charged particle beam equipment

Abstract

The present invention provides a charged particle beam device which makes it possible to precisely manage the temperature when a cold field emission electron source is heated. Provided is a charged particle beam device comprising: a cold field emission electron source which is provided with a tip having a sharpened end, a filament connected to the tip, and an auxiliary electrode covering the filament and having an opening through which the tip protrudes; an extraction electrode to which an extraction voltage for extracting electrons from the cold field emission electron source is applied; and an acceleration electrode to which an acceleration voltage for accelerating the electrons extracted from the cold field emission electron source is applied. The charged particle beam device is characterized in that, when the tip and the filament are heated, a voltage that is positive with respect to the tip is applied to the auxiliary electrode to cause thermoelectrons emitted from the tip and the filament to accumulate at the auxiliary electrode, and the current is measured.

Description

[Technical Field]

[0001] The present invention relates to a charged particle beam device. [Background technology]

[0002] Charged particle beam devices irradiate a sample with a charged particle beam, such as an electron beam, and generate an observation image of the sample by detecting secondary electrons, transmitted electrons, backscattered electrons, and X-rays emitted from the sample. Obtaining an observation image with high spatial resolution requires a high-brightness electron source, such as a cold field emission (CFE) electron source. A CFE electron source emits an electron beam by concentrating an electric field at the tip of a sharpened single crystal (tip). Because residual gas adheres to the tip, causing the emission current to become unstable, the tip is periodically cleaned by applying a heating pulse.

[0003] However, when a heating pulse is applied, thermionic emission may occur from the tip and other parts of the CFE electron source. Such thermionic emission may cause serious damage to various parts of the charged particle beam device. Patent Document 1 discloses that when an electric field and a heating pulse are applied to the CFE electron source for cleaning, undesired thermionic emission from the tip and other parts is suppressed by applying a negative voltage to a cup-shaped suppression electrode that covers the entire surface except for the tip tip. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-73521 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not give sufficient consideration to temperature control of the CFE electron source to which the heating pulse is applied. Although the temperature of the CFE electron source can be estimated from the amount of emitted thermoelectrons, if the thermoelectron emission from the tip and other parts is suppressed, it becomes difficult to accurately estimate the temperature and to precisely control the temperature.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a charged particle beam device that is capable of precisely controlling the temperature when a cold cathode field emission electron source is heated. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a charged particle beam device capable of precisely controlling the temperature when a cold cathode field emission electron source is heated, the charged particle beam device comprising: a cold cathode field emission electron source having a tip with a sharpened tip, a filament connected to the tip, and an auxiliary electrode covering the filament and having an opening through which the tip protrudes; an extraction electrode to which an extraction voltage is applied for extracting electrons from the cold cathode field emission electron source; and an acceleration electrode to which an acceleration voltage is applied for accelerating the electrons extracted from the cold cathode field emission electron source, wherein when the tip and the filament are heated, a positive voltage is applied to the auxiliary electrode with respect to the tip, so that thermoelectrons emitted from the tip and the filament are collected by the auxiliary electrode and a current is measured. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a charged particle beam device that can precisely control the temperature when a cold cathode field emission electron source is heated. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the overall configuration of a scanning electron microscope, which is an example of a charged particle beam device. [Figure 2] FIG. 1 is a schematic cross-sectional view showing an example of the cold cathode field emission electron source and its peripheral configuration according to a first embodiment. [Figure 3] FIG. 1 is a schematic cross-sectional view showing an example of the cold cathode field emission electron source and its peripheral configuration according to a second embodiment. [Figure 4A] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 4B] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 4C] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 4D] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 5A] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 5B] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 6] FIG. 10 is a schematic cross-sectional view showing an example of the cold cathode field emission electron source and its peripheral configuration according to a fifth embodiment. [Figure 7] 10 is a schematic cross-sectional view showing an example of a potential distribution in the vicinity of a chip according to a fifth embodiment. [Figure 8] FIG. 1 is a diagram showing an example of an optimum voltage range to be applied to the auxiliary electrode and the extraction electrode. [Figure 9] A diagram showing an example of the optimum voltage range applied to the auxiliary electrode and extraction electrode when the tip protrusion length T is changed. [Figure 10A] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 10B] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 10C] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. [Figure 10D] FIG. 10 is a diagram showing an example of changes in voltage applied to each electrode. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of a charged particle beam device according to the present invention will be described with reference to the accompanying drawings. The charged particle beam device is a device that irradiates a sample with a charged particle beam such as an electron beam, detects secondary electrons, transmitted electrons, reflected electrons, X-rays, and the like emitted from the sample, and generates an observation image of the sample. [Example]

[0011] The overall configuration of a scanning electron microscope, which is an example of a charged particle beam device, will be described using Figure 1. A scanning electron microscope is a device that irradiates a sample 602 with an electron beam 601 and detects secondary electrons and backscattered electrons emitted from the sample to generate an observation image of the sample 602, and is equipped with a cylindrical body 603 and a sample chamber 604. The interior of the cylindrical body 603 is divided from the top into a first vacuum chamber 605, a second vacuum chamber 606, and a third vacuum chamber 607. Each vacuum chamber has an opening in the center through which the electron beam 601 passes, and is differentially evacuated. Each vacuum chamber and the sample chamber 604 will be described below.

[0012] The first vacuum chamber 605 is evacuated by an ion pump 608 and a non-evaporable getter pump 609, and the pressure is kept at 10 -8 Ultra-high vacuum in the Pa range, preferably 10 -9 The first vacuum chamber 605 is evacuated to an extremely high vacuum of 100 Pa or less. Inside the first vacuum chamber 605, a CFE electron source 201, an extraction electrode 106, and an acceleration electrode 109 are arranged. The CFE electron source 201 is an electron source that emits electrons by utilizing electric field concentration, and is held by an insulator 610 and electrically insulated from the cylindrical body 603. The extraction electrode 106 is an electrode to which an extraction voltage is applied to extract electrons from the CFE electron source 201. The extraction electrode 106 has a cup-like shape that encloses the CFE electron source 201, and an opening through which the electron beam 601 passes is provided on the central axis. The acceleration electrode 109 is an electrode to which an acceleration voltage is applied, and an opening through which the electron beam 601 passes is provided on the central axis. Application of the acceleration voltage to the acceleration electrode 109 forms an electric field in the acceleration space 112 to accelerate the electron beam 601. The CFE electron source 201 and its surrounding configuration will be described later with reference to FIG. 2.

[0013] The second vacuum chamber 606 is evacuated by an ion pump 611. A condenser lens 612 is disposed in the second vacuum chamber 606. The condenser lens 612 focuses the electron beam 601.

[0014] A detector 616 is disposed in the third vacuum chamber 607. The detector 616 detects secondary electrons and backscattered electrons emitted from the sample 602. A plurality of detectors 616 may be provided, and may be disposed in the sample chamber 604, the first vacuum chamber 605, or the second vacuum chamber 606.

[0015] The sample chamber 604 is evacuated by a turbo molecular pump 613. In the sample chamber 604, an objective lens 614 and a sample 602 are placed.

[0016] The CFE electron source 201, extraction electrode 106, acceleration electrode 109, condenser lens 612, objective lens 614, detector 616, ion pump 608, turbo molecular pump 613, and the like provided in the cylindrical body 603 and sample chamber 604 are connected to a control unit 617. The control unit 617 is a device that controls the operation of each unit and generates an observation image of the sample 602 based on a signal detected by the detector 616, and is, for example, a computer, an electronic board, or an electric circuit. Note that controlling the operation of each unit includes adjusting the voltage and current applied to each unit, receiving values ​​of voltage and current measured in each unit, and the like.

