Ion beam device and charged particle beam adjustment method

Abstract

This ion beam device comprises: a gas field ionization ion source 1 that has an emitter 11 and an extraction electrode 13 facing the emitter; a first voltage electric power supply 111 that generates an electric field in the emitter; a second voltage electric power supply 112 that generates an electric field in the extraction electrode; a beam irradiation column 7 that includes a first lens 71 and a second lens 76 that are capable of focusing an ion beam that is emitted from the gas field ionization ion source, and a deflector 73 that is disposed between the first lens and the second lens and is capable of deflecting the ion beam; and a third voltage electric power supply 110 that is connected to the second lens, wherein the second lens is disposed closer to a sample chamber side than the first lens, and the third voltage electric power supply is connected to the first voltage electric power supply and is caused to float by the output voltage of the first voltage electric power supply.

Description

Ion beam device and charged particle beam adjustment method

[0001] The present invention relates to an ion beam device and a method for adjusting a charged particle beam.

[0002] The electron beam is focused through an electromagnetic lens, and the sample is scanned with the beam. The charged particles (secondary electrons) emitted from the sample are detected, allowing the structure of the sample surface to be observed. This is called a scanning electron microscope (SEM).

[0003] Gas field ionization source (GFIS) technology can be used to evaluate the three-dimensional structure of a sample with high resolution and in a short time. GFIS applies a high voltage to a metallic emitter tip, preferably with a radius of curvature of approximately 100 nm or less, to concentrate an electric field at the tip. An ionized gas is introduced into the vicinity of the tip, and the gas molecules are field-ionized and extracted as an ion beam.

[0004] The ion beam emitted from a GFIS has a narrower energy spread and a smaller light source size than those emitted from liquid metal ion sources or ion sources using plasma phenomena, so a scanning ion microscope using a GFIS (GFIS-SIM) can finely focus the ion beam. However, to make the GFIS bright enough for practical use, the tip of the emitter must be sharpened to the atomic level.

[0005] The GFIS is characterized by its ability to change the ion species extracted by changing the gas molecules. By extracting low-mass ions such as hydrogen or helium when observing the sample surface, and high-mass ions such as neon or argon when processing the sample surface, it is possible to reduce damage to the sample during observation and, conversely, increase the processing speed when processing the sample.

[0006] Furthermore, the ion beam emitted from a GFIS has a shorter wavelength than an electron beam at the same acceleration. This reduces aberrations due to diffraction and allows for a smaller beam divergence angle. This means that the focal depth of the observed image (SIM image) is deeper. This is advantageous when simultaneously observing objects at different depths. Furthermore, because secondary electron detection signals are obtained without compromising sample surface information even when irradiating the sample at high acceleration, it is possible to achieve both surface-sensitive and high-resolution observations. In contrast, SEM typically reduces the electron beam acceleration to obtain surface-sensitive images, but reducing acceleration generally has the disadvantage of reducing resolution.

[0007] U.S. Patent No. 6,277,633 discloses a retarding field analyzer for a charged particle beam system. The retarding field analyzer uses existing components of the charged particle beam system, eliminating the need to insert a separate retarding field analyzer. Using existing column components reduces the time required to analyze the beam. Additionally, using the imaging capabilities of the existing column facilitates alignment of the beam with the analyzer.

[0008] JP 2014-89953 A

[0009] As mentioned above, to obtain practical levels of ion beam brightness with the GFIS, the emitter tip must be sharp enough to terminate at just a few atoms. Furthermore, the structure may be subject to sudden destruction, and in such cases, the sharpness must be reproducibly restored. Furthermore, since sample observation using the device is essentially impossible during the formation and restoration processes required to achieve atomic sharpness, these processes must be completed within a very short time.

[0010] On the other hand, narrowing the energy width of the ion beam is important for observing samples with high resolution using an ion beam. It is known that lenses that focus ion beams have aberrations, which increase the diameter (probe diameter) at the point where the ion beam is narrowest. There are several types of aberrations, but one known as chromatic aberration is known to increase in proportion to the energy width of the ion beam. For this reason, a narrow energy width of the ion beam is desirable for observing samples with high resolution.

[0011] It is known that the energy width of an ion beam varies depending on the conditions under which the ion beam is extracted from the ion source. The electric field at the emitter tip is particularly important. However, it is extremely difficult to determine the electric field at the emitter tip. This is because, even if the same voltage is applied to the emitter, the electric field at the emitter tip varies depending on the shape of the emitter, such as its sharpness, which is generally difficult to control. As explained above, in a GFIS, the emitter tip must be sharp enough to terminate at just a few atoms. Since the electric field at the emitter tip can change depending on the number of atoms, this change can be particularly significant. For this reason, it is difficult to identify the conditions for improving the resolution of a GFIS.

[0012] The energy spread of the ion beam can be measured. Therefore, if the energy spread of the ion beam is confirmed before use, it is possible to operate the equipment under conditions favorable for obtaining high-resolution microscopic images. However, equipment for measuring the energy spread of the ion beam is generally large and expensive, and introducing such equipment as an additional device poses a cost issue.

[0013] Furthermore, as disclosed in Patent Document 1, there is also a method for measuring the energy width of an ion beam using a focusing lens, which is an original component of the optical column of an ion beam instrument. In an ion beam focusing lens, a voltage is applied to an electrode having an aperture through which the ion beam passes to achieve focusing, generating a spatial potential distribution at the aperture. This potential distribution can be repurposed to measure the energy width of the ion beam. In other words, the focusing lens is used as a retarding-type energy analyzer that utilizes the phenomenon of ion beam shielding due to this spatial potential distribution. The energy distribution of the ion beam can be determined by measuring the amount of ion beam passing through while changing the voltage applied to the focusing lens. This method makes it possible to identify conditions favorable for obtaining high-resolution microscopic images and operate the instrument under those conditions without adding additional cost or space to existing equipment.

