JP2022181997A - Electron Source, Charged Particle Beam Device, and Charged Particle Beam System - Google Patents

Abstract

To minimize the variation of a break location between a plurality of filaments as much as possible by having a break portion of a filament that breaks by using it as a heat electron source be close to the filament tip.SOLUTION: An electron source emits thermal electrons by energizing and heating a filament. The filament includes a first part defined as a tip portion including a tip opposing a sample from which heat electrons are emitted and a second part defined as a non-tip portion other than the tip portion. The cross-sectional area of the first part of the filament is smaller than the cross-sectional area of the second part.SELECTED DRAWING: Figure 2A

Description

The present disclosure relates to electron sources, charged particle beam devices, and charged particle beam systems.

The structure of the sample surface can be observed by focusing an electron beam through an electromagnetic field lens, irradiating the sample while scanning it, and detecting charged particles (secondary electrons) emitted from the sample. This is called a scanning electron microscope (SEM). This technique is widely used for visualization of fine structures. SEMs are also widely used for observation of the shape and composition of materials such as metals, observation of the shape and morphology of biological specimens, and inspection applications for pattern dimensions and defect management of semiconductor devices.

An important point when using the SEM technique is to keep the current of the electron beam emitted from the electron source stable. If the current of the irradiated electron beam fluctuates, the brightness of the image observed with the SEM fluctuates, degrading the image quality. In the worst case, the emission of the electron beam may be stopped for some reason, and the observation may be forced to stop.

There are various types of electron sources. Schottky electron sources and field emission electron sources have very long lives and can be used continuously for one to two years. On the other hand, a type of electron source that uses thermoelectrons generated by heating a metal such as tungsten in a filament is called a thermoelectron source or a thermoelectron emitting electron source. This method is based on a very simple principle, can obtain a highly stable electron beam in the short term, and can construct an apparatus at a low cost. However, in this method, since the filament is used at a high temperature, the sublimation wears the filament, thins the filament, and eventually breaks it. This filament life is generally about 50 hours, which is very short compared to the life of the electron sources of the other methods.

If the filament breaks during observation or analysis that requires a long period of time, the observation or analysis will have to be restarted from the beginning. Since it is also necessary to prepare in advance, it leads to a decrease in the utilization efficiency of the apparatus. Also, although it is possible to replace the filament in advance before it breaks, it consumes more filament, resulting in an increase in cost. Therefore, it is very important to extend the life of the thermionic electron source in the first place. In addition, it is also important to accurately know the timing of filament breakage in advance.

Regarding the filament used for the electron source, for example, Patent Document 1 discloses a technique of machining the tip of the tungsten filament by using electric discharge machining or the like while leaving a part of the shape of a spherical surface at the tip.

Further, Patent Document 2 discloses that the heat durability of the filament is improved by configuring the tip portion of the filament to be thicker than the non-tip portion (forming the filament by bending a ribbon-shaped metal member). do.

Further, in Patent Document 3, welding of a filament wire having a small curvature radius and serving as a high-intensity electron beam source and diameter reduction processing of a thermionic emission part can be easily manufactured by one welding, and two wires are used. , the diameter of the filament is reduced toward the tip, the curvature radius of the tip is 100 μm or less, and the material of the two strands is the same metal or alloy.

JP 2019-091621 A JP 2018-085351 A JP 2013-134874 A

As mentioned above, in SEM using a thermionic electron source, it is very important to extend the life of the thermionic source, and in addition, it is also important to know the exact timing of filament breakage in advance. Become.

By the way, the filament of the thermionic electron source is generally shaped so that the center of the filament is positioned closest to the sample. Hereinafter, this protruding central portion will be referred to as the tip portion. The point at which the thermionic electron source emits thermionic electrons is mainly the tip of the filament. power is controlled. Therefore, the method of using the electron source with the highest efficiency is that the tip of the filament becomes the hottest. That is, when the filament breaks, it is desirable that the filament is worn preferentially from the tip and breaks at the tip.

