WO2017018432A1 - 荷電粒子線装置 - Google Patents
荷電粒子線装置 Download PDFInfo
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- WO2017018432A1 WO2017018432A1 PCT/JP2016/071942 JP2016071942W WO2017018432A1 WO 2017018432 A1 WO2017018432 A1 WO 2017018432A1 JP 2016071942 W JP2016071942 W JP 2016071942W WO 2017018432 A1 WO2017018432 A1 WO 2017018432A1
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- charged particle
- deflector
- particle beam
- objective lens
- visual field
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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, ion-optical arrangement
- H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
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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, ion-optical arrangement
-
- 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
- H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
- H01J37/1471—Arrangements for directing or deflecting the discharge along a desired path for centering, aligning or positioning of ray or beam
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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, ion-optical arrangement
- H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
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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
- H01J37/21—Means for adjusting the focus
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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
- H01J37/248—Components associated with high voltage supply
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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
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- 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
- H01J2237/04—Means for controlling the discharge
- H01J2237/047—Changing particle velocity
- H01J2237/0473—Changing particle velocity accelerating
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- 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
- H01J2237/1536—Image distortions due to scanning
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- 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
- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2813—Scanning microscopes characterised by the application
- H01J2237/2817—Pattern inspection
Definitions
- the present invention relates to a charged particle beam apparatus, and more particularly to a charged particle beam apparatus including a deflector that moves a visual field position.
- a charged particle beam apparatus such as a scanning electron microscope is used for measurement and inspection of a fine semiconductor device pattern.
- the scanning electron microscope is a device that performs measurement and inspection using an image obtained by scanning a focused electron beam on a sample.
- Patent Document 1 discloses a charged particle beam apparatus including an image shift deflector and an aberration corrector that corrects an aberration that occurs during image shift according to the amount of image shift movement.
- Patent Document 2 a control device that controls an optical system so that a landing angle (an incident angle of an electron beam with respect to a sample) is vertical regardless of an image shift amount, and correction of aberrations such as astigmatism generated at that time.
- a charged particle beam apparatus including a corrector for performing the above is disclosed.
- JP 2014-53074 A Patent No. 5767777 (corresponding US Patent Publication US2012 / 0286160)
- the deflection chromatic aberration and the deflection geometric aberration are desirable to correct together.
- the voltage applied to the multipole element, rotationally symmetric lens, and deflector included in the aberration corrector according to the amount and direction of movement of the field of view.
- the visual field movement amount is large, the focus shift due to the curvature of field of the objective lens occurs, so the focus must be corrected with one of the lenses.
- the position of the objective lens object point fluctuates, and the deflection sensitivity (image movement amount per unit current) of the field moving deflector changes.
- the time until the current settles to the set value is constant regardless of the position of the objective lens object point, so if the deflection sensitivity changes, an image can be acquired from the input of the visual field movement signal Time to become fluctuates.
- a charged particle beam apparatus in which the first object is to perform large visual field movement while suppressing the amount of off-axis at the time of visual field movement that is a cause of aberrations. Furthermore, a charged particle beam apparatus is proposed which has a second object of correcting deflection chromatic aberration and deflection geometric aberration together.
- an objective lens for focusing a charged particle beam emitted from a charged particle source and irradiating the sample and a deflector for visual field movement for deflecting the charged particle beam are described below.
- a charged particle beam apparatus comprising: an accelerating tube disposed between the visual field moving deflector and the objective lens; a power source for applying a voltage to the accelerating tube; and deflection by the visual field moving deflector.
- a charged particle beam apparatus provided with a control device for controlling the voltage applied to the power supply according to conditions is proposed.
- an objective lens that focuses a charged particle beam emitted from a charged particle source and irradiates the sample, and a field movement deflector that deflects the charged particle beam.
- a charged particle beam apparatus comprising: a focus adjustment lens disposed between the object point of the objective lens and the objective lens; an acceleration tube disposed between the charged particle source and the sample; and
- a charged particle beam apparatus is proposed that includes a power source for applying a voltage or a current to the focus adjustment lens and the accelerator tube, and controls the voltage or the current to be applied to the power source according to a deflection condition by the visual field moving deflector.
- the first aspect it is possible to achieve both suppression of the amount of off-axis from the ideal optical axis of the charged particle beam and large visual field movement.
