 mm, α = 8.89 mrad, M3 = 0.0249.

In this case, Cs, Cc, α, M3, and Ds are the same as the simulation data 2. Since ΔV / Vi becomes large, the probe diameter becomes very large.

Next, an example in which the potential plate 22 is arranged on the top of the sample 23 will be described. The opening diameter of the potential plate 22 is 5 mm, and the sample 23 is 6 mm. The sample measurement surface is Z = −4 mm (distance from the second objective lens 26). The distance between the sample stage 24 and the potential plate 22 is 8 mm, and the distance between the sample measurement surface and the potential plate 22 is 5 mm.

The acceleration voltage Vacc is −10 kV, the potential plate 22 is 0 V potential, the sample 23 is retarded at Vdecel = −9 kV, and the numerical value when Vi = 1 kV is simulated. Here, the first objective lens 18 is not used, and only the second objective lens 26 is used for focusing.

(Simulation data 4)

The result is shown in FIG.

Dprobe = 5.72 nm, Dg = 0.924, Ds = 2.93, Dc = 4.66, Dd = 1.26,

Cs = 0.260 mm, Cc = 0.330 mm, α = 28.2 mrad, M3 = 0.0247.

When the retarding voltage Vdecel is −9 kV, the energy of the irradiated electrons is 1 keV. Compared to when the acceleration voltage is -1 kV, the probe diameter is greatly improved.

Next, an example is shown in which the first objective lens 18 is added to this condition and used, and the intensity is adjusted appropriately (taken as 0.37 times the AT (ampere turn) required in the simulation data 1).

(Simulation data 5)

The result is shown in FIG.

Dprobe = 4.03 nm, Dg = 1.60, Ds = 0.682, Dc = 2.92, Dd = 2.17

Cs = 0.112 mm, Cc = 0.357 mm, α = 16.3 mrad, M3 = 0.0430.

Here you can see that Dprobe is decreasing. In the simulation data 4, Dc (= 4.66) jumped and increased. Therefore, α can be reduced by adding a little first objective lens 18. Dc depends on Cc and α from the above [Equation 4]. Cc is a little larger, but α is considerably smaller. Therefore, Dc is small. [Equation 1] shows that Dprobe can be reduced by using the first objective lens 18.

FIG. 6B shows α = 28.2 mrad compared to α = 8.89 mrad in FIG. 6A, which is a large value due to the retarding. That is, it turns out that it is a strong lens. Also, it can be seen that Dd is also reduced. In FIG. 6C, it can be seen that α is decreased by adjusting α with the first objective lens 18.

Here, it is important to adjust the α by reducing the hole diameter of the objective lens aperture 16, but in this case, the probe current is reduced. However, even if α is adjusted using the first objective lens 18, the probe current does not decrease. Therefore, the secondary electrons 21a and the reflected electrons 21b generated from the sample 23 are not reduced.

Also, when the sensitivity of the detector 20 is improved by applying the retarding voltage, the probe current can be reduced. Furthermore, the hole diameter of the objective lens aperture 16 can be reduced to reduce α. In addition, the reduction ratio M1 × M2 by the condenser lens 15 can be reduced. Therefore, adjustment is necessary because there is a balance with Dg, Ds, Dc, and Dd, but the probe diameter may be further reduced. The probe diameter can be optimized by the objective lens aperture 16 and the first objective lens 18.

Also, depending on the sample 23, if the lens has a shallow depth of focus, the lens may be focused only on the top surface or the bottom surface of the unevenness. In such a case, even if the probe diameter is the same, the smaller the α is, the deeper the focal depth becomes, and the better the appearance may be. The first objective lens 18 can be used to optimize the image so that it can be seen easily.

Next, specific examples of various usages of the apparatus in the first embodiment will be shown.

FIG. 6B shows a simulation in which the acceleration voltage Vacc is set to −10 kV and the sample 23 is retarded at −9 kV. For example, the acceleration voltage Vacc is set to −4 kV and the sample 23 is set to −3.9 kV. = 100V. The closer the ratio of the acceleration voltage and the retarding voltage is to 1, the smaller the aberration coefficient. In the above description, the case where D = 8 mm and d = 20 mm is shown for the magnetic pole of the second objective lens 26. However, if D = 2, d = 6, etc., there are limitations on the sample height and acceleration voltage. However, the performance can be improved.

