JP6204388B2 - Charged particle beam apparatus and scanning electron microscope - Google Patents

Description

  The present invention relates to a charged particle beam apparatus. More specifically, the present invention relates to a charged particle beam apparatus capable of improving performance.

  Examples of the charged particle beam apparatus include a scanning electron microscope (hereinafter abbreviated 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, a contrivance is made for shortening the focal length of the lens from the viewpoint of increasing the 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 and reduce the thickness of the lens, 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 as viewed 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 Patent Document 1 below, the first objective lens and the second objective lens are not operated simultaneously, and 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 example (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 JP-A-6-181041

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

  A charged particle beam apparatus according to one aspect of the present invention includes a charged particle source, an acceleration power source connected to the charged particle source, provided to accelerate a charged particle beam emitted from the charged particle source, and the charging A charged particle beam apparatus having an objective lens for focusing a particle beam on a sample, wherein the objective lens is a first objective lens installed on a side where the charged particle beam is incident on the sample; A second objective lens installed on the opposite side of the sample from which the charged particle beam is incident, and the charged particle beam device includes a first objective that varies an intensity of the first objective lens. A lens power source; a second objective lens power source that varies an intensity of the second objective lens; and a control device that controls the first objective lens power source and the second objective lens power source. The apparatus includes the first objective. A function of independently controlling the intensity of the second objective lens and the intensity of the second objective lens, a function of controlling the intensity simultaneously, a function of focusing the charged particle beam on the sample only by the first objective lens, and the charged particles A function of focusing a line on the sample with only the second objective lens, and simultaneously using the first objective lens and the second objective lens, the opening angle of the charged particle beam incident on the sample is changed to the first objective lens. And a function of focusing on the sample while being variable by one objective lens.

  A charged particle beam apparatus according to another aspect of the present invention includes a charged particle source, an acceleration power source connected to the charged particle source, provided to accelerate a charged particle beam emitted from the charged particle source, and the charging A charged particle beam apparatus having an objective lens for focusing a particle beam on a sample, wherein the objective lens is a first objective lens installed on a side where the charged particle beam is incident on the sample; A second objective lens installed on the opposite side of the sample from which the charged particle beam is incident, and the charged particle beam device includes a first objective that varies an intensity of the first objective lens. A lens power source; a second objective lens power source that varies the intensity of the second objective lens; and a first control device that controls the first objective lens power source and the second objective lens power source. The first control device is A function of independently controlling the intensity of one objective lens and the intensity of the second objective lens, and a function of simultaneously controlling the intensity; and the charged particle beam device scans the charged particle beam two-dimensionally A two-stage deflection member, the two-stage deflection member having an upper-stage deflection member and a lower-stage deflection member, and an upper-stage deflection power source that varies the strength or voltage of the upper-stage deflection member; A lower deflection power source that varies the strength or voltage of the lower deflection member, and a second control device that controls the upper deflection power source and the lower deflection power source, the upper deflection member and the lower deflection member comprising: The charged particle beam is installed on the side where the charged particle beam comes from the inside of the first objective lens, and the second control device is configured to use a current ratio or voltage ratio of the upper deflection power source and the lower deflection power source. Is variable.

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

  Preferably, the lower deflection member is a plurality of coils each having a different number of turns, and the second control device controls one of the plurality of coils to be used.

  Preferably, when only the first objective lens power source 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, When only the objective lens power source 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 supply for decelerating the charged particle beam, which applies a negative potential to the sample.

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

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. It is a figure explaining adjustment of the opening angle (alpha) by the 1st objective lens in the 1st Embodiment of this invention, (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.

  Next, embodiments 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.