[0017] A display unit 618 and an input unit 619 are connected to the control unit 617. The display unit 618 is a device that displays an observation image, and is, for example, a liquid crystal display or a touch panel. The display unit 618 may also display feature quantities calculated from the observation image, values ​​of voltages and currents applied to each unit, values ​​of voltages and currents measured at each unit, etc. The input unit 619 is a device used to input observation conditions and operating conditions, and is, for example, a keyboard, a mouse, or a touch panel.

[0018] The voltage and current applied to each component, or the operating status of the device, etc. are recorded in the control unit 617 and can be displayed at any time on the display unit 618 or on the display unit of an information terminal such as a computer in a remote location, so that users and maintenance personnel can refer to them.

[0019] In one example, values ​​such as the extraction voltage V1, acceleration voltage V0, auxiliary voltage Vs, and emission current of the CFE electron source 201 in a steady-state image observation state are displayed on the display unit 618. When the emission current of the CFE electron source 201 decreases to a preset value or when a certain amount of time has passed since flushing, the display unit 618 displays a message indicating that flushing is necessary. A user or maintenance technician can manually perform flushing by viewing this message. Flushing may be performed automatically or at other times, such as during a change in acceleration voltage, a movement of the observation location on the sample, a change in the observation sample, an adjustment of the focal position, an adjustment of the current of various voltages, or a change in the emission current of the electron source.

[0020] The display unit 618 may display the voltage and current applied to each component during flushing. For example, the acceleration voltage V0, extraction voltage V1, and auxiliary voltage Vs during flushing may be displayed. Also, the current measured at the auxiliary electrode 202 or extraction electrode 106 shown in FIG. 2, the temperature calculated from the measured current, the current supplied from the flushing power supply 113 shown in FIG. 2 to the filament 102, and the time for which current is supplied to the filament 102 may be displayed. From these results, it may be determined whether the device is flushing with V0 applied. Furthermore, a user or maintenance technician may refer to the flushing conditions and adjust the conditions via the input unit 619 to optimize subsequent flushings.

[0021] Alternatively, the information during flushing may be recorded in the power supply or control unit 617, etc., rather than displayed on the display unit 618, and may be referenced by the user or maintenance personnel at any time. When multiple scanning electron microscopes are operated in parallel in a factory or the like, the flushing conditions and operating status records of the multiple devices can be referenced, optimal conditions determined as appropriate, and fed back to all the devices, optimizing the operating conditions of the multiple devices. As a result, the reproducibility of the observation images of the entire device can be improved, and downtime can be reduced.

[0022] An example of the configuration of a CFE electron source 201 and its surroundings will be described with reference to Fig. 2. The CFE electron source 201 has a tip 101, a filament 102, a pin 103, an insulator 104, and an auxiliary electrode 202. The tip 101 is made of metal with a sharpened tip, for example. <310> Direction and <111> The tip 101 is a tungsten single crystal with a directional orientation, and the radius of curvature of its tip is approximately 100 nm. The tip 101 is welded to the tip of the filament 102. The filament 102 is a tungsten polycrystalline wire shaped like a V-shaped hairpin. Pins 103 are welded to both ends of the filament 102. The two pins 103 are metal terminals, and are electrically insulated from each other by being held by insulators 104. The tip 101, filament 102, and pins 103 are at the same electrical potential.

[0023] An extraction power supply 108 is connected between the pin 103 and the extraction electrode 106. The extraction power supply 108 applies an extraction voltage V1, which is a positive voltage with respect to the tip 101, to the extraction electrode 106. The extraction voltage V1 is, for example, about 2 kV to 4 kV. The application of the extraction voltage V1 concentrates an electric field at the tip of the tip 101, and the intensity of the electric field becomes 3×10 9 When the potential is equal to or greater than V / m, tunneling electrons are field-emitted from the tip of the tip 101. The tunneling electrons pass through an aperture in an aperture 107 that is disposed on the central axis of the extraction electrode 106 and has the same potential as the extraction electrode 106.

[0024] An acceleration power supply 111 is connected between the acceleration electrode 109 and the tip 101. The acceleration power supply 111 applies an acceleration voltage V0, which is a positive voltage with respect to the tip 101, to the acceleration electrode 109. The acceleration voltage V0 is, for example, approximately 5 kV to 300 kV. In other words, if the acceleration electrode 109 is at ground potential, a voltage of approximately −5 kV to −300 kV is applied to the tip 101. By applying the extraction voltage V1 and the acceleration voltage V0, an electric field due to a voltage difference of V0-V1 is formed in the acceleration space 112 between the extraction electrode 109 and the acceleration electrode 109, and the electron beam passing through the acceleration space 112 is accelerated to the acceleration voltage V0. The electric field formed in the acceleration space 112 also functions as an electrostatic lens, focusing the electron beam. The electron beam accelerated in the acceleration space 112 passes through an aperture in the aperture 110, which is located on the central axis of the acceleration electrode 109 and has the same potential as the acceleration electrode 109, and is irradiated onto the sample 602.

[0025] The emission current from the tip of the tip 101 decreases due to the adhesion of hydrogen and organic gases as residual gases to the electron emission surface at the tip of the tip 101. Therefore, a pulse current is supplied from a flushing power supply 113 connected between the pins 103 to heat the filament 102 and the tip 101, and a cleaning process called flashing is periodically performed. In other words, the residual gas at the tip of the tip 101 is desorbed by flashing, and the reduced emission current is returned to its initial value. The timing of flashing may be determined based on an operator's instruction or may be automatically determined based on the decrease in the emission current from the tip of the tip 101. The pulse current is supplied for a few seconds or less, preferably one second or less.

[0026] Organic gases such as CO and CO2, which adhere firmly to the tip 101, begin to desorb when heated to 1600°C or higher and are completely desorbed when heated to 1900°C or higher. Hydrogen, the main component of residual gas, desorbs when heated to 1500°C or higher. Insufficient purification results in unreproducible electron beam currents and unreproducible observed images. Meanwhile, blunting of the tip 101 tip (increase in curvature radius) begins when heated to 2200°C or higher and progresses rapidly when heated to 2400°C or higher. As the tip 101 becomes blunt, the electric field strength at the tip 101 decreases, reducing the number of tunnel electrons emitted. Therefore, a higher extraction voltage is required to obtain a given current. When the tip 101 becomes blunt and the voltage required for field emission exceeds the specifications of the extraction power supply, the electron source reaches the end of its life and must be replaced. Based on these factors, the flashing temperature is preferably between 1600°C and 2400°C, and more preferably between 1900°C and 2200°C. In other words, it is important to precisely control the temperature when the tip 101 and filament 102 are heated by flashing, thereby achieving both tip cleanliness and a long life. The temperature during flashing is optimized by feeding back the temperature measurement results to the flashing conditions.

[0027] Heating above 1600°C causes the filament 102 and tip 101 to emit thermoelectrons 205, 206, and 207. These thermoelectrons increase exponentially with the temperature during flashing, and may cause damage to various parts. Therefore, an auxiliary electrode 202 is provided as an electrode that covers the filament 102.

[0028] Auxiliary electrode 202 is held by insulator 104 and is electrically insulated from pin 103. Auxiliary electrode 202 is cup-shaped and has opening 203 through which the tip of tip 101 protrudes. The size of opening 203 is made as small as possible to prevent thermions from leaking out of auxiliary electrode 202, and is set to, for example, a diameter of 1 mm or less, more preferably 0.6 mm or less.