In addition, when the acceleration voltage is −10 kV and there is no retarding, the secondary electron 21 a can be detected by the secondary electron detector 19, but cannot be detected by the semiconductor detector 20. However, if the acceleration voltage is −20 kV and the retarding voltage is −10 kV, the secondary electrons 21 a enter the semiconductor detector 20 with an energy of about 10 keV and can be detected.

Further, when the acceleration voltage is set to -10.5 kV and the retarding voltage is set to -0.5 kV, the secondary electrons 21a cannot be detected with high sensitivity by the semiconductor detector 20. However, at this time, the secondary electrons 21 a can be detected by the secondary electron detector 19. That is, the secondary electrons 21a can be captured by the secondary electron detector 19 when the retarding voltage is low, and the amount that can be detected by the semiconductor detector 20 increases as the retarding voltage is gradually increased. As described above, the secondary electron detector 19 is also useful during adjustment in which the retarding voltage is raised while focusing.

The second objective lens 26 according to the first embodiment is designed so as to be able to focus 30 keV primary electrons at Z = −4.5 mm. If the sample position is close to the second objective lens 26, for example, at the position of Z = −0.5 mm, primary electrons of 100 keV can also be focused. When the retarding is not performed, the insulating plate 25 (insulating film) may not be placed on the second objective lens 26. Therefore, in this case, the second objective lens 26 can sufficiently focus the primary electron beam 12 having an acceleration voltage of −100 kV. Preferably, the second objective lens 26 has a charged particle beam accelerated with an acceleration power source of either −30 kV to −10 kV, as viewed from a position closest to the magnetic pole sample of the objective lens, and is 0 mm to 4.5 mm. Are designed to be focusable at any height position.

The case where the acceleration voltage is −15 kV, the sample 23 is −5 kV, and −6 kV is applied to the potential plate 22 will be described. The primary electrons are 10 keV when they hit the sample 23. The energy of the secondary electrons 21a emitted from the sample 23 is 100 eV or less. Since the potential of the potential plate 22 is 1 kV lower than the potential of the sample 23, the secondary electrons 21 a cannot exceed the potential plate 22. Therefore, the secondary electrons 21a cannot be detected. The reflected electrons 21 b having an energy of 1 keV or more emitted from the sample 23 can pass through the potential plate 22. Furthermore, there is a potential difference of 6 kV between the potential plate 22 and the detector 20 below the first objective lens 18, and the reflected electrons 21 b are accelerated and enter the detector 20. By making the voltage of the potential plate 22 adjustable in this way, the potential plate 22 can be used as an energy filter, and the sensitivity can be increased by further accelerating the signal electrons 21.

Next, the case where the sample height is 7 mm, for example, will be described.

At this time, even when the retarding is performed, the measurement is performed at a position of about Z = −7.75 mm including the thickness of the insulating plate 25 and the sample stage 24 from the upper magnetic pole 26b. In this case, the primary electron beam 12 of 30 keV cannot be focused only by the second objective lens 26. However, the primary electron beam 12 can be focused with the help of the first objective lens 18 without lowering the acceleration voltage.

Further, depending on the height of the sample 23, there are cases where it is possible to observe with better performance by focusing only with the first objective lens 18 (see FIG. 2). Thus, the optimal usage can be selected depending on the sample 23.

In the above description, the case where the distance between the first objective lens 18 and the second objective lens 26 is 40 mm has been described, but this distance may be fixed or movable. The smaller the distance between the first objective lens 18 and the second objective lens 26, the smaller the reduction ratio M3. The opening angle α can be increased. Α can be adjusted by this method.

