Electron source and device operating with a beam of charged particles

Abstract

A charged particle beam device comprising: an electron gun (201) comprising: a tip (202), a suppressor (203) arranged behind a distal end of the tip (202), an extraction electrode (204) having a bottom surface and a cylindrical portion (302) and enclosing the tip (202) and the suppressor (203), an insulator (208) holding the suppressor (203) and the extraction electrode (204), and a conductive metal (301) provided between the suppressor (203) and the cylindrical portion (302) of the extraction electrode (204), wherein a voltage lower than a voltage applied to the tip (202) is applied to the conductive metal (301).

Description

Technical area

[0001] The present invention relates to an electron source that supplies an electron beam to be emitted to a sample, and a charged particle beam device using the electron source. Technical background

[0002] A charged particle beam device generates an observation image of a sample by emitting a charged particle beam like an electron beam toward the sample and detecting transmitted electrons, secondary electrons, backscattered electrons, X-rays, and the like emitted from the sample. The generated image must have high spatial resolution and, when repeatedly generated, good reproducibility. To achieve this, the brightness of the emitted electron beam must be high and the current stable. An example of such an electron beam emitting device is a Schottky emission electron gun (hereinafter referred to as an SE electron gun). PTL 1 describes an example of the SE electron gun structure.

[0003] In recent years, semiconductor devices and materials have become more complex, requiring a charged particle beam device for inspecting and measuring them to observe a large number of samples or points on the same sample in a short period of time. In addition, the throughput of these observations needs to be increased. These short-duration observations can be implemented by emitting a high current from the electron gun and shortening the time required to generate an image.

[0004] The documents DE 11 2014 006 978 B4, DE 11 2011 104 535 B4, DE 11 2010 002 063 B4, JP 2013 - 225 521 A and JP H06 - 318 441 A disclose further devices operating with a beam of charged particles. Citation listPatent literature

[0005] PTL 1: JP H08 - 171879 A Summary of the inventionTechnical problem

[0006] The inventors' research has revealed that when a high current is emitted from the SE electron gun described in PTL 1, a very small discharge (hereinafter referred to as a very small discharge) occurs irregularly many times, and the current of the electron beam fluctuates. In an image formed at the time of such a current fluctuation, the spatial resolution is deteriorated and reproducibility cannot be achieved. When observing with high spatial resolution using an inspection device or a measuring device, reproducibility with an accuracy of 0.1 nm is required, so a change in spatial resolution due to the very small discharge cannot be allowed, which directly leads to a reduction in device performance.Furthermore, because the timing of the very small discharge generation and the magnitude of the current fluctuation due to the discharge are random, it is difficult to predict the generation of the very small discharge and correct the deterioration of spatial resolution in a system. Such a problem, which occurs with the large current discharge, is not described in PTL 1.

[0007] An object of the invention is to provide an electron source capable of reducing a very small discharge and stably emitting a high-current electron beam, and a charged particle beam apparatus using the same. Solution to the problem

[0008] To achieve the above object, the invention provides a charged particle beam device having the features of claim 1, which comprises an electron gun including a tip, a suppressor disposed behind a distal end of the tip, an extraction electrode having a bottom surface and a cylindrical portion and enclosing the tip and the suppressor, an insulator holding the suppressor and the extraction electrode, and a conductive metal provided between the suppressor and the cylindrical portion of the extraction electrode. A voltage lower than a voltage applied to the tip is applied to the conductive metal.

[0009] To achieve the above object, the invention provides a charged particle beam device having the features of claim 12, which comprises an electron gun including a tip, a suppressor disposed behind a distal end of the tip, a conductive support portion supporting the suppressor, an extraction electrode having a bottom surface and a cylindrical portion and enclosing the tip and the suppressor, an insulator supporting the support portion and the extraction electrode, and a conductive metal provided between the support portion and the cylindrical portion of the extraction electrode. A voltage lower than a voltage applied to the tip is applied to the conductive metal.

[0010] Further, to achieve the above object, the invention provides an electron source having the features of claim 15, comprising: a tip, a suppressor disposed behind a distal end of the tip, an insulator holding a terminal electrically connected to the tip and the suppressor, and a conductive metal disposed on a side surface of the suppressor. Beneficial effect

[0011] According to the invention, an electron source capable of stably emitting a high-current electron beam and a charged particle beam apparatus using the electron source can be provided. Brief description of the drawings

[0012] They show: Fig. 1 is a schematic diagram of a scanning electron microscope as an example of a charged particle beam device according to a first embodiment, Fig. 2 is a schematic diagram of a configuration around a prior art SE electron gun, Fig. 3A is a schematic diagram of a configuration around an SE electron gun according to the first embodiment, Fig. 3B is a perspective view of a configuration example of an electron source of the SE electron gun according to the first embodiment, Fig. 4 a diagram of a current change of an electron beam when a very small discharge occurs in the SE electron gun, Fig. 5 a schematic diagram of a mechanism in which the very small discharge occurs in the SE electron gun, Fig. 6 is a schematic diagram of a mechanism for preventing the very small discharge in the SE electron gun according to the first embodiment, Fig. 7 is a schematic diagram of a configuration around an SE electron gun according to a second embodiment, Fig. 8 is a schematic diagram of a configuration around an SE electron gun according to a third embodiment, Fig. 9 is a schematic diagram of a configuration around an SE electron gun according to a fourth embodiment, Fig. 10 is a schematic diagram of a configuration around an SE electron gun according to a fifth embodiment, Fig. 11 is a schematic diagram of a configuration around an SE electron gun according to a sixth embodiment, Fig. 12 is a schematic diagram of a configuration around an SE electron gun according to a seventh embodiment, Fig. 13 is a schematic diagram of a configuration around an SE electron gun according to an eighth embodiment, and Fig. 14 is a schematic diagram of a configuration around an SE electron gun according to a ninth embodiment. Description of embodiments

[0013] Hereinafter, various embodiments of an electron source and a charged particle beam device according to the invention will be described sequentially with reference to the drawings. One example of the charged particle beam device includes an electron microscope that forms an observation image of a sample by emitting an electron beam toward the sample and detecting secondary electrons or backscattered electrons emitted from the sample. A scanning electron microscope will be described below as an example of the charged particle beam device, but the invention is not limited to this and can also be applied to other charged particle beam devices. [First embodiment]

[0014] A first embodiment is a scanning electron microscope having an electron gun including a tip, a suppressor disposed behind the distal end of the tip, an extraction electrode having a bottom surface and a cylindrical portion and enclosing the tip and the suppressor, an insulator holding the suppressor and the extraction electrode, and a conductive metal provided between the suppressor and the cylindrical portion of the extraction electrode, wherein a voltage lower than the voltage of the tip is applied to the conductive metal.