[0014] However, because the above-mentioned electric potential distribution is not spatially uniform, the stopping power of the ion beam changes depending on the position. Even if the energy is exactly the same, when an ion beam with a spatial spread is incident on this electric potential distribution, it may be stopped or passed through, and the subsequent particle trajectory may differ depending on the incident position. In other words, this non-uniformity of the electric field distribution reduces the energy resolution of energy analysis.

[0015] To improve this energy resolution, it is necessary to suppress the spatial spread of the ion beam at the point where the potential distribution is incident. One method for suppressing this is to use an aperture with a narrow diameter that limits the spatial spread of the beam. This method limits the spread by physically blocking the beam before it enters the potential distribution. While this improves the energy resolution, it also reduces the amount of current of the ion beam analyzed at the focusing lens, thereby decreasing the analysis throughput.

[0016] Another suppression method is to focus the ion beam at the center of the potential distribution. This ion beam is focused using a focusing lens located closer to the ion source than the focusing lens that generates the potential distribution for energy analysis. Ideally, this method can both limit the spatial spread and the current of the ion beam to be analyzed. However, it has been found that this method significantly reduces energy resolution due to misalignment between the ion beam and the potential distribution.

[0017] The misalignment between the ion beam and the potential distribution can be resolved to some extent by detecting the ion beam positional deviation when the voltage applied to the focusing lens is changed. However, to detect the misalignment, it is necessary to set the magnitude of the potential distribution generated by the focusing lens so that the beam follows a trajectory that focuses the beam on the sample surface, which is placed after the focusing lens. The magnitude of the potential distribution for focusing the beam on the sample surface is significantly different from the magnitude of the potential distribution for actual energy analysis, making it difficult to accurately detect the ion beam positional deviation.

[0018] That is, in this method, there is a trade-off between energy resolution and analytical throughput, and in order to solve this problem, it is necessary to accurately measure the positional deviation between the ion beam and the potential distribution.

[0019] An ion beam apparatus according to one embodiment of the present invention includes a gas field ion source having an emitter and an extraction electrode facing the emitter, a first voltage power supply connected to the emitter and generating an electric field in the emitter, a second voltage power supply connected to the extraction electrode and generating an electric field in the extraction electrode, a beam irradiation column including first and second lenses capable of focusing an ion beam emitted from the gas field ion source, and a deflector disposed between the first and second lenses and capable of deflecting the ion beam, a third voltage power supply connected to the second lens, and a sample chamber in which a sample stage is disposed that carries a sample to be irradiated with the ion beam that has passed through the beam irradiation column, the second lens being disposed closer to the sample chamber than the first lens, and the third voltage power supply being connected to the first voltage power supply and being floated by the output voltage of the first voltage power supply.

[0020] The ion beam device according to the present invention makes it possible to accurately align an ion beam with the saddle point of the potential distribution of the focusing lens. This makes it possible to quickly determine the energy distribution of the ion beam incident on the focusing trajectory into the potential distribution of the focusing lens with high energy resolution. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0021] 1 is a configuration example of an ion beam device; FIG. 2 is a histogram showing the energy distribution of an ion beam; FIG. 3 is a diagram showing the results of calculating the potential distribution of an electrostatic focusing lens; FIG. 4 is a diagram showing the potential distribution on the axis of an electrostatic focusing lens; FIG. 5 is a diagram showing the potential distribution in the radial direction on a surface including the maximum value of the potential distribution on the axis of an electrostatic focusing lens; FIG. 6 is a detailed diagram showing the potential distribution in the radial direction on a surface including the maximum value of the potential distribution on the axis of an electrostatic focusing lens; FIG. 7 is a diagram showing differences in the passing position of an ion beam incident on a potential distribution; FIG. 8 is a diagram showing the influence of the trajectory of an ion beam incident on a potential distribution; FIG. 9 is a diagram showing the relationship between a retarding voltage and the degree of inhibition of an ion beam; FIG. 10 is a diagram showing the relationship between a deflector output and a retarding voltage at which a characteristic point appears; FIG. 11 is a configuration example of a deflector; FIG. 12 is a diagram showing the relationship between the focusing action of a focusing lens and the energy width; FIG. 13 is a diagram showing the relationship between the focusing action of a focusing lens and the energy width; FIG. 14 is an example of the energy distribution of an ion beam emitted from a hydrogen gas field ionization ion source; FIG. 15 is an example of the energy distribution of a filtered ion beam; FIG. 16 is a configuration example of an ion beam device that filters a hydrogen ion beam using an RFA. 1 is an example of an adjustment procedure before energy analysis, an example of an ion beam position adjustment procedure, and an example of a focus lens focusing action adjustment procedure.

[0022] To facilitate understanding of the present invention, the following will first explain the problems with current ion beam devices, then outline the basic principles of the present invention, and then explain the specific configuration of the ion beam device according to the present embodiment with reference to the drawings.

[0023] FIG. 1 is a configuration diagram of an ion beam device 1000 according to this embodiment. Here, the configuration is described as an ion beam device including a gas field ion source, but a liquid metal ion source, a plasma ion source, or a magnetic optical trap ion source (MOTIS) can also be used as the ion source. Alternatively, the device can be configured as a charged particle beam device including an electron source instead of an ion source. In the following description, when referring to the optical elements of the ion beam device, the ion source side may be referred to as the upstream side and the sample side, which is the final destination, as the downstream side according to the flow of the ion beam.