However, when the inventors of the present invention examined the pattern of filament breakage in detail under various conditions, it was found that the position where the filament breaks is not necessarily the tip, but rather, it is very often broken at a portion other than the tip. Do you get it. This means that the filament was worn preferentially from the tip portion of the filament to the portion other than the tip portion, that is, the temperature of the portion other than the tip portion was higher than that of the tip portion of the filament.

On the other hand, the tip of the filament is where the thermionic electron source emits thermionic electrons. Power is still controlled. In other words, the breakage of the portion other than the tip of the filament means that the temperature of the portion other than the tip of the filament was unnecessarily increased.

In addition, the fracture position varied greatly depending on the filament. It was found that this variation is greatly affected by individual differences in the shape and electrical characteristics of the electron source and the filament during manufacturing. Furthermore, it was also found that when the filament breaking position varies, the time required for the filament to break also varies greatly.

Needless to say, the unnecessarily heated portion of the filament other than the tip means unnecessary wear of the filament due to sublimation, which is a major cause of shortening the life of the thermoelectron source. In addition, the variation in fracture position depending on the filament is a major cause of variation in the lifetime of the thermoelectron source, making it difficult to accurately determine the lifetime of the thermoelectron source.

Therefore, in order to prolong the life of the thermionic electron source, it is very important to keep the tip of the filament at the highest temperature without unnecessarily raising the temperature of parts other than the tip of the filament. Therefore, in order to accurately know the timing of filament breakage in advance, it is important to prevent the filament breakage position from varying. In other words (to summarize these two points of view), the tip of the filament is the hottest, and it is a very important issue to keep the filament break position from varying from the tip of the filament. In this regard, although Patent Document 1, Patent Document 2, and Patent Document 3 all disclose embodiments related to filaments of thermoelectron sources, it cannot be said that this problem is fully taken into consideration. In particular, although Patent Document 2 mentions the problem of prolonging the life of the filament, since the filament tip portion is configured to be thicker than the other portion, the portion other than the filament tip portion is broken. It can be said that there is a high possibility of doing so.

In view of such circumstances, the present disclosure proposes a technique for minimizing variations in fracture positions among a plurality of filaments by using a filament as a thermoelectron source so that the fractured portion of the filament is close to the tip of the filament.

In order to solve the above problems, the inventors have made intensive studies, and have developed an electron source that emits thermoelectrons by electrically heating a filament, wherein the filament has a tip facing a sample from which the thermoelectrons are emitted. and a second portion defined as a non-tip portion other than the tip portion, wherein the cross-sectional area of the first portion of the filament is smaller than the cross-sectional area of the second portion; I ended up creating an electron source.

Further features related to the present disclosure will become apparent from the description of the specification and the accompanying drawings. Aspects of the present disclosure are also realized by means of the elements and combinations of various elements and aspects of the detailed description that follows and the claims that follow.
The description herein is merely exemplary and is not intended to limit the scope or application of this disclosure in any way.

According to the technique of the present disclosure, by using a filament as a thermoelectron source, the fractured portion of the filament that is to be fractured can be brought close to the tip of the filament, and variations in the fractured position among a plurality of filaments can be suppressed.

It is a figure which shows the structural example of the electron beam generator 10 which concerns on this embodiment. It is a figure which illustrates the characteristic of the cross-sectional area of the filament 11 by this embodiment. 4 is a diagram illustrating a configuration in which a portion 18 of the filament 11 other than the tip portion is covered with a material having a higher emissivity than the material forming the filament 11 according to the present embodiment; FIG. 1 is a diagram showing a configuration example of a scanning electron microscope 100 as an example of a charged particle beam device including an electron beam generator 10. FIG. 4 is a diagram showing the relationship between the average distance from the center of the filament to the breaking position and the ratio of the cross-sectional area of the tip of the filament to the cross-sectional area of the portion other than the tip in Example 1. FIG. 4 is a diagram showing the relationship between the average and standard deviation of the time until the filament breaks and the ratio of the cross-sectional area of the tip of the filament to the cross-sectional area of the portion other than the tip in Example 1. FIG. FIG. 5 is a diagram showing a simulation result of a temperature profile according to Example 1; FIG. 10 is a diagram showing the average distance from the center of the filament to the breaking position and the average and standard deviation of the time until the filament breaks in Example 2; FIG. 10 is a diagram showing simulation results of a temperature profile for Example 2;

