JP2014212063A - Scanning charged particle beam microscope, control method of scanning charged particle beam microscope, and axis alignment method of scanning charged particle beam microscope - Google Patents

Abstract

A scanning charged particle microscope capable of easily performing axis alignment is provided. In the scanning charged particle microscope 100, a control unit 22 controls a first control signal for controlling a part of the multistage deflectors 31, 32 and the other of the multistage deflectors 31, 32. A second control signal for controlling a part of the first control signal, the first control signal including first scan rotation information for rotating the scanning direction of the charged particle beam EB by a first angle, The control signal includes second scan rotation information for rotating the scanning direction of the charged particle beam EB by a second angle, and the control unit 22 makes the first angle different from the second angle, The control signal and the second control signal are output to the scanning unit 3, and the scanning unit 3 scans the charged particle beam EB on the aperture 9 based on the first control signal and the second control signal, and the image generation unit 24 Based on the detection result of the detection unit 6, Generate an aperture image. [Selection] Figure 1

Description

  The present invention relates to a scanning charged particle microscope, a method for controlling a scanning charged particle microscope, and an axis alignment method for a scanning charged particle microscope.

  For example, a scanning electron microscope (SEM) is known as a scanning charged particle microscope.

  In a scanning electron microscope, an electron beam accelerated and emitted from an electron gun is focused and irradiated on a sample by an objective lens, thereby detecting electrons (secondary electrons and reflected electrons) emitted from the sample, A scanned image is acquired.

  In such a scanning electron microscope, it is necessary to align the axis for aligning the electron beam with the axis of the objective lens. This axis alignment is generally performed by superimposing a modulation signal on the excitation current or acceleration voltage of the objective lens (current Wobbler, voltage Wobbler) and observing the scanning image.

  When the electron beam is deviated with respect to the axis of the objective lens, vertical and horizontal fluctuations synchronized with the Wobbler period are observed in the scanned image. Whether or not the axes are aligned is determined by whether or not the shaking stops. As a method of stopping the shaking, the movable objective aperture is moved (or the alignment coil is controlled) to change the incident position and the incident angle of the electron beam on the objective lens. While observing the scanned image, the above-mentioned axis alignment operation is performed until the shaking stops. Note that axis alignment using the current Wobler is referred to as current axis alignment, and axis alignment using the voltage Wobbler is referred to as voltage axis alignment.

  When such axis alignment is automatically performed, first, the current value of the objective lens is discretely changed by a predetermined step width, and a plurality of scanning images (still images) corresponding to the current value of the objective lens are obtained. get. When there is no axis, there is a shift (there is a displacement) in the observation center position of each acquired scanned image. Using image analysis, the amount and direction of displacement of the image corresponding to the current value of the objective lens are calculated, and the objective of the electron beam is controlled by feedback control of the movable objective aperture and alignment coil so that such displacement does not occur. Current axis alignment is performed by changing the incident position and angle of incidence on the lens. In the above procedure, voltage axis alignment can be performed by replacing the objective lens current with the acceleration voltage.

  As such an axis alignment method, for example, Patent Document 1 discloses a method of detecting the center of an aperture from an acquired image and changing the output of a deflection signal so that an electron beam passes through the center of the aperture. .

  Further, for example, Patent Document 2 discloses a method of scanning the opening of an objective lens with an electron beam and adjusting the axis of the electron beam based on an image detected thereby.

JP-A-9-69350 JP 2005-174812 A

  However, in the above-described electron beam axis alignment method, the axis alignment operation is complicated and requires skill. Further, when the axis alignment is automatically performed, for example, it is necessary to obtain a plurality of scanning images corresponding to the current value of the objective lens, and to perform the axis alignment operation from the plurality of scanning images, which takes time. There was a problem.

  The present invention has been made in view of the above points, and one of the objects according to some aspects of the present invention is to provide a scanning charged particle microscope and a scanning charged particle microscope capable of easily performing axial alignment. It is an object of the present invention to provide a control method for the above and an axis alignment method for a scanning charged particle microscope.

(1) A scanning charged particle microscope according to the present invention includes:
A charged particle beam source for generating a charged particle beam;
An objective lens for focusing the charged particle beam emitted from the charged particle beam source;
A scanning unit having a multi-stage deflector and scanning the charged particle beam focused by the objective lens on an object;
An aperture disposed on the rear side of the scanning unit;
A detection unit for detecting electrons emitted from the object by being irradiated with the charged particle beam;
An image generation unit configured to generate an image based on a detection result of the detection unit;
A control unit for controlling the scanning unit;
Including
The controller is
A first control signal for controlling a part of the multi-stage deflector;
A second control signal for controlling another part of the multistage deflector;
Produces
The first control signal is:
First scanning information for scanning the charged particle beam;
First scan rotation information for rotating the scanning direction of the charged particle beam by a first angle;
Including
The second control signal is:
Second scanning information for scanning the charged particle beam;
Second scan rotation information for rotating the scanning direction of the charged particle beam by a second angle;
Including
The control unit outputs the first control signal and the second control signal to the scanning unit by making the first angle different from the second angle,
The scanning unit scans the charged particle beam on the aperture based on the first control signal and the second control signal,
The detection unit detects electrons emitted by scanning the charged particle beam on the aperture,
The image generation unit generates an aperture image based on the detection result of the detection unit.