  The following embodiments of the present invention exemplify apparatuses and methods for embodying the technical idea of the present invention. The technical idea of the present invention is based on the material and shape of components. The structure, arrangement, etc. are not specified 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 that accelerates a primary electron beam (charged particle beam) 12 emitted from the electron source 11, and a condenser lens that focuses the accelerated primary electron beam 12. 15, an objective lens aperture 16 excluding unnecessary portions of the primary electron beam 12, a two-stage deflection coil 17 that two-dimensionally scans the primary electron beam 12 on the sample 23, and the primary electron beam 12 on the sample 23. This is an electron beam apparatus including objective lenses 18 and 26 for focusing and a detector 20 for detecting signal electrons 21 (secondary electrons 21a and reflected electrons 21b) emitted from a sample 23.

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

  The control device 45 can independently control the strength of the first objective lens 18 and the strength of the second objective lens 26, and 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 (thermoelectron 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 as the electron source 11, and an acceleration voltage −0 is provided between the electron source 11 and the anode plate (ground potential), for example. Apply 5 kV to -30 kV. The Wehnelt electrode 13 is given a negative potential with respect to the potential of the electron source 11, whereby the amount of the primary electron beam 12 generated from the electron source 11 is controlled. A crossover diameter, which is the first minimum diameter of the primary electron beam 12, is created immediately in front of the electron source 11. This minimum diameter is called the electron source size So.

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

  The primary electron beam 12 that has passed through the objective lens stop 16 passes through the scanning two-stage deflection coil 17 and passes through the first objective lens 18. 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 through which the charged particle beam that passes through the upper device is finally emitted. In the first embodiment, the hole exists in the first objective lens 18. 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 to the lower part of the first objective lens 18 so that the hole and the opening overlap each other. Alternatively, a plurality of detectors 20 are used, and the plurality of detectors 20 do not block the trajectory of the primary electron beam 12, and the detection unit of the detector 20 has as little gap as possible except for the hole of the upper device. Thus, it is attached to the lower part of the first objective lens 18.

  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. In addition, the first objective lens 18 is used to optimize each control value so as to obtain an easy-to-view image by controlling the opening angle α and adjusting the reduction ratio, lens shape, and depth of focus. Used. Further, when the primary electron beam 12 cannot be focused only by the second objective lens 26, the first objective lens 18 can assist.

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

  When the retarding is not performed, the potential plate 22 of FIG. 1 may be removed, and 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 5 mm or less from the upper part (upper surface) of the second objective lens 26.

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. Since the magnetic flux density rapidly decreases when the sample 23 moves away from the surface of the sample 23, the secondary electrons 21 a are unwound from the swirl and diverge, and are deflected by the drawn electric field from the secondary electron detector 19, and are then incident on the secondary electron detector 19. Be captured. That is, the secondary electron detector 19 is arranged so that the electric field generated from the secondary electron detector 19 attracts the secondary electrons emitted from the sample by the charged particle beam . The number of secondary electrons 21a entering the detector 19 can be increased.

  Next, an outline of the case of retarding will be described with reference to FIG. 4A is an equipotential line during retarding, FIG. 4B is a magnetic flux density distribution B (z) on the optical axis of the second objective lens, and FIG. 4C is a graph of charged particles during retarding. Showing speed.

  As shown in FIG. 4B, since 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, 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). The primary electron beam 12 is more susceptible to the influence of a magnetic field as the speed is lower. Therefore, the closer to the sample 23, the stronger the lens, and the second objective lens 26 becomes a further low aberration lens.

  Further, the signal electrons 21 are accelerated by the electric field generated by the retarding voltage of the sample 23, and the energy is amplified and enters the detector 20, so that 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, it is very easy to put in and out of the sample if the gap between the first objective lens 18 and the second objective lens 26 is about 30 mm.

  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 upper part of the central magnetic pole 26a has a shape with a smaller diameter toward the upper part. The lower part of the central magnetic pole 26a is cylindrical and has no through hole in the central axis. The upper magnetic pole 26b has a disk shape with an opening having an opening diameter d at the center, and is tapered toward the center and becomes thinner near the center of gravity of the central magnetic pole 26a. 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 d−D ≧ 4 mm.