Also, when the retarding voltage is high, the signal electrons 21 pass near the optical axis and easily enter the opening for the primary electrons of the detector 20 to pass. Therefore, the smaller the opening of the detector 20, the better. Sensitivity is good when the opening of the detector 20 is about Φ1 to Φ2 mm. By adjusting the aperture diameter and height of the potential plate 22 and slightly shifting the position of the potential plate 22 from the optical axis, the trajectory of the signal electrons 21 is adjusted to improve the sensitivity so that the signal electrons 21 hit the detector 20. There is a way. Further, it is also possible to insert an E-Crosby (ExB) to be applied by directing an electric field and a magnetic field between the first objective lens 18 and the second objective lens 26, and the signal electrons 21 may be bent slightly. Since the traveling direction of the primary electrons and the traveling direction of the signal electrons 21 are opposite, a weak electric field and magnetic field may be provided to bend the signal electrons 21 slightly. If it is slightly bent, it can be detected without entering the opening at the center of the detector 20. Alternatively, an electric field may be applied between the first objective lens 18 and the second objective lens 26 from the side with respect to the optical axis. Even if it does in this way, a primary electron is hard to be influenced, and if it is only a lateral shift, there will be little influence on an image. For example, the trajectory of the signal electrons 21 can be controlled using an electric field generated by the collector electrode of the secondary electron detector 19 or the like.

In FIG. 3, the second objective lens 26 is used as the main lens. When the sample stage 24 is at the ground potential, the secondary electrons 21 a are detected by the secondary electron detector 19. The reflected electrons 21b are detected by the semiconductor detector 20, the Robinson detector 20, or the like. When the sample 23 and the detector 20 are separated from each other by about 10 mm to 20 mm, they can be detected with high sensitivity. However, if the distance is approximately 40 mm, the number of reflected electrons 21b that do not enter the detector 20 increases, and the amount of reflected electrons 21b detected decreases. At this time, when a retarding voltage is applied to the sample 23, the secondary electrons 21a are detected by the semiconductor detector 20, the Robinson detector 20, or the like. Further, by applying the retarding voltage, the spread of the reflected electrons 21b can be suppressed, and the semiconductor detector 20 or the Robinson detector 20 can be detected with high sensitivity. Thus, retarding can be used even when the potential plate 22 is not provided.

FIG. 2 shows a case where the sample 23 is thick and the first objective lens 18 is used as the objective lens. In FIG. 2, the stage which moves the potential plate 22 can be utilized and used as a sample stage. This XY moving stage can also move in a direction approaching the first objective lens 18. Thereby, the apparatus is used like a general-purpose SEM. The reflected electrons 21b are detected by the semiconductor detector 20 or the Robinson detector 20, and the secondary electrons 21a are detected by the secondary electron detector 19. Usually, the sample 23 is at the ground potential, but it can be simply retarded (retarding can be performed without the potential plate 22).

When only the second objective lens power source 42 is used, the apparatus is arranged so that the distance between the second objective lens 26 and the sample measurement surface is closer than the distance between the first objective lens 18 and the sample measurement surface. Thus, when only the first objective lens power supply 41 is used, the distance between the first objective lens 18 and the sample measurement surface is closer than the distance between the second objective lens 26 and the sample measurement surface. The device is configured.

When the retarding is performed in FIG. 1, the potential of the sample 23 becomes negative. It is also possible to apply a positive voltage to the potential plate 22 while keeping the sample 23 at the GND level (this method is called a boosting method). It is also possible to apply a negative voltage to the sample 23 and apply a positive potential to the potential plate 22 to further improve the performance as a low acceleration SEM. As an example, a case where the first objective lens 18 is set to the ground potential, +10 kV is applied to the potential plate 22, and the sample 23 is set to the ground potential will be described. The acceleration voltage is -30 kV. The primary electrons are 30 keV when passing through the first objective lens 18, are accelerated toward the potential plate 22 from the first objective lens 18, and decelerate toward the sample 23 around the potential plate 22. The simulation data in this case is shown below. The shapes of the sample 23 and the potential plate 22 are the same as in the simulation data 4.

(Simulation data 6)

Dprobe = 1.31 nm, Dg = 0.904, Ds = 0.493, Dc = 0.389, Dd = 0.710,

Cs = 1.29 mm, Cc = 2.56 mm, α = 9.13 mrad, M3 = 0.0244.

According to the above results, the probe diameter is improved compared to the case without boosting (simulation data 2).

The signal electrons 21 are accelerated between the sample 23 and the potential plate 22, but are decelerated between the potential plate 22 and the detector 20. When the detector 20 is the semiconductor detector 20, the reflected electrons 21b can be detected. However, since the semiconductor detector 20 is at the ground potential, the secondary electrons 21a are decelerated and cannot be detected. The secondary electrons 21 a can be detected by the secondary electron detector 19. If the retarding voltage is applied to the sample 23, the semiconductor detector 20 can also detect the secondary electrons 21a.