[0015] An overall configuration of the scanning electron microscope according to the present embodiment will be described with reference to Fig. 1. The scanning electron microscope generates an observation image of a sample by emitting an electron beam 115 toward the sample 112 and detecting secondary electrons or backscattered electrons emitted from the sample. The observation image is generated by scanning the sample with a focused electron beam and associating the position at which the electron beam is emitted with the amount of detected secondary electrons or the like.

[0016] The scanning electron microscope includes a cylindrical body 125 and a sample chamber 113. The interior of the cylindrical body 125, viewed from above, is divided into a first vacuum chamber 119, a second vacuum chamber 126, a third vacuum chamber 127, and a fourth vacuum chamber 128. An opening through which the electron beam 115 passes is defined at the center of each vacuum chamber, and the interior of each vacuum chamber is maintained in a vacuum state by differential pumping. The respective vacuum chambers are described below.

[0017] The first vacuum chamber 119 is evacuated by an ion pump 120 and a non-evaporable getter (NEG) pump 118, and the pressure is reduced to an ultra-high vacuum of about 10 -8 Pa, preferably an extremely high vacuum of 10 -9 Pa or below. In particular, the NEG pump 118 has a high pumping speed at 10 -9Pa or below in extremely high vacuum.

[0018] An SE electron gun 101 is located within the first vacuum chamber 119. The SE electron gun 101 is held by an insulator 116 and is electrically insulated from the cylindrical body 125. A control electrode 102 is located below the SE electron gun 101. The observation image is obtained by emitting the electron beam 115 from the SE electron gun 101 and finally emitting the electron beam 115 to the sample 112. A configuration of the SE electron gun 101 will be described in detail later.

[0019] The second vacuum chamber 126 is evacuated by an ion pump 121. An accelerating electrode 103 is located in the second vacuum chamber 126. The third vacuum chamber 127 is evacuated by an ion pump 122. A converging lens 110 is located in the third vacuum chamber 127.

[0020] The fourth vacuum chamber 128 and the sample chamber 113 are evacuated by a turbomolecular pump 109. A detector 114 is located in the fourth vacuum chamber 128. An objective lens 111 and the sample 112 are located in the sample chamber 113.

[0021] The operation of the respective configurations and the process until the electron beam 115 emitted by the SE electron gun 101 generates the observation image are described below.

[0022] A control voltage is applied to the control electrode 102 to form an electrostatic lens between the SE electron gun 101 and the control electrode 102. The electron beam 115 is focused by the electrostatic lens and adjusted to a desired optical magnification.

[0023] An accelerating voltage of approximately 0.5 kV to 60 kV is applied to the accelerating electrode 103 with respect to the SE electron gun 101 to accelerate the electron beam 115. The lower the accelerating voltage, the less damage to the sample, and the higher the accelerating voltage, the better the spatial resolution. The converging lens 110 focuses the electron beam 115 and adjusts the current and aperture angle. Multiple converging lenses can be provided, and they can be located in different vacuum chambers.

[0024] Finally, the electron beam 115 is reduced to a very small spot by the objective lens 111, and the sample 112 is irradiated with the electron beam 115 while being scanned. At the same time, secondary electrons, backscattered electrons, and X-rays reflecting the surface shape and material are emitted from the sample. The secondary electrons, backscattered electrons, and X-rays are detected by the detector 114 to obtain the observation image of the sample. Multiple detectors can be provided, and the detectors can be arranged in the sample chamber 113 and the other vacuum chambers.

[0025] A configuration around a SE electron gun 201 from the prior art is described with reference to Fig. 2. The prior art SE electron gun 201 mainly comprises a SE tip 202, a suppressor 203, and an extraction electrode 204.

[0026] The SE tip 202 is a single crystal with a tungsten <100> -orientation, and its distal end is sharpened and has a radius of curvature of less than 0.5 µm. Zirconia 205 is deposited on the center of the single crystal. The SE tip 202 is welded to a filament 206. Both ends of the filament 206 are connected to a corresponding terminal 207. The two terminals 207 are held by an insulator 208 and electrically insulated from each other. The two terminals 207 extend coaxially to the SE tip 202 and are connected to a power source via a feedthrough (not shown). The SE tip 202 is heated by constantly passing a current through the terminals 207 and exciting and heating the filament 206 from 1500 K to 1900 K. At this temperature, the zirconia 205 diffuses and moves onto a surface of the SE tip 202, covering it up to a (100) crystal plane in the center of the distal end of the electron source.The (100) plane is characterized by a reduced work function when covered with zirconium oxide. Therefore, thermal electrons are emitted from the heated (100) plane, producing the electron beam 115. The total amount of emitted electron beams is called the emission current and is typically about 50 µA.

[0027] The suppressor 203 is a cylindrical metal and covers a portion different from the distal end of the SE tip 202. The cylinder of the suppressor 203 extends in the axial direction parallel to the SE tip 202 and is held fitted in the insulator 208. The suppressor 203 and the terminals 207 are electrically insulated from each other by the insulator 208. The suppressor 203 applies a suppression voltage of -0.1 kV to -0.9 kV to the SE tip 202. The SE tip 202 is characterized by emitting thermal electrons from a side surface. However, by applying such a negative voltage to the suppressor 203, unnecessary thermal electrons are prevented from being emitted from the side surface.

[0028] The distal end of the SE tip 202 typically protrudes from the suppressor 203 by about 0.25 mm. By precisely positioning it to within 1 mm or less and advancing it a small distance, only the distal end of the SE tip 202 contributes to the emission of the electron beam, and the proportion of unnecessary electrons emitted from the side surface is reduced as much as possible. Furthermore, a protrusion of about 0.25 mm provides the advantage of applying a sufficient electric field to the distal end of the electron source by an extraction voltage configuration described later.

[0029] The extraction electrode 204 is a cup-shaped metal cylinder in which a bottom surface and a cylinder are integrally formed, with the bottom surface of the extraction electrode 204 facing the SE tip 202. The extraction electrode 204 is held fitted in an insulator 210 and is electrically insulated from the suppressor 203. The extraction electrode 204 applies an extraction voltage of approximately +2 kV to the SE tip 202. Because the distal end of the SE tip 202 is sharpened, a strong electric field is concentrated at the distal end. As the applied electric field increases, the effective work function of the surface decreases due to a Schottky effect, and more electron beams can be emitted.

[0030] The distance between the SE tip 202 and the bottom surface of the extraction electrode 204 is typically about 0.5 mm. By arranging them at such a short distance, a sufficiently strong electric field can be applied to the distal end of the electron source even at a low extraction voltage. A diaphragm 209 is provided at the bottom surface of the extraction electrode 204, and electrons that have passed through the diaphragm 209 are ultimately used to form the image. A thin molybdenum plate is used for the diaphragm 209, and the diameter of the aperture of the diaphragm 209 is typically about 0.1 mm to 0.5 mm. By making the aperture small, unnecessary electrons are prevented from passing through the diaphragm, thus preventing the observation image from deteriorating.

