Scanning electron microscope

Abstract

The utility model discloses a scanning electron microscope system, comprising an electron source used for generating electron beams; an acceleration convergence field is generated between the electric lens and the electron source, and the electric lens is used for increasing the movement speed of the electron beams and converging the electron beams for the first time; the first magnetic lens is used for converging the electron beams for the second time; the second magnetic lens is used for carrying out third convergence on the electron beams; the third magnetic lens is used for carrying out fourth convergence on the electron beams; the Wien filter is used for keeping incident electron beams not deflected and deflecting signal electrons; the deflection device comprises two magnetic deflectors and an electric deflector and is used for changing the movement direction of the electron beam; the detector comprises a first detector and a movable second detector and is used for detecting signal electrons generated by the sample; at least one diaphragm; the sample table is used for bearing a sample.

Description

Technical Field

[0001] The utility model relates to the field of charged particle beam instruments and equipment, in particular to scanning electron microscope instruments and equipment. Background Art

[0002] Scanning electron microscopes are widely used in the fields of semiconductor quality inspection, scientific research, engineering quality control, etc. From a broad perspective, different application scenarios mainly require the following aspects: the field of view, resolution, depth of field, electron beam energy, beam current density, and type of signal electrons of the microscope.

[0003] For example, as the semiconductor process node has reached 3nm or even smaller, it is becoming increasingly difficult to further reduce the size of the device. Therefore, semiconductor manufacturing is developing in the three-dimensional direction. At this time, electron microscope imaging is required to have a high aspect ratio. At the same time, because the signal at the bottom of the deep trench is difficult to be received by the detector, the incident electron beam needs to have a high beam density. In other applications, the observed sample is sensitive to high-energy electron beams. If a high-energy electron beam is used to irradiate the sample, the sample will be easily deformed and damaged (for example: photoresist). At the same time, because the high-energy electron beam will bring serious charging effects, affecting the imaging quality, low-energy electron beams are required to observe and image the sample. At the same time, different imaging fields and resolutions need to be used according to different imaging requirements in the application, and different signal electrons are used for imaging according to different observation purposes.

[0004] Based on the above analysis, higher requirements are placed on the multifunctionality of scanning electron microscopes, which can adapt to different observation samples and imaging requirements. Summary of the invention

[0005] The purpose of the utility model is to provide a scanning electron microscope, which can work in three different modes to meet the observation requirements in different situations. To achieve the above purpose, the utility model provides the following technical solutions: On the one hand, the utility model provides a scanning electron microscope, including:

[0006] An electron source for generating an electron beam;

[0007] An electric lens, used to generate an accelerating and converging field with the electron source, increase the moving speed of the electron beam and converge the electron beam for the first time;

[0008] A first magnetic lens, used for converging the electron beam passing through the electric lens for a second time;

[0009] A second magnetic lens, used for converging the electron beam passing through the first magnetic lens for a third time;

[0010] a third magnetic lens, used for converging the electron beam passing through the second magnetic lens for a fourth time;

[0011] A Wien filter, used for keeping the electron beam generated by the electron source from being deflected, while deflecting the signal electrons generated by the sample and irradiating them onto the first detector;

[0012] A deflection device, comprising two magnetic deflectors and one electric deflector, located inside the third magnetic lens and coaxially with the optical axis, for changing the moving direction of the electron beam;

[0013] a detector, comprising a first detector located above the third magnetic lens and a movable second detector located below the third magnetic lens, which is coaxially placed with the detector and the optical axis and is used to detect signal electrons generated by the sample;

[0014] at least one aperture for limiting the passing electron beam;

[0015] The sample stage is used to place the sample to be observed.

[0016] Preferably, the electron source is a field emission electron source, and the electron source is connected to an adjustable voltage V1, and the adjustment range of V1 is -30kV≤V1≤-5kV.

[0017] Preferably, the electric lens is composed of three coaxially placed electrode plates, which are the first electrode plate, the second electrode plate and the third electrode plate from top to bottom, wherein the first electrode plate close to the electron source is the anode.

