Charged particle gun

Abstract

Though high-brightness charged particle sources have high brightness, the angular current density thereof is low, and when a large current is acquired, aberration in the electron lens system increases and spatial resolution deteriorates.　The present invention narrows the emission angle of the charged particle beam and adjusts the angular current density by treating a composite extraction electrode composed of two electrodes as one electrode disposed directly below an emitter, and forming a convex potential distribution on the emitter side and a concave potential distribution at the emitter tip using the voltage combination applied to the two electrodes. Since the lens effect from the composite extraction electrode acts directly below the emitter tip, aberration is extremely small and there is no deterioration of the spatial resolution even when a large current is acquired.

Description

charged particle gun

[0001] The present invention relates to a device for controlling the brightness and angular current density of a charged particle beam emitted from a charged particle source in a charged particle gun equipped with the charged particle source.

[0002] As an example of a charged particle emission device, a cold-cathode field emission electron gun will be described with reference to the drawings. Figure 8 shows a conventional cold-cathode field emission electron gun. The cold-cathode field emission electron gun is housed in a high-vacuum container (not shown). An electric field is formed between the emitter 101 and the extraction electrode 102 by an extraction voltage applied to the extraction electrode 102. A particularly strong electric field is formed at the tip of the emitter 101, causing electrons (charged particles 104) to be emitted from the tip of the emitter 101. The strength of the electric field is shown as the density of equipotential lines 107 representing the potential distribution between the emitter 101 and the extraction electrode 102. As shown in the figure, the density of the equipotential lines 107 at the tip of the emitter 101 is extremely high, indicating a strong electric field. An acceleration voltage is applied to the emitter 101 from an acceleration power supply 108. An extraction voltage is applied to the extraction electrode 102 from an extraction power supply 109.

[0003] AV Crewe, DN Eggenberger, J. Wall, LM Welter, “Electron Gun Using a Field Emission Source”, The review of scientific instruments, Vol.39, Num.4, 1967

[0004] As shown in Figure 8, in order to emit charged particles 104 from the emitter 101, a sufficiently strong electric field must be formed at the tip of the emitter 101. Figure 9 shows a case in which a strong electric field is formed at the tip of the emitter 101, using a cold cathode field emission electron gun as an example. Arc-shaped equipotential lines 107 are densely formed near the tip of the emitter 101 according to the surface shape, and the emitted charged particles 104 (electrons) fly away due to forces acting in the normal direction of the equipotential lines 107, forming a virtual light source 114 where the charged particle trajectories asymptote 113 of the charged particles 104 (electrons) emitted in each direction intersect at a minimum. When the emitter 101 is viewed from downstream, the emitted charged particles 104 appear to be emitted from the virtual light source 114. Therefore, it is common to use a charged particle beam formed by charged particles 104 (electrons) emitted from the emission surface of the emitter 101 with a large emission angle, and the angle is limited by an aperture 115 located between the emitter 101 and a sample (not shown). However, if the emission angle 116 is limited to a small angle, the number of charged particles 104 passing through the aperture 115 decreases, and when the electron beam passing through the aperture 115 is used in, for example, a charged particle microscope, the signal-to-noise ratio of the observed value becomes extremely poor. Furthermore, if the hole diameter of the aperture 115 is increased to increase the emission angle 116 in order to improve the signal-to-noise ratio, the aberration of an electron lens (not shown) located downstream of the emitter 101 becomes large. Therefore, when used in, for example, a charged particle microscope, the diameter of the charged particle beam at the sample (not shown) becomes large, resulting in poor resolution. Furthermore, if the emission angle of the charged particle beam is large, most of the charged particles 104 (electrons) forming the charged particle beam collide with the extraction electrode 102 or the aperture 115 (not shown), generating secondary electrons 117 and gas molecules 118 from the surfaces of the extraction electrode 102 or the aperture 115. The emitted secondary electrons 117 are accelerated and collide with the emitter 101, damaging the emitter 101, and the emitted gas molecules 118 deteriorate the degree of vacuum, reducing the amount of emission and inducing damage to the emitter 101 due to discharge.

[0005] An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a charged particle gun which does not deteriorate the degree of vacuum even when a large current is emitted from the emitter, and which can maintain high resolution without reducing the signal-to-noise ratio even when the angle of the electron beam emitted from the emitter is limited.

[0006] In order to solve the above problems, the present invention provides a charged particle gun equipped with a charged particle source, characterized in that it comprises an emitter that emits charged particles, and a composite extraction electrode consisting of an electric field suppression electrode arranged directly below the emitter and an extraction electrode arranged directly below the electric field suppression electrode.

[0007] Furthermore, the charged particle gun is characterized in that, when the radius r of the emitter is 1 μm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter have a negative charge based on the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter have a positive charge, the absolute value |Vex-Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.0079 or more and 3.645 or less.

