Charged particle beam apparatus and control method thereof

Abstract

To provide a charged particle beam device capable of improving SNR of reflected electrons, and to provide a control method therefor.SOLUTION: A charged particle beam apparatus comprising: a charged particle source configured to emit a charged particle beam to irradiate a sample; a deflector configured to deflect trajectories of secondary electrons and reflected electrons emitted from the sample; a reflected electron detector configured to detect the reflected electrons; and a control unit configured to acquire an observation image based on a detection signal output from the reflected electron detector and control operations of respective units, wherein the charged particle beam apparatus further comprises an absorption plate disposed between the deflector and the reflected electron detector and having a concave portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a charged particle beam device that detects backscattered electrons generated by irradiating a sample with a charged particle beam, and particularly to improving the SNR (Signal-to-Noise Ratio) of backscattered electrons. [Background technology]

[0002] A charged particle beam device detects secondary electrons and backscattered electrons generated in a sample irradiated with a charged particle beam such as an electron beam, and acquires an observation image of the sample based on the detection signal. When observing the bottom of a deep hole or trench in a sample, it is important to detect backscattered electrons emitted from the bottom.

[0003] Patent Document 1 discloses that the trajectories of secondary electrons and reflected electrons emitted from a sample irradiated with an electron beam are deflected, and only the reflected electrons that pass through a pinhole in an aperture plate are detected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-15130 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not give sufficient consideration to electrons generated by secondary electrons colliding with the aperture plate. When electrons generated on the aperture plate due to the collision of secondary electrons pass through the pinhole and are detected, they become noise, reducing the SNR of the reflected electrons.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a charged particle beam device capable of improving the SNR of reflected electrons and a control method thereof. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a charged particle beam device comprising: a charged particle source that emits a charged particle beam to be irradiated onto a sample; a deflector that deflects the trajectories of secondary electrons and backscattered electrons emitted from the sample; a backscattered electron detector that detects the backscattered electrons; and a control unit that acquires an observation image based on a detection signal output from the backscattered electron detector and controls the operation of each unit, and is characterized in that the device further comprises an absorber plate that is arranged between the deflector and the backscattered electron detector and has a recessed portion.

[0008] The present invention also provides a control method for a charged particle beam device comprising: a charged particle source that emits a charged particle beam to be irradiated onto a sample; a deflector that deflects the trajectories of secondary electrons and backscattered electrons emitted from the sample; a backscattered electron detector that detects the backscattered electrons; a second backscattered electron detector that is provided in a different orientation from the backscattered electron detector and detects the backscattered electrons; a filter that is disposed between the deflector and the second backscattered electron detector and blocks the secondary electrons; and a control unit that acquires an observation image based on a detection signal output from the backscattered electron detector or the second backscattered electron detector and controls the operation of each unit, wherein the control unit controls the deflector in accordance with the energy difference between the backscattered electrons and the secondary electrons. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a charged particle beam device and a control method thereof that can improve the SNR of reflected electrons. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of the overall configuration of a scanning electron microscope according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating an example of an absorption plate having a recessed portion. [Figure 3] FIG. 10 is a diagram illustrating another example of an absorption plate having a recessed portion. [Figure 4] FIG. 10 is a diagram illustrating another example of a backscattered electron detector. [Figure 5]FIG. 1 is a diagram showing an example of the overall configuration of a scanning electron microscope according to a second embodiment. [Figure 6] FIG. 10 is a diagram showing another example of the overall configuration of the scanning electron microscope according to the second embodiment. [Figure 7] FIG. 10 is a diagram showing an example of a processing flow of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a charged particle beam device according to the present invention will be described with reference to the accompanying drawings. The charged particle beam device is a device, such as a scanning electron microscope, that detects secondary electrons and backscattered electrons generated from a sample by irradiating the sample with a charged particle beam such as an electron beam, and generates an observation image based on the detection signals. [Example]

[0012] An example of the overall configuration of a scanning electron microscope according to the first embodiment will be described with reference to Figure 1. The scanning electron microscope comprises a microscope body 100 and a control unit 120. The microscope body 100 is provided with an electron source 101, an aperture 106, a scanning deflector 102, an objective lens 103, a sample stage 104, a secondary particle deflector 109, an absorbing plate 110, and a backscattered electron detector 111. The inside of the microscope body 100 is evacuated by a vacuum pump or the like, and a sample 105 is held on the sample stage 104.