[0018] Preferably, the first electrode plate and the third electrode plate of the electric lens are grounded, and the second electrode plate is connected to an adjustable voltage V2, and the adjustment range of V2 is V1≤V2≤0;

[0019] Preferably, the pole shoe opening directions of the first magnetic lens, the second magnetic lens and the third magnetic lens are all toward the optical axis.

[0020] Preferably, the Wien filter is located inside the third magnetic lens, below the first detector, and above the deflection device.

[0021] Preferably, the magnetic deflector in the deflection device is an annular deflector with a magnetic core.

[0022] Preferably, the electric deflector in the deflection device is composed of octopole or dodecapole columnar deflection electrodes.

[0023] Preferably, the two magnetic deflectors are located above the opening of the third magnetic lens pole shoe and below the Wien filter, and the electric deflector is located at the opening of the third magnetic lens pole shoe.

[0024] Preferably, the first detector in the detectors may be a semiconductor detector or a scintillator photomultiplier tube detector.

[0025] Preferably, the second detector in the detectors is a movable semiconductor detector, which can be inserted under the third magnetic lens or removed as needed.

[0026] Preferably, the sample stage is connected to an adjustable voltage V3, and the adjustment range of V3 is V1≤V3≤0. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the structure of a scanning electron microscope provided in an embodiment of the utility model;

[0028] Figure 2 (a)- Figure 2 (b) is a schematic diagram of observing a sample using control method A in an embodiment of the present invention;

[0029] Figure 3 (a)- Figure 3 (b) is a schematic diagram of observing a sample using control method B in the embodiment of the present invention;

[0030] Figure 4 (a)- Figure 4 (b) is a schematic diagram of using control method C to observe a sample according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the utility model clearer, the technical solution in the utility model will be clearly and completely described below in conjunction with the drawings of the utility model. The following is used to illustrate the utility model but is not used to limit the scope of the utility model.

[0032] Figure 1The schematic diagram of the structure of the scanning electron microscope provided in the embodiment of the utility model is shown in FIG. 100, which is the optical axis, i.e., the central axis of the electron optics. 101 is an electron source. According to the embodiment of the utility model, the electron source is a field emission electron source for emitting an electron beam. The electron source 101 is connected to an adjustable voltage V1, and the adjustment range of V1 is -30kV≤V1≤-5kV. 102 is an electric lens, which includes three electrode plates, namely, the first electrode plate 102a, the second electrode plate 102b and the third electrode plate 102c from top to bottom, wherein the first electrode plate 102a and the third electrode plate 102c are grounded, the second electrode plate 102b is connected to an adjustable voltage V2, and the adjustment range of V2 is V1≤V2≤0, and the first electrode plate 102a serves as an anode. 103 is a first magnetic lens, the pole shoe of which opens toward the optical axis 100. 104 is an aperture. According to a characteristic embodiment of the utility model, the aperture can be a single aperture with a single aperture, or a plurality of aperture arrays with different apertures. 105 is a second magnetic lens, the opening of which opens toward the optical axis 100. 106 is a first detector. According to a characteristic embodiment of the utility model, the detector is a semiconductor detector. According to another characteristic embodiment of the utility model, the detector is a scintillator photomultiplier tube detector. 107 is a third magnetic lens, also generally referred to as an objective lens. The pole shoe of the third magnetic lens is located below the magnetic lens, and the opening direction of the pole shoe faces the optical axis. The magnetic field generated by the lens is confined to the pole shoe opening and will not leak to the sample, so it can be used to observe magnetic samples. 108 is a Wien filter, located inside the third magnetic lens 107 and below the first detector 106, and is used to keep the electron beam generated by the electron source moving from top to bottom from being deflected, and at the same time, deflect the signal electrons generated by the sample moving from bottom to top to be irradiated onto the first detector 106. 109 is a deflection device, including two magnetic deflectors 109a, 109b, and an electric deflector 109c. The three deflectors are coaxially placed with the objective lens 107, and the axis is the electron optical center axis. The two magnetic deflectors 109a and 109b are located below the Wien filter 108 and above the electric deflector 109c. The electric deflector 109c is located at the pole shoe opening of the third magnetic lens 107. 110 is the second detector, which is a movable semiconductor detector installed on a retractable arm 111. When it is needed to detect signal electrons, the telescopic arm is controlled to move to insert it under the third magnetic lens, and when it is not needed, it is moved out from under the third magnetic lens. 112 is a sample stage, on which a sample can be mounted. The sample stage can be a three-dimensional (X, Y, Z) motion platform or a five-dimensional (X, Y, Z, R, T) motion platform. The sample stage is connected to a voltage V3, and the variation range of V3 is: V1≤V3≤0. When V3≠0, the sample stage decelerates the incident electron beam and accelerates the emitted signal electrons.

