WO2015133214A1 - 走査電子顕微鏡 - Google Patents

走査電子顕微鏡 Download PDF

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Publication number
WO2015133214A1
WO2015133214A1 PCT/JP2015/053033 JP2015053033W WO2015133214A1 WO 2015133214 A1 WO2015133214 A1 WO 2015133214A1 JP 2015053033 W JP2015053033 W JP 2015053033W WO 2015133214 A1 WO2015133214 A1 WO 2015133214A1
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Prior art keywords
slit
electron beam
electron
selection
transmittance
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Ceased
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PCT/JP2015/053033
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English (en)
French (fr)
Japanese (ja)
Inventor
早田　康成
健良 大橋
貴文 三羽
範次 高橋
源 川野
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Hitachi High Tech Corp
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Hitachi High Technologies Corp
Hitachi High Tech Corp
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Priority to US15/123,828 priority Critical patent/US10134558B2/en
Publication of WO2015133214A1 publication Critical patent/WO2015133214A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • 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 or ion-optical arrangement
    • H01J37/05—Electron or ion-optical arrangements for separating electrons or ions according to their energy or mass
    • 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 or ion-optical arrangement
    • H01J37/10—Lenses
    • H01J37/145—Combinations of electrostatic and magnetic lenses
    • 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
    • H01J37/21—Means for adjusting the focus
    • 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
    • H01J37/261—Details
    • H01J37/263—Contrast, resolution or power of penetration
    • 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
    • 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
    • H01J37/29—Reflection microscopes
    • H01J37/292—Reflection microscopes using scanning ray
    • 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
    • H01J2237/05—Arrangements for energy or mass analysis
    • H01J2237/057—Energy or mass filtering
    • 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
    • H01J2237/153—Correcting image defects, e.g. stigmators
    • H01J2237/1534—Aberrations
    • 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

Definitions

  • the present invention relates to an inspection / measurement apparatus using an electron beam.
  • a scanning electron microscope (SEM) used for observation, inspection, and measurement of a sample using an electron beam accelerates electrons emitted from an electron source, and irradiates them by focusing them on the sample surface by electrostatic or electromagnetic lenses. This is called primary electrons. Secondary electrons (low energy electrons are sometimes referred to as secondary electrons and high energy electrons are sometimes referred to as reflected electrons) are emitted from the sample by the incidence of primary electrons. By detecting these secondary electrons while deflecting and scanning the electron beam, it is possible to obtain a scanned image of a fine pattern or composition distribution on the sample. Further, an absorption current image can be formed by detecting electrons absorbed in the sample.
  • SEM scanning electron microscope
  • One of the basic functions of a scanning electron microscope is the resolution of the electron beam.
  • various methods have been tried.
  • One of them is a technique for reducing the energy dispersion of the electron beam using an energy filter. This reduces chromatic aberration by reducing energy dispersion and improves resolution.
  • the energy filter achieves energy dispersion reduction by having an orbital disperser that disperses the trajectories of electrons of different energies in the electron beam and a selection slit that selects the energy range of the dispersed electron beam.
  • Energy filters are classified into methods called omega filters, Wien filters, etc., according to the method of dispersing the electron trajectory.
  • Patent Document 1 describes a technique for measuring the intensity of an electron beam on a plate including a selection slit.
  • Patent Document 2 describes a method for optimizing the position of an electron beam on an energy selection slit by minimizing the current (slit current) flowing through the energy selection slit.
  • Patent Document 3 discloses a mechanical slit moving mechanism for slit selection.
  • Patent Document 1 a time for two-dimensional scanning of the electron beam on the selected slit is required, and the time used for the original purpose of the electron microscope is reduced.
  • frequent two-dimensional scanning on the selected slit may cause instability of the electron beam and should be avoided as much as possible.
  • Patent Document 2 there is no viewpoint for long-term stable operation of the apparatus, and no consideration is given to fluctuations in the slit irradiation current.
  • Patent Document 3 only describes a mechanical movement mechanism of an adjustment slit.
  • An object of the present invention is to solve these problems and to provide an energy filter that realizes stable reduction of energy dispersion.
  • the present invention includes a plurality of means for solving the above problems.