- simultaneous correction of deflection chromatic aberration and deflection geometric aberration when performing a visual field movement over a large area focus correction that keeps the waiting time until image acquisition constant, and harmonics of the deflector It is possible to realize a large visual field movement at high speed and high accuracy while simultaneously suppressing the amount of off-axis at the time of visual field movement for reducing aberration due to components.
- summary of the scanning electron microscope provided with the deflector for visual field movement The figure which shows the track
- summary of the scanning electron microscope provided with the deflector for visual field movement The figure explaining the outline
- stage movement involves mechanical movement, it takes considerable time to move. Further, the positioning accuracy is low with respect to the image shift.
- Image shift has the advantage that the field of view can be moved more accurately in a shorter time than the stage movement because the amount of deflection is controlled by the current supplied to the deflector and the applied voltage, but for example, a field of view of several tens of ⁇ m or more.
- the beam is greatly deviated from the ideal optical axis, so that the image quality may be deteriorated.
- the trajectory of primary electrons passes through the center of the objective lens, so that the landing angle varies in proportion to the amount of image shift.
- primary electrons may pass through the position of the front focal point of the objective lens.
- the primary electrons travel away from the objective lens, so that deflection chromatic aberration, deflection coma aberration, or deflection geometric aberration occurs, resulting in a reduction in resolution and field movement accuracy. This phenomenon becomes more apparent as the image shift amount increases.
- FIG. 2 is a diagram illustrating the trajectory of an electron beam deflected by an image shift deflector (field-of-view movement deflector). Due to the vertical landing (the beam reaching the sample is perpendicular to the sample surface or parallel to the ideal optical axis of the electron beam), the two-stage deflector causes the primary electrons (electron beam) to pass through the front focal point of the objective lens. Is set to Under these optical conditions, if the objective lens is designed to achieve a short focal length, the front focal length (the distance between the objective lens main surface and the intersection of the electron beam directly above the objective lens and the ideal optical axis of the electron beam) is short. Become.
- the focal length is shortened, the inclination of the primary electrons at the front focal point increases, and the off-axis amount (dn) at the lower deflector position increases. For this reason, it is necessary to install a deflector that can accurately give a large deflection angle to the primary electrons passing through a position off the center, which severely restricts the design and power supply specifications of the deflector. Further, since the focal length of the secondary electrons emitted from a position away from the optical axis due to the image shift is also shortened, the axis is largely separated after passing through the objective lens and the yield is reduced.
- the deflection intensity of the deflector is increased to perform a large image shift, the electrons emitted from the sample are deflected by the deflector for image shift. Due to this deflection, for example, when an image shift of several hundred ⁇ m is executed, the trajectory of signal electrons fluctuates, and the electron detection efficiency decreases.
- FIG. 1 is a diagram showing an example of a scanning electron microscope provided with a deflector for visual field movement.
- the scanning electron microscope illustrated in FIG. 1 includes an aberration correction unit including two rotationally symmetric lenses 07 and 08, a first aberration correction deflector 21, and a second aberration correction deflector 22. 301 is provided.
- the image shift deflector including the magnetic field deflector 23 and the electrostatic deflector 24 is disposed between the image shift deflector and the main surface of the objective lens 12, and a predetermined voltage is applied thereto.
- the acceleration tube 11 is provided.
- a positive voltage is applied to the accelerating tube 11 from a power source (not shown) according to the image shift amount (the signal amount of the magnetic deflector 23 and the electrostatic deflector 24).
- a focus adjustment lens 09 that is controlled to compensate for a focus condition that changes in accordance with a voltage applied to the acceleration tube 11 is provided. By adjusting the focus adjustment lens 09 according to the set potential of the accelerating tube 11, the fluctuation of the primary electron trajectory in the aberration corrector is suppressed, and the aberration correction condition is satisfied.
- the optical element control unit 300 is a control device that controls each component of the scanning electron microscope, and controls the scanning electron microscope based on input conditions such as an input device (not shown).
- the intensity ratio of the magnetic field type deflector 23 and the electrostatic type deflector 24 constituting the image shift deflector is set so that electrons emitted from the sample are arranged near the detector or the detector and emitted from the sample.
