Charged particle gun

Abstract

While a high-brightness charged particle source has high brightness, its angular current density is low, and when acquiring a large current, the aberration of the electron lens system becomes large, degrading the spatial resolution. The composite extraction electrode, which is made up of two electrodes, is treated as a single electrode placed directly under the emitter, and the voltages applied to the two electrodes are combined to form a convex potential distribution on the emitter side and a concave potential distribution at the emitter tip, thereby narrowing the emission angle of the charged particle beam and adjusting the angular current density. The lens effect of the composite extraction electrode works directly under the emitter tip, so aberration is extremely small, and there is no degradation of spatial resolution even when acquiring a large current.

Description

[Technical field]

[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. [Background technology]

[0002] As an example of a device for emitting charged particles, a cold cathode field emission electron gun will be described with reference to the drawings. FIG. 8 shows a conventional cold cathode field emission electron gun. The cold cathode field emission electron gun is placed in a container (not shown) that maintains a high vacuum. An electric field is formed between the emitter 101 and the extraction electrode 102 by an extraction voltage applied to the extraction electrode 102, and a strong electric field is formed particularly at the tip of the emitter 101, and electrons (charged particles 104) are emitted from the tip of the emitter 101. The strength of the electric field is illustrated as the density of equipotential lines 107 as 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. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 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 Summary of the Invention [Problem to be solved by the invention]

[0004] As shown in Fig. 8, in order to emit the charged particles 104 from the emitter 101, a sufficiently strong electric field must be formed at the tip of the emitter 101. Fig. 9 shows a case where a strong electric field is formed at the tip of the emitter 101, taking a cold cathode field emission electron gun as an example. The arc-shaped equipotential lines 107 are densely formed in the vicinity of the tip of the emitter 101 according to the surface shape, and the emitted charged particles 104 (electrons) fly away under the force in the normal direction of the equipotential lines 107, so that a virtual light source 114 is formed where the charged particle trajectory 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, the charged particle beam formed by the charged particles 104 (electrons) emitted from the emission surface of the emitter 101 has a large emission angle, and the charged particle beam is generally limited in angle by an aperture 115 between the emitter 101 and a sample (not shown). However, if the emission angle 116 is limited to a small angle, the number of the 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. In addition, 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 the electron lens (not shown) downstream of the emitter 101 becomes large, and when used in, for example, a charged particle microscope, the charged particle beam diameter at the sample position (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 conventional technology 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 restricted. [Means for solving the problem]

[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 particle emitted from the emitter is 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 particle emitted from the emitter is 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.

[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 particle emitted from the emitter is 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 particle emitted from the emitter is 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.

[0009] The charged particle gun is further 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 particle emitted from the emitter is 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 particle emitted from the emitter is 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.

[0010] The charged particle gun is characterized in that the distance L0 between the emitter and the electric field suppression electrode and the distance L between the electric field suppression electrode and the extraction electrode is 0 or more and 4×L or less.

[0011] The charged particle gun is 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 characterized in that a potential distribution protrudes in a convex shape toward the emitter side from a hole in the electric field suppression electrode.

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

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

[0016] The charged particle gun is characterized in that a ratio L0 / R of a radius R of the hole in the electric field suppression electrode to a 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 amount of emission current is adjusted by changing the electric field strength applied to the tip of the emitter using the combined voltage {Vsu, Vex}.

[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 emission current amount and the charged particle trajectory are adjusted by the combined voltage {Vsu, Vex}.

[0021] The charged particle gun is also characterized in that the combined voltage {Vsu, Vex} is used to keep the electric field strength applied to the emitter tip constant, thereby adjusting 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 the charged particle gun, the emitter is any one of a thermionic electron emission source, a thermal field emission type electron source, a cold cathode type electron source, a nanotip, a carbon nanotube, a superconducting electron source, a stacked type electron source, an emitter array, a liquid metal ion source, and a helium ion source. Effect of the Invention

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

[0025] By adjusting the voltage 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 changed continuously.

[0027] When the present invention is applied to a charged particle microscope, in the high brightness mode, the sample surface can be analyzed with high spatial resolution, and in the large angular current density mode, 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.

