WO2015053300A1 - Electron microscope - Google Patents

Electron microscope Download PDF

Info

Publication number
WO2015053300A1
WO2015053300A1 PCT/JP2014/076883 JP2014076883W WO2015053300A1 WO 2015053300 A1 WO2015053300 A1 WO 2015053300A1 JP 2014076883 W JP2014076883 W JP 2014076883W WO 2015053300 A1 WO2015053300 A1 WO 2015053300A1
Authority
WO
WIPO (PCT)
Prior art keywords
electron
electron source
current
emission
flushing
Prior art date
Application number
PCT/JP2014/076883
Other languages
French (fr)
Japanese (ja)
Inventor
大西　崇
渡辺　俊一
Original Assignee
株式会社日立ハイテクノロジーズ
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社日立ハイテクノロジーズ filed Critical 株式会社日立ハイテクノロジーズ
Priority to JP2015541606A priority Critical patent/JP6129982B2/en
Publication of WO2015053300A1 publication Critical patent/WO2015053300A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/073—Electron guns using field emission, photo emission, or secondary emission electron sources
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/245—Detection characterised by the variable being measured
    • H01J2237/24507—Intensity, dose or other characteristics of particle beams or electromagnetic radiation
    • H01J2237/24514—Beam diagnostics including control of the parameter or property diagnosed
    • H01J2237/24535—Beam current

