Electron beam application device

Abstract

An electron beam application device according to the present invention is characterized by comprising: a photocathode 1 provided with a photoelectric film 10; a cathode heater 2 for heating the photocathode 1; an atomic hydrogen generating means 4 for generating atomic hydrogen by dissociating a hydrogen molecule; control means 7, 8 for controlling the surface cleaning of the surface of the photoelectric film 10; and a measuring means 18 for measuring the probe value of an electron beam probe 27 emitted from the photocathode 1. The present invention is further characterized in that, when the probe value measured by the measuring means 18 is lower than a predetermined value, the control means 7, 8 determine a surface cleaning condition of the photoelectric film 10, control the cathode heater 2 and the atomic hydrogen generating means 4 under the determined surface cleaning condition, and perform the surface cleaning of the surface of the photoelectric film 10.

Description

Electron beam application equipment

[0001] The present invention relates to an electron beam application device such as an electron microscope.

[0002] High-resolution electron microscopes require a monochromatic electron source with high brightness and a narrow energy spread of the emitted electron beam. Photoexcitation electron sources utilizing negative electron affinity (NEA) have the advantage of an extremely narrow energy spread and monochromaticity that surpasses that of previous high-performance electron sources, as well as high brightness. Furthermore, because short pulsed electron beams can be easily obtained by pulsing the excitation light, they are also useful for time-resolution measurements.

[0003] The photocathode that emits the electron beam in this photoexcited electron gun has a GaAs surface. A process called NEA (Natural Energy Actuator) activation (NEA) is used to create a low-work-function surface on the GaAs surface by adsorbing Cs and oxygen. In actual devices, a surface cleaning process is essential to remove oxides and carbides from the surface that may form during the initial state of the photocathode immediately after insertion into the electron gun or due to gas adsorption during operation within the electron gun. As disclosed in Patent Document 1, this process involves heating the photocathode and irradiating its surface with atomic hydrogen, which is dissociated from hydrogen molecules. To introduce hydrogen, as shown in Patent Document 1, hydrogen gas is introduced from a hydrogen cylinder by manually operating a variable leak valve and reducing the pressure.

[0004] On the other hand, the needle-shaped metal cathodes used in conventional high-brightness electron guns, i.e., field emission electron sources and SE (Schottky emission) electron sources, require constant surface conditions for stable operation, and for this reason, the electron gun is maintained in an ultra-high vacuum atmosphere. However, gas is emitted by electron beam impact and gas flows in from the sample chamber. In particular, when carbon atoms adsorb onto the cathode, they form carbides with materials such as W that make up the electron source, which cannot be easily removed, resulting in a decrease in probe current and an increase in noise.

[0005] Patent Document 2 discloses a method for reducing and removing adsorbed carbon on the surface of a needle-shaped electron source by irradiating it with atomic hydrogen, and also discloses a method for introducing hydrogen, in which hydrogen is generated by heating a hydrogen storage alloy, and a method for heating a hydrogen-permeable membrane such as Pd inserted between a vessel containing hydrogen and a vacuum chamber.

[0006] JP 2002-313273 A JP 2007-172862 A

[0007] In conventional photoexcitation electron guns, the surface cleaning process of the photocathode is performed manually, which means the activation process takes more than an hour, and the variable leak valve requires skilled operation, making it difficult for users of electron beam application equipment to use. Furthermore, in conventional electron guns using needle-shaped metal cathodes, the process of removing carbon and other contaminants from the surface of the photocathode must be started manually, which limits the continuous time that observations can be performed with high brightness and stable current.

[0008] An electron beam application device according to one embodiment of the present invention comprises a photocathode equipped with a photoelectric film, a cathode heater for heating the photocathode, atomic hydrogen generating means for dissociating hydrogen molecules to generate atomic hydrogen, control means for controlling surface cleaning of the surface of the photoelectric film, and measurement means for measuring the probe value of the electron beam probe emitted from the photocathode, and is characterized in that when the probe value measured by the measurement means falls below a predetermined value, the control means determines surface cleaning conditions for the photoelectric film and controls the cathode heater and atomic hydrogen generating means according to the determined surface cleaning conditions to perform surface cleaning of the surface of the photoelectric film.