Next, with reference to FIG. 7, the movement of the intersection of the deflection trajectories by adjusting the two-stage deflection coil 17 will be described. The two-stage deflection coil 17 scans the sample 23 two-dimensionally. The electron source side of the two-stage deflection coil 17 is called an upper stage deflection coil 17a, and the sample side is called a lower stage deflection coil 17b.

As shown in FIG. 1, the two-stage deflection coil 17 includes an upper deflection power source 43 that varies the strength of the upper deflection coil 17a, a lower deflection power source 44 that varies the strength of the lower deflection coil 17b, and an upper deflection power source 43. And a control device 45 that controls the lower deflection power source 44.

The upper deflection coil 17a and the lower deflection coil 17b are installed on the side from which the primary electron beam 12 comes in as viewed from the inside of the first objective lens 18 (upstream from the lens main surface of the first objective lens 18). When the lower deflection member is placed at the position of the lens main surface, it is installed upstream of the outer magnetic pole 18b (see FIG. 7; reference numeral 18a in FIG. 7 indicates the inner magnetic pole). The use current ratio between the upper deflection power supply 43 and the lower deflection power supply 44 is variable by the control device 45.

7A, the two-stage deflection coil 17 forms an orbit where electrons pass near the intersection of the optical axis and the main surface of the first objective lens 18. When the first objective lens 18 is used as the main lens (FIG. 2), the setting is performed as described above. When the second objective lens 26 is used as the main lens, the deflection aberration increases as shown in FIG. 7A, and the lower magnification image is distorted. When the second objective lens 26 is used as the main lens, as shown in FIG. 7B, the intensity ratio of the upper deflection coil 17a and the lower deflection coil 17b is such that electrons are emitted from the main surface of the second objective lens 26 and light. The trajectory is adjusted to pass near the intersection with the axis. The adjustment is performed by a control device 45 that adjusts a use current ratio between the upper deflection power supply 43 and the lower deflection power supply 44. By doing so, image distortion is reduced. Instead of shifting the intersection (crossing point) of the deflection trajectory by adjusting the current ratio used, a method of switching coils with different numbers of turns with a relay or the like (providing a plurality of coils with different numbers of turns and using a coil with a controller) In the case of an electrostatic lens, a method of switching the voltage (a method of changing the working voltage ratio) may be employed.

As shown in FIG. 7, the deflection coil 17 may be disposed in a gap in the first objective lens 18. The deflection coil 17 may be in the first objective lens 18 or may be positioned further upstream of the charged particle beam than that as shown in FIG. When electrostatic deflection is employed, a deflection electrode is employed instead of the deflection coil.

[Second Embodiment]

Referring to FIG. 8, a simple apparatus configuration without the first objective lens 18 will be described.

Here, the semiconductor detector 20 is placed under the lower deflection coil 17b. When the first objective lens 18 is not provided, the distance between the lower deflection coil 17b and the second objective lens 26 can be shortened accordingly. Such an apparatus configuration is suitable for downsizing. Compared to the first embodiment, the apparatus can be similarly used in the second embodiment, except that the first objective lens 18 is used. The distance between the detector 20 and the second objective lens 26 is set to be 10 mm to 200 mm apart.

In the apparatus of FIG. 8, an upper apparatus that emits the primary electron beam 12 toward the sample 23 is configured by the configuration from the electron source 11 to the lower deflection coil 17b. Further, the lower device is constituted by the potential plate 22 and members disposed below the potential plate 22. The sample 23 is held in the lower device. The upper device has a hole through which the charged particle beam that passes through the upper device is finally emitted. The hole exists in the lower deflection coil 17b. The detector 20 is attached below the hole. The detector 20 also has an opening through which the primary electron beam 12 passes, and the detector 20 is attached below the lower deflection coil 17b so that the hole and the opening overlap.