Definitions

  • the present invention relates to an electron microscope.
  • the present invention relates to a cold cathode field emission (Cold-FE) electron gun that generates a particularly bright electron beam and an electron microscope equipped with the Cold-FE electron gun.
  • Cold-FE cold cathode field emission
  • An electron microscope is an observation device that uses an electron beam to obtain an enlarged image of a sample and information on constituent elements.
  • the electron microscope mainly includes an electron gun, an electron optical system, a sample holder, a detector, a control device, and a power supply unit.
  • An electron gun is a device that generates an electron beam.
  • the electron optical system is a device that transports electrons generated by an electron gun and irradiates a sample.
  • the electron optical system also has a function of converging and deflecting an electron beam by an electromagnetic lens.
  • the sample holder is a device that fixes a substance to be observed (that is, a sample) on the electron beam path in the electron optical system, and moves and tilts it as necessary.
  • the electron gun and the electron optical system are maintained in a vacuum in order to pass an electron beam without colliding with air molecules, and are equipped with a vacuum exhaust device for that purpose.
  • Electrons irradiated on the sample generate reflected electrons, secondary electrons, transmitted electrons, scattered electrons, X-rays, and the like due to the interaction with atoms constituting the sample.
  • the detector measures these electrons and X-rays.
  • the power supply unit supplies power necessary for the operation of the electron gun, the electron optical system, the detector, and the like, and performs precise control.
  • the control device controls the power supply, analyzes information obtained by the detector, and processes, displays, or records an enlarged image of the sample and the elemental composition of the sample in an easy-to-see state for the operator.
  • An electron gun generates electrons used for observation as free electrons in a vacuum based on various principles. Furthermore, the generated free electrons are accelerated by the potential difference potential to form a group of electrons having kinetic energy, that is, an electron beam.
  • the electron dose per unit time generated by the electron source in the electron gun is called the emission current. Further, a part of this emission current is taken out through the diaphragm, and irradiated onto the sample to generate probe electrons for obtaining an enlarged image or the like.
  • the probe electron dose per unit time is called a probe current.
  • Cold-FE electron gun which is a kind of electron gun
  • Cold-FE electron guns use tungsten single crystals with sharp tips sharpened by electropolishing as electron sources.
  • An extraction voltage of several kilovolts is applied between the extraction electrode adjacent to the electron source and the electron source. Electric field concentration occurs at the tip of the electron source. Due to this high electric field, electrons due to field emission are emitted from the tip of the electron source.
  • the amount of electron beam emitted is the emission current described above. In the Cold-FE electron source, the emission current is emitted from the electron source within a solid angle range of about 1 steradian.
  • the emission current is influenced by the surface condition of the electron source as well as the extraction voltage (or the electric field strength at the tip of the electron source).
  • the Cold-FE electron source is a tungsten single crystal placed in an electron gun whose residual gas pressure is lowered by a vacuum pump.
  • the work function of the electron source generally decreases. Therefore, the amount of electron beam emission decreases as the residual gas molecules collide with the electron source and are adsorbed.
  • the emission current gradually decreases under a constant extraction voltage.
  • a process for cleaning the surface of the electron source by, for example, re-releasing the adsorbed gas molecules into a vacuum is required. This is achieved by instantaneously heating the single crystal. Therefore, many Cold-FE electron guns are cleaned by heating the electron source by welding the electron source to the filament tip and heating the filament for a short time. This is called flushing. When flushing is performed, the tip of the electron source is cleaned. In the Cold-FE electron gun, this flushing is performed periodically to obtain a constant emission current. The required flushing frequency varies with the residual gas pressure in the electron gun.
  • the Cold-FE electron gun requires flushing of the electron source.
  • the electron source flushing maintains the cleanness of the tip of the electron source, and a stable emission current can be obtained.
  • the flushing causes movement (drift) of the tungsten atoms at the tip of the electron source due to heat, so that the physical shape of the tip gradually changes each time flushing is repeated. This change is usually due to the attractive force acting between the atoms in the crystal, causing the physical shape of the sharply pointed tip to gradually round (this is the “rounding” of the electron source tip. Called).
  • the radius of curvature of the electron source tip gradually increases, and as a result, the electric field concentration at the electron source tip is weakened.
  • the extraction voltage for obtaining the same emission current or probe current increases.
  • the extraction voltage gradually increases over the usage period of the electron gun. If this extraction voltage exceeds the limit voltage of the electron gun (determined by the power supply capability and the insulation performance within the wiring and the electron gun), sufficient probe current cannot be obtained from this electron source, and the electron source must be replaced. Necessary.
  • the strength of flushing can be adjusted as the amount of current flowing through the filament.
  • the electron source By passing more current, or for a relatively long period of time, the electron source becomes hotter “strong flushing”. At this time, the tip of the electron source is further cleaned, but the degree of rounding is large.
  • the temperature at the tip of the electron source becomes relatively low, resulting in “weak flushing” with less rounding per flushing.
  • the tip is not sufficiently cleaned. In such a case, the extraction voltage required for extracting the same emission current becomes high, or the field emission becomes unstable and the probe current largely fluctuates in a short time. An observation image cannot be obtained.
  • the required flashing strength is defined as the filament current
  • the flushing with sufficient strength is performed in advance at a frequency that is considered sufficient in advance, so that both the cleaning of the electron source and the lifetime of the electron source are achieved. I was planning.
  • the flushing period during the operation of the electron gun is performed by the user judging whether the probe current is not reduced or unstable, or whether a good observation image is obtained.
  • the problem to be solved is that an electron microscope user or an electron microscope control device obtains an appropriate flashing timing and flashing strength in an electron microscope equipped with a Cold-FE electron gun.
  • the present invention adopts the configuration described in the claims to solve the problem.
  • the emission current which is the total current obtained by field emission from the electron source, is measured, and the measured value is used to indicate the appropriate flashing time and intensity to the user, or automatically Implement appropriate flushing.
  • the Cold-FE electron gun of the present invention can obtain a more stable probe current without replacing the electron source for a longer period of time by performing flushing with an appropriate intensity at an appropriate time. As a result, it is possible to obtain an electron microscope that does not require maintenance for a long time and can obtain a higher quality observation image.
  • the measurement results of the temporal change in the emission current emitted from a clean electron source or an electron source with gas molecules attached are shown, and in the embodiment of the invention, which is used to distinguish between a clean electron source and an electron source with gas molecules attached It is a measurement result and explanatory drawing explaining how to carry out.
  • the Example of invention it is the figure which illustrated the display which notified the time of strong flushing and the strong flushing to the user automatically from the temporal change of emission current, and the cleanliness of the electron source.
  • FIG. 1 shows an electron microscope equipped with a Cold-FE electron gun as an example of an embodiment for carrying out the invention.
  • the electron microscope includes an electron gun 1, an electron optical system 2, a sample holder 3, a detector 4, a control device 5, and a power supply unit 6.
  • the electron gun 1 and the electron optical system 2 have vacuum evacuation devices 11 and 21, respectively. However, depending on the scale of the electron microscope, there may be a single vacuum evacuation device. In some cases, a large number of vacuum evacuation devices are provided.
  • the electron gun 1 including the Cold-FE electron source 101 generates an electron beam 10.
  • the electron optical system 2 converges and deflects the electron beam 10 and irradiates the sample 31.
  • the sample holder 3 holds the sample 31 and moves, tilts and exchanges as necessary.
  • the detector 4 measures reflected electrons, secondary electrons, transmitted electrons, scattered electrons, X-rays, etc. generated by the sample 31.
  • the power supply unit 6 supplies power to the electron gun 1 and the electron optical system 2, adjusts the output, and controls the electron beam to a state requested by the operator. Moreover, the information from the detector 4 is converted into a digital signal.
  • the control device 5 controls the electron gun 1 and the electron optical system 2 through the power supply system 6, processes information from the detector 4, and displays or records the information in a form visible to the operator.
  • the power supply system 6 is divided into a control / detection system power supply 61 and an electron gun power supply 62.
  • FIG. 2 shows details of the structure of the Cold-FE electron gun 1 having an acceleration voltage of several hundred kilovolts, which is an embodiment of the present invention.
  • the electron gun 1 includes an electron source 101 (cold cathode field emission electron source), an extraction electrode 103, and an acceleration tube 105.
  • the electron gun 1 is connected to an electron gun power source 62 and is given a high potential.
  • An extraction voltage (V 1 ) of several kilovolts is applied to the extraction electrode 103 by an extraction power source 621.
  • V 1 an extraction voltage
  • the acceleration tube 105 includes a plurality of intermediate electrodes 104, 106, 107, 108, and 109, and the electron beam is further accelerated while passing through the intermediate electrodes.
  • the electron source 101 and the extraction electrode 103 are under a negative high voltage (V 0 ) of several hundred kilovolts by the acceleration power source 623.
  • the anode 110 is at ground potential and is at zero potential. The electron beam is accelerated by this potential difference, and the electrons passing through the anode 110 are electron beams having V 0 energy.
  • the extraction power source 621 has a function of stably applying an extraction voltage to the extraction electrode 103 and a function of measuring a current flowing through the power source.
  • An ammeter 63 is shown in the figure.
  • the extraction electrode is insulated from other electrodes by an insulator, and apart from a minute discharge current, all of the flowing current is due to an emission current due to field emission from the electron source. Therefore, if the current flowing between the extraction electrode and the electron source with the extraction power source is measured by the ammeter 63, this is approximately equal to the emission current. This value is Ie.
  • the extraction power source and the electron gun power source send this current amount Ie as measurement data to the control device 5 shown in FIG. 1 as a digital signal.
  • the control device 5 records this emission current data.
  • the flushing power source 624 is a power source that controls the current flowing through the filament 102 to which the electron source is fixed.
  • the flushing power source 624 supplies current to the filament 102 to which the electron source is fixed.
  • the filament 102 is heated by this Joule heat, the temperature of the electron source 101 rises, and the surface of the electron source 101 is cleaned.
  • the flushing intensity at this time is controlled by the magnitude of the current flowing through the filament, for example, by the control device controlling the flushing power source 624.
  • FIG. 3 shows a typical example of the temporal change in the emission current emitted from the electron source after the flushing and the probe current that has passed through the diaphragm 121.
  • the emission current decreases relatively monotonously, but the probe current maintains (1) a value close to a high constant value for a certain period of time. Thereafter, (2) after a rapid decrease, (3) shift to a low constant value.
  • the emission current is physically an electron beam emitted from a relatively wide area of the electron source surface, whereas the probe current is near the tip of the electron source. And an electron beam emitted from a relatively narrow area emitted from the electron beam. For this reason, the field emission (emission current) from the tip of the electron source consisting of a large number of atoms decreases stably, whereas the probe current shows a relatively unstable behavior, and the increase / decrease stepwise. It may be seen.
  • the region on the electron source involved in the generation of the probe current is narrow, and only a relatively small number of atoms on a specific crystal plane contribute to the emission, so the probe current varies widely due to the stochastic effect of residual gas molecules. It is thought that it is to do.
  • the probe current starts to decrease sharply.
  • the amount of current also fluctuates unstable. This can be determined by measuring the probe current.
  • the timing ( ⁇ 50 ) at which the emission current is reduced to 50% of the emission current Ie 0 immediately after the flushing shown in the figure corresponds to the time when the probe current is almost 80%. Confirmed to do.
  • the electron source can be utilized most effectively if the emission current is measured and flushing is performed at the timing ( ⁇ 50 ) when Ie is reduced to 0.5Ie 0 .
  • the dialog box or the like to recommend flushing when reduced to 50% of the flushing after emission current Ie 0, prompting the flushing user.
  • flushing is performed at the timing when the user removes the seat or replaces the sample to clean the electron source.
  • a display example to the user is shown in FIG.
  • a dialog such as 91 is displayed on the screen of the control device 5 being viewed by the user to prompt the user to flush.
  • the user instructs the control device 5 to perform flushing by a button on the dialog or other method, and cleans the electron source.
  • the control device 5 senses the information and automatically performs flushing. In this case, it is desirable to notify the user by issuing a dialog such as 92 that the flushing has been performed.
  • the elapsed time from the last flushing, the next flushing time, and the current emission current which is a measure of the time until the next flushing, are displayed on the control device 5 in a manner like 93 to alert the user. can do.
  • the last flushing time, the next flushing time expected from the emission current value, and the current emission current Ie value are compared with the initial emission current Ie 0 and displayed in the form of a band graph. .
  • the control device can know the appropriate time for flushing, and can notify the user in an easy-to-understand manner. In response to this information, the control device can prompt the user to perform flushing or automatically perform flushing to keep the electron source in a good state.
  • flushing is performed for cleaning the surface of the electron source. How much flushing is required for cleaning the surface of the electron source depends on the surface condition of the electron source. Depends on. An electron source to which a larger amount of gas molecules is adsorbed needs to be cleaned by strong flushing, but can be cleaned by weak flushing if the amount of attached gas molecules is small. Gas molecule adsorption is thought to depend on the type of residual gas molecules adsorbed on the electron source, and qualitatively lighter atoms (such as hydrogen atoms) are removed from the electron source at a relatively low temperature, but heavy. When molecules (such as hydrocarbons) are adsorbed, strong flushing is required.
  • the temporal change of the probe current will not be standard as shown in the lower part of FIG.
  • the stable region (1) becomes shorter, the unstable region (2) arrives earlier, or the stable region (1) does not appear and a constant value region (3) with low luminance appears immediately after flushing.
  • FIG. 5 shows an example of temporal changes in the emission current corresponding to the state where these electron sources are clean and the state where many gas molecules remain.
  • the time variation of the emission current is recorded in a clean electron source state, it stabilizes at about 1/10 (0.1 Ie 0 ) of the initial emission current after a certain time.
  • the emission current in the stable period becomes a large value such as 1/5 or 1/3 of the initial value, and does not decrease any further.
  • the emission current after a long period of time has elapsed compared to Ie 0 does not converge to 0.1Ie 0, it becomes a larger value than that of the Ie 0.
  • Whether the electron source is cleaned may be determined by measuring the convergence value of the emission current after long-term observation.
  • the time shown on the horizontal axis is normalized with the time ( ⁇ 50 ) when the emission current becomes 0.5 Ie 0 being 1.
  • the group (A) where the electron source is cleaned is convex upward at 0.5 ⁇ 50 .
  • the curve representing the temporal change of the emission current is convex downward in the group (B) at this time.
  • the group (C) indicating an intermediate cleanliness is intermediate between (A) and (B).
  • the control device 5 records the temporal change of the emission current measured as the output from the electron gun power supply 62, and particularly the time ⁇ 50 when the emission current Ie becomes 0.5Ie 0.
  • the emission current Ie 0.5 at time 0.5 ⁇ 50 is extracted.
  • Ie 0.5 and Ie 0 are compared, and if the value is, for example, 75% or more, it is determined that the electron source is clean.
  • Ie 0.5 is less than this value, it is judged that many gas molecules remain in the electron source, and it is recommended that the flashing intensity is automatically increased or the user is notified to perform strong flushing.
  • a display example to the user is shown in FIG.
  • a dialog such as 94 is displayed on the screen of the control device 5 viewed by the user, prompting the user to perform strong flushing.
  • the user instructs the control device 5 to perform flushing by a button on the dialog or other method, and cleans the electron source by intensely heating it.
  • the control device 5 senses the information and automatically performs strong flushing. In this case, it is desirable to notify the user that a strong flushing has been performed by issuing a dialog such as 95.
  • the time when Ie 0.5 was last measured and the value of Ie 0.5 which is a measure of the degree of cleanliness of the electron source, can be displayed on the control device 5 by a method such as 96 to alert the user.
  • a method such as 96 to alert the user.
  • the time when Ie 0.5 was last measured and the cleanliness of the chip that can be distinguished from Ie 0.5 are displayed in the form of a band graph. If there are many gas molecules attached to the chip, the user can perform strong flushing and determine the effect by this band graph.
  • Electron gun evacuation apparatus 101
  • Electron source 102
  • Filament 103
  • Extraction electrode 104
  • Adjustment electrode 105
  • Accelerating tube 106
  • Intermediate electrode 107
  • Intermediate electrode 109
  • Anode 17
  • Ion pump 2
  • Electron optical system 21
  • Electron optical System vacuum evacuation device 3
  • Sample holder 31
  • Control device 6
  • Power supply 61
  • Example of dialog prompting user to flush 92
  • Example of dialog notifying the user of flushing 93
  • Example of display notifying the user of flushing time 94
  • Example of dialog prompting the user to perform strong flushing 95 Display example to notify the cleanliness of the electron source in Example 96 user of the dialog to notify the