[0029] The distance L between the auxiliary electrode 202 and the extraction electrode 106 is typically about 400 μm to 800 μm, and more preferably about 500 μm to 600 μm. The protrusion length T, which is the length by which the tip of the tip 101 protrudes from the opening 203 of the auxiliary electrode 202, is typically about 50 μm to 750 μm, and more preferably about 50 μm to 350 μm. The diameter of the opening of the aperture 107 of the extraction electrode 106 is typically 1 mm or less, and more preferably 0.5 mm or less, in order to reduce thermions that enter the acceleration space 112.

[0030] An auxiliary power supply 204 and an ammeter 116 are connected between the auxiliary electrode 202 and the pin 103. The auxiliary power supply 204 applies an auxiliary voltage Vs, which is a voltage to the chip 101. The auxiliary voltage Vs is set to a positive, negative, or zero voltage depending on the situation. For example, during flashing, a positive voltage is set as the auxiliary voltage Vs, and is typically set to 0.1 kV to 1 kV, more preferably 0.1 kV to 0.6 kV.

[0031] By setting the auxiliary voltage Vs to a positive voltage, the thermoelectrons 205 emitted from the base side of the filament 102 among the thermoelectrons 205, 206, and 207 are incident on the auxiliary electrode 202 and measured by the ammeter 116. The measurement value by the ammeter 116 is sent to the control unit 617 and converted into temperature using, for example, the Richardson-Dushman equation. Note that the measurement value by the ammeter 116 may also be converted into temperature using a table created by measuring in advance the relationship between the heating temperatures of the tip 101 and filament 102 and the amount of thermoelectrons. In other words, most of the thermoelectrons emitted from the filament 102 are measured by the ammeter 116 to calculate the temperature, allowing precise control of the temperature when the CFE electron source is heated.

[0032] Note that the auxiliary voltage Vs is preferably greater than the extraction voltage V1. By setting the extraction voltage V1<auxiliary voltage Vs, the thermoelectrons are subjected to a repulsive force from the extraction electrode 106 due to the potential gradient between the auxiliary electrode 202 and the extraction electrode 106. As a result, the number of thermoelectrons 206 returning to the auxiliary electrode 202 increases among the thermoelectrons 206 and 207 passing through the opening 203 of the auxiliary electrode 202. In other words, since a larger number of thermoelectrons emitted from the tip 101 and the filament 102 are measured by the ammeter 116, the heating temperatures of the tip 101 and the filament 102 can be determined more accurately. Furthermore, by setting the extraction voltage V1<auxiliary voltage Vs, the trajectory of the thermoelectrons is bent by the repulsive force, and the number of thermoelectrons 207 passing through the opening of the aperture 107 decreases. As a result, the number of thermoelectrons 207 entering the acceleration space 112 can be reduced. The effect of reducing the number of thermoelectrons 207 entering the acceleration space 112 will be described later in Example 3. In addition, the electric field at the tip of the tip 101 formed by the auxiliary voltage Vs and the extraction voltage V1 during flashing is sufficiently low, 3×10 9 Therefore, problems such as build-up (described later) and mixing of thermal electrons with tunnel electrons do not occur.

[0033] As described above, in Example 1, by applying a positive voltage relative to the tip 101 to the auxiliary electrode 202, which covers the filament 102 and has an opening 203 through which the tip 101 protrudes, the thermoelectrons emitted during flashing are collected by the auxiliary electrode 202. The temperatures of the tip 101 and the filament 102 are calculated based on the current measured by the auxiliary electrode 202, allowing for precise temperature control during flashing. Furthermore, precise temperature control during flashing allows for appropriate desorption of residual gas without blunting the tip of the tip 101. As a result, highly reproducible observation images can be obtained while maintaining a predetermined electron beam current, and the life of the CFE electron source can be extended.

[0034] The flashing temperature can also be managed by connecting the ammeter 116 to the extraction power supply 108 instead of the auxiliary power supply 204. In this case, most of the thermoelectrons collide with the auxiliary electrode, so the amount of current measured by the extraction electrode is small. On the other hand, in a typical CFE electron source without an auxiliary electrode, the extraction power supply 108 may have two power supply capacities and switch to a circuit with a higher capacity during flashing to measure the thermoelectrons. However, the extraction power supply 108 has two power supply capacities, which increases costs. By using the CFE electron source with the auxiliary electrode of Example 1, there is no need to provide two power supply capacities in the extraction power supply, thereby reducing costs.

[0035] In addition, since the auxiliary electrode 202 is located behind the tip of the chip and is not irradiated with tunneling electrons, the power capacity of the auxiliary power supply 204 can be determined based on the current amount of thermoelectrons emitted during flashing. Therefore, there is no need to provide the auxiliary power supply 204 with two power capacity systems, as was done with conventional extraction power supplies, thereby reducing costs. Also, the flashing temperature can be managed by connecting an ammeter 116 to the flashing power supply 113 and measuring the total current amount of thermoelectrons. [Example]

[0036] In the first embodiment, the auxiliary voltage Vs and the extraction voltage V1 during flushing are set to positive voltages. In the second embodiment, the auxiliary voltage Vs during flushing is set to a positive voltage, and the extraction voltage V1 is set to zero or a negative voltage. Since some of the configurations and functions described in the first embodiment can be applied to the second embodiment, the same configurations and functions are designated by the same reference numerals and descriptions thereof will be omitted.

[0037] An example of the configuration of the CFE electron source 201 and its periphery will be described with reference to Fig. 3. The configuration of the CFE electron source 201 and its periphery is the same as that of Example 1. However, the extraction voltage V1 applied to the extraction electrode 106 by the extraction power supply 108 is zero or a negative voltage.

[0038] Because the extraction voltage V1 is zero or a negative voltage, the potential gradient between the auxiliary electrode 202 and the extraction electrode 106 is larger than in the first embodiment, and the repulsive force is stronger. As a result, the number of thermoelectrons 206 that pass through the aperture 203 and return to the auxiliary electrode 202 increases. Furthermore, the thermoelectrons 207 (denoted as thermoelectrons 208 in FIG. 3 ) that passed through the aperture of the diaphragm 107 in the first embodiment cannot overcome the potential gradient and cannot pass through the aperture, and instead return to the auxiliary electrode 202. In other words, since all of the thermoelectrons emitted from the tip 101 and the filament 102 are measured by the ammeter 116, the heating temperatures of the tip 101 and the filament 102 can be determined more accurately. As a result, the second embodiment also achieves improved reproducibility of the observed image and a longer lifespan of the electron source.

[0039] Furthermore, since the thermoelectrons 207 that had passed through the opening of the aperture 107 disappear, the thermoelectrons become zero and do not invade the acceleration space 112. The effect of the disappearance of the thermoelectrons 207 invading the acceleration space 112 will be described later in Example 4.