- the conditions so as to go to a secondary electron generating member that generates new secondary electrons due to collision of electrons fluctuations in the yield of detected electrons can be suppressed even when an image shift of 100 ⁇ m or more is performed.
- the focus adjustment lens 09 be closer to the sample 14 than the deflection aberration corrector 301 and the objective lens object point position in order not to change the incidence condition on the deflection aberration corrector 301 and the objective lens object point position.
- FIG. 3 illustrates another example of a scanning electron microscope provided with a field moving deflector.
- the optical system illustrated in FIG. 3 includes a deflection aberration corrector 301 including rotationally symmetric lenses 07 and 08 and a deflector 21, and corrects a deflection aberration that occurs during image shift. Further, by applying a positive voltage determined by the range of the image shift to be used to the accelerating tube 11, the amount of primary electrons off-axis at the position of the deflector 23 can be reduced, depending on the amount of off-axis. In addition to suppressing the generated aberration, it is possible to suppress a decrease in signal electrons emitted from the sample.
- an image shift deflector magnetic field type deflection
- the beam is deflected by the device 23 and the electrostatic deflector 24).
- the primary electrons 51 pass through the front focal position 202 of the objective lens 12 for vertical landing on the sample 13.
- the objective lens When the objective lens is shortened for higher resolution and the installation of a four-direction detector, the inclination of primary electrons at the front focal point increases, and the off-axis amount (dn, from the ideal optical axis 201 at the deflector position).
- the off-axis amount increases. If the influence of the aberration depending on the amount of off-axis is not negligible due to the increase of the amount of off-axis, the aberration becomes obvious, and the resolution is reduced and complicated control is required.
- the acceleration tube 11 to which a positive voltage can be applied is arranged so as to cover the front focal position of the objective lens 12, thereby suppressing the inclination of the primary electrons 51 as described above. More specifically, in the ideal optical axis direction of the electron beam, the moving range of the front focal position that moves in accordance with the change in the excitation condition of the objective lens and at least a part of the acceleration tube 13 have the same height.
- An acceleration tube 13 is disposed. Normally, the acceleration tube 11 is OFF, and the front focal length of the objective lens 12 is set to be short.
- the distance from the front focal point 203 to the objective lens main surface can be extended, and the inclination of the primary electrons 51 in the acceleration space can be relaxed.
- the amount of off-axis generated at the lower position of the image shift deflector when image shift is executed is smaller than when the acceleration tube is OFF (in the case of FIG. 2, the amount of off-axis is changed from dn to da. can do).
- Reduction of the off-axis amount means suppression of the deflection angle of the image shift deflector (deflection signal supplied to the image shift deflector) and suppression of the influence of the harmonic component of the deflection field.
- the excitation condition (focusing condition) of the objective lens is also changed in order to make the electron beam vertically land on the sample 13.
- the electrostatic lens main surface generated when a voltage is applied to the accelerator tube is generated closer to the electron source than the lens main surface of the objective lens, the main lens of the combined objective lens and accelerator tube is applied by voltage application to the accelerator tube. Since the surface position is away from the sample and the focal length is increased, the resolution is lowered.
- the electron beam is off-axis (image shift) or a large off-axis (for example, an image shift of a predetermined value or more), the image is not shifted by selectively applying the voltage of the acceleration tube 11.
- the resolution of the apparatus is increased by shortening the focal length, and when the image shift or the large image shift is performed. Realizes higher resolution by suppressing the amount of off-axis.
- the primary electrons 51 extracted from the electron source 01 by the first anode 02 and accelerated by the second anode 03 are focused by the first condenser lens 04 and then pass through the objective aperture 05. Thereafter, the light is focused by the second condenser lens 06.
- the primary electrons 51 that have passed through the second condenser lens 06 enter the deflection aberration corrector 301, are deflected by the deflector 21 in a direction perpendicular to the ideal optical axis of the beam, and pass off the axis of the aberration generating lens 07. Aberrations necessary for correction.
- the deflector 22 installed at the focal position of the first aberration correction lens 07 is turned back along the ideal optical axis and focused on the main surface of the second aberration correction lens 08.
- the primary electrons 51 that have passed through the deflection aberration corrector 301 are deflected by the deflector 23 so as to pass through the front focal point of the objective lens.
- the deflected primary electrons pass through the acceleration space created by applying a voltage to the accelerating tube 11 and then focused on the sample by the objective lens 12.