[0033] The above respectively introduces the position structure and function of each component of the scanning electron microscope of the embodiment of the utility model. At the same time, the utility model also proposes a control method for the scanning electron microscope, which can make the scanning electron microscope work in three different modes (mode A, mode B and mode C), suitable for three different observation situations. The following is a detailed description of the working method of the scanning electron microscope in three different modes through three embodiments in combination with schematic diagrams. It should be noted that when the scanning electron microscope is working in three different modes, one or several devices are in a non-working state. For the convenience of explanation, annotations will be made in the figure or the device will not be drawn. Example

[0034] In this embodiment, the scanning electron microscope operates in mode A. Figure 2 (a)- Figure 2 (b) shows that in this mode, the third magnetic lens 107 is in a closed state. Figure 2 In (a), "OFF" is used as an indication. The current in the magnetic lens excitation coil is zero, and no magnetic field is generated at the pole shoe, which has no focusing effect on the electron beam. At the same time, the electric deflector 109c (not shown) in the deflection device is in a grounded state and has no deflection effect on the electron beam. At this time, the two magnetic deflectors 109a and 109b in the deflection device are used to deflect the electron beam. The signal electrons are imaged simultaneously through the first detector 106 and the second detector 110. The electric lens 102, the first magnetic lens 103 and the second magnetic lens 105 have a converging effect on the electron beam.

[0035] Specifically, a voltage V1 is applied to the electron source 101, and the range of V1 is -15kV≤V1≤-5kV. The first plate (anode) and the third plate in the electric lens 102 are grounded, and a voltage V2 is applied to the second plate, and the range of V2 is V1≤V2≤0. Figure 2 As shown in (b), the electric lens generates an electric field 202, which converges the electron beam emitted by the electron source. A current is applied to the excitation coil of the first magnetic lens 103, so that the magnetic lens 103 generates a magnetic field, as shown in FIG. Figure 2 As shown in (b), the magnetic field forms a magnetic lens 203, which further produces a second convergence effect on the electron beam moving downward. The electron beam that has been converged for the second time passes through an aperture 104. According to the embodiment of the utility model, the aperture 104 can be a single-aperture aperture or an aperture array with different aperture sizes. Apertures of different sizes can be selected as needed. A current is applied to the excitation coil of the second magnetic lens 105, so that the magnetic lens 105 generates a magnetic field, such as Figure 2As shown in (b), the magnetic field constitutes a magnetic lens 205, which produces a third (final) convergence effect on the electron beam. The electron beam then passes through the central hole of the first detector 106 and the central hole of the Wien filter 108. In this mode, the electric deflector 109c in the deflection device 109 is in a grounded state, and only two magnetic deflectors 109a and 109b are used to deflect the electron beam. The deflected electron beam finally passes through the central hole of the second detector and irradiates the sample on the sample stage 112. According to an embodiment of the utility model, this mode A is a double deflection after the mirror. By controlling the focusing strength of the electric lens, the first magnetic lens and the second magnetic lens, and adjusting the size of the aperture hole at the same time, the electron beam angle 220 focused on the sample is very small, and the deflection center 221 is at a large distance from the sample. Therefore, the imaging characteristics are: the image has a large field of view, a large depth of field and a lower resolution. According to an embodiment of the utility model, the field of view S in this working mode is A 1mm≤S A ≤5mm. According to an embodiment of the utility model, a voltage V3 is applied to the sample stage, and the range of V3 is: V1≤V3≤0. When V3≠0, the sample stage decelerates the incident electron beam and accelerates the outgoing signal electrons. The sample generates signal electrons under the irradiation of the incident electron beam, and the signal electrons are mainly divided into secondary electrons 113 and backscattered electrons 114. The backscattered electrons are mainly detected by the second detector 110. The secondary electrons 113 move upward, pass through the central hole of the second detector, enter the third magnetic lens, and are detected by the first detector after being deflected by the Wien filter.