[0031] The SE tip 202 is positioned and welded onto the central axis of the insulator 208 using a highly precise jig. The outer periphery of the insulator 208 and the inner periphery of the suppressor 203, the outer periphery of the suppressor 203 and the inner periphery of the insulator 210, and the outer periphery of the insulator 210 and the inner periphery of the extraction electrode 204 are assembled by fitting on the order of 10 µm. Therefore, the SE tip 202, the suppressor 203, and the extraction electrode 204 have a highly precise coaxial structure, allowing the electrodes to be precisely positioned.

[0032] Because the SE tip 202 and the suppressor 203 have a coaxial structure, the potential distribution generated by the suppressor 203 near the SE tip 202 is uniform. Therefore, unnecessary electrons emitted from the side surface of the SE tip 202 can be uniformly reduced in all directions. In addition, electrons emitted from the SE tip 202 are not bent by a potential unevenness in space, allowing the electron beam to be emitted on a single axis.

[0033] Because the SE tip 202 and the extraction electrode 204 are coaxially arranged, the aperture 209 can also be arranged coaxially. Therefore, there is no possibility that the electron beam cannot be obtained due to a displacement of the aperture 209, which prevents the passage of emitted electrons. Furthermore, the distribution of the electric field applied to the distal end of the SE tip 202 is uniform due to the aperture 209, and the electron beam can be emitted on-axis.

[0034] In this way, the SE electron gun must be mounted with high precision and a small dimension of 1 mm or less to effectively emit the electron beam from the distal end of the electron source, reduce unnecessary electrons emitted from the side surface of the electron source, and implement a uniform potential distribution in the space of the electron gun. Therefore, the SE electron gun is characterized by having a very narrow space and maintaining a voltage difference on the order of kV.

[0035] A configuration around the SE electron gun 101 according to the present embodiment and a configuration of its electron source will be described with reference to FIG. Fig. 3A and Fig. 3B. The electron gun according to the present embodiment includes the electron source including the SE tip 202, the filament 206, the insulator 208, and an additional suppressor 303 with a shield electrode 301 formed of a conductive metal. It is characterized by using an insulator 310 with a step, and defining a gap 311 between a lower surface of the insulator 310 and an inner peripheral surface of the cylinder of the extraction electrode 204. The electron source according to the present embodiment includes the SE tip 202, the suppressor 303 disposed behind the distal end of the tip, an insulator 208 holding the terminals 207 electrically connected to the tip and the suppressor, and the shield electrode 301 disposed on the side surface of the suppressor.The shield electrode 301 is made of a conductive metal to which a voltage lower than the voltage applied to the tip is applied. The same reference numerals denote the same components as described above, and their descriptions are omitted.

[0036] As in Fig. As shown in Fig. 3A, a step is provided on the bottom surface of the insulator 310. For convenience, a surface below it (in the moving direction of the electron beam 115) is referred to as a lower surface 312, and a surface above it is referred to as an upper surface 313. The lower surface 312 is located on the shield electrode 303 side, and the upper surface 313 is located on the extraction electrode 204 side. Accordingly, the gap 311 is defined between the lower surface 312 of the insulator 310 and the inner peripheral surface of the extraction electrode 204.

[0037] As in the Fig. 3A and Fig. As shown in Figure 3B, the shield electrode 301 integrally formed of the conductive metal is provided on the side surface of the suppressor 303. The cylindrical portion on the side surface of the suppressor 303 extends in the axial direction of the SE tip 202 and is held by fitting by the insulator 310. The shield electrode 301 is provided on the side surface of the cylindrical portion of the suppressor 303 and protrudes laterally. In other words, the shield electrode 301 is configured to extend perpendicular to the axial direction of the SE tip 202. In other words, the shield electrode 301 is located between the suppressor 303 and the cylindrical portion of the extraction electrode 204.The voltage difference between the shield electrode 301 and the extraction electrode 204 is maintained by the vacuum between the shield electrode 301 and the extraction electrode 204, and they are thereby electrically insulated.

[0038] The shield electrode 301 further includes a cylindrical portion 302 extending toward the insulator 310 side. The upper end of the cylindrical portion 302 extends toward the gap 311. The cylindrical portion 302 of the shield electrode 301 has the same axis as the cylinder of the extraction electrode 204 and extends parallel thereto. Because the cylinder of the extraction electrode 204 extends in the axial direction of the SE tip 202, the cylindrical portion 302 also extends in the axial direction of the SE tip 202. Therefore, the lower surface 312 of the insulator 310 is covered with the shield electrode 301 and the cylindrical portion 302 and is not affected by the extraction electrode 204.The shield electrode 301, which has the cylindrical portion 302, is not in contact with the insulator 310, thereby preventing an unnecessary electric field from concentrating on the surface of the shield electrode 301. The outer peripheral side surface of the shield electrode 301 is subjected to the difference between the suppression voltage and the extraction voltage. Therefore, the side surface of the shield electrode is curved or flat to prevent an unnecessary electric field from concentrating. A function of preventing a very small discharge by the present configuration will be described later. The insulator 208 and the insulator 310 may be made of other electrically insulating materials such as glass.In the SE electron gun 101 according to the present embodiment, the radius of curvature of the distal end of the SE tip 202 is at least 0.5 μm, more preferably at least 1.0 μm. When a high current is emitted, Coulomb interaction between electrons occurs, and when a high current is emitted at a radius of curvature, the brightness of the electron beam decreases in the prior art. By increasing the radius of curvature of the distal end of the SE electron source, the emission area of the electron beam increases and the current density at the surface decreases. Therefore, the influence of the Coulomb interaction is weakened, and a decrease in brightness at a high current is prevented.

[0039] When a distal end curvature radius of 0.5 µm is used, the emission current is set to 300 µA or higher, so that higher brightness can be achieved at this curvature radius than in the prior art. To achieve this emission current, the extraction voltage is typically set to at least 3 kV. When a distal end curvature radius of 1 µm is used, the emission current is set to 600 µA or higher, so that higher brightness can be achieved than in the prior art. To achieve this emission current, the extraction voltage is typically set to 5 kV or higher.