  According to such a scanning charged particle microscope, an aperture image can be obtained by making the first angle of the first control signal different from the second angle of the second control signal. Thereby, axis alignment can be performed based on the aperture image. Since the position of the axis of the objective lens can be easily specified in the aperture image, the axis alignment can be easily performed by performing the axis alignment based on the aperture image.

  Axis alignment refers to an operation in which a charged particle beam is incident so as to coincide with the axis of the objective lens.

(2) In the scanning charged particle microscope according to the present invention,
The aperture may be disposed on a main surface of the objective lens.

(3) In the scanning charged particle microscope according to the present invention,
The center of the aperture of the aperture may coincide with the position of the axis of the objective lens.

(4) In the scanning charged particle microscope according to the present invention,
An axis alignment unit that aligns the charged particle beam with the axis of the objective lens based on the aperture image may be included.

(5) A control method of the scanning charged particle microscope according to the present invention includes:
A charged particle beam source for generating a charged particle beam; an objective lens for focusing the charged particle beam emitted from the charged particle beam source; and a multistage deflector, wherein the focused lens beam is focused by the objective lens A scanning unit for scanning a charged particle beam on an object, an aperture disposed on the rear side of the scanning unit, and an electron emitted from the object by being irradiated with the charged particle beam A scanning charged particle microscope control method comprising: a detecting unit that performs detection; and an image generating unit that generates an image based on a detection result of the detecting unit,
Control signal generation for generating a first control signal for controlling a part of the multistage deflector and a second control signal for controlling another part of the multistage deflector Process,
A scanning step of controlling the scanning unit based on the first control signal and the second control signal to scan the charged particle beam on the aperture;
A detection step of detecting electrons emitted by scanning the charged particle beam on the aperture by the detection unit;
An image generation step for generating an aperture image based on the detection result of the detection unit by the image generation unit;
Including
The first control signal is:
First scanning information for scanning the charged particle beam;
First scan rotation information for rotating the scanning direction of the charged particle beam by a first angle;
Have
The second control signal is:
Second scanning information for scanning the charged particle beam;
Second scan rotation information for rotating the scanning direction of the charged particle beam by a second angle;
Have
In the control signal generation step, the first angle is different from the second angle.

  According to such a scanning charged particle microscope control method, an aperture image can be obtained by making the first angle of the first control signal different from the second angle of the second control signal. Thereby, axis alignment can be performed based on the aperture image. Since the position of the axis of the objective lens can be easily specified in the aperture image, the axis alignment can be easily performed by performing the axis alignment based on the aperture image.

(6) In the control method of the scanning charged particle microscope according to the present invention,
The aperture may be disposed on a main surface of the objective lens.

(7) In the control method of the scanning charged particle microscope according to the present invention,
The center of the aperture of the aperture may coincide with the position of the axis of the objective lens.

(8) In the control method of the scanning charged particle microscope according to the present invention,
A step of aligning the charged particle beam with the axis of the objective lens based on the aperture image may be included.

(9) The method of axial alignment of the scanning charged particle microscope according to the present invention is as follows:
A scanning charged particle microscope axial alignment method that scans a charged particle beam on an object with a multistage deflector, detects electrons emitted from the object, and generates an image.
The rotation angle of scan rotation in some of the deflectors of the multistage deflector is different from the rotation angle of scan rotation in the other deflectors of the multistage deflector, An aperture scanning step of scanning the charged particle beam on an aperture disposed on a rear stage side of the multistage deflector;
An aperture image generating step for generating an aperture image based on the detection result of the electrons emitted by the aperture scanning step;
An axis alignment step of aligning the charged particle beam with the axis of the objective lens based on the aperture image;
including.

  According to such an axis alignment method of the scanning charged particle microscope, the rotation angle of the scan rotation in some of the deflectors in the multistage deflector is set to the other deflector in the multistage deflector. An aperture image can be obtained by making the angle different from the rotation angle of scan rotation. Thereby, axis alignment can be performed based on the aperture image. Since the position of the axis of the objective lens can be easily specified in the aperture image, the axis alignment can be easily performed by performing the axis alignment based on the aperture image.

(10) In the scanning charged particle microscope axial alignment method according to the present invention,
The aperture may be disposed on a main surface of the objective lens.

(11) In the scanning charged particle microscope axial alignment method according to the present invention,
The center of the aperture of the aperture may coincide with the position of the axis of the objective lens.

The figure which shows the structure of the scanning charged particle microscope which concerns on this embodiment. The figure for demonstrating the scanning control part of the scanning charged particle microscope which concerns on this embodiment. The figure for demonstrating the scan rotation in an upper stage deflector. The figure for demonstrating the scan rotation in a lower stage deflector. The flowchart which shows an example of the axis alignment process in the scanning charged particle microscope which concerns on this embodiment. The figure for demonstrating operation | movement of the scanning part in the axis alignment process of this embodiment. The figure for demonstrating operation | movement of the scanning part in the axis alignment process of this embodiment. The figure for demonstrating operation | movement of the scanning part in the axis alignment process of this embodiment. The figure for demonstrating operation | movement of the scanning part in the axis alignment process of this embodiment. The figure which shows an example of the scanning image (aperture image) of an aperture. The figure which shows an example of the scanning image (aperture image) of an aperture. The figure which shows the structure of the scanning charged particle microscope which concerns on a 1st modification. The figure which shows the structure of the scanning charged particle microscope which concerns on a 2nd modification. The figure which shows the structure of the scanning charged particle microscope which concerns on a 3rd modification.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. Configuration of Scanning Charged Particle Microscope First, the configuration of the scanning charged particle microscope according to the present embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a scanning charged particle microscope 100 according to the present embodiment.