- the resolution is improved by using the acceleration electrode 13 to which a positive voltage is applied and the negative voltage application power source 15 for applying a negative voltage to the wafer 14 in combination. ing.
- a positive voltage is applied to the acceleration tube 11 installed separately from the acceleration electrode 13 according to the range of image shift to be used.
- the resolution is determined by the magnetic field distribution and potential distribution in the vicinity of the sample. Therefore, by separating the booster electrode and the accelerating tube, there is an advantage that the change in resolution is small when the optical mode is changed.
- the voltage applied to the accelerating tube 11 can suppress the off-axis amount as the applied voltage increases.
- the voltage applied to the accelerating tube 11 depends on the image shift amount. It is desirable to adjust. Specifically, when the amount of deflection of the primary electrons 51 by the image shift deflector is large, the deflection effect on the electrons emitted from the sample is increased accordingly. Therefore, for example, by applying a larger voltage to the acceleration tube 11 as the image shift amount is larger, the trajectory of electrons emitted from the sample can be adjusted toward the detector 10 or the like. Note that control may be performed such that a predetermined voltage is applied when the image shift amount is equal to or greater than a predetermined value.
- FIG. 4 is a diagram illustrating an example in which acceleration tubes 11 a and 11 b divided into two are installed in the vicinity of the objective lens 12.
- the optical system illustrated in FIG. 4 further includes shadow detectors 41 and 42. Although only two detectors are shown in FIG. 4, the shadow detector is composed of four detectors in which two detectors are arranged in the direction perpendicular to the paper with the ideal optical axis of the beam as the center. It will be described as a thing.
- a reflected electron trajectory 52 when the voltage of the accelerator tube is 0 V is indicated by a dotted line.
- the reflected electrons emitted in the right (left) direction are focused by the lens action of the objective lens and then detected by the detector 41 (42).
- the front focal length of the objective lens is shortened, the separation of reflected electrons emitted to the left and right is improved.
- a positive voltage is applied to the acceleration tubes 11a and 11b.
- the reflected electron trajectory 13 at this time is indicated by a solid line.
- a shadow contrast image acquisition mode (first optical mode) and a high-speed multipoint measurement mode (second optical mode) are prepared, and these two modes can be switched.
- first optical mode a shadow contrast image acquisition mode
- second optical mode high-speed multipoint measurement mode
- the voltage applied to the accelerating tube may be relatively increased as compared with the first optical mode.
- the voltage applied to the acceleration tube may be adjusted according to the magnitude of the image shift amount. In this case, the voltage applied to the acceleration tube is increased as the off-axis amount is larger.
- FIG. 1 shows a schematic diagram of an optical system according to the third embodiment.
- a focus adjusting lens 9 is disposed between the detector 10 and the deflection aberration corrector 301.
- this optical system is shown below. Because of the large deflection, when a positive voltage is applied to the acceleration tube 11 or the objective lens 14 is weakly excited, the objective lens object point set on the main surface of the second aberration correction lens 11 is shifted.
- the focus adjustment lens 09 is operated so as to fix the position of the object plane P1 according to the excitation amount of the acceleration tube 11 and the objective lens 14.
- the excitation amount of the accelerating tube 11 and the objective lens is adjusted to change to the optical mode that suppresses the off-axis amounts of primary electrons and secondary electrons. Since the trajectory in the aberration corrector can be maintained, aberration correction can be performed in the deflected optical mode, and deterioration in image quality that occurs during image shift can be suppressed.
- the fourth embodiment is shown in FIG.
- acceleration tubes 11, 13, 13 'for accelerating the entire optical path of the primary electrons 51 are provided, and a magnetic field deflector 23 for image shift and an electrostatic deflector 24 are placed in the magnetic field of the objective lens 12. It is installed in.
- image shift field movement
- image shift is performed using the preliminary deflector 25, the magnetic field deflector 23, and the electrostatic deflector 24.
- the electrons emitted from the sample in the optical system shown in the present embodiment are subjected to the convergence action of the objective lens and the deflection actions of the deflectors 23 and 24 until reaching the detector 15.
- the magnetic field type deflector 23 and the electrostatic deflector 24 are used as the image shift deflector.
