JP4594116B2 - Charged beam scanning width calibration method, microscope using charged particle beam, and charged particle beam calibration sample - Google Patents

Description

  The present invention relates to a charged particle beam scanning width calibration method, a microscope using a charged particle beam, and a charged particle beam calibration sample.

  As a microscope apparatus using a charged particle beam, a composite microscope apparatus (microscope apparatus) configured by combining a scanning electron microscope (SEM) and a scanning tunnel microscope (STM) has been developed. This composite microscope apparatus has a configuration in which an STM function is mounted on an SEM.

  In this composite microscope apparatus, when the target portion on the sample is measured at an extremely fine atomic level using STM, the region on the sample including the target portion can be observed with the SEM in advance. . Thereby, the measurement accuracy by STM can be improved. As an example of such a composite microscope apparatus, there is an apparatus disclosed in Patent Document 1, for example.

JP-A-5-209713

  In the above composite microscope apparatus, when the region on the sample is observed with the SEM, it is necessary to accurately calibrate the scanning width of the electron beam (charged particle beam) on the sample in advance. By accurately calibrating the scanning width of the electron beam in this way, it is possible to accurately scan the electron beam on the sample corresponding to the set magnification. As a result, the magnification calibration in the SEM is accurately performed.

  In particular, when scanning a minute region (for example, a region of the order of 100 nm) on a sample including a target portion to be measured at an atomic level by STM with an electron beam for SEM observation, the minute region is supported. Therefore, it is necessary to accurately calibrate the scanning width of the electron beam.

  However, a calibration sample conventionally used for calibration of the scanning width of an electron beam in an SEM is composed of a grating or mesh having a pitch of several hundred nm to several hundred μm. Therefore, in the calibration of the scanning width of the electron beam based on such a relatively wide pitch, it is difficult to accurately set the scanning width when scanning a minute region of the order of 100 nm with the electron beam.

  The present invention has been made in view of such points, and charged particles that can accurately calibrate the scanning width of a charged particle beam when scanning a minute region on a sample with a charged particle beam. An object of the present invention is to provide a beam scanning width calibration method.

  It is another object of the present invention to provide a microscope using a charged particle beam capable of executing the scanning width calibration method.

  Furthermore, an object of the present invention is to provide a charged particle beam calibration sample used in the microscope.

  The charged particle beam scanning width calibration method according to the present invention scans a charged particle beam on a sample arranged in a sample chamber, thereby obtaining a beam scan image of the sample surface, and probing provided in the sample chamber. A scanning width calibration method for a charged particle beam in a microscope that scans a probe of a mechanism on a sample and thereby obtains a probe scan image of the sample surface, and detects the scanning movement amount of the probe based on the beam scan image A first detection step; a second detection step of detecting the scanning movement amount of the probe based on the probe scanning image; and a scanning movement amount S1 of the probe determined by the first detection step and a second detection step. A comparison step for comparing the scanning movement amount S2 of the probe obtained by the above and a beam running for correcting the scanning width of the charged particle beam based on the comparison result of the comparison step And having a width correction process.

  In addition, a microscope using a charged particle beam according to the present invention scans a charged particle beam on a sample arranged in the sample chamber, thereby acquiring a beam scan image of the sample surface, and is provided in the sample chamber. A microscopic device that scans the probe of the probing mechanism on the sample and thereby obtains a probe scan image of the sample surface, the first detection means for detecting the scanning movement amount of the probe based on the beam scan image; Second detection means for detecting the scanning movement amount of the probe based on the probe scanning image, scanning movement amount S1 of the probe obtained by the first detection means, and scanning of the probe obtained by the second detection means Comparing means for comparing the movement amount S2, and beam scanning width calibration means for calibrating the scanning width of the charged particle beam based on the comparison result of the comparing means. To.

  Furthermore, the charged particle beam calibration sample according to the present invention is a calibration sample used in the microscope, and is provided with a probe scanning sample unit for acquiring a probe scanning image for beam scanning calibration. It is characterized by being.

  In the present invention, the scanning movement amount S1 of the probe detected based on the beam scanning image is compared with the scanning movement amount S2 of the probe detected based on the probe scanning image. Based on the comparison result, charged particles are compared. Calibrate the beam scan width.

  Here, the second scanning movement amount S2 detected based on the probe scanning image is obtained with high accuracy. Therefore, the scanning width of the charged particle beam is calibrated based on the comparison between the first scanning movement amount S1 detected based on the beam scanning image and the second scanning movement amount S2 obtained with high accuracy. It will be.