[0013] The electron source 101 emits an electron beam that is irradiated onto a sample 105. The aperture 106 has a hole through which the electron beam passes near the optical axis. The size of the hole is within the range of 0.1 to 10 mm and can be changed depending on the purpose of observation. In order to prevent charging due to collision of the electron beam, at least the surface of the aperture 106 is made of a conductor.

[0014] The scanning deflector 102 deflects the electron beam so that the observation area of ​​the sample 105 is scanned. The objective lens 103 focuses the electron beam deflected by the scanning deflector 102 onto the sample 105. The sample stage 104 that holds the sample 105 moves horizontally and vertically to set the observation area to a predetermined position. Backscattered electrons 107 and secondary electrons 108 are emitted from the sample 105 that is irradiated with the electron beam. When a negative voltage is applied to the sample 105 via the sample stage 104, the backscattered electrons 107 and secondary electrons 108 are accelerated by the voltage applied to the sample 105.

[0015] The secondary particle deflector 109 is a Wien filter that forms an electric field and a magnetic field that are perpendicular to each other, and deflects the trajectories of the reflected electrons 107 and secondary electrons 108 that have passed through the aperture 106 without deflecting the electron beam irradiated onto the sample 105. Note that since the secondary electrons 108 have lower energy than the reflected electrons 107, the deflection angle of the secondary electrons 108 by the secondary particle deflector 109 is larger than that of the reflected electrons 107.

[0016] The backscattered electron detector 111 detects the backscattered electrons 107 deflected by the secondary particle deflector 109, and transmits a detection signal to the control unit 120. The control unit 120 is, for example, a computer, and generates an observation image based on the detection signal transmitted from the backscattered electron detector 111, and controls the operation of each unit provided in the mirror body 100.

[0017] The absorbing plate 110 is disposed between the secondary particle deflector 109 and the backscattered electron detector 111, and is a plate that absorbs the secondary electrons 108 deflected by the secondary particle deflector 109, and has a recess 110A.

[0018] 2, an example of an absorber plate 110 having a recessed portion 110A will be described. The recessed portion 110A is a hole having an opening size of 2R and a depth of D, and is provided at a position where secondary electrons 108 deflected by the secondary particle deflector 109 reach. Since the absorber plate 110 has the recessed portion 110A, the secondary electrons 108 collide with the absorber plate 110 at the recessed portion 110A, and electrons generated in the absorber plate 110 by the collision are absorbed by the absorber plate 110 while undergoing multiple scattering in the recessed portion 110A. As a result, it is possible to prevent the electrons generated in the absorber plate 110 from being detected by the backscattered electron detector 111, thereby improving the SNR (Signal-to-Noise Ratio) of the backscattered electrons 107.

[0019] Furthermore, it is preferable that the opening size 2R of the recessed portion 110A is larger than the beam diameter of the secondary electrons 108. When the opening size 2R is larger than the beam diameter of the secondary electrons 108, all of the secondary electrons 108 are incident on the recessed portion 110A, and therefore, a proportion of the electrons generated in the absorbing plate 110 that are absorbed by the absorbing plate 110 increases. Note that the beam diameter of the secondary electrons 108 is approximately the same as the size of the hole in the diaphragm 106, so the opening size 2R of the recessed portion 110A may be larger than the size of the hole in the diaphragm 106. For example, when the size of the hole in the diaphragm 106 is within the range of 0.1 to 10 mm, the opening size 2R of the recessed portion 110A may be set to 10 mm or more.

[0020] Furthermore, it is preferable that the difference between the tilt angle of recess 110A with respect to the optical axis and the deflection angle of secondary electrons 108 be within a predetermined value, and it is best that both angles are equal. When the difference between the tilt angle of recess 110A and the deflection angle of secondary electrons 108 is within a predetermined value, the amount of secondary electrons 108 that reaches the bottom surface of recess 110A increases, making it easier for multiple scattering to occur in electrons generated by absorber plate 110, and increasing the proportion of electrons absorbed by absorber plate 110.

[0021] Furthermore, it is preferable that the value D / 2R obtained by dividing the depth D of recess 110A by the size 2R of the opening be large. The graph illustrated in Figure 2 shows the result of calculating the relationship between D / 2R and the probability that electrons generated according to a cosine distribution due to collision of secondary electrons 108 with the bottom surface of recess 110A will escape from recess 110A. Note that the escape probability Pe of electrons from recess 110A can be calculated by the following equation when tan θ = R / D.

