Ion beam apparatus 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

[Technical Field]

[0001] The present invention relates to an ion beam apparatus and a charged particle beam adjustment method. [Background technology]

[0002] By focusing an electron beam through an electromagnetic field lens and irradiating a sample with this beam while scanning, the structure of the sample surface can be observed by detecting the charged particles (secondary electrons) emitted from the sample. 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. In GFIS, a high voltage is applied to a metal emitter tip, preferably with a tip radius of curvature of about 100 nm or less, to concentrate the electric field at the tip, and a gas (ionized gas) is introduced nearby to field ionize the gas molecules and extract them as an ion beam.

[0004] The ion beam emitted from a GFIS has a narrower energy range and smaller light source size compared to ion beams emitted from liquid metal ion sources or plasma-based ion sources. Therefore, scanning ion microscopes (GFIS-Scanning Ion Microscopes: GFIS-SIMs) using GFIS can focus the ion beam very precisely. However, in order to achieve sufficient brightness for practical use, the tip of the emitter of the GFIS needs to be sharpened at the atomic level.

[0005] A key feature of GFIS is its ability to change the type of ions extracted by altering the gas molecules. When observing the sample surface, low-mass ions such as hydrogen or helium can be extracted, while when processing the sample surface, high-mass ions such as neon or argon can be extracted. This reduces damage to the sample during observation or, conversely, increases the processing speed during sample processing.

[0006] Furthermore, the ion beam emitted from a GFIS has the characteristic of having a shorter wavelength compared to an electron beam at the same acceleration. Therefore, aberrations due to diffraction are reduced, and the beam angle can be made smaller. This means that the depth of focus of the observed image (SIM image) is increased. This is advantageous when simultaneously observing objects at different depth positions. Another characteristic is that a secondary electron detection signal can be obtained that does not impair information on the sample surface even when irradiating the sample at high acceleration, enabling observation that combines sample surface sensitivity with high resolution. In contrast, while SEMs typically reduce electron beam acceleration to obtain sample surface-sensitive images, generally, reducing acceleration has the disadvantage of decreasing resolution.

[0007] Patent Document 1 discloses a retarding field analyzer for a charged particle beam system. The retarding field analyzer uses existing components of the charged particle beam system and eliminates the need to insert a separate retarding field analyzer. By using existing column components, the time required to analyze the beam is reduced. In addition, by using the imaging capabilities of the existing column, beam and analyzer alignment is made easier. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2014-89953 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] As mentioned above, in order to obtain a practical level of ion beam brightness with GFIS, it is necessary to achieve a sharpness so that the tip of the emitter terminates with only a few atoms. Furthermore, this structure can be suddenly destroyed, in which case it is necessary to regenerate the sharpness with good reproducibility. Moreover, since it is basically impossible to observe the sample using the instrument during the formation process to obtain this atomic sharpness and the regeneration process, these processing times must be completed in a very short time.

[0010] On the other hand, narrowing the energy width of the ion beam is important for observing a sample with high resolution using an ion beam. Aberrations exist in the lens that focuses the ion beam, and it is known that this increases the diameter of the position where the ion beam is most narrowly focused (probe diameter). There are several types of aberrations, but among them, chromatic aberration is known to increase in proportion to the energy width of the ion beam. For this reason, a smaller energy width of the ion beam is desirable for observing a sample 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. Among these conditions, the electric field at the emitter tip is particularly important. However, knowing the electric field at the emitter tip is extremely difficult. This is because, even when the same voltage is applied to the emitter, the electric field at the emitter tip changes depending on the shape of the emitter, such as its sharpness, which is generally difficult to control. In GFIS, as explained earlier, a sharpness such that the emitter tip is terminated by only a few atoms is required, and since the electric field at the emitter tip can change with a difference of just a few atoms, this change can be particularly pronounced. For this reason, it is difficult to identify the conditions for improving the resolution in GFIS.

[0012] Here, the energy width of the ion beam can be measured. Therefore, by confirming the energy width of the ion beam before use, it becomes possible to operate the instrument under conditions that are advantageous for obtaining high-resolution microscope images. However, instruments for measuring the energy width of an ion beam are generally large and expensive, and there are cost challenges in introducing them as additional equipment.