- the deflection intensities B1 and E1 of the magnetic field type deflector 23 and the electrostatic type deflector 24 are operated at a ratio expressed by the equation (1).
- E1 qB1 ⁇ v0 (1)
- q represents an elementary charge
- v0 represents the velocity of secondary electrons emitted from the sample.
- the primary electrons 51 that have passed through the deflection aberration corrector 301 are preliminarily deflected by the image shift preliminary deflector 25.
- Preliminarily deflected primary electrons enter the axis of the objective lens and are deflected by the magnetic deflector 23 and the electrostatic deflector 24 installed at the same position in the lens field (in the leakage magnetic field of the objective lens).
- the signal electrons emitted from the sample are given to the primary electrons with a deflection angle necessary for image shift. Even if it passes through the positions of the deflectors 23 and 24, it can be detected by the detector 10 without being deflected.
- the secondary electron trajectory when deflected only by the magnetic deflector 23 is shown at 52.
- the secondary electrons emitted from the sample are subjected to the deflection action of the deflector 23, pass through the trajectory of the dotted line 52, and collide with the acceleration tube 11, so that they cannot be detected.
- FIG. 7 shows the acceleration tube 11 divided into two parts (11, 13).
- the higher the voltage of the accelerating tube the larger the effect can be obtained.
- the acceleration tube is divided into two parts as 11 and 13, and the electric field strength on the sample surface is accelerated by the acceleration tube 11 and the optical path of the primary electrons 51 is accelerated by 13, thereby suppressing dielectric breakdown and charge-up.
- the electrostatic lens 31 when a high voltage is applied to the acceleration tube 11, a large potential difference is generated between the acceleration tube 11 and the acceleration tube 13, and the electrostatic lens 31 is formed.
- the lens action of the electrolens 31 forms a composite lens of the electrostatic lens 31 and the magnetic field lens 32, and the lens main surface is separated from the sample.
- the objective lens main surface 32 and the main surface of the electrostatic lens 31 may be made to coincide with each other.
- the acceleration tube 13 is made very small. It is difficult to realize due to design reasons such as the need to make. Therefore, when it is desired to acquire an image with high resolution, the same voltage is applied to the acceleration tubes 11 and 13, and when a large visual field shift (image shift) is to be performed, the acceleration tube 13 is relative to the acceleration tube 11.
- a high voltage is applied to the lens, it is possible to achieve both high resolution by bringing the lens main surface close to the sample and reduction in resolution by suppressing the amount of off-axis of the beam during image shift.
- the aberration of the deflector and the lens in each section can be reduced, but between the accelerating tube 11 and the accelerating tubes 13 ′ and 13 ′′. If there is a potential difference, the lens action occurs in the space where the potential difference occurs, and the resolution decreases. Therefore, if you want to acquire a high-resolution image without image shift, apply the same voltage to all the accelerator tubes, and if you want to move a large field of view, the section where the off-axis occurs due to deflection. It is desirable to perform control so as to increase the electric potential (inside the acceleration tubes 11, 13, 13 ').
- FIG. 6 shows a flowchart in the case where high-speed multipoint measurement is executed using the optical system shown in FIG. 1 as a fifth embodiment.
- step 001 information on measurement points is read from the design data of the device to be measured.
- step 002 an image shift range necessary for measurement is determined.
- the optical mode determination unit 301 determines a necessary image shift range from the measurement point density in the design data read by the user or S001.
- the voltage and current of the acceleration tube 11 (13, 13 ′, 13 ′′) and the focus adjustment lens 09 are obtained from the image shift range determined in step 002, and the obtained values are passed to the optical element control unit 300. Set the current value and voltage value of the lens.
- the optical element control unit 300 in FIG. 1 or the like includes an input device (not shown), and can select a measurement mode, input an image shift range, an address to be measured, and the like. Next, the stage is moved from the measurement point data read in step 003 to the measurement point.
- step 004 the image shift amount is set to 0, focus and stigma adjustment are performed, and a low-magnification image of several thousand times is acquired.
- the focus and stigma amount at this time are recorded in the focus and stigma recording unit 302.
- the height of the wafer is estimated from the recorded focus value and the set optical condition value.
- step 005 the low-magnification image acquired by the measurement position calculation unit 303 is compared with the design data, and the distance from the current visual field position to each measurement point is calculated.