[0008] Furthermore, the charged particle gun is characterized in that, when the radius r of the emitter is 100 nm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter have a negative charge based on the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter have a positive charge, the absolute value |Vex - Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.0079 or more and 1.825 or less.

[0009] Furthermore, the charged particle gun is characterized in that, when the radius r of the emitter is 100 nm or more and 1 μm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter have a negative charge based on the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter have a positive charge, the absolute value |Vex - Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.365 or more and 3.645 or less.

[0010] In addition, the charged particle gun has a distance L between the emitter and the electric field suppression electrode. ０ is a distance L between the electric field suppression electrode and the extraction electrode, and is 0 or more and 4×L or less.

[0011] The charged particle gun is also characterized in that potentials are applied independently to the electric field suppression electrode and the extraction electrode.

[0012] The charged particle gun is also characterized in that the potential applied to the electric field suppression electrode is lower than the potential applied to the extraction electrode.

[0013] The charged particle gun is also characterized in that a potential distribution protrudes in a convex shape from the hole in the electric field suppression electrode toward the emitter side.

[0014] The charged particle gun is also characterized in that the emitter tip is disposed so as to pierce the potential distribution that exudes in a convex shape, and the emitter tip has a potential distribution that is formed in a concave shape.

[0015] The charged particle gun is also characterized in that the side of the hole in the emitter side surface of the electric field suppression electrode is bowl-shaped or inclined.

[0016] The charged particle gun is also characterized in that the ratio L0 / R of the radius R of the hole in the electric field suppression electrode to the distance L0 between the electric field suppression electrode and the tip of the emitter is 1 or less.

[0017] The charged particle gun is also characterized in that the composite extraction electrode operates as a single electron lens by a combined voltage {Vsu, Vex} of a voltage Vsu applied to the electric field suppression electrode and a voltage Vex applied to the extraction electrode.

[0018] The charged particle gun is also characterized in that the intensity of the electric field applied to the tip of the emitter is changed by the combined voltage {Vsu, Vex} to adjust the amount of emission current.

[0019] The charged particle gun is also characterized in that the combined voltage {Vsu, Vex} is used to change the potential distribution between the emitter and the composite extraction electrode, thereby adjusting the trajectory of the charged particles emitted from the emitter.

[0020] The charged particle gun is also characterized in that the amount of emission current and the trajectory of the charged particles are adjusted by the combined voltage {Vsu, Vex}.

[0021] The charged particle gun is also characterized in that the combined voltage {Vsu, Vex} keeps the electric field strength applied to the tip of the emitter constant and adjusts the trajectory of the emitted charged particles while maintaining the emission current constant.

[0022] The charged particle gun is also characterized in that the converted brightness and angular current density of the emitted charged particle beam are adjusted by the combined voltage {Vsu, Vex}.

[0023] In addition, in the charged particle gun, the emitter is any one of a thermionic electron emission source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, and a helium ion source.

[0024] High-brightness charged particle sources have high brightness but low angular current density, and brightness drops significantly when a large current flows. However, the present invention can minimize the drop in brightness even when a large current flows, and increase the angular current density.

[0025] By adjusting the voltages applied to the two electrodes, the characteristics (brightness, angular current density) of the charged particle beam emitted from the charged particle source can be set to a high brightness mode or a large angular current density mode.

[0026] The high brightness mode and the large angular current density mode are not separate, but the degree of the two modes can be continuously changed.

[0027] When the present invention is applied to a charged particle microscope, the sample surface can be analyzed with high spatial resolution in the high brightness mode, and the sample surface can be analyzed with a large current while maintaining high spatial resolution without reducing the signal-to-noise ratio even when the angle of the electron beam is restricted in the high angular current density mode.

[0028] When the present invention is applied to a charged particle microscope, the degree of high brightness mode and large angular current density mode can be continuously changed according to the characteristics of the sample to be observed, thereby making it possible to observe the sample under the optimum conditions.

[0029] In the high angular current density mode, the emission angle of the emitted charged particle beam becomes small, so the charged particles do not collide with the electrode to which voltage is applied to extract the charged particles, and gas is not generated from the electrode, which does not cause a deterioration in the vacuum around the emitter.In addition, because the charged particles do not collide with the electrode, contaminants do not adhere to the electrode surface, and the emitter is not damaged by discharge caused by the attached particles becoming charged.

[0030] When the present invention is applied to a charged particle microscope, the angular current density can be changed, so there is no need for an electron lens for adjusting the amount of current on the sample side as viewed from the emitter, and the charged particle microscope can be made compact.

[0031] When the present invention is applied to a charged particle microscope, the charged particles emitted from the emitter can be made immediately parallel to the optical axis, so that a sample can be observed with a highly coherent charged particle beam.

[0032] When the present invention is applied to a charged particle microscope, the emission angle is small and the diameter of the charged particle beam does not deviate significantly from the optical axis, so that the aberration generated by the electron lens located on the sample side as viewed from the emitter can be kept small, and even when the charged particle beam is focused on the surface of the sample, the spread of the diameter of the charged particle beam due to aberration is small.