[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 apparatus. In an ion beam focusing lens, a voltage is applied to an electrode having an aperture through which the ion beam passes in order to obtain a focusing effect, creating a spatial potential distribution at that aperture. This potential distribution can be repurposed for measuring the energy width of an ion beam. In other words, the focusing lens is used as a retarding-type energy analyzer that utilizes the phenomenon of shielding the ion beam with this spatial potential distribution. By measuring the amount of ion beam passing through while changing the voltage applied to the focusing lens, the energy distribution of the ion beam can be determined. With this method, it is possible to confirm conditions that are advantageous for obtaining high-resolution microscope images and operate the apparatus under those conditions without incurring additional costs or wasting space on existing equipment.

[0014] However, because the above 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 spatial extent is incident on this potential distribution, it may be stopped, pass through, or its 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 the energy analysis.

[0015] To improve this energy resolution, it is necessary to suppress the spatial spreading of the ion beam at the potential distribution incidence site. One method of suppression is to use an aperture with a narrow diameter that limits the spatial spreading of the beam. In this method, the beam is physically blocked before it enters the potential distribution, thereby limiting the spreading. This improves the energy resolution, but the current flowing through the ion beam being analyzed at the focusing lens decreases, thus reducing the analysis throughput.

[0016] Another suppression method involves injecting the ion beam so that it is focused at the center of the potential distribution. This focusing of the ion beam uses a preceding focusing lens positioned closer to the ion source than the focusing lens that generates the potential distribution for energy analysis. Ideally, this method can achieve both spatial spread limitation and the amount of current of the ion beam to be analyzed. However, it has been found that this method significantly impairs energy resolution due to the misalignment between the ion beam and the potential distribution.

[0017] Regarding the misalignment between the ion beam and the potential distribution, it is possible to mitigate this to some extent by detecting the misalignment of the ion beam when the voltage applied to the focusing lens is changed. However, in order to detect this misalignment, it is necessary to set the potential distribution generated by the focusing lens to a size that causes the beam to focus on the sample surface, which is located further downstream from the focusing lens. Since the size of the potential distribution required to focus the beam on the sample surface is significantly different from the size of the potential distribution used for actual energy analysis, it is difficult to precisely detect the misalignment of the ion beam.

[0018] In other words, this method presents conflicting challenges regarding energy resolution and analytical throughput. To overcome these challenges, it is necessary to accurately measure the positional shift between the ion beam and the potential distribution. [Means for solving the problem]

[0019] An ion beam device according to an embodiment of the present invention includes a gas field ionization ion source having an emitter and an extraction electrode facing the emitter, a first voltage power supply connected to the emitter for generating an electric field in the emitter, a second voltage power supply connected to the extraction electrode for generating an electric field in the extraction electrode, a first lens and a second lens capable of focusing the ion beam emitted from the gas field ionization ion source, and a deflector disposed between the first lens and the second lens for deflecting the ion beam, a beam irradiation column, a third voltage power supply connected to the second lens, and a sample chamber in which a sample stage for mounting a sample irradiated with the ion beam passing through the beam irradiation column is disposed. The second lens is disposed closer to the sample chamber side than 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.

Advantages of the Invention

[0020] According to the ion beam device of the present invention, it is possible to accurately align the ion beam with the saddle point of the potential distribution of the focusing lens. As a result, it is possible to quickly know the energy distribution of the ion beam incident on the focusing orbit in the potential distribution of the focusing lens with high energy resolution. Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a configuration example of an ion beam device. [Figure 2] It is a histogram showing the energy distribution of an ion beam. [Figure 3A] It is a diagram showing the result of calculating the potential distribution of an electrostatic focusing lens. [Figure 3B] It is a diagram showing the axial potential distribution of an electrostatic focusing lens. [Figure 3C] It is a diagram showing the radial potential distribution on a plane including the maximum value of the axial potential distribution of an electrostatic focusing lens. [Figure 3D] It is a detailed diagram showing the radial potential distribution on a plane including the maximum value of the axial potential distribution of an electrostatic focusing lens. [Figure 4] This figure shows the difference in the passing position of an ion beam incident on a potential distribution. [Figure 5] This figure shows the effect of the ion beam's trajectory on the potential distribution. [Figure 6] This figure shows the relationship between retarding voltage and the degree of ion beam inhibition. [Figure 7] This figure shows the relationship between the deflector output and the retarding voltage at which characteristic points appear. [Figure 8] This is an example of a deflector configuration. [Figure 9] This diagram illustrates the relationship between the focusing effect of a focusing lens and its energy range. [Figure 10] This diagram shows the relationship between the focusing effect of a focusing lens and its energy range. [Figure 11] This is an example of the energy distribution of an ion beam emitted from a hydrogen gas field ionization ion source. [Figure 12] This is an example of the energy distribution of a filtered ion beam. [Figure 13] This is an example of an ion beam system configuration that filters a hydrogen ion beam using an RFA (Radio Frequency Filter). [Figure 14] This is an example of a preparatory procedure before energy analysis. [Figure 15] This is an example of an ion beam positioning procedure. [Figure 16] This is an example of a procedure for adjusting the focusing action of a focusing lens. [Modes for carrying out the invention]