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Sources, Ion Sources (AREA)

Abstract

　The purpose of the present invention is to measure the emission current in an electron microscope provided with a cold cathode field emission type electron gun (1), to determine the cleanliness factor of the electron source (101). Taking the time at which the emission current reaches 0.5 immediately after flashing as the occasion at which the electron source (101) is to be cleaned, the temporal change of the emission current subsequent to flashing is used to estimate the cleanliness factor of the electron source (101), and stronger flashing is carried out.

Description

電子顕微鏡electronic microscope
　本発明は、電子顕微鏡に関する。例えば、特に高輝度な電子線を発生する冷陰極電界放出型（Cold-FE）電子銃およびこのCold-FE電子銃を備えた電子顕微鏡に関する。 The present invention relates to an electron microscope. For example, the present invention relates to a cold cathode field emission (Cold-FE) electron gun that generates a particularly bright electron beam and an electron microscope equipped with the Cold-FE electron gun.
　電子顕微鏡は電子線を用いて試料の拡大像や構成元素の情報を得る観察装置である。電子顕微鏡はおもに、電子銃、電子光学系、試料ホルダ、検出器、制御装置、電源部から構成される。 An electron microscope is an observation device that uses an electron beam to obtain an enlarged image of a sample and information on constituent elements. The electron microscope mainly includes an electron gun, an electron optical system, a sample holder, a detector, a control device, and a power supply unit.
　電子銃は電子線を生成する装置である。電子光学系は、電子銃で発生した電子を輸送し、試料に照射する装置である。電子光学系はまた、電子線を電磁レンズにより収束し、また偏向する機能も担っている。試料ホルダは、観察対象となる物質（すなわち試料）を、電子光学系内の電子線通路上に固定し、必要に応じて移動、傾斜させる装置である。電子銃、電子光学系は、空気分子と衝突することなく電子線を通過させるために内部が真空に保たれており、そのための真空排気装置を備えている。試料に照射された電子は、試料を構成する原子との相互作用により、反射電子、二次電子、透過電子、散乱電子、Ｘ線等を発生する。検出器では、これらの電子やＸ線を測定する。電源部は、電子銃、電子光学系、検出器等の動作に必要な電力を供給するとともに、精密な制御を行う。制御装置は、電源を制御するとともに、検出器で得られた情報を解析し、試料の拡大像や、試料の元素組成として、オペレーターに見やすい状態に処理し、表示しまたは記録する。 An electron gun is a device that generates an electron beam. The electron optical system is a device that transports electrons generated by an electron gun and irradiates a sample. The electron optical system also has a function of converging and deflecting an electron beam by an electromagnetic lens. The sample holder is a device that fixes a substance to be observed (that is, a sample) on the electron beam path in the electron optical system, and moves and tilts it as necessary. The electron gun and the electron optical system are maintained in a vacuum in order to pass an electron beam without colliding with air molecules, and are equipped with a vacuum exhaust device for that purpose. Electrons irradiated on the sample generate reflected electrons, secondary electrons, transmitted electrons, scattered electrons, X-rays, and the like due to the interaction with atoms constituting the sample. The detector measures these electrons and X-rays. The power supply unit supplies power necessary for the operation of the electron gun, the electron optical system, the detector, and the like, and performs precise control. The control device controls the power supply, analyzes information obtained by the detector, and processes, displays, or records an enlarged image of the sample and the elemental composition of the sample in an easy-to-see state for the operator.
　電子顕微鏡を用いて、より精密な試料拡大像や試料の組成元素分析結果を得る。このために電子銃の果たす役割は大きい。 Using an electron microscope, obtain a more precise sample magnified image and sample composition element analysis results. For this reason, the role played by electron guns is significant.
　電子銃は、観察に用いる電子をさまざまな原理により真空中の自由電子として生成する。さらに、発生した自由電子を電位差ポテンシャルにより加速し、運動エネルギーを持つ電子の群すなわち電子線とする。電子銃内で、電子源が発生した単位時間あたりの電子線量をエミッション電流と呼ぶ。また、このエミッション電流の一部を絞りを通して取り出し、試料に照射して拡大像等を得るためのプローブ電子を生成する。単位時間あたりのプローブ電子線量をプローブ電流と呼ぶ。 An electron gun generates electrons used for observation as free electrons in a vacuum based on various principles. Furthermore, the generated free electrons are accelerated by the potential difference potential to form a group of electrons having kinetic energy, that is, an electron beam. The electron dose per unit time generated by the electron source in the electron gun is called the emission current. Further, a part of this emission current is taken out through the diaphragm, and irradiated onto the sample to generate probe electrons for obtaining an enlarged image or the like. The probe electron dose per unit time is called a probe current.
　以下、電子銃の一種である冷陰極電界放出型(Cold-FE)電子銃について説明する。Cold-FE電子銃では、電子源として、先端を電界研磨によって鋭く尖らせたタングステン単結晶を利用している。電子源に近接した引出電極と電子源の間に数キロボルトの引出電圧が印加される。電子源の先端部に電界集中が起きる。この高い電界により、電子源先端から電界放出による電子が放射される。放射される電子線の量が上で述べたエミッション電流である。Cold-FE電子源においては、エミッション電流は電子源から１ステラジアン程度の立体角の範囲に放出される。 Hereinafter, a cold cathode field emission (Cold-FE) electron gun, which is a kind of electron gun, will be described. Cold-FE electron guns use tungsten single crystals with sharp tips sharpened by electropolishing as electron sources. An extraction voltage of several kilovolts is applied between the extraction electrode adjacent to the electron source and the electron source. Electric field concentration occurs at the tip of the electron source. Due to this high electric field, electrons due to field emission are emitted from the tip of the electron source. The amount of electron beam emitted is the emission current described above. In the Cold-FE electron source, the emission current is emitted from the electron source within a solid angle range of about 1 steradian.
　エミッション電流は、引出電圧（あるいは電子源先端での電界強度）のほか、電子源の表面状態に影響される。Cold-FE電子源は真空ポンプによって残留ガス圧力を低くした電子銃内に置かれるタングステン単結晶である。しかし、わずかに残ったガス分子が電子源に吸着すると、電子源の仕事関数は一般に低下する。よって、残留ガス分子が電子源に衝突し、吸着するにつれて電子線放出量が減少することになる。この結果、電子銃の運転中、エミッション電流は一定の引出電圧下で徐々に低下する。 The emission current is influenced by the surface condition of the electron source as well as the extraction voltage (or the electric field strength at the tip of the electron source). The Cold-FE electron source is a tungsten single crystal placed in an electron gun whose residual gas pressure is lowered by a vacuum pump. However, when a few remaining gas molecules are adsorbed to the electron source, the work function of the electron source generally decreases. Therefore, the amount of electron beam emission decreases as the residual gas molecules collide with the electron source and are adsorbed. As a result, during operation of the electron gun, the emission current gradually decreases under a constant extraction voltage.
　Cold-FE電子銃を利用するには、吸着したガス分子を真空中に再放出する等により、電子源表面を清浄化する工程が必要となる。これは単結晶を瞬間的に加熱することで達成される。よって、多くのCold-FE電子銃は、電子源をフィラメント先端に溶接しておき、このフィラメントを短時間通電加熱することで電子源を熱し、清浄化を行う。これをフラッシングと呼ぶ。フラッシングを実施すると電子源先端が清浄化される。Cold-FE電子銃ではこのフラッシングを定期的に実施することで、一定のエミッション電流を得る。必要なフラッシング頻度は電子銃内の残留ガス圧力により変化する。 In order to use a Cold-FE electron gun, a process for cleaning the surface of the electron source by, for example, re-releasing the adsorbed gas molecules into a vacuum is required. This is achieved by instantaneously heating the single crystal. Therefore, many Cold-FE electron guns are cleaned by heating the electron source by welding the electron source to the filament tip and heating the filament for a short time. This is called flushing. When flushing is performed, the tip of the electron source is cleaned. In the Cold-FE electron gun, this flushing is performed periodically to obtain a constant emission current. The required flushing frequency varies with the residual gas pressure in the electron gun.
　上述のようにCold-FE電子銃では電子源のフラッシングが必要である。電子源フラッシングにより電子源先端の清浄度が維持され、安定したエミッション電流が得られる。反面、フラッシングにより、電子源先端部のタングステン原子の熱による移動（ドリフト）が発生するため、フラッシングを繰り返すたびに先端部の物理的形状は徐々に変化する。この変化は、通常、結晶内の原子同士に働く引力のため、鋭く尖った先端部の物理的形状が徐々に丸くなってゆく方向への変化となる（これを電子源先端部の「丸まり」と呼ぶ）。 As mentioned above, the Cold-FE electron gun requires flushing of the electron source. The electron source flushing maintains the cleanness of the tip of the electron source, and a stable emission current can be obtained. On the other hand, the flushing causes movement (drift) of the tungsten atoms at the tip of the electron source due to heat, so that the physical shape of the tip gradually changes each time flushing is repeated. This change is usually due to the attractive force acting between the atoms in the crystal, causing the physical shape of the sharply pointed tip to gradually round (this is the “rounding” of the electron source tip. Called).
　　したがって、フラッシングを繰り返して長期間電子源を使用していると、電子源先端の曲率半径が徐々に大きくなり、それに伴い、電子源先端部での電界集中が弱まる結果となる。これは、同一のエミッション電流またプローブ電流を得るための引出電圧が上昇することを意味する。一定のエミッション電流を維持するよう引出電圧を定めると、電子銃の利用期間にわたり、引出電圧が徐々に上昇することとなる。この引出電圧が電子銃の制限電圧（電源の能力と、配線や電子銃内の絶縁性能によって定まる）を越えると、この電子源から十分なプローブ電流を得ることができなくなり、電子源の交換が必要となる。 Therefore, if the electron source is used for a long time by repeating flushing, the radius of curvature of the electron source tip gradually increases, and as a result, the electric field concentration at the electron source tip is weakened. This means that the extraction voltage for obtaining the same emission current or probe current increases. When the extraction voltage is determined so as to maintain a constant emission current, the extraction voltage gradually increases over the usage period of the electron gun. If this extraction voltage exceeds the limit voltage of the electron gun (determined by the power supply capability and the insulation performance within the wiring and the electron gun), sufficient probe current cannot be obtained from this electron source, and the electron source must be replaced. Necessary.