[0033] When the present invention is applied to a charged particle microscope specialized for semiconductor sample inspection, the sample surface can be observed and measured with high spatial resolution even when the amount of current irradiated onto the sample is large, thereby reducing the time required for sample observation and increasing measurement speed.

[0034] When the present invention is applied to a transmission electron microscope, a sample can be observed with a highly coherent charged particle beam.

[0035] When the present invention is applied to a charged particle microscope equipped with an emitter having a tip radius of 1 μm or less, a sample can be observed with a highly coherent charged particle beam having a high current density.

[0036] FIG. 1 is a schematic diagram showing an embodiment of the present invention; FIG. 2 is a schematic diagram explaining an example of operation of a composite extractor electrode according to the present invention; FIG. 3 is a schematic diagram explaining an example of operation of a composite extractor electrode according to the present invention; FIG. 4 is a schematic diagram explaining an embodiment of a composite extractor electrode according to the present invention; FIG. 5 is a schematic diagram explaining an example of operation of a composite extractor electrode according to the present invention; FIG. 6 is a charged particle trajectory diagram explaining an example of operation of a composite extractor electrode according to the present invention; FIG. 7 is a schematic diagram showing another embodiment of a charged particle gun according to the present invention; FIG. 8 is a schematic diagram showing the configuration of a conventional charged particle gun; FIG. 9 is a schematic diagram explaining the operation of a conventional charged particle gun.

[0037] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same functions will be assigned the same reference numerals, and repeated description thereof may be omitted.

[0038] The charged particle device includes a charged particle gun equipped with a charged particle source.

[0039] The charged particle gun comprises an emitter that emits charged particles, and a composite extraction electrode that is composed of an electric field suppression electrode that is arranged directly below the emitter on an optical axis centered on the emitter, and an extraction electrode that is arranged directly below the electric field suppression electrode.

[0040] When the radius r of the emitter is 1 μm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter are negatively charged with respect to the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter are positively charged, the absolute value |Vex-Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.0079 or more and 3.645 or less.

[0041] Furthermore, when the radius r of the emitter is 100 nm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter are negatively charged with respect to the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter are positively charged, the absolute value |Vex-Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.0079 or more and 1.825 or less.

[0042] Furthermore, when the radius r of the emitter is 100 nm or more and 1 μm or less, the voltage Vsu applied to the electric field suppression electrode is 0 V or more when the charged particles emitted from the emitter are negatively charged with respect to the potential of the emitter, and the voltage Vsu applied to the electric field suppression electrode is 0 V or less when the charged particles emitted from the emitter are positively charged, the absolute value |Vex-Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less, and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.365 or more and 3.645 or less.

[0043] The distance L between the emitter and the electric field suppression electrode ０ is the distance L between the electric field suppression electrode and the extraction electrode, and is 0 or more and 4×L or less.

[0044] The radius R of the hole in the electric field suppression electrode and the distance L between the electric field suppression electrode and the tip of the emitter ０ Relative to L ０ / R is 1 or less.

[0045] The voltage applied to the electric field suppression electrode and the voltage applied to the extraction electrode form a potential distribution that seeps out in a convex shape from the hole in the electric field suppression electrode toward the emitter, forming a strong electric field at the tip of the emitter.

[0046] A potential is applied to the electric field suppression electrode and the extraction electrode independently, and the potential applied to the electric field suppression electrode is lower than the potential applied to the extraction electrode.

[0047] A potential distribution protrudes in a convex shape from the hole in the electric field suppression electrode toward the emitter, and the tip of the emitter is positioned so as to pierce the protruding potential distribution in a convex shape, so that a concave potential distribution is formed at the tip of the emitter.

[0048] The side of the hole in the emitter side surface of the field suppression electrode is bowl-shaped or inclined.

[0049] The emitter may be, for example, a thermionic electron source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, or a helium ion source.

[0050] FIG. 1 shows one embodiment of the present invention. A detailed description will be given below with reference to the drawings. A composite extractor electrode 106, located directly below an emitter 101 that emits charged particles 104, comprises a field suppression electrode 103 and an extractor electrode 102 located directly below the field suppression electrode 103. A field suppression voltage is applied to the field suppression electrode 103 from a field suppression power supply 110, and an extractor voltage is applied to the extractor electrode 102 from an extractor power supply 109. The voltages applied to each electrode cause a convex potential distribution to leak out from the holes in the field suppression electrode 103 toward the emitter 101 between the emitter 101 and the field suppression electrode 103. In the figure, this potential distribution is represented by equipotential lines 107, and a higher density of the equipotential lines 107 indicates a stronger electric field strength. The emitter 101 is positioned so that it penetrates the convex potential distribution, creating a strong electric field at the tip of the emitter 101. The charged particles 104 are emitted from the tip of the emitter 101 by the strong electric field, and the emitted charged particles 104 fly away due to a force acting in the normal direction of the equipotential lines 107, so that the emitted charged particles 104 fly away without deviating significantly from the optical axis 105 due to the convex potential distribution.