[0022] To facilitate understanding of the present invention, the challenges of current ion beam systems will be explained below. Next, the basic principles of the present invention will be outlined. Following that, the specific configuration of the ion beam system according to this embodiment will be explained using drawings.

[0023] Figure 1 is a diagram of the ion beam apparatus 1000 according to this embodiment. Here, we describe the configuration of an ion beam apparatus including a gas field ionization ion source, but a liquid metal ion source, plasma ion source, or MOTIS (Magnetic optical trap ion source) can also be used as the ion source. Alternatively, it can be configured as a charged particle beam apparatus including an electron source instead of an ion source. In the following explanation, when referring to the optical elements of the ion beam apparatus, 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 ionization ion source 1 comprises 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 at a position opposite to the emitter electrode 11. The emitter electrode 11 is cooled as needed by a refrigerator or a refrigerant 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, and the potential difference between the two forms an electric field near the tip of the emitter electrode 11 that positively ionsize the gas.

[0025] The high-voltage power supplies 111 and 112 can be controlled independently of each other, thereby allowing independent control of the ion beam acceleration voltage and the extraction voltage for ionization field formation. In order to freely change the ion beam acceleration voltage 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 poles, or a power supply with negative polarity relative to the potential supplied by the high-voltage power supply 111. This makes it possible to set the ion beam acceleration voltage below the extraction voltage required to extract ions.

[0026] To emit an ion beam 15 from the emitter electrode 11 of the gas field ionization ion source 1, a high voltage is first applied between the emitter electrode 11 and the extraction electrode 13. The application of the high voltage concentrates the 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 a 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 other 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 ionization ion source 1 is 10 when there is no gas introduction by the gas introduction mechanism. -7 It is preferable to maintain an ultra-high vacuum of Pa or less. To achieve an ultra-high vacuum in the vacuum chamber, a so-called baking process, in which the entire vacuum chamber is heated to 100 degrees Celsius or higher, may be included in the startup operation of the gas field ionization ion source 1.

[0028] 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 inside of the gas field ionization ion source 1, the emitter electrode 11, the extraction electrode 13, etc. The refrigerator can be a mechanical refrigerator such as a Gifford-McMahon type (GM type) or pulse tube type, or a refrigerant such as liquid helium, liquid nitrogen, or solid nitrogen can be used. Furthermore, 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 to be terminated by one, two, or three or more metal atoms that make up the emitter 11.

[0029] Since the ion beam 15 emitted from the emitter electrode 11 is highly directional, a separate drive mechanism may be provided for the emitter electrode 11 to allow adjustment of the position and angle of the emitter electrode 11 to favorable conditions for focusing the ion beam 15. The emitter electrode drive mechanism may be configured to be manually adjustable by the user or automatically adjusted by an emitter electrode drive mechanism controller.

[0030] The ion beam apparatus 1000 comprises a gas field ionization ion source 1, a beam irradiation column 7, and a sample chamber 3. When observing the sample surface, an ion beam 15 emitted from the gas field ionization ion source 1 passes through the beam irradiation column 7 and irradiates the 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 comprises a focusing lens 71, an aperture 72, a deflector 73, and an objective lens 76. The focusing lens 71, deflector 73, and objective lens 76 are supplied with voltage by the focusing lens power supply 113, the deflector power supply 731, and the 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, 8, or 16 electrodes, as needed. The number of electrodes in the deflector power supply needs to be increased according to the number of electrodes.

[0032] The focusing lens 71 shows 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. Electrodes 710 and 712 are typically positioned at ground potential, but a power supply may be provided to supply voltage as needed.

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

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

[0035] There are several types of aberrations that occur when focusing with a lens. Among them, 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 of each particle is expressed as a frequency using the number of particles that actually possess that energy, as shown in histogram 2 in Figure 2. 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-value position of the peak in the distribution, can be used. Alternatively, the width can be determined by fitting the energy distribution with a known function such as a Gaussian distribution.