[0024] The gas field ion source 1 includes an emitter electrode (emitter tip) 11 having a needle-shaped tip, an extraction electrode 13, and high-voltage power supplies 111 and 112. The extraction electrode 13 has an opening facing the emitter electrode 11. The emitter electrode 11 is cooled as needed by a refrigerator or a cryogen such as liquid nitrogen or liquid helium. The high-voltage power supply 111 applies a voltage to the emitter electrode 11, and the high-voltage power supply 112 applies a voltage to the extraction electrode 13. The potential difference between the two creates an electric field near the tip of the emitter electrode 11 that positively ions the gas.

[0025] The high-voltage power supplies 111 and 112 can be controlled independently of each other, thereby enabling independent control of the acceleration voltage of the ion beam and the extraction voltage for forming the ionization field. In order to freely change the acceleration voltage of the ion beam regardless of the magnitude of the ionization energy, it is desirable that the high-voltage power supply 112 connected to the extraction electrode 13 be a power supply capable of outputting both positive and negative polarities, or a power supply with negative polarity based on the potential supplied by the high-voltage power supply 111. This makes it possible to set the acceleration voltage of the ion beam lower than the extraction voltage required to extract ions.

[0026] To emit an ion beam 15 from the emitter electrode 11 of the gas field ion source 1, a high voltage is first applied between the emitter electrode 11 and the extraction electrode 13. The application of a high voltage concentrates an electric field at the tip of the emitter electrode 11. For example, to emit a hydrogen ion beam, the strength of the electric field formed at the tip is set to be strong enough to positively ionize hydrogen. In this state, if a gas containing hydrogen gas is introduced near the emitter electrode 11 using the gas introduction mechanism, a hydrogen ion beam will be emitted from the tip of the emitter electrode 11. Similarly, ion beams can be extracted from gases such as helium, neon, argon, krypton, nitrogen, and oxygen by adjusting the voltage and introducing the gas appropriately.

[0027] The vacuum chamber containing the gas field ion source 1 has a temperature of 1000 K when no gas is introduced by the gas introduction mechanism. －７It is preferable that the vacuum chamber be maintained at an ultra-high vacuum of 100 Pa or less. In order to achieve an ultra-high vacuum in the vacuum chamber, the start-up operation of the gas field ion source 1 may include so-called baking, in which the entire vacuum chamber is heated to 100 degrees or more.

[0028] In order to increase the brightness of the ion beam, it is preferable to adjust the cooling temperature of the emitter electrode 11 using a refrigerator. The refrigerator cools the interior of the gas field ion source 1, the emitter electrode 11, the extraction electrode 13, etc. The refrigerator may be, for example, a mechanical refrigerator such as a Gifford-McMahon type (GM type) or a pulse tube type, or may use a refrigerant such as liquid helium, liquid nitrogen, or solid nitrogen. In addition, in order to increase the brightness of the ion beam, it is preferable to increase the sharpness of the emitter 11 as much as possible. For example, it is desirable to configure the tip of the emitter 11 so that it terminates with several, such as one, two, or three, metal atoms that make up the emitter 11.

[0029] Since the ion beam 15 emitted from the emitter electrode 11 has a very high directivity, a drive mechanism may be provided separately for the emitter electrode 11 so that the position and angle of the emitter electrode 11 can be adjusted to achieve conditions favorable for focusing the ion beam 15. The emitter electrode drive mechanism may be configured so that it can be manually adjusted by a user or automatically adjusted by an emitter electrode drive mechanism controller.

[0030] The ion beam device 1000 includes a gas field ion source 1, a beam irradiation column 7, and a sample chamber 3. When observing a sample surface, an ion beam 15 emitted from the gas field ion source 1 passes through the beam irradiation column 7 and is irradiated onto a sample 31 placed on a sample stage inside the sample chamber 3. Secondary particles (e.g., secondary electrons) emitted from the sample 31 are detected by a secondary particle detector 33.

[0031] The beam irradiation column 7 includes a focusing lens 71, an aperture 72, a deflector 73, and an objective lens 76. Voltages are supplied to the focusing lens 71, the deflector 73, and the objective lens 76 by a focusing lens power supply 113, a deflector power supply 731, and an objective lens power supply 110, respectively. The electrodes of the deflector 73 can be configured with multiple electrodes that generate an electric field, such as 4-pole, 8-pole, or 16-pole electrodes, as needed. The number of poles of the deflector power supply must be increased depending on the number of electrodes.

[0032] The focusing lens 71 is an example of an electrostatic lens composed of three electrodes, electrodes 710, 711, and 712. A high voltage is supplied to the central electrode 711 from the focusing lens power supply 113. The electrodes 710 and 712 are typically set to be at ground potential, but a power supply may be provided to supply voltage as needed.

[0033] The objective lens 76 is an example of an electrostatic lens configured with three electrodes, electrodes 760, 761, and 762. A high voltage is supplied to the central electrode 761 from the objective lens power supply 110. The electrodes 760 and 762 are typically set to be at ground potential, but a power supply may be provided to supply voltage as needed.

[0034] The ion beam 15 is focused by a focusing lens 71, the beam diameter is restricted by an aperture 72, and the beam is further focused to form a fine shape on the sample surface by an objective lens 76. The deflector 73 is used for axial adjustment to reduce aberrations during focusing by the lens, and for scanning the ion beam on the sample.