[Third embodiment]

In the third embodiment, a field emission type is used for the electron source 11. The field emission type has higher brightness than the thermionic emission type, the size of the light source is small, the ΔV of the primary electron beam 12 is also small, and is advantageous in terms of chromatic aberration. In the third embodiment, for comparison with the first embodiment, the lower part from the second stage condenser lens 15b of the first embodiment is the same as that of the first embodiment, and the electron source section Is a field emission type, and the first-stage condenser lens 15a is eliminated. The ΔV of the primary electron beam 12 is set to 0.5 eV, and the electron source size So is set to 0.1 μm. The performance when Z = −4 mm, the acceleration voltage Vacc is −30 kV, and the first objective lens 18 is OFF is as follows.

(Simulation data 7)

Dprobe = 0.974 nm, Dg = 0.071, Ds = 0.591, Dc = 0.248, Dd = 0.730,

Cs = 1.69 mm, Cc = 3.36 mm, α = 8.88 mrad, M3 = 0.0249

The field emission electron source has higher brightness than the thermal electron emission type. Furthermore, since the condenser lens 15 is in one stage, the probe current is larger than that in the thermoelectron emission type. Nevertheless, it can be seen that the probe diameter is small. Dd shows the largest value.

In the following example, the acceleration voltage Vacc is set to −1 kV (Vi = 1 kV). When the first objective lens 18 is used, the second objective lens 26 is used to focus the electrons. The condenser lens 15 is adjusted so that the probe current does not change. In that case, it is as follows.

(Simulation data 8)

Dprobe = 8.48 nm, Dg = 0.071, Ds = 0.591, Dc = 7.45, Dd = 4.00,

Cs = 1.68 mm, Cc = 3.36 mm, α = 8.88 mrad, M3 = 0.0249

As described above, in the thermionic emission type (simulation data 3), since Dprobe = 15.6 nm, it can be seen that the field emission type electron source is better.

Next, an example in which the potential plate 22 and the sample 23 are arranged as shown in FIG. 1 will be described. The sample measurement surface is set to Z = −4 mm.

The calculation results are shown below when the acceleration voltage Vacc is −10 kV, the potential plate 22 is 0 V potential, and the sample 23 is −9 kV (Vi = 1 kV). Here, the first objective lens 18 is not used, and the second objective lens 26 is used for focusing.

(Simulation data 9)

Dprobe = 3.92 nm, Dg = 0.071, Ds = 2.90, Dc = 2.32, Dd = 1.26,

Cs = 0.260 mm, Cc = 0.330 mm, α = 28.1 mrad, M3 = 0.0248

Ds is the largest value among aberrations. This is because the closer to the sample 23, the slower the electron speed and the more easily affected by the magnetic field, and the closer the sample 23 is, the larger the magnetic flux density is. Therefore, α is too large. Since Ds is proportional to the cube of α, it is large. It may be improved by using the first objective lens 18.

Next, data is shown when the first objective lens 18 is used and the intensity is optimally adjusted (when it is about 0.31 times the AT (ampere turn) of simulation data 1).

(Simulation data 10)

Dprobe = 2.68 nm, Dg = 0.103, Ds = 1.03, Dc = 1.68, Dd = 1.82,

Cs = 0.279 mm, Cc = 0.344 mm, α = 19.5 mrad, M3 = 0.0358

だけ Although only the aberration coefficient is seen, the probe diameter is further improved by adjusting α.

Here, in order to compare with the first embodiment, the hole diameter of the objective lens aperture 16 is made the same as 21.8 microns. In the case of the field emission type, since the brightness is high and the condenser lens 15 is formed in one step, the hole diameter can be further reduced. Therefore, diffraction aberration becomes the main aberration.

As described above, according to the present embodiment, by using the second objective lens 26 and performing retarding, a lens system in which α is increased is obtained, and the lens system is capable of reducing diffraction aberration. That is, the second objective lens with low aberration can be realized in the charged particle beam apparatus. Signal electrons can be detected with high sensitivity, and high resolution can be realized at low cost.

According to the present embodiment, since the signal electrons do not pass through the first objective lens, the detection unit can have a simple structure. Since the magnetic flux density on the optical axis of the second objective lens has a stronger distribution as it is closer to the sample, the objective lens becomes a low aberration lens. When a negative potential is applied to the sample, the closer to the sample, the stronger the lens, and the objective lens further becomes a low aberration lens. The signal electrons are accelerated by the electric field generated by the retarding voltage of the sample, and the energy is amplified and enters the detector. Therefore, the detector becomes highly sensitive. With the above configuration, a high-resolution charged particle beam apparatus can be realized.