[0040] When electrons are emitted from a metal material such as the extraction electrode 204 or the aperture 209, electron impact desorption gas is emitted. The emitted amount of electron impact desorption gas increases proportionally to the intensity of the emitted current and the applied extraction voltage. Therefore, when an emission current of 300 µA or 500 µA or greater, which is a high current, is emitted from the SE tip 202 at a high extraction voltage, an amount of electron impact desorption gas one or more orders of magnitude higher than in the prior art is generated, and the pressure of the Fig. 1. If the pressure is in the order of 10 -7Pa, the surface of the SE tip 202 will be damaged, the shape of the SE tip 202 will collapse, and the stability of the current may be affected. However, in the electron microscope according to the present embodiment, the vacuum chamber 119 is evacuated by the NEG pump 118 and the ion pump 120 at a high pumping speed. Therefore, the pressure deterioration is reduced even when a high current is emitted, and the pressure in the vacuum chamber 119 can be maintained at 10 -8 Pa or below. Therefore, the surface of the SE tip 202 is not damaged and a stable electron beam can be obtained even at the high current.

[0041] Next, an operation of the SE electron gun 101 according to the present embodiment for preventing a very small discharge will be described with reference to the Fig. 4 to 6.

[0042] With reference to Fig. Figure 4 describes a change in the current of the electron beam when a very small discharge occurs. The very small discharge occurs instantaneously and ends after a short time of at most 1 second, as is clear from the figure. At this time, the current of the electron beam decreases immediately and then returns to its original value. The pressure in the first vacuum chamber may increase instantaneously simultaneously with the very small discharge, and the pressure in the first vacuum chamber also returns to its original value within a few seconds.

[0043] The discharge that poses a problem in the electron gun is typically called flashover or breakdown. Once the discharge occurs, it causes melting of the electron source, breakdown of a high-voltage power supply, dielectric breakdown of the insulator, and the like, resulting in a strong discharge, after which the electron beam can no longer be obtained unless the electron source, power supply, and insulator are replaced. On the other hand, the very small discharge is characterized by a temporary decrease in current and then continuous electron beam, which is a relatively mild discharge. For example, the discharge in the prior art occurs when a high extraction voltage of about +10 kV is applied to the extraction electrode.On the other hand, the very small discharge does not occur even when a similarly high extraction voltage is applied, but it occurs only when electron beam emission occurs at a high current while the extraction voltage is applied, and the frequency of occurrence increases with increasing current. Furthermore, as the current increases, the threshold of the extraction voltage at which the very small discharge occurs decreases. The very small discharge has a different generation mechanism from the prior art discharge and represents a different phenomenon. Hereinafter, to distinguish the discharge from the very small discharge, the discharge that has been considered a problem in the prior art is referred to as a large discharge.

[0044] With reference to Fig. 5 describes a mechanism in which the very small discharge in the Fig. 2. Because the electron gun is axially symmetrical, only one side surface is shown. Furthermore, a potential distribution 510 in a space defined by the voltages applied to the tip 202, the suppressor 203, and the extraction electrode 204 is schematically represented by dashed lines.

[0045] The distal end of the SE tip 202 protrudes from the suppressor 203, and a side beam 501 is emitted from an equivalent (100) crystal plane located on the side surface of the SE tip 202. The side beam 501 is emitted in an oblique direction and collides with the extraction electrode 204. Furthermore, a portion of the electron beam 115 emitted from the (100) plane at the center of the distal end of the electron source also collides with the aperture 209. The intensity of the current colliding with the extraction electrode 204 or the aperture 209 is at least 90% of the emission current. The SE electron gun is characterized in that most of the current emitted from the electron source is emitted into a narrow space within the gun.

[0046] When the electrons collide with metal materials such as the extraction electrode 204 and the aperture 209, a portion of them are emitted toward the vacuum side as backscattered electrons. The emission angle of the backscattered electrons exhibits a spread, and its distribution is generally based on the cosine law with a specular reflection component as the peak. Furthermore, the energy of the backscattered electrons also has a distribution, with electrons whose energy is conserved during emission by elastic scattering and electrons whose energy is lost by inelastic scattering. Therefore, each backscattered electron has a different trajectory. Here, a trajectory diagram using the backscattered electrons 502 is described as a typical example.

[0047] The backscattered electrons 502 emitted by the extraction electrode 204 move toward the suppressor 203, but their energy is at most equal to the extraction voltage and they cannot reach the suppressor 203. Therefore, the backscattered electrons 502 are pushed back by a repulsive force acting in the vertical direction of the potential distribution and collide again with the extraction electrode 204. A portion of the backscattered electrons 502 is emitted as backscattered electrons 503 and collides with a cylindrical inner surface of the extraction electrode 204. A portion of the backscattered electrons 503 is re-emitted as backscattered electrons 504 and pushed back to the potential distribution of the suppressor 203 and collides again with the extraction electrode 204. A portion of the backscattered electrons 504 becomes backscattered electrons 505 and finally collides with the insulator 210.

[0048] The secondary electron emission rate of the insulator 210 is greater than 1, and when an electron collides with the insulator 210, more than one secondary electron is emitted. The energy of the emitted secondary electrons 506 is only a few electron volts, and due to the repulsive force of the potential distribution, they reach the extraction electrode 204 and are absorbed by it. As a result, the number of electrons on the surface 507 of the insulator 210, with which the backscattered electrons 505 collide, decreases, and the surface 507 becomes positively charged.

[0049] A potential difference greater than that before charging is formed by a leakage path between a contact point 511 between the suppressor 203 and the insulator 210 and the positively charged surface 507. The electric field applied to the contact point 510 becomes stronger as the distance between the contact point 511 and the surface 507 decreases. As a result, electric field emission occurs at the contact point 511, and a large number of electrons are emitted. While receiving the repulsive force of the potential distribution, the electrons move along the leakage path or a space of the insulator 210 and reach the extraction electrode 204. The very small discharge is generated by current transfer between the electrodes, and the voltage difference between the electrodes changes, so the current of the electron beam fluctuates.

[0050] In summary, when a high current is emitted from the SE electron gun, a large number of electrons are supplied to the narrow space inside the gun. These electrons are pushed back to the extraction electrode by the potential distribution formed between the suppressor 203 and the extraction electrode 204, and backscattered electrons are repeatedly generated. The backscattered electrons eventually reach the insulator 210, and the surface of the insulator 210 becomes locally positively charged. As the voltage difference between the positively charged surface 507 and the suppressor 203 increases and an electric field concentration occurs, a very small discharge occurs.

[0051] A mechanism by which the SE electron gun 101 according to the present embodiment prevents the very small discharge will be described with reference to Fig. 6. Similar to the prior art SE electron gun, in the SE electron gun 101 according to the present embodiment, the side beam 501 emitted from the SE tip 202 collides with the extraction electrode 204, thereby emitting backscattered electrons 502. The backscattered electrons 502 are pushed back by the repulsive force due to the potential distribution generated between the suppressor 303 and the extraction electrode 204 and collide with the extraction electrode 204 again. Thereafter, the backscattered electrons 502 are re-emitted from the extraction electrode and collide again.