[0040] As described above, in the second embodiment, a positive voltage relative to the tip 101 is applied to the auxiliary electrode 202, and a zero or negative voltage is applied to the extraction electrode 106, so that the auxiliary electrode 202 collects more thermoelectrons emitted during flashing. The temperatures of the tip 101 and the filament 102 are calculated based on the current measured by the auxiliary electrode 202, allowing for more precise temperature control during flashing. Furthermore, residual gas can be appropriately desorbed without blunting the tip of the tip 101, thereby improving the reproducibility of observed images and extending the life of the CFE electron source. [Example]

[0041] In the first and second embodiments, a positive voltage is applied to the auxiliary electrode 202 during flashing, and thermoelectrons are collected and measured by the auxiliary electrode 202. In the third embodiment, precise temperature control is performed by collecting thermoelectrons by setting the auxiliary voltage Vs and the extraction voltage V1 to positive voltages during flashing, and further, downtime of the device is reduced by keeping the acceleration voltage V0 applied during flashing. Note that some of the configurations and functions described in the first and second embodiments can be applied to the third embodiment, and therefore, the same configurations and functions are designated by the same reference numerals and descriptions thereof are omitted.

[0042] During steady-state imaging, the CFE electron source emits tunneling electrons at currents ranging from several μA to several hundred μA from the electron-emitting surface at the tip. During flashing, on the other hand, it temporarily emits thermoelectrons at currents ranging from several mA to several hundred mA from the tip and filament. In other words, the thermoelectron current is approximately 1,000 times greater than the tunneling electron current. Because the power capacity of the accelerating power supply 111 is based on the steady-state tunneling electron current, flashing while the accelerating voltage is applied causes excessive current to flow through the accelerating power supply, resulting in a power supply capacity shortage. This can result in a sudden change in the accelerating voltage, causing discharge and potentially power supply failure. Furthermore, when a large number of thermoelectrons accelerated to high energy collide with the accelerating electrode, electron-stimulated desorption gases and ions are generated. These can deteriorate the vacuum in the electron gun and, if they collide with the electron source, can damage it. To avoid these device failures, charged particle beam instruments equipped with a typical CFE electron source without an auxiliary electrode temporarily stop imaging and stop applying the accelerating voltage before flashing.

[0043] For example, when flashing is performed using a charged particle beam device with an acceleration voltage of 100 kV and a step-down and step-up rate of 2 kV / s, the acceleration voltage is first stepped down from 100 kV to 0 V over 50 seconds, and then the application of the acceleration voltage is stopped. Next, flashing is performed within a few seconds, more preferably within 1 second. Then, the acceleration voltage is increased again from 0 V to 100 kV over 50 seconds. Adding all of these steps together, image observation must be stopped for at least 100 seconds to perform flashing. This time during which image observation is stopped is called downtime. The higher the acceleration voltage, the longer the time required for stepping down and stepping up, resulting in longer downtime. Downtime can be reduced by increasing the step-down and step-up rates, but these rates can cause abrupt changes in the electric field, potentially resulting in discharge. For this reason, there is a limit to the speed at which the voltage can be stepped down and increased. The step-down and step-up rates are typically 3 kV / s or less, more preferably 2 kV / s or less.

[0044] In the manufacturing process of semiconductor devices, scanning electron microscopes and other instruments are required to observe more devices in a shorter time, thereby reducing manufacturing costs and time. Therefore, the need for long downtime each time flushing is required increases the manufacturing cost and time of semiconductor devices. In addition, in the manufacturing process of semiconductor devices, it is sometimes important to measure the dimensions of the devices with high reproducibility, and the reproducibility of the observed images is therefore important.

[0045] The CFE electron source 201 described in the first embodiment precisely controls the temperature by collecting thermoelectrons during flashing with an auxiliary electrode. At this time, most of the thermoelectrons collide with the auxiliary electrode 202, so the current amount of the thermoelectrons 207 entering the acceleration space 112 is about 1 / 100 of that of a general CFE electron source without the auxiliary electrode 202. This current amount is about 10 times that of tunneling electrons in a steady state. Therefore, by increasing the power capacity of the acceleration power supply 111 by 10 times compared to the conventional case, the acceleration power supply will not break down even if flashing is performed while an acceleration voltage is applied.

[0046] Furthermore, as explained in the first embodiment, by setting the extraction voltage V1<auxiliary voltage Vs, the current of the thermoelectrons 207 entering the acceleration space 112 is further reduced to the same level as the current of tunneling electrons in steady state. As a result, even if the power capacity of the acceleration power supply 111 remains the same as before, the acceleration power supply will not malfunction due to insufficient power capacity even when flashing is performed while the acceleration voltage is applied. Furthermore, since there is no need to increase the power capacity, the power supply cost can be reduced. In addition, the amount of electron-stimulated desorption gas and ions generated is reduced to the same level as in steady state, suppressing deterioration of the vacuum in the electron gun and reducing the possibility of damage to the electron source. For the above reasons, flashing is possible even while the V0 voltage is applied, and downtime can be reduced by eliminating the time required to increase and decrease the acceleration voltage V0.

[0047] An example of the change over time in the voltage applied to each electrode will be described using Figures 4A to 4D. An example of the change in voltage during flashing of a conventional CFE electron source without an auxiliary electrode will be described using Figure 4A. Here, the acceleration voltage V0 during tunneling electron emission (when observing an image) was 100 kV, the extraction voltage V1 was 2 kV, the voltage drop and increase rates were 2 kV / sec, the extraction voltage V1 during flashing was 0.2 kV, and the flashing time was 1 sec.

[0048] When flashing is performed with a conventional CFE electron source without an auxiliary electrode, the extraction voltage V1 is first reduced from 2 kV to 0.2 kV, and field emission and image observation are stopped. This process takes 0.9 seconds. Next, the acceleration voltage V0 is reduced from 100 kV to 0 kV, and application of the acceleration voltage V0 is stopped. This process takes 50 seconds. Next, flashing is performed. This process takes 1 second. Next, the acceleration voltage V0 is increased from 0 kV to 100 kV, and application of V0 is resumed. This process takes 50 seconds. Finally, the extraction voltage V1 is increased from 0.2 kV to 2 kV, and field emission and image observation are resumed. This process takes 0.9 seconds. The total time required for these steps is 102.8 seconds, which is the downtime required for each flashing.

[0049] Figure 4B shows an example of a CFE electron source equipped with an auxiliary electrode. The auxiliary voltage Vs is constant at 0.3 kV, the extraction voltage V1 is reduced from 2 kV during image observation to 0.2 kV during flashing, and then increased back to 2 kV. The acceleration voltage V0 is constant at 100 kV. The extraction voltage V1 is reduced from 2 kV to 0.2 kV in 0.9 s, maintained at 0.2 kV during flashing in 1 s, and increased from 0.2 kV to 2 kV in 0.9 s. The time when no image observation is performed is limited to 2.8 s. This configuration eliminates the time required to reduce and increase V0 by maintaining constant the acceleration voltage V0 during field emission (image observation) and flashing, significantly reducing downtime compared to conventional methods. Furthermore, with this configuration, the auxiliary voltage Vs during field emission (image observation) and flashing are constant, which has the advantage of eliminating the time required to step down and step up the auxiliary voltage Vs. Furthermore, during flashing, the auxiliary voltage Vs is 0.3 kV, the extraction voltage V1 is 0.2 kV, and the extraction voltage V1 is less than the auxiliary voltage Vs, so the heating temperatures of the tip 101 and filament 102 can be determined more accurately.