[Fourth embodiment]

Next, an apparatus configuration of an SEM (an example of a charged particle apparatus) in the fourth embodiment will be described. In the following description, configurations similar to those in the above-described embodiment (including modified examples of each configuration) are denoted by the same reference numerals as those described above, and detailed descriptions thereof are omitted.

The general configuration of the first embodiment is the same as that of the fourth embodiment as follows. In the upper device, the configuration from the electron source 11 to the first objective lens 18 is arranged. The primary electron beam 12 is emitted from the upper device toward the sample 23. A second objective lens 26 is disposed in the lower device. A sample 23 is held in the lower apparatus. The secondary electron detector 19 and the detector 20 are provided in the same manner. The secondary electron detector 19 is provided to detect the signal electrons 21 of the secondary electrons 21a.

FIG. 9 is a cross-sectional view showing an example of the device configuration of the SEM according to the fourth embodiment of the present invention.

In the SEM shown in FIG. 9, the upper device, the second objective lens 26, the secondary electron detector 19, the potential plate 22 and the like are provided in the same manner as that shown in FIG. In this SEM, retarding is performed. Thus, in the fourth embodiment, the SEM basically has the same configuration as that shown in FIG. In the fourth embodiment, the SEM differs from that shown in FIG. 1 in that a detector 720 for detecting the reflected electrons 21b is disposed on the lower surface of the potential plate 22 (the surface on the sample 23 side). ing.

The detector 720 is provided with a hole through which the primary electron beam 12 and the secondary electron 21a pass. As the detector 720, for example, a microchannel plate, a Robinson detector, a semiconductor detector, or the like is used.

As described above, in the apparatus shown in FIG. 9, the detector 720 is arranged at a position relatively close to the sample 23. Since the solid angle of the incident reflected electrons 21b is large and the detection sensitivity of the reflected electrons 21b is improved, the sample 23 can be observed with higher sensitivity.

In the fourth embodiment, the detector 20 may be disposed above the potential plate 22. The size of the hole 720a of the detector 720 may be small enough to allow the primary electron beam 12 to pass through. For example, the hole 720a is a circular through hole, and the diameter is preferably about 1 to 2 millimeters, for example. By reducing the hole 720a in this way, most of the reflected electrons 21b cannot pass above the potential plate 22. Therefore, since most of the signal electrons 21 incident on the secondary electron detector 19 or the detector 20 become the secondary electrons 21a, a clear secondary electron image that is not mixed with the reflected electron image can be obtained.

[Others]

Although the present invention has been described by the above embodiment, it should not be understood that the description and drawings of this disclosure limit the present invention. For example, the trajectory of the charged particle beam from the charged particle source to the sample 23 is drawn in a straight line in the figure. However, when an energy filter is inserted, the track is bent. The charged particle beam trajectory may be bent. Such a case is also included in the technical scope described in the claims. In addition, in the ion beam microscope, in the case of negative ion charged particles, it can be understood that it can be applied in the same manner as in the first embodiment because it can have the same concept as electrons. In the case of ions, the mass is heavier than electrons, so the condenser lens 15 may be an electrostatic lens, the deflection coil 17 may be an electrostatic deflection, and the first objective lens 18 may be an electrostatic lens. The objective lens 26 uses a magnetic lens.

From the above description, it can be understood that the present invention can be easily applied to an electron beam apparatus such as EPMA, which is a charged particle beam apparatus, an electron beam drawing apparatus, or an ion beam apparatus such as an ion beam microscope. When positive ion charged particles are used like a He + ion source, a positive acceleration power source 14 is used as an acceleration power source for the ion source. When the retarding is not performed, the apparatus can be configured in the same manner as in the first embodiment. When performing the retarding, the retarding power supply 27 is switched to the positive power supply, and the apparatus can be configured in the same manner as in the above-described embodiment. At this time, if the potential plate 22 is at the ground potential, the signal electrons 21 emitted from the sample 23 are negatively charged, and thus are pulled back to the sample 23. In this case, the potential plate power supply 28 may be adjusted so that the potential of the potential plate 22 is higher than the potential of the sample 23. For example, the charged particle beam acceleration power source 14 may be set to +7 kV, the upper device may be set to the ground potential, the potential plate 22 may be set to +6 kV, and the sample 23 may be set to +5 kV. Then, the signal electrons 21 can be detected by the detector 720 placed at the position of the potential plate 22.