[0051] In the present invention, when the charged particles 104 emitted from the emitter 101 are negatively charged, the voltage Vsu applied to the electric field suppression electrode 103 is 0 V or higher, based on the potential of the emitter 101. When the charged particles 104 emitted from the emitter 101 are positively charged, the voltage Vsu applied to the electric field suppression electrode 103 is 0 V or lower. However, to easily explain the convex potential distribution, it is assumed that the charged particles 104 emitted from the emitter 101 are negatively charged, and that the potential of the electric field suppression electrode 103 is the same as that of the emitter 101.

[0052] Even when the voltage Vsu applied to the electric field suppression electrode 103 is greater than 0 V, the emitted charged particles 104 fly under the force acting in the normal direction of the equipotential lines 107, and therefore the convex potential distribution causes the emitted charged particles 104 to take a trajectory more aligned with the optical axis 105, without loss of generality in explaining the present invention. Conversely, when the voltage Vsu applied to the electric field suppression electrode 103 is less than 0 V, the amount of charged particles emitted from the emitter 101 decreases, and the lens effect of the composite extraction electrode 106 is too strong, resulting in the formation of a crossover and a further reduction in the angular current density.

[0053] A high voltage is applied to the extraction electrode 102, causing the charged particles 104 to be emitted from the tip of the emitter 101. However, the electric field suppression electrode 103 causes the potential distribution seeping out of the holes in the electric field suppression electrode 103 to be convex on the emitter 101 side. In other words, the electric field suppression electrode 103 only contributes to making the shape of the potential distribution created by the voltage applied to the extraction electrode 102 convex. However, the electric potential of the electric field suppression electrode 103 does not necessarily have to be the same as that of the emitter 101, and a voltage may be applied to the electric field suppression electrode 103. In other words, the composite extraction electrode 106 can change the shape of the potential distribution and the electric field strength applied to the tip of the emitter 101 by applying voltages to the electric field suppression electrode 103 and the extraction electrode 102. For example, the shape of the potential distribution can be changed while maintaining the electric field strength applied to the tip of the emitter 101 constant. This allows the trajectory of the charged particles 104 to be changed while keeping the amount of emitted current constant.

[0054] 2 shows a case where a voltage Vsu and a voltage Vex are applied to the field suppression electrode 103 and the extraction electrode 102, respectively, which constitute the composite extraction electrode 106. The combination of voltages {Vsu, Vex} causes the composite extraction electrode 106 to function as an electron lens. The voltage combination changes the shape of the potential distribution indicated by the equipotential lines 107, which in turn changes the electric field strength applied to the tip of the emitter 101, thereby changing the quantity (amount of current) of charged particles 104 emitted from the emitter 101 and the trajectories of the charged particles 104. When two voltage combinations, {Vsu1, Vex1} and {Vsu2, Vex2}, are applied, the charged particles emitted by the voltage combinations are explicitly shown as charged particles (Vsu1, Vex1) 104a and charged particles (Vsu2, Vex2) 104b, respectively. If the electric potential is kept constant downstream of the extraction electrode 102, the charged particle 104 moves straight without receiving any force. Therefore, the asymptote of the trajectory of the charged particle 104 is drawn as a charged particle trajectory asymptote (Vsu1, Vex1) 113a and a charged particle trajectory asymptote (Vsu2, Vex2) 113b depending on the voltage combination, and a virtual light source (Vsu1, Vex1) 114a and a virtual light source (Vsu2, Vex2) 114b are formed at the positions where they intersect with the optical axis 105, respectively.

[0055] 3 shows the difference in the potential distribution shape at the tip of the emitter 101 and the trajectory of the charged particles 104 when the electric field suppression electrode 103 is present and when it is not. Fig. 3(a) shows the case without the electric field suppression electrode 103, which is a conventional configuration and method in which the charged particles 104 are emitted from the emitter 101 only by the voltage applied to the extraction electrode 102. A wedge-shaped potential distribution is formed at the tip of the emitter 101. Fig. 3(b) shows the case in which the electric field suppression electrode 103 is disposed between the emitter 101 and the extraction electrode 102, and the convex potential distribution seeps out from the hole in the electric field suppression electrode 103 between the emitter 101 and the electric field suppression electrode 103. The emitter 101 is positioned so as to penetrate the convex potential distribution, and the charged particles 104 (Vsu, Vex) emitted from the emitter 101 are subjected to a force in the direction of the optical axis 105. This allows the emission angle 116 of the charged particles 104 (Vsu, Vex) to be smaller than that shown in FIG. 3( a). FIG. 3( c) explicitly illustrates the composite extractor electrode 106, which is composed of the electric field suppression electrode 103 and the extractor electrode 102 shown in FIG. 3( b). The composite extractor electrode 106 can be treated as if it were a single electrode, and can simultaneously change both the shape of the potential distribution and the electric field strength. This makes it possible to simultaneously change the converted luminance Br and the angular current density I' using the composite extractor electrode 106. The above-mentioned operation will now be described in detail.