[0050] Figure 4C shows an example in which the auxiliary voltage Vs is -0.3 kV during imaging and 0.3 kV during flashing, the extraction voltage V1 is 2 kV during imaging and 0.2 kV during flashing, and the acceleration voltage V0 is constant at 100 kV. The time for increasing or decreasing the auxiliary voltage Vs and extraction voltage V1 is 0.9 s, the flashing time is 1 s, and the time without imaging is limited to 2.8 s. Even with this configuration, downtime can be significantly reduced compared to conventional configurations by flashing while applying the acceleration voltage V0. Furthermore, the auxiliary power supply 204 in this configuration is capable of outputting both positive and negative voltages. Having the auxiliary power supply 204 with both positive and negative polarities offers the advantage of precisely controlling the temperature during flashing, regardless of whether Vs is positive or negative during steady-state imaging. When Vs is negative during electron emission, a higher extraction voltage is required to emit the same amount of current compared to when Vs is positive. A high extraction voltage reduces the influence of electron-electron interactions, which has the advantage of producing a brighter electron beam. Furthermore, since the extraction voltage V1 is lower than the auxiliary voltage Vs during flashing, the heating temperatures of the tip 101 and filament 102 can be determined more accurately.

[0051] Figure 4D shows an example in which the auxiliary voltage Vs is constant at 0.3 kV, the extraction voltage V1 is 2 kV during image observation and 0.2 kV during flashing, and the acceleration voltage V0 is reduced from 100 kV during first image observation to 50 kV during second image observation. The extraction voltage V1 is increased or decreased over a 0.9-second period, the flashing period is 1 second, and the time without image observation is limited to 2.8 seconds. Furthermore, because the extraction voltage V1 is less than the auxiliary voltage Vs during flashing, the heating temperatures of the tip 101 and filament 102 can be determined more accurately. Furthermore, flashing is performed during the period when the acceleration voltage V0 is changed, thereby avoiding unnecessary downtime. It should be noted that flashing can also be performed during periods when the observation location is moved, the sample 602 is replaced, the focal position is adjusted, or the voltages and currents applied to various components are adjusted. This eliminates additional downtime due to the flashing process. Since flushing downtime is effectively zero, downtime for the entire equipment operation is reduced.

[0052] As shown in Figure 4A, in a conventional CFE electron source without an auxiliary electrode, flashing was performed by stopping the application of V0 (unit: kV). Since the voltage step-down and step-up speeds are typically 3 kV / s or less to avoid discharge, flashing required V0 / 3 seconds to step down and V0 / 3 seconds to step up, resulting in a downtime of at least V0 × 2 / 3 seconds. Furthermore, since the voltage step-down and step-up speeds are more preferably 2 kV / s or less, it required V0 / 2 seconds to step down and V0 / 2 seconds to step up, resulting in a downtime of at least V0 seconds.

[0053] On the other hand, in the scanning electron microscope of Example 3, flashing is performed while V is applied, eliminating the need for time to decrease and increase V. As a result, the downtime required for flashing can be typically V × 2 / 3 seconds or less, and more preferably V seconds or less.

[0054] As described above, in Example 3, applying a positive voltage to the auxiliary electrode 202 and the extraction electrode 106 relative to the tip 101 reduces the risk of device shutdown due to insufficient capacity of the acceleration power supply 111, deterioration of the electron gun pressure, or discharge, and allows flashing while the acceleration voltage V0 is applied. As a result, the downtime required for flashing can be significantly reduced compared to conventional methods. Furthermore, since more thermoelectrons emitted during flashing are collected by the auxiliary electrode 202 and the temperatures of the tip 101 and filament 102 are calculated based on the current measured by the auxiliary electrode 202, the temperature during flashing can be more precisely controlled. Furthermore, residual gas can be appropriately desorbed without blunting the tip 101, improving the reproducibility of observed images and extending the life of the CFE electron source. [Example]

[0055] In the third embodiment, it was described that the auxiliary voltage Vs and the extraction voltage V1 during flushing are set to positive voltages, thereby collecting thermoelectrons during flushing and further reducing downtime of the device. In the fourth embodiment, it is described that the auxiliary voltage Vs during flushing is set to a positive voltage and the extraction voltage V1 is set to zero or a negative voltage, thereby achieving both precise temperature control and reduced downtime. Note that some of the configurations and functions described in the first to third embodiments can be applied to the fourth embodiment, and therefore the same reference numerals are used for the same configurations and functions, and their description will be omitted.

[0056] As explained in the second embodiment, by setting the auxiliary voltage Vs during flashing to a positive voltage and the extraction voltage V1 to zero or a negative voltage, the number of thermoelectrons penetrating into the acceleration space 112 becomes zero. As a result, even if flashing is performed while the acceleration voltage V0 is applied, problems such as breakdowns due to insufficient capacity of the acceleration power supply 111, deterioration of pressure in the electron gun, and damage to the electron source do not occur, and downtime can be reduced.

[0057] An example of the change in voltage applied to each electrode will be described using Figures 5A and 5B. Figure 5A shows an example in which the auxiliary voltage Vs is constant at 0.3 kV, the extraction voltage V1 is reduced from 2 kV during image observation to 0 kV during flashing, and then increased back to 2 kV, and the acceleration voltage V0 is constant at 100 kV. The extraction voltage V1 is increased or decreased over a period of 1 s, the flashing period is 1 s, and the time during which no image observation is performed is limited to 3 s, significantly reducing downtime compared to conventional methods. Furthermore, during flashing, the auxiliary voltage Vs is 0.3 kV and the extraction voltage V1 is 0 kV. This increases the potential gradient between the auxiliary electrode 202 and the extraction electrode 106 compared to Figures 4B to 4D, allowing all thermoelectrons to be measured, resulting in more accurate determination of the heating temperature.

[0058] FIG. 5B shows an example in which the auxiliary voltage Vs is constant at 0.3 kV, the extraction voltage V1 is stepped down from 2 kV during image observation to -0.1 kV during flashing, and then stepped up again to 2 kV, and the acceleration voltage V0 is constant at 100 kV. The extraction voltage V1 is stepped up and down for 1.05 s, the flashing time is 1 s, and the time when no image observation is performed is limited to 3.1 s, significantly reducing downtime compared to conventional systems. In this configuration, the extraction power supply 108 is capable of outputting both positive and negative polarities. Furthermore, during flashing, the auxiliary voltage Vs is 0.3 kV and the extraction voltage V1 is -0.1 kV, so all thermoelectrons are measured, allowing for more accurate determination of the heating temperature.

[0059] Even in Example 4, the auxiliary voltage Vs during tunneling electron emission (during image observation) can be made negative, as explained in Fig. 4C. Furthermore, as explained in Fig. 4D, flashing may be performed not only when the acceleration voltage V0 is changed, but also during periods when the observation location is moved, the sample 602 is replaced, the focal position is adjusted, or the voltage or current applied to each part is adjusted.

[0060] As described above, in Example 4, by applying a positive voltage to the auxiliary electrode 202 relative to the tip 101 and a zero or negative voltage to the extraction electrode 106, flashing can be performed while the acceleration voltage V0 is applied without the risk of the device shutting down due to insufficient capacity of the acceleration power supply 111, a deterioration in the electron gun pressure, or discharge. As a result, the downtime required for flashing can be significantly reduced compared to conventional CFE electron sources. Furthermore, by collecting more thermoelectrons emitted during flashing on the auxiliary electrode 202 and calculating the temperatures of the tip 101 and filament 102 based on the current measured by the auxiliary electrode 202, the temperature during flashing can be more precisely controlled. Furthermore, residual gas can be appropriately desorbed without blunting the tip 101, improving the reproducibility of observed images and extending the life of the CFE electron source. [Example]

[0061] In the first to fourth embodiments, a positive voltage is applied to the auxiliary electrode 202 during flashing, and thermoelectrons are collected and measured by the auxiliary electrode 202. In the fifth embodiment, a zero or negative voltage is applied to the auxiliary electrode 202 during flashing, and the extraction voltage V1 applied to the extraction electrode 106 is controlled, and thermoelectrons are collected and measured by the extraction electrode 106. Note that some of the configurations and functions described in the first to fourth embodiments can be applied to the fifth embodiment, and therefore, the same configurations and functions are designated by the same reference numerals and will not be described again.