　ここで、フラッシングはフィラメントに流す電流の量として強さが調整できる。より多くの電流を流す、または比較的長時間電流を流すことで、電子源はより高温の「強いフラッシング」となる。このとき、電子源先端はより清浄化されるが、反面丸まりの程度も大きい。反対に、より少ない電流を流す、または比較的短時間に限り電流を流すと、電子源先端の温度は相対的に低くなり、フラッシング一回あたりの丸まりの程度が少ない「弱いフラッシング」となる。一方で、先端の清浄化が不十分となる場合が存在する。このようなときには、同一のエミッション電流を引き出すために必要な引出電圧が高くなり、あるいは電界放出が不安定になり短時間にプローブ電流が大きく変動したり、電子銃の輝度が低下して良好な観察像が得られなくなる。なるべく長期にわたって電子源交換が不要、かつ、なるべく清浄化した電子源が発生した電子線を利用するためには、適切なフラッシング強度を適切な時機に行うことが必要である。従来の電子銃においては、必要なフラッシング強度をフィラメント電流として規定し、あらかじめ十分と思われる強度のフラッシングをあらかじめ十分と考えられる頻度で行うことで、電子源の清浄化と電子源寿命の両立を図っていた。また電子銃の運転中のフラッシング時期については、プローブ電流が減少または不安定化していないか、良好な観察像を得られているかどうかをユーザーが判断して実施していた。 Here, the strength of flushing can be adjusted as the amount of current flowing through the filament. By passing more current, or for a relatively long period of time, the electron source becomes hotter “strong flushing”. At this time, the tip of the electron source is further cleaned, but the degree of rounding is large. On the other hand, when a smaller amount of current is passed or a current is passed only for a relatively short time, the temperature at the tip of the electron source becomes relatively low, resulting in “weak flushing” with less rounding per flushing. On the other hand, there are cases where the tip is not sufficiently cleaned. In such a case, the extraction voltage required for extracting the same emission current becomes high, or the field emission becomes unstable and the probe current largely fluctuates in a short time. An observation image cannot be obtained. In order to use an electron beam that does not require replacement of the electron source for as long a period as possible and generates a clean electron source as much as possible, it is necessary to perform an appropriate flushing intensity at an appropriate time. In conventional electron guns, the required flashing strength is defined as the filament current, and the flushing with sufficient strength is performed in advance at a frequency that is considered sufficient in advance, so that both the cleaning of the electron source and the lifetime of the electron source are achieved. I was planning. In addition, the flushing period during the operation of the electron gun is performed by the user judging whether the probe current is not reduced or unstable, or whether a good observation image is obtained.
　解決しようとする課題は、Cold-FE電子銃を備える電子顕微鏡において、適切なフラッシング時機およびフラッシング強度を電子顕微鏡ユーザーまたは電子顕微鏡制御装置が得ることである。 The problem to be solved is that an electron microscope user or an electron microscope control device obtains an appropriate flashing timing and flashing strength in an electron microscope equipped with a Cold-FE electron gun.
　本発明は、特許請求の範囲に記載の構成を採用し、課題を解決する。例えば、Cold-FE電子銃において、電子源からの電界放出によって得られる総電流であるエミッション電流を測定し、その測定値を用いて、ユーザーに適切なフラッシング時期と強度を指示し、または自動的に適切なフラッシングを実施する。 The present invention adopts the configuration described in the claims to solve the problem. For example, in a Cold-FE electron gun, the emission current, which is the total current obtained by field emission from the electron source, is measured, and the measured value is used to indicate the appropriate flashing time and intensity to the user, or automatically Implement appropriate flushing.
　本発明のCold-FE電子銃は、適切な時期に適切な強度のフラッシングが行われることにより、より安定したプローブ電流を、より長期間電子源を交換することなく得ることができる。これにより、長期間メンテナンスが不要で、より高品質の観察像が得られる電子顕微鏡を得ることができる。 The Cold-FE electron gun of the present invention can obtain a more stable probe current without replacing the electron source for a longer period of time by performing flushing with an appropriate intensity at an appropriate time. As a result, it is possible to obtain an electron microscope that does not require maintenance for a long time and can obtain a higher quality observation image.
発明の実施例である電子顕微鏡を示す図である。It is a figure which shows the electron microscope which is the Example of invention. 発明の実施例の一例である電子銃を示す図である。It is a figure which shows the electron gun which is an example of the Example of invention. 冷陰極電界放出型電子銃において、清浄な電子源から放出されるエミッション電流とプローブ電流の時間的変化を模式的に例示した図である。It is the figure which illustrated typically the time change of the emission current and probe current which are emitted from a clean electron source in a cold cathode field emission type electron gun. 発明の実施例において、エミッション電流の値よりユーザーにフラッシング時機やフラッシングを自動的に行ったこと、また次のフラッシング時機を通知する表示を例示した図である。In the Example of invention, it is the figure which illustrated the display which notifies the user that the flushing time and flushing were performed automatically from the value of the emission current, and the next flushing time. 冷陰極電界放出型電子銃において、ガス分子が付着した電子源から放出されるエミッション電流の時間的変化を清浄な電子源からのエミッション電流の比較として模式的に例示した図である。In a cold cathode field emission type electron gun, it is the figure which illustrated typically the temporal change of the emission current discharge | released from the electron source which the gas molecule adhered to as a comparison of the emission current from a clean electron source. 清浄な電子源やガス分子が付着した電子源から放出されるエミッション電流の時間的変化の測定結果を示し、発明の実施例において清浄な電子源とガス分子が付着した電子源との判別をどのように行うかを説明した測定結果および説明図である。The measurement results of the temporal change in the emission current emitted from a clean electron source or an electron source with gas molecules attached are shown, and in the embodiment of the invention, which is used to distinguish between a clean electron source and an electron source with gas molecules attached It is a measurement result and explanatory drawing explaining how to carry out. 発明の実施例において、エミッション電流の時間的変化よりユーザーに強いフラッシングの時機や強いフラッシングを自動的に行ったこと、また電子源の清浄度を通知する表示を例示した図である。In the Example of invention, it is the figure which illustrated the display which notified the time of strong flushing and the strong flushing to the user automatically from the temporal change of emission current, and the cleanliness of the electron source.
　発明を実施する形態の例としての、Cold-FE電子銃を備えた電子顕微鏡を図１に示す。電子顕微鏡は、電子銃１、電子光学系２、試料ホルダ３、検出器４、制御装置５、電源部６を持つ。図１において、電子銃１と電子光学系２は、それぞれ真空排気装置１１、２１を持っているが、電子顕微鏡の規模によっては、真空排気装置を一系統のみ備えている場合もあり、またより多数に細分化された多数の真空排気装置を備える場合もある。Cold-FE電子源１０１を備えた電子銃１は電子線１０を発生する。電子光学系２は電子線１０を収束、偏向させ、試料３１に照射する。試料ホルダ３は試料３１を保持し、必要に応じて移動、傾斜、交換する。検出器４は、試料３１が発生した反射電子、二次電子、透過電子、散乱電子、Ｘ線等を測定する。電源部６は、電子銃１、電子光学系２に電源を供給するとともに、出力を調整し、電子線をオペレーターが要求する状態に制御する。また、検出器４からの情報をデジタル信号に変換する。制御装置５は、電源系６を通して電子銃１、電子光学系２を制御するとともに、検出器４からの情報を処理し、オペレーターに見える形で表示または記録する。図では電源系６を制御・検出系電源６１と、電子銃電源６２に分けた。 FIG. 1 shows an electron microscope equipped with a Cold-FE electron gun as an example of an embodiment for carrying out the invention. The electron microscope includes an electron gun 1, an electron optical system 2, a sample holder 3, a detector 4, a control device 5, and a power supply unit 6. In FIG. 1, the electron gun 1 and the electron optical system 2 have vacuum evacuation devices 11 and 21, respectively. However, depending on the scale of the electron microscope, there may be a single vacuum evacuation device. In some cases, a large number of vacuum evacuation devices are provided. The electron gun 1 including the Cold-FE electron source 101 generates an electron beam 10. The electron optical system 2 converges and deflects the electron beam 10 and irradiates the sample 31. The sample holder 3 holds the sample 31 and moves, tilts and exchanges as necessary. The detector 4 measures reflected electrons, secondary electrons, transmitted electrons, scattered electrons, X-rays, etc. generated by the sample 31. The power supply unit 6 supplies power to the electron gun 1 and the electron optical system 2, adjusts the output, and controls the electron beam to a state requested by the operator. Moreover, the information from the detector 4 is converted into a digital signal. The control device 5 controls the electron gun 1 and the electron optical system 2 through the power supply system 6, processes information from the detector 4, and displays or records the information in a form visible to the operator. In the figure, the power supply system 6 is divided into a control / detection system power supply 61 and an electron gun power supply 62.
　ここで、本発明の実施例である加速電圧数百キロボルトのCold-FE電子銃１の構造の詳細を図２に示す。電子銃１は、電子源１０１（冷陰極電界放出電子源）、引出電極１０３、加速管１０５を備え、電子銃電源６２と接続され、高い電位が与えられている。引出電極１０３には、引出電源６２１により数キロボルトの引出電圧（Ｖ1）が印加される。ここで、電子源１０１はするどく尖った先端形状を持っているため、電子源１０１の先端部には強い電界が発生する。この時、電界放出の原理に基づき、電子源１０１より放出された電子は、電子源１０１と引出電極１０３との電位差によって初期的に加速され、引出電極１０３に照射される。これがエミッション電流である。エミッション電流の一部は、引出電極１０３に設けられた陽極絞り１２１の孔を通過し、加速管１０５へ入射する。加速管１０５は、複数の中間電極１０４、１０６、１０７、１０８、１０９を備えており、電子線はこの中間電極を通過しつつさらに加速される。電子源１０１、引出電極１０３は、加速電源６２３によって数百キロボルトの負の高電圧（Ｖ0）下にある。陽極１１０は接地電位であり、ゼロ電位である。この電位差により電子線が加速され、陽極１１０を通過した電子はＶ0のエネルギーを持った電子線となっている。 Here, FIG. 2 shows details of the structure of the Cold-FE electron gun 1 having an acceleration voltage of several hundred kilovolts, which is an embodiment of the present invention. The electron gun 1 includes an electron source 101 (cold cathode field emission electron source), an extraction electrode 103, and an acceleration tube 105. The electron gun 1 is connected to an electron gun power source 62 and is given a high potential. An extraction voltage (V 1 ) of several kilovolts is applied to the extraction electrode 103 by an extraction power source 621. Here, since the electron source 101 has a very sharp tip shape, a strong electric field is generated at the tip of the electron source 101. At this time, based on the principle of field emission, electrons emitted from the electron source 101 are initially accelerated by the potential difference between the electron source 101 and the extraction electrode 103 and are irradiated on the extraction electrode 103. This is the emission current. Part of the emission current passes through the hole of the anode aperture 121 provided in the extraction electrode 103 and enters the acceleration tube 105. The acceleration tube 105 includes a plurality of intermediate electrodes 104, 106, 107, 108, and 109, and the electron beam is further accelerated while passing through the intermediate electrodes. The electron source 101 and the extraction electrode 103 are under a negative high voltage (V 0 ) of several hundred kilovolts by the acceleration power source 623. The anode 110 is at ground potential and is at zero potential. The electron beam is accelerated by this potential difference, and the electrons passing through the anode 110 are electron beams having V 0 energy.