[0028] When the present invention is applied to a charged particle microscope, the degree of the high brightness mode and the 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 optimal conditions.

[0029] In the large angular current density mode, the emission angle of the emitted charged particle beam becomes small, so the charged particles do not collide with the electrodes to which voltage is applied to extract the charged particles, and gas is not generated from the electrodes, so there is no deterioration of the vacuum around the emitter. In addition, because the charged particles do not collide with the electrodes, contaminants do not adhere to the electrode surface, and the emitter is not damaged by discharge caused by the adhesions becoming charged.

[0030] When the present invention is applied to a charged particle microscope, the angular current density can be changed, so that an electron lens for adjusting the amount of current is not required 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 immediately made parallel to the optical axis, making it possible to observe a sample 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 on the sample side as viewed from the emitter can be kept small, and even if the charged particle beam is focused on the surface of the sample, the spread of the charged particle beam diameter 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 if the amount of current irradiated to the sample is large, thereby shortening the time required for sample observation and increasing the 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 an emitter tip radius of 1 μm or less, a sample can be observed with a highly coherent charged particle beam having a high current density. [Brief description of the drawings]

[0036] [Figure 1] 1 is a schematic diagram showing an embodiment of the present invention; [Diagram 2] 5A to 5C are schematic diagrams illustrating an example of the operation of a composite extraction electrode according to the present invention. [Diagram 3] 5A to 5C are schematic diagrams illustrating an example of the operation of a composite extraction electrode according to the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating an embodiment of a composite extraction electrode according to the present invention. [Diagram 5] 5A to 5C are schematic diagrams illustrating an example of the operation of a composite extraction electrode according to the present invention. [Figure 6] 5 is a charged particle trajectory diagram for explaining an example of the operation of the composite extraction electrode according to the present invention. FIG. [Figure 7] FIG. 11 is a schematic diagram showing another embodiment of the charged particle gun according to the present invention. [Figure 8] FIG. 1 is a schematic diagram showing the configuration of a conventional charged particle gun. [Figure 9] 1 is a schematic diagram illustrating the operation of a conventional charged particle gun. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that components having the same functions are designated by 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 composed of an electric field suppression electrode arranged directly below the emitter on an optical axis centered on the emitter, and an extraction electrode 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 L0 between the emitter and the electric field suppression electrode and the distance L between the electric field suppression electrode and the extraction electrode is 0 or more and 4×L or less.

[0044] 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.

[0045] A voltage applied to the electric field suppression electrode and a 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 on the emitter side, forming a strong electric field at the tip of the emitter.

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

[0047] A convex potential distribution protrudes from the hole in the electric field suppression electrode toward the emitter, and the tip of the emitter is positioned so as to penetrate into the convex potential distribution, 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 electric field suppression electrode is bowl-shaped or inclined.

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

[0050] An embodiment of the present invention is shown in FIG. 1. The following is a detailed description based on the drawings. A composite extraction electrode 106 arranged directly under an emitter 101 that emits charged particles 104 is composed of an electric field suppression electrode 103 and an extraction electrode 102 arranged directly under the electric field suppression electrode 103. An electric field suppression voltage is applied to the electric field suppression electrode 103 from an electric field suppression power supply 110, and an extraction voltage is applied to the extraction electrode 102 from an extraction power supply 109. The voltages applied to each electrode cause a convex potential distribution to seep out from the hole in the electric field suppression electrode 103 to the emitter 101 side between the emitter 101 and the electric field suppression electrode 103. In the figure, the potential distribution is shown by equipotential lines 107, and a high density of the equipotential lines 107 indicates a strong electric field strength. The emitter 101 is arranged so as to pierce the convex potential distribution, and a strong electric field is formed at the tip of the emitter 101. The charged particle 104 is emitted from the tip of the emitter 101 by the strong electric field, and the emitted charged particle 104 flies away due to a force in the normal direction of the equipotential line 107, so that the emitted charged particle 104 flies away without deviating significantly from the optical axis 105 due to the convex potential distribution.