[0062] An example of the configuration of the CFE electron source 201 and its periphery will be described with reference to Fig. 6. The configuration of the CFE electron source 201 and its periphery is the same as that of Example 1. However, the auxiliary voltage Vs applied to the auxiliary electrode 202 by the auxiliary power supply 204 is zero or a negative voltage, and the ammeter 116 is connected to the extraction electrode 106.

[0063] Because the auxiliary voltage Vs is negative, the potential gradient formed between the filament 102 and the auxiliary electrode 202 acts to repel the thermoelectrons emitted from the filament. As a result, the only thermoelectrons emitted from the tip 101 and filament 102 during flashing are thermoelectrons 301 emitted from the tip of the tip 101, which enter the extraction electrode 106 and are measured by the ammeter 116. In other words, the thermoelectrons 205 and 206 shown in Figure 3 cannot be emitted. Even if the auxiliary voltage Vs is zero, a similar potential gradient is created due to space charge limitation, and thermoelectrons cannot be emitted. The measurement value by the ammeter 116 is sent to the control unit 617 and converted to temperature. By measuring only the thermoelectrons 301 emitted from the tip of the tip 101, the temperature of the tip of the tip 101 can be calculated more accurately. The temperature difference between the filament 102 and the tip of the tip 101 during flashing is several tens of degrees Celsius to approximately 100 degrees Celsius. The important thing about flashing is to clean the electron emission surface at the tip of the tip 101. By measuring only the thermoelectrons emitted from the tip of the tip 101 and calculating the temperature, the temperature of the electron emission surface can be controlled more accurately, improving the reproducibility and lifespan of electron emission.

[0064] An example of the potential distribution near the tip 101 will be described using Figure 7. In Figure 7, the area near the tip 101 is enlarged, and equipotential lines 303 are shown by dotted lines when the auxiliary voltage Vs is -0.2 kV and the extraction voltage V1 is 0.3 kV during flashing. The area around the auxiliary electrode 202, to which a negative voltage is applied, has a negative potential, while the areas around the extraction electrode 106 and the aperture 107, to which a positive voltage is applied, have a positive potential. The point where the equipotential lines of zero potential intersect with the tip 101 is defined as a boundary point 304. The position of the boundary point 304 varies depending on the auxiliary voltage Vs, the extraction voltage V1, and the protrusion length T of the tip 101.

[0065] On the surfaces of the chip 101 and filament 102, the area above the boundary point 304 is a region 305 covered with a negative potential, while the area below is a region 306 covered with a positive potential. In the region 305 covered with a negative potential, the emitted thermoelectrons are pushed back, while in the region 306 covered with a positive potential, the thermoelectrons are emitted, and most of the thermoelectrons 301 enter the extraction electrode 106 and the aperture 107, while only a small portion of the thermoelectrons 302 pass through the opening of the aperture 107.

[0066] Increasing the absolute value of the auxiliary voltage Vs, which is a negative voltage, moves the position of the boundary point 304 downward, and decreases the number of thermoelectrons 301 emitted from the tip 101. Increasing the absolute value of the extraction voltage V1, which is a positive voltage, moves the position of the boundary point 304 upward, and increases the number of thermoelectrons 301 emitted from the tip 101.

[0067] By making the current of the thermoelectrons 301 equal to the current of tunneling electrons emitted in a steady state, it is possible to reduce costs and control the temperature without changing the power capacity of the extraction power supply 108. The current of tunneling electrons is 1 μA to several hundred μA, and the current density of the thermoelectrons emitted during flashing at 2000°C is approximately 650 A / m 2 In order to make the thermoelectrons 301 1 μA or more, the surface area of ​​the region 306 covered by the positive potential must be 1500 μm 2Since the shape of the tip of tip 101 is a cone with a half apex angle of approximately 10 degrees, the position of boundary point 304 should be 50 μm or more from the tip of tip 101. Note that, since the current density of the thermoelectrons decreases as the temperature during flashing decreases, it is desirable to increase the surface area of ​​region 306 covered by a positive potential and increase the amount of thermoelectrons that can be measured.

[0068] If flashing is performed while applying the same high extraction voltage V1 as during field emission, a change in shape called buildup occurs on the electron emission surface at the tip of the tip 101. This is a buildup of 3×10 9 This is because when the tip 101 is heated to 1600°C or higher under a strong electric field of 100V / m, tungsten atoms on the tip surface diffuse and move, causing the low-index planes of the crystal to grow. If the tip shape changes, the amount of current emitted before and after flashing changes. As a result, the signal-to-noise ratio and voltage conditions of the observed image change, making it impossible to obtain reproducible images.

[0069] In addition, compared to tunneling electrons, thermal electrons have lower brightness and a larger energy spread. Therefore, if flashing is performed while field emission is occurring, thermal electrons will be mixed into the tunneling electrons used for image observation, degrading the resolution of the observed image. To avoid this buildup and mixing of thermal electrons, the extraction voltage during flashing is lowered and the electric field strength at the tip is set to 3 x 10 9 It needs to be less than V / m.

[0070] The optimal voltage ranges to be applied to the auxiliary electrode and extraction electrode will be explained using Figure 8. Figure 8 shows an example of the results of calculating the optimal voltage range 403 to be applied to both electrodes, in a space where the vertical axis represents the auxiliary voltage Vs and the horizontal axis represents the extraction voltage V1, so as to satisfy the conditions described below. In calculating the optimal voltage range 403, the protrusion length T of the tip 101 was set to 250 μm, and the distance L between the auxiliary electrode 202 and the extraction electrode 106 was set to 800 μm.

[0071] As described with reference to FIG. 7, in order to make the thermoelectrons 301 emitted from the tip of the tip 101 1 μA or more, the position of the boundary point 304 where the equipotential line of zero potential intersects with the tip 101 must be 50 μm or more from the tip of the tip 101. Also, in order to prevent buildup at the tip of the tip 101, the electric field strength at the tip of the tip 101 during flashing must be 3×10 9 The auxiliary voltage Vs and the extraction voltage V1 are set to satisfy these conditions.

[0072] 8 represents a combination of auxiliary voltage Vs and extraction voltage V1 that results in zero potential at a position 50 μm from the tip of tip 101. In other words, in the region above line 401, the position 50 μm from the tip of tip 101 has a positive potential, and thermoelectrons of 1 μA or more can be measured.

[0073] The straight line 402 in FIG. 8 indicates that the electric field strength at the tip of the tip 101 is 3×10 9 This is a combination of auxiliary voltage Vs and extraction voltage V1 such that V / m is obtained. Both lines 401 and 402 show that the amount of thermoelectrons and the electric field become constant by increasing the negative auxiliary voltage Vs in accordance with the extraction voltage V1. Here, in the region below line 402, the electric field strength at the tip of tip 101 is 3×10 9 V / m or less, field emission stops, and no build-up occurs even if flashing is performed further.