  Next, a specific example of the magnetic pole is 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 has D = 8 mm, the opening diameter d of the upper magnetic pole 26b is preferably 12 mm to 32 mm. More preferably, it is 14 mm to 24 mm. As d increases, the magnetic flux density distribution on the optical axis becomes gentler and wider, and the AT (ampere turn: product of coil turns N [T] and current I [A]) required for focusing is reduced. There is a merit that can be. However, when the relationship between the aperture 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 sample 23 having a thickness of 5 mm is focused 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 poles are saturated and cannot be focused. On the other hand, if D is increased, performance deteriorates. On the other hand, if the difference in size between d and D is smaller than 4 mm, the magnetic pole is too close to be saturated and cannot be 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. If it 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 is used and adjustment to reduce α is necessary, and the operability is deteriorated.

  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 set to 2 mm, d is set to 5 mm, and the thickness of the sample 23 is set to 5 mm, the magnetic pole is saturated only by the second objective lens 26 and cannot be focused. 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 electrically insulating portion is made thick, 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 portion 26f is vacuum-tight with an O-ring or brazing between the upper magnetic pole 26b and the central magnetic pole 26a. 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 the upper magnetic pole 26b and the vacuum vessel are not shown in the drawing, they are coupled so as to be airtight by an O-ring. By doing so, the second objective lens 26 can be exposed to the atmosphere except for the surface on the vacuum side, and the second objective lens 26 can be easily cooled.

  The second objective lens 26 can be placed in the vacuum vessel, but if the coil part 26e is on the vacuum side, it becomes a gas emission source, and the degree of vacuum becomes worse. In addition, if the vacuum side and the atmosphere side are not hermetically separated in this way, the sample moves because the gas passes through the place where the second objective lens 26 and the insulating plate 25 are in contact with each other when vacuuming is performed. There is.

  The coil portion 26e can be set to a coil current of 6000AT, for example. The coil generates heat, and when the temperature rises, the coating of the wire melts, causing a short circuit. Since the second objective lens 26 can be exposed to the atmosphere, the cooling efficiency is increased. For example, if the base of the lower surface of the second objective lens 26 is made of aluminum, it can be made like 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.

  The retarding unit will be described with reference to FIG.

  For example, a polyimide film or a polyester film having a thickness of about 0.1 mm to 0.5 mm is placed on the second objective lens 26 as the insulating plate 25. Then, a non-magnetic conductive sample stage 24 is placed thereon. The sample stage 24 is, for example, an aluminum plate having a bottom surface of 250 μm and processed into a curved shape that is separated from the insulating plate 25 as the peripheral edge approaches the peripheral edge, and further, a gap between the curved surface portion and the insulating plate 25 is provided with an insulating material 31. It shall be filled with. 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.

  A 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 insulating material so that the position of the sample 23 can be changed from outside the vacuum. The sample stage stage plate 29 is connected to an XY stage (not shown) and can be moved from outside the vacuum.

  On the sample 23, a conductive plate (hereinafter referred to as a potential plate 22) having a circular opening is disposed. 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 circular opening of the potential plate 22 preferably has a diameter of about 2 mm to 20 mm. More preferably, the diameter is 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 should be thin so that electrons can easily pass through and the aperture ratio should be 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. The potential plate 22 can be increased in withstand voltage with respect to the sample stage 24 by being separated from the conductive sample stage 24 at a place other than the vicinity of the sample 23.