[0036] According to the imaging characteristics of the scanning electron microscope of this embodiment, the main application scenarios of this mode A include: searching for the observed target in a large range before high-resolution imaging; and requiring large-depth-of-field stereoscopic imaging of the observed target. Example

[0037] In this embodiment, the scanning electron microscope operates in mode B. Figure 3 (a)- Figure 3 (b) shows that in this mode, the second magnetic lens 105 is in a closed state. Figure 3 In (a), "OFF" is used to indicate that the current in the magnetic lens excitation coil is zero, no magnetic field is generated at the pole shoe, and there is no focusing effect on the electron beam. At the same time, the electric deflector 109c in the deflection device is in a grounded state and does not deflect the electron beam. At this time, the two magnetic deflectors 109a and 109b in the deflection device are used to deflect the electron beam. The signal electrons are imaged simultaneously through the first detector 106 and the second detector 110. The electric lens 102, the first magnetic lens 103 and the third magnetic lens (objective lens) 107 have a converging effect on the electron beam.

[0038] Specifically, a voltage V1 is applied to the electron source 101, and the range of V1 is -15kV≤V1≤-5kV. The first plate (anode) and the third plate in the electric lens 102 are grounded, and a voltage V2 is applied to the second plate, and the range of V2 is V1≤V2≤0. Figure 3 As shown in (b), the electric lens generates an electric field 302, which converges the electron beam emitted by the electron source. A current is applied to the excitation coil of the first magnetic lens 103, so that the magnetic lens 103 generates a magnetic field, such as Figure 3 As shown in (b), the magnetic field constitutes a magnetic lens 303, which further produces a second converging effect on the electron beam moving downward. The electron beam that has been converged for the second time passes through an aperture 104. According to an embodiment of the utility model, the aperture 104 can be a single-hole aperture or an aperture array with different aperture sizes. Apertures of different sizes can be selected and used as needed. No current is applied to the excitation coil in the second magnetic lens 105, so that the magnetic lens 105 does not generate a magnetic field, and the electron beam does not generate a converging effect when passing through the second magnetic lens. Subsequently, the electron beam passes through the center hole of the first detector 106 and enters the third magnetic lens. Current is applied to the excitation coil of the third magnetic lens 107, so that the magnetic lens 107 generates a magnetic field at the pole shoe opening, as shown in FIG. Figure 3 (b) shows that the magnetic field constitutes a magnetic lens 307. In this mode, the electric deflector 109c in the deflection device 109 is in a grounded state, and only two magnetic deflectors 109a and 109b are used to deflect the electron beam. The deflected electron beam is converged by the magnetic field generated by the third magnetic lens, and finally irradiated onto the sample on the sample stage 112 through the central hole of the second detector. According to an embodiment of the utility model, this mode B is a double deflection in front of the mirror, which controls the focusing strength of the electric lens, the first magnetic lens and the third magnetic lens, and adjusts the size of the aperture hole at the same time, and adjusts the beam angle 320 of the electron beam focused on the sample, so that the focused electron beam has the smallest beam spot size, that is, the image has the best resolution at this time, and at the same time, the distance between the deflection center 321 and the sample is smaller than that in mode A. Therefore, the imaging characteristics of the scanning electron microscope in this mode B are: high resolution and medium-sized field of view and depth of field. According to an embodiment of the utility model, the field of view S in this working mode is as follows: B : 30μm≤S B≤1mm. According to an embodiment of the utility model, a high voltage V3 is applied to the sample stage, and the range of V3 is: V1≤V3≤0. When V3≠0, the sample stage decelerates the incident electron beam and accelerates the outgoing signal electrons. The sample generates signal electrons under the irradiation of the incident electron beam, and the signal electrons are mainly divided into backscattered electrons 113 and secondary electrons 114. The backscattered electrons are mainly detected by the second detector 110. The secondary electrons 114 move upward, pass through the central hole of the second detector, enter the third magnetic lens, and are detected by the first detector after being deflected by the Wien filter.