Preferred embodiments and examples of the present invention will now be described with reference to the drawings. It should be noted that the following embodiments and examples are merely examples for facilitating understanding of the technology of the present disclosure, and do not limit the technology of the present disclosure unless otherwise specified.
This embodiment discloses a charged particle beam apparatus for irradiating a sample with a charged particle beam, and a thermionic emission electron source used therein. A detailed description will be given below.

(1) Embodiment <Configuration Example of Electron Beam Generator>
FIG. 1 is a diagram showing a configuration example of an electron beam generator 10 according to this embodiment. The electron beam generator 10 includes a DC power supply 111 for applying a DC current to a filament attached to a terminal A 117 and a terminal B 118, an accelerating voltage power supply 119, a Wehnelt electrode 14, a Wehnelt electrode power supply 141, an anode 15, and a measuring device. 115 and a controller 116 .

The filament 11 is composed of a fine wire or ribbon of a metal such as tungsten. The filament 11 is heated by the Joule heating phenomenon by applying current using the DC power supply 111, and emits electrons by the thermoelectron emission phenomenon. Also, the filament 11 is connected to the terminal A117 and the terminal B118 by welding or the like. Each terminal is connected and fixed to the insulator 12 . The potential of the filament 11 is adjusted by the accelerating voltage power supply 119, and the generated electrons form an electron beam accelerated by this potential. Emission of the electron beam is adjusted by the Wehnelt electrode 14 and the Wehnelt electrode power supply 141 . Anode 15 is typically connected to ground potential, but may be energized if desired.

In this embodiment, the filament 11 is bent in a curved shape at the center and protrudes at the tip. When the electron source is used in a charged particle beam device, this tip portion is arranged on the sample side and functions as a thermionic emission portion. The shape of the filament is not limited to this, and a filament of any shape may be used as long as the tip portion functioning as the thermionic emission portion is arranged on the sample side. The length and cross-sectional shape of the filament 11 may be arbitrarily selected as long as a desired temperature can be obtained at the tip portion when a current is applied by the DC power source 111 . As an example, it can be a thin wire with a total length of 12 mm and a diameter of 120 μm.

<Characteristics of filament>
FIG. 2 is a diagram showing features of the configuration of the filament 11 according to this embodiment.
(i) Regarding the cross-sectional area of the filament 11 FIG. 2A is a diagram illustrating characteristics of the cross-sectional area of the filament 11 . As shown in FIG. 2A, the cross-sectional area of the tip of the filament 11 is smaller than the cross-sectional area of the portion other than the tip. Filament 11 has a tip portion 17 removed from the uniform filament. By doing so, the resistance of the tip portion increases locally, the Joule heating phenomenon is promoted in the tip portion, and the temperature of the tip portion tends to rise. According to the studies of the present inventors, if the ratio of the cross-sectional area of the tip of the filament 11 to the cross-sectional area of the portion other than the tip is 0.81 or less, the shape and electrical characteristics that occur during the manufacture of the electron source and the filament It is preferable because the tip portion of the filament can be heated to the highest temperature even if individual differences such as the above are taken into account. When this ratio is 0.81 or less, the portion other than the tip of the filament does not become unnecessarily hot, so that the thermionic source has a long average life.