[0009] According to the present invention, the surface cleaning of photocathodes and needle-shaped cathodes can be performed automatically in a short time with good reproducibility and without requiring skill, making it possible to form an electron gun that can obtain a stable probe current for a long period of time, and resulting in an easy-to-use electron beam application device.

[0010] FIG. 1 is a schematic diagram of an electron beam application device using a photoexcited electron gun according to Example 1 of the present invention. FIG. 2 is a time course diagram of the operation of each component during surface cleaning according to Example 1 of the present invention. FIG. 3 is a flowchart of automatic surface cleaning according to Example 1 of the present invention. FIG. 4 is a history diagram of probe current values ​​(Ip) according to Example 1 of the present invention. FIG. 5 is a flowchart of operation of an electron beam application device using a photoexcited electron gun according to Example 1 of the present invention. FIG. 6 is an example of hydrogen generation means according to Example 1 of the present invention. FIG. 7 is an example of hydrogen generation means according to Example 1 of the present invention. FIG. 8 is a schematic diagram of an electron beam application device using a needle-shaped electron source according to Example 2 of the present invention. FIG. 9 is a flowchart of operation of an electron beam application device using a needle-shaped electron source according to Example 3 of the present invention. FIG. 10 is an example of hydrogen generation means according to Examples 1 to 3 of the present invention.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are designated by the same reference numerals, and detailed description of overlapping parts will be omitted.

[0012] FIG. 1A is a schematic diagram of an electron beam application device using a photoexcited electron gun according to a first embodiment of the present invention. The photocathode 1 is a transmission-type photocathode with a photoelectric film 10 provided on the surface of a transparent substrate 11, with the electron beam emission surface and the excitation light incidence surface facing opposite directions. The photocathode 1 can be positioned in two positions: an electron gun position on the right side of FIG. 1A and a surface cleaning position on the left side, using a linear introducer 17. The photoelectric film 10 is made of a material primarily consisting of single-crystal GaAs, as described in Patent Document 1. By lowering the work function of the surface and irradiating excitation light from the backside, the photocathode 1 is a highly bright, monochromatic electron beam source that utilizes negative electron affinity (NEA).

[0013] With the photocathode 1 at the electron gun position, excitation light 21 generated from a laser light source 22 is directed by an electron gun controller 19 onto a photoelectric film 10 whose surface has a low work function due to Cs and oxygen, and is transmitted through a window 23 at the top of a vacuum vessel 29 and irradiated onto a small area by a condenser lens 20. The electrons emitted as a result are accelerated between the electron gun 15 and the extraction electrode 26 to form an electron beam probe 27, which passes through an aperture 28 from the electron gun 15 and enters an electron optical system column 30 and is used as a microscope.

[0014] The electron optical system column 30 contains a sample 50 to be measured, a secondary electron detector 51, and electron optical components 52. The electron optical components 52 control an electron beam probe 27 consisting of an electron lens, a deflector, and the like. The elements of the electron optical system column 30, namely the secondary electron detector 51, the electron optical components 52, the sample 50, and the electron gun controller 19 controlled by the system control device 8, function as an electron microscope that uses the electron beam probe 27 to observe the microstructure of the surface of the sample 50. This electron optical system column 30 is typically used as a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.

[0015] The energy of the electron beam probe 27 is determined by the potential of the photocathode 1. The photocathode 1 is in electrical contact with a cathode contact (not shown), and an acceleration voltage (V0) is applied to it from an external power supply (not shown) in response to instructions from the electron gun controller 19. The energy of the electron beam probe 27 is determined by this acceleration voltage (V0). The emission current emitted from the photocathode 1 is monitored on the power supply side.

[0016] Furthermore, a probe current measuring means 18 is disposed within the electron optical system column 30, which monitors the probe current value (Ip) of the electron beam probe 27 and communicates the value to the system control device 8. The probe current measuring means 18 is composed of, for example, an aperture 39 and a current detector 38, and measures the current due to electrons irradiating the aperture 39 with a portion of the electron beam probe 27 that spreads from the center of the orbit.

[0017] The work function of the surface of the photoelectric film 10 is reduced by depositing Cs by heating the Cs source 9 with current and introducing oxygen gas by the oxygen generating means 5, which is called the surface activation process. These processes are controlled automatically by electrical signals from the surface controller 7.