[0039] According to the imaging characteristics of the scanning electron microscope of this embodiment, the main application scenarios of this mode B include: high-resolution imaging of samples; controlling the beam size and V3 voltage to observe samples that are susceptible to charging effects. Example

[0040] In this embodiment, the scanning electron microscope operates in mode C. Figure 4 (a)- Figure 4 (b) shows that in this mode, the three magnetic lenses 103, 105 and 107 are all in working state. At the same time, the current of the deflection coils in the two magnetic deflectors 109a and 109b in the deflection device is zero, no deflection magnetic field is generated, and no deflection effect is produced on the electron beam. The electric deflector 109c is in working state and deflects the electron beam. The signal electron is imaged through the first detector 106. The electric lens 102, the first magnetic lens 103, the second magnetic lens 105 and the third magnetic lens (objective lens) 107 are comprehensively controlled to converge the electron beam.

[0041] Specifically, a voltage V1 is applied to the electron source 101, and the range of V1 is -30kV≤V1≤-15kV. The first plate (anode) and the third plate in the electric lens 102 are grounded, and a voltage V2 is applied to the second plate, and the range of V2 is V1≤V2≤0. Figure 4 As shown in (b), the electric lens generates an electric field 402, which converges the electron beam emitted by the electron source. A current is applied to the excitation coil of the first magnetic lens 103, so that the magnetic lens 103 generates a magnetic field, as shown in FIG. Figure 3 As shown in (b), the magnetic field forms a magnetic lens 403, which further produces a second convergence effect on the electron beam moving downward. The electron beam that has been converged for the second time passes through an aperture 104. According to the embodiment of the utility model, the aperture 104 can be a single-hole aperture or an aperture array with different aperture sizes. Apertures of different sizes can be selected as needed. A current is applied to the excitation coil in the second magnetic lens 105, so that the magnetic lens 105 generates a magnetic field, such as Figure 4As shown in (b), the magnetic field forms a magnetic lens 405, which further produces a third convergence effect on the electron beam moving downward. Then the electron beam passes through the central hole of the first detector 106 and enters the third magnetic lens. A current is applied to the excitation coil of the third magnetic lens 107, so that the magnetic lens 107 generates a magnetic field at the pole shoe opening, as shown in FIG. Figure 4 (b) shows that the magnetic field constitutes a magnetic lens 407. In this mode, no current is applied to the coils of the two magnetic deflectors 109a and 109b in the deflection device 109, and no deflection effect is produced on the electron beam. The electric deflector 109c in the deflection device is in a working state, and a deflection effect is produced on the electron beam. According to an embodiment of the utility model, the electric deflector is located at the opening of the pole shoe of the third magnetic lens, and the deflection electric field generated by the electric deflector coincides with the magnetic field generated by the third magnetic lens. According to an embodiment of the utility model, in this mode C, the second detector is in a removed state, and the signal electrons generated by the sample are not detected, which makes it more convenient to bring the sample close to the third magnetic lens and achieve high-resolution observation at a short working distance. According to an embodiment of the utility model, in this mode C, the size of the electric lens, the first magnetic lens, the second magnetic lens, the third magnetic lens and the aperture are comprehensively adjusted, so that the electron beam irradiated on the sample has the characteristics of a small beam spot and a high beam current density. At the same time, in this mode C, the sample stage is in a grounded state, so the energy E of the electron beam incident on the sample is ≥15keV. As Figure 4 As shown in (b), at this time, the distance between the deflection center 421 and the sample is small. Since the electron beam has the characteristic of high beam density, the characteristics of scanning electron microscope imaging in this mode C are: the image has a small field of view, high resolution and large depth of field, which is suitable for observing deep holes and deep groove structures with high aspect ratio (High Aspect Ratio). According to the embodiment of the utility model, the field of view S in this working mode is C 100nm≤S C ≤30μm. At this time, the first detector is mainly used to receive the high-energy backscattered electron signal 413 generated on the sample. The backscattered electron 413 moves upward after being emitted from the sample, passes through the pole shoe hole of the third magnetic lens, and is deflected by the Wien filter and detected by the first detector.