On the other hand, if the cross-sectional area ratio is too small, the tip of the filament 11 will break in a short period of time due to wear due to sublimation, although this is preferable for making the tip of the filament 11 the hottest. As a result of studies by the inventors, it has been found that the cross-sectional area ratio should preferably be 0.49 or more in order not to impair the average life of the electron source. As described above, the ratio of the cross-sectional area of the tip portion of the filament 11 to the cross-sectional area of the portion other than the tip portion can be set to 0.49 or more and 0.81 or less.

(ii) Covering the portion other than the tip portion of the filament 11 with a covering material FIG. 2B illustrates a configuration in which the portion 18 other than the tip portion of the filament 11 is covered with a material having a higher emissivity than the material forming the filament 11. It is a figure to do. By doing so, the heat dissipation of the portion other than the tip portion of the filament 11 is promoted, the temperature rise of the portion other than the tip portion is suppressed, and as a result, the temperature of the tip portion tends to rise. The portion of the filament 11 to be covered may be all of the portion other than the tip portion, or may be a part of the portion other than the tip portion where it is particularly desired to suppress the temperature rise. As a material for covering the filament 11, a material that can easily obtain a high emissivity is used. As a result of examination by the inventors, a material containing at least one selected from carbon, silicon oxide, titanium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, and zirconium oxide is used as the coating material for the filament 11. found to be usable. These materials are particularly preferable because the tip portion of the filament can be heated to the highest temperature even if individual differences in shape, electrical characteristics, etc. that occur during manufacture of the electron source and filament are taken into account.

(iii) Tip and Non-Tip As described above, the filament 11 is bent into a curved shape (approximately at the center), and when in use, the electron beam is placed so that the curved portion of the filament 11 faces the object to be irradiated with the charged particle beam. It is installed in the beam generator 10 . Therefore, it can be said that the tip of the filament 11 is the portion at the minimum distance from the object to be irradiated with the charged particle beam. A portion within a certain range centered on the tip can be defined as a tip portion (a portion with a reduced cross-sectional area, or a portion not covered with the covering material). The manufacturer can appropriately determine to which range from the tip of the filament 11 the cross-sectional area is to be reduced, or from which portion of the filament 11 to be covered with the coating material. However, in the former case, it is actually difficult to uniformly reduce the cross-sectional area of the filament 11 . Therefore, the manufacturer defines the portion of the filament 11 that has been processed to reduce the cross-sectional area or the portion that is not covered with the coating material as the tip portion of the filament 11, and the portion that has not been processed or the portion not covered with the coating material. The portion covered with the coating material can be defined as the non-tip portion of filament 11 .

<Application to charged particle beam equipment>
FIG. 3 is a diagram showing a configuration example of a scanning electron microscope 100 as an example of a charged particle beam device including the electron beam generator 10 configured as described above.

A scanning electron microscope 100 includes an electron beam generator 10 that emits an electron beam 31, a first focusing lens 21, a second focusing lens 22, a first deflection coil 23, a second deflection coil 24, and an objective lens. 25, a detector 27, evacuation means 28 and 29, a sample stage 30, a vacuum gauge 41, a power supply 211 for focusing lens, a power supply 231 for deflection coil, and a power supply 251 for objective lens.

The electron beam 31 extracted by the electron beam generator 10 is focused by the first focusing lens 21 and the second focusing lens 22 as required, and is irradiated onto the sample 26 . The configuration of these two lenses makes it possible to freely change the current amount and the aperture angle when the sample 26 is irradiated with the electron beam 31 . The deflection amount of the electron beam 31 is adjusted by the first deflection coil 23 and the second deflection coil 24 as necessary. A scanning electron microscope (SEM) image can be obtained by scanning the electron beam 31 over the sample 26 and detecting the resulting emitted signal electrons with the detector 27 . Electron beam 31 may finally be focused by objective lens 25 .

The first condenser lens 21, the second condenser lens 22, the first deflection coil 23, the second deflection coil 24, and the objective lens 25 are respectively operated by a condenser lens power supply 211, a deflection coil power supply 231, and an objective lens power supply 251. A current or voltage is applied. Further, the inside of the housing can be evacuated by the exhaust means 28 and 29 so that the electron beam 31 is not scattered by gas molecules.