  As shown in FIG. 1, the scanning charged particle microscope 100 includes a charged particle beam source 1, a focusing lens 2, a scanning unit 3, an objective lens 4, a sample stage 5, a detection unit 6, and a movable objective aperture 7. And an alignment coil 8, an aperture 9, a display unit 10, an operation unit 12, a storage unit 14, and a processing unit 20.

  The scanning charged particle microscope 100 scans a charged particle beam on an object (sample S or aperture 9), and electrons (secondary electrons) emitted from the object when the charged particle beam is scattered in the object. Or backscattered electrons) to detect an image (scanned image). The charged particle beam is, for example, an electron or an ion. Here, a case where the scanning charged particle microscope 100 is a scanning electron microscope (SEM) using an electron beam EB as a charged particle beam will be described.

  An electron beam source (charged particle beam source) 1 generates an electron beam EB. The electron beam source 1 is, for example, a known electron gun, and emits an electron beam EB by accelerating electrons emitted from the cathode at the anode. The electron gun used as the electron beam source 1 is not particularly limited, and for example, a thermionic emission type, a thermal field emission type, a cold cathode field emission type, or the like can be used. The electron beam source 1 is supplied with an acceleration voltage for accelerating electrons emitted from the cathode from the driving unit 1a.

  The converging lens 2 is disposed downstream of the electron beam source 1 (on the downstream side of the electron beam EB). The focusing lens 2 is a lens for focusing the electron beam EB. In the illustrated example, the electron beam EB is focused by the two-stage focusing lens 2.

  The scanning unit 3 is disposed at the subsequent stage of the focusing lens 2. The scanning unit 3 includes an upper deflector 31 and a lower deflector 32, and scans an electron beam EB focused by the focusing lens 2 and the objective lens 4 on the object.

  The upper deflector 31 and the lower deflector 32 are electromagnetic coils for scanning the electron beam EB. The upper deflector 31 and the lower deflector 32 deflect the electron beam EB two-dimensionally, respectively. The upper deflector 31 and the lower deflector 32 are controlled by the scanning control unit 22 and perform scanning of the electron beam EB.

  The objective lens 4 is arranged at the rear stage of the scanning unit 3. The objective lens 4 is a lens for focusing the electron beam EB and irradiating the sample S. The scanning charged particle microscope 100 performs axis alignment (hereinafter also simply referred to as “axis alignment”) for making the electron beam EB coincide with the axis of the objective lens 4 (for example, the mechanical axis of the objective lens 4) Z.

The sample stage 5 can hold the sample S and move the sample S. The sample stage 5 can perform operations such as horizontal movement, vertical movement, rotation, and tilting of the sample S, for example.

  The detection unit 6 detects electrons (secondary electrons and reflected electrons) emitted from the object by being irradiated with the electron beam EB. Although not shown, the detection unit 6 includes, for example, a scintillator and a photomultiplier tube. Detection signals (intensity signals) of secondary electrons and reflected electrons detected by the detection unit 6 are sent to the bus line 30 via the A / D conversion unit 6a. The detection signal is stored in the storage unit 14 as image data synchronized with the scanning signal of the electron beam EB. In the illustrated example, the detection unit 6 is disposed between the objective lens 4 and the sample S (sample stage 5). That is, the detection unit 6 is, for example, an out-lens detector. The arrangement of the detection unit 6 is not particularly limited, and may be arranged, for example, above the objective lens 4.

  The movable objective aperture 7 is disposed between the focusing lens 2 and the scanning unit 3. The movable objective aperture 7 is a diaphragm for shielding only the electron beam EB near the axis Z of the objective lens 4 out of the electron beam EB incident on the objective lens 4 and shielding other electron beams EB. The electron beam EB can be aligned with the axis Z of the objective lens 4 by adjusting the position of the movable objective aperture 7.

  The alignment coil 8 is disposed between the focusing lens 2 and the scanning unit 3. The alignment coil 8 is a deflection coil for deflecting the electron beam EB and aligning the electron beam EB with the axis Z of the objective lens 4. The alignment coil 8 can deflect the electron beam EB two-dimensionally.

  The aperture 9 is disposed on the rear stage side (downstream side of the electron beam EB) of the scanning unit 3. More preferably, the aperture 9 is disposed between the upper magnetic pole (inner magnetic pole) 41 and the lower magnetic pole (outer magnetic pole) 42 of the objective lens 4. In the illustrated example, the aperture 9 is disposed on the main surface of the objective lens 4. The aperture 9 is, for example, a metal plate provided with an opening 9b. In the illustrated example, the opening 9b is circular as viewed from the traveling direction of the electron beam EB. The diameter of the opening 9b is, for example, about several hundred μm. The aperture 9 is disposed so that the center of the opening 9 b coincides with the axis Z of the objective lens 4. The shape of the opening 9b of the aperture 9 is not particularly limited as long as the axis Z of the objective lens 4 can be specified. The aperture 9 may be fixed to the main surface of the objective lens 4 or may be configured to be movable. That is, the aperture 9 may be a fixed diaphragm or a movable diaphragm.