　ここで、引出電源６２１は、引出電極１０３に安定的に引出電圧を印加する機能とともに、電源に流れる電流を測定する機能がある。電流計６３として図中に示す。引出電極は碍子により他の電極と絶縁されており、微小な放電電流を別にすると、流れる電流はすべて電子源からの電界放出によるエミッション電流によるものである。したがって、引出電源で引出電極と電子源との間に流れる電流を電流計６３で測定すれば、これがエミッション電流にほぼ等しくなる。この値をIeとする。 Here, the extraction power source 621 has a function of stably applying an extraction voltage to the extraction electrode 103 and a function of measuring a current flowing through the power source. An ammeter 63 is shown in the figure. The extraction electrode is insulated from other electrodes by an insulator, and apart from a minute discharge current, all of the flowing current is due to an emission current due to field emission from the electron source. Therefore, if the current flowing between the extraction electrode and the electron source with the extraction power source is measured by the ammeter 63, this is approximately equal to the emission current. This value is Ie.
　引出電源および電子銃電源は、この電流量Ieを測定データとしてデジタル信号として、図１に示された制御装置５に送る。制御装置５は、このエミッション電流データを記録する。 The extraction power source and the electron gun power source send this current amount Ie as measurement data to the control device 5 shown in FIG. 1 as a digital signal. The control device 5 records this emission current data.
　フラッシング電源６２４は、電子源が固定されているフィラメント１０２に流す電流を制御する電源である。制御装置からフラッシングを実施する指令が入ると、フラッシング電源６２４は、電子源が固定されているフィラメント１０２に電流を流す。このジュール熱によりフィラメント１０２が加熱され、電子源１０１の温度が上昇し、電子源１０１表面が清浄化される。このときのフラッシング強度は、制御装置がフラッシング電源６２４をコントロールすることで、たとえばフィラメントに流す電流の大小により制御される。 The flushing power source 624 is a power source that controls the current flowing through the filament 102 to which the electron source is fixed. When a command to perform flushing is input from the control device, the flushing power source 624 supplies current to the filament 102 to which the electron source is fixed. The filament 102 is heated by this Joule heat, the temperature of the electron source 101 rises, and the surface of the electron source 101 is cleaned. The flushing intensity at this time is controlled by the magnitude of the current flowing through the filament, for example, by the control device controlling the flushing power source 624.
　フラッシング後、電子源から放出されるエミッション電流と、絞り１２１を通過したプローブ電流の時間的な変化について、典型的な例を図３に示す。フラッシング後、エミッション電流は比較的単調に減少するが、プローブ電流は一定時間、（１）高い一定値に近い値を維持する。その後、（２）急激な減少を経て、（３）低い一定値に移行する。高い輝度のプローブ電流による良好な観察像を得るためには、（１）の領域で装置を利用することが望ましい。 FIG. 3 shows a typical example of the temporal change in the emission current emitted from the electron source after the flushing and the probe current that has passed through the diaphragm 121. After the flushing, the emission current decreases relatively monotonously, but the probe current maintains (1) a value close to a high constant value for a certain period of time. Thereafter, (2) after a rapid decrease, (3) shift to a low constant value. In order to obtain a good observation image with a probe current with high luminance, it is desirable to use the apparatus in the region (1).
　エミッション電流とプローブ電流で時間的変化が異なる理由として、物理的に、エミッション電流が電子源表面の比較的広い範囲から電界放出された電子線であるのに対し、プローブ電流が電子源の先端付近から放出された比較的せまい領域から電界放出された電子線であることがあげられる。このため、数多くの原子からなる電子源先端部からの電界放出（エミッション電流）が安定して減少してゆくのに対して、プローブ電流は比較的不安定な挙動を示し、段階的な増減が見られることがある。これはプローブ電流の発生にかかわる電子源上の領域が狭く、特定の結晶面の比較的少数の原子だけが放出に寄与しているため、残留ガス分子による確率的な影響によってプローブ電流が幅広く増減するためであると考えられる。 The reason why the temporal change differs between the emission current and the probe current is that the emission current is physically an electron beam emitted from a relatively wide area of the electron source surface, whereas the probe current is near the tip of the electron source. And an electron beam emitted from a relatively narrow area emitted from the electron beam. For this reason, the field emission (emission current) from the tip of the electron source consisting of a large number of atoms decreases stably, whereas the probe current shows a relatively unstable behavior, and the increase / decrease stepwise. It may be seen. This is because the region on the electron source involved in the generation of the probe current is narrow, and only a relatively small number of atoms on a specific crystal plane contribute to the emission, so the probe current varies widely due to the stochastic effect of residual gas molecules. It is thought that it is to do.
　いま、実験より得られた測定結果によれば、ほとんどの場合、プローブ電流が、図で示したフラッシング直後のプローブ電流Ip0の80％以下に減少すると、プローブ電流の急激な減少が始まり、また電流量も不安定に変動する。このことをプローブ電流を測定して判断することもできるが、ここで、引出電源によってすでに計測されているエミッション電流変化に着目する。エミッション電流が、図で示したフラッシング直後のエミッション電流Ie0の50％（図で0.5Ie0で示す）まで減少したタイミング（τ50）が、ほぼ上記のプローブ電流が80％となる時間に相当することが確認された。 Now, according to the measurement results obtained from experiments, in most cases, when the probe current decreases to 80% or less of the probe current Ip 0 immediately after the flushing shown in the figure, the probe current starts to decrease sharply. The amount of current also fluctuates unstable. This can be determined by measuring the probe current. Here, attention is paid to the emission current change already measured by the extraction power source. The timing (τ 50 ) at which the emission current is reduced to 50% of the emission current Ie 0 immediately after the flushing shown in the figure (shown as 0.5Ie 0 in the figure) corresponds to the time when the probe current is almost 80%. Confirmed to do.
　このことから、エミッション電流を計測し、Ieが0.5Ie0まで減少したタイミング（τ50）にフラッシングを行えば、もっとも有効に電子源を活用できると言える。 From this, it can be said that the electron source can be utilized most effectively if the emission current is measured and flushing is performed at the timing (τ 50 ) when Ie is reduced to 0.5Ie 0 .
　そこで、本発明の実施例においては、計測したエミッション電流をモニタし、フラッシング直後エミッション電流Ie0の50％まで減少したときにフラッシングを勧めるダイアログ等を表示し、ユーザーにフラッシングを促す。また、ユーザーが席を外し、または試料を交換するタイミングにフラッシングを実施し、電子源の清浄化を行う。 Therefore, in the embodiment of the present invention to monitor the emission current measured, the dialog box or the like to recommend flushing when reduced to 50% of the flushing after emission current Ie 0, prompting the flushing user. In addition, flushing is performed at the timing when the user removes the seat or replaces the sample to clean the electron source.
　ユーザーへの表示例を図４に示す。ユーザーが見ている制御装置５の画面に、９１のようなダイアログを表示させ、ユーザーにフラッシングを促す。ユーザーはダイアログ上のボタン、または他の方法により制御装置５にフラッシング実施を命令し、電子源を清浄化させる。または、装置が操作されていない場合、また試料交換作業が行われている場合、その情報を制御装置５が感知し、自動的にフラッシングを行う。この場合、ユーザーにフラッシングが行われた旨、９２のようなダイアログを出し通知することが望ましい。また、最後のフラッシングからの経過時間や、次のフラッシング時間、および次回フラッシングまでの時間の目安となる現在のエミッション電流を、９３のような方法で制御装置５に表示し、ユーザーの注意を喚起することができる。９３では最後にフラッシングを行った時刻、エミッション電流値から予想される次回のフラッシング時刻、および現在のエミッション電流Ieの値を初期エミッション電流Ie0と比較し、帯グラフの形で表示したものである。 A display example to the user is shown in FIG. A dialog such as 91 is displayed on the screen of the control device 5 being viewed by the user to prompt the user to flush. The user instructs the control device 5 to perform flushing by a button on the dialog or other method, and cleans the electron source. Alternatively, when the apparatus is not operated or when a sample exchange operation is performed, the control device 5 senses the information and automatically performs flushing. In this case, it is desirable to notify the user by issuing a dialog such as 92 that the flushing has been performed. Also, the elapsed time from the last flushing, the next flushing time, and the current emission current, which is a measure of the time until the next flushing, are displayed on the control device 5 in a manner like 93 to alert the user. can do. In 93, the last flushing time, the next flushing time expected from the emission current value, and the current emission current Ie value are compared with the initial emission current Ie 0 and displayed in the form of a band graph. .
　このようにすることで、挙動が比較的不安定であり、また電子光学系の設定条件により値が異なる場合があるプローブ電流を計測するよりも、簡単に電子源へのガス吸着の程度を推定することができ、フラッシングに適切な時機を制御装置が知ることができ、またわかりやすくユーザーに通知することができる。またこの情報に応じて、制御装置はユーザーにフラッシングを促し、または自動的にフラッシングを実施し、電子源を良好な状態に保つことができる。 By doing so, it is easier to estimate the degree of gas adsorption to the electron source than to measure the probe current whose behavior is relatively unstable and the value may vary depending on the setting conditions of the electron optical system. Therefore, the control device can know the appropriate time for flushing, and can notify the user in an easy-to-understand manner. In response to this information, the control device can prompt the user to perform flushing or automatically perform flushing to keep the electron source in a good state.