- step 006 the image shift condition calculation unit 304 obtains the image shift magnification and the rotation angle in the image shift direction that vary depending on the sample height, and the optical conditions of the aberration correction unit 201 for image shifting the distance calculated in step 006, and The conditions of the image shift deflectors 23 and 24 are set.
- the image shift condition calculation unit the aberration correction condition obtained by simulation or experiment and the setting condition of the image shift deflector are functionalized, and using this function, the optical element that gives the desired image shift amount is made a function. Determine the set current and voltage.
- the focus stigma correction amount calculation unit 305 calculates a focus adjustment amount and a stigma adjustment amount that are generated when a desired image shift is performed, and adds the values stored in the focus and stigma recording unit 302 to the focus. And adjust the amount of stigma.
- the image distortion vertical magnification, horizontal magnification, rotation angle, orthogonality
- the image distortion is obtained by applying feedback to the input signal to the scan coil 27. Correct.
- step 009 an image of the measurement point is acquired.
- step 010 it is confirmed whether there are any unmeasured measurement points in the image shiftable range. If there is an unmeasured measurement point in the image shiftable range, the process returns to step 006. If there are no unmeasured measurement points, the process proceeds to step 011. In step 011, it is confirmed whether there are any unmeasured measurement points in the wafer. If there is an unmeasured measurement point, the process returns to step 002 to move the stage. If there are no unmeasured measurement points, the process proceeds to step 012 to end the measurement.
- the sample height is calculated from the focus current value at the time of image acquisition (step 004) for obtaining the distance to the measurement point after moving the stage, and the third-order positional deviation amount due to the image shift magnification, the rotation direction, and distortion aberration is calculated.
- an image with little degradation in resolution, secondary electron yield and landing angle fluctuation can be obtained even when an image shift of several hundred microns is executed, so that high-speed, high-precision multipoint measurement can be executed.
- FIG. 8 is a diagram showing an example of a scanning electron microscope provided with a deflector for visual field movement.
- the scanning electron microscope illustrated in FIG. 8 includes an aberration correction unit 301 including two rotationally symmetric lenses 07 and 08, a first aberration correction deflector 21, and a second aberration correction deflector 22. This corrects deflection chromatic aberration that occurs when the field of view moves.
- the field-moving deflector composed of the magnetic field-type deflector 23 and the electrostatic deflector 24 is disposed between the field-moving deflector and the virtual deflection fulcrum 204 at the time of moving the field, and has a predetermined voltage or current.
- a focus adjustment lens 09 to which is applied is provided. By controlling the voltage or current applied to the focus adjustment lens 09 in accordance with the amount of visual field movement, focus adjustment is performed while suppressing fluctuations in the primary electron trajectory in the aberration correction unit and satisfying aberration correction conditions.
- the deflection of the visual field movement deflector 23 is performed.
- a control for keeping the sensitivity (image movement amount per unit current) constant and a control for simultaneously correcting the deflection geometric aberration of the objective lens 12 that becomes obvious when the field of view moves greatly will be described.
- this optical system is shown below.
- a focus shift occurs due to the curvature of field of the objective lens 12, and thus it is necessary to adjust the focus using any one of the lenses.
- the object lens object point position changes, so that the deflection sensitivity of the field movement deflector 23 changes for each field movement amount.
- the relaxation time of the current applied to the deflector is constant, so the time until an image can be acquired changes, and in any field movement amount and movement direction.
- the lens must be focused on the sample 14 side of the visual field moving deflector 23.
- the object point position of the objective lens does not change, but the current amount of the objective lens changes, so that the visual field movement accuracy due to the influence of heat generation and hysteresis may be lowered. Therefore, the focus when moving the visual field is adjusted by the focus adjustment lens 09.
- the focus adjustment lens 09 By using an electromagnetic lens or electrostatic lens that is less affected by heat generation and hysteresis as the focus adjustment lens 09, the field movement accuracy is reduced due to heat generation and hysteresis of the lens while maintaining the deflection sensitivity of the field movement deflector 23 constant. Can be suppressed.
- the focus adjustment lens 09 and the deflection aberration corrector 301 are used in combination, the focus adjustment lens 09 is arranged closer to the sample than the deflection aberration corrector 301 so that the incident condition to the deflection aberration corrector 301 is not changed. Focus adjustment is possible.