  The aperture 9 may be an orifice for a low vacuum scanning electron microscope. That is, the aperture 9 may be a diaphragm for creating a pressure difference between the electron optical system and the sample chamber R when performing differential evacuation between the electron optical system and the sample chamber R.

  The electron beam source 1, the focusing lens 2, the objective lens 4, the sample stage 5, and the alignment coil 8 are driven and controlled by the corresponding driving units 1a, 2a, 4a, 5a, and 8a. Each drive unit 1 a, 2 a, 4 a, 5 a, 8 a is connected to the bus line 30, and a drive signal is supplied from the optical system control unit 28 via the bus line 30. Each drive part 1a, 2a, 4a, 5a, 8a drives the electron beam source 1, the focusing lens 2, the objective lens 4, the sample stage 5, and the alignment coil 8 based on the supplied drive signal.

  The display unit 10 displays processing results of the processing unit 20 as characters, graphs, and other information based on display signals input from the processing unit 20 via the bus line 30. The display unit 10 displays the image (scanned image) generated by the image generation unit 24, for example. The display unit 10 is, for example, a CRT, LCD, touch panel display, or the like.

The operation unit 12 performs a process of acquiring an operation signal corresponding to an operation by the user and sending the operation signal to the processing unit 20 via the bus line 30. The operation unit 12 is, for example, a button, a key, a touch panel type display, a microphone, or the like.

  The storage unit 14 stores programs, data, and the like for the processing unit 20 to perform various types of calculation processing and control processing. The storage unit 14 is used as a work area of the processing unit 20 and is also used to temporarily store operation signals input from the operation unit 12, calculation results executed by the processing unit 20 according to various programs, and the like. The For example, image data in which the detection signal is synchronized with the scanning signal is stored in the storage unit 14. The storage unit 14 is connected to the bus line 30.

  The processing unit (CPU) 20 performs various types of calculation processing according to programs stored in the storage unit 14. The processing unit 20 functions as a scanning control unit 22, an image generation unit 24, an axis alignment unit 26, and an optical system control unit 28 described below by executing a program stored in the storage unit 14. However, at least a part of the processing unit 20 may be realized by hardware (dedicated circuit).

  The scanning control unit 22 controls the scanning unit 3. Specifically, the scanning control unit 22 performs a process of generating a first control signal for controlling the upper deflector 31 and a second control signal for controlling the lower deflector 32. Each of the first control signal and the second control signal includes scanning information for scanning the electron beam EB and scan rotation information for rotating the scanning direction of the electron beam EB by a given angle.

  FIG. 2 is a diagram for explaining the scanning control unit 22. As shown in FIG. 2, the scanning control unit 22 includes a scanning signal generation unit 22a, a calculation unit 22b, and an addition unit 22c.

  The scanning signal generator 22a generates scanning signals X0 and Y0 including scanning information for scanning the electron beam EB. Scan information refers to a raster scan that scans a two-dimensional region by scanning a two-dimensional region (scan region) one-dimensionally with a point to obtain a scan line, and scanning with the scan line in the orthogonal direction. Information to do. The scanning signal X0 is, for example, a signal including information for obtaining a scanning line by scanning the electron beam EB in the X direction in a one-dimensional manner, and is a sawtooth wave in the illustrated example. The scanning signal Y0 is, for example, a ramp wave that moves the position of the scanning line in the Y direction.

The calculation unit 22b and the addition unit 22c add scan rotation (raster rotation) information for rotating the scanning direction of the electron beam EB by a given angle to the scanning signals X0 and Y0 (superimposing the scan rotation signal). ), First control signals X ₃₁ ′, Y ₃₁ ′ and second control signals X ₃₂ ′, Y ₃₂ ′ are generated.

  Here, the scan rotation will be described. FIG. 3 is a diagram for explaining scan rotation in the upper deflector 31. FIG. 4 is a diagram for explaining scan rotation in the lower deflector 32. Note that the X axis shown in FIGS. 3 and 4 is an axis corresponding to the X direction, and is an axis parallel to the scanning line. The Y axis is an axis corresponding to the Y direction and is an axis orthogonal to the X axis.

  As shown in FIGS. 3 and 4, scan rotation refers to rotating the scanning region of the electron beam EB by rotating the scanning direction of the electron beam EB. That is, by performing the scan rotation, the X axis and the Y axis shown in FIGS. 3 and 4 can be newly set as the X ′ axis and the Y ′ axis.

Here, in the upper deflector 31, when the rotation angle (scan rotation angle) in the scanning direction of the electron beam is α, the first control signals X ₃₁ ′ and Y ₃₁ ′ are
X ₃₁ ′ = X0 cos α + Y0 sin α (1)
Y ₃₁ ′ = −X0 sin α + Y0 cos α (2)
It becomes.

Calculating unit 22b and the adder unit 22c, using the above equation (1) and (2), by applying a scan rotation information to the scanning signal X0, Y0 (information on the rotation angle alpha), the first control signal _{X 31} ', Y ₃₁ ' is generated.

Further, in the lower deflector 32 shown in FIG. 4, when the rotation angle (scan rotation angle) in the scanning direction of the electron beam is β, the second control signals X ₃₂ ′ and Y ₃₂ ′ are
X ₃₂ '= X0 cos β + Y0 sin β (3)
Y ₃₂ ′ = −X0 sin β + Y0 cos β (4)
It becomes.