  As a result, the scanning width of the charged particle beam is calibrated based on the second scanning movement amount S2 measured with high accuracy, and the scanning width of the charged particle beam is accurately calibrated.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a microscope using a charged particle beam in the present invention. This microscope apparatus is composed of a composite microscope apparatus configured by combining a scanning electron microscope (SEM) and a scanning tunneling microscope (STM).

  In the figure, an electron beam (charged particle beam) 10 emitted from the electron gun 1 toward the sample 15 is irradiated in a state of being finely focused on the sample 15 by the focusing lens 2 and the objective lens 4. At this time, the electron beam 10 is appropriately deflected by the scanning coil 3. As a result, the electron beam 10 scans the sample 15. The focusing lens 2, the scanning coil 3, and the objective lens 4 constitute an electron optical system 24. The electron optical system 24 and the electron gun 1 are arranged in a lens barrel (not shown).

  Here, the sample 15 in the figure is a beam calibration sample (charged particle beam calibration sample), and a probe scanning sample section 15a is arranged at the center thereof. Note that the sample 15 is arranged in a sample chamber (not shown), and details of the structure of the sample 15 will be described later.

  On the sample 15 scanned with the electron beam 10, detected electrons 11 such as secondary electrons are generated. The generated detected electrons 11 are detected by the electron detector 12.

  The electron detector 12 outputs a detection signal based on the detection result of the detected electrons 11. This detection signal is amplified, A / D converted, and sent to the SEM image data forming unit 13. The SEM image data forming unit 13 forms SEM image (beam scanning image) data based on the detection signal from the electron detector 12, and the SEM image data is sent to the bus line 16.

  A probing mechanism 23 is provided in the sample chamber. The probing mechanism 23 includes a scanner 5, a probe 7 attached to the tip of the scanner 5, and a positioning sensor 8 disposed on the side surface of the scanner 5. The probing mechanism 23 scans the tip of the probe 7 in the XY direction on the surface of the sample 15 and detects a tunnel current through the probe 7 at this time, thereby acquiring a probe scan image composed of an STM image. Is to do. Note that the contour of the tip of the probe 7 is formed in an arc shape, and its radius of curvature is about 10 nm. Such a probe 7 is formed by electrolytic etching of a tungsten wire.

  Here, when the probe 7 is scanned in the XY direction on the surface of the sample 15, the position of the probe 7 is detected by the positioning sensor 8, and the detection result is A / D converted and sent to the bus line 16. It is done.

  The tunnel current detected through the probe 7 of the probing mechanism 23 is amplified and sent to the comparison unit 9. The comparison unit 9 compares a preset reference current with the detected tunnel current, and outputs a feedback amount in the Z direction of the probe 7 obtained based on the comparison result to the drive unit 5a as a feedback signal. .

  Thereby, the probe 7 is scanned in the XY direction on the sample surface in a state where the detected tunnel current is equal to the reference current, and the feedback amount in the Z direction of the probe 7 at this time can be obtained in the comparison unit 9. it can.

  A feedback signal based on the feedback amount obtained in the comparison unit 9 in this way is sent to the STM image data forming unit 14. The STM image data forming unit 14 forms STM image (probe scanning image) data based on the feedback signal from the comparison unit 9, and the STM image data is sent to the bus line 16.

  The sample 15 is placed on the sample stage mechanism 6 disposed in the sample chamber. The sample stage mechanism 6 is for moving the sample 15 in the X direction, the Y direction, and the Z direction in the drawing, and for tilting and rotating the sample 15.

  Here, the electron gun 1, the focusing lens 2, the scanning coil 3, and the objective lens 4 (driving objects 1 to 4) disposed in the lens barrel are driven by corresponding driving units 1 a to 4 a, respectively. Further, the scanner 5 (drive target 5) and the sample stage mechanism 6 (drive target 6) of the probing mechanism 23 arranged in the sample chamber are driven by corresponding drive units 5a and 6a, respectively.

  Each drive unit 1 a to 6 a is connected to a bus line 16. A control unit 22 is connected to the bus line 16. Thereby, each said driving object 1-6 is drive-controlled by the control part 22 via the corresponding drive parts 1a-6a, respectively.

  The bus line 16 is connected to a first detection unit 17, a second detection unit 18, a comparison unit 19, a beam scanning width calibration unit 20, and a display unit 22.