<Prediction of Life of Filament 11>
Usability is greatly improved if it is possible to know how long the thermionic source (filament 11) of the electron beam generator 10 has (how much life is left during use (remaining life)). do. In order to achieve this, the following processing is performed. In this embodiment, regarding the thermionic source, the detailed shape of the filament 11 including individual differences, the shape of the welded portion of the filament 11, the shape of the terminal A 117 and the terminal B 118, the initial electrical characteristics such as resistance, etc. The relationship between the characteristics and the time until breakage of each filament 11 (for example, the time until breakage when used at rated current) is investigated. This is done for many thermionic sources, and the results are put into a database. Based on this database, machine learning can be performed to create a function that outputs the lifetime expected from the initial characteristics of each thermionic source. Such a function is possible because, in the thermionic source according to the present embodiment, there is no variation in the breaking position of the filament 11, and variation in life is small. Even if machine learning is attempted, it is extremely difficult to create a function that outputs the lifetime of a thermionic source with large variations in lifetime.

Initial characteristics such as individual shape data and electrical characteristic data of the filament 11 can be measured in advance at the time of manufacture and stored in a file server (not shown) on the Internet. A code for accessing these data is attached to the main body or case of the thermoelectron source. By inputting this code into the control device 116 and transmitting it to the file server, the user can obtain data corresponding to the code (data indicating the relationship between the initial characteristics of the filament and the time until the filament breaks). can be downloaded. To enable this, controller 116 may be configured to include a personal computer or the like. Alternatively, a mode for grasping the initial characteristics of the filament 11 may be provided using the scanning electron microscope 100 .

Given the initial properties of the thermionic source, the expected lifetime can be determined using a function derived from machine learning. For example, as teaching data, data on individual differences in thermoelectron sources (filaments) and data on lifespans corresponding to individual differences are given to create a learning model. On the other hand, data on individual differences after manufacturing is applied to the learning model to estimate the lifespan, which is stored in a database. This lifespan calculation may be performed by the control device 116, or the control device 116 may be configured to access the results of calculations performed by a server on the Internet. This allows the user to know the approximate life span of the product (thermal electron source: filament 11) when used at the rated current.

However, the current of the electron beam to be used varies depending on the user's application, and the circumstances in which the electron beam generator 10 and the scanning electron microscope 100 are placed also vary. Since the wear rate of the filament changes successively depending on these usage environments, the service life as the calculation result and the function used for the calculation can be updated as needed. In other words, data on how long it took each user to reach the end of life of the thermionic source (historical data: rated current information during use, filament properties (shape, electrical characteristics, size, constituent materials, etc.) ) and usage time until the end of life) can be added to the database at any time and updated. With these, the more data is accumulated, the more accurate the life expectancy can be predicted. Also, if the user uses the electron beam generator 10 at a current of 80% of the rated current (which becomes history data), the service life data downloaded from the database is appropriately corrected based on the history data (corrected by the controller 116). history data may be transmitted to the file server for correction) and presented to the user (remaining life is displayed on the display screen).

The life of the thermoelectron source predicted as described above can be notified to the user at any time. For example, the display of a personal computer connected to controller 116 can be used to display life as a number. A display such as an LED or a sound generator such as a buzzer may be attached to the outside of the electron beam generator 10 or the outside of the scanning electron microscope 100 to provide a function to notify that the remaining life is short. Alternatively, the user can be notified of the life as a numerical value or that the life is short by electronic means such as e-mail or short message through the Internet line connected to the control device 116 .

(2) Examples

<Example 1>
Example 1 relates to a configuration in which the cross-sectional area of the tip portion of the filament is made smaller than that of the non-tip portion.