[0035] There are several types of aberrations that occur when a lens focuses an ion beam. Among these, chromatic aberration increases as the energy distribution width of each particle in the ion beam 15 increases, hindering the focusing of the ion beam 15. The energy distribution width (hereinafter referred to as energy width) is the width 21 when the energy possessed by a particle is expressed as a frequency in terms of the number of particles that actually possess that energy, as shown in histogram 2 in Figure 2, for example. Here, the width 21 can be determined using various scales. For example, the full width at half maximum (FWHM), which is the width at the half-maximum position relative to the peak of the distribution, can be used. The width can also be determined by fitting the energy distribution to a known function, such as a Gaussian distribution.

[0036] The energy width of the ion beam 15 varies depending on the conditions under which the ion beam is extracted. Among these, the voltage difference (extraction voltage) between the emitter 11 and the extraction electrode 13 is an important condition that determines the energy width. In other words, setting an optimal value for the extraction voltage to reduce the energy width is important for observing the sample surface.

[0037] However, the energy width depends on the strength of the electric field formed at the tip of the emitter 11. Because the strength of the electric field also depends on the shape of the emitter 11, the same extraction voltage value is not always optimal. The shape of the emitter 11 may change due to the chemical or physical influence of surrounding gas molecules during ion beam emission. Furthermore, if the atomic structure formed at the tip to improve the sharpness of the emitter 11 is altered, some work to repair it may cause the change. Once the emitter 11 is introduced into the device, it is very difficult to confirm its shape, and therefore it is similarly difficult to confirm the strength of the electric field formed at the tip.

[0038] Therefore, measuring the energy spread of an ion beam is a useful function for maintaining the instrument in optimal condition. The energy spread and absolute energy of an ion beam can be measured using a retarding electric field analyzer (RFA). An RFA applies a voltage to an electrode so that the retarding field, which stops the beam, increases or decreases in stages. This electrode is typically a grid-type electrode or an electrode with an aperture, configured so that the beam passes through. The energy of the particles constituting the beam can be analyzed from the relationship between the applied voltage and the amount of beam passing through. Using an RFA typically requires the installation of additional equipment separate from the ion beam instrument. It also requires an operating mechanism for inserting and retracting the electrode into the beam path and a power supply for applying voltage to the electrode. This increases costs. Furthermore, the positional relationship between the beam and the electrode is an important parameter that determines the energy resolution of energy analysis, and this requires precise adjustment of the electrode position or the beam position, which is time-consuming.

[0039] On the other hand, it is possible to avoid the need for additional equipment by using a focusing lens in an ion beam instrument as a retarding electrode for RFA. Even in this case, precise adjustment of the beam position is required. To adjust the ion beam position, a technique typically used for sample observation in an ion beam instrument can be adapted. For example, the voltage applied to the focusing lens is wobbled and the ion beam position is observed to change in response to the wobbled voltage. By adjusting the voltage applied to the focusing lens in advance so that the ion beam is focused on the surface of a sample placed in the instrument, the presence or absence of ion beam position fluctuations can be determined by detecting whether the microscope image of the sample oscillates in response to the wobbled voltage. However, because the retarding voltage used to block the ion beam with the focusing lens is strictly different from the voltage used to focus the ion beam on the sample surface, precise position adjustment using this wobbler technique is difficult.

[0040] The ion beam device of this embodiment can perform both a mode for focusing an ion beam on a sample surface for observation using a focusing lens and a mode for performing energy analysis of the ion beam at the same time, and further enables the energy analysis to be performed quickly with high throughput.

[0041] 1, a voltage is applied to an electrode 761 of the objective lens 76 using the objective lens power supply 110 to generate a potential distribution 764. This potential distribution 764 can be used to make the ion beam 15 follow a trajectory that focuses the ion beam 15 on the surface of the sample 31, or the potential distribution can be increased to a level that stops the ion beam 15, and the magnitude of the potential distribution can be gradually changed to perform energy analysis.

[0042] The objective lens power supply 110 is floated by the output voltage of the high-voltage power supply 111, which supplies voltage to the emitter electrode 11. By using the output voltage of the high-voltage power supply 111 as the reference voltage for the objective lens power supply 110, the maximum required output voltage of the objective lens power supply 110 can be reduced. The voltage applied to the electrode 761 required to stop the ion beam 15 is approximately the same as the voltage applied to the emitter electrode 11. In the power supply configuration of this embodiment, the objective lens power supply 110 is floated, and then the high-voltage power supply 111 is connected and its output is added, thereby significantly reducing the maximum output voltage required of the objective lens power supply 110. Typically, with a constant-voltage power supply, the higher the maximum output voltage, the larger the minimum setting range of the output voltage. In the power supply configuration of this embodiment, the maximum output voltage of the objective lens power supply 110 can be reduced, thereby narrowing the setting range of the output voltage, allowing for more precise setting of the retarding voltage. This precise setting of the retarding voltage has the effect of enabling measurement of ion beams with a narrow energy range.

[0043] Furthermore, in a constant voltage power supply, the greater the maximum output voltage or the greater the actual output voltage, the greater the fluctuation in voltage over time. Since the relative value of the potential on the particle emission side and the potential on the retarding side is important in an RFA, floating the objective lens power supply 110 using the high voltage power supply 111 can offset most of the fluctuation in power supply and reduce its impact. This stabilizes the magnitude of the potential distribution 764 relative to the ion beam 15 for a long period of time, thereby enabling the adjustment of the positioning of the ion beam 15 and the focusing action of the focusing lens 71, as will be described later.

[0044] However, there may be cases where it is not desirable to vary the electric field of the objective lens 76 in conjunction with the high-voltage power supply 111. In such cases, for example, a second objective lens power supply, which is a high-voltage power supply with a normal configuration that is not floated by the output voltage of the high-voltage power supply 111, may be separately provided, and the objective lens power supply 110 and the second objective lens power supply may be switchable.