  The first detection means 17 is for detecting the scanning movement amount of the probe 7 based on the SEM image. The second detection means 18 is for detecting the scanning movement amount of the probe 7 based on the STM image. The comparison means 19 includes the scanning movement amount (first scanning movement amount) of the probe 7 obtained by the first detection means and the scanning movement amount (second scanning movement) of the probe 7 obtained by the second detection means. The amount). The beam scanning width calibration means 20 is for calibrating the scanning width of the electron beam 10 based on the comparison result of the comparison means 19. The display unit 22 is for displaying the acquired SEM image or STM image. In addition, the control part 21 mentioned above controls each said component.

  Here, the structure of the sample 15 which is a beam calibration sample will be described with reference to FIG. As shown in the figure, the sample 15 is provided with a probe scanning sample portion 15a in the center thereof. The probe scanning sample portion 15a is a sample portion that the probe 7 of the probing mechanism 23 scans on the surface thereof, and is made of a sample material for STM. Specifically, it is made of graphite. The atomic arrangement pitch of this graphite is about 0.246 nm.

  In the sample 15, a mesh portion 15 b having a pitch of several hundred nm to several hundred μm is provided in the central peripheral portion where the probe scanning sample portion 15 a is provided. Note that a grating portion having the same pitch may be provided in the peripheral portion. This peripheral portion is used when executing a calibration method similar to the electron beam scanning width calibration method performed in the prior art.

  A method for calibrating the scanning width of the electron beam (charged particle beam) in the microscope having the above configuration will be described below.

  First, the control unit 21 drives and controls the scanner 5 of the probing mechanism 23 via the drive unit 5 a to bring the tip of the probe 7 closer to the surface of the probe scanning sample unit 15 a. Then, the tunnel current is detected via the probe 7, and the tip of the probe 7 is brought close to the surface of the probe scanning sample portion 15a until the detected tunnel current becomes equal to a predetermined reference current. In a state where a tunnel current equal to the reference current is detected through the probe 7, the control unit 21 temporarily stops the movement of the probe 7.

  In this state, the control unit 21 drives and controls the electron gun 1 and the electron optical system 24, and scans the electron beam 10 emitted from the electron gun 1 on the probe scanning sample unit 15 a of the sample 15. The scanning width at this time is about 100 nm, and the tip of the probe 7 is included in the scanning region.

  The detected electrons 11 generated by the scanning of the electron beam 10 are detected by the electron detector 12. The electron detector 12 outputs a detection signal based on the detection result of the detected electrons 11. This detection signal is amplified, A / D converted, and sent to the SEM image data forming unit 13. The SEM image data forming unit 13 forms SEM image (beam scanning image) data based on the detection signal from the electron detector 12, and the SEM image data is output to the bus line 16.

  Then, the SEM image data is sent to the first detection means 17 via the bus line 16. The first detection means 17 stores this SEM image data as first image data in a storage unit (not shown) provided inside. An image of the probe 7 (probe image) in the SEM image at this time is shown by a solid line in FIG.

  Next, the control unit 21 drives and controls the scanner 5 of the probing mechanism 23 via the drive unit 5a, and scans and moves the tip of the probe 7 in the X direction on the surface of the probe scanning sample unit 15a. At this time, the control unit 21 accurately performs the scanning movement of the probe 7 in the X direction based on the detection result of the positioning sensor 8.

  In the scanning of the probe 7 in the X direction, the tunnel current is detected through the probe 7. The tunnel current detected through the probe 7 is amplified and sent to the comparison unit 9. The comparison unit 9 compares the reference current with the detected tunnel current, and outputs a feedback amount in the Z direction of the probe 7 obtained based on the comparison result to the drive unit 5a as a feedback signal.

  Thus, the probe 7 is scanned in the X direction on the surface of the probe scanning sample portion 15a in a state where the detected tunnel current is equal to the reference current, and the feedback amount in the Z direction of the probe 7 at this time is compared with the comparison portion 9. Can be obtained in

  A feedback signal based on the feedback amount obtained in the comparison unit 9 is sent to the STM image data forming unit 14. The STM image data forming unit 14 forms STM image (probe scanning image) data based on the feedback signal from the comparison unit 9, and this STM image data is sent to the second detection means 18 via the bus line 16. . An example of an STM image based on the STM image data formed in this way is shown in FIG. The example shown in the figure is an STM image corresponding to the XY plane.