[0042] According to the imaging characteristics of the scanning electron microscope of this embodiment, the main application scenarios of this mode C include: imaging deep holes and deep groove structures with high aspect ratios; the sample has good conductivity and is not prone to charging effects under high-energy electron irradiation.

[0043] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only a specific embodiment of the utility model and is not intended to limit the scope of protection of the utility model. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the utility model should be included in the scope of protection of the utility model.

Claims

1. A scanning electron microscope, characterized in that include: An electron source for generating an electron beam; An electric lens, used to generate an accelerating and converging field with the electron source, increase the moving speed of the electron beam and converge the electron beam for the first time; A first magnetic lens, used for converging the electron beam passing through the electric lens for a second time; A second magnetic lens, used for converging the electron beam passing through the first magnetic lens for a third time; a third magnetic lens, used for converging the electron beam passing through the second magnetic lens for a fourth time; A Wien filter, used for keeping the electron beam generated by the electron source from being deflected, while deflecting the signal electrons generated by the sample and irradiating them onto the first detector; A deflection device, comprising two magnetic deflectors and one electric deflector, located inside the third magnetic lens and coaxially with the optical axis, for changing the moving direction of the electron beam; a detector, comprising a first detector located above the third magnetic lens and a movable second detector located below the third magnetic lens, which is coaxially placed with the detector and the optical axis and is used to detect signal electrons generated by the sample; at least one aperture for limiting the passing electron beam; The sample stage is used to place the sample to be observed.

2. The scanning electron microscope according to claim 1, characterized in that The electron source is a field emission electron source, and the electron source is connected to an adjustable voltage V1, and the adjustment range of V1 is -30kV≤V1≤-5kV.

3. The scanning electron microscope according to claim 1, characterized in that The electric lens is composed of three coaxially placed electrode plates, which are the first electrode plate, the second electrode plate and the third electrode plate from top to bottom, wherein the first electrode plate close to the electron source is the anode.

4. The scanning electron microscope according to claim 1, characterized in that The first electrode plate and the third electrode plate of the electric lens are grounded, and the second electrode plate is connected to an adjustable voltage V2, and the adjustment range of V2 is V1≤V2≤0.

5. The scanning electron microscope according to claim 1, characterized in that The pole shoe opening directions of the first magnetic lens, the second magnetic lens and the third magnetic lens are all toward the optical axis.

6. The scanning electron microscope according to claim 1, characterized in that The Wien filter is located inside the third magnetic lens, below the first detector, and above the deflection device.

7. The scanning electron microscope according to claim 1, characterized in that The magnetic deflector in the deflection device is an annular deflector with a magnetic core.

8. The scanning electron microscope according to claim 1, characterized in that The electric deflector in the deflection device is composed of octopole or dodecapole columnar deflection electrodes.

9. The scanning electron microscope according to claim 1, characterized in that: The two magnetic deflectors are located above the opening of the third magnetic lens pole shoe and below the Wien filter, and the electric deflector is located at the opening of the third magnetic lens pole shoe.

10. The scanning electron microscope according to claim 1, characterized in that The first detector among the detectors may be a semiconductor detector or a scintillator photomultiplier tube detector.

11. The scanning electron microscope according to claim 1, characterized in that: The second detector in the detectors is a movable semiconductor detector, which can be inserted under the third magnetic lens or removed as needed.

12. The scanning electron microscope according to claim 1, characterized in that The sample stage is connected to an adjustable voltage V3, and the adjustment range of V3 is V1≤V3≤0.

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