In Example 1, thermoelectron sources having filaments having various ratios of the cross-sectional area of the tip portion to the cross-sectional area of portions other than the tip portion were fabricated. Specifically, a thin wire immersed in an etchant made of an alkaline solution containing ferricyanate is brought into contact with the filament tip of a commercially available thermionic electron source from the direction opposite to the filament tip. It was made by Various changes in the cross-sectional area ratio were realized by changing the contact time. After contacting the wire, the tip of the filament was washed with water and alcohol to remove the etchant. Such a thermionic electron source can also be produced by simply immersing the tip of the filament in an etchant consisting of an alkaline solution containing ferricyanate. It can also be produced by masking the portion other than the tip of the filament and using a physical etching method such as ion etching.

The thermionic electron source thus prepared was attached to a scanning electron microscope 100, and the DC power supply 111 was adjusted so as to continuously generate a constant electron beam current. .

FIG. 4 is a diagram showing the relationship between the average distance from the center of the filament to the breaking position and the cross-sectional area ratio for filaments having different cross-sectional area ratios. When the cross-sectional area of the tip portion and the cross-sectional area of the portion other than the tip portion were equal, that is, when the cross-sectional area ratio was 1, the fracture position was about 400 μm away from the center of the filament. That is, when the cross-sectional area ratio is 1, the temperature of the filament other than the tip is higher than that of the tip, and the temperature of the filament other than the tip is unnecessarily increased. On the other hand, as the cross-sectional area ratio was decreased, the fracture position approached the center of the filament. In particular, when the cross-sectional area ratio was reduced to 0.81, the average distance from the center of the filament to the breaking position decreased sharply. In addition, the variation in fracture position also decreased sharply. When the cross-sectional area ratio was 0.81, the average distance from the center of the filament to the fracture position was 40 μm or less, which was about 1/10 of that when the cross-sectional area ratio was 1. When the cross-sectional area ratio was 0.81 or less, the average distance from the center of the filament to the fracture position slightly decreased. When the cross-sectional area ratio is 0.81 or less, it can be safely said that breakage occurred almost at the tip, and it can be seen that the tip of the filament had the highest temperature.

FIG. 5 is a diagram showing the average and standard deviation of the time required for each filament in FIG. 4 to break. When the cross-sectional area ratio is reduced to 0.81, as described above, the temperature of the filament is not increased unnecessarily, and the tip of the filament reaches the highest temperature, which prevents the filament from breaking. The time it takes to reach the end, that is, the life span has become longer. In addition, the standard deviation of the service life was also reduced because the variation in the fracture position was reduced. On the other hand, when the cross-sectional area ratio is less than 0.49, portions other than the tip of the filament are not heated unnecessarily, and although the tip of the filament reaches the highest temperature, the tip of the filament is worn. Faster and shorter life.

In order to verify the effect of making the cross-sectional area of the tip of the filament smaller than the cross-sectional area of the portion other than the tip, the temperature distribution of the filament was calculated by the finite element method simulation. FIG. 6 is a diagram showing the result of filament temperature distribution calculation by finite element method simulation in Example 1. FIG. The dashed line in FIG. 6 shows the temperature profile calculated in a model that simulates a case where the cross-sectional area ratio is 1 and the maximum temperature is at a position about 400 μm away from the center of the filament. In contrast, the solid line shows the temperature profile calculated by changing only the filament shape in this model and setting the cross-sectional area ratio to 0.81. In the latter case, the maximum temperature is almost at the center of the filament, which supports the results of FIGS. 4 and 5 described above.

<Example 2>
Example 2 relates to a form in which the non-tip portion of the filament is covered with a covering material.

In Example 2, a thermoelectron source having a filament coated with a paint containing silicon oxide, zirconium oxide, chromium oxide, and iron oxide as main components, a so-called black body paint (paint 1), except for the tip. made. This was produced by applying paint to the portion other than the tip portion of the filament of a commercially available thermionic electron source, and baking and drying it. Similarly, in place of paint 1, a carbon black paint (paint 2), a black paint containing titanium oxide as a main component (paint 3), a black paint containing copper oxide, iron oxide, manganese oxide, and cobalt oxide as main components (Paint 4) was used to fabricate a thermionic electron source having a filament that was coated except for the tip.