The above embodiments and modifications should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

11 ... charged particle source (electron source)
12 ... charged particle beam (primary electron beam)
DESCRIPTION OF SYMBOLS 13 ... Wehnelt electrode 14 ... Acceleration power supply 15 ... Condenser lens 15a ... First stage condenser lens 15b ... Second stage condenser lens 16 ... Objective lens aperture 17 ... Second stage deflection coil 17a ... Upper stage deflection coil 17b ... Lower stage deflection coil 18 ... First stage Objective lens 18a ... inner magnetic pole 18b ... outer magnetic pole 18c ... hole 19 ... secondary electron detector 20 ... detector (semiconductor detector, Robinson detector or MCP detector)
21 ... Signal electrons (21a ... secondary electrons, 21b ... reflected electrons)
22 ... Potential plate 23 ... Sample 24 ... Sample stand 25 ... Insulating plate 26 ... Second objective lens 26a ... Central magnetic pole 26b ... Upper magnetic pole 26c ... Side magnetic pole 26d ... Lower magnetic pole 26e ... Coil 26f ... Sealing portion 27 ... Retarding power supply 28 ... Potential plate power supply 29 ... Sample stage stage plate 30 ... Cylindrical discharge prevention electrode 31 ... Insulating material 41 ... First objective lens power supply 42 ... Second objective lens power supply 43 ... Upper deflection power supply 44 ... Lower deflection power supply 45 ... Control Apparatus 720 ... Detector (semiconductor detector, Robinson detector or MCP detector)