[0045] The potential distribution 764 generally has a saddle point near the center of the electrode. Figure 3A shows the potential distribution at the opening of the central electrode of a three-electrode objective lens, i.e., the electrode corresponding to electrode 761 (see Figure 1), calculated using the finite element method. Note that Figure 3A shows the potential distribution when a voltage of 20 kV is applied to electrode 761 and the electrodes corresponding to electrodes 760 and 762 are grounded. As shown in Figure 3A, if the direction of ion beam propagation, i.e., the optical axis, is taken as the Z axis and the radial direction perpendicular to it is taken as the r axis, the potential distribution in the Z axis direction at r = 0 is shown in Figure 3B. Furthermore, Figure 3C shows the radial potential distribution at the Z value (Z = 4.5 mm) where the potential is maximized in the graph of Figure 3B. Furthermore, Figure 3D shows a graph showing only the vicinity of the center (r = 0) of the potential distribution in Figure 3C, with the minimum value of the potential distribution set to 0.

[0046] As can be seen from the above results of the finite element method, the potential distribution generated by the objective lens has a saddle point near the center of the aperture. In this embodiment, by aligning the ion beam with this saddle point, the energy resolution of energy analysis using the retarding method can be improved. As mentioned above, in the wobbler method, the voltage applied to the electrode 761 is set to a value that allows the ion beam to focus directly above the sample 31, and is smaller than the voltage required to stop the beam, making precise positioning difficult.

[0047] FIG. 4 illustrates the effect of misalignment between the ion beam and the potential distribution. In the potential distribution near the saddle point shown in FIG. 3D , when a parallel ion beam with a diameter of 10 μm is irradiated at a position r=0 (ion beam 151), the width 153 of the potential distribution through which the ion beam passes is at most approximately 0.05 V. Under these conditions, the energy resolution in energy analysis is reduced by the width of the potential distribution of approximately 0.05 V. On the other hand, when a similar parallel ion beam with a diameter of 10 μm is irradiated at a position r=15 μm (ion beam 152), the width 154 of the potential distribution increases to approximately 0.55 V. When energy analysis is performed under these conditions, the energy resolution is reduced by the influence of this potential width of 0.55 V. Here, the typical energy width of a GFIS is approximately 0.5 to 2.0 eV, depending on the conditions and ion species, so this degradation of energy resolution due to the axis misalignment is unacceptable.

[0048] When a parallel beam is incident on the potential distribution 764, the diameter of the ion beam 15 can be limited using the aperture 72, thereby narrowing the potential distribution width and reducing degradation of energy resolution. However, in this case, the current amount of the ion beam 15 is limited, significantly reducing analysis throughput. For example, although the ion beam 158 has the same axial misalignment (r = -15 μm) as the ion beam 152, the diameter is limited to 5 μm, thereby reducing the potential distribution width, which degrades energy resolution, from approximately 0.55 V (potential distribution width 154) to approximately 0.3 V. On the other hand, assuming that the current density of the ion beam 158 is the same as that of the ion beam 152, the current amount is one-quarter. Therefore, it takes four times as long to obtain analysis results with the same signal-to-noise ratio as the analysis results using the ion beam 152.

[0049] The current of the ion beam can be increased by making the beam a focused trajectory relative to the potential distribution 764. However, not only the position of the ion beam but also its trajectory has a significant effect on the energy resolution. Figure 5 shows a schematic diagram of an ion beam that is focused on the ion source side, above the saddle point of the potential distribution, and is incident with an axial offset from the center. In this case, the width 157 of the potential distribution is approximately 0.25 V. Energy analysis under these conditions is affected by this potential distribution width of approximately 0.25 V, resulting in a decrease in energy resolution. If the focusing effect of the focusing lens 71 is increased and the focal point is further shifted upward from the ion beam 156, the width of the potential distribution will further increase.

[0050] As we have seen so far, adjusting the position of the ion beam 15, its trajectory conditions, and in particular the focusing effect of the focusing lens 71, are important for improving the resolution of energy analysis. First, the procedure for aligning the ion beam 15 will be explained, and then the adjustment of the focusing effect of the focusing lens 71 will be explained. Figure 14 shows the flow of these adjustments.

[0051] First, each optical element is roughly adjusted (S01). If alignment has already been achieved to a certain extent, this step may be omitted. Typically, this involves the position and angle of the emitter 11 and the position of the aperture. The positional deviation of the emitter 11 position and angle and the aperture position can be roughly detected by the oscillation (wobbler) of the focusing lens power supply 113 connected to the focusing lens 71. For example, each optical element is mechanically adjusted so that the position of the ion beam 15 on the sample 31 does not fluctuate in response to fluctuations in the output voltage of the focusing lens power supply 113.

[0052] The alignment of the ion beam 15 with the potential distribution 764 is performed by actually using the potential distribution 764 to stop the ion beam 15 (S02, S03). The degree to which the ion beam 15 is stopped can be observed by observing the ion beam 20 recoiled by the potential distribution 764. The ion beam 20 may be observed via a conversion plate 77 that converts ions into secondary electrons 22. The secondary electrons 22 are detected by a detector 201.

[0053] The method for observing the degree of inhibition of the ion beam 15 is not limited to observing the recoiled ion beam 20. For example, the amount of ion beam 15 passing through the potential distribution 764 may be converted into secondary electrons in the sample 31 and detected by a secondary electron detector (secondary particle detector) 33. Alternatively, the current can be directly detected using a Faraday cup separately installed next to the sample. However, the space in which the sample is installed may change depending on the user's usage method, and the amount detected may vary depending on the surface condition of the sample and the surrounding magnetic field. Furthermore, when a Faraday cup is used, it takes time to move the position of the sample and set it so that the ion beam is incident on the Faraday cup. Observing the degree of inhibition using the detector 201 can solve these problems.