The calculation unit 22b and the addition unit 22c use the above formulas (3) and (4) to add scan rotation information (information about the rotation angle β) to the scan signals X0 and Y0, and the second control signal X _32. ', Y ₃₂ ' is generated.

The scanning control unit 22 outputs the first control signals X ₃₁ ′ and Y ₃₁ ′ to the upper deflector 31 via the amplifier 3a. Further, the scanning control unit 22 outputs the second control signals X ₃₂ ′ and Y ₃₂ ′ to the lower deflector 32 via the amplifier 3a.

Here, when the axis alignment is performed, the scanning control unit 22 sets the rotation angle (first angle) α of the upper deflector 31 and the rotation angle (second angle) β of the lower deflector 32 to be different from each other. The control signals X ₃₁ ′ and Y ₃₁ ′ and the second control signals X ₃₂ ′ and Y ₃₂ ′ are output to the scanning unit 3. That is, the rotation angle α of the scan rotation in the upper deflector 31 is made different from the rotation angle β of the scan rotation in the lower deflector 32. Thereby, the scanning unit 3 scans the electron beam EB on the aperture 9. Therefore, a scanning image (aperture image) of the aperture 9 is obtained. As will be described later, the axis alignment can be easily performed by performing the axis alignment based on the aperture image.

  When obtaining a scanned image of the sample S (when observing the sample S), the scanning control unit 22 performs scanning by setting the rotation angle α of the upper deflector 31 and the rotation angle β of the lower deflector 32 to be the same. Output to part 3. Thereby, the scanning unit 3 scans the electron beam EB on the sample S. Therefore, a scanning image (sample image) of the sample S is obtained.

  The image generation unit 24 generates an image (scanned image) based on the detection result of the detection unit 6. Specifically, the image generation unit 24 stores the detection signal of the detection unit 6 in the storage unit 14 as image data in synchronization with the scanning signal, and generates a display signal from the image data. Based on this display signal, the display unit 10 displays a scanned image.

  The optical system control unit 28 controls the electron beam source 1, the focusing lens 2, the objective lens 4, the sample stage 5, and the alignment coil 8. Specifically, the optical system control unit 28 generates and outputs control signals for controlling the electron beam source 1, the focusing lens 2, the objective lens 4, the sample stage 5, and the alignment coil 8. Each control signal is input to the electron beam source 1, the focusing lens 2, the objective lens 4, the sample stage 5, and the alignment coil 8 via the corresponding driving units 1 a, 2 a, 4 a, 5 a, and 8 a.

2. Operation of Scanning Charged Particle Microscope Next, the operation of the scanning charged particle microscope will be described. Here, an axis alignment method of the scanning charged particle microscope 100 will be described. FIG. 5 is a flowchart showing an example of the axis alignment process in the scanning charged particle microscope 100. 6 to 9 are diagrams for explaining the operation of the scanning unit 3 in the axis alignment processing of the scanning charged particle microscope 100. FIG.

FIG. 6 is a diagram showing a state before the axis alignment process of the scanning charged particle microscope 100 is performed, that is, a state where the electron beam EB is not on the axis Z of the objective lens 4. In FIG. 6, the scanning charged particle microscope 100 is in a state where the sample S can be scanned to obtain a scanned image of the sample S. Specifically, the scanning control unit 22 sets the rotation angle α (see FIG. 3) and the rotation angle β (see FIG. 4) to the same angle (for example, α = β = 0 °), and controls the first control signal X ₃₁ ′. , Y ₃₁ ′ and second control signals X ₃₂ ′, Y ₃₂ ′ are generated and output to the scanning unit 3. The scanning unit 3 transmits the electron beam EB based on the first control signals X ₃₁ ′, Y ₃₁ ′ including information of α = 0 and the second control signals X ₃₂ ′, Y ₃₂ ′ including information of β = 0. Scan on sample S. The detection unit 6 detects electrons emitted from the sample S when the sample S is irradiated with the electron beam EB. The image generation unit 24 generates an image based on the detection result of the detection unit 6.

  As shown in FIG. 6, when α = β, the electron beam EB is incident on the sample S through a predetermined point (deflection fulcrum) F on the main surface 4 f of the objective lens 4. That is, even when the electron beam EB is scanned on the sample S, the electron beam EB passes through the deflection fulcrum F on the main surface 4 f of the objective lens 4. Specifically, the upper deflector 31 deflects the electron beam EB in a predetermined direction (for example, + X direction), and the lower deflector 32 deflects the electron beam EB in a direction opposite to the predetermined direction (for example, −X direction). Look back. As a result, the electron beam EB is incident on the sample S through the deflection fulcrum F. In FIG. 6, since there is no axis, the position of the deflection fulcrum F is deviated from the axis Z of the objective lens 4.

  In a state where the scanning charged particle microscope 100 does not have an axis as shown in FIG. 6, for example, the user operates the operation unit 12 to start a program for performing an axis alignment process, whereby the scanning charged particle microscope 100 ( The processing unit 20) starts the axis alignment process shown in FIG.