　次に、フラッシング強度について、フラッシングは電子源表面清浄化のために実施するものであるが、電子源表面清浄化のためにどの程度の強さのフラッシングが必要かについては、電子源の表面状態に依存する。より多量のガス分子が吸着した電子源は、強いフラッシングでの清浄化が必要であるが、付着したガス分子が少量であれば弱いフラッシングで清浄化できる。ガス分子吸着量は電子源に吸着された残留ガス分子の種類にもよると考えられ、定性的にはより軽い原子（水素原子など）が比較的低温で電子源から取り除かれるのに対し、重い分子（炭化水素など）が吸着した場合、強いフラッシングが必要となる。 Next, regarding the flushing strength, flushing is performed for cleaning the surface of the electron source. How much flushing is required for cleaning the surface of the electron source depends on the surface condition of the electron source. Depends on. An electron source to which a larger amount of gas molecules is adsorbed needs to be cleaned by strong flushing, but can be cleaned by weak flushing if the amount of attached gas molecules is small. Gas molecule adsorption is thought to depend on the type of residual gas molecules adsorbed on the electron source, and qualitatively lighter atoms (such as hydrogen atoms) are removed from the electron source at a relatively low temperature, but heavy. When molecules (such as hydrocarbons) are adsorbed, strong flushing is required.
　電子源表面が十分に清浄化されていない場合、プローブ電流の時間的な変化は、図３下で示したような標準的なものにならない。安定領域（１）が短くなり、不安定領域（２）が早くやってきたり、安定領域（１）が現れず、フラッシング直後から輝度の低い一定値の領域（３）が現れることがある。 If the surface of the electron source is not sufficiently cleaned, the temporal change of the probe current will not be standard as shown in the lower part of FIG. In some cases, the stable region (1) becomes shorter, the unstable region (2) arrives earlier, or the stable region (1) does not appear and a constant value region (3) with low luminance appears immediately after flushing.
　今、これらの電子源が清浄な状態、多くのガス分子が残留している状態にそれぞれ対応するエミッション電流の時間的変化の例を図５に示す。清浄な電子源状態でエミッション電流の時間変化を記録すると、一定時間ののち、初期エミッション電流の1/10程度（0.1Ie0）で安定化する。一方、清浄でない状態の電子源で同様の測定を行うと、安定期のエミッション電流は初期値の1/5、1/3など大きな値となり、それ以上減少しなくなる。 FIG. 5 shows an example of temporal changes in the emission current corresponding to the state where these electron sources are clean and the state where many gas molecules remain. When the time variation of the emission current is recorded in a clean electron source state, it stabilizes at about 1/10 (0.1 Ie 0 ) of the initial emission current after a certain time. On the other hand, if the same measurement is performed with an electron source in an unclean state, the emission current in the stable period becomes a large value such as 1/5 or 1/3 of the initial value, and does not decrease any further.
　これは定性的には次のように理解される。電子源の清浄化が不十分である場合、電子源の状態は清浄には戻らず、図３上に示した標準的なエミッション電流の減少曲線の左端ではなく、その途中までしか清浄化されない。フラッシング後、図３の左端ではなく、途中からエミッション電流変化が始まることになる。電子銃の引出電圧は、エミッション電流が一定値（たとえば10μＡ）となるように選ばれるので、逆にフラッシング直後のエミッション電流Ie0はいかなる場合も同一となる。しかし、そこからの減少度合いは、清浄電子源からの標準的なエミッション電流グラフ（図３上）を拡大し、Ie＝10μAに合わせたようなカーブを描く。このため、Ie0に比べて長時間が経過したあとのエミッション電流が0.1Ie0に収束せず、Ie0に比べもっと大きな値となる。電子源が清浄化されているかどうかは、長期間観察後のエミッション電流の収束値を測定すればよい。 This is qualitatively understood as follows. When the electron source is not sufficiently cleaned, the state of the electron source does not return to the clean state, but is cleaned only halfway, not the left end of the standard emission current decrease curve shown in FIG. After the flushing, the emission current change starts not in the left end of FIG. 3 but in the middle. Since the extraction voltage of the electron gun is selected so that the emission current becomes a constant value (for example, 10 μA), conversely, the emission current Ie 0 immediately after the flushing is the same in any case. However, the degree of decrease from there expands the standard emission current graph from the clean electron source (on FIG. 3) and draws a curve that matches Ie = 10 μA. For this reason, the emission current after a long period of time has elapsed compared to Ie 0 does not converge to 0.1Ie 0, it becomes a larger value than that of the Ie 0. Whether the electron source is cleaned may be determined by measuring the convergence value of the emission current after long-term observation.
　ところが、上の長期間観察は、通常行わない。上記のように0.5Ie0となった時刻τ50においてユーザーにフラッシングを促す場合はなおさらである。 However, the above long-term observation is not usually performed. This is especially true when the user is prompted to flush at time τ 50 when 0.5Ie 0 is reached.
　ここで多数エミッション電流データを観察した実験結果によると、その減少傾向に確たる傾向があることがわかった。図６に示す。この図においては、横軸で示した時間はエミッション電流が0.5Ie0となった時間（τ50）を１として規格化されている。ここで電子源がフラッシングにより清浄化されているかどうかについてグループ分けを行うと、電子源が清浄化されたグループ（Ａ）は、0.5τ50において上に凸であることがわかる。一方、清浄でない場合グループ（Ｂ）はこの時刻において、エミッション電流の時間的変化を表すカーブが下に凸となる。中間的な清浄度を示すグループ（Ｃ）は（Ａ）と（Ｂ）の中間となる。 According to the experimental results of observing a large number of emission current data, it was found that there was a tendency to confirm the decreasing trend. As shown in FIG. In this figure, the time shown on the horizontal axis is normalized with the time (τ 50 ) when the emission current becomes 0.5 Ie 0 being 1. Here, when grouping is performed on whether or not the electron source is cleaned by flushing, it can be seen that the group (A) where the electron source is cleaned is convex upward at 0.5τ 50 . On the other hand, when it is not clean, the curve representing the temporal change of the emission current is convex downward in the group (B) at this time. The group (C) indicating an intermediate cleanliness is intermediate between (A) and (B).
　そこで、本発明の実施例においては、制御装置５において、電子銃電源６２からの出力として計測したエミッション電流の時間的変化を記録し、特にエミッション電流Ieが0.5Ie0となった時刻τ50と、時刻0.5τ50におけるエミッション電流Ie0.5を抜き出す。Ie0.5とIe0を比較し、たとえば75%以上の値であれば、電子源は清浄であると判別する。一方、Ie0.5がこの値に満たない場合、電子源に多くのガス分子が残っていると判断し、フラッシング強度を自動的に強め、またはユーザーに通知して強いフラッシングを実施するよう勧める。 Therefore, in the embodiment of the present invention, the control device 5 records the temporal change of the emission current measured as the output from the electron gun power supply 62, and particularly the time τ 50 when the emission current Ie becomes 0.5Ie 0. The emission current Ie 0.5 at time 0.5τ 50 is extracted. Ie 0.5 and Ie 0 are compared, and if the value is, for example, 75% or more, it is determined that the electron source is clean. On the other hand, when Ie 0.5 is less than this value, it is judged that many gas molecules remain in the electron source, and it is recommended that the flashing intensity is automatically increased or the user is notified to perform strong flushing.
　ユーザーへの表示例を図７に示す。前回のIe0.5値を判断基準とし、ユーザーが見ている制御装置５の画面に、９４のようなダイアログを表示させ、ユーザーに強いフラッシングを促す。ユーザーはダイアログ上のボタン、または他の方法により制御装置５にフラッシング実施を命令し、電子源を強く加熱することで清浄化させる。または、装置が長時間操作されていない場合など、その情報を制御装置５が感知し、自動的に強いフラッシングを行う。この場合、ユーザーに強いフラッシングが行われた旨、９５のようなダイアログを出し通知することが望ましい。また、最後にIe0.5を計測した時間や、電子源の清浄度合いの目安となるIe0.5の値を、９６のような方法で制御装置５に表示し、ユーザーの注意を喚起することができる。９６では最後にIe0.5を計測した時刻、Ie0.5から判別できるチップの清浄度を帯グラフの形で表示したものである。チップのガス分子付着が多い場合、ユーザーは強いフラッシングを行い、その効果をこの帯グラフで判別することができる。 A display example to the user is shown in FIG. Based on the previous Ie 0.5 value as a criterion, a dialog such as 94 is displayed on the screen of the control device 5 viewed by the user, prompting the user to perform strong flushing. The user instructs the control device 5 to perform flushing by a button on the dialog or other method, and cleans the electron source by intensely heating it. Alternatively, when the device has not been operated for a long time, the control device 5 senses the information and automatically performs strong flushing. In this case, it is desirable to notify the user that a strong flushing has been performed by issuing a dialog such as 95. In addition, the time when Ie 0.5 was last measured and the value of Ie 0.5 , which is a measure of the degree of cleanliness of the electron source, can be displayed on the control device 5 by a method such as 96 to alert the user. In 96, the time when Ie 0.5 was last measured and the cleanliness of the chip that can be distinguished from Ie 0.5 are displayed in the form of a band graph. If there are many gas molecules attached to the chip, the user can perform strong flushing and determine the effect by this band graph.
　これらの実施態様によれば、従来のCold-FE電子銃に比べ、電子源の清浄度について的確な情報が得られ、適切な時期に適切な強度のフラッシングが行われることにより、より安定したプローブ電流を、より長期間電子源を交換することなく得ることができる。これにより、長期間メンテナンスが不要で、より高品質の観察像が得られる電子顕微鏡を得ることができる。 According to these embodiments, compared to the conventional Cold-FE electron gun, accurate information on the cleanliness of the electron source can be obtained, and flushing with an appropriate intensity is performed at an appropriate time, so that a more stable probe can be obtained. A current can be obtained without replacing the electron source for a longer period of time. As a result, it is possible to obtain an electron microscope that does not require maintenance for a long time and can obtain a higher quality observation image.
　１　　　電子銃
　１０　　電子線
　１１　　電子銃真空排気装置
　１０１　電子源
　１０２　フィラメント
　１０３　引出電極
　１０４　調整電極
　１０５　加速管
　１０６　中間電極
　１０７　中間電極
　１０８　中間電極
　１０９　中間電極
　１１０　陽極
　１７　　イオンポンプ
　２　　　電子光学系
　２１　　電子光学系真空排気装置
　３　　　試料ホルダ
　３１　　試料
　４　　　検出器
　５　　　制御装置
　６　　　電源部
　６１　　制御・検出系電源
　６２　　電子銃電源
　６２１　　引出電源
　６２２　　調整電源
　６２３　　加速電源
　６２４　　フィラメント加熱電源
　９１　ユーザーにフラッシングを促すダイアログの例
　９２　ユーザーにフラッシング実施を通知するダイアログの例
　９３　ユーザーにフラッシング時機を通知する表示の例
　９４　ユーザーに強いフラッシングを促すダイアログの例
　９５　ユーザーに強いフラッシング実施を通知するダイアログの例
　９６　ユーザーに電子源の清浄度を通知する表示の例 DESCRIPTION OF SYMBOLS 1 Electron gun 10 Electron beam 11 Electron gun evacuation apparatus 101 Electron source 102 Filament 103 Extraction electrode 104 Adjustment electrode 105 Accelerating tube 106 Intermediate electrode 107 Intermediate electrode 108 Intermediate electrode 109 Intermediate electrode 110 Anode 17 Ion pump 2 Electron optical system 21 Electron optical System vacuum evacuation device 3 Sample holder 31 Sample 4 Detector 5 Control device 6 Power supply 61 Control / detection system power supply 62 Electron gun power supply 621 Extraction power supply 622 Adjustment power supply 623 Acceleration power supply 624 Filament heating power supply 91 Example of dialog prompting user to flush 92 Example of dialog notifying the user of flushing 93 Example of display notifying the user of flushing time 94 Example of dialog prompting the user to perform strong flushing 95 Display example to notify the cleanliness of the electron source in Example 96 user of the dialog to notify the