[0036] The energy width of the ion beam 15 changes depending on the conditions under which the ion beam is extracted. Among these, the voltage difference between the emitter 11 and the extraction electrode 13 (extraction voltage) is a crucial factor that affects the energy width. In other words, setting the optimal extraction voltage value to minimize 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. Since 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. Also, if the atomic structure formed at the tip to improve the sharpness of the emitter 11 changes, it may change due to some work to repair it. Once the emitter 11 is introduced into the device, it is very difficult to confirm its shape, and similarly, it is difficult to confirm the strength of the electric field formed at its tip.

[0038] Therefore, measuring the energy width of the ion beam is a useful function for keeping the instrument in optimal condition at all times. The energy width and absolute energy of the ion beam can be measured using a retarding electric field analyzer (RFA). An RFA applies a voltage to an electrode so that the retarding electric field that stops the beam is gradually increased or decreased. This electrode is either a grid electrode or an electrode with an aperture, which is normally configured to allow the beam to pass through. The relationship between the applied voltage and the amount of beam that passes through allows for the analysis of the energy of the particles that make up the beam. Using an RFA usually requires the installation of additional equipment separate from the ion beam apparatus. It also requires an operating mechanism to insert or retract the electrode into or out of the beam path, as well as a power supply to apply voltage to the electrode. Therefore, there is a challenge in that costs are increased. Furthermore, the positional relationship between the beam and the above electrode is an important parameter that affects the energy resolution of the energy analysis, and it is necessary to adjust the position of the electrode or the beam to a high degree, which is a challenge in that it is time-consuming.

[0039] On the other hand, it is possible to avoid adding equipment by using a focusing lens within the ion beam apparatus as the retarding electrode for RFA. Even in this case, it is necessary to precisely adjust the beam position. For adjusting the ion beam position, a method typically used when observing a sample in an ion beam apparatus can be adapted. For example, the voltage applied to the focusing lens is fluctuated (wabura), and it is observed whether the position of the ion beam changes in accordance with the fluctuation. If the voltage applied to the focusing lens is adjusted in advance so that the ion beam is focused onto the surface of the sample placed in the apparatus, it is possible to determine whether or not there is a fluctuation in the position of the ion beam by detecting whether the microscope image of the sample vibrates in accordance with the above fluctuation. However, since 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 onto the sample surface with the focusing lens, precise position adjustment is difficult with this wabura method.

[0040] The ion beam apparatus of this embodiment enables a high degree of compatibility between a mode for focusing the ion beam on the sample surface for observation and a mode for performing energy analysis of the ion beam, using a focusing lens. Furthermore, it enables the above energy analysis to be performed rapidly and with high throughput.

[0041] In Figure 1, a potential distribution 764 is generated by applying a voltage to the electrode 761 of the objective lens 76 using the objective lens power supply 110. This potential distribution 764 allows for the selection of whether to focus the ion beam 15 on the surface of the sample 31, or to increase the potential distribution to the point of stopping the ion beam 15, and then gradually change the magnitude of the potential distribution to perform energy analysis.

[0042] The objective lens power supply 110 is floating at the output voltage of the high-voltage power supply 111 that supplies voltage to the emitter electrode 11. By setting the reference voltage of the objective lens power supply 110 to the output voltage of the high-voltage power supply 111, 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 almost the same as the voltage applied to the emitter electrode 11. In the power supply configuration of this embodiment, by connecting the high-voltage power supply 111 after the objective lens power supply 110 is floating and adding its output, the maximum output voltage required of the objective lens power supply 110 can be significantly reduced. Normally, with a constant voltage power supply, the smaller the maximum output voltage, the larger the minimum setting range of the output voltage tends to be. In the power supply configuration of this embodiment, the maximum output voltage of the objective lens power supply 110 can be reduced, and therefore the setting range of the output voltage can be reduced, making it possible to set the retarding voltage more precisely. The precise setting of the retarding voltage has the effect of enabling measurement of ion beams with a small energy width.

