Observation device and observation method

Abstract

To provide an observation device and observation method of an observation object capable of observing the observation object in a low noise.SOLUTION: An observation device according to an embodiment, comprises: an insulation film having a first main surface and a second main surface; a conductive film laminated on the first main surface of the insulation film; an electrode that faces the second main surface of the insulation film via an observation object; a signal generator that applies an AC signal to the electrode; a scanning device that scans a beam along a front surface of the conductive film; a reference signal generation unit that generates a reference signal on the basis of a first detection signal derived from a signal detected by the conductive film when the AC signal is applied to the electrode without irradiating the beam to the conductive film; a difference unit that outputs an output signal expressing a difference between the reference signal and a second detection signal derived from a signal detected by the conductive film when the AC signal is applied to the electrode while scanning the beam on the conductive film; and an observation unit that observes the observation object on the basis of the output signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an observation device and an observation method. [Background technology]

[0002] Optical microscopes using visible light are widely used to observe samples. The spatial resolution of optical microscopes is limited to about 200 nm due to the diffraction limit of visible light. When higher spatial resolution is required, electron microscopes using electron beams with shorter wavelengths than visible light are used. Generally, when observing a sample using an electron microscope, pretreatment is performed to reduce damage to the sample caused by the electron beam, such as coating the surface of the sample with gold or platinum, or staining the sample with heavy metals. Even with these pretreatments, images obtained by electron microscopes contain many artifacts, and it is not easy to obtain high-contrast images. In addition, it is difficult to analyze the composition of the sample using this technique.

[0003] The electrochemical impedance method described in Non-Patent Document 1 below is known as a technique for analyzing the composition of a sample. The electrochemical impedance method can analyze the composition of a sample by measuring the impedance of the sample and analyzing the electrochemical characteristics of the sample. However, since the electrochemical impedance method measures the impedance of the entire sample, it is difficult to measure the characteristics of a minute region in the sample.

[0004] On the other hand, Patent Document 1 describes a scanning electron microscope having an outer frame having windows at the top and bottom, a first insulating thin film and a second insulating thin film arranged inside the outer frame, and a conductive thin film laminated on the first insulating thin film, and equipped with an observation holder that holds a sample between the first insulating thin film and the second insulating thin film. This scanning electron microscope scans and irradiates a conductive thin film formed on the first insulating thin film with a pulsed electron beam whose intensity is changed in a pulsed manner, generates an image of the sample based on the potential change on the outward surface of the second insulating thin film, and is capable of analyzing the composition of the sample from the difference in the image corresponding to the pulsed electron beam.

[0005] Furthermore, Patent Document 2 and Non-Patent Documents 2 and 3 describe impedance microscopes that include a first insulating thin film, a second insulating thin film facing the first insulating thin film, a conductive thin film formed on the first insulating thin film, and an electrode facing the second insulating thin film. These impedance microscopes apply an AC signal to the electrode and scan the conductive thin film with an electron beam. Then, the impedance characteristics of the sample are observed with a resolution of micrometer or nanometer by analyzing the signal transmitted from the electrode to the conductive thin film. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6652265 [Patent Document 2] International Publication No. 2019 / 244468 [Non-patent literature]

[0007] [Non-Patent Document 1] W. Kuangand SO Nelson, “Low-frequency dielectric properties of biological tissues: areview with some new insights”, Transactions of the ASAE. 41(1): 173-184, 1998 [Non-Patent Document 2] ToshihikoOgura, “Direct observation of unstained biological samplesin water using newly developed impedance scanning electron microscopy”, PLOSONE, Vol.14(8), e0221296(17pp), 2019 [Non-Patent Document 3] T. Ogura “Development of multi-frequency impedance scanning electron microscopy”, PLOS ONE, Vol.17(1),e0263098, 2022 Summary of the Invention [Problem to be solved by the invention]

[0008] In the impedance microscope described above, when an electron beam is scanned along the surface of the conductive thin film formed on the first insulating thin film while an AC signal is applied to the electrodes, the electrons of the electron beam are scattered, causing a local change in the impedance of the first insulating film. This causes a change in the signal detected by the conductive thin film depending on the irradiation position of the electron beam. The signal component of this change (hereinafter referred to as the "observation signal component") contains information about the electrical characteristics of the object located directly below the irradiation position, so it is possible to generate an image of the sample from the observation signal component.