[0074] In Example 5, the auxiliary voltage Vs is set to zero or a negative potential, so the triangular region surrounded by the Vs=0 line and the lines 401 and 402 is the optimal voltage range 403. Using the auxiliary voltage Vs and extraction voltage V1 in the optimal voltage range 403 during flashing allows the temperature of the tip of the chip 101 to be calculated, reduces the cost of the extraction power supply 108, prevents buildup at the tip of the chip 101, and prevents thermoelectrons from mixing with tunneling electrons. Note that in region 404, located to the right of the intersection 405 between lines 401 and 402, below line 401 and above line 402, the amount of thermoelectrons 301 is insufficient to control the flashing temperature, and the tip of the chip 101 builds up, causing thermoelectrons to mix with tunneling electrons. Therefore, region 404 is considered an inappropriate voltage range.

[0075] The optimum voltage range to be applied to the auxiliary electrode and extraction electrode when the tip protrusion length T is changed will be explained using Figure 9. Figure 9 shows an example of the calculation results of the optimum voltage range 504 when the protrusion length T is changed from 50 μm to 750 μm. In calculating the optimum voltage range 504, the distance L between the auxiliary electrode 202 and the extraction electrode 106 was set to 800 μm.

[0076] As described with reference to FIG. 8, the optimum voltage range 504 is the range between the line of Vs=0, the line where the potential is zero at a position 50 μm from the tip of the tip 101, and the line where the electric field strength at the tip of the tip 101 is 3×10 9 When the protrusion length T changes, the two lines other than the line of Vs=0 also change, and the shorter the protrusion length T, the more the two lines shift to the upper right. Note that when T=50 μm, the electric field strength at the tip of the tip 101 is 3×10 9 Line 501, where V / m, is expressed as Vs = -0.150V1 + 1.18. Line 502, where the potential is zero at a position 50 μm from the tip of tip 101 when T = 650 μm, is expressed as Vs = -5.49V1. The intersection of the two lines moves on curve 503, which is expressed as Vs = -146 / (V1 - 4.13) + 6.40.

[0077] Therefore, even if the protrusion length T changes, by using the auxiliary voltage Vs and extraction voltage V1 within the optimal voltage range 504 during flashing, the temperature at the tip of the tip 101 can be accurately calculated, the cost of the extraction power supply 108 can be reduced, buildup at the tip of the tip 101 can be prevented, and thermions can be prevented from mixing with tunnel electrons. Even if the distance L between the auxiliary electrode 202 and the extraction electrode 106 is another length, for example, from 400 μm to 600 μm, the same effect can be achieved by using the auxiliary voltage Vs and extraction voltage V1 within the optimal voltage range 504 during flashing. The optimal voltage range 504 is expressed as a region that satisfies -5.49V1≦Vs≦-0.150V1+1.18 and -146 / (V1-4.13)+6.40≦Vs≦0 (unit: kV).

[0078] As described above, in the fifth embodiment, the auxiliary electrode 202 applies a zero or negative voltage to the tip 101, and the extraction voltage V1 applied to the extraction electrode 106 is controlled. The extraction electrode 106 then collects and measures the thermoelectrons, thereby enabling more precise control of the temperature at the tip of the tip during flashing. Furthermore, the residual gas can be appropriately desorbed without blunting the tip of the tip 101, thereby improving the reproducibility of the observed image and extending the life of the CFE electron source. Furthermore, the reproducibility of the observed image is improved by preventing buildup on the electron emission surface at the tip of the tip 101 and preventing the thermoelectrons from mixing with the tunneling electrons used for image observation. [Example]

[0079] In the fifth embodiment, it has been described that a zero or negative voltage is applied to the auxiliary electrode 202 during flashing, and the extraction voltage V1 applied to the extraction electrode 106 is controlled to collect and measure thermoelectrons by the extraction electrode 106. In the sixth embodiment, it will be further described that the downtime of the apparatus is reduced by keeping the acceleration voltage V0 applied during flashing. Note that some of the configurations and functions described in the first to fifth embodiments can be applied to the sixth embodiment, and therefore, the same configurations and functions will be designated by the same reference numerals and will not be described again.

[0080] Of the thermoelectrons shown in FIG. 7, only a small portion of the thermoelectrons 302 near the central axis pass through the aperture 107 and enter the acceleration space 112. The amount of current is about the same as that of the tunneling electrons used for steady-state image observation. Therefore, even if flashing is performed while the V0 voltage is applied, a malfunction due to insufficient power supply capacity of the acceleration power supply 111 will not occur. In addition, there is little possibility of a deterioration in the vacuum level of the electron gun or damage to the electron source. Therefore, flashing can be performed while the acceleration voltage V0 is applied, reducing downtime.

[0081] An example of the change in voltage applied to each electrode will be described using Figures 10A to 10D. Figure 10A shows an example in which the auxiliary voltage Vs is constant at -0.2 kV, the extraction voltage V1 is reduced from 2 kV during image observation to 0.3 kV during flashing and then increased back to 2 kV, and the acceleration voltage V0 is constant at 100 kV. The extraction voltage V1 is increased or decreased for 0.85 s, maintained at 0.3 kV during flashing for 1 s, and the time when no image observation is performed is limited to 2.7 s. Furthermore, because the auxiliary voltage Vs is constant at -0.2 kV, thermoelectrons are not emitted from the filament 102 but only from the tip of the tip 101. As a result, the temperature at the tip of the tip 101 can be calculated more accurately. Furthermore, buildup and mixing of thermoelectrons with tunneling electrons do not occur.

[0082] Figure 10 shows an example in which the auxiliary voltage Vs is 0.3 kV during imaging and 0 kV during flashing, the extraction voltage V1 is 2 kV during imaging and 0.1 kV during flashing, and the acceleration voltage V0 is constant at 100 kV. The time for which the auxiliary voltage Vs and extraction voltage V1 are increased or decreased is 0.95 s, the flashing time is 1 s, and the time during which no imaging is performed is limited to 2.9 s. Furthermore, the auxiliary voltage Vs during flashing is -0.2 kV, so no thermoelectrons are emitted from the filament 102, and only thermoelectrons 301 emitted from the tip of the tip 101 are measured. This allows for more accurate calculation of the temperature at the tip of the tip 101. Furthermore, buildup and thermoelectron contamination with tunneling electrons do not occur.

[0083] FIG. 10C shows an example in which the auxiliary voltage Vs is −0.2 kV during image observation and −1.3 kV during flashing, the extraction voltage V1 is constant at 2 kV, and the acceleration voltage V0 is constant at 100 kV. The time during which the auxiliary voltage Vs is increased or decreased is 0.55 s, the flashing time is 1 s, and the time during which no image observation is performed is limited to 2.1 s. Furthermore, since the auxiliary voltage Vs is −1.3 kV during flashing, no thermoelectrons are emitted from the filament 102, and only thermoelectrons 301 emitted from the tip of the tip 101 are measured, allowing for more accurate calculation of the temperature at the tip of the tip 101. Because the extraction voltage V1 is constant, discharge due to the increase or decrease in V1 is unlikely to occur. Furthermore, buildup and the incorporation of thermoelectrons into tunneling electrons do not occur.

[0084] FIG. 10D shows an example in which the auxiliary voltage Vs is 1 kV during image observation and -0.6 kV during flashing, the extraction voltage V1 is constant at 1 kV, and the acceleration voltage V0 is constant at 100 kV. The auxiliary voltage Vs is increased or decreased for 0.8 s, the flashing time is 1 s, and the time during which no image observation is performed is limited to 2.6 s. Furthermore, since the auxiliary voltage Vs is -0.6 kV during flashing, no thermoelectrons are emitted from the filament 102, and only thermoelectrons 301 emitted from the tip of the tip 101 are measured. This allows for more accurate calculation of the temperature at the tip of the tip 101. Furthermore, since the extraction voltage V1 is constant, discharge is unlikely to occur. Furthermore, buildup and the mixing of thermoelectrons with tunneling electrons do not occur.