[0018] Increasing the brightness of the electron beam probe 27 is extremely important because it leads to higher resolution and shorter observation time for the electron microscope. To achieve this, it is essential to make the surface of the photoelectric film 10 a clean GaAs surface free of oxides and carbides before surface activation. In the present invention, the photocathode 1 is placed at the surface cleaning position using a linear introducer 17, and the removal of oxides and carbides using atomic hydrogen is automated. The surface cleaning system consists of the cathode heater 2, atomic hydrogen generator 4, hydrogen generating means 3, and heating element (hydrogen heater) 6 shown in FIG. 1A, which are operated by electrical signals from a surface controller 7.

[0019] FIG. 1B is a timeline diagram of the operation of each component during surface cleaning according to Example 1 of the present invention. The cathode heater 2 is energized to heat the photocathode 1, raising its temperature (Tc) from 400°C to 500°C. The hydrogen generating means 3 generates hydrogen by heating, and is heated to the H2 source temperature (Th2) by the heating element (hydrogen heater) 6 to the desired pressure. As a result, the gas pressure (P) within the electron gun increases. At the same time, the W filament (HC (hydrogen cracking) heater) of the atomic hydrogen generator 4 is energized and heated to the HC heater temperature (Thc), dissociating hydrogen molecules to generate highly reactive atomic hydrogen. This HC heater temperature is selected from the range of 1800°C to 2000°C. This state is maintained for an automatically determined surface cleaning time (tcl), after which the current values ​​are stopped and both the temperature and pressure return to their original values.

[0020] These surface cleaning conditions are automatically set by the surface controller 7 and the system control device 8. In conventional devices, this process was performed manually, and the temperature increase process for each heater could not be performed simultaneously but was performed sequentially, which required a long time. However, in the present invention, the processes can be performed simultaneously, which has the advantage of shortening the process time.

[0021] FIG. 2A is a flowchart of automatic surface cleaning according to Example 1 of the present invention. This process is primarily performed by signals from the surface controller 7. Initially, since conditions vary depending on the surface history of the photocathode 1, if there is a probe current value (Ip) measured under standard conditions when the emission current increases due to activation or Cs addition, the surface cleaning conditions are determined based on the history of this probe current value (Ip). The history of the probe current value (Ip) is a record of the probe current value (Ip) after activation or Cs addition, and in this example, is stored in the storage of the system control device 8. Note that the probe current value (Ip) varies depending on the acceleration voltage (V0) and the intensity of the excitation light 21, so it is determined by measuring the current value under constant acceleration and constant excitation light intensity, i.e., standard conditions. In practice, even if the acceleration voltage (V0) or the intensity of the excitation light 21 is different, the probe current value (Ip) measured under those conditions may be converted to the acceleration voltage and excitation light intensity under standard conditions and used. Alternatively, if the conditions are stable, conversion may be performed from the value of the emission current from the photocathode 1. If the photocathode 1 is new and there is no measured probe current value (Ip), the surface cleaning conditions are set to the initial values.

[0022] Next, the power to the cathode heater 2, HC heater (W filament of the atomic hydrogen generator 4), and heating element (hydrogen heater) 6 is controlled to achieve the set surface cleaning conditions, and these are maintained for the set predetermined time (tcl), after which the power to each heater is stopped and the process is completed.

[0023] The surface cleaning conditions are determined as follows. In the case of a new photocathode 1 with a protective film formed on the surface in a crystal growth apparatus, a clean surface can be obtained with light surface cleaning. The surface cleaning conditions in this case are, for example, hydrogen pressure (P): 1×10^-4 Pa, HC heater temperature (Thc): 1800°C, cathode temperature (Tc): 400°C, and surface cleaning time (tcl): 10 to 20 minutes [Condition 1].

[0024] FIG. 2B is a history diagram of the probe current value (Ip) according to Example 1 of the present invention. After replacing the photocathode 1, if the surface of the photoelectric film 10 is only slightly contaminated, the probe current value (Ip) remains almost unchanged even after activation or Cs addition. This region is indicated by A in FIG. 2B. When the surface of the photoelectric film 10 becomes slightly contaminated with oxides or carbides, the probe current value (Ip) gradually decreases even after activation or Cs addition. This region is indicated by B in FIG. 2B. Furthermore, when a sample containing a large amount of gas is observed in the electron optical system column 30, the probe current value (Ip) decreases significantly. This region is indicated by C in FIG. 2B. When the probe current value (Ip) falls below a predetermined value (Ic), it is determined that surface cleaning is necessary.