[0009] However, most of the detection signal detected by the conductive thin film is a component that does not contain information about the object of observation derived from the AC signal input to the electrode, and the observation signal component that contributes to the generation of an image is very small. Generally, the ratio of the observation signal component to the total amplitude of the detection signal is about 1 / 1000. In other words, since the detection signal detected by the conductive thin film has a low signal-to-noise ratio, it is difficult to generate a high-contrast image using the detection signal. In order to increase the contrast of the image, it is possible to increase the dose of the electron beam, but an increase in the dose leads to an increase in the diameter of the electron beam, which causes a decrease in spatial resolution. In addition, an increase in the dose of the electron beam leads to contamination of the first insulating film.

[0010] In view of the above, an object of the present disclosure is to provide an observation device and an observation method for an observation object that are capable of observing an observation object with low noise. [Means for solving the problem]

[0011] An observation device according to one embodiment includes an insulating film having a first main surface and a second main surface, a conductive film stacked on the first main surface of the insulating film, an electrode facing the second main surface of the insulating film across an object to be observed, a signal generator that applies an AC signal to the electrode, a scanning device that scans a beam along a surface of the conductive film, a reference signal generating unit that generates a reference signal based on a first detection signal derived from a signal detected at the conductive film when an AC signal is applied to the electrode without irradiating the conductive film with a beam, a differential unit that outputs an output signal indicating the difference between the reference signal and a second detection signal derived from a signal detected at the conductive film when an AC signal is applied to the electrode while scanning the beam over the conductive film, and an observation unit that observes the object to be observed based on the output signal.

[0012] The first detection signal derived from the signal detected at the conductive film when an AC signal is applied to the electrode without irradiating the conductive film with a beam corresponds to a component derived from the AC signal that does not contribute to image generation of the observed object. In the observation device according to this embodiment, the observed object is observed based on an output signal indicating the difference between a second detection signal derived from the signal detected at the conductive film when an AC signal is applied to the electrode while scanning the conductive film with a beam, and a reference signal based on the first detection signal. The output signal is a signal in which input signal components that do not contribute to image generation have been removed and the proportion of observation signal components has been increased. Therefore, by using the output signal, the observed object can be observed with low noise and high contrast. It is possible.

[0013] In one aspect, the device may further include another insulating film disposed between the insulating film and the electrode, and the observation object may be disposed between the insulating film and the other insulating film. In this aspect, the observation object can be stably held between the insulating film and the other insulating film.

[0014] In one embodiment, the observation device may further include an AC amplifier that amplifies the output signal. By amplifying the output signal from which input signal components that do not contribute to image generation have been removed, the observation target can be observed with high contrast.

[0015] In one aspect, the reference signal generating unit may adjust the phase and amplitude of the AC signal to generate a reference signal that is similar to the first detection signal. Since the first detection signal has the same frequency as the AC signal, the reference signal that is similar to the first detection signal can be generated by adjusting the phase and amplitude of the AC signal. Then, the reference signal can be used to remove input signal components that do not contribute to image generation from the second detection signal.

[0016] In one aspect, the reference signal generating unit may generate the reference signal by adjusting the phase of the first detection signal. By adjusting the phase of the first signal to generate the reference signal, the reference signal can be used to remove input signal components that do not contribute to image generation from the second detection signal.

[0017] In one aspect, the signal generator may apply an AC signal containing multiple frequency components to the electrodes. The observation device may further include an AC amplifier that amplifies the output signal, and multiple extraction devices that extract multiple frequency components from the amplified output signal. In this aspect, by observing the object to be observed based on the output signal of the multiple frequency components, it becomes possible to analyze the characteristics of the object to be observed in more detail.