[0056] The indexes for evaluating the performance of the emitter 101 are the converted luminance Br and the angular current density I', which are expressed by Equations 1 and 2, respectively.

[0057]

[0058]

[0059] where, I: amount of emission current [A], r: radius of light source [m], θ: charged particle emission angle [rad], V: extraction voltage [V], and π: circumference constant.

[0060] The converted luminance Br is a conserved quantity, does not change at any convergence point on the axis, and is specific to the emitter 101. The emission current amount I includes factors attributable to the physical properties of the emitter 101 (e.g., work function, crystallinity, orientation, etc.) and factors attributable to the external environment of the emitter 101 (e.g., degree of vacuum, temperature, electric field strength F applied to the emitter surface, etc.), but it is assumed that factors other than the electric field strength F are constant, and the emission current amount I is a function of only the electric field strength F. Therefore, if the electric field strength F at the tip of the emitter 101 is constant, the emission current amount I is also constant.

[0061] In the case shown in FIG. 3( a), the emission current amount I is uniquely determined by the voltage applied to the extraction electrode 102. Furthermore, since the potential distribution and electric field strength are also uniquely determined, the trajectory of the charged particle 104 (Vex) emitted from the emitter 101 is also determined, and the emission angle 116 is also determined. On the other hand, when the composite extraction electrode 106 shown in FIGS. 3( b) and 3(c) is used, the emission current amount I, the trajectory of the charged particle 104 (Vsu, Vex), and the emission angle 116 are determined by the voltage combination {Vsu, Vex}. In this case, the converted luminance Br is also calculated by Equation 1 and Equation 2, but the extraction voltage V in Equation 1 is the voltage Vex applied to the extraction electrode 102. The emission current amount I, the light source radius r, and the charged particle emission angle θ change depending on the voltage Vex and the voltage applied to the electric field suppression electrode 103. Here, the light source radius r refers to the virtual light source 114 (Vsu, Vex). When the composite extraction electrode 106 is regarded as a single electrode, the magnitude of the aberration (spherical aberration and chromatic aberration) caused by the lens action of the composite extraction electrode is reflected in the magnitude of the virtual light source 114 (Vsu, Vex), which is the converted luminance Br ～ This becomes:

[0062] Now, consider a case where two voltage combinations {Vsu, Vex} are set, {Vsu1, Vex1} and {Vsu2, Vex2}, so that the emission current amount I is constant. Since the charged particles 104 (Vsu, Vex) are subjected to a force in the normal direction of the equipotential lines, in the composite extractor electrode 106, increasing the voltage applied to the electric field suppression electrode 103 causes the charged particles 104 (Vsu, Vex) to move in a direction diverging from the optical axis, whereas increasing the voltage applied to the extractor electrode 102 causes the charged particles 104 (Vsu, Vex) to move in a direction converging toward the optical axis. Now, change the state where the two voltage combinations are equal, {Vsu0, Vex0}, to a state where Vex1<Vex0<Vex2. Because Vex1 becomes smaller, Vsu1 must be set to Vsu1>Vsu0 in order to maintain the emission amount I. In this case, the charged particles 104a (Vsu1, Vex1) diverge more. Also, since Vex2 becomes larger, Vsu2<Vsu0 must be satisfied in order to maintain the emission amount I. In this case, the charged particles 104b (Vsu2, Vex2) converge more. Also, the converted brightness of each electric field combination can be expressed by Equations 3 and 4, respectively, from Equations 1 and 2.

[0063] The index for {Vsu1, Vex1} is expressed as 1, and the index for {Vsu2, Vex2} is expressed as 2.

[0064]

[0065]

[0066] Now, since the amount of emission I is constant, the electric field strength F applied to the tip of the emitter 101 is also constant, so the converted brightnesses expressed by equations 3 and 4 are equal (Br1=Br2).

[0067]

[0068] Since θ1>θ2 and Vex1<Vex2, it is not necessarily the case that r1<r2. However, as described above, if the composite extraction electrode 106 is regarded as one electrode, aberration due to the lens action formed by the electrode is added, and the virtual light source becomes larger than r2 (denoted as r3), and the converted luminance Br2 decreases (this is called Br2 ～ The converted brightness Br2 ～ becomes a new conserved quantity. On the other hand, the angular current density I' becomes larger as the emission angle 116 (θ2) becomes smaller, as shown in Equation 2. Therefore, by adjusting the voltage combination {Vsu, Vex}, the converted luminance Br2 ～ The angular current density I' can be changed by changing the converted luminance Br2 ～ However, if the composite extraction electrode 106 is disposed within 1 mm from the tip of the emitter 101, the charged particles 104 (Vsu, Vex) are close to the optical axis 105, so the aberration is reduced, and the converted luminance Br2 ～ Therefore, by adjusting the voltages applied to the electric field suppression electrode 103 and the extraction electrode 102 that constitute the composite extraction electrode 106, the reduction in the converted luminance Br2 ～ and the angular current density I' are in a trade-off relationship.