[0054] When the ion beam 15 is to be stopped, the output of the objective lens power supply 110, i.e., the retarding voltage, is gradually increased or decreased. The degree to which the ion beam is stopped changes with the change in the retarding voltage, and the degree 221 of ion beam stoppage evaluated by the amount of current detected by the detector 201 changes as shown in FIG. 6 . At this time, the change in the degree 221 of stoppage has several characteristic points for a certain retarding voltage, such as a stoppage start point 222, an inflection point 223, and a stoppage end point 224.

[0055] These feature points contain information about where the ion beam 15 is located relative to the potential distribution 764. In other words, if the ion beam 15 is located at a location with a high potential in the potential distribution, these feature amounts can be detected with a relatively small retarding voltage. Conversely, if the ion beam is located at a location with a low potential, these feature amounts can be detected with a relatively large retarding voltage.

[0056] On the other hand, the position through which the ion beam 15 must pass in order to improve the resolution of the energy analysis is the saddle point 225. At this position, the potential is smallest as shown in Fig. 3C, and therefore the value of the retarding voltage required for the above-mentioned characteristic point to appear is largest. In other words, the position of the ion beam 15 at which the retarding voltage at which the above-mentioned characteristic point appears is the highest can be said to be the position that provides the best energy resolution for the energy analysis.

[0057] Therefore, the output of the deflector 73 is changed by the deflector power supply 731, the position of the ion beam 15 is changed, and the characteristic quantities for each output, i.e., the retarding voltage at which the inflection point 223 is observed, for each position of the ion beam 15 are plotted as shown in FIG. 7 . For example, the retarding voltage at which the inflection point 223 appears is larger for deflector output A than for deflector output B. Therefore, the ion beam position provided by deflector output A is closer to the saddle point 225. By finding the envelope 233 by fitting or the like from similar data for several deflector outputs and then finding the deflector output C that provides the maximum, it is possible to determine the deflector output conditions under which the ion beam position is closest to the saddle point 225. If a power supply configuration were adopted in which a non-floating high-voltage power supply were separately connected to the electrode 761 of the objective lens 76 and a voltage were applied independently of the high-voltage power supply 111, such evaluation would be difficult to perform due to the significant influence of fluctuations in the high-voltage power supply.

[0058] FIG. 15 shows a flow for controlling the deflector 73 to search for the saddle point 225. The deflector output is set (S11), the retarding voltage is varied, and a retarding voltage that provides a characteristic point (e.g., inflection point 223) of the degree of ion beam retardation is detected (S12, S13), and the data point is recorded (S14). Note that the retardation start point 222 or the retardation end point 224 may also be used as the characteristic point. The data points recorded in steps S11 to S14 correspond to the circles shown in FIG. 7. If a maximum point is detected from the envelope 233 of these data points (Yes in S15), the position through which the ion beam 15 passes when the output of the deflector 73 is set to a deflector output that provides the maximum point of the envelope 233 can be identified as the saddle point 225.

[0059] FIG. 8 shows an example of the configuration of the deflector 73. While FIG. 8 shows a configuration including four electrodes arranged to surround the ion beam 15, the deflector 73 may also be configured to include more than four electrodes, for example, eight electrodes. The deflector 73 shown in FIG. 8 can be considered a combination of a first deflector (deflector A) and a second deflector (deflector B), and the direction in which the deflector A deflects the ion beam 15 is perpendicular to the direction in which the deflector B deflects the ion beam 15. The deflector A also includes opposing electrodes 732 a and 732 b, with the first deflector power supply 7320 connected to the electrode 732 a and the electrode 732 b connected to ground potential. Alternatively, a power supply that outputs a voltage of the opposite polarity to that of the first deflector power supply 7320 may be connected to the electrode 732 b. Similarly, the deflector B has electrodes 733a and 733b facing each other, and the electrode 733a is connected to a second deflector power supply 7330, while the electrode 733b is connected to a ground potential. Alternatively, the electrode 733b may be connected to a power supply that outputs a voltage of the opposite polarity to that of the second deflector power supply 7330.

[0060] 8, the process for optimizing the ion beam position as shown in Fig. 15 is performed for each of the deflector A and the deflector B. By finding the maximum of the envelope 233 for each of the deflector A and the deflector B, it becomes possible to know the optimal output of each of the deflector power supplies 7320 and 7330, and it becomes possible to find the saddle point 225 on a plane perpendicular to the optical axis of the ion beam.

[0061] Next, the procedure for adjusting the focusing action of the focusing lens 71 (S04) will be described. Differentiating the ion beam retardation degree 221 (see FIG. 6) with respect to the retarding voltage, histogram 2 as shown in FIG. 2 can be obtained. The histogram 2 obtained here has a width that is determined by conditions downstream of the extraction electrode, separate from the true energy distribution of the ion beam 15. This width depends on the range and potential width of the ion beam when the ion beam 15 is incident on the potential distribution 764, as shown in FIGS. 4 and 5 . The focusing action of the focusing lens 71 is adjusted by the voltage value of the focusing lens power supply 113.

[0062] 16 shows the flow of adjusting the focusing action of the focusing lens 71. As shown in FIG. 9, when the energy width (width 21 (see FIG. 2)) is evaluated at a certain voltage value of the focusing lens power supply 113, data points indicated by circles are obtained (S21 to S23). The focusing action of the focusing lens 71 is operated incrementally or incrementally, and the width 21 at each focusing action is evaluated. This results in multiple data points, and an envelope 241 is obtained by fitting these data points. The focusing action that gives the minimum point of the envelope 241 is the optimal adjustment value 242 of the focusing action that is sought (S24).