  • an electron source that generates an electron beam
  • an orbital disperser that disperses orbits of electrons having different energies in the electron beam
  • a dispersion A selection slit plate having a selection slit for selecting the energy range of the electron beam
  • a transmittance monitor unit for monitoring the transmittance of the electron beam that passes through the selection slit.
  • the present invention it is possible to efficiently monitor information on the position of the electron beam on the selected slit, and as a result, energy dispersion can be reduced and resolution can be stabilized.
  • FIG. 1 is an overall schematic diagram of a scanning electron microscope according to Embodiment 1.
  • FIG. FIG. 3 is a shape diagram of an electron beam on a selection slit plate according to the first embodiment.
  • 5 is a flowchart of an adjustment process of an electron beam position on a selected slit plate according to the first embodiment.
  • FIG. 6 is a diagram illustrating an example of signals obtained by scanning an electron beam on a selected slit plate according to the first embodiment.
  • FIG. 3 is an overall schematic diagram of a scanning electron microscope according to a second embodiment.
  • FIG. 6 is a diagram illustrating a selection slit plate and an electron beam according to the third embodiment.
  • 10 is a flowchart of transmittance measurement timing using the signal intensity of slit secondary electrons according to the fourth embodiment.
  • FIG. 10 is a flowchart of an electron beam position adjustment process on a selected slit plate according to a fifth embodiment. 10 is a flowchart for performing focus correction according to the sixth embodiment.
  • FIG. 10 is a diagram showing the shape of an electron beam on a selection slit plate of Example 7.
  • FIG. 10 is an electron beam trajectory diagram of Example 7.
  • FIG. 10 is a diagram showing a monitor screen of Example 8.
  • FIG. 10 is a setting value table for each reference value mode according to the ninth embodiment.
  • FIG. 1 shows an overall schematic diagram of the scanning electron microscope of this example.
  • primary electrons 116 emitted from the electron source 100 are a first condenser lens 103, a first electrostatic deflector 150, a first electromagnetic deflector 151, a second electrostatic deflector 160, and a second electromagnetic.
  • An image is formed on the sample 114 on the stage 115 by the deflector 161, the second condenser lens 105, and the objective lens 113.
  • the set of the first electrostatic deflector 150 and the first electromagnetic deflector 151 acts as an orbital disperser that disperses the trajectories of electrons having different energies in the electron beam, and the second electrostatic deflector arranged with the selection slit interposed therebetween.
  • the device 160 and the second electromagnetic deflector 161 act as an optical element for correcting the orbital dispersion.
  • a negative high voltage is applied to the first and second electrostatic deflectors 150 and 160 in order to improve the generation efficiency of deflection chromatic aberration. Therefore, the first and second electrostatic deflectors 150 and 160 have an effect of acting as a deceleration type electrostatic lens.
  • a positive voltage is applied to the magnetic path on the objective lens 113, and a negative voltage is applied to the sample 114. Since the electrostatic lens is formed here, the objective lens 113 is a magnetic field electric field superimposing lens. The opening of the objective lens 113 faces the sample side, and has a lens structure called a semi-in lens type.
  • the secondary electrons 117 emitted from the sample 114 are detected by the detector 121 in the middle. Detected and form a secondary electron signal. If the sample state is the same, this secondary electron signal corresponds to the amount of current transmitted through a selection slit 302 described later.
  • the primary electrons on the sample are scanned two-dimensionally by the first scanning deflector 106 and the second scanning deflector 108, and as a result, a two-dimensional image can be obtained.
  • the first and second scanning deflectors 106 and 108 are electrostatic deflectors.
  • the two-dimensional image is displayed on the display device 147.
  • the set of the first electrostatic deflector 150 and the first electromagnetic deflector 151 and the set of the second electrostatic deflector 160 and the second electromagnetic deflector 161 are often referred to as “ExB” (E cross B).
  • FIG. 2 is a diagram showing the shape of the electron beam on the selection slit plate 170.