[0022] Pe=(1-cos2θ) / 2…(Equation 1) According to the graph in FIG. 2, when D / 2R is 2 or more, Pe can be made less than 10%.

[0023] Another example of the absorber plate 110 having the recess 110A will be described with reference to FIG. 3. FIG. 3(a) shows a case where electrons 301 generated at the bottom surface of the recess 110A emit secondary electrons or reflected electrons at the side surface of the recess 110A. It is preferable to prevent such secondary electrons and reflected electrons from being detected by the reflected electron detector 111. Therefore, as shown in FIG. 3(b), the size of the bottom surface of the recess 110A may be made larger than the size of the opening, thereby reducing the probability that electrons 301 generated at the bottom surface will emit secondary electrons or reflected electrons at the side surface of the recess 110A.

[0024] 3(c), a secondary electron detector 302 for detecting secondary electrons 108 may be provided on the bottom surface of the recess 110A. The secondary electron detector 302 detects secondary electrons 108 incident on the recess 110A and transmits a detection signal to the control unit 120. The control unit 120 may generate an observation image based on the detection signal transmitted from the secondary electron detector 302, or may adjust the focus of the objective lens 103 or the position of the sample stage 104.

[0025] Another example of the backscattered electron detector 111 will be described with reference to Fig. 4. The backscattered electron detector 111 illustrated in Fig. 4(a) has a reflector 401 and a detector 402. The reflector 401 is provided at a position where the backscattered electrons 107 deflected by the secondary particle deflector 109 reach, and emits reflected plate electrons 403 when the reflected electrons 107 collide with the reflector 401. The reflected plate electrons 403 are secondary electrons emitted from the reflector 401 when the reflected electrons 107 collide with the reflector 401. The detector 402 detects the reflected plate electrons 403 emitted from the reflector 401, and transmits a detection signal to the control unit 120. Note that the energy of the reflected plate electrons 403 is relatively low, at 50 eV or less, and therefore the detector 402 used is one that forms an electric field that attracts the reflected plate electrons 403.

[0026] 4(b), the reflector 401 in FIG. 4(a) is divided into an inner reflector 401A and an outer reflector 401B, and voltages are applied to the inner reflector 401A and the outer reflector 401B individually under the control of the control unit 120. The inner reflector 401A is disposed closer to the electron source 101, and the outer reflector 401B is disposed farther from the electron source 101.

[0027] The backscattered electrons 107 include high-energy backscattered electrons 107H having relatively high energy and low-energy backscattered electrons 107L having relatively low energy. The high-energy backscattered electrons 107H have a relatively small deflection angle, so they collide with inner reflector 401A and emit reflector electrons 403 from inner reflector 401A. The low-energy backscattered electrons 107L have a relatively large deflection angle, so they collide with outer reflector 401B and emit reflector electrons 403 from outer reflector 401B.

[0028] When the control unit 120 applies a positive voltage, for example, 50 V, to the inner reflector 401A, the reflector electrons 403 emitted from the inner reflector 401A are drawn back to the inner reflector 401A. As a result, only the reflector electrons 403 emitted from the outer reflector 401B are detected by the detector 402, and an observation image is generated by low-energy reflected electrons 107L. On the other hand, when the control unit 120 applies a positive voltage to the outer reflector 401B, an observation image is generated by high-energy reflected electrons 107H. That is, by individually applying voltages to the divided inner reflector 401A and outer reflector 401B as shown in FIG. 4(b), the energy of the reflected electrons 107 can be discriminated. [Example]

[0029] In the first embodiment, the separation of the backscattered electrons 107 and the secondary electrons 108 was described by utilizing the difference in deflection angle in the secondary particle deflector 109 based on the energy difference between the backscattered electrons 107 and the secondary electrons 108. Depending on the value of the negative voltage applied to the sample 105 via the sample stage 104, the energy difference between the backscattered electrons 107 and the secondary electrons 108 may be small, making it difficult to separate the backscattered electrons 107 and the secondary electrons 108 in the secondary particle deflector 109. In the second embodiment, the separation of the backscattered electrons 107 and the secondary electrons 108 regardless of the energy difference will be described.

[0030] An example of the overall configuration of a scanning electron microscope according to Example 2 will be described with reference to Fig. 5. The scanning electron microscope illustrated in Fig. 5 is configured by adding a second backscattered electron detector 501 and a filter 502 to the configuration shown in Fig. 1.