[0043] Furthermore, in a constant voltage power supply, the time variation of the voltage typically increases as the maximum output voltage increases, or as the actual output voltage increases. In RFA, the relative value of the potential on the particle emission side and the potential on the retarding side is important. Therefore, by using a high-voltage power supply 111 to suspend the objective lens power supply 110, most of the power supply fluctuations can be canceled out, reducing their impact. This stabilizes the magnitude of the potential distribution 764 with respect to the ion beam 15 for a long period of time, enabling adjustments to the alignment of the ion beam 15 and the focusing action of the focusing lens 71, as will be explained later.

[0044] However, there are cases where it is not desirable to fluctuate 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 and is not affected by the output voltage of the high-voltage power supply 111, may be provided separately, and the objective lens power supply 110 and the second objective lens power supply may be made switchable.

[0045] The potential distribution 764 generally has a saddle point near the center of the electrode. Figure 3A shows the result of determining the potential distribution at the aperture of the electrode corresponding to the central electrode of an objective lens with three electrodes, i.e., electrode 761 (see Figure 1), using the finite element method. Note that Figure 3A shows the potential distribution when a voltage of 20kV is applied to electrode 761, and electrodes corresponding to electrodes 760 and 762 are grounded. As shown in Figure 3A, if the direction of propagation of the ion beam, the so-called 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 direction direction r=0 is as shown in Figure 3B. Furthermore, Figure 3C shows the radial potential distribution at the Z value (Z=4.5mm) where the potential is maximum in the graph of Figure 3B. Furthermore, Figure 3D is a graph that displays only the area near 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 finite element method results, a saddle point exists near the center of the aperture in the potential distribution generated by the objective lens. In this embodiment, by aligning the ion beam to this saddle point, the energy resolution of energy analysis by retarding method can be improved. As mentioned above, in the Wobler method, the voltage applied to electrode 761 is the value required to take a trajectory that focuses directly above the sample 31, and is smaller than the voltage required to stop the beam, making precise position adjustment difficult.

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

[0048] When a parallel beam is incident on a potential distribution 764, the potential distribution width can be reduced and the degradation of energy resolution can be mitigated by limiting the diameter of the ion beam 15 using aperture 72. However, in this case, the current of the ion beam 15 is limited, which significantly reduces the analysis throughput. For example, ion beam 158 has the same axial misalignment (r = -15 μm) as ion beam 152, but by limiting its diameter to 5 μm, the potential distribution width that degrades energy resolution can be reduced from approximately 0.55 V (potential distribution width 154) to approximately 0.3 V. On the other hand, assuming that the current density of ion beam 158 is the same as that of ion beam 152, the current is 1 / 4. Therefore, it takes four times as long to obtain analysis results with the same signal-to-noise ratio as analysis results with ion beam 152.

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

[0050] As we have seen, the alignment of the ion beam 15, the conditions of its orbit, and especially the adjustment of the focusing action of the focusing lens 71 are important for improving the resolution of energy analysis. First, we will explain the procedure for aligning the ion beam 15, and then we will explain the adjustment of the focusing action of the focusing lens 71. Figure 14 shows the flow of these adjustments.

[0051] First, rough adjustments are made to each optical element (S01). This step may be omitted if the alignment has already been achieved to a certain extent. Typically, this involves the position and angle of the emitter 11 and the position of the aperture. The positional deviations of the emitter 11 and aperture can be roughly detected by the oscillation (wobbling) 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 in the sample 31 does not fluctuate with respect to fluctuations in the output voltage of the focusing lens power supply 113.

[0052] Alignment between the ion beam 15 and the potential distribution 764 is performed by actually stopping the ion beam 15 with the potential distribution 764 (S02, S03). To observe the degree to which the ion beam 15 is stopped, it is advisable to observe the ion beam 20 that has been recoiled by the potential distribution 764. The ion beam 20 may also be observed via a conversion plate 77 that converts ions into secondary electrons 22. The secondary electrons 22 are detected by the detector 201.

[0053] The method for observing the degree to which the ion beam 15 is stopped is not limited to observing the recoiled ion beam 20. For example, the amount of ion beam 15 that passes through the potential distribution 764 may be converted into secondary electrons by the sample 31 and detected by the secondary electron detector (secondary particle detector) 33. Alternatively, the current can be directly detected using a Faraday cup separately placed next to the sample. However, the conditions of the space in which the sample is placed may change depending on the user's usage, and the amount to be detected will change depending on the surface condition of the sample and the surrounding magnetic field. Also, when using a Faraday cup, time is required 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 stopping using the detector 201 can solve these problems.