[0051] In the present invention, when the charged particle 104 emitted from the emitter 101 is negatively charged, the voltage Vsu applied to the electric field suppression electrode 103 is 0 V or more, and when the charged particle 104 emitted from the emitter 101 is positively charged, the voltage Vsu applied to the electric field suppression electrode 103 is 0 V or less, but in order to easily explain the convex potential distribution, the charged particle 104 emitted from the emitter 101 is assumed to be negatively charged, and the potential of the electric field suppression electrode 103 is assumed to be the same as that of the emitter 101.

[0052] Even if the voltage Vsu applied to the electric field suppression electrode 103 is greater than 0V, the emitted charged particles 104 fly under the force in the normal direction of the equipotential lines 107, and the emitted charged particles 104 take a trajectory more along the optical axis 105 due to the convex potential distribution, so there is no loss of generality in explaining the present invention. On the other hand, when the voltage Vsu applied to the electric field suppression electrode 103 is less than 0V, the amount of charged particles emitted from the emitter 101 decreases, and the lens effect of the composite extraction electrode 106 is too strong, forming a crossover, and further reducing the angular current density.

[0053] A high voltage is applied to the extraction electrode 102 so that the charged particles 104 are emitted from the tip of the emitter 101, but the electric field suppression electrode 103 makes the potential distribution seeping out from the holes of the electric field suppression electrode 103 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 there are cases where a voltage is 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 the voltage applied to the electric field suppression electrode 103 and the extraction electrode 102. For example, the shape of the potential distribution can be changed while keeping the electric field strength applied to the tip of the emitter 101 constant. This makes it possible to change the trajectory of the charged particles 104 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 electric field suppression electrode 103 and the extraction electrode 102 constituting the composite extraction electrode 106, respectively. The composite extraction electrode 106 is operated as an electron lens by a combination of voltages {Vsu, Vex}. The voltage combination changes the shape of the potential distribution shown by the shape of the equipotential lines 107, changes the electric field strength applied to the tip of the emitter 101, and changes the amount (amount of current) of the charged particles 104 emitted from the emitter 101 and the trajectory of the charged particles 104. Now, when two combinations of voltages {Vsu1, Vex1} and {Vsu2, Vex2} are applied, the charged particles emitted by the voltage combinations are explicitly shown as charged particle (Vsu1, Vex1) 104a and charged particle (Vsu2, Vex2) 104b, respectively. If the electric potential is kept constant downstream of the extraction electrode 102, the charged particle 104 will move straight without receiving any force, and therefore the voltage combination will draw the asymptote of the trajectory of the charged particle 104 as a charged particle trajectory asymptote (Vsu1, Vex1) 113a and a charged particle trajectory asymptote (Vsu2, Vex2) 113b, and at the points where these intersect with the optical axis 105, a virtual light source (Vsu1, Vex1) 114a and a virtual light source (Vsu2, Vex2) 114b, respectively, are formed.

[0055] Fig. 3 shows the difference in the electric potential distribution shape at the tip of the emitter 101 and the trajectory of the charged particle 104 when the electric field suppression electrode 103 is not present and when it is present. Fig. 3(a) shows the case when the electric field suppression electrode 103 is not present, and shows the conventional configuration and method in which the charged particle 104 is emitted from the emitter 101 only by the voltage applied to the extraction electrode 102. A wedge-shaped electric potential distribution is formed at the tip of the emitter 101. Fig. 3(b) shows the case when the electric field suppression electrode 103 is placed between the emitter 101 and the extraction electrode 102, and the convex electric 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 disposed so as to pierce the convex potential distribution, and the charged particle 104 (Vsu, Vex) emitted from the emitter 101 receives a force in the direction of the optical axis 105, so that the emission angle 116 of the charged particle 104 (Vsu, Vex) can be made smaller than that shown in FIG. 3(a). FIG. 3(c) explicitly shows the composite extractor electrode 106 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 intensity. This makes it possible to simultaneously change the converted luminance Br and the angular current density I' by the composite extractor electrode 106. The above-mentioned operation will be described in detail below in principle.

[0056] The performance of the emitter 101 is evaluated using the converted luminance Br and the angular current density I', which are expressed by Equation 1 and Equation 2, respectively.