Claims

A charged particle source;
An acceleration power source connected to the charged particle source, provided to accelerate the charged particle beam emitted from the charged particle source;
A charged particle beam apparatus having an objective lens for focusing the charged particle beam on a sample,
The objective lens is
A first objective lens installed on the side on which the charged particle beam is incident on the sample;
A second objective lens installed on the opposite side to the side on which the charged particle beam is incident on the sample,
The charged particle beam device comprises:
A first objective lens power source for varying the intensity of the first objective lens;
A second objective lens power source for varying the intensity of the second objective lens;
A controller for controlling the first objective lens power source and the second objective lens power source;
The control device includes a function of independently controlling the intensity of the first objective lens and the intensity of the second objective lens, a function of simultaneously controlling the intensity, and the charged particle beam using only the first objective lens. A function of focusing on the sample, a function of focusing the charged particle beam on the sample with only the second objective lens, and simultaneously using the first objective lens and the second objective lens, A charged particle beam device having a function of varying an opening angle incident on the sample with the first objective lens and focusing the sample on the sample.
A charged particle source;
An acceleration power source connected to the charged particle source, provided to accelerate the charged particle beam emitted from the charged particle source;
A charged particle beam apparatus having an objective lens for focusing the charged particle beam on a sample,
The objective lens is
A first objective lens installed on the side on which the charged particle beam is incident on the sample;
A second objective lens installed on the opposite side to the side on which the charged particle beam is incident on the sample,
The charged particle beam device comprises:
A first objective lens power source for varying the intensity of the first objective lens;
A second objective lens power source for varying the intensity of the second objective lens;
A first control device for controlling the first objective lens power source and the second objective lens power source;
The first control device has a function of independently controlling the strength of the first objective lens and the strength of the second objective lens, and a function of controlling the strength simultaneously.
The charged particle beam device has a two-stage deflecting member that two-dimensionally scans the charged particle beam,
The two-stage deflection member has an upper deflection member and a lower deflection member,
An upper deflection power source for varying the strength or voltage of the upper deflection member;
A lower deflection power source for varying the strength or voltage of the lower deflection member;
A second control device for controlling the upper deflection power source and the lower deflection power source;
The upper deflection member and the lower deflection member are installed on the side from which the charged particle beam comes from the inside of the first objective lens,
The second control device is a charged particle beam device that varies a use current ratio or a use voltage ratio of the upper deflection power supply and the lower deflection power supply.
A charged particle source;
An acceleration power source connected to the charged particle source, provided to accelerate the charged particle beam emitted from the charged particle source;
A charged particle beam apparatus having an objective lens for focusing the charged particle beam on a sample,
The objective lens is
A first objective lens installed on the side on which the charged particle beam is incident on the sample;
A second objective lens installed on the opposite side to the side on which the charged particle beam is incident on the sample,
The charged particle beam device comprises:
A first objective lens power source for varying the intensity of the first objective lens;
A second objective lens power source for varying the intensity of the second objective lens;
A first control device for controlling the first objective lens power source and the second objective lens power source;
The first control device has a function of independently controlling the strength of the first objective lens and the strength of the second objective lens, and a function of controlling the strength simultaneously.
The charged particle beam device has a two-stage deflecting member that two-dimensionally scans the charged particle beam,
The two-stage deflection member has an upper deflection member and a lower deflection member,
An upper deflection power source for varying the strength or voltage of the upper deflection member;
A lower deflection power source for varying the strength or voltage of the lower deflection member;
A second control device for controlling the upper deflection power source and the lower deflection power source;
The upper deflection member and the lower deflection member are installed on the side from which the charged particle beam comes from the inside of the first objective lens,
The lower deflection member is a plurality of coils each having a different number of turns,
The second control device is a charged particle beam device that controls one of the plurality of coils to be used.
The charged particle beam device according to claim 2 or 3, wherein the deflection member is a deflection coil or a deflection electrode.
When using only the first objective lens power source, the distance between the first objective lens and the measurement sample surface is made closer than the distance between the second objective lens and the measurement sample surface;
The distance between the second objective lens and the measurement sample surface is set closer to the distance between the first objective lens and the measurement sample surface when only the second objective lens power source is used. The charged particle beam device according to any one of the above.
The charged particle beam apparatus according to any one of claims 1 to 5, further comprising a retarding power source for decelerating the charged particle beam that applies a negative potential to the sample.
A detector arranged so as not to block the trajectory through which the charged particle beam passes;
The charged particle beam apparatus according to claim 1, wherein the detector is attached to a lower part of an upper apparatus that emits the charged particle beam toward the sample.
The charged particle beam device according to claim 7, wherein a distance between the detector and the second objective lens is 10 mm to 200 mm.
The charge according to claim 7 or 8, wherein the detector is a semiconductor detector, a phosphor emission type detector, or a microchannel plate detector, and is disposed within 3 cm from the trajectory of the charged particle beam. Particle beam device.
A secondary electron detector having an electric field that attracts electrons;
10. The secondary electron detector is arranged according to any one of claims 1 to 9, wherein the secondary electron detector is arranged such that an electric field generated from the secondary electron detector attracts secondary electrons emitted from the sample by the charged particles. The charged particle beam apparatus described.
The second objective lens is configured such that the charged particle beam accelerated by setting the acceleration power source to any one of −30 kV to −10 kV is viewed from a position closest to the sample of the magnetic pole of the second objective lens, The charged particle beam apparatus according to any one of claims 1 to 10, wherein the charged particle beam apparatus can be focused to a position at any height of 0 mm to 4.5 mm.
An insulating plate disposed on the second objective lens;
A conductive sample stage disposed on the insulating plate;
The charged particle beam apparatus according to claim 1, wherein the second objective lens and the conductive sample stage are insulated.
13. The charged particle beam apparatus according to claim 12, wherein the conductive sample stage is shaped so as to move away from the insulating plate as it approaches the peripheral edge.
The charged particle beam apparatus according to claim 12 or 13, wherein a space between the insulating plate and the conductive sample stage is filled with an insulating material.
Further comprising a potential plate with an opening on the conductive sample stage,
The charged particle beam apparatus according to claim 12, wherein a ground potential, a positive potential, or a negative potential is applied to the potential plate.
The charged particle beam device according to claim 15, wherein the opening of the potential plate has a circular shape or a mesh shape having a diameter of 2 mm to 20 mm.
The charged particle beam apparatus according to claim 15 or 16, wherein the potential plate has a shape separated from the conductive sample stage at a place other than near the sample.
The charged particle beam apparatus according to any one of claims 15 to 17, further comprising moving means for moving the potential plate.
A scanning electron microscope comprising the charged particle beam device according to any one of claims 1 to 18.