A performance test similar to that of Example 1 was performed on the thermoelectron source thus produced. FIG. 7 is a diagram showing the results of performance tests. In FIG. 7, the result without coating is the same as the result of Example 1 when the cross-sectional area ratio is 1. Compared to the results without coating, the average distance from the center of the filament to the break point decreased sharply for the filaments coated with paints 1 to 4 except for the tip. In addition, the variation in fracture position also decreased sharply. In any of the filaments coated with paints 1 to 4 except for the tip, the average distance from the center of the filament to the fracture position is 40 μm or less, which is about 1/10 of that when there is no coating, and the tip is almost the same. It can be safely said that breakage occurred at 100.degree. C., and the tip of the filament was the hottest. In addition, in any of the filaments coated with the paints 1 to 4 except for the tip, the temperature of the filament is not increased unnecessarily, and the tip of the filament reaches the highest temperature. As a result, the time required for the filament to break, that is, the life of the filament was lengthened. In addition, the standard deviation of the service life was also reduced because the variation in the fracture position was reduced.

The emissivity of a tungsten filament is said to be about 0.4, depending on its surface condition. On the other hand, the emissivity of the filaments coated with the paints 1 to 4 is difficult to measure because the coating is applied to a minute part called the filament, but it is estimated to be about 0.7 to 0.95 from the properties of the paint. . In any case, if the portion other than the tip portion of the filament is covered with a material having a higher emissivity than tungsten, heat dissipation from the portion other than the tip portion of the filament will be promoted, and as a result, the tip portion of the filament will be the hottest. can.

In order to verify the effect of covering the portion of the filament other than the tip portion with a material having a high emissivity, the filament temperature distribution was calculated by the finite element method simulation as in the first embodiment. FIG. 8 is a diagram showing the result of filament temperature distribution calculation by finite element method simulation in Example 2. FIG. The dashed line in FIG. 8 shows the result of no coating, and is a temperature profile calculated in a model that simulates the case where the maximum temperature is at a position about 400 μm away from the center of the filament. This is identical to the temperature profile shown by the dashed line in FIG. On the other hand, the solid line indicates that only the emissivity of the filament in this model is changed, the emissivity of the portion other than the tip is set to 0.7, and the tip is made of a material with a higher emissivity than tungsten. It is a temperature profile calculated by simulating a filament coated on the other side. In the latter case, the maximum temperature is almost at the center of the filament, which supports the result of FIG. 7 mentioned above.

(3) Summary (i) In this embodiment, the filament in the electron source includes a first portion defined as a tip portion including a tip facing a sample from which thermoelectrons are emitted, and a non-tip portion other than the tip portion. and a defined second portion. The cross-sectional area of the first portion of the filament is smaller than the cross-sectional area of the second portion. By doing so, the broken portion of the filament that breaks when used as a thermionic electron source can be brought close to the tip of the filament, and variations in the broken position among the plurality of filaments can be suppressed. Since the broken portion can be located near the tip of the filament, it is possible to provide a thermoelectron source with a long life and small variations in life. Also, the user can know the lifetime of the thermoelectron source with high accuracy. Therefore, the utilization efficiency of the device is improved.

In order to suppress variations in the lifetime of the thermionic source, for example, the cross-sectional area of the portion defined as the tip portion of the filament (first portion) and the portion defined as the non-tip portion of the filament (second The filament can be configured such that the ratio of the cross-sectional area of the portion) is 0.49 or more and 0.81 or less.