[0031] The second backscattered electron detector 501, like the backscattered electron detector 111, detects the backscattered electrons 107 deflected by the secondary particle deflector 109 and transmits a detection signal to the control unit 120. The second backscattered electron detector 501 is placed in a different orientation from the backscattered electron detector 111, and for example, when the backscattered electron detector 111 is placed in a direction with an azimuth angle of 0°, the second backscattered electron detector 501 is placed in a direction with an azimuth angle of 180°.

[0032] The filter 502 is a mesh electrode disposed between the secondary particle deflector 109 and the second backscattered electron detector 501, and blocks the secondary electrons 108 when a negative voltage is applied to the filter 502. Since the filter 502 blocks the secondary electrons 108, the second backscattered electron detector 501 detects only the backscattered electrons 107 out of the backscattered electrons 107 deflected by the secondary particle deflector 109 and the secondary electrons 108.

[0033] Another example of the overall configuration of the scanning electron microscope of Example 2 will be described with reference to Fig. 6. The scanning electron microscope illustrated in Fig. 6 is obtained by adding a pipe 601 to the configuration of Fig. 5. The pipe 601 is a thin metal tube at ground potential, and is arranged in the vicinity of the second backscattered electron detector 501 and the filter 502 so as to cover the electron beam emitted from the electron source 101. The electron beam covered by the pipe 601 is not deflected by the electric field formed by the filter 502 and the like.

[0034] An example of the processing flow of the second embodiment will be described for each processing step with reference to FIG.

[0035] (S701) The control unit 120 acquires the imaging conditions, which include the voltages applied to the electron source 101 and the sample 105.

[0036] (S702) Based on the imaging conditions acquired in S701, the control unit 120 calculates the energy difference between the backscattered electrons 107 and secondary electrons 108 that are emitted from the sample 105 and reach the secondary particle deflector 109. For example, when the voltage applied to the electron source 101 is −11 kV and the voltage applied to the sample 105 is −1 kV, the backscattered electrons 107 emitted from the sample 105 have an energy of 10 keV, and the secondary electrons 108 have an energy of 50 eV. By the time they reach the secondary particle deflector 109, they are accelerated by the voltage applied to the sample 105, so the energy of the backscattered electrons 107 becomes 11 keV, and the energy of the secondary electrons 108 becomes approximately 1 keV. As a result, the energy difference between the two is approximately 10 keV. Furthermore, when −5 kV is applied to the electron source 101 and −4 kV is applied to the sample 105, the reflected electrons 107 and secondary electrons 108 that reach the secondary particle deflector 109 have energies of 5 keV and approximately 4 keV, respectively, with an energy difference between the two of approximately 1 keV.

[0037] (S703) The control unit 120 determines whether the energy difference calculated in S702 is equal to or greater than a threshold. If the energy difference is equal to or greater than the threshold, the process proceeds to S704. If the energy difference is not equal to or greater than the threshold, the process proceeds to S705. The threshold is set in advance. For example, if the threshold is 2 keV and −11 kV is applied to the electron source 101 and −1 kV is applied to the sample 105, the energy difference between the backscattered electrons 107 and the secondary electrons 108 is approximately 10 keV, which is equal to or greater than the threshold, and the process proceeds to S704. If the threshold is 2 keV and −5 kV is applied to the electron source 101 and −4 kV is applied to the sample 105, the energy difference between the backscattered electrons 107 and the secondary electrons 108 is approximately 1 keV, which is less than the threshold, and the process proceeds to S705.

[0038] (S704) The control unit 120 controls the secondary particle deflector 109 to deflect the trajectories of the backscattered electrons 107 and secondary electrons 108 emitted from the sample 105 toward the backscattered electron detector 111. The deflected secondary electrons 108 are absorbed by the absorbing plate 110 having the recessed portion 110A, and the backscattered electrons 107 enter the backscattered electron detector 111.

[0039] (S705) The control unit 120 controls the secondary particle deflector 109 to deflect the trajectories of the backscattered electrons 107 and secondary electrons 108 emitted from the sample 105 toward the second backscattered electron detector 501. The deflected secondary electrons 108 are blocked by a filter 502, and the backscattered electrons 107 enter the backscattered electron detector 111.