[0018] In one aspect, a method for observing an object to be observed using an observation device is provided. The observation device includes an insulating film having a first main surface and a second main surface, a conductive film laminated on the first main surface of the insulating film, an electrode facing the second main surface of the insulating film across the object to be observed, a signal generator for applying an AC signal to the electrode, and a scanning device for scanning a beam along the surface of the conductive film. The observation method includes the steps of: generating a reference signal based on a first detection signal derived from a signal detected at the conductive film when an AC signal is applied to the electrode without irradiating the conductive film with a beam; outputting an output signal indicating a difference between the reference signal and a second detection signal derived from a signal detected at the conductive film when an AC signal is applied to the electrode while scanning the conductive film with the beam; and observing the object to be observed based on the output signal.

[0019] As described above, according to the method of the present embodiment, an object to be observed can be observed with low noise and high contrast. Effect of the Invention

[0020] According to the present disclosure, an object to be observed can be observed with low noise. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating an observation device according to an embodiment. [Diagram 2] 1 is a flowchart showing a method for observing an observation object according to an embodiment. [Diagram 3] FIG. 13 is a diagram illustrating an observation device according to another embodiment. [Figure 4] FIG. 1 is a diagram illustrating a conventional observation device. [Diagram 5] 1 is an impedance amplitude image of an observed object generated in an experimental example. [Figure 6] 13 is an impedance amplitude image of an object to be observed generated in a comparative experimental example. [Figure 7] FIG. 13 is a diagram showing a modified example of the observation device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant description will not be repeated. The dimensional ratios of the drawings do not necessarily correspond to those in the description.

[0023] Fig. 1 is a diagram that shows a schematic diagram of an observation device 1 according to an embodiment. The observation device 1 shown in Fig. 1 is an impedance microscope that generates an image of an observation object 2. The observation device 1 is capable of observing the observation object 2 with a spatial resolution at a micrometer level or a nanometer level without performing a pretreatment such as staining on the observation object 2. Note that observing the observation object 2 includes not only generating an image of the observation object 2 but also analyzing the composition of the observation object 2.

[0024] The observation device 1 includes a sample holder 10 that holds an observation target 2. As shown in FIG. 1, the sample holder 10 includes a first insulating film 11, a second insulating film (another insulating film) 12, a conductive film 13, an electrode 14, and an outer frame body 15. The first insulating film 11, the second insulating film 12, the conductive film 13, and the electrode 14 are housed in the outer frame body 15. The outer frame body 15 includes, for example, an upper portion and a lower portion, and the upper portion is made of a conductor such as aluminum, and the lower portion is made of an insulator such as acrylic resin. The upper portion and the lower portion of the outer frame body 15 may be integrally made of the same material. An upper opening 15a is formed in the upper portion of the outer frame body 15.

[0025] The first insulating film 11 has a first main surface 11a and a second main surface 11b that face each other. The first main surface 11a faces the upper opening 15a of the outer frame body 15, and the second main surface 11b is disposed on the opposite side of the first main surface 11a.

[0026] The second insulating film 12 has a first main surface 12a and a second main surface 12b opposed to each other, and is disposed below the first insulating film 11. The first main surface 12a of the second insulating film 12 is disposed opposite to the second main surface 11b of the first insulating film 11, and the second main surface 12b of the second insulating film 12 is provided on the opposite side to the first main surface 12a. That is, the second insulating film 12 faces the first insulating film 11.

[0027] The first insulating film 11 and the second insulating film 12 are made of a material having high insulating properties and high pressure resistance, such as silicon nitride (SiN). A space S in which an observation object 2 is placed is formed between the second main surface 11b of the first insulating film 11 and the first main surface 12a of the second insulating film 12. The observation object 2 is placed together with the aqueous solution 3 in the space S.

[0028] The observation object 2 may be an organic sample such as bacteria, viruses, proteins, and protein complexes, or may be ceramic or metal particles. The observation object may also be a liquid food such as milk or mayonnaise, a cosmetic product such as sunscreen or hand cream, or an industrial lubricant such as machine oil or gear oil.