- the visual field moving deflector 23 is controlled so that the deflection trajectory 51 at the time of vertical landing is antisymmetric with respect to a plane perpendicular to the optical axis 50 passing through the virtual deflection fulcrum 204 at the time of visual field movement.
- the direction of occurrence of anisotropic deflection geometric aberration is reversed between the focus adjustment lens 09 and the objective lens 12 and cancels out.
- the magnitude of the deflection geometric aberration generated by the focus adjustment lens 09 and the objective lens 12 varies depending on the strength of each lens and the position where the deflection trajectory 51 during vertical landing passes through each lens, but the direction in which the deflection geometric aberration occurs is the deflection trajectory. Since it is determined by the symmetry of 51, it is always reversed before and after the symmetry plane 401. Therefore, the arrangement of this optical system makes it possible to correct or reduce the deflection geometric aberration when the field of view is moved.
- the above control makes it possible to move the field of view while maintaining the vertical landing at high speed and high accuracy while keeping the waiting time until image acquisition constant.
- FIG. 9 shows the optical system of the seventh embodiment.
- a focus adjustment lens 09 is provided between the visual field movement deflector 23 and the virtual deflection fulcrum 204 at the time of visual field movement
- an acceleration tube 11 is provided between the visual field movement deflector 23 and the objective lens 12.
- a method for correcting or reducing the deflection geometric aberration of the objective lens 12 and the aberration due to the harmonic component of the field movement deflector 23 simultaneously using the focus adjustment lens 09 and the acceleration tube 11 will be described.
- the deflection geometric aberration of the objective lens 12 is controlled by controlling the field movement deflector 23 so that the deflection trajectory 51 at the time of vertical landing is antisymmetric with respect to the symmetry plane 401 as described in the first embodiment. Can be corrected or reduced.
- the aberration due to the harmonic component of the field movement deflector 23 is difficult to be corrected by the lens, it is necessary to control so as not to generate the aberration. Therefore, a positive voltage is applied to the acceleration tube 11. In this case, since the primary electrons are accelerated when entering the accelerating tube 11 from the visual field moving deflector 23, the inclination of the deflection trajectory 54 becomes smaller than the trajectory 51 when the accelerating tube 11 is turned off.
- the off-axis of the primary electrons at the position of the field movement deflector 23 is reduced, and the generation of aberration due to the harmonic component can be suppressed.
- the accelerating tube 11 and the visual field moving deflector 23 are controlled so that the trajectory after entering the accelerating tube 11 coincides with the trajectory 51 when the accelerating tube 11 is turned off, the symmetry of the deflection trajectory with respect to the symmetry plane 401 is Therefore, it is possible to reduce the aberration of the field movement deflector 23 without affecting the correction / reduction of the deflection geometric aberration of the objective lens 12 by this control.
- FIG. 10 shows an optical system in which the acceleration tubes 13 and 13 ′ are arranged between the electron source and the field movement deflector 23.
- the voltage or current applied to the focus adjustment lens 09 and the objective lens 12 is set as follows. By appropriately controlling, it is possible to keep the deflection trajectory 51 at the time of vertical landing unchanged. Therefore, the focus adjustment lens 09 and the acceleration tubes 11, 13, and 13 'can be used together without affecting the deflection geometric aberration correction of the objective lens 12.