  The potential plate 22 is arranged so as not to be discharged by separating a distance of about 1 mm to 15 mm from the sample 23. 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 not, the primary electron beam 12 is decelerated before being focused by the second objective lens 26, and the effect of reducing aberration 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 short, the equipotential lines have a distribution that protrudes farther toward the electron gun than the opening of the potential plate 22, and the primary electrons are There may be a case where the vehicle decelerates before reaching the plate 22. The smaller the opening diameter of the potential plate 22, the more effective it is to reduce the leakage of the electric field. However, it is necessary to prevent the signal electrons 21 from being absorbed by the potential plate 22. For this reason, it is important to adjust the potential difference between the sample 23 and the potential plate 22 within a range where no discharge occurs, adjust the distance between the sample 23 and the potential plate 22, and appropriately select the opening diameter of the potential plate 22. It becomes.

  FIG. 4B is a diagram for explaining the magnetic flux density distribution B (z) on the optical axis of the second objective lens 26. 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.

  FIG. 4C is a diagram illustrating the speed of charged particles during 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 near the potential plate 22, but the velocity becomes slower as it approaches the sample 23 from around the potential plate 22, and is easily affected by the magnetic field. Become. Since the magnetic field generated by the second objective lens 26 is stronger as it is closer to the sample 23, the effect of both is combined, and the closer the sample 23 is, the stronger the lens becomes, and the lens has a smaller 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. That is, since the distance between the first objective lens 18 and the second objective lens 26 can be set to a distance of 10 mm to 200 mm, for example, in the case of a flat sample 23, the distance between the sample 23 and the potential plate 22 is set. If the gap 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 different arrangement examples of the samples. Further, as shown in FIG. 5, a cylindrical discharge preventing electrode 30 having a cylindrical shape whose upper surface is R-processed may be installed around the sample 21 on the sample table 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 phosphorson-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, the center of the detection unit is located on the optical axis, and the detector 20 having an opening through which primary electrons pass is used as 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 has a value 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. Both the secondary electrons 21a and the reflected electrons 21b are accelerated, the energy is amplified and enters the detector 20, and the signal becomes large.

  In a general-purpose SEM, the electrons are usually focused by a lens such as the first objective lens 18. The first objective lens 18 is usually designed so as to have a higher resolution as the sample 23 is brought closer to the first objective lens 18. However, the semiconductor detector 20 has a thickness, and the sample 23 needs to be separated from the first objective lens 18 by the thickness. If it is too close, the secondary electrons 21a are difficult to enter the secondary electron detector 19 outside the first objective lens 18. Therefore, in the general-purpose SEM, a thin semiconductor detector 20 having an opening through which primary electrons pass is used at a position directly below the first objective lens 18. 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. 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 directly under 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 a probe diameter. The following formula is used as a formula for evaluating the probe diameter.

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

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

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

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

  [Expression 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.

  A case where the primary electron beam 12 is focused by the first objective lens 18 will be described. This corresponds to a general purpose SEM.

  The ΔV of the primary electron beam 12 is 1 V, and the electron source size So 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, and M3 = 0.05575.

  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 = -4 mm,

  (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, and M3 = 0.0249.

  As described above, it can be seen that the SEM performance is greatly improved by using the second objective lens 26.

  In addition, 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 will be described in which 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). 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 results are 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, and 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 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 set to 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 results are 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, and M3 = 0.0247.

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

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

  (Simulation data 5)

  The results are shown in FIG.

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

  Cs = 0.512 mm, Cc = 0.357 mm, α = 16.3 mrad, and M3 = 0.0430.

  Here, it can be seen that Dprobe decreases. 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 much smaller. Therefore, Dc is small. From [Equation 1], it can be seen that Dprobe can be reduced by using the first objective lens 1.

  In contrast to α = 8.89 mrad in FIG. 6A, α = 28.2 mrad in FIG. 6B, 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.

  What is important here is that the hole diameter of the objective lens aperture 16 can be reduced to adjust α, 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.

  Further, 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. It is also possible to reduce the reduction ratio M1 × M2 by the condenser lens 15. Therefore, adjustment is necessary because there is a balance with Dg, Ds, Dc, and Dd, but the probe diameter may be further reduced, and the probe diameter can be optimized by the objective lens aperture 16 and the first objective lens 18. .