  • the first electrostatic deflector 150 and the first electromagnetic deflector 151 are deflected in the opposite direction (left-right direction in FIG. 2) in the direction orthogonal to the longitudinal direction of the selection slit 302, and deflected chromatic aberration on the selection slit plate 170. Is only generating. Since the deflection chromatic aberration produces a horizontally long beam, the electron beam 303 has a horizontally long beam shape. By extracting a part of the electron beam 303 by the selection slit 302, energy dispersion can be reduced. In general, an energy filter based on this principle is called a Wien filter.
  • a slit current measuring unit 180 for example, an ammeter
  • a ratio calculating unit 181 for example, a calculation circuit and software for the ratio of the slit current and the secondary electron signal
  • the ratio A transmittance monitor unit is provided which includes a change amount calculation unit 182 (the calculation unit 181 can be used as a calculation circuit).
  • This transmittance monitor unit can monitor the transmittance of the electron beam 303 transmitted through the selection slit 302.
  • the transmittance may be the ratio of the amount of electron beam (current amount) transmitted through the selection slit 302 to the amount of electron beam (current amount) impinging on the selection slit plate 170 or hitting the selection slit plate 170.
  • a ratio of the sum of the electron beam amount and the electron beam amount transmitted through the selection slit 302 to the electron beam amount transmitted through the selection slit 302 may be used.
  • the amount of current of electrons emitted from the electron source generally varies.
  • the initial decrease in the amount of current is particularly large, and even in the Schottky type electron source, there is an increase or decrease in the amount of current called pulsation. Therefore, the amount of current applied to the selection slit plate 170 is not necessarily constant.
  • the intensity of the secondary electron signal (transmitted electron signal when viewed from the selection slit 302) generated from the slit current and the electrons transmitted through the selection slit 302 depends on the amount of current applied to the selection slit plate 170 and the slit of the electron beam 303. Determined by transmittance.
  • the slit beam transmittance most reflects the position of the electron beam on the selected slit plate 170, the intensity of the secondary electron signal generated from the slit current and the electrons transmitted through the selected slit 302 alone is not sufficient.
  • monitoring the position variation is advantageous in view of the efficiency of the monitor, an error due to the amount of current applied to the selected slit plate 170 occurs. Therefore, a monitor value substantially corresponding to the transmittance can be obtained by determining the ratio of the intensity of the secondary electron signal generated from the electrons transmitted through the selection slit 302 and the slit current.
  • the position variation of the electron beam 303 on the selection slit plate 170 affects the characteristics of the transmitted electron beam.
  • a direct effect is a change in the amount of current, which affects the SN of the acquired image.
  • Another important characteristic change is that the center energy shifts.
  • the focal position on the sample changes, and the resolution of the electron beam on the sample changes.
  • the energy dispersion value eventually changes, causing a resolution variation through chromatic aberration.
  • Such a variation in resolution cannot be ignored as a factor of characteristic deterioration particularly in a CDSEM that requires measurement of an imaging pattern dimension with good reproducibility. Therefore, it is important for the stable operation of the apparatus to use the transmittance that can sense the correct position change of the electron beam as the monitor value.
  • the intensity of the slit current flowing through the selection slit plate 170 and the transmission electron signal (secondary electron 117 corresponding to the amount of transmission current) of the selection slit 302 is measured for each measurement sample, and the ratio is determined as the transmittance. Monitor value. Further, in order to know the change, the change amount of the ratio is calculated. Note that the change amount of the ratio to be calculated may be an absolute value of a changing value or a change rate indicating a relative change.
  • the calculation units 181 and 182 can be integrated, and the components may be shared.
  • FIG. 3 shows a flowchart of the adjustment process of the electron beam position on the selected slit plate in the present embodiment.
  • the monitor value corresponding to the transmittance is obtained in step S01, and the transmittance is measured.
  • a change from the initial value of the transmittance is calculated in step S02, and in step S03, it is determined whether or not the value exceeds the reference value. If the value exceeds the reference value, the change on the selected slit plate 170 is determined. It is determined that the electron beam position has greatly shifted, and the electron beam 303 is scanned on the selection slit plate 170 in step S04, and the electron beam position on the selection slit plate 170 is adjusted in step S05.
  • the relative position between the electron beam 303 and the selection slit 302 can be adjusted to a predetermined position, generally the position where the center of the electron beam 303 is the center of the selection slit 302. .