[0063] By adjusting the focusing action of the focusing lens 71 after adjusting the ion beam position by the deflector 73, the focusing point of the ion beam 15 is positioned at the saddle point 225. However, there are cases where the ion beam 15 does not pass through the saddle point 225 due to the adjustment of the focusing action of the focusing lens 71. Therefore, as shown in Fig. 14, steps S02 to S04 are repeatedly performed (S05) to reduce the positional deviation before and after the adjustment of the focusing action of the focusing lens 71. After the high-precision adjustment is completed, energy analysis is performed.

[0064] It is preferable that the outputs of the high-voltage power supplies 111 and 112 are constant during the alignment adjustment work (S02 to S03) of the ion beam 15 and the adjustment work (S04) of the focusing action of the focusing lens 71. By keeping the emission conditions of the ion beam 15 constant, the changes in the inhibition start point 222, the inflection point 223, the inhibition end point 224, and the width 21 depend only on the conditions downstream of the extraction electrode 13, that is, the conditions of energy analysis, which is advantageous for optimizing the conditions of energy analysis.

[0065] As explained above, the influence of the potential distribution width of the potential distribution 764 that blocks the ion beam can be reduced by adjusting the positioning of the ion beam 15 and the focusing lens action. Experimental results that clearly demonstrate this effect are shown in FIG. 10 . FIG. 10 shows the results of measuring the width 21 after adjusting the position of the ion beam 15 using the procedure described above and then changing the focusing action of the focusing lens 71. The voltage conditions applied to the emitter tip 11 and the extraction electrode 13 were kept constant. Specifically, the acceleration of the ion beam 15 was 20 kV, and the ion beam 15 was restricted by apertures 72 with diameters of 30 μm, 20 μm, and 10 μm, and the energy width of the ion beam was measured based on the potential distribution generated in the objective lens 76.

[0066] Calculations have shown that the parallel beam condition 250 is near 11.4 kV. Under this condition, the width 21 is smallest when the beam is limited by the smallest aperture (10 μm), and the width 21 is largest when the beam is limited by the largest aperture (30 μm). This is consistent with the discussion of the ion beam width at the potential distribution position and the width of the potential distribution, as explained above.

[0067] In contrast, for any aperture diameter, there is a minimum value for width 21 near the lens condition (focusing lens condition 251) where the beam is focused near the potential distribution generated in the objective lens. Furthermore, the minimum value of width 21 near focusing lens condition 251 is almost the same for the maximum aperture diameter of 30 μm and the minimum aperture diameter of 10 μm.

[0068] Considering that the conditions for ion beam extraction in the ion source are constant and the original energy width of the ion beam 15 remains unchanged, this result can be considered to reflect the energy resolution of the energy analysis under each focusing lens condition. First, the energy resolution for a parallel beam is improved by reducing the aperture diameter. Furthermore, it has been suggested that under aligned conditions, the energy analysis under the focusing lens condition is optimal for any aperture diameter, and that the energy resolution does not depend on the aperture diameter. Under these focusing lens conditions, the focal point 2510 of the ion beam 156 coincides with the saddle point 225, and it is considered that the influence of the potential distribution width is minimized regardless of the aperture diameter.

[0069] If the extraction conditions from the ion source are constant, changing the aperture diameter from 10 μm to 30 μm is expected to increase the current by approximately nine times. Increasing the ion beam current during energy analysis has the effect of improving the throughput of energy analysis. Furthermore, changing from parallel beam conditions to focused beam conditions for analysis also has the effect of improving the throughput of energy analysis by increasing the current.

[0070] Furthermore, the RFA configured with an electrostatic lens can function not only to analyze the energy of the ion beam 15, but also to function as a filter that unifies ion species present in the ion beam. Among gas field ionization ion sources, a hydrogen field ionization ion source that ionizes hydrogen gas can ionize three types of ions, H ＋ , H ２ ＋ , H ３ ＋ It is known that H is released. ３ ＋ is known to have higher energy than the other two hydrogen ion species. For example, H ２ ＋ and H ３ ＋ The energy distribution of the ion beam, which is composed of the relatively low energy H ２ ＋Spectrum 80 and relatively high energy H ３ ＋ When the sample 31 is observed with such an ion beam, the ion beam may be separated into minute parts due to the earth's magnetic field, and the observed image may appear multiplexed.

[0071] Therefore, by configuring the ion beam device 1001 as shown in FIG. 13, a single ion species H ３ ＋ 13, the same components as those in the ion beam system 1000 shown in FIG. 1 are denoted by the same reference numerals, and a description of the overlapping components will be omitted.

[0072] The ion beam device 1001 includes a first objective lens 76 and a second objective lens 7600 downstream of the first objective lens 76. The first objective lens 76 is provided with a filter power supply 1100, and the power supply configuration is the same as that of the objective lens power supply 110 shown in FIG. 1. The difference from the objective lens power supply 110 is that the output voltage is a voltage that is generated at the position of the potential distribution 764 generated by the objective lens 76, and the H ２ ＋ The ion beam 1500 that has passed through the first objective lens 76 is focused onto the sample 31 by the second objective lens 7600. The strength of the second objective lens 7600 is controlled by an objective lens power supply 7601.