[0029] A rectangular frame member 17 is disposed on the first insulating film 11. The frame member 17 defines an observation window 7 for observing the observation object 2 on its inside. The observation window 7 is a region for observing the observation object 2. The conductive film 13 is laminated on the first main surface 11a of the first insulating film 11 via the frame member 17. The conductive film 13 is a thin film having electrical conductivity, and is made of a metal such as tungsten. The conductive film 13 is formed on the first main surface 11a of the first insulating film 11 by, for example, a sputtering method. As shown in FIG. 1, inside the observation window 7, the conductive film 13 is in contact with the first main surface 11a of the first insulating film 11, and outside the observation window 7, the conductive film 13 is separated from the first main surface 11a of the first insulating film 11 via the frame member 17.

[0030] The electrode 14 is disposed below the second insulating film 12. As shown in FIG. 1, the electrode 14 is an elongated conductive member, and its tip is disposed inside the outer frame 15. The tip of the electrode 14 faces the second main surface 11b of the first insulating film 11 across the observation object 2. The electrode 14 is fixed to the bottom of the outer frame 15 via an insulating member 16. As will be described later, the electrode 14 receives an input signal 101 from the signal generator 22 and generates an electric field between the electrode 14 and the conductive film 13 in the sample holder 10.

[0031] The second insulating film 12 is supported on a rectangular frame member 18. The frame member 18 is supported on the bottom surface of the outer frame body 15 via a sealing member 19. The sealing member 19 is, for example, an O-ring, and seals the inside of the outer frame body 15.

[0032] The observation device 1 further includes a scanning device 21, a signal generator 22, a control device 23, and a signal processing device 24. The scanning device 21 irradiates the conductive film 13 with a beam L and scans the conductive film 13 along the surface thereof. Specifically, the scanning device 21 includes an irradiation unit 21a and a scanning unit 21b. The irradiation unit 21a emits the beam L. Examples of the beam L emitted from the irradiation unit 21a include a charged particle beam such as an electron beam, a proton beam, or an ion beam, or a laser beam. When the beam L is an electron beam, an electron gun is used as the irradiation unit 21a. In this case, the irradiation unit 21a continuously emits a converged electron beam toward the conductive film 13.

[0033] The scanning unit 21b deflects the beam L emitted from the irradiation unit 21a in a two-dimensional direction along the surface of the conductive film 13, and scans the beam L over the conductive film 13. As the scanning unit 21b, for example, a deflection coil that deflects the trajectory of the beam L by magnetic force is used. The scanning unit 21b scans the beam L over a region of the conductive film 13 that overlaps with the observation window 7.

[0034] When the beam L is irradiated onto the surface of the conductive film 13, electrons are scattered at the irradiation position of the beam L and absorbed by the first insulating film 11, forming an insulation-reduced region 20 in which the insulation is locally reduced in the first insulating film 11. That is, the impedance of the first insulating film 11 changes locally at a position directly below the irradiation position of the beam L. The size of the insulation-reduced region 20 depends on the diameter of the beam L irradiated onto the conductive film 13. Therefore, by narrowing the diameter of the beam L, the image resolution can be improved.

[0035] The signal generator 22 applies an AC signal as an input signal 101 to the electrode 14. For example, the signal generator 22 applies a sine wave as the input signal 101 to the electrode 14. The amplitude and frequency of the input signal 101 are appropriately selected according to the characteristics of the object 2 to be observed.

[0036] When an input signal 101 is applied to the electrode 14, an electric field is formed between the conductive film 13 and the electrode 14. The electric field is an AC electric field whose direction changes periodically according to the frequency of the input signal 101 applied to the electrode 14. The input signal 101 is propagated to the conductive film 13 by the electric field formed between the conductive film 13 and the electrode 14. As a result, a signal according to the impedance between the conductive film 13 and the electrode 14 is detected by the conductive film 13.

[0037] At this time, when the conductive film 13 is irradiated with the beam L while the input signal 101 is applied to the electrode 14, an insulation-reduced region 20 is formed in the first insulating film 11, causing a local change in the impedance between the electrode 14 and the conductive film 13, and causing a change in the signal detected by the conductive film 13. In the following description, the signal component of this change is referred to as the "observation signal component." The observation signal component contains information about the electrical characteristics of the object placed directly under the insulation-reduced region 20. As will be described later, the signal processing device 24 observes the observation target 2 based on the observation signal component contained in the signal detected by the conductive film 13.