  • the specific process of position adjustment is performed by using the first electrostatic deflector 150, the first electromagnetic deflector 151, the first aligner 102, etc. as a deflection scanning unit that deflects and scans the electron beam 303 on the selected slit plate 170.
  • a relative position between the electron beam 303 and the selection slit 302 is adjusted by using a deflector or a slit moving mechanism 171.
  • FIG. 4 shows an example of signals by electron beam scanning.
  • FIG. 4A shows the positional relationship between the electron beam 303 and the selection slit 302. The center coincides with the Y direction, but the center of the electron beam 303 is shifted to the left side of the drawing in the X direction. Shows the case.
  • FIG. 4B shows a profile of a transmission electron signal (secondary electron signal) generated from electrons transmitted through the selection slit 302 when the electron beam 303 is scanned in the X and Y directions under this condition.
  • the upper diagram shows the profile of the transmitted electron signal with respect to the Y-direction scanning position
  • the lower diagram shows the profile of the transmitted electron signal with respect to the X-direction scanning position.
  • the longitudinal direction of the shape of the selection slit 302 and the shape of the electron beam 303 is different, different transmission electron signal profiles are shown in the X direction and the Y direction. That is, in the case of the profile for the Y-direction scanning position in the upper diagram of FIG. 4B, the center of the electron beam 303 and the selection slit 302 in the Y direction coincides, so that the profile of the transmitted electron signal is at the scanning center. On the other hand, it is symmetrical. On the other hand, in the case of the profile for the X-direction scanning position in the lower diagram of FIG. 4B, the center of the electron beam 303 is shifted to the left with respect to the center of the selection slit 302. Since the scanning distance is increased in order to make the transmitted electron signal zero by moving all the positions to the right side of 302, the profile center is shifted to the right with respect to the scanning center. That is, the difference between the scanning center and the profile center is an amount to be adjusted.
  • the Wien filter used in this embodiment two deflectors are used to irradiate the selection slit 302 without bending the electron beam 303. Therefore, there is an advantage that the present embodiment can be effectively used such that the scanning and adjustment of the electron beam position can be performed by using a deflector of a Wien filter whose incident angle to the selection slit 302 is stable.
  • the transmittance was monitored for each wafer.
  • the resolution of the electron beam on the sample can be controlled to 1.5 nm ⁇ 0.15 nm.
  • the monitor timing of the transmittance is not limited to each wafer, and can be operated for each lot or for a predetermined time.
  • the electron source that generates the electron beam the orbital disperser that disperses the orbits of the electrons with different energies of the electron beam, and the selection that selects the energy range of the dispersed electron beam.
  • the orbital disperser can be configured to include a pair of overlapping electromagnetic deflectors and electrostatic deflectors to disperse electron trajectories with different energies of the electron beam. Further, by having a second set of overlapping second electromagnetic deflector and second electrostatic deflector, the set and the second set are arranged with a selection slit in between. Acts as a correction optical element for orbital dispersion.
  • the transmittance monitor unit includes a transmission electron signal measurement unit for a selection slit, a measurement unit for a slit current flowing through the selection slit plate, a calculation unit for calculating a ratio of signals from the two measurement units, The calculation unit is configured to calculate the amount of change in the ratio.
  • a deflection scanning unit that deflects and scans the electron beam on the selected slit is provided, and when the change in transmittance exceeds a reference value, the deflection scanning unit deflects and scans the electron beam on the selected slit.
  • the deflection scanning unit is a deflector that deflects an electron beam or a slit moving mechanism that moves the selected slit plate.
  • FIG. 5 shows an overall schematic diagram of the scanning electron microscope of the present embodiment.
  • Slit detector 411 for detecting slit secondary electrons 415 generated by irradiation of electron beam 303 to selected slit plate 170
  • slit detection system control unit 412 for controlling slit detector 411
  • selection slit 302 are transmitted.
  • a Faraday cup 413 for measuring the transmitted electron beam current, a transmitted current measuring unit 414 for measuring the current, a slit signal indicating the signal intensity of the slit secondary electrons detected by the slit detector 411, and a transmitted current measuring unit 414 This is a point having a slit signal for calculating the ratio of the transmission current measured in step 4 and a ratio 481 of the transmission current ratio.