(ii) Alternatively, the second portion of the filament may be coated with a material having a higher emissivity than the material forming the filament. Also by doing so, the broken portion of the filament to be broken when used as a thermoelectron source can be brought close to the tip of the filament, and variations in the broken position among the plurality of filaments can be suppressed. Since the broken portion can be located near the tip of the filament, it is possible to provide a thermoelectron source with a long life and small variations in life. Also, the user can know the lifetime of the thermoelectron source with high accuracy. Therefore, the utilization efficiency of the device is improved. In addition to making the cross-sectional area of the first portion smaller than the cross-sectional area of the second portion, the second portion may be coated with a material having a higher emissivity than the filament material.

In order to suppress the variation in the lifetime of the thermionic source, for example, carbon, silicon oxide, titanium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, and copper oxide are used as materials with a higher emissivity than the material constituting the filament. Alternatively, a coating containing at least one material selected from zirconium oxide can be used.

(iii) A charged particle beam system can be configured by a charged particle beam device having an electron source having a filament having the above characteristics and a computer. At this time, the computer (which may be a computer directly connected to the charged particle beam device or a file server connected via a network) stores information on the life of the electron source (database) corresponding to multiple types of properties of the filament. ) and predicts and notifies the life of the electron source (for example, the life when the rated current is used) based on the input filament shape or electrical characteristics. In addition, the computer has a learning model that outputs information on the life of the electron source corresponding to the shape or electrical characteristics of the filament, acquires the usage history including the current value when the electron source is in use, and stores the usage history Based on this, the remaining life of the filament in use may be predicted, and the predicted value may be presented to the user.

REFERENCE SIGNS LIST 10 Electron beam generator 11 Filament 12 Insulator 14 Wehnelt electrode 15 Anode 17 Part of removed filament tip 18 Part other than tip of filament covered with high emissivity material 100 Scanning electron microscope 111 DC power supply 115 measuring instrument 116 control device 117 terminal A
118 terminal B
119 Acceleration voltage power supply 141 Wehnelt electrode power supply 21 First focusing lens 22 Second focusing lens 23 First deflection coil 24 Second deflection coil 25 Objective lens 26 Sample 27 Detector 28 Exhaust means 29 Exhaust means 211 Power supply for focusing lens 231 Deflection coil power source 251 objective lens power source 31 electron beam 41 vacuum gauge

Claims (8)

An electron source that emits thermoelectrons by energizing and heating a filament,
The filament includes a first portion defined as a tip portion including a tip facing a sample from which the thermoelectrons are emitted, and a second portion defined as a non-tip portion other than the tip portion,
An electron source, wherein the cross-sectional area of the first portion of the filament is smaller than the cross-sectional area of the second portion. In claim 1,
The electron source, wherein the ratio of the cross-sectional area of the first portion to the cross-sectional area of the second portion is 0.49 or more and 0.81 or less. An electron source that emits thermoelectrons by energizing and heating a filament,
The filament includes a first portion defined as a tip portion including a tip facing a sample from which the thermoelectrons are emitted, and a second portion defined as a non-tip portion other than the tip portion,
The electron source, wherein the second portion of the filament is coated with a material having a higher emissivity than the material forming the filament. In claim 3,
The material having a higher emissivity than the material constituting the filament contains at least one material selected from carbon, silicon oxide, titanium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, or zirconium oxide. , the electron source. A charged particle beam apparatus comprising the electron source according to any one of claims 1 to 4. A charged particle beam device according to claim 5;
a computer that provides information on the lifetime of the electron source to the charged particle beam device;
The computer holds information on the lifetime of the electron source corresponding to a plurality of types of properties of the filament, and executes processing for predicting and notifying the lifetime of the electron source based on the shape or electrical characteristics of the input filament. , charged particle beam system. In claim 6,
A charged particle beam system, wherein the computer holds information about the lifetime of the electron source when using the filament at rated current. In claim 6,
The computer has a learning model that outputs information on the life of the electron source corresponding to the shape or electrical characteristics of the filament, acquires a usage history including a current value when the electron source is in use, and based on the usage history a charged particle beam system for predicting the remaining life of the filament in use and presenting the results of the prediction.

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