[0057]

number

[0058]

number

[0059] Where: I: Emission current [A] r: Light source radius [m] θ: Charged particle emission angle [rad] V: Extraction voltage [V] π: Pi It is.

[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. In addition, since the potential distribution and the electric field intensity 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 FIG. 3(b) and FIG. 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 one 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 size of the virtual light source 114 (Vsu, Vex) to obtain a converted luminance Br ~ It becomes.

[0062] Now, consider the case where two voltage combinations {Vsu, Vex}, {Vsu1, Vex1} and {Vsu2, Vex2}, are set such that the emission current I is constant. Since the charged particle 104(Vsu, Vex) is subjected to a force in the normal direction of the equipotential line, in the composite extraction electrode 106, when the voltage applied to the electric field suppression electrode 103 is increased, the charged particle 104(Vsu, Vex) travels in a direction diverging from the optical axis, and when the voltage applied to the extraction electrode 102 is increased, the charged particle 104(Vsu, Vex) travels in a direction converging toward the optical axis. Now, starting from a state where the two voltage combinations are equal {Vsu0, Vex0}, a state of Vex1 < Vex0 < Vex2 is set. Since Vex1 becomes smaller, in order to maintain the emission amount I, Vsu1 > Vsu0 must be set. In this case, the charged particle 104a(Vsu1, Vex1) diverges more. Also, since Vex2 becomes larger, in order to maintain the emission amount I, Vsu2 < Vsu0 must be set. In this case, the charged particle 104b(Vsu2, Vex2) converges more. Further, the converted luminance of each of the electric field combinations is represented by Equation 1 and Equation 2, respectively, as Equation 3 and Equation 4.

[0063] Express the index for the case of {Vsu1, Vex1} as 1 and the index for the case of {Vsu2, Vex2} as 2.

[0064]

Equation

[0065]

Equation

[0066] Now, since the emission amount I is constant, and thus the electric field strength F applied to the tip of the emitter 101 is also constant, the converted luminance represented by Equation 3 and Equation 4 is equal (Br1 = Br2). Therefore, r2 becomes Equation 5.

[0067]

Number

[0068] Since θ1 > θ2 and Vex1 < Vex2, it is not necessarily the case that r1 < r2. However, as described above, considering the composite extraction electrode 106 as one electrode, the aberration due to the lens action formed by this electrode is added, and the virtual light source becomes larger than r2 (denoted as r3), and the converted luminance Br2 decreases (denoted as Br2 ~ ). This converted luminance Br2 ~ becomes the new storage amount. On the other hand, the angular current density I’ increases from Equation 2 as the emission angle 116 (θ2) becomes smaller. Therefore, by adjusting the voltage combination {Vsu, Vex}, the converted luminance Br2 ~ and the angular current density I’ can be changed. At this time, although the converted luminance Br2 ~ decreases due to the aberration of the composite extraction electrode 106, if the composite extraction electrode 106 is arranged within 1 mm from the tip of the emitter 101, the aberration becomes smaller because the charged particles 104 (Vsu, Vex) are close to the optical axis 105, and the decrease in the converted luminance Br2 ~ also becomes smaller. Therefore, by adjusting the voltages applied to the field suppression electrode 103 and the extraction electrode 102 that constitute the composite extraction electrode 106, an inverse relationship between the converted luminance Br2 ~ and the angular current density I’ is established.

[0069] Especially 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 that require a large current with a small angular current density. However, when the composite extraction electrode 106 is used, the converted luminance Br2 ~ and the angular current density I’ can be adjusted to the optimal converted luminance Br2 ~ and the angular current density I’ according to the inverse relationship between them.

[0070] In the composite extraction electrode 106, the potential distribution that seeps out in a convex shape from the hole in the electric field suppression electrode 103 toward the emitter 101 is expressed by the Davisson-calbic equation (not shown), and the potential Φ0 at the axial center of the electric field suppression electrode 103 shown in Figure 1 is expressed by the formula 6.

[0071]

number

[0072] Where: R: Radius of the electric field suppression electrode hole [m] L: Distance between the electric field suppression electrode and the extraction electrode [m] Vsu: Extraction voltage [V] α: Coefficient [-] It is.