[0069] In particular, in the case of a field emission electron source called a high brightness electron source, the field emission electron source has high brightness but is not suitable for devices requiring a large current because of its small angular current density. However, when the composite extraction electrode 106 is used, the converted brightness Br2 ～ The optimal converted luminance Br2 is determined by the trade-off relationship between the angular current density I' and the ～ and the angular current density I' can be adjusted to the above.

[0070] In the composite extraction electrode 106, the potential distribution that protrudes in a convex shape from the hole of the electric field suppression electrode 103 toward the emitter 101 is expressed by the Davisson-calbic equation (not shown). The potential Φ ０ becomes number 6.

[0071]

[0072] where R: radius of the field suppression electrode hole [m], L: distance between the field suppression electrode and the extraction electrode [m], Vsu: extraction voltage [V], and α: coefficient [−].

[0073] If the thickness of the electric field suppression electrode 103 is extremely small, the coefficient α is expressed by the formula 7 and is approximately 0.318. Furthermore, when an electric field analysis is performed by numerical calculation assuming that the thickness of the electric field suppression electrode 103 is 1 mm, the coefficient α is 0.274, and therefore, without loss of generality, the coefficient α can be expressed by the formula 8.

[0074]

[0075]

[0076] In FIG. 1, in order to (thermal) field emit electrons from the tip of the emitter 101, it is generally necessary to ７ It is necessary to apply an electric field strength Fe of at least [V / m] to the tip of the emitter 101, and generally, the electric field strength Fe is expressed by the following equation (9).

[0077]

[0078] Here, β is a shape factor coefficient due to the shape and dimensions of the emitter 101 and the field suppression electrode 103. Now, assuming that electrons are emitted by a (thermal) field, and the β is indefinite, the voltage range applied to the field suppression electrode 103 is considered in the case of a nanotip, a Schottky emitter (TFE: Thermal Field Emission), or a cold cathode (CFE: Cold Field Emission), and the Φ ０ The values ​​of are expressed as Equations 10 and 11.

[0079]

[0080]

[0081] The voltage Φ ０ The numerical values ​​of Equations 12 and 13 obtained by transforming Equation 6 from the range of α and the range of the coefficient α are shown in FIG.

[0082]

[0083]

[0084] In particular, the R / L expressed by Equation 13 is shown for Vex = 500V, 1kV, 2kV, 5kV, 10kV, and 20kV, but it is not limited to these values ​​and may be considered to be continuous from 500V to 20kV without loss of generality. Furthermore, since the R / L represents a ratio related to the electrode position, it is a condition required for the composite extraction electrode 106 in the charged particle gun according to the present invention. Furthermore, the voltage Φ ０ is not limited to equation (10) or equation (11), and when the tip radius of the emitter 101 is 1 μm, the R / L of the composite extraction electrode 106 satisfies equation (14).

[0085]

[0086] In addition, when the tip radius of the emitter 101 is 100 nm or less, the R / L of the composite extraction electrode 106 satisfies the formula (15).

[0087]

[0088] In addition, when the tip radius of the emitter 101 is 100 nm or more and 1 μm or less, the R / L of the composite extraction electrode 106 satisfies Equation 16.

[0089]

[0090] The above-mentioned formulas (14) to (16) show the ratio of the hole diameter R of the electric field suppression electrode 103 to the distance L between the electric field suppression electrode 103 and the extractor electrode 102 for (thermal) field emission of electrons from the tip of the emitter 101 using the composite extractor electrode 106. The trajectory of the charged particle 104 shown in FIG. 1 is determined by the voltage combination {Vsu, Vex} applied to the composite extractor electrode 106 or the distance L between the tip of the emitter 101 and the electric field suppression electrode 103. ０Depending on the value of , the electron lens effect created by the composite extractor electrode 106 may cause a crossover on the optical axis 105 after being emitted from the tip of the emitter 101. The trajectory of the charged particle 104 will be explained using Figure 5. The electron lens principal surface 122 of the electron lens created by the composite extractor electrode 106 can be located near the center of the electric field suppression electrode 103, but for simplicity's sake, it is assumed to be located at the center of the electric field suppression electrode 103. Furthermore, since a virtual light source position is created near the tip of the emitter 101, for simplicity's sake, it is assumed to be located at the tip of the emitter 101. An electron lens with the center of the electric field suppression electrode 103 as the electron lens principal surface 122 becomes a single-hole lens, and is explicitly shown as a single-hole lens 121 in Figure 1. The focal length f of the single-hole lens 121 is expressed by Equation 17 from the Davisson-calbic equation (not shown) when the potentials of the emitter 101 and the electric field suppression electrode 103 are equal.