[0025] When the surface of the photoelectric film 10 gradually becomes contaminated and the probe current value (Ip) falls below a predetermined value (Ic), the surface cleaning conditions are, for example, hydrogen pressure (P): 2×10^-4 Pa, HC heater temperature (Thc): 1900°C, cathode temperature (Tc): 400°C, and surface cleaning time (tcl): 20 minutes (Condition 2). Furthermore, when the rate of decrease in the probe current value (Ip) is large due to dense oxygen gas adsorption on the surface of the photoelectric film 10, stronger surface cleaning conditions are selected, for example, hydrogen pressure (P): 2×10^-4 Pa, HC heater temperature (Thc): 2000°C, cathode temperature (Tc): 500°C, and surface cleaning time (tcl): 20 to 30 minutes (Condition 3).

[0026] FIG. 3 is a flowchart of the operation of an electron beam application device using a photoexcited electron gun according to the first embodiment of the present invention. First, the photocathode 1 is moved to the surface cleaning position. This is achieved by applying an electrical signal from the surface controller 7 to the power of the linear introducer 17. Next, the automatic surface cleaning process shown in FIG. 2A is performed. If the photocathode 1 is new, the surface of the photoelectric film 10 is first cleaned under the above-mentioned [Condition 1]. Next, the photocathode 1 is moved to the electron gun position by the linear introducer 17, and the surface of the photoelectric film 10 is activated using Cs and oxygen. Electron beam emission is achieved by irradiating the photocathode 1 with excitation light 21. A predetermined acceleration voltage (V0) is then applied to the photocathode 1 to emit an electron beam, generating an electron beam probe 27. The probe current measurement means 18 of the electron optical system column 30 measures the probe current (Ip) at random or continuously. If the probe current (Ip) is above a predetermined value, electron beam emission continues, and sample observation, etc., is performed.

[0027] When measurement is completed in the electron optical system column 30, the electron beam is stopped and the measurement is terminated. If the probe current value (Ip) decreases while measurement is continuing, the Cs source 9 is energized and Cs is added. If this causes the probe current value (Ip) to recover to a predetermined value or higher, electron beam emission is continued. If the probe current value (Ip) does not reach the predetermined value, surface cleaning is required, and in this case electron emission must be interrupted, so a GUI display on the display of the electron beam application device indicates that surface cleaning (cleaning) is required. If image acquisition is in progress, this is simply displayed continuously. After image acquisition is completed, the electron beam is stopped, and if measurement is not completed, the photocathode 1 is moved to the surface cleaning position and automatic surface cleaning is performed.

[0028] In this case, the surface controller 7 retrieves the historical data of the probe current value (Ip) from the storage of the system control device 8 as shown in Fig. 2A, and selects the aforementioned [Condition 1], [Condition 2], [Condition 3], or an intermediate condition, as shown in Fig. 2B, to perform automatic surface cleaning. Due to the system configuration, this selection is made by the system control device 8, and the result can be communicated to the surface controller 7, with the same effect being achieved.

[0029] 4A shows an example of the hydrogen generation means 3. A cylindrical hydrogen storage alloy 12 with a hole in the center is provided as the hydrogen generation means 3 in a vacuum in which an electron gun 15 is provided inside a vacuum vessel 29. A heating element (hydrogen heater) 6 is inserted into the hole in the hydrogen storage alloy 12 from the atmosphere side outside the vacuum vessel 29, and when electricity is applied to the wiring 13 of the heating element (hydrogen heater) 6, the temperature of the hydrogen storage alloy 12 rises and hydrogen is generated.

[0030] The H2 source temperature (Th2) may be determined to be constant by measuring the hydrogen pressure in advance so as to generate the desired hydrogen pressure (P). In this case, the desired hydrogen pressure can be reproduced by simple conditions such as the power or current value of the heating element (hydrogen heater) 6. A non-evaporative getter material may be used as the hydrogen storage alloy 12. A cartridge heater or the like is used as the heating element (hydrogen heater) 6. The H2 source temperature (Th2) varies depending on the type and amount of alloy, but is selected from the range of 200°C to 700°C.