  • Others are the same as those of the first embodiment shown in FIG.
  • the slit secondary electrons 415 generated by the irradiation of the electron beam 303 to the selection slit plate 170 are obtained.
  • the slit signal (in other words, the reflected electron signal of the selected slit plate) that is the signal intensity detected by the slit detector 411 and the transmitted electron beam current that has passed through the selected slit measured by the Faraday cup 413 instead of the secondary electrons 117 This is different from the first embodiment in that (transmission current) is used.
  • the monitor value of the transmittance in this embodiment is obtained by calculating the ratio of the reflected electron signal of the selected slit plate 170 which is the signal intensity of the slit secondary electrons 415 and the transmitted current which is the transmitted electron beam current of the selected slit 302. Therefore, it is obtained from the amount of change in the ratio. That is, the transmittance of the electron beam that passes through the selected slit can be monitored by these transmittance monitor units.
  • the trajectory of the electron beam after passing through the selected slit is controlled by a deflector.
  • the merit of this embodiment is that the insulation process and wiring for measuring the slit current are not required, and the selection slit that is measured by the Faraday cup while the secondary electrons are affected by the surface state of the sample.
  • the transmitted electron beam current transmitted is accurate and reliable.
  • the transmittance can be monitored by a combination of the transmission electron signal (the signal amount of the secondary electrons 117) and the slit signal (slit secondary electrons 415) used in the first embodiment. Further, the transmittance may be monitored by a combination of the slit current and the transmission current (transmission electron beam current transmitted through the selected slit measured by the Faraday cup) used in the first embodiment.
  • the transmittance was monitored for each lot.
  • the resolution of the electron beam on the sample can be controlled to 1.5 nm ⁇ 0.25 nm.
  • the electron source that generates the electron beam the orbital disperser that disperses the orbits of the electrons with different energies of the electron beam, and the selection that selects the energy range of the dispersed electron beam.
  • the transmittance monitor unit includes a transmission current amount measuring unit, and a selection slit.
  • the reflection electron signal measurement unit of the plate, a calculation unit that calculates the ratio of signals from the two measurement units, and a calculation unit that calculates the amount of change in the ratio are used.
  • FIG. 6 is a diagram showing a selective slit plate and an electron beam used in this embodiment. Other overall configurations are the same as those in the first or second embodiment.
  • the selective slit plate 500 has a large size opening (transmission opening 503) capable of transmitting substantially the entire electron beam in the vicinity of the selection slit 501 for reducing energy dispersion.
  • the electron beam 502 is electrically moved between two openings (selection slit 501 and transmission opening 503), and two transmission electron signals or transmission currents are measured. Then, from the ratio of these two values, the transmittance of the electron beam is obtained as the ratio of the electron beam that passes through the selective slit 501 to the entire electron beam generated from the electron source, and is used as the monitor value. That is, it is possible to monitor the transmittance of the electron beam transmitted through the selection slit 501 by these transmittance monitor units.
  • the merit of the present embodiment is that the measurement of the transmittance does not require the measurement of the slit current or the slit secondary electrons, and the transmittance can be obtained as an absolute value.
  • this embodiment has a transmission aperture that transmits the entire electron beam in the vicinity of the selection slit as the selection slit plate, and the transmittance monitor unit transmits a transmission electron signal or transmission that transmits the selection slit.
  • a first measurement value of current a measurement unit that measures a second measurement value of a transmission electron signal or transmission current that is transmitted through the transmission aperture, and a calculation unit that calculates a ratio of the first and second measurement values And a calculation unit for calculating the amount of change in the ratio.
  • the present embodiment it is possible to efficiently monitor the information regarding the electron beam position on the selected slit, and as a result, it is possible to realize stabilization of energy dispersion reduction and resolution improvement,
  • the measurement of the transmittance does not require the measurement of the slit current or the slit secondary electrons, and the transmittance can be obtained as an absolute value.
  • the slit secondary electron signal can always be measured, and the time used for the original purpose is not reduced.