First, the scan control unit 22 controls the first control signals X ₃₁ ′ and Y ₃₁ ′ for controlling the upper deflector 31 and the second control signals X ₃₂ ′ and Y ₃₂ ′ for controlling the lower deflector ₃₂ . Is generated (S10). The scanning control unit 22 makes the rotation angle α different from the rotation angle β (for example, α = 10 °, β = 0 °), and controls the first control signal X ₃₁ ′, Y ₃₁ ′ and the second control signal X _32. ', Y ₃₂ ' is generated. The values of the rotation angle α and the rotation angle β are appropriately set depending on the scanning magnification and the diameter of the aperture 9. The scanning control unit 22 supplies the first control signals X ₃₁ ′ and Y ₃₁ ′ including information of α = 10 ° and the second control signals X ₃₂ ′ and Y ₃₂ ′ including information of β = 0 ° to the scanning unit 3. Output.

Based on the first control signals X ₃₁ ′, Y ₃₁ ′ including information of α = 10 ° and the second control signals X ₃₂ ′, Y ₃₂ ′ including information of β = 0 °, the scanning unit 3 EB is scanned (S11). Thereby, in the scanning unit 3, only the upper deflector 31 is subjected to scan rotation of α = 10 °.

FIG. 7 is a diagram illustrating the scanning unit 3 that operates based on the first control signals X ₃₁ ′ and Y ₃₁ ′ and the second control signals X ₃₂ ′ and Y ₃₂ ′ in which α ≠ β. As shown in FIG. 7, when α ≠ β, the electron beam EB is scanned in a predetermined scanning region A on the main surface 4 f of the objective lens 4. Thereby, the electron beam EB can be scanned on the aperture 9.

Next, the detection unit 6 detects the emitted electrons by scanning the electron beam EB on the aperture 9 (S12), and the image generation unit 24 generates an aperture image based on the detection result of the detection unit 6. Generate (S13).

  FIG. 10 is a diagram illustrating an example of an aperture image. The dark part outside the circular bright part shown in FIG. 10 corresponds to the part where the electron beam EB is cut by the aperture 9 installed on the main surface 4 f of the objective lens 4. That is, the circular bright portion shown in FIG. 10 corresponds to the opening 9b of the aperture 9 shown in FIG. Since the center of the opening 9b of the aperture 9 is arranged so as to coincide with the axis Z of the objective lens 4, the position of the center of the circular bright portion in FIG. 10 represents the position of the axis of the objective lens 4. Yes.

  Next, the axis alignment unit 26 performs axis alignment based on the aperture image (S14). Specifically, the axis aligning unit 26 uses, for example, pattern matching or the like from the aperture image to obtain a position between the center of the circular bright portion of the aperture image shown in FIG. 10 and the center position of the scanning region (scanned image). The amount of deviation and the direction of deviation are calculated. Then, the axis alignment unit 26 operates the alignment coil 8 so that the center of the circular bright portion of the aperture image coincides with the center of the scanning region based on the calculated shift amount and shift direction. Thereby, the electron beam EB can be aligned with the axis of the objective lens 4.

FIG. 8 shows the scanning unit 3 that operates based on the first control signals X ₃₁ ′ and Y ₃₁ ′ and the second control signals X ₃₂ ′ and Y ₃₂ ′ when α ≠ β with the axes aligned. FIG. As shown in FIG. 8, the position of the center of the scanning area A coincides with the position of the center of the opening 9 b of the aperture 9. FIG. 11 is a diagram illustrating an example of an aperture image in a state where the axes are aligned. As shown in FIG. 11, it can be seen that the center of the circular bright portion of the aperture image coincides with the center of the scanning region (scanned image), and the axis is aligned.

Next, the scanning control unit 22 generates first control signals X ₃₁ ′ and Y ₃₁ ′ and second control signals X ₃₂ ′ and Y ₃₂ ′ with α = β (for example, α = β = 0 °) ( S15). Thereby, the electron beam EB can be scanned on the sample S in a state where there is an axis. FIG. 9 is a diagram illustrating the scanning unit 3 when α = β in a state where the axes are aligned. As shown in FIG. 9, the position of the deflection fulcrum F and the position of the axis Z of the objective lens 4 coincide with each other on the main surface 4 f of the objective lens 4.

  The axis alignment is completed through the above steps.

  The scanning charged particle microscope 100 has the following features, for example.

In the scanning charged particle microscope 100, the scanning control unit 22 makes the rotation angle α different from the rotation angle β (α ≠ β), and controls the first control signals X ₃₁ ′, Y ₃₁ ′ and the second control signal X ₃₂ ′. , Y ₃₂ ′ are output to the scanning unit 3, and the scanning unit 3 transmits the electron beam EB to the aperture 9 based on the first control signals X ₃₁ ′, Y ₃₁ ′ and the second control signals X ₃₂ ′, Y ₃₂ ′. Scanning above, the image generation unit 24 generates an aperture image based on the detection result of the detection unit 6. Thereby, axis alignment can be performed based on the aperture image. Since the position of the axis Z of the objective lens 4 can be easily specified in the aperture image, the axis alignment of the electron beam EB can be easily performed by performing the axis alignment based on the aperture image.

  For example, when the axis alignment is performed using the current Wobbler or the like, a plurality of still images (scanned images) corresponding to the objective lens current value must be acquired. On the other hand, in the scanning charged particle microscope 100, since the axis alignment is performed based on the aperture image, for example, the position of the axis Z of the objective lens 4 is specified from one still image (scanned image) and the axis alignment is performed. It can be performed. Therefore, according to the scanning charged particle microscope 100, it is possible to shorten the time for acquiring a scanned image for axial alignment, and it is possible to easily perform axial alignment in a short time.