  In addition, depending on the sample 23, if the lens has a shallow depth of focus, the lens may focus 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, 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.

  Further, 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 a 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) does not have to be placed on the second objective lens 26. Therefore, the second objective lens 26 uses the primary electron beam 12 having an acceleration voltage of −100 kV. It can be focused sufficiently. Preferably, the second objective lens 26 has a charged particle beam accelerated with an accelerating power source set to any one of −30 kV to −10 kV, as viewed from a position closest to the sample of the magnetic pole of the objective lens. 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. When hitting the sample 23, the primary electrons become 10 keV. The energy when the secondary electrons 21a are emitted from the sample 23 is 100 eV or less. Since the potential plate 22 has a potential 1 kV lower than that 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, it can be used as an energy filter, and the sensitivity can be increased by further accelerating the signal electrons 21.

  Next, a case where the height of the sample 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, it is possible to focus without the acceleration voltage being lowered with the help of the first objective lens 18.

  Further, depending on the height of the sample 23, it may be 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.

  Further, when the retarding voltage is high, the signal electrons 21 easily pass through the vicinity of the optical axis and 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 so that the signal electrons 21 strike the detector 20 and the sensitivity is improved. There is a way to do it. Further, ExB may be inserted 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 are sufficient if the signal electrons 21 are bent a little. 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 providing 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 configured such 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. When only the first objective lens power supply 41 is used, the apparatus is configured such that 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. Is done.

  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). Of course, 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 will be described in which 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. 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, and M3 = 0.0244.

  According to the above results, the probe diameter is improved as compared with 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, the semiconductor detector 20 decelerates the secondary electrons 21a due to the ground potential and cannot detect it. The secondary electrons 21 a can be detected by the secondary electron detector 19. Of course, if a retarding voltage is applied to the sample 23, the semiconductor detector 20 can also detect the secondary electrons 21a.

  Next, referring to FIG. 7, moving 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.

  In FIG. 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 a main lens, as shown in FIG. 7B, the upper stage is set so that electrons pass along the intersection of the main surface of the second objective lens 26 and the optical axis. The intensity ratio between the deflection coil 17a and the lower deflection coil 17b is adjusted by a control device 45 that adjusts the 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 (cross point) of the deflection trajectory by adjusting the current ratio used, a system in which coils with different winding numbers are switched by a relay or the like (a plurality of coils having different winding numbers are provided, and the coil to be used is controlled by a control device). In the case of an electrostatic lens, a method of switching the voltage (a method of varying 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]

  With reference 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 17 b. 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 next 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 is understood 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 result is 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

  Among aberrations, Ds is the largest value. 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. Ds is large because it is proportional to the cube of α. It may be improved by using the first objective lens 18.

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

  (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

  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 diaphragm 16 is made the same as 21.8 microns. However, in the case of the field emission type, the luminance is bright, and the condenser lens 15 is made one stage. Therefore, 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. Further, signal electrons can be detected with high sensitivity, and high resolution can be realized at low cost.

  Further, 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. Further, 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. In addition, 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, so that the detector has high sensitivity. With the above configuration, a high-resolution charged particle beam apparatus can be realized.

  Although the present invention has been described with reference to the above embodiments, 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.

  The above-described 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 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

Claims (22)