Claims (6)

  1. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の数値を入力情報に用いて、電子源の加熱清浄化を行う時期をユーザーに通知する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using this emission current value as input information, a function to notify the user when the electron source is heated and cleaned,
    With an electron microscope.
  2. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の数値を入力情報に用いて、電子源の加熱清浄化を自動的に実施する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using the numerical value of this emission current as input information, automatically heating and cleaning the electron source,
    With an electron microscope.
  3. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の数値を入力情報に用いて、電子源の加熱清浄化を行うべき時期の目安となる情報をユーザーに通知する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using this emission current value as input information, a function for notifying the user of information that is an indication of when to heat and clean the electron source,
    With an electron microscope.
  4. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の時間的な変化を入力情報に用いて、電子源のガス分子付着を推定し、電子源の強い加熱清浄化を行うべき時期をユーザーに通知する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using this temporal change in emission current as input information, estimating the adhesion of gas molecules in the electron source and notifying the user when the electron source should be strongly heated and cleaned,
    With an electron microscope.
  5. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の時間的な変化を入力情報に用いて、電子源のガス分子付着を推定し、電子源の強い加熱清浄化を自動的に実施する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using this temporal change in emission current as input information, estimating the adhesion of gas molecules in the electron source, and automatically performing strong heat cleaning of the electron source,
    With an electron microscope.
  6. 　冷陰極電界放出型電子銃を備えた電子顕微鏡において、
    　電界放出により発生した電流であるエミッション電流を測定する機能と、
    　このエミッション電流の時間的な変化を入力情報に用いて、電子源のガス分子付着を推定し、電子源の強い加熱清浄化を行うべき時期の目安となる情報をユーザーに通知する機能と、
    　を持った電子顕微鏡。     In an electron microscope equipped with a cold cathode field emission electron gun,
    The ability to measure the emission current, which is the current generated by field emission,
    Using this temporal change in emission current as input information, estimating the adhesion of gas molecules in the electron source, and notifying the user of information that is a guideline for when the electron source should be strongly heated and cleaned,
    With an electron microscope.
PCT/JP2014/076883 2013-10-10 2014-10-08 Electron microscope WO2015053300A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2015541606A JP6129982B2 (en) 2013-10-10 2014-10-08 electronic microscope