[0031] The same effect can be obtained if the heating element (hydrogen heater) 6 is in contact with the hydrogen storage alloy 12 in the vacuum of the vacuum vessel 29 as shown in Figure 4B. In this case, the wiring 13 of the heating element (hydrogen heater) 6 is drawn to the outside of the vacuum vessel 29 by a feedthrough 14. Furthermore, the same effect can be obtained if, instead of the hydrogen storage alloy 12, aluminum or magnesium hydride is used as the hydrogen generating means 3 and hydrogen is generated by heating these through thermal decomposition.

[0032] 4C, the hydrogen generating means 3 may be configured such that a gas container 24 is filled with a hydrogen-containing gas and connected to a vacuum container 29 in which an electron gun 15 is installed via vacuum piping 16 separated by a hydrogen-permeable membrane 25, and the hydrogen-permeable membrane 25 is heated by a heating element (hydrogen heater) 6. The hydrogen-permeable membrane 25 may be made of a metal such as Pd, Ta, Nb, or V. In this case, the H source temperature (Th2) is the heating temperature of the hydrogen-permeable membrane 25 and is selected from the range of approximately 150°C to 300°C.

[0033] Since the vacuum pipe 16 is connected to a vacuum vessel 29 with an ultra-high vacuum atmosphere, it is recommended to degas it by baking at about 200°C before use. Because the hydrogen-permeable membrane 25 often has good hydrogen permeability at about 200°C, when it is desired to control the gas pressure at temperatures higher than 200°C and when safety in the event of a gas leak is taken into consideration, it is easier to use the gas filled in the gas vessel 24 if it is diluted with an inert gas such as Ar rather than 100% hydrogen. The degree of dilution is selected such that the volume of the inert gas is, for example, 10 to 10,000 parts by volume of hydrogen per part by volume.

[0034] In this embodiment, the linear introducer 17 moves the position of the photocathode 1 using an electrical signal, and is powered by conventional means such as compressed air, a motor, etc. Alternatively, the linear introducer 17 may be manually repositioned so that the position of the photocathode 1 can be changed according to instructions on the GUI display on the display of the electron beam application device. This can be easily performed without requiring the operator to be skilled, and has the similar effect of providing an electron beam application device that is easy to use.

[0035] In this embodiment, the electron beam emitted from the photocathode 1 is highly bright and uniform in energy, contributing to high-resolution, high-speed measurements in an electron microscope. Furthermore, if a short-pulse laser light source 22 is used, a pulsed electron beam can be obtained without adding components to the electron optical system, making it useful for measurements such as time resolution. In this embodiment, the hydrogen emission from the hydrogen generating means 3 is controlled by the power of the heating element (hydrogen heater) 6, as shown in FIG. 2A. However, the same effect can be achieved by monitoring the degree of vacuum in the vacuum vessel 29, where the electron gun 15 is installed, and controlling the amount of power supplied to the heating element (hydrogen heater) 6 to keep it constant.

[0036] In this embodiment, surface cleaning is performed on the photocathode 1 at the surface cleaning position, and surface activation with Cs and oxygen is performed at the electron gun position, but surface activation may also be performed at the surface cleaning position. Also, by arranging the various elements so that surface cleaning can be performed at the electron gun position, the linear introducer 17 for moving the photocathode 1 can be omitted.

[0037] According to this embodiment, in an electron beam application apparatus using a photoexcited electron source that uses a photocathode as the electron gun, surface cleaning to prevent instability of the probe current can be automated, so that anyone can use the electron gun in an easy-to-use manner, and in an electron beam application apparatus using this, sample observation can be performed stably for a long period of time.

[0038] 5 is a schematic diagram of an electron beam application device using a needle-shaped electron source according to a second embodiment of the present invention. The FE electron source 37 is a field emission electron source that emits electrons by concentrating an electric field at the tip of a needle-shaped metal 31, and is configured such that the needle-shaped metal 31 is mounted on a stem 33 via a filament 32. A typical W metal is used for the needle-shaped metal 31. The stem 33 has two electrodes (F1, F2) with an insulator base and is electrically connected to an electron source controller 34.

[0039] The extraction electrode 26 facing the FE electron source 37 is fixed to the vacuum vessel 29 by an insulator 35 and is electrically connected to an electron source controller 34. The vacuum vessel 29 containing the FE electron source 37 is maintained in an ultra-high vacuum range by a vacuum pump (not shown). Also provided are an atomic hydrogen generator 4 as a means for generating atomic hydrogen, hydrogen generating means 3, a heating element (hydrogen heater) 6, and an atomic hydrogen controller 36.