  The second detection means 18 detects the scanning movement amount in the X direction scanning of the probe 7 based on the STM image data. Here, the 2nd detection means is provided with the memory | storage part which is not shown in figure, and the preset movement amount set beforehand is stored in this memory | storage part. In the present embodiment, the set movement amount is, for example, 12.3 nm corresponding to 50 pitches (0.246 nm × 50) of the atomic arrangement pitch of graphite constituting the probe scanning sample portion 15a.

  The second detection means 18 determines whether or not the scanning movement amount reaches the set movement amount while detecting the scanning movement amount when the probe 7 scans in the X direction. Then, when the scanning movement amount reaches the set movement amount, a detection signal to that effect is sent to the control unit 21. The control unit 21 stops the scanning drive of the probe 7 based on the detection signal. As a result, the probe 7 is stopped after scanning the probe scanning sample portion 15a in the X direction with a scanning movement amount of 12.3 nm.

  At the same time, the second detection means 18 sends 12.3 nm data that is the scanning movement amount of the probe 7 to the comparison means 19 as second scanning movement amount data. The comparison unit 19 includes a storage unit (not shown), and stores the second scanning movement amount data in the storage unit.

  In the above state, scanning with the electron beam 10 that is the same as the scanning condition of the electron beam 10 described above is performed. The scanning width and scanning area of the electron beam 10 on the probe scanning sample portion 15a at this time are the same as those in the scanning of the electron beam 10 described above.

  The detected electrons 11 generated based on the scanning of the electron beam 10 are detected by the electron detector 12. Similarly to the above, the electron detector 12 sends a detection signal to the SEM image data forming unit 13 based on the detection result of the detected electrons 11. The SEM image data forming unit 13 forms SEM image data at this time based on the detection signal from the electron detector 12, and sends the SEM image data to the first detection unit 17 via the bus line 16. Here, the SEM image data at this time is defined as second image data.

  The first detection means 17 creates composite image data of the first image data stored in the storage unit and the second image data. In the image based on the composite image data, as shown in FIG. 3, the probe image 7a in the first image data indicated by the solid line and the probe image 7b in the second image data indicated by the alternate long and short dash line are the same. It is included in the scanning area.

  And the 1st detection means 17 detects the scanning movement amount (distance S in FIG. 3) of the probe 7 based on the said synthesized image data by performing a predetermined image process. For example, the scanning movement amount of the probe 7 is detected by obtaining the coordinates of the tip portions 7c and 7d of the probe images 7a and 7b in the image and calculating the difference between the coordinates. Thereafter, the first detection means 17 sends the scanning movement amount data of the probe 7 detected thereby to the comparison means 9 as first scanning movement amount data.

  The comparison unit 9 compares the second scanning movement amount data stored in the storage unit with the first scanning movement amount data. Specifically, if the scanning movement amount in the first scanning movement amount data sent at this time is “S1” and the scanning movement amount in the stored second scanning movement amount data is “S2,” “a = S1 / S2 "is executed. That is, a calculation is performed to divide the first scanning movement amount by the second scanning movement amount. Here, in this embodiment, since “S2 = 12.3 nm”, “a = S1 / 12.3”. “A” obtained from this calculation result is a correction coefficient for the scanning width of the electron beam 10.

  Data of the correction coefficient a obtained from the calculation result of the comparison means 19 is sent to the beam width calibration means 20. The beam width calibration unit 20 includes a storage unit (not shown), and stores data of the correction coefficient a in the storage unit. Then, the beam width calibration unit 20 reads the data of the correction coefficient a stored in the storage unit, and calibrates the scanning width of the electron beam 10 based on the read correction coefficient a.

  That is, when the correction coefficient a is 1 or more, the scanning movement amount S1 obtained from the SEM image data is larger than the scanning movement amount S2 obtained from the STM image data. In this case, since the scanning width of the electron beam 10 is set small, the scanning width of the electron beam 10 is calibrated by setting the scanning width to the correction coefficient multiple.

  When the correction coefficient a is less than 1, the scanning movement amount S1 obtained from the SEM image data is smaller than the scanning movement amount S2 obtained from the STM image data. In this case, since the scanning width of the electron beam 10 is set large, the scanning width of the electron beam 10 is calibrated by setting the scanning width to the correction coefficient multiple.

  As described above, in the present invention, the scanning movement amount (first scanning movement amount) S1 of the probe detected based on the beam scanning image, and the scanning movement amount of the probe (second scanning amount) detected based on the probe scanning image. And the scanning width of the charged particle beam is calibrated based on the comparison result.