[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 about 0.318. When the thickness of the electric field suppression electrode 103 is set to 1 mm and an electric field analysis is performed by numerical calculation, the coefficient α is 0.274. Therefore, without loss of generality, the coefficient α is expressed by the formula 8.

[0074]

number

[0075]

number

[0076] In FIG. 1, in order to emit electrons from the tip of the emitter 101 (thermal field emission), it is generally necessary to use a current of 5×10 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]

number

[0078] Here, β is a shape factor coefficient due to the shape and dimensions of the emitter 101 and the electric field suppression electrode 103. Now, assuming that electrons are emitted from a (thermal) electric field, and the β is indefinite, the voltage range applied to the electric field suppression electrode 103 is considered in the case of a nano tip, a Schottky emitter (TFE: Thermal Field Emission) or a cold cathode (CFE: Cold Field Emission), the value of Φ0 becomes Equation 10 and Equation 11, respectively.

[0079]

number

[0080]

number

[0081] The values ​​of Equations 12 and 13 obtained by transforming Equation 6 from the range of the voltage Φ0 and the range of the coefficient α are shown in FIG.

[0082]

number

[0083]

number

[0084] In particular, the R / L expressed by formula 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 expresses 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 Φ0 is not limited to formula 10 or formula 11, and the R / L of the composite extraction electrode 106 satisfies formula 14 when the tip radius of the emitter 101 is 1 μm.

[0085]

number

[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]

number

[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 the formula (16).

[0089]

number

[0090] The above 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 extraction electrode 102 for (thermal) field emission of electrons from the tip of the emitter 101 using the composite extraction electrode 106, but the trajectory of the charged particle 104 shown in FIG. 1 may have a crossover on the optical axis 105 after being emitted from the tip of the emitter 101 due to the action of the composite extraction electrode 106 as an electron lens, depending on the voltage combination {Vsu, Vex} applied to the composite extraction electrode 106 or the value of the distance L0 between the tip of the emitter 101 and the electric field suppression electrode 103. The trajectory of the charged particle 104 will be explained using FIG. 5. The electron lens main surface 122 of the electron lens formed by the composite extraction electrode 106 can be located near the center of the electric field suppression electrode 103, but for the sake of simplicity, it is assumed to be located at the center of the electric field suppression electrode. Moreover, since a virtual light source position is created near the tip of the emitter 101, for the sake of simplicity, the virtual light source position is assumed to be the tip of the emitter 101. An electron lens with the center of the electric field suppression electrode 103 as the electron lens main surface 122 becomes a single-hole lens, which is explicitly shown as single-hole lens 121 in the figure. 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]

number

[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. In addition, when a virtual light source 114 is present at a distance L0 from the electron lens main surface 122 to the emitter 101, and the charged particle 104d is at a distance L1 from the electron lens main surface 122 on the opposite side of the crossover to the emitter 101, the relationship shown in Expression 18 is satisfied.

[0093]

Number

[0094] Therefore, from number 18, L1 is represented by number 19.

[0095]

Number

[0096] From number 17, when L0 = f = 4×L, the charged particle 104e emitted from the virtual light source 114 becomes parallel to the optical axis 105 after passing through the electron lens main plane 122.

[0097] From number 19, when L0 < f = 4×L, L1 < 0, and the crossover is formed as a virtual image on the emitter 101 side of the electron lens main plane 122. Assuming the virtual light source position is at a distance L0a from the electron lens main plane 122 to the emitter 101 side and the crossover can be formed at a distance L1a from the electron lens main plane 122 to the emitter 101 side, the charged particle 104f is emitted with this crossover as the virtual light source 114.

[0098] Therefore, in the charged particle gun according to the present invention, the condition for not forming a crossover after the charged particle 104 is emitted from the emitter 101 is represented by number 20.