[0052] In the SE electron gun 101 according to the present embodiment, because the shield electrode 301 is provided in the suppressor 303, a negative potential distribution generated by the suppressor voltage is broadened, making it less likely for backscattered electrons to reach the insulator 310. Specifically, the backscattered electrons cannot collide with the lower surface 312 of the insulator 310 because it is surrounded by the shield electrode 301 and its cylindrical portion 302. The backscattered electrons eventually collide with the upper surface 313 of the insulator 310 more frequently than in the prior art, and then positively charge the surface 517 of the insulator 310. The insulator 310 has a step on its bottom surface, and the upper surface 313 and the lower surface 312 of the insulator are separated from each other.Therefore, the creepage distance between the contact point 511 between the insulator 310 and the suppressor 303 and the positively charged surface 517 is long enough, and no high electric field is applied to the contact point 511. Therefore, no electric field emission occurs, and the very small discharge is prevented.

[0053] Another effect of the present embodiment is that a narrow path 601 can be defined between the cylindrical portion 302 and the inner peripheral surface of the extraction electrode 204 by causing the cylindrical portion 302 of the shielding electrode 301 to have the same axis as the cylinder of the extraction electrode 204 and extending the cylindrical portion 302 parallel to the extraction electrode 204 for a certain distance. In the narrow path 601, the potential distribution becomes narrow and the flight distance of the backscattered electrons becomes short, so that a high number of recollisions occurs. Each time a collision occurs, the number of backscattered electrons decreases by several tens of percent. As the number of recollisions increases, the absolute number of backscattered electrons reaching the insulator 310 increases, and thus the amount of charging decreases, so that the very small discharge is prevented.

[0054] Another effect is that the potential distribution within the shield electrode 301 is uniform and the electric field is small because the contact point 511 is surrounded by the shield electrode 301. For example, even when electrons are emitted from the contact point 511, the force exerted on the electrons is small and the probability of the electrons reaching the extraction electrode 204 is low, so the very small discharge is less likely to occur.

[0055] Another effect is that even if the creepage distance of the bottom surface of the insulator 310 is increased, the probability that the electrons travel along the creepage distance and reach the extraction electrode 204 is reduced, and the very small discharge is reduced. In addition, the strong discharge associated with the increase in the creepage distance is less likely to occur. In the SE electron gun according to the present embodiment, an SE tip 202 with a distal end curvature radius of 0.5 μm or 1.0 μm or more is used, and an extraction voltage of 3 kV or 5 kV or more is applied to the extraction electrode 204. Furthermore, the extraction voltage increases to 10 kV or more when an SE electron source with a higher distal end curvature is used.Even in this case, by increasing the creepage distance of the insulator 310, the electric field in the creepage direction is reduced and the risk of a strong discharge is also reduced.

[0056] Another effect is that a simple structure can be maintained without increasing the number of components because the suppressor 303 and the shield electrode 301 are integrally formed. This has the advantage of reducing costs. Furthermore, similar to the related-art SE electron gun, the insulator 208, the suppressor 303, the insulator 310, and the extraction electrode 204 can be assembled by fitting, and the coaxial arrangement and the electrode can be positioned with high accuracy. Therefore, in the electron gun 101 according to the present embodiment, efficient electron beam emission from the electron source, reduction of the emission of unnecessary electrons from the side surface of the electron source, and uniform potential distribution in the space of the electron gun can also be implemented.

[0057] Ions are generated by electron impact desorption from the metal irradiated with the electron beam. Collision with the ions also positively charges the insulator 210, and a very small discharge can occur by the same mechanism. However, in the SE electron gun 101 according to the present embodiment, the very small discharge caused by the ions can be prevented. [Second embodiment]

[0058] The first embodiment discloses that the shield electrode 301 formed integrally with the suppressor 303 and the stepped insulator 310 are used, and that the position where backscattered electrons collide with the surface of the insulator 310 is separated from the suppressor 303, thereby preventing a very small discharge. A second embodiment describes a configuration of an SE electron gun in which a suppressor and a shield electrode are constructed differently. Except for the shield electrode, the configuration is the same as that of the first embodiment, so its description will be omitted.

[0059] The SE electron gun according to the second embodiment will be described with reference to Fig. 7. A shield electrode 701 has a different structure than the suppressor 203 and is made of a conductive metal. An inner peripheral surface of the shield electrode 701 and an outer peripheral surface of the suppressor 203 are assembled and held by fitting. Furthermore, an outer peripheral surface of the shield electrode 701 and an inner peripheral surface of the insulator 310 are assembled by fitting. As a result, the tip 202, the suppressor 203, the shield electrode 701, and the extraction electrode 204 have a coaxial structure and can be accurately positioned. When the shield electrode 701 and the suppressor 203 come into contact with each other, the shield electrode 701 and the suppressor 203 have the same potential, and a suppression voltage is applied.

[0060] In the SE electron gun according to the present embodiment, similarly to the SE electron gun 101 according to the first embodiment, an end surface of a cylindrical portion 722 of the shield electrode 701 reaches the gap 311 provided in the insulator 310 with a step. Therefore, the effect of the step described with reference to Fig. 6 described process and the very small discharge can be prevented.

[0061] Because the number of components in the electron gun according to the present embodiment increases, the number of fitting sections increases, resulting in a possibility of deteriorating axial accuracy and increasing costs. However, if the shield electrode 701 is constructed differently from the suppressor 203, the suppressor 203 used in the prior art SE electron gun 201 can be eliminated. Using a standardized suppressor structure offers the advantages of reducing the cost of manufacturing the suppressor and allowing the SE electron source with a commercially available suppressor to be used as is. [Third Embodiment]

[0062] The second embodiment describes a configuration in which a suppressor and a shield electrode are constructed differently. A third embodiment describes a configuration in which the position where the insulator 310 is fitted into the suppressor is changed and the size of a shield electrode is reduced. Except for the shield electrode, the configuration is the same as that of the first embodiment, so its description will be omitted.

[0063] An SE electron gun according to the third embodiment will be described with reference to Fig. 8. A suppressor 702 according to the present embodiment has a shield electrode 703 at its upper end and side surface, and the suppressor 702 and the shield electrode 703 are integrally formed as in the first embodiment. An outer peripheral surface of a cylindrical portion with the lower surface 312 of the insulator 310 and an inner peripheral surface of the suppressor 702 are held and assembled by fitting. Thus, each electrode has a coaxial structure and is accurately positioned.

[0064] In the SE electron gun according to the present embodiment, the position of the contact point 511 is changed between the suppressor 702 serving as the starting point of the electric field emission and the insulator 310. However, similar to the SE electron gun 101 according to the first embodiment, an end surface of a cylindrical portion 723 of the shield electrode 703 reaches the gap 311 provided in the step-having insulator 310. Thereby, the contact point 511 is covered with a potential of the shield electrode 703, and a very small discharge is generated by a Fig. 6 described process is prevented.