[0054] When stopping the ion beam 15, 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 retarding voltage, and the degree of ion beam stopping 221, which is evaluated by the amount of current detected by the detector 201, changes as shown in Figure 6. At this time, the change in the degree of stopping 221 has several characteristic points with respect to a given retarding voltage. For example, the stopping start point 222, the inflection point 223, the stopping end point 224, etc.

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

[0056] On the other hand, the position through which the ion beam 15 should pass in order to improve the resolution of the energy analysis is the saddle point 225. At this position, as shown in Figure 3C, the potential is at its lowest, and therefore the retarding voltage required for the above-mentioned characteristic points to appear is at its highest. In other words, the position of the ion beam 15 where the retarding voltage for the above-mentioned characteristic points to appear is the position that provides the best energy resolution for the energy analysis.

[0057] Therefore, by changing the output of the deflector 73 with the deflector power supply 731 to change the position of the ion beam 15, and further illustrating the characteristic quantities for each output, i.e., for each position of the ion beam 15, such as the retarding voltage at which the inflection point 223 is observed, we get the result shown in Figure 7. For example, deflector output A has a larger retarding voltage at which the inflection point 223 appears than deflector output B. Therefore, the ion beam position given by deflector output A is closer to the saddle point 225. By obtaining the envelope 233 from similar data for several deflector outputs using fitting, etc., and finding the deflector output C that gives a maximum, it is possible to find the deflector output conditions at which the ion beam position is closest to the saddle point 225. Note that if a separate high-voltage power supply that is not floating around is connected to the electrode 761 of the objective lens 76, and a power supply configuration is adopted in which the voltage is applied independently of the high-voltage power supply 111, such evaluation would be difficult to perform due to the large influence of fluctuations in the high-voltage power supply.

[0058] Figure 15 shows the flow for controlling the deflector 73 to search for the saddle point 225. The deflector output is set (S11), the retarding voltage is varied to detect the retarding voltage that gives a characteristic point of the degree of ion beam retardation (e.g., inflection point 223) (S12, S13), and data points are recorded (S14). Alternatively, the retardation start point 222 or retardation end point 224 may be used as characteristic points. The data points recorded in steps S11 to S14 correspond to the circles shown in Figure 7. If a local maximum 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 the deflector output that gives the local maximum of the envelope 233 can be identified as the saddle point 225.

[0059] Figure 8 shows an example configuration of the deflector 73. Figure 8 shows a configuration including four electrodes arranged to surround the ion beam 15, but it is also possible to configure it to include four or more electrodes, for example, eight electrodes. The deflector 73 shown in Figure 8 can be considered as a combination of a first deflector (deflector A) and a second deflector (deflector B), and the direction in which deflector A deflects the ion beam 15 and the direction in which deflector B deflects the ion beam 15 are orthogonal. Furthermore, deflector A is equipped with electrodes 732a and 732b facing each other, with the first deflector power supply 7320 connected to electrode 732a and electrode 732b connected to ground potential. Alternatively, a power supply that outputs a voltage with the opposite polarity to the first deflector power supply 7320 may be connected to electrode 732b. Similarly, deflector B is equipped with electrodes 733a and 733b facing each other, with electrode 733a connected to a second deflector power supply 7330 and electrode 733b connected to ground potential. Alternatively, a power supply outputting a voltage with the opposite polarity to that of the second deflector power supply 7330 may be connected to electrode 733b.

[0060] If the deflector 73 has a four-pole configuration as shown in Figure 8, the ion beam position optimization process shown in Figure 15 is performed for each of the deflector A and deflector B. By finding the maximum of the envelope 233 for each of the deflector A and deflector B, it becomes possible to determine the optimal output of the deflector power supplies 7320 and 7330, and to determine 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 Figure 6) with respect to the retarding voltage yields histogram 2 as shown in Figure 2. The histogram 2 obtained here has a width that is added by the conditions downstream of the extraction electrode, separate from the true energy distribution of the ion beam 15. This width depends on the range of the ion beam and the potential width when the ion beam 15 is incident on the potential distribution 764, as shown in Figures 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] Figure 16 shows the adjustment flow of the focusing action of the focusing lens 71. As shown in Figure 9, when the energy width (width 21 (see Figure 2)) is evaluated at a certain voltage value of the focusing lens power supply 113, data points indicated by circles are obtained (S21~S23). The focusing action of the focusing lens 71 is operated incrementally or subtractively, and the width 21 for each focusing action is evaluated. Multiple data points are obtained, and by fitting these data points, an envelope 241 is obtained. The focusing action that gives the minimum point of the envelope 241 becomes the optimal adjustment value 242 of the desired focusing action (S24).