[0091]

[0092] Therefore, the charged particle 104c incident parallel to the optical axis 105 has the crossover with the optical axis 105, and the crossover is on the opposite side of the emitter 101 from the electron lens main surface 122. Also, a distance L ０ There is a virtual light source 114 at L. The charged particle 104d passes through the crossover on the opposite side of the emitter 101 from the electron lens main surface 122. １ When the distance is .gtoreq..times ...

[0093]

[0094] Therefore, from Equation 18, L1 is expressed by Equation 19.

[0095]

[0096] From number 17, L ０ When f=4×L, the charged particle 104 e emitted from the virtual light source 114 becomes parallel to the optical axis 105 after passing through the electron lens main surface 122 .

[0097] From number 19, L ０<If f = 4 × L, L １ <0, and the crossover can be formed as a virtual image on the emitter 101 side of the electron lens main surface 122. The virtual light source position is set at a distance L from the electron lens main surface 122 to the emitter 101 side. ０ a, and the crossover is a distance L from the electron lens main surface 122 to the emitter 101 side. １ a, and the charged particles 104 f are emitted from the crossover as the virtual light source 114 .

[0098] Therefore, in the charged particle gun according to the present invention, the condition under which the charged particles 104 do not cross over after being emitted from the emitter 101 is expressed by Equation 20.

[0099]

[0100] In the charged particle gun according to the present invention, when the emitter 101 is a nanotip with a radius r of 50 nm, for example, the radius R of the hole of the electric field suppression electrode 103, the distance L between the electric field suppression electrode 103 and the extraction electrode 102, and the distance L between the tip of the emitter 101 and the electric field suppression electrode 103 are ０ When the voltage Vem applied to the emitter 101, the voltage Vsu applied to the electric field suppression electrode 103, and the voltage Vex applied to the extraction electrode 102 are as follows, Equation 15 and Equation 20 are satisfied.

[0101] R / L=0.4 R=0.2mm L=0.5mm L ０ =0.2mm Vm=0V Vsu=0V Vex=2.2kV

[0102] Furthermore, when the emitter 101 is a Schottky emitter with a radius r of 0.5 μm, for example, if the radius R of the hole in the electric field suppression electrode 103, the distance L between the electric field suppression electrode 103 and the extraction electrode 102, the distance L0 between the tip of the emitter 101 and the electric field suppression electrode 103, the voltage Vem applied to the emitter 101, the voltage Vsu applied to the electric field suppression electrode 103, and the voltage Vex applied to the extraction electrode 102 are as follows, then the following equations will satisfy Equation 16 and Equation 20:

[0103] R / L=0.5 R=1mm L=2mm L ０ =0.5mm Vem=0V Vsu=0V Vex=20kV

[0104] 6A shows the calculation results of the potential distribution and the trajectory of the charged particles 104 (electrons) when the emitter 101 is used as a field emission electron source and the composite extractor electrode 106 is used, and the charged particles 104 (electrons) are emitted from the emitter 101 with an emission current of 10 nA using a combination of voltages {Vsu=150 V, Vex=150 V} applied to the extractor electrode 102 and the extractor electrode 102 constituting the composite extractor electrode 106. ９ [A / m ２ / sr / V], angular current density 7.22×10 －７ [A / sr]. Figure 6(b) shows the calculation results of the potential distribution and the trajectory of the charged particle 104 (electron) when the emitter 101 is the same as that shown in Figure 6(a), the composite extractor electrode 106 is used, and the charged particle 104 (electron) is emitted from the emitter 101 with a combination of voltages {Vsu = 0 V, Vex = 6000 V} applied to the extractor electrode 102 and the extractor electrode 102 constituting the composite extractor electrode 106. The electric field strength applied to the tip of the emitter 101 shown in Figure 6(a) is the same, and the emission current is also the same. Equivalent luminance 2.65 x 10 ８ [A / m ２ / sr / V], angular current density 7.97×10 －５ [A / sr]. In this way, a trade-off relationship between the converted luminance and the angular current density is established.

[0105] As shown in Figure 6 (b), the emitter side of the hole in the electric field suppression electrode 103 is bowl-shaped or inclined, so the equipotential lines 107 that have leaked out to the emitter side leak out in a more convex shape along the inclined surface of the hole in the electric field suppression electrode 103, and the charged particles 104 emitted from the tip of the emitter 101 in the normal direction of the equipotential lines 107 are subjected to a force and are bent more toward the optical axis 105.

[0106] Furthermore, when the radius R of the electric field suppression electrode 103 becomes smaller, the normal to the equipotential line 107 does not leak out to the emitter side of the hole in the electric field suppression electrode 103. Therefore, when the radius R of the hole in the electric field suppression electrode and the distance L between the electric field suppression electrode and the tip of the emitter become smaller, ０ Relative to L ０ / R is 1 or less.