[0040] In a conventional method of use, the needle-shaped metal 31 is heated to approximately 2000°C or higher before generating the electron beam to remove oxides and carbides adhering to the surface. To achieve this, a process called flashing is performed in which current is momentarily passed between the electrodes (F1, F2) to heat the filament 32 to a high temperature and heat the needle-shaped metal 31. Next, an acceleration voltage (V0) is applied to the electrodes (F1, F2) and an extraction voltage is applied to the extraction electrode 26, and electrons emitted from the needle-shaped metal 31 are guided to the electron optical system column 30 as the electron beam probe 27 and used to observe the sample 50.

[0041] When hydrogen gas remaining in the vacuum chamber 29 is adsorbed onto the surface of the needle-shaped metal 31 and the probe current value (Ip) of the electron beam probe 27 decreases, a process called mild flushing is performed in which a power lower than that used for flushing is momentarily supplied between the electrodes (F1, F2) to bring the temperature of the needle-shaped metal 31 to about 1000°C or less, thereby removing the hydrogen gas adsorbed on the surface. This process takes an extremely short time, on the order of 0.01 seconds to several seconds. This restores the probe current value (Ip).

[0042] However, in the case of long-term operation, gases other than hydrogen gas, such as those containing carbon, may enter the system, and mild flushing cannot remove the surface adsorption, resulting in a decrease in the probe current (Ip) and an increase in noise. To eliminate this, high-temperature flushing at approximately 2000°C is performed, but this also causes the migration of W atoms, changing the shape of the tip of the needle-like metal 31. As a result, changes in the extraction voltage and the conditions in the electron optical column 30 are required, making this system inconvenient and unsuitable for long-term automatic measurement.

[0043] FIG. 6 is a flowchart of the operation of an electron beam application device using a needle-shaped electron source according to a second embodiment of the present invention. In this embodiment, atomic hydrogen generating means (3, 4, 6) and an atomic hydrogen controller 36 are provided, and the device is automatically operated in a high-brightness state. FIG. 6 shows an example of operation after high-temperature flashing. First, electron emission is initiated and SEM observation is performed. When the SEM measurement is complete, electron emission is stopped and the device is terminated. This termination of measurement is determined by the user or the system control device performing the automatic measurement. During the SEM measurement, the probe current value (Ip) is monitored as needed by the probe current measuring means 18. If the probe current value (Ip) is equal to or greater than a specified value, the device continues. If the probe current value (Ip) falls short of the specified value, the needle-shaped metal 31 is heated to approximately 1000°C or less in a short period of time. If the probe current value (Ip) recovers, electron emission is continued and SEM observation is continued. This is the same as the conventional mild flashing process.

[0044] If the probe current value (Ip) does not recover, a GUI display on the display of the SEM system control device 8 indicates the need for surface cleaning, and a signal is issued from the atomic hydrogen controller 36 to raise the H source temperature (Th2) of the heating element (hydrogen heater) 6 of the hydrogen generation means 3 and the HC heater temperature (Thc) of the W filament (HC heater) of the atomic hydrogen generator 4, thereby generating atomic hydrogen. Next, current is momentarily applied between the electrodes (F1, F2) to raise the filament 32 to a high temperature, and the needle-shaped metal 31 is heated to approximately 1000°C or less for a short period of time under conditions similar to mild flashing. This process is repeated until the probe current value (Ip) recovers to a predetermined value. After recovery, current is stopped to the heating element (hydrogen heater) 6 and the W filament (HC heater) of the atomic hydrogen generator 4, thereby stopping the generation of atomic hydrogen. This removes surface carbides, returning the tip surface of the needle-shaped metal 31 to its original state, and SEM observation can be continued.

[0045] In this example, the surface cleaning process using atomic hydrogen is performed during SEM image observation, but in the case of high-precision measurements where noise and slight current fluctuations must be avoided, the observation may be temporarily stopped as in Example 1. Furthermore, in this example, cleaning was judged based on a decrease in the probe current value (Ip), but adding the amount of fluctuation in the probe current value (Ip), i.e., an increase in noise, to the criteria for judgment has the advantage of further stabilizing the results.