[0063] After adjusting the ion beam position with the deflector 73, the focusing action of the focusing lens 71 is adjusted so that the focus point of the ion beam 15 is located at the saddle point 225. However, as the focusing action of the focusing lens 71 is adjusted, the ion beam 15 may not pass through the saddle point 225. Therefore, as shown in Figure 14, steps S02 to S04 are repeated (S05) to reduce the positional shift before and after adjusting the focusing action of the focusing lens 71. After high-precision adjustment is completed, energy analysis is performed.

[0064] During the alignment adjustment of the ion beam 15 (S02-S03) and the adjustment of the focusing action of the focusing lens 71 (S04), it is preferable that the outputs of the high-voltage power supplies 111 and 112 remain constant. This is because keeping the emission conditions of the ion beam 15 constant makes the changes in the stopping start point 222, inflection point 223, stopping end point 224, and width 21 depend only on the conditions downstream of the extraction electrode 13, i.e., the conditions for energy analysis, which is advantageous for optimizing the conditions for energy analysis.

[0065] As explained above, the influence of the potential distribution width of the potential distribution 764 that restricts the ion beam can be reduced by adjusting the positioning of the ion beam 15 and the focusing lens action. Figure 10 shows experimental results that succinctly demonstrate this effect. Figure 10 shows the results of measuring the width 21 after adjusting the positioning of the ion beam 15 using the procedure described above and changing the focusing action of the focusing lens 71. The voltage conditions applied to the emitter tip 11 and the extraction electrode 13 are kept constant. Specifically, the ion beam 15 is accelerated at 20kV, and the ion beam 15 is restricted by apertures 72 with diameters of 30μm, 20μm, and 10μm, and the energy width of the ion beam is measured by the potential distribution generated in the objective lens 76.

[0066] Calculations show that parallel beam condition 250 corresponds to approximately 11.4 kV. Under this condition, the smallest width 21 occurs when the beam is restricted with the smallest diameter aperture (10 μm), and the largest width 21 occurs when the beam is restricted with the largest aperture (30 μm). This is consistent with the discussion above regarding the relationship between the ion beam width and the potential distribution width at the potential distribution location.

[0067] In contrast, for any aperture diameter, a minimum width of 21 exists near the lens condition (focusing lens condition 251) in which the beam focuses near the potential distribution generated in the objective lens. Furthermore, the minimum width of 21 near focusing lens condition 251 is almost identical to the evaluation result for the largest aperture diameter of 30 μm and the evaluation result for the smallest 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 has not changed, this result can be considered as a result reflecting the energy resolution of the energy analysis under each focusing lens condition. First, the energy resolution in a parallel beam is improved by reducing the aperture diameter. Furthermore, it is suggested that under the condition of alignment, the energy analysis under the focusing lens condition is optimal for any aperture diameter, and its energy resolution is independent of the aperture diameter. Under this focusing lens condition, the focusing 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, an increase in current of approximately 9 times can be expected by changing the aperture diameter from 10 μm to 30 μm. Increasing the current of the ion beam during energy analysis has the effect of improving the throughput of energy analysis. Furthermore, analyzing from the parallel beam condition to the focused beam condition also has the effect of improving the throughput of energy analysis by increasing the current.

[0070] Furthermore, by using an RFA composed of electrostatic lenses, not only can the energy analysis of the ion beam 15 be performed, but the electrostatic lens can also function as a filter to make the ion species mixed in the ion beam single. Among gas field ionization ion sources, in a hydrogen field ionization ion source that ionizes hydrogen gas, three types of ions H + , H2 + , H3 + are known to be emitted. Among these, H3 + is known to have a higher energy than the other two hydrogen ion species. For example, the energy distribution of an ion beam composed of H2 + and H3 + is, as shown in Fig. 11, a spectrum 80 composed of relatively low-energy H2 + and a relatively high-energy H3 +The resulting spectrum is as shown in 81. When the sample 31 is observed with such an ion beam, the ion beam may be separated into tiny fragments by the Earth's magnetic field, potentially causing the observed image to appear as multiple images.