  • monitoring of this signal change can be expected to detect any abnormality.
  • the irradiation electron beam varies as described above, it is imperfect as a monitor of the position of the electron beam on the selective slit plate. Therefore, in this embodiment, when the signal intensity change of the secondary electrons of the slit exceeds the reference value, the transmittance is measured to determine whether the electron beam position needs to be adjusted.
  • FIG. 7 shows a flowchart of the transmittance measurement timing using the signal intensity of the slit secondary electrons.
  • step S06 the signal intensity of the slit secondary electrons is measured.
  • a specific configuration is detected by the slit detector 411 in FIG.
  • step S07 the rate of change in signal strength is calculated.
  • step S08 it is determined whether or not the value exceeds the reference value. If the value exceeds the reference value, the transmittance is measured in step S09.
  • the change rate indicating the relative change is described as the change amount of the signal intensity, but may be an absolute value of the changing value.
  • the point that the intensity of the secondary electron signal of the slit is used as a reference for determining the timing for monitoring the transmittance of the electron beam, but this idea is based on other signals (slit current, transmitted electron signal, (Transmission current). In addition, it is considered effective to monitor the transmittance for each wafer or lot in parallel with this timing.
  • this embodiment measures the transmission electron signal or transmission current of the selection slit, the reflection electron signal of the selection slit plate, or the slit current flowing through the selection slit plate, and the amount of change in the measured value is the reference value.
  • the transmittance monitor unit measures the transmittance of the electron beam at the selected slit. Thereby, the timing for monitoring the transmittance of the electron beam can be determined.
  • FIG. 1 The processing flow of this example is shown in FIG.
  • the overall configuration according to the present embodiment is the same as that of FIG. 1 or FIG. 5, and is different from FIG. 3 in that a plurality of reference values are provided as a processing flow.
  • the transmittance is monitored in steps S10, S11, and S12 to determine whether the change is less than the first reference value. This is the same processing as steps S01, S02, and S03 in FIG. If it is greater than or equal to the first reference value, it is determined that the position of the electron beam on the selected slit plate has greatly deviated, and the process moves to the adjustment of the electron beam position.
  • the position adjustment is performed by the deflection scanning unit by the deflection scanning of the electron beam on the selected slit plate.
  • a method of adjusting the beam position on the slit by correction by a deflector such as the first electrostatic deflector 150, the first electromagnetic deflector 151, or the first aligner 102, and a machine by the slit moving mechanism 171
  • a method of adjusting the relative electron beam position by driving a slit stage (not shown).
  • the mechanical position control by driving the slit stage does not have a position resolution as much as the position control of the electric electron beam, but it can be moved greatly, and it is important to use both properly.
  • step S13 the accumulated value of the deflector correction is referred to, and in step S14, it is determined whether the value is greater than or equal to the second reference value. If the value is less than or equal to the second reference value, deflection by the deflector is performed in step S15. The beam position on the slit is adjusted by adjusting the intensity of the amount. On the other hand, if it is greater than or equal to the second reference value, in step S16, the displacement of the electron beam trajectory increases, so that the movement is adjusted by driving the slit stage to adjust the relative electron beam position.
  • this embodiment determines whether the accumulated value of the electron beam correction by the deflector is larger than the second reference value in the deflection scanning of the electron beam on the selected slit plate, and the accumulated value is If it is less than the second reference value, the position of the electron beam is adjusted by the deflector, and if the accumulated value is greater than or equal to the second reference value, the selected slit position is adjusted by the slit moving mechanism.
  • the electron beam position adjustment on the selected slit plate it is possible to perform adjustment in consideration of both accuracy due to position resolution and position adjustment speed.
  • the movement of the electron beam on the selected slit plate shifts the center value of the energy of the electron beam. This changes the focal position of the electron beam on the sample surface, which causes variations in resolution.
  • manual focus correction is always performed, so this variation is hardly realized.
  • the transmittance is monitored, and the focus correction is performed when the change is equal to or greater than the reference value.
  • the overall configuration of the scanning electron microscope of this example is the same as that of Example 1 or 2.
  • FIG. 9 shows a flowchart of this embodiment.