  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 first objective lens that is installed on a side where the charged particle beam is incident on a sample and focuses the charged particle beam on the sample;
  A second objective lens that is placed on the opposite side of the sample where the charged particle beam is incident, and focuses the charged particle beam on the sample;
  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;
With
  When using only the first objective lens power source, the sample is disposed between the first objective lens and the second objective lens;
  When only the second objective lens power source is used, the charged particle beam apparatus is configured such that the distance between the second objective lens and the measurement sample surface is closer than the distance between the first objective lens and the measurement sample surface.   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 first objective lens that is installed on a side where the charged particle beam is incident on a sample and focuses the charged particle beam on the sample;
  A second objective lens that is placed on the opposite side of the sample where the charged particle beam is incident, and focuses the charged particle beam on the sample;
  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;
With
  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;
  When only the second objective lens power source is used, the charged particle beam apparatus is configured such that the distance between the second objective lens and the measurement sample surface is closer than the distance between the first objective lens and the measurement sample surface.   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 first objective lens that is installed on a side where the charged particle beam is incident on a sample and focuses the charged particle beam on the sample;
  A second objective lens that is placed on the opposite side of the sample where the charged particle beam is incident, and focuses the charged particle beam on the sample;
  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;
With
  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.
  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;
  When only the second objective lens power source is used, the charged particle beam apparatus is configured such that the distance between the second objective lens and the measurement sample surface is closer than the distance between the first objective lens and the measurement sample surface.   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 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 for the first objective lens. A function of focusing the sample only on the lens, a function of focusing the charged particle beam on the sample only by the second objective lens, and the charging using the first objective lens and the second objective lens simultaneously. The opening angle of the particle beam incident on the sample is varied by the first objective lens so that the opening angle is smaller than when the charged particle beam is focused on the sample by the second objective lens alone. And a charged particle beam device having a function of focusing on the sample.   A two-stage deflecting member for two-dimensionally scanning 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,
  5. The charged particle beam device according to claim 1, wherein the second control device varies a use current ratio or a use voltage ratio of the upper deflection power supply and the lower deflection power supply. 6.   Having a two-stage deflection member for two-dimensionally scanning 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 charged particle beam device according to claim 1, wherein the second control device controls one of the plurality of coils to be used.   The charged particle beam apparatus according to claim 5, wherein the deflection member is a deflection coil or a deflection electrode.   The charged particle beam apparatus according to claim 1, further comprising a retarding power supply for decelerating the charged particle beam that applies a negative potential to the sample.   The second objective lens sees the charged particle beam accelerated by setting the acceleration power source to any one of −30 kV to −10 kV 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 8, 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.   The charged particle beam apparatus according to claim 10, 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 10 or 11, 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 device according to claim 10, 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 13, wherein the opening of the potential plate has a circular shape or a mesh shape with a diameter of 2 mm to 20 mm.   The charged particle beam apparatus according to claim 13 or 14, wherein the potential plate has a shape that is separated from the conductive sample stage at a place other than the vicinity of the sample.   The charged particle beam apparatus according to claim 13, further comprising a moving unit that moves the potential plate.   The moving means is a stage connected to the potential plate;
  The charged particle beam apparatus according to claim 16, wherein the stage can mount the sample.   The magnetic pole forming the second objective lens is
    A central magnetic pole whose central axis coincides with the ideal optical axis of the charged particle beam;
    The top pole,
    A cylindrical side pole,
    A disk-shaped lower magnetic pole,
  The upper part of the central magnetic pole close to the sample side has a shape with a smaller diameter toward the upper part, and the lower part of the central magnetic pole has a cylindrical shape,
  18. The upper magnetic pole is a magnetic pole having a circular opening at the center, and has a disk shape that tapers toward the center and becomes thinner near the center of gravity of the central magnetic pole. 18. Charged particle beam equipment.   The charged particle beam apparatus according to claim 18, wherein a surface of the central magnetic pole on the sample side and a surface of the upper magnetic pole on the sample side are the same height.   The upper tip diameter D of the central magnetic pole is larger than 6 mm and smaller than 14 mm,
  The charged particle beam device according to claim 18 or 19, wherein a relationship between a diameter d of the circular opening of the upper magnetic pole and the upper tip diameter D of the central magnetic pole is dD ≧ 4 mm.   21. The charged particle beam apparatus according to claim 1, wherein a thermoelectron source type is used as the charged particle source.   A scanning electron microscope comprising the charged particle beam device according to any one of claims 1 to 21.