[0038] The control device 23 is a computer equipped with a processor, a storage device, an input device, a display device, a communication device, etc., and controls the overall operation of the observation device 1. The control device 23, for example, loads a program stored in the storage device and executes the loaded program on the processor, thereby realizing various functions. In the control device 23, an operator can use the input device to input commands and the like in order to manage the observation device 1, and the operating status of the observation device 1 can be visualized and displayed on the display device.

[0039] More specifically, the control device 23 is communicatively connected to the scanning device 21 and the signal generator 22, and controls the operations of the scanning device 21 and the signal generator 22. For example, the control device 23 controls the scanning device 21 to control the ON / OFF and irradiation position of the output of the beam L. The control device 23 also controls the signal generator 22 to control the application and stop of the application of the input signal 101 to the electrode 14.

[0040] As shown in FIG. 1, the signal processing device 24 includes an AC amplifier 31, a high-pass filter 32, a phase amplitude adjuster 33, a differential amplifier 34, an AC amplifier 35, a lock-in amplifier (extraction device) 36, and an observation unit (observation device) 50.

[0041] The AC amplifier 31 is connected to the conductive film 13, and amplifies the detection signal 111 detected by the conductive film 13 in response to the input of the input signal 101, and outputs it as a detection signal 112. The AC amplifier 31 amplifies the detection signal 111 by, for example, 10 times or more. The high-pass filter 32 removes low-frequency components from the amplified detection signal 112, and outputs it as a detection signal 113. The cut-off frequency of the high-pass filter 32 is, for example, 20 kHz. By setting the cut-off frequency to 20 kHz, it is possible to efficiently remove drift components from the detection signal 112. The detection signal 113 output from the high-pass filter 32 is output to a first terminal of the differential amplifier 34.

[0042] The phase and amplitude adjuster 33 functions as a reference signal generating section (reference signal generating circuit) that generates a reference signal 102 based on a detection signal 113 derived from a detection signal 111 detected by the conductive film 13. Specifically, the phase and amplitude adjuster 33 receives an input signal 101 from the signal generator 22, adjusts the amplitude and phase of the input signal 101 to generate a reference signal 102, and outputs the reference signal 102 to a second terminal of the differential amplifier 34. The reference signal 102 is a signal that is approximate to a detection signal 113 that is output via the AC amplifier 31 and the high-pass filter 32 when the input signal 101 is applied to the electrode 14 without irradiating the conductive film 13 with the beam L. For example, the phase amplitude adjuster 33 adjusts the amplitude and phase of the input signal 101 to generate the reference signal 102 so that the difference between the detection signal 113 input / output to the first terminal of the differential amplifier 34 when the input signal 101 is applied to the electrode 14 without irradiating the conductive film 13 with the beam L and the input signal 101 input to the second terminal of the differential amplifier 34 becomes small (i.e., so that the output of the differential amplifier 34 approaches 0).

[0043] The differential amplifier 34 functions as a differential section (differential circuit) that outputs the difference between the detection signal 113 input to the first terminal and the reference signal 102 input to the second terminal as an output signal 114. As described above, the reference signal 102 is approximate to the detection signal (first detection signal) 113 derived from the signal detected on the conductive film 13 when the input signal 101 is input to the electrode 14 without irradiating the conductive film 13 with the beam L. That is, the reference signal 102 corresponds to a component derived from the input signal 101 that does not contribute to image generation. Therefore, the output signal 114 of the differential amplifier 34 corresponds to a signal obtained by removing the component not including the information of the observation object 2 from the detection signal 113. Therefore, the output signal 114 is a signal with a high ratio of the signal component of the observation object 2.

[0044] The AC amplifier 35 amplifies the output signal 114 of the differential amplifier 34 and outputs it as an output signal 115. The AC amplifier 35 amplifies the output signal 114 by, for example, 100 times or more. The lock-in amplifier 36 extracts the frequency component of the input signal 101 from the output signal 115 and outputs the values ​​of the real part and the imaginary part of the current signal component as an output signal 116. Note that in one embodiment, the output signal 116 may be generated using a high-precision band-pass filter or a spectrum analyzer instead of the lock-in amplifier 36.