  • the transmittance is monitored in steps S17, S18, and S19 to determine whether the change is less than the reference value.
  • the change rate indicating the relative change is described as the change amount of the monitor value.
  • the absolute value of the change value may be used.
  • the monitor value of the transmittance is the transmission electron signal or transmission current of the selection slit, the reflection electron signal of the selection slit plate, or the slit current flowing through the selection slit plate, as in the first or second embodiment.
  • step S20 focus correction is performed in step S20. In this way, it is possible to suppress fluctuations in resolution with a small number of focus correction operations.
  • focus correction reference value is smaller than the first reference value for determining whether or not to perform the electron beam position adjustment of the fifth embodiment.
  • focus correction may be performed by changing the current of the objective electromagnetic coil that is usually performed, but here, it is handled by changing the stage voltage. Since the cause of the focus change is a change in the energy of the electron beam, the stage voltage was changed in order to keep the irradiation energy to the sample constant.
  • the electron source that generates the electron beam the orbital disperser that disperses the orbits of the electrons with different energies of the electron beam, and the selection that selects the energy range of the dispersed electron beam.
  • a selection slit plate having a slit, an objective lens for irradiating the sample with an electron beam, a stage on which the sample is placed, a transmission electron signal or transmission current of the selection slit, a reflection electron signal of the selection slit plate, or a slit current flowing through the selection slit plate
  • a transmittance monitor section for monitoring the above-mentioned, and when the amount of change in the monitored value is larger than the reference value, the focus correction on the sample is performed.
  • FIG. 10 is a diagram showing the shape of the electron beam on the selected slit plate in this example. 10, the shape of the electron beam 1003 has a width in the longitudinal direction of the selection slit 302 as compared with FIG.
  • the electron beam 1101 (electron beam 1003 in FIG. 10) irradiating the selection slit 302 forms a focal point on the slit as shown in FIG. This is to enhance the selectivity by the energy dispersion selection slit 302. However, this is not always necessary in the longitudinal direction of the selection slit 302.
  • the ratio of the slit current value measured by the slit ammeter 1104 and the transmission current value measured by the transmission ammeter 1105 is calculated by the arithmetic unit 1106 to thereby obtain the electron beam.
  • the transmittance of 1101 is monitored.
  • the longitudinal direction of the selection slit 302 of the electron beam 1003 in other words, the direction approximately perpendicular to the direction in which the trajectory of the electron beam 1003 is dispersed. It is desirable to irradiate the selection slit plate 170 with a larger width than in the case of in-focus.
  • a method of setting the focus state on the selection slit plate 170 to a defocus state or combining astigmatism and defocus to give a width only in the longitudinal direction of the selection slit 302 of the electron beam 1003. is effective.
  • This example describes an example of a monitor screen.
  • FIG. 12 is a diagram showing a monitor screen in the present embodiment.
  • the selection result of the monitor value, the monitor frequency, and the reference value level is displayed on the screen.
  • a graph showing changes in past monitor values is drawn.
  • monitor history ON / OFF display is also provided.
  • a monitoring method suitable for the state of the apparatus can be selected with reference to these.
  • This example describes the setting of the reference value.
  • the reference value used in each of the above-described embodiments varies depending on the resolution, throughput, etc. required by the apparatus, and thus needs to be set as appropriate.
  • the value may be set in advance or may be set each time while actually measuring.
  • a table is recorded in advance in the recording device 145 in FIG. 1, and the table is set with reference to the table at the time of setting.
  • FIG. 13 shows a setting value table for each mode in the case of the reference value of the transmittance change rate for adjusting the electron beam position on the selected slit plate.
  • the reference value in the high resolution mode 1, the reference value is small, and fine control is performed.
  • the high-speed mode 2 priority is given to throughput, and fine adjustment is omitted, and the reference value at that time is large.
  • the large current mode 3 is a mode in which a large current is passed in order to maintain the signal intensity, and the reference value at that time is medium. Further, in the case of the high focus depth mode 4, the reference value at that time is set to be medium.
  • the present invention is not limited to the above-described embodiments, and includes various modifications.
  • the present invention is also effective for other types of energy filters such as an omega filter and a gamma filter.
  • a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment.

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