[0046] According to this embodiment, in an electron beam application device using a needle-shaped electron source for the electron gun, surface cleaning to prevent instability of the probe current can be automated, so that anyone can use the electron gun in an easy-to-use manner, and in an electron beam application device using this, sample observation can be performed stably for long periods of time.

[0047] 7 is a schematic diagram of an electron beam application apparatus using a needle-shaped electron source according to a third embodiment of the present invention. The difference from the second embodiment shown in FIG. 5 is that the electron gun 15 is configured with an electron source chamber 40 accommodating the electron source and a differential pumping chamber 41, atomic hydrogen is generated in the differential pumping chamber 41, and atomic hydrogen is supplied to the electron source chamber 40 via an aperture 28 between the electron source chamber 40 and the differential pumping chamber 41.

[0048] As for the control process of the third embodiment, the same effect can be obtained by the flow chart of FIG. 6 of the second embodiment. However, in the third embodiment, the amount of atomic hydrogen entering the electron source chamber 40 is significantly reduced compared to the amount of atomic hydrogen released from the atomic hydrogen generator 4, so it is advisable to increase the hydrogen supply rate. Alternatively, atomic hydrogen can be generated continuously for a long period of time, rather than instantaneously, and the FE electron source 37 can be mildly flushed during this period to remove gas adsorbed on the surface, thereby similarly obtaining a stable probe current value (Ip) for a long period of time. Furthermore, compared to the configuration of the second embodiment shown in FIG. 5 in which atomic hydrogen is directly irradiated onto the FE electron source 37, noise in the probe current value (Ip) is reduced. Furthermore, by limiting the amount of hydrocarbon gases that can contaminate the electron source and adsorb and desorb into the surrounding area and flow into the electron source chamber 40, long-term stability can be achieved.

[0049] In the above-described first to third embodiments, the hydrogen generating means 3 and the atomic hydrogen generator 4, which serve as the hydrogen generation source, have been illustrated as a connected, integrated unit. However, similar effects can be achieved even if they are placed separately as long as hydrogen molecules are supplied to the atomic hydrogen generator 4. An example of this is shown in FIG. 8 . FIG. 8 is a schematic diagram of the cross-sectional structure of the electron gun 15 viewed from above. In the electron gun 15, the electron source portion 43 is located in the center of a cylindrical vessel, and the vacuum vessel 29 is evacuated by an ion pump 42 and a non-evaporable getter pump 44 disposed in the peripheral portion to maintain an ultra-high vacuum. The non-evaporable getter pump 44 is normally operated at room temperature, but generates hydrogen by heating with a heating element (hydrogen heater) 6. This hydrogen spreads throughout the vacuum vessel 29 in which the electron gun 15 is installed, and atomic hydrogen is generated by the atomic hydrogen generator 4, which is separately placed near the electron source portion 43, and can be used to clean the surface of the electron source, achieving the same effects as in the first to third embodiments.

[0050] In addition, in the above-described Examples 1 to 3, a hydrogen cracking heater (HC heater) with a high-temperature W filament was used as the atomic hydrogen generator 4, but any means for dissociating hydrogen molecules will have a similar effect, and for example, atomic hydrogen dissociated by converting hydrogen gas into plasma may be used. It is well known that plasma can be generated by applying high voltage or high frequency, irradiating with laser light, or the like.

[0051] Furthermore, while the above-described first and second embodiments use a W needle-shaped metal 31 as the FE electron source 37, other high-brightness electron sources are also sensitive to surface contamination, and similar effects can be achieved by applying the present invention to them. For example, a Schottky emission (SE) electron source employs a W (100) surface with Zr—O adsorbed and heated, and a high-melting-point conductor such as a metal hexaboride or metal carbide, typically CeB6, can be used as the needle-shaped metal 31, providing similar effects. In particular, when an FE or SE electron source is operated with a constantly heated needle-shaped cathode, long-term stability can be achieved by adjusting the probe current (Ip) to generate atomic hydrogen intermittently or continuously.