[0045] The observation unit 50 includes an impedance measuring unit 37a, an amplitude measuring unit 37b, a phase measuring unit 37c, and an image generating unit 38. The impedance measuring unit 37a, the amplitude measuring unit 37b, and the phase measuring unit 37c measure impedance information, amplitude information, and phase information based on the output signal 116 output from the lock-in amplifier 36. For example, the impedance information is calculated from the amplitude of the input signal 101 from the signal generator 22 and the current signal component output from the lock-in amplifier 36 using Ohm's law.

[0046] The amplitude of the detection signal 111 changes depending on the impedance between the conductive film 13 and the electrode 14. For example, when the aqueous solution 3 is water, the aqueous solution 3 has a relatively high relative dielectric constant of about 80. Therefore, when only the aqueous solution 3 exists between the electrode 14 and the region of reduced insulation 20 in the space S, the impedance between the electrode 14 and the region of reduced insulation 20 becomes small, and the attenuation of the signal becomes small. As a result, the amplitude of the output signal 116 output from the lock-in amplifier 36 becomes large.

[0047] On the other hand, for example, when the observation object 2 is a biological sample composed of amino acids, lipids, etc., the observation object 2 has a low relative dielectric constant of about 2 to 5. Therefore, as shown in Fig. 1, when the observation object 2 is present between the electrode 14 and the region of reduced insulation 20 in the space S, the impedance between the electrode 14 and the region of reduced insulation 20 becomes high, and the attenuation of the signal becomes large. As a result, the amplitude of the output signal 116 output from the lock-in amplifier 36 becomes small.

[0048] Using such a relationship, the impedance measuring unit 37a calculates impedance information based on the output signal 116. Furthermore, the amplitude measuring unit 37b and the phase measuring unit 37c acquire amplitude information and phase information based on the output signal 116. To calculate the impedance information, amplitude information and phase information from the output signal 116, a known method described in, for example, Non-Patent Document 2 is used. The calculated impedance information, amplitude information and phase information are output to the image generating unit 38.

[0049] The image generating unit 38 generates images (impedance image, amplitude image, and phase image) of the observation object 2 based on the impedance information, amplitude information, and phase information corresponding to the irradiation position of the beam L. As described above, the beam L is two-dimensionally scanned over the area overlapping the observation window 7 of the conductive film 13. The image generating unit 38 plots the impedance, amplitude, or phase according to the irradiation position of the beam L at each position (pixel) on the image corresponding to the irradiation position of the beam L to generate an image of the observation object 2. That is, the image generating unit 38 observes the observation object 2 based on the output signal 116.

[0050] Alternatively, the impedance measuring unit 37a may measure resistance, inductance, and conductance individually as impedance information, and the image generating unit 38 may generate a resistance image, an inductance image, and a conductance image. The impedance information, amplitude information, and phase information vary depending on the composition of the observation object 2 and the aqueous solution 3 present on the path of the AC signal, so the impedance information, amplitude information, and phase information include information on the composition of the observation object 2. Therefore, the observation unit 50 may perform a composition analysis of the observation object 2 based on the impedance information, amplitude information, and phase information.

[0051] Next, a method for observing an observation object using the observation device 1 will be described with reference to Fig. 2. Fig. 2 is a flowchart showing a method for observing an observation object according to one embodiment.

[0052] As shown in FIG. 2, in the observation method according to the embodiment, first, an input signal 101 is applied from the signal generator 22 to the electrode 14 (step ST1). The input signal 101 applied to the electrode 14 is, for example, a sine wave having a frequency of 200 kHz and a peak-to-peak value of 10 V. At this time, the beam L is not irradiated from the scanning device 21. When the input signal 101 is applied to the electrode 14, an AC signal corresponding to the input signal 101 is propagated to the conductive film 13 arranged on the first insulating film 11, and a detection signal 111 is detected in the conductive film 13. At this time, the detection signal 111 detected in the conductive film 13 is an AC signal having a frequency of 200 kHz and a peak-to-peak value of about 1 V.