[0065] By changing the fitting position between the suppressor 702 and the insulator 310 as in the present embodiment, the size of the shield electrode 703 can be reduced. This provides the advantage of reducing the diameter of the extraction electrode 204 and miniaturizing the SE electron gun. In addition, because the shape of the shield electrode 703 can be simplified, there is the advantage of easily manufacturing the suppressor 702 with an integrated configuration and reducing costs. [Fourth Embodiment]

[0066] The third embodiment describes a configuration in which the fitting position of the insulator 310 is changed and the size of the shielding electrode is reduced. A fourth embodiment describes an embodiment of an electron source obtained by changing the structure of the shielding electrode at the Fig. 2, and in which a suppressor 704 and a shield electrode 705 are integrated. Except for the shield electrode 705, the configuration is similar to that of the first embodiment, so its description will be omitted.

[0067] An SE electron gun according to the present embodiment will be described with reference to Fig. 9. The suppressor 704 according to the present embodiment has the shield electrode 705 integrated with the suppressor 704 on a side surface of the suppressor 704. Unlike the shield electrode 301 according to the first embodiment, the shield electrode 705 does not have a cylindrical portion. The shield electrode 705 protrudes in the outer circumferential direction and covers the contact point 511 between the suppressor 704 and the insulator 210 only from below. Therefore, a positively charged portion of the surface of the insulator 210 is separated from the contact point 511 by an amount corresponding to the protrusion of the shield electrode 705. This can reduce the frequency of a very small discharge compared to the SE electron gun 201 of the prior art.

[0068] Since the SE electron gun according to the present embodiment does not have the single-step insulator 310 described in the first embodiment, the creepage distance cannot be sufficiently extended. In addition, since the contact point 511 is not covered with the cylindrical portion 302 of the shield electrode, an electric field is easily applied to the contact point 511. Therefore, compared with the first embodiment, the effect of preventing a very small discharge is limited and the frequency is reduced. However, by simply changing the suppressor 704 according to the present embodiment, it can be mounted on the SE electron gun 201 of the prior art, offering the advantage of reducing the frequency of a very small discharge while reducing the development cost. [Fifth Embodiment]

[0069] According to the fourth embodiment, the structure of a shielding electrode is changed, and it can be mounted on a prior art SE electron gun. A fifth embodiment describes a configuration in which an opening is provided in an extraction electrode to reduce the absolute number of backscattered electrons reaching an insulator, thereby enhancing the effect of preventing a very small discharge. According to the present embodiment, when an opening of the aperture 209 is provided, at least two openings are provided in the extraction electrode. Except for the extraction electrode, the configuration is the same as that of the first embodiment, so its description is omitted.

[0070] An SE electron gun according to the fifth embodiment will be described with reference to Fig. 10. An extraction electrode 801 according to the present embodiment has an opening 802 different from the opening of the aperture 209 on its bottom surface. In addition, an opening 803 is provided in a cylindrical surface of the extraction electrode 801 at a position opposite to the cylindrical portion 802 of the shield electrode 301. When the extraction electrode 801 is irradiated with the side beam 501 emitted from the tip 202, backscattered electrons are emitted. Of the backscattered electrons 804, some having low energy pass through the opening 802 in the bottom surface and move out of the SE electron gun. This reduces the absolute number of backscattered electrons that finally reach the insulator 310.

[0071] On the other hand, even if high-energy backscattered electrons 805 travel across the opening 802 in the bottom surface, after repeated recollisions, many of them exit the SE electron gun through the opening 803 of a cylindrical surface. In the narrow path 601 between the extraction electrode 801 and the cylindrical portion 302, the potential distribution is narrow, and a large number of backscattered electrons recollide. By providing the opening 803 at this position, many backscattered electrons exit the SE electron gun, and the absolute number of backscattered electrons that eventually reach the insulator 310 can be effectively reduced. With the opening 802 and the opening 803 of the extraction electrode 801 as described above, the degree of charging of the insulator 310 is reduced, and further, a very small discharge can be prevented.

[0072] By increasing the diameter of the aperture 209 so that the side beam 501 is emitted at the aperture 209 and providing an opening at an emission position of the side beam 501 at the aperture 209, the very small discharge can also be prevented by the same effect as described above. [Sixth Embodiment]

[0073] The fifth embodiment describes a configuration in which an opening is provided in an extraction electrode to reduce the absolute number of backscattered electrons reaching an insulator, thereby enhancing the effect of preventing a very small discharge. A sixth embodiment describes a configuration in which a protrusion is provided on the inside of the extraction electrode to reduce the absolute number of backscattered electrons reaching the insulator, thereby enhancing the effect of preventing a very small discharge. Except for the extraction electrode, the configuration is the same as that of the first embodiment, so its description is omitted.

[0074] An SE electron gun according to the sixth embodiment will be described with reference to Fig. 11. An extraction electrode 809 according to the present embodiment has a protrusion 813 on the bottom surface. In addition, a protrusion 814 is provided on a cylindrical surface. The protrusion 813 on the bottom surface is formed integrally with the extraction electrode 809, and the aperture 209 is arranged below the protrusion 813. Further, the protrusion 813 has a tapered part, and the diameter of an opening of the protrusion 813 is larger on the aperture 209 side than on the SE tip 202 side. An extraction voltage is applied to the protrusion 813. An upper surface of the protrusion 813 facing the suppressor 303 is flat to prevent concentration of an unnecessary electric field.

[0075] The protrusion 814 on the cylindrical surface is formed integrally with the extraction electrode 809, and the extraction voltage is applied to the protrusion 814. An end surface of the protrusion 814 on the suppressor 303 side has a tapered portion, and the diameter of an opening is larger on the lower surface than on the upper surface. The end surface of the protrusion 814 opposite the suppressor 303 is flat to prevent the concentration of an unnecessary electric field.

[0076] Among the side beams emitted from the SE tip 202, a side beam 812 having a large emission angle collides with the aperture 209 and then emits backscattered electrons 816. Because the backscattered electrons 816 are emitted with a peak in a mirror surface direction, most of the backscattered electrons 816 collide with a lower surface of the tapered part of the protrusion 813. Backscattered electrons 817 emitted from this lower surface collide with the aperture 209. In this way, by providing the protrusion 813 to the side beam 812 having a large emission angle, repeated recollision of a large number of backscattered electrons occurs at a pocket portion created between the tapered part of the protrusion 813 and the aperture 209, thereby reducing the number of backscattered electrons. This makes it impossible for the electrons to reach the insulator 310.