[0073] The ion beam 1500 filtered by the first objective lens 76 has an energy distribution as shown in Fig. 12. The ion species becomes single, and the energy width of the ion beam as a whole is reduced, which has the effect of improving the focusing performance of the ion beam. ２ ＋ It is also possible to pass only

[0074] The above embodiments and modifications have been described in detail to make the present invention easier to understand, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of one embodiment or modification. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment or modification with other configurations.

[0075] 1: gas field ion source, 11: emitter electrode (emitter tip), 13: extraction electrode, 15, 151, 152, 156, 158, 1500: ion beam, 153, 154, 157: width of potential distribution, 2: histogram, 20: recoiled ion beam, 21: width, 22: secondary electrons, 201: detector, 221: ion beam suppression degree, 222: suppression start point, 223: inflection point, 224: suppression end point, 225: saddle point, 233, 241: envelope, 242: optimum adjustment value, 250: parallel beam condition, 251: focused beam condition, 2510: focusing point, 110: objective lens Lens power supply, 1100: filter power supply, 111, 112: high voltage power supply, 113: focusing lens power supply, 3: sample chamber, 31: sample, 33: secondary particle detector, 7: beam irradiation column, 71: focusing lens, 710, 711, 712: electrodes, 72: aperture, 73: deflector, 731: deflector power supply, 732, 733: electrodes, 7320, 7330: deflector power supply, 76: objective lens, 760, 761, 762: electrodes, 764: potential distribution, 7600: objective lens, 7601: objective lens power supply, 77: conversion plate, 80, 81: spectrum, 1000, 1001: ion beam device.

Claims

1. An ion beam device comprising: a gas field ion source having an emitter and an extraction electrode facing the emitter; a first voltage power supply connected to the emitter and generating an electric field in the emitter; a second voltage power supply connected to the extraction electrode and generating an electric field in the extraction electrode; a beam irradiation column comprising a first lens and a second lens capable of focusing an ion beam emitted from the gas field ion source, and a deflector arranged between the first lens and the second lens and capable of deflecting the ion beam; a third voltage power supply connected to the second lens; and a sample chamber in which is arranged a sample stage carrying a sample to be irradiated with the ion beam that has passed through the beam irradiation column, wherein the second lens is arranged on the sample chamber side of the first lens, and the third voltage power supply is connected to the first voltage power supply and is floated by the output voltage of the first voltage power supply.

2. An ion beam apparatus according to claim 1, wherein the energy distribution of the ion beam is obtained by generating an electric field in the second lens that stops the ion beam using the third voltage power supply.

3. An ion beam apparatus according to claim 2, wherein the energy distribution of the ion beam is obtained for each of a plurality of states in which the electric field generated in the extraction electrode by the second voltage power supply is changed.

4. An ion beam apparatus according to claim 2, wherein the energy distribution of the ion beam is obtained with the deflector adjusted so that the ion beam is positioned at a saddle point of the potential distribution of the second lens.

5. An ion beam device according to claim 4, wherein the energy distribution of the ion beam is obtained with the focusing action of the first lens adjusted so that the focal point of the ion beam is located at a saddle point of the potential distribution of the second lens.

6. An ion beam device as claimed in claim 1, wherein the beam irradiation column comprises a third lens disposed between the second lens and the sample chamber, and the third lens irradiates the sample with an ion beam of an ion species that has passed through the second lens among the ion species mixed in the ion beam.

7. An ion beam device according to claim 1, wherein the beam irradiation column is provided with a fourth voltage power supply, and the connection with the second lens is switchable between the third voltage power supply and the fourth voltage power supply.

8. A charged particle beam adjustment method for adjusting a charged particle beam emitted from a charged particle source and traveling in a charged particle optical column, the charged particle optical column comprising a first electrostatic lens and a second electrostatic lens capable of focusing the charged particle beam, and a deflector disposed between the first electrostatic lens and the second electrostatic lens and capable of deflecting the charged particle beam, the method comprising: a first step of detecting a retarding voltage at which a change in the degree of inhibition of the charged particle beam by the potential distribution of the second electrostatic lens becomes a predetermined characteristic point by changing a retarding voltage applied to the second electrostatic lens; and a second step of determining an amount of deflection of the charged particle beam by the deflector that positions the charged particle beam at a saddle point of the potential distribution, based on a relationship between the amount of deflection of the charged particle beam by the deflector and a retarding voltage at which a change in the degree of retardation becomes a predetermined characteristic point, the relationship being indicated by a plurality of data points obtained by executing the first step while changing the amount of deflection of the charged particle beam by the deflector.

9. A method for adjusting a charged particle beam as claimed in claim 8, further comprising a third step of changing the focusing action of the charged particle beam by the first electrostatic lens, measuring the energy width of the charged particle beam, and detecting an adjustment value that provides a focusing action with which the energy width is minimized.

10. A method for adjusting a charged particle beam according to claim 9, comprising repeating the first to third steps to adjust the amount of deflection by the deflector and the focusing effect of the first electrostatic lens, and then measuring the energy distribution of the charged particle beam.

11. A method for adjusting a charged particle beam as claimed in claim 10, wherein the charged particle source is a gas field ion source comprising an emitter and an extraction electrode facing the emitter, a first voltage power supply for generating an electric field in the emitter is connected to the emitter, a second voltage power supply for generating an electric field in the extraction electrode is connected to the extraction electrode, a third voltage power supply for applying the retarding voltage is connected to the second electrostatic lens, and the third voltage power supply is connected to the first voltage power supply and is floated by the output voltage of the first voltage power supply.

12. A method for adjusting a charged particle beam as claimed in claim 11, comprising measuring the energy distribution of the charged particle beam for each of a plurality of states in which the electric field generated in the extraction electrode by the second voltage power supply is changed, thereby searching for an optimal output voltage of the second voltage power supply.

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