[0099]

Number

[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 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 satisfy the following equations:

[0101] R / L=0.4 R=0.2mm L=0.5mm L0=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, 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 satisfy the following equations:

[0103] R / L=0.5 R=1mm L=2mm L0=0.5mm Vem=0V Vsu=0V Vex=20kV

[0104] 6(a) shows the calculation results of the potential distribution and the trajectory of the charged particle 104 (electron) when the emitter 101 is used as a field emission electron source and the composite extraction electrode 106 is used to apply a combination of voltages {Vsu=150V, Vex=150V} to the extraction electrode 102 and the extraction electrode 102 constituting the composite extraction electrode 106, respectively, and the charged particle 104 (electron) is emitted from the emitter 101 with an emission current of 10 nA. The converted luminance is 2.4×10 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 extraction electrode 106 is used, and the charged particle 104 (electron) is emitted from the emitter 101 with a combination of voltages {Vsu=0V, Vex=6000V} applied to the extraction electrode 102 and the extraction electrode 102 constituting the composite extraction electrode 106. The electric field intensity applied to the tip of the emitter 101 shown in Figure 6(a) is the same as the emission current. The converted luminance is 2.65 x 10 8 [A / m 2 / sr / V], angular current density 7.97×10 -5 [A / sr]. In this way, the converted luminance and the angular current density have a trade-off relationship.

[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 that the equipotential line 107 that has leaked out to the emitter side leaks out in a more convex shape along the inclined surface of the hole in the electric field suppression electrode 103, and the charged particle 104 emitted from the tip of the emitter 101 is subjected to a force in the normal direction of the equipotential line 107, and is bent more toward the optical axis 105.

[0106] Furthermore, as 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, so 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 set to 1 or less. EXAMPLES

[0107] A charged particle gun comprises an emitter that emits charged particles, a composite extraction electrode composed of an electric field suppression electrode arranged directly below the emitter on an optical axis centered on the emitter and an extraction electrode arranged directly below the electric field suppression electrode, a suppression electrode arranged 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 a hole in the electric field suppression electrode to the emitter side, forming a strong electric field at the tip of the emitter.

[0108] An embodiment of the present invention is shown in FIG. 7. The following is a detailed description based on the drawings. The operation of this embodiment is the same as that of embodiment 1, but when a temperature is applied to the emitter 101, a suppression electrode 111 arranged 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 so that the thermoelectrons do not fly to the sample side (not shown). In addition, the converted luminance and angular current density are optimally adjusted by a combination of voltages applied to the electric field suppression electrode 103, the extraction electrode 102, and the suppression electrode 111, respectively.

[0109] The present invention is not limited to the above-described embodiments, and may also include a method for controlling the brightness and angular density of a charged particle beam emitted from a charged particle source. [Explanation of symbols]

[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 lines 108: Acceleration power supply 109: Pull-out 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 orbit asymptotes (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 electron 118: Gas molecules 119: Suppression power supply 120: Thermionic 121: Single hole lens 122: Electron lens main surface

Claims

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

2. The 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 to 4×L.

2. The charged particle gun according to claim 1 .

3. 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 is used to operate the composite extraction electrode as a single electron lens; 2. The charged particle gun according to claim 1 .

4. The combined voltage {Vsu, Vex} is used to change the electric field strength applied to the tip of the emitter, thereby adjusting the amount of emission current and the trajectory of the charged particles emitted from the emitter.

4. The charged particle gun according to claim 3, wherein the charged particle gun is a laser beam.

5. The combined voltage {Vsu, Vex} is used to make the electric field strength applied to the emitter tip constant, and adjust the trajectory of the emitted charged particles while maintaining the emission current constant.

4. The charged particle gun according to claim 3, wherein the charged particle gun is a laser beam.

6. Adjusting the equivalent brightness and angular density of the emitted charged particle beam by the combined voltage {Vsu, Vex}; 4. The charged particle gun according to claim 3, wherein the charged particle gun is a laser beam.

7. The side of the hole on the emitter side surface of the electric field suppression electrode is bowl-shaped or inclined.

2. The charged particle gun according to claim 1 .

8. a ratio L0 / R of a radius R of the hole of the electric field suppression electrode to a distance L0 between the electric field suppression electrode and the tip of the emitter is 1 or less; 2. The charged particle gun according to claim 1 .

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

10. A charged particle gun comprising: A charged particle device comprising:

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