[0053] The detection signal 111 detected by the conductive film 13 is amplified, for example, ten times by the AC amplifier 31 and output as a detection signal 112 to the high-pass filter 32. The high-pass filter 32 removes low-frequency components from the detection signal 112 and outputs it as a detection signal (first detection signal) 113. The detection signal 113 corresponds to a component that does not contain information about the observation object 2 derived from the input signal 101 that does not contribute to image generation. The detection signal 113 is output to a first terminal of the differential amplifier 34.

[0054] Next, the phase and amplitude adjuster 33 generates the reference signal 102 (step ST2). Specifically, the phase and amplitude adjuster 33 adjusts the phase and amplitude of the input signal 101 received from the signal generator 22, and outputs it to the second terminal of the differential amplifier 34. Then, the amplitude and phase of the input signal 101 are adjusted so that the output of the differential amplifier 34 approaches 0, to generate the reference signal 102. That is, the reference signal 102 has substantially the same amplitude and phase as the detection signal 113 output from the high-pass filter 32 when the conductive film 13 is not irradiated with the beam L and the input signal 101 is applied to the electrode 14.

[0055] Next, while the input signal 101 is applied to the electrode 14, the beam L is scanned over the conductive film 13 (step ST3). The irradiation of the beam L causes a local change in the impedance of the first insulating film 11 at the irradiation position, and accordingly, a detection signal 111 detected by the conductive film 13 changes. The detection signal 111 detected by the conductive film 13 passes through the AC amplifier 31 and the high-pass filter 32, and is output to a first terminal of the differential amplifier 34 as a detection signal (second detection signal) 113.

[0056] Next, the differential amplifier 34 calculates the difference between the detection signal 113 output from the high-pass filter 32 and the reference signal 102 output from the phase amplitude adjuster 33, and outputs an output signal 114 indicating the difference (step ST4). The output signal 114 output from the differential amplifier 34 is an AC signal having a peak-to-peak value of, for example, about 0.1 V. This output signal 114 corresponds to a signal obtained by removing components that do not contribute to image formation from the detection signal 113 output from the high-pass filter 32 when the conductive film 13 is scanned with the beam L. Therefore, the output signal 114 is a signal with a high proportion of observation signal components.

[0057] Next, the output signal 114 is amplified, for example, 100 times by the AC amplifier 35 (step ST5). As described above, the output signal 114 is a signal with a high S / N ratio from which components that do not contribute to image generation have been removed, so it is possible to amplify the output signal 114 at a high amplification factor using the AC amplifier 35. As a result, the observation signal components can be significantly amplified.

[0058] Next, the lock-in amplifier 36 extracts the frequency components of the input signal 101 from the output signal 115 output from the AC amplifier 35 (step ST6). Next, impedance information, amplitude information, and phase information are acquired based on the output signal 116 output from the lock-in amplifier 36 (step ST7).

[0059] Next, the observation object 2 is observed. Specifically, the image generating unit 38 generates images (impedance image, amplitude image, and phase image) of the observation object based on the impedance information, amplitude information, and phase information corresponding to the irradiation position of the beam L (step ST8).

[0060] As described above, the observation device 1 generates an image based on the output signal 114 indicating the difference between the detection signal 113 and the reference signal 102. The output signal 114 is a signal from which components that do not contribute to image generation have been removed and the proportion of observation signal components has been increased. Therefore, by generating an image of the observation object 2 based on the output signal 114, a high-contrast image with less noise can be generated. Therefore, the observation object 2 can be observed as an image. Note that in one embodiment, a composition analysis of the observation object 2 may be performed based on impedance information, amplitude information, and phase information without generating an image of the observation object 2.

[0061] Next, an observation device according to another embodiment will be described. Fig. 3 is a diagram showing a schematic view of an observation device 1A according to another embodiment. In the following, differences from the observation device 1 shown in Fig. 1 will be mainly described, and overlapping descriptions will be omitted.