[0071] Therefore, by configuring the ion beam apparatus 1001 as shown in Figure 13, a single ion species H3 + This makes it possible to irradiate the sample 31 with an ion beam composed of these components. In Figure 13, components common to the ion beam apparatus 1000 shown in Figure 1 are indicated with the same reference numerals, and explanations of redundant components are omitted.

[0072] The ion beam apparatus 1001 is equipped with a first objective lens 76 and a second objective lens 7600 downstream of it. The first objective lens 76 is provided with a filter power supply 1100, and its power supply configuration is the same as that of the objective lens power supply 110 shown in Figure 1. The difference from the objective lens power supply 110 is that the output voltage is at the position of the potential distribution 764 generated from the objective lens 76, and H2 in the ion beam 15. + The voltage is such that it only suppresses the ion beam. 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 intensity of the second objective lens 7600 is controlled by the objective lens power supply 7601.

[0073] The ion beam 1500 filtered by the first objective lens 76 has an energy distribution as shown in Figure 12. This results in a single ion species and a reduction in the overall energy width of the ion beam, improving the focusing performance of the ion beam. Furthermore, by adjusting the output voltage of the filter power supply 1100, H2 + It is also possible to allow only certain things to pass through.

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

[0075] 1: Gas field ionization 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: Rebounded ion beam, 21: Width, 22: Secondary electrons, 201: Detector, 221: Degree of ion beam arrest, 222: Start point of arrest, 223: Inflection point, 224: End point of arrest, 225: Saddle point, 233, 241: Envelope, 242: Optimal adjustment value, 250: Parallel beam condition, 251: Focused beam condition, 2510: Focus 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 apparatus.

Claims

1. A gas field ionization 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 at 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 ionization ion source, and a deflector positioned 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, It has a sample chamber in which a sample stage is arranged, which holds a sample that is irradiated with an ion beam that has passed through the beam irradiation column, The second lens is positioned closer to the sample chamber than the first lens. The third voltage power supply is connected to the first voltage power supply and is suspended at the output voltage of the first voltage power supply in an ion beam apparatus.

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

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

4. In claim 2, An ion beam apparatus that acquires the energy distribution of the ion beam with the deflector adjusted so that the ion beam is positioned at the saddle point of the potential distribution of the second lens.

5. In claim 4, An ion beam apparatus for acquiring the energy distribution of an ion beam, wherein the focusing action of the first lens is adjusted so that the focal point of the ion beam is located at the saddle point of the potential distribution of the second lens.

6. In claim 1, The beam irradiation column comprises a third lens positioned between the second lens and the sample chamber. The third lens is an ion beam apparatus that irradiates the sample with an ion beam of ion species that have passed through the second lens from among the ion species mixed in the ion beam.

7. In claim 1, The beam irradiation column is equipped with a fourth voltage power supply, An ion beam apparatus that allows switching between the third voltage power supply and the fourth voltage power supply for the connection to the second lens described above.

8. A charged particle beam adjustment method for adjusting a charged particle beam emitted from a charged particle source and traveling through a charged particle optical column, The charged particle optical column comprises a first electrostatic lens and a second electrostatic lens capable of focusing the charged particle beam, and a deflector positioned between the first electrostatic lens and the second electrostatic lens, capable of deflecting the charged particle beam. A first step involves changing the retarding voltage applied to the second electrostatic lens to detect a retarding voltage at which the change in the degree to which the charged particle beam is restrained by the potential distribution of the second electrostatic lens becomes a predetermined characteristic point. A charged particle beam adjustment method comprising: a second step of determining the amount of deflection of the charged particle beam by the deflector to position 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 where the change in the degree of restraint is a predetermined characteristic point, as shown by a plurality of data points obtained by performing the first step while changing the amount of deflection of the charged particle beam by the deflector.

9. In claim 8, A charged particle beam adjustment method further comprising a third step of changing the focusing effect 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 effect that minimizes the energy width.

10. In claim 9, A charged particle beam adjustment method 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. In claim 10, The charged particle source is a gas field ionization ion source, The gas field ionization ion source comprises an emitter and an extraction electrode facing the emitter. A first voltage power supply is connected to the emitter to generate an electric field in the emitter. A second voltage power supply is connected to the extraction electrode to generate an electric field in the extraction electrode. A third voltage power supply for applying the retarding voltage is connected to the second electrostatic lens. A charged particle beam adjustment method wherein the third voltage power supply is connected to the first voltage power supply and is suspended at the output voltage of the first voltage power supply.

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

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