[0040] (S706) The backscattered electron detector 111 or the second backscattered electron detector 501 detects the backscattered electrons 107 and transmits a detection signal to the control unit 120. The control unit 120, to which the detection signal has been transmitted, generates an observation image based on the detection signal. The generated observation image is displayed on a display device such as a liquid crystal display, or stored in a storage device such as a hard disk drive (HDD) or a solid state drive (SSD).

[0041] The process flow described with reference to FIG. 7 allows the backscattered electrons 107 and secondary electrons 108 to be separated regardless of the energy difference.

[0042] The above describes an embodiment of the electron microscope of the present invention. The present invention is not limited to the above embodiment, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, multiple components disclosed in the above embodiment may be combined as appropriate. Furthermore, some components may be deleted from all the components shown in the above embodiment. [Explanation of symbols]

[0043] 100: mirror body, 101: electron source, 102: scanning deflector, 103: objective lens, 104: sample stage, 105: sample, 106: aperture, 107: backscattered electrons, 107H: high-energy backscattered electrons, 107L: low-energy backscattered electrons, 108: secondary electrons, 109: secondary particle deflector, 110: absorbing plate, 110A: recessed portion, 111: backscattered electron detector, 120: control unit, 301: electrons, 302: secondary electron detector, 401: reflector, 401A: inner reflector, 401B: outer reflector, 402: detector, 403: reflector electrons, 501: second backscattered electron detector, 502: filter, 601: pipe.

Claims

1. a charged particle source that emits a charged particle beam to be irradiated onto a sample; a deflector for deflecting the trajectories of secondary electrons and reflected electrons emitted from the sample; a backscattered electron detector for detecting the backscattered electrons; A charged particle beam device comprising: a control unit that acquires an observation image based on a detection signal output from the backscattered electron detector and controls operations of each unit; a charged particle beam device further comprising an absorber plate having a recess, the absorber plate being disposed between the deflector and the backscattered electron detector;

2. The charged particle beam device according to claim 1, The charged particle beam device is characterized in that the size of the opening of the recess is larger than the beam diameter of the secondary electrons.

3. The charged particle beam device according to claim 1, A charged particle beam device, characterized in that the difference between the tilt angle of the recess with respect to the optical axis and the deflection angle of the secondary electrons is within a predetermined value.

4. The charged particle beam device according to claim 1, A charged particle beam device characterized in that the value D / 2R obtained by dividing the depth D of the recess by the size 2R of the opening is 2 or more.

5. The charged particle beam device according to claim 1, A charged particle beam device, wherein the size of the bottom surface of the recess is larger than the size of the opening of the recess.

6. The charged particle beam device according to claim 1, The charged particle beam device is characterized in that a secondary electron detector for detecting the secondary electrons is provided on the bottom surface of the recess.

7. The charged particle beam device according to claim 1, The backscattered electron detector includes a reflector on which the backscattered electrons collide, and a reflector electron detector that detects reflector electrons emitted from the reflector.

8. The charged particle beam device according to claim 7, the reflector is divided into an inner reflector disposed closer to the charged particle source and an outer reflector disposed farther from the charged particle source; The charged particle beam device is characterized in that the control unit applies voltages to the inner reflector and the outer reflector individually.

9. The charged particle beam device according to claim 1, a second backscattered electron detector that is provided in a different orientation from the backscattered electron detector and detects the backscattered electrons; a filter disposed between the deflector and the second backscattered electron detector for blocking the secondary electrons;

10. The charged particle beam device according to claim 9, a pipe disposed in the vicinity of the backscattered electron detector and the filter so as to cover the charged particle beam;

11. The charged particle beam device according to claim 9, The charged particle beam device is characterized in that the control unit controls the deflector in accordance with an energy difference between the reflected electrons and the secondary electrons.

12. a charged particle source that emits a charged particle beam to be irradiated onto a sample; a deflector for deflecting the trajectories of secondary electrons and reflected electrons emitted from the sample; a backscattered electron detector for detecting the backscattered electrons; a second backscattered electron detector that is provided in a different orientation from the backscattered electron detector and detects the backscattered electrons; a filter disposed between the deflector and the second backscattered electron detector, the filter blocking the secondary electrons; A control method for a charged particle beam device comprising: acquiring an observation image based on a detection signal output from the backscattered electron detector or the second backscattered electron detector; and controlling an operation of each component; The control method comprises controlling the deflector in accordance with an energy difference between the reflected electrons and the secondary electrons.

Images