[0052] 1: photocathode, 2: cathode heater, 3: hydrogen generating means, 4: atomic hydrogen generator, 5: oxygen generating means, 6: heating element (hydrogen heater), 7: surface controller, 8: system control device, 9: Cs source, 10: photoelectric film, 11: transparent substrate, 12: hydrogen storage alloy, 13: wiring, 14: feedthrough, 15: electron gun, 16: vacuum piping, 17: linear introducer, 18: probe current measuring means, 19: electron gun controller, 20: condenser lens, 21: excitation light, 22: laser light source, 23: window, 24: gas Container, 25: hydrogen permeable membrane, 26: extraction electrode, 27: electron beam probe, 28: aperture, 29: vacuum container, 30: electron optical system column, 31: needle-shaped metal, 32: filament, 33: stem, 34: electron source controller, 35: insulator, 36: atomic hydrogen controller, 37: FE electron source, 38: current detector, 39: aperture, 40: electron source chamber, 41: differential evacuation chamber, 42: ion pump, 43: electron source part, 44: non-evaporative getter pump, 50: sample, 51: secondary electron detector, 52: electron optical component.

Claims

1. An electron beam application device comprising: a photocathode with a photoconductive film, a cathode heater for heating the photocathode, atomic hydrogen generating means for dissociating hydrogen molecules to generate atomic hydrogen, control means for controlling surface cleaning of the surface of the photoconductive film, and measurement means for measuring a probe value of an electron beam probe emitted from the photocathode, wherein when the probe value measured by the measurement means falls below a predetermined value, the control means determines surface cleaning conditions for the photoconductive film and controls the cathode heater and the atomic hydrogen generating means under the determined surface cleaning conditions to perform surface cleaning of the photoconductive film.

2. An electron beam application apparatus according to claim 1, wherein said control means determines the surface cleaning conditions of said photoconductive film based on a history of probe values ​​measured by said measurement means.

3. An electron beam application device as described in claim 2, further comprising a hydrogen generating means for generating hydrogen molecules and a hydrogen heater for heating said hydrogen generating means, wherein said control means controls said hydrogen heater under the determined surface cleaning conditions.

4. The electron beam application device according to claim 2, further comprising a display, and prior to performing surface cleaning of the surface of the photoconductive film, a GUI display is displayed on the display indicating that surface cleaning is required.

5. An electron beam application device as described in claim 2, comprising an electron source chamber housing the photocathode and a differential pumping chamber, wherein the atomic hydrogen generating means is provided in the differential pumping chamber and supplies atomic hydrogen to the electron source chamber through an aperture between the electron source chamber and the differential pumping chamber.

6. An electron beam application device as described in claim 2, further comprising a Cs source, and if the probe value measured by the measurement means does not recover to a predetermined value or higher even after adding Cs from the Cs source, surface cleaning of the surface of the photoconductive film is performed.

7. An electron beam application apparatus according to claim 3, wherein said atomic hydrogen generating means and said hydrogen generating means are disposed separately, and said atomic hydrogen generating means is provided near said photocathode.

8. An electron beam application apparatus comprising a needle-shaped metal, a filament for heating the needle-shaped metal, atomic hydrogen generating means for dissociating hydrogen molecules to generate atomic hydrogen, control means for controlling surface cleaning of the surface of the needle-shaped metal, and measurement means for measuring a probe value of an electron beam probe emitted from the needle-shaped metal, wherein when the probe value measured by the measurement means falls below a predetermined value, the control means determines surface cleaning conditions for the needle-shaped metal, controls the filament and the atomic hydrogen generating means according to the determined surface cleaning conditions, and performs surface cleaning of the needle-shaped metal.

9. An electron beam application apparatus according to claim 8, wherein said control means determines the surface cleaning conditions of said needle-like metal based on a history of probe values ​​measured by said measurement means.

10. An electron beam application apparatus as described in claim 9, further comprising hydrogen generating means for generating hydrogen molecules and a hydrogen heater for heating said hydrogen generating means, wherein said control means controls said hydrogen heater under the determined surface cleaning conditions.

11. The electron beam application device according to claim 9, further comprising a display, and prior to performing surface cleaning of the surface of the needle-shaped metal, a GUI display is displayed on the display indicating that surface cleaning is required.

12. An electron beam application device as described in claim 9, comprising an electron source chamber containing the needle-shaped metal and a differential pumping chamber, wherein the atomic hydrogen generating means is provided in the differential pumping chamber and supplies atomic hydrogen to the electron source chamber through an aperture between the electron source chamber and the differential pumping chamber.

13. An electron beam application apparatus according to claim 10, wherein said atomic hydrogen generating means and said hydrogen generating means are disposed separately, and said atomic hydrogen generating means is provided near said needle-like metal.