[0077] A side beam 810 emitted from the SE tip 202 at a small angle collides with the aperture 209 and then emits backscattered electrons 811. The backscattered electrons 811 pass through the opening of the protrusion 813 and collide with the extraction electrode 809, emitting backscattered electrons 818. The backscattered electrons 818 collide with the lower surface of the protrusion 814 and emit backscattered electrons 819. Thus, by providing the protrusion 814 with a small emission angle, the side beam 810 repeatedly recollides a large number of backscattered electrons at the pocket portion created between the lower surface of the protrusion 814 and the extraction electrode 809, thereby reducing the number of backscattered electrons. This makes it impossible for the electrons to reach the insulator 310.

[0078] The protrusion 813 and the protrusion 814 of the extraction electrode 809 reduce the absolute number of backscattered electrons reaching the insulator 310 and the degree of charging of the insulator 310. This can further prevent very small discharges.

[0079] Another effect is that a narrow path 815 is defined between the protrusion 814 and the suppressor 303. The narrow path 815 has a small solid angle under which the backscattered electrons can move, making it difficult for them to leave the narrow path 815. In addition, the potential distribution is narrow, forcing the backscattered electrons to collide with the protrusion 814 in large numbers. This effectively reduces the number of backscattered electrons reaching the insulator 310. [Seventh Embodiment]

[0080] The sixth embodiment describes a configuration in which a protrusion is provided on the inside of an extraction electrode to reduce the absolute number of backscattered electrons reaching an insulator, thereby enhancing the effect of preventing a microscopic discharge. A seventh embodiment describes a configuration in which the inner diameter of a contact portion between the extraction electrode and the insulator is smaller than the inner diameter of a cylindrical portion of the extraction electrode. In other words, a neck portion is provided in the extraction electrode, the neck portion and the insulator are held by fitting, and the absolute number of backscattered electrons is reduced, thereby improving the effect of preventing a microscopic discharge.Except for the extraction electrode, the configuration is the same as that of the first embodiment, so its description is omitted.

[0081] An SE electron gun according to the seventh embodiment will be described with reference to Fig. 12. The extraction electrode according to the present embodiment is divided into a bottom portion 821 and a cylindrical portion 824 for assembly. Furthermore, a neck portion 822 is provided at an upper portion of the cylindrical portion 824 of the extraction electrode. The neck portion 822 and an insulator 820 are held by fitting. Furthermore, the insulator 820 and the suppressor 303 are held by fitting. Furthermore, the length of the cylindrical portion 302 of the suppressor 303 extends to the vicinity of the neck portion 822.

[0082] Because the cylindrical portion 302 is elongated, the length of the narrow path 601 defined between the cylindrical portion 302 of the shielding electrode 301 and the cylindrical portion 824 of the extraction electrode is elongated. Additionally, a narrow path 823 is provided between the neck portion 822 and the cylindrical portion 302. As the distances between the narrow paths increase, the frequency with which backscattered electrons collide with the lower portion 821 of the extraction electrode increases, and the number of backscattered electrons reaching the insulator 820 increases. This reduces the charging strength of the insulator 820 and prevents the very small discharge. [Eighth Embodiment]

[0083] The seventh embodiment describes a configuration in which a neck portion is provided in an extraction electrode to reduce the absolute number of backscattered electrons and thereby enhance the effect of preventing a very small discharge. An eighth embodiment describes a configuration in which an insulator is formed by a semiconductive material or a semiconductive or conductive thin film is provided on the surface of the insulator to prevent charging and enhance the effect of preventing a very small discharge. Except for the insulator, the configuration is similar to that of the first embodiment, so its description is omitted.

[0084] An SE electron gun according to the eighth embodiment will be described with reference to Fig. 13. According to the present embodiment, a semiconductive insulator 830 is used instead of the insulator 310 according to the first embodiment. The semiconductive insulator 830 has an electrical conductivity between that of a metal and that of an insulator and a volume resistivity of about 10 10 Ωcm to 10 12 Ωcm. By using the semiconducting insulator 830, even if a dark current increases, a voltage difference can be maintained between the extraction electrode 204 and the suppressor 303. On the other hand, when the backscattered electrons collide with the semiconducting insulator 830, electrons are immediately supplied from the semiconducting insulator 830 near it if the surface of the semiconducting insulator 830 is charged, so the charge is reduced. Therefore, no electric field emission occurs from the contact point 511, and a very small discharge can be prevented.

[0085] The same effect can also be achieved by providing a semiconducting coating 831 on the surface of an insulator. The semiconducting coating 831 is a thin film with a volume resistivity of about 10 10 Ωcm to 10 12 Ωcm, and it has a thickness of a few µm. Even if the backscattered electrons collide with the semiconducting coating 831, the charge is immediately reduced and a very small discharge can be prevented.

[0086] The semiconductive coating 831 is not limited to being provided on the entire surface of the insulator, and it exerts the same effect even if it is provided on only a part of the surface. When the semiconductive coating 831 is provided on a part of the surface, the conductivity of the semiconductive coating 831 can be increased, and the volume resistivity can be increased to 10. 10 Ωcm or less. If the portion to be covered is limited to a very small part of the surface, a conductive metal thin film may be formed, or a film may be formed by metallization. Furthermore, providing a semiconductive coating or metal coating near the contact point 511 has the additional effect of reducing the concentration of the electric field at the contact point 511. [Ninth Embodiment]

[0087] The eighth embodiment describes a configuration in which an insulator is semiconductive or a semiconductive coating is applied to the insulator to prevent charging and enhance the effect of preventing a very small discharge. A ninth embodiment describes a configuration in which a suppressor is held by a conductive support portion and the absolute number of backscattered electrons is reduced to enhance the effect of preventing a very small discharge.That is, the ninth embodiment is an embodiment of a charged particle beam apparatus having an electron gun including a tip, a suppressor disposed behind a distal end of the tip, a conductive support portion holding the suppressor, an extraction electrode having a bottom surface and a cylindrical portion enclosing the tip and the suppressor, an insulator holding the support portion and the extraction electrode, and a conductive metal provided between the support portion and the cylindrical portion of the extraction electrode, wherein a voltage lower than a voltage applied to the tip is applied to the conductive metal.

[0088] The SE electron gun according to the ninth embodiment will be described with reference to Fig.14. Except for the support portion, the configuration is similar to that of the first embodiment, so its description is omitted. As shown in the figure, the suppressor 303 according to the present embodiment is supported by a support portion 840. The support portion 840 is a conductive metal cylinder and is configured coaxially with the suppressor 303. The support portion 840 comes into contact with the suppressor 303 and therefore has the same potential as the suppressor 303. The support portion 840 is held by fitting it into the insulator 310. The insulator 310 and a cylinder of the extraction electrode 204 are held by fitting it. This maintains accurate positioning and coaxial arrangement between the SE tip 202 and the extraction electrode 204. A feedthrough 841 is connected to the terminal 207, and current is supplied to the filament 206.The shield electrode 301 is provided on a side surface of the support portion 840 and covers the lower surface 312 of the insulator 310 together with the cylindrical portion 302.