[0107] A charged particle gun comprises an emitter that emits charged particles, a composite extraction electrode consisting of an electric field suppression electrode positioned directly below the emitter on an optical axis centered on the emitter, and an extraction electrode positioned directly below the electric field suppression electrode, a suppression electrode positioned from the tip of the emitter to the emitter needle side, and a voltage applied to the electric field suppression electrode, a voltage applied to the extraction electrode, and a voltage applied to the suppression electrode form a potential distribution that seeps out in a convex shape from the hole in the electric field suppression electrode toward the emitter, thereby forming a strong electric field at the tip of the emitter.

[0108] An embodiment of the present invention is shown in Figure 7. A detailed description will be given below with reference to the drawings. The operation of this embodiment is the same as that of embodiment 1, except that a suppression electrode 111, located on the emitter needle side from the tip of the emitter 101, repels thermoelectrons 120 emitted from the emitter needle by a suppression voltage applied to the suppression electrode 111 from a suppression power supply 119 when a temperature is applied to the emitter 101, preventing the thermoelectrons 120 from traveling toward the sample (not shown). Furthermore, the equivalent luminance and angular current density are optimally adjusted by the combination of voltages applied to the field suppression electrode 103, the extraction electrode 102, and the suppression electrode 111, respectively.

[0109] Although the present invention has been described above as an example of an embodiment, it is not limited to this example and includes a method for controlling the brightness and angular density of a charged particle beam emitted from a charged particle source.

[0110] 101: Emitter 102: Extraction electrode 103: Electric field suppression electrode 104: Charged particle 104a: Charged particle (Vsu1, Vex1) 104b: Charged particle (Vsu2, Vex2) 104c: Charged particle 104d: Charged particle 104e: Charged particle 104f: Charged particle 105: Optical axis 106: Composite extraction electrode 107: Equipotential line 108: Acceleration power supply 109: Extraction power supply 110: Electric field suppression power supply 111: Suppression electrode 112: Charged particle beam 113: Charged particle trajectory asymptote 113a: Charged particle trajectory asymptote (Vsu1, Vex1) 113b: Charged particle trajectory asymptote (Vsu2, Vex2) 114: Virtual light source 114a: Virtual light source (Vsu1, Vex1) 114b: Virtual light source (Vsu2, Vex2) 115: Aperture 116: Emission angle 117: Secondary electrons 118: Gas molecules 119: Suppression power source 120: Thermal electrons 121: Single-hole lens 122: Electron lens main surface

Claims

1. A charged particle gun comprising: an emitter that emits charged particles; and a composite extraction electrode consisting of an electric field suppression electrode located directly below the emitter and an extraction electrode located directly below the electric field suppression electrode; wherein the emitter radius r is 1 μm or less; when the charged particles emitted from the emitter have a negative charge relative to the emitter potential, the voltage Vsu applied to the electric field suppression electrode is a positive voltage of 0 V or more, and when the charged particles emitted from the emitter have a positive charge, the voltage Vsu applied to the electric field suppression electrode is a negative voltage of 0 V or less; the absolute value |Vex - Vsu| of the difference between the voltage Vsu applied to the electric field suppression electrode and the voltage value Vex applied to the extraction electrode is 20 kV or less; and the ratio R / L of the radius R of the hole in the electric field suppression electrode to the distance L between the electric field suppression electrode and the extraction electrode is 0.0079 or more and 3.645 or less.

2. Distance L between the emitter and the electric field suppression electrode ０ 2. The charged particle gun according to claim 1, wherein the distance L between the field suppression electrode and the extraction electrode is 0 to 4×L.

3. The charged particle gun according to claim 1, characterized in that the combined extraction electrode is operated as a single electron lens by a combined voltage {Vsu, Vex} of the voltage Vsu applied to the electric field suppression electrode and the voltage Vex applied to the extraction electrode.

4. The charged particle gun according to claim 3, wherein the intensity of the electric field applied to the tip of the emitter is changed by the combined voltage {Vsu, Vex} to adjust the amount of emission current and the trajectory of the charged particles emitted from the emitter.

5. The charged particle gun according to claim 3, wherein the combined voltage {Vsu, Vex} keeps the electric field strength applied to the emitter tip constant, and adjusts the trajectory of the emitted charged particles while maintaining the emission current constant.

6. The charged particle gun according to claim 3, wherein the combined voltages {Vsu, Vex} adjust the converted brightness and angular current density of the emitted charged particle beam.

7. The charged particle gun according to claim 1, wherein the side of the hole in the emitter-side surface of the field suppression electrode is bowl-shaped or inclined.

8. The charged particle gun according to claim 1, wherein the ratio L0 / R of the radius R of the hole in the electric field suppression electrode to the distance L0 between the electric field suppression electrode and the tip of the emitter is 1 or less.

9. The charged particle gun according to claim 1, wherein the emitter is one of a thermionic electron source, a thermal field emission electron source, a cold cathode electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked electron source, an emitter array, a liquid metal ion source, and a helium ion source.

10. A charged particle device comprising a charged particle gun according to any one of claims 1 to 9.

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