  Here, the second scanning movement amount S2 detected based on the probe scanning image is obtained by high-accuracy measurement. Therefore, the scanning width of the charged particle beam is calibrated based on the comparison between the first scanning movement amount S1 detected based on the beam scanning image and the second scanning movement amount S2 obtained with high accuracy. It will be.

  Thus, the scanning width of the charged particle beam is calibrated based on the second scanning movement amount S2 measured with high accuracy, and the scanning width of the charged particle beam is accurately calibrated.

  In the above example, the STM image is applied as the probe scanning image. However, as the probe scanning image, a scanning image obtained using another scanning probe microscope (SPM) is applied. Also good.

1 is a schematic calibration diagram showing a microscope using a charged particle beam in the present invention. It is a figure which shows the sample for beam calibration in this invention. It is a figure which shows the image of the probe 7 in a SEM image and its synthetic image. It is a figure which shows the example of an STM image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Focusing lens, 3 ... Scanning coil, 4 ... Objective lens, 5 ... Scanner, 6 ... Sample stage mechanism, 7 ... Probe, 8 ... Positioning sensor, 9 ... Comparison part, 10 ... Electron beam (charge) Particle beam), 11 ... electron to be detected, 12 ... electron detector, 13 ... SEM image data forming unit, 14 ... STM image data forming unit, 15 ... sample (sample for beam calibration), 16 ... bus line, 17 ... first DESCRIPTION OF SYMBOLS 1 detection means, 18 ... 2nd detection means, 19 ... Comparison means, 20 ... Beam scanning width calibration means, 21 ... Control part, 22 Display part, 23 ... Probing mechanism

Claims (12)

A charged particle beam is scanned on the sample placed in the sample chamber, thereby obtaining a beam scanning image of the sample surface, and a probe of a probing mechanism provided in the sample chamber is scanned on the sample, thereby A method for calibrating a scanning width of a charged particle beam in a microscope that acquires a scanning image of a probe of a probe, comprising: a first detection step of detecting a scanning movement amount of the probe based on the beam scanning image; and a scanning movement amount of the probe. A second detection step that is detected based on the probe scan image, a scanning movement amount S1 of the probe obtained by the first detection step, and a scanning movement amount S2 of the second probe obtained by the second detection step; And a beam scanning width calibration step for calibrating the scanning width of the charged particle beam based on the comparison result of the comparison step. Scan width calibration method of the child beam. The charged particle beam scanning width correction coefficient is obtained in the comparison step, and the charged particle beam scanning width calibration is performed based on the correction coefficient in the beam scanning width calibration step. Particle beam scanning width correction method. 3. The charged particle beam scanning width calibration method according to claim 2, wherein the correction coefficient is calculated by a ratio of the first scanning movement amount S1 and the second scanning movement amount S2. 4. The charged particle beam scanning width calibration method according to claim 1, wherein the probe scanning image is an STM image. 5. The charged particle beam scanning width calibration method according to claim 1, wherein the charged particle beam is an electron beam. A charged particle beam is scanned on the sample placed in the sample chamber, thereby obtaining a beam scanning image of the sample surface, and a probe of a probing mechanism provided in the sample chamber is scanned on the sample, thereby A first detection means for detecting the scanning movement amount of the probe based on the beam scanning image, and a first detection unit for detecting the scanning movement amount of the probe based on the probe scanning image. 2 and a comparison means for comparing the scanning movement amount S1 of the probe obtained by the first detection means with the scanning movement amount S2 of the probe obtained by the second detection means, and a comparison result of the comparison means And a beam scanning width calibration means for calibrating the scanning width of the charged particle beam based on the microscope. 7. The charging according to claim 6, wherein the comparison means obtains a correction coefficient for the scanning width of the charged particle beam, and the beam scanning width calibration means calibrates the scanning width of the charged particle beam based on the correction coefficient. Microscope using particle beam. 8. The microscope using a charged particle beam according to claim 7, wherein the correction coefficient is calculated by a ratio of the first scanning movement amount S1 and the second scanning movement amount S2. 9. A microscope using a charged particle beam according to claim 6, wherein the probe scanning image is an STM image. 10. A microscope using a charged particle beam according to claim 6, wherein the charged particle beam is an electron beam. 7. A calibration sample used in a microscope using a charged particle beam according to claim 6, wherein a probe scanning sample section for obtaining a probe scanning image for beam scanning calibration is provided. A charged particle beam calibration sample. The charged particle beam calibration sample according to claim 11, wherein the probe scanning sample portion is arranged in the center, and a grating portion or a mesh portion is provided around the probe scanning sample portion.

Images