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2013-212424 2013-10-10
JP2013212424 2013-10-10

Publications (1)

Publication Number Publication Date
WO2015053300A1 true WO2015053300A1 (en) 2015-04-16

Family

ID=52813116

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2014/076883 WO2015053300A1 (en) 2013-10-10 2014-10-08 Electron microscope

Country Status (2)

Country Link
JP (1) JP6129982B2 (en)
WO (1) WO2015053300A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019155540A1 (en) * 2018-02-07 2019-08-15 株式会社日立ハイテクノロジーズ Cleaning device
US11398364B2 (en) * 2019-10-07 2022-07-26 Jeol Ltd. Electron gun, electron microscope, three-dimensional additive manufacturing apparatus, and method of adjusting current of electron gun

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0487244A (en) * 1990-07-27 1992-03-19 Hitachi Ltd Scanning type electron microscope
JPH0525654U (en) * 1991-09-17 1993-04-02 株式会社日立製作所 Scanning electron microscope
JPH0845455A (en) * 1994-07-27 1996-02-16 Jeol Ltd Operation state judging method for field emission type electron gun
JPH08129981A (en) * 1994-10-28 1996-05-21 Hitachi Ltd Field emission type electron gun and electron beam device
JP2005235469A (en) * 2004-02-18 2005-09-02 Jeol Ltd Charged particle beam device and control method of charged particle beam device
JP2011171088A (en) * 2010-02-18 2011-09-01 Hitachi High-Technologies Corp Field-emission electron gun, and control method therefor

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0487244A (en) * 1990-07-27 1992-03-19 Hitachi Ltd Scanning type electron microscope
JPH0525654U (en) * 1991-09-17 1993-04-02 株式会社日立製作所 Scanning electron microscope
JPH0845455A (en) * 1994-07-27 1996-02-16 Jeol Ltd Operation state judging method for field emission type electron gun
JPH08129981A (en) * 1994-10-28 1996-05-21 Hitachi Ltd Field emission type electron gun and electron beam device
JP2005235469A (en) * 2004-02-18 2005-09-02 Jeol Ltd Charged particle beam device and control method of charged particle beam device
JP2011171088A (en) * 2010-02-18 2011-09-01 Hitachi High-Technologies Corp Field-emission electron gun, and control method therefor

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019155540A1 (en) * 2018-02-07 2019-08-15 株式会社日立ハイテクノロジーズ Cleaning device
CN111727488A (en) * 2018-02-07 2020-09-29 株式会社日立高新技术 Cleaning device
JPWO2019155540A1 (en) * 2018-02-07 2021-01-28 株式会社日立ハイテク Cleaning equipment
US11244806B2 (en) 2018-02-07 2022-02-08 Hitachi High-Tech Corporation Cleaning device
JP7132254B2 (en) 2018-02-07 2022-09-06 株式会社日立ハイテク cleaning equipment
CN111727488B (en) * 2018-02-07 2023-06-06 株式会社日立高新技术 Cleaning device
US11398364B2 (en) * 2019-10-07 2022-07-26 Jeol Ltd. Electron gun, electron microscope, three-dimensional additive manufacturing apparatus, and method of adjusting current of electron gun

Also Published As

Publication number Publication date
JPWO2015053300A1 (en) 2017-03-09
JP6129982B2 (en) 2017-05-17

Similar Documents

Publication Publication Date Title
EP1993119B1 (en) Charged particle beam emitting device and method for operating a charged particle beam emitting device
JP6191778B2 (en) Mass spectrometer
JP6001292B2 (en) Emitter fabrication method
EP2068343B1 (en) Charged particle source with automated tip formation
JP5290238B2 (en) electronic microscope
JP2011210492A (en) Focused ion beam device
US9336979B2 (en) Focused ion beam apparatus with precious metal emitter surface
JP6501891B2 (en) Ion beam apparatus and method of cleaning gas field ionization ion source
JP6129982B2 (en) electronic microscope
US8188451B1 (en) Electron generation and delivery system for contamination sensitive emitters
JP2011171009A (en) Focused ion beam device
JP2008251300A (en) X-ray inspection device
JP5989959B2 (en) Focused ion beam device
US20230420224A1 (en) Operating a gas supply device for a particle beam device
JP5723730B2 (en) Emitter, gas field ion source, and ion beam device
JP5432028B2 (en) Focused ion beam device, tip end structure inspection method, and tip end structure regeneration method
JP2008140623A (en) Electron beam source device
US8890093B2 (en) Charged particle beam apparatus and method for forming observation image
WO2023067681A1 (en) Charged particle beam device
JP2000251751A (en) Liquid metal ion source and flow impedance measuring method of liquid metal ion source
JP5592136B2 (en) Chip tip structure inspection method
JP6236480B2 (en) Emitter fabrication method
JP2010257854A (en) Ion beam device

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14851678

Country of ref document: EP

Kind code of ref document: A1

DPE1 Request for preliminary examination filed after expiration of 19th month from priority date (pct application filed from 20040101)
ENP Entry into the national phase

Ref document number: 2015541606

Country of ref document: JP

Kind code of ref document: A

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14851678

Country of ref document: EP

Kind code of ref document: A1