[0089] Moreover, according to the present embodiment, the trajectory of the backscattered electrons is controlled by the shield electrode 301, which is integrally constructed with the support portion 840 of the suppressor 303, and the position where the backscattered electrons collide with the insulator 310 is separated from the contact point 511. This reduces the increase in an electric field at the contact point 511 due to charging, and a micro discharge can be prevented. Furthermore, the distance between the SE tip 202 and the insulator 310 is increased by providing the support portion 840 of the suppressor 303. This increases the number of collisions until the backscattered electrons reach the insulator 310, and reduces the absolute number of electrons, so that a micro discharge can be effectively prevented.As described in the present embodiment, the shield electrode 301 can be attached to a component other than the suppressor itself. Furthermore, even if another conductive component is added to the suppressor 303 or the support portion 840 and brought into contact with the suppressor 303 or the support portion 840, the same effect can be achieved by providing the additional component with the shield electrode 301.

[0090] The invention is not limited to the above-mentioned embodiments and includes various modifications. For example, the SE tip 202 according to the present invention may be an electric field emission cold cathode electron source, a thermal electron source, or a light excitation electron source. The material of the SE tip 202 is not limited to tungsten and may be LaB6, CeB6, or a carbon-based material. Furthermore, the above-mentioned embodiments have been described in detail for a simple understanding of the invention, and the invention is not necessarily limited to having all of the above-described configurations. A part of a configuration of one embodiment may be replaced with a configuration of another embodiment, and the configuration of the other embodiment may be added to the configuration of one embodiment.Furthermore, a portion of the configuration of each embodiment may be added to, removed from, or replaced by another configuration. List of reference symbols 101 SE Electron Cannon 102 Control electrode 103 Acceleration electrode 109 Turbomolecular pump 110 convex lens 111 Objective lens 112 Sample 113 Sample chamber 114 Detector 115 Electron beam 116 Insulator 118 Non-evaporable getter pump 119 first vacuum chamber 120 ion pump 121 Ion pump 122 Ion pump 125 cylindrical body 126 second vacuum chamber 127 third vacuum chamber 128 fourth vacuum chamber 201 SE electron gun from the state of the art 202 SE-peak 203 Oppressors 204 Extraction electrode 205 Zirconium oxide 206 threads 207 connection 208 Insulator 209 aperture 210 Insulator 301 Shielding electrode 302 cylindrical section 303 Oppressors 310 Insulator 311 space 312 lower surface 313 upper surface 501 Side beam 502 backscattered electron 503 Backscattered electron 504 Backscattered electron 505 Backscattered electron 506 secondary electron 507 area 510 Potential distribution 511 contact point 517 area 601 narrow path 701 Shielding electrode 702 oppressors 703 Shielding electrode 704 Oppressors 705 Shielding electrode 722 cylindrical section 723 cylindrical section 801 Extraction electrode 802 Opening 803 Opening 804 backscattered electron 805 backscattered electron 810 side beam 811 Backscattered electron 812 side beam 813 lead 814 lead 815 narrow path 816 backscattered electron 817 backscattered electron 818 backscattered electron 819 Backscattered electron 820 Insulator 821 lower section of the extraction electrode 822 neck section 823 narrow path 824 cylindrical section of the extraction electrode 830 semiconducting insulator 831 semiconducting coating 840 support section 841 Implementation

Claims

[1] A charged particle beam device comprising: an electron gun (201) comprising: a tip (202), a suppressor (203) arranged behind a distal end of the tip (202), an extraction electrode (204) having a bottom surface and a cylindrical portion (302) and enclosing the tip (202) and the suppressor (203), an insulator (208) holding the suppressor (203) and the extraction electrode (204), and a conductive metal (301) provided between the suppressor (203) and the cylindrical portion (302) of the extraction electrode (204), wherein a voltage lower than a voltage applied to the tip (202) is applied to the conductive metal (301). [2] A charged particle beam apparatus according to claim 1, wherein a step is provided on an end face of the insulator (310) and a gap (311) is provided between the insulator (310) and the cylindrical portion of the extraction electrode (204). [3] A charged particle beam device according to claim 2, wherein a part of the conductive metal (301) extends to the gap (311). [4] A charged particle beam device according to claim 3, wherein the conductive metal (301) and the suppressor (203) are integrally formed. [5] A charged particle beam apparatus according to claim 4, wherein the conductive metal (301) has a cylindrical structure, and the cylindrical structure extends coaxially with the cylindrical portion of the extraction electrode (204). [6] A charged particle beam apparatus according to claim 4, wherein at least two openings (802, 803) are provided in the extraction electrode (204). [7] A charged particle beam apparatus according to claim 4, wherein at least one protrusion (814) is provided within the extraction electrode (204). [8] A charged particle beam device according to claim 4, wherein the inner diameter of a contact portion between the extraction electrode (204) and the insulator (310) is smaller than the inner diameter of the cylindrical portion of the extraction electrode (204). [9] A charged particle beam device according to claim 4, wherein the insulator (310) is made of a semiconductive material or a semiconductive or conductive thin film is provided on the surface of the insulator (310). [10] A charged particle beam device according to claim 4, wherein the radius of curvature of the distal end of the tip (202) is set to a value greater than 0.5 µm. [11] A charged particle beam device according to claim 4, wherein a vacuum chamber in which the tip (202) is located is evacuated by a non-evaporable getter pump. [12] A charged particle beam device comprising: an electron gun (101) comprising: a tip (202), a suppressor (203) arranged behind a distal end of the tip (202), a conductive support portion holding the suppressor (203), an extraction electrode (204) having a bottom surface and a cylindrical portion and enclosing the tip (202) and the suppressor (203), an insulator holding the support portion and the extraction electrode (204), and a conductive metal (301) provided between the support portion and the cylindrical portion of the extraction electrode (204), wherein a voltage lower than a voltage applied to the tip (202) is applied to the conductive metal (301). [13] A charged particle beam apparatus according to claim 12, wherein a step is provided on an end face of the insulator (310) and a gap (311) is provided between the insulator and the cylindrical portion of the extraction electrode (204). [14] A charged particle beam device according to claim 13, wherein a part of the conductive metal (301) extends to the gap (311). [15] Electron source comprising: a peak (202), a suppressor (203) disposed behind a distal end of the tip (202), an insulator (210) holding a terminal (207) electrically connected to the tip (202) and the suppressor (203), and a shield electrode (705) made of a conductive metal, which is provided integrally on a side surface of the suppressor (203).

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