[0085] As described above, in Example 6, the auxiliary electrode 202 applies a zero or negative voltage relative to the tip 101, while controlling the extraction voltage V1 applied to the extraction electrode 106. The extraction electrode 106 then collects and measures the thermoelectrons, thereby enabling more precise control of the tip tip temperature during flashing. Furthermore, flashing can be performed while the acceleration voltage V0 is applied, without the risk of the device shutting down due to insufficient capacity of the acceleration power supply 111, the deterioration of the electron gun pressure, or discharge. As a result, the downtime required for flashing can be significantly reduced compared to conventional CFE electron sources. Furthermore, residual gas can be appropriately desorbed without blunting the tip 101, thereby improving the reproducibility of observed images and extending the life of the CFE electron source. Furthermore, the reproducibility of observed images can be improved by preventing buildup on the electron emission surface at the tip of the tip 101 and preventing the thermoelectrons from mixing with the tunneling electrons used for image observation.

[0086] The above describes several embodiments of the present invention. The present invention is not limited to the above embodiments, and the components can be modified within the scope of the invention. For example, instead of single crystal tungsten, a low work function material such as CeB6 or LaB6, or a surface-inactive material such as a carbon-coated material, can be used as the tip 101. A nanowire electron source or a single-atom electron source having a sharpened tip with a radius of curvature of several tens of nanometers or a few atoms to one atom can also be used. Furthermore, multiple components disclosed in the above embodiments can be appropriately combined. Furthermore, some components can be omitted from all of the components shown in the above embodiments. [Explanation of symbols]

[0087] 101...tip, 102...filament, 103...pin, 104...insulator, 106...extraction electrode, 107...diaphragm, 108...extraction power supply, 109...acceleration electrode, 110...diaphragm, 111...acceleration power supply, 112...acceleration space, 113...flushing power supply, 116...ammeter, 201...CFE electron source, 202...auxiliary electrode, 203...aperture, 204...auxiliary power supply, 205...thermion, 206...thermion, 207...thermion, 208...thermion, 301...thermion, 302...thermion, 303...equipotential line, 304...boundary point, 305...area covered by negative potential, 306...area covered by positive potential , 401...straight line, 402...straight line, 403...optimum voltage range, 404...area, 405...intersection, 501...straight line, 502...straight line, 503...curve, 504...optimum voltage range, 601...electron beam, 602...sample, 603...cylinder, 604...sample chamber, 605...first vacuum chamber, 606...second vacuum chamber, 607...third vacuum chamber, 608...ion pump, 609...non-evaporative getter pump, 610...insulator, 611...ion pump, 612...condenser lens, 613...turbomolecular pump, 614...objective lens, 616...detector, 617...control unit, 618...display unit, 619...input unit

Claims

1. a cold cathode field emission electron source having a tip with a sharpened tip, a filament connected to the tip, and an auxiliary electrode covering the filament and having an opening through which the tip protrudes; an extraction electrode to which an extraction voltage is applied for extracting electrons from the cold cathode field emission electron source; a charged particle beam device including an acceleration electrode to which an acceleration voltage is applied for accelerating electrons extracted from the cold cathode field emission electron source, A charged particle beam device characterized in that, when the tip and the filament are heated, a positive voltage is applied to the auxiliary electrode with respect to the tip, thereby causing the auxiliary electrode to collect thermoelectrons emitted from the tip and the filament and measuring the current.

2. The charged particle beam device according to claim 1, A charged particle beam device, characterized in that when the tip and the filament are heated, an auxiliary voltage applied to the auxiliary electrode is made larger than the extraction voltage.

3. The charged particle beam device according to claim 2, A charged particle beam device, characterized in that the extraction voltage is set to zero or a negative voltage when the tip and the filament are heated.

4. The charged particle beam device according to claim 1, A charged particle beam device characterized in that a power supply that applies an auxiliary voltage to the auxiliary electrode during image observation can apply both positive and negative voltages to the tip.

5. The charged particle beam device according to claim 1, A charged particle beam device characterized in that the tip and the filament are heated during a period in which any of the following is performed: changing the acceleration voltage, moving the observation point, replacing the sample, adjusting the focal position, or adjusting the voltage or current applied to each part.

6. The charged particle beam device according to claim 1, a display unit that displays at least one of the acceleration voltage, the extraction voltage, the auxiliary voltage applied to the auxiliary electrode, the current measured at the auxiliary electrode, the calculated temperature, the current supplied to the filament, and the time for which the current is supplied to the filament when the tip and the filament are heated.

7. The charged particle beam device according to claim 1, a control unit that records at least one of the acceleration voltage, the extraction voltage, the auxiliary voltage applied to the auxiliary electrode, the current measured at the auxiliary electrode, the calculated temperature, the current supplied to the filament, and the time for which the current is supplied to the filament when the tip and the filament are heated.

8. The charged particle beam device according to claim 1, A charged particle beam device, characterized in that the acceleration voltage is applied when the tip and the filament are heated.

9. The charged particle beam device according to claim 3, A charged particle beam device, characterized in that the acceleration voltage is applied when the tip and the filament are heated.

10. The charged particle beam device according to claim 5, A charged particle beam device, characterized in that the acceleration voltage is applied when the tip and the filament are heated.

11. The charged particle beam device according to claim 6, A charged particle beam device, characterized in that the acceleration voltage is applied when the tip and the filament are heated.

12. a cold cathode field emission electron source having a tip with a sharpened tip, a filament connected to the tip, and an auxiliary electrode covering the filament and having an opening through which the tip protrudes; an extraction electrode to which an extraction voltage is applied for extracting electrons from the cold cathode field emission electron source; a charged particle beam device including an acceleration electrode to which an acceleration voltage is applied for accelerating electrons extracted from the cold cathode field emission electron source, When the tip and the filament are heated, the auxiliary voltage applied to the auxiliary electrode is Vs, and the extraction voltage is V1. In this charged particle beam device, thermions emitted from the tip are collected by the extraction electrode and a current is measured in a state where −5.49V1≦Vs≦−0.150V1+1.18 and −146 / (V1−4.13)+6.40≦Vs≦0 (unit: kV) are satisfied, where Vs is an auxiliary voltage applied to the auxiliary electrode and V1 is an extraction voltage.

13. The charged particle beam device according to claim 12, A charged particle beam device, characterized in that the acceleration voltage is applied when the tip and the filament are heated.

14. a cold cathode field emission electron source having a tip with a sharpened tip, a filament connected to the tip, and an auxiliary electrode covering the filament and having an opening through which the tip protrudes; an extraction electrode to which an extraction voltage is applied for extracting electrons from the cold cathode field emission electron source; an acceleration electrode to which an acceleration voltage is applied for accelerating electrons extracted from the cold cathode field emission electron source; A charged particle beam device comprising a control unit that controls the operation of each unit, The control unit applies a positive voltage to the auxiliary electrode with respect to the tip when the tip and the filament are heated, thereby causing the auxiliary electrode to collect thermoelectrons emitted from the tip and the filament, and calculates the temperatures of the tip and the filament based on the current measured by the auxiliary electrode.

Images