  Furthermore, since the aperture image is a method of looking at the shadow of the aperture 9, it is easy to contrast. Therefore, even a flat sample S that is difficult to contrast or a sample S having a periodic structure such as a mesh can be easily aligned.

  In the scanning charged particle microscope 100, the aperture 9 is disposed on the main surface 4 f of the objective lens 4. For this reason, the position of the axis Z of the objective lens 4 can be easily specified using the aperture image.

  In the scanning charged particle microscope 100, since the center of the opening 9b of the aperture 9 and the axis position of the objective lens 4 coincide with each other, the position of the axis of the objective lens 4 can be easily specified using the aperture image. Can do.

  In the scanning charged particle microscope 100, the axis alignment unit 26 aligns the electron beam EB with the axis of the objective lens 4 based on the aperture image, so that the axis alignment can be automated.

3. Next, a modified example of the scanning charged particle microscope 100 according to the present embodiment will be described. Hereinafter, differences from the scanning charged particle microscope 100 described above will be described, and description of similar points will be omitted.

(1) First Modification First, a first modification will be described. FIG. 12 is a diagram showing a configuration of a scanning charged particle microscope 200 according to the first modification.

  In the scanning charged particle microscope 100 shown in FIG. 1 described above, the axis alignment unit 26 performs axis alignment based on the aperture image. That is, the axis alignment unit 26 automatically performed axis alignment based on the aperture image.

  On the other hand, in the scanning charged particle microscope 200, as shown in FIG. 12, the user manually moves at least one of the movable objective aperture 7 and the alignment coil 8 based on the aperture image without having the axis alignment unit. Operate to adjust the axis.

  Specifically, the user confirms the aperture image (see FIG. 10) displayed on the display unit 10 and the center position of the circular bright portion of the aperture image and the center position of the scanning region (scanned image). Is operated (see FIG. 11), the movable objective aperture 7 is operated. Note that the user controls the excitation current of the alignment coil 8 not via the movable objective aperture 7 but through the operation unit 12, so that the center position of the circular bright portion of the aperture image and the center position of the scanning region are You may perform the operation | work which matches.

(2) Second Modification Next, a second modification will be described. FIG. 13 is a diagram illustrating a configuration of a scanning charged particle microscope 300 according to the second modification.

  In the scanning charged particle microscope 100 shown in FIG. 1 described above, the axis alignment unit 26 operates the alignment coil 8 to perform axis alignment.

On the other hand, in the scanning charged particle microscope 300, as shown in FIG. 13, the axis alignment unit 26 operates the movable objective aperture 7 to perform axis alignment. The movable objective aperture 7 is driven and controlled by the driving unit 7a. The drive unit 7a is connected to the bus line 30 and the bus line 3
A drive signal is supplied from the optical system control unit 28 via 0. The drive unit 7a drives the movable objective aperture 7 based on the drive signal.

  Although not shown, the axis alignment unit 26 may perform axis alignment by controlling both the alignment coil 8 and the movable objective aperture 7.

(3) Third Modification Next, a third modification will be described. FIG. 14 is a diagram showing a configuration of a scanning charged particle microscope 400 according to the third modification.

  In the scanning charged particle microscope 100 shown in FIG. 1 described above, the scanning unit 3 is a two-stage deflection system having an upper stage deflector 31 and a lower stage deflector 32.

  On the other hand, in the scanning charged particle microscope 400, as shown in FIG. 14, the scanning unit 3 is a multistage deflection system having multistage deflectors 31, 32, 33, and 34 of three or more stages.

  In the illustrated example, the scanning unit 3 includes four stages of deflectors 31, 32, 33, and 34, but the number of stages is not particularly limited. In such a multistage deflection system, when an aperture image is obtained, a first control signal for controlling some of the multistage deflectors 31, 32, 33, and 34, and the multistage deflectors 31, An aperture image can be obtained by making the rotation angle of the scan rotation different in the second control signal for controlling the other part of the deflectors 32, 33, and 34. That is, the rotation angle α of the scan rotation in some of the multi-stage deflectors 31, 32, 33, 34 is set to the other part of the multi-stage deflectors 31, 32, 33, 34. An aperture image can be obtained by making it different from the rotation angle β of the scan rotation in the deflector.

(4) Fourth Modification Next, a fourth modification will be described.

In the scanning charged particle microscope 100 shown in FIG. 1 described above, the first control signals X ₃₁ ′ and Y ₃₁ ′ and the second control signals X ₃₂ ′ and Y ₃₂ ′ are scanned by making the rotation angle α different from the rotation angle β. An aperture image was obtained by outputting the difference to the rotation angle of the scan rotation of the upper deflector 31 and the rotation angle of the scan rotation of the lower deflector 32.

  On the other hand, although not shown, the scanning direction of the electron beam EB is rotated by mechanically rotating at least one of the upper deflector 31 and the lower deflector 32 using a drive unit such as a motor. An aperture image may be obtained.