Abstract
Description
ここで、qは素電荷、v0は試料から放出された二次電子の速度を表す。このような構成によれば、試料から放出された電子を偏向させることなく、試料に到達する電子ビームを選択的に偏向することが可能となる。
Claims (18)
- 荷電粒子源から放出された荷電粒子ビームを集束して試料に照射する対物レンズと、前記荷電粒子ビームを偏向する視野移動用偏向器を備えた荷電粒子線装置において、
前記視野移動用偏向器と前記対物レンズとの間に配置される加速管と、当該加速管に電圧を印加する電源と、前記視野移動偏向器による偏向条件に応じて、前記電源に印加する電圧を制御する制御装置を備えたことを特徴とする荷電粒子線装置。 - 請求項1において、
前記加速管は、前記荷電粒子ビームの理想光軸方向において、前記対物レンズの前側焦点位置と同じ高さに配置されることを特徴とする荷電粒子線装置。 - 請求項1において、
前記制御装置は、前記視野移動用偏向器による視野移動を行わない、或いは所定値以下のイメージシフトを行う第1の光学モードと、前記視野移動用偏向器による視野移動を行う第2の光学モードとを備え、第2の光学モードが選択されたときに、第1の光学モードが選択されたときと比較して、前記加速管に大きな正の電圧を印加することを特徴とする荷電粒子線装置。 - 請求項1において、
前記加速管は、少なくとも前記荷電粒子源側に配置される第1電極と、前記試料側に配置される第2電極から構成され、前記制御装置は、前記第1電極に印加する電圧を、前記視野移動偏向器による偏向条件に応じて制御することを特徴とする荷電粒子線装。 - 請求項4において、
前記第2電極には、正の電圧が印加されることを特徴とする荷電粒子線装置。 - 請求項5において、
前記制御装置は、前記視野移動用偏向器による視野移動を行わない、或いは所定値以下のイメージシフトを行う第1の光学モードと、前記視野移動用偏向器による視野移動を行う第2の光学モードとを備え、前記第1の光学モードが選択されたときには、前記第1電極と前記第2電極に同じ正の電圧を印加することを特徴とする荷電粒子線装置。 - 請求項1において、
前記荷電粒子源と前記加速管との間に、前記荷電粒子ビームのフォーカスを調整するフォーカス調整用レンズを備え、前記制御装置は前記加速管に印加される電圧の変動、及び前記対物レンズの焦点距離の変動の少なくとも1つに応じて、前記フォーカス調整用レンズを制御することを特徴とする荷電粒子線装置。 - 請求項7において、
前記制御装置は、前記対物レンズの物点位置を固定するように、前記フォーカス調整用レンズを制御することを特徴とする荷電粒子線装置。 - 請求項1において、
前記視野移動用偏向器は、磁場型偏向器と静電型偏向器から構成されることを特徴とする荷電粒子線装置。 - 請求項9において、
前記制御装置は、前記試料から放出された電子を所定の方向に導く条件で、前記荷電粒子ビームの視野移動を行うように、前記磁場型偏向器と静電型偏向器の偏向比率を調整することを特徴とする荷電粒子線装置。 - 請求項9において、
前記前記磁場型偏向器と前記静電型偏向器は、前記対物レンズの漏洩磁場内に配置されていることを特徴とする荷電粒子線装置。 - 荷電粒子源から放出された荷電粒子ビームを集束して試料に照射する対物レンズと、前記荷電粒子ビームを偏向する視野移動用偏向器を備えた荷電粒子線装置において、
前記対物レンズの物点位置よりも試料側に配置されるフォーカス調整用レンズと当該フォーカス調整用レンズに電圧もしくは電流を印加する電源と、前記視野移動偏向器による偏向条件に応じて、前記電源に印加する電圧もしくは電流を制御する制御装置を備えたことを特徴とする荷電粒子線装置。 - 請求項12において、
前記フォーカス調整用レンズは、前記荷電粒子ビームの理想光軸方向において、前記視野移動用偏向器と視野移動時の仮想偏向支点の間に配置されることを特徴とする荷電粒子線装置。 - 請求項12において、
前記制御装置は、前記対物レンズの物点位置を固定するように、前記フォーカス調整用レンズを制御することを特徴とする荷電粒子線装置。 - 請求項12において、
前記荷電粒子源と前記対物レンズとの間に、前記荷電粒子ビームを加速する加速管と、当該加速管に電圧を印加する電源を備え、前記制御装置は前記加速管に印加される電圧の変動、及び前記対物レンズの焦点距離の変動の少なくとも1つに応じて、前記フォーカス調整用レンズを制御することを特徴とする荷電粒子線装置。 - 請求項12において、
前記視野移動用偏向器は、磁場型偏向器と静電型偏向器から構成されることを特徴とする荷電粒子線装置。 - 請求項16において、
前記制御装置は、前記試料から放出された電子を所定の方向に導く条件で、前記荷電粒子ビームの視野移動を行うように、前記磁場型偏向器と静電型偏向器の偏向比率を調整することを特徴とする荷電粒子線装置。 - 請求項16において、
前記前記磁場型偏向器と前記静電型偏向器は、前記対物レンズの漏洩磁場内に配置されていることを特徴とする荷電粒子線装置。
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