  In addition, embodiment mentioned above and each modification are examples, and are not necessarily limited to these. For example, it is possible to combine the embodiment and each modification as appropriate.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Charged particle beam source (electron beam source), 1a ... Drive part, 2 ... Converging lens, 2a ... Drive part, 3 ... Scanning part, 3a ... Amplifier, 4 ... Objective lens, 4a ... Drive part, 4f ... Main surface 5 ... Sample stage, 5a ... Driver, 6 ... Detector, 6a ... A / D converter, 7 ... Moving objective aperture, 7a ... Driver, 8 ... Alignment coil, 8a ... Driver, 9 ... Aperture, 9b ... Opening part, 10 ... Display part, 12 ... Operation part, 14 ... Storage part, 20 ... Processing part, 22 ... Scanning control part, 22a ... Scanning signal generation part, 22b ... Calculation part, 22c ... Addition part, 24 ... Image Generation unit 26 ... Axis alignment unit 28 28 Optical system control unit 30 Bus line 31 Upper stage deflector 32 Lower deflector 100, 200, 300, 400 Scanning charged particle microscope

Claims (11)

A charged particle beam source for generating a charged particle beam;
An objective lens for focusing the charged particle beam emitted from the charged particle beam source;
A scanning unit having a multi-stage deflector and scanning the charged particle beam focused by the objective lens on an object;
An aperture disposed on the rear side of the scanning unit;
A detection unit for detecting electrons emitted from the object by being irradiated with the charged particle beam;
An image generation unit configured to generate an image based on a detection result of the detection unit;
A control unit for controlling the scanning unit;
Including
The controller is
A first control signal for controlling a part of the multi-stage deflector;
A second control signal for controlling another part of the multistage deflector;
Produces
The first control signal is:
First scanning information for scanning the charged particle beam;
First scan rotation information for rotating the scanning direction of the charged particle beam by a first angle;
Including
The second control signal is:
Second scanning information for scanning the charged particle beam;
Second scan rotation information for rotating the scanning direction of the charged particle beam by a second angle;
Including
The control unit outputs the first control signal and the second control signal to the scanning unit by making the first angle different from the second angle,
The scanning unit scans the charged particle beam on the aperture based on the first control signal and the second control signal,
The detection unit detects electrons emitted by scanning the charged particle beam on the aperture,
The image generation unit is a scanning charged particle microscope that generates an aperture image based on a detection result of the detection unit. In claim 1,
The aperture is a scanning charged particle microscope arranged on a main surface of the objective lens. In claim 1 or 2,
A scanning charged particle microscope in which the center of the aperture of the aperture coincides with the position of the axis of the objective lens. In any one of Claims 1 thru | or 3,
A scanning charged particle microscope including an axis alignment unit that aligns the charged particle beam with the axis of the objective lens based on the aperture image. A charged particle beam source for generating a charged particle beam; an objective lens for focusing the charged particle beam emitted from the charged particle beam source; and a multistage deflector, wherein the focused lens beam is focused by the objective lens A scanning unit for scanning a charged particle beam on an object, an aperture disposed on the rear side of the scanning unit, and an electron emitted from the object by being irradiated with the charged particle beam A scanning charged particle microscope control method comprising: a detecting unit that performs detection; and an image generating unit that generates an image based on a detection result of the detecting unit,
Control signal generation for generating a first control signal for controlling a part of the multistage deflector and a second control signal for controlling another part of the multistage deflector Process,
A scanning step of controlling the scanning unit based on the first control signal and the second control signal to scan the charged particle beam on the aperture;
A detection step of detecting electrons emitted by scanning the charged particle beam on the aperture by the detection unit;
An image generation step of generating an aperture image based on a detection result of the detection unit by the image generation unit;
The first control signal is:
First scanning information for scanning the charged particle beam;
First scan rotation information for rotating the scanning direction of the charged particle beam by a first angle;
Have
The second control signal is:
Second scanning information for scanning the charged particle beam;
Second scan rotation information for rotating the scanning direction of the charged particle beam by a second angle;
Have
The method for controlling a scanning charged particle microscope, wherein, in the control signal generation step, the first angle and the second angle are different. In claim 5,
The method for controlling a scanning charged particle microscope, wherein the aperture is disposed on a main surface of the objective lens. In claim 5 or 6,
A method for controlling a scanning charged particle microscope, wherein a center of an aperture of the aperture and a position of an axis of the objective lens coincide with each other. In any one of Claims 5 thru | or 7,
A method for controlling a scanning charged particle microscope, comprising: aligning the charged particle beam with an axis of the objective lens based on the aperture image. A scanning charged particle microscope axial alignment method that scans a charged particle beam on an object with a multistage deflector, detects electrons emitted from the object, and generates an image.
The rotation angle of scan rotation in some of the deflectors of the multistage deflector is different from the rotation angle of scan rotation in the other deflectors of the multistage deflector, An aperture scanning step of scanning the charged particle beam on an aperture disposed on a rear stage side of the multistage deflector;
An aperture image generating step for generating an aperture image based on the detection result of the electrons emitted by the aperture scanning step;
An axis alignment step of aligning the charged particle beam with the axis of the objective lens based on the aperture image;
A method for axial alignment of a scanning charged particle microscope. In claim 9,
A method for axial alignment of a scanning charged particle microscope, wherein the aperture is disposed on a main surface of the objective lens. In claim 9 or 10,
An axis alignment method for a scanning charged particle microscope, wherein the center of the aperture of the aperture coincides with the position of the axis of the objective lens.