[0062] The signal generator 22 of the observation device 1A applies an input signal 201 including a plurality of frequency components to the electrode 14. For example, the input signal 201 includes a fundamental wave having a fundamental frequency and a harmonic having a frequency that is n times (n=2, 3, . . . N) the fundamental frequency. For example, when the fundamental frequency is 20 kHz, the signal generator 22 applies an input signal having a frequency of 20 kHz to 200 kHz to the electrode 14.

[0063] The observation device 1A includes a reference signal generating unit 40 instead of the phase amplitude adjuster 33. The reference signal generating unit 40 includes an AD conversion unit 41, a phase adjustment unit 42, and a DA conversion unit 43. When the conductive film 13 is not irradiated with a beam and an input signal 201 is applied to the electrode 14, the AD conversion unit 41 receives the detection signal 113 output from the high-pass filter 32, samples the detection signal 113, and converts it into a digital signal 211. The phase adjustment unit 42 adjusts the phase of the digital signal 211. The phase adjustment unit 42 is, for example, a personal computer. The phase adjustment unit 42 adjusts the phase of the digital signal 211 so that the detection signal 113 output from the high-pass filter 32 and the reference signal 213 output from the DA conversion unit 43 coincide with each other. The phase adjustment unit 42 stores the digital signal 212 after the phase adjustment in the storage unit 44.

[0064] The DA conversion unit 43 converts the digital signal 212 stored in the storage unit 44 into an analog signal and outputs it to the second terminal of the differential amplifier 34 as a reference signal 213. The reference signal 213 has substantially the same amplitude and phase as the detection signal 113 output from the high-pass filter 32 when the conductive film 13 is not irradiated with the beam L and the input signal 101 is applied to the electrode 14. In other words, the reference signal generation unit 40 generates the reference signal 213 by adjusting the phase of the detection signal 113 output from the high-pass filter 32 when the conductive film 13 is not irradiated with the beam L and the input signal 201 is applied to the electrode 14.

[0065] Next, while the input signal 201 is being applied to the electrode 14, the beam L is scanned over the conductive film 13. The irradiation of the beam L causes a local change in the impedance of the first insulating film 11 at the irradiation position, and accordingly, a change occurs in the detection signal 111 detected by the conductive film 13. The detection signal 111 detected by the conductive film 13 passes through the AC amplifier 31 and the high-pass filter 32, and is output as a detection signal 113 to a first terminal of the differential amplifier 34.

[0066] The differential amplifier 34 outputs an output signal 114 indicating the difference between the detection signal 113 output from the high-pass filter 32 and the reference signal 213 output from the DA conversion unit 43. The output signal 114 is a signal in which components that do not contribute to image generation have been removed and the proportion of observation signal components has been increased. The output signal 114 output from the differential amplifier 34 is amplified by the AC amplifier 35.

[0067] The observation device 1A also includes a plurality of lock-in amplifiers 36 that extract a plurality of frequency components from the output signal 115 output from the AC amplifier 35. The plurality of lock-in amplifiers 36 are extraction devices that respectively extract frequency components that are n times (n=1, 2,...N) the fundamental frequency from the amplified output signal 115. The observation device 1A may include a plurality of bandpass filters or spectrum analyzers as a plurality of extraction devices instead of the plurality of lock-in amplifiers 36 of the observation device 1A.

[0068] The impedance measuring unit 37a, the amplitude measuring unit 37b, and the phase measuring unit 37c acquire impedance information, amplitude information, and phase information based on output signals 116 from the multiple lock-in amplifiers 36. The image generating unit 38 generates an image of the observed object 2 based on the impedance information, amplitude information, and phase information for each of the multiple frequency components.

[0069] In the observation device 1A described above, an image can be generated for each of a plurality of frequency components based on the output signal 116. Since the propagation characteristics of the input signal 201 differ depending on the frequency, it becomes possible to analyze the composition of the observation object 2 in more detail from the images generated for each of the plurality of frequency components.

[0070] In one embodiment, the observation section 50 of the observation device 1A may generate an impedance spectrum from the impedance measured for each of a plurality of frequency components, without generating an image of the observation object 2, and analyze the impedance spectrum to perform composition analysis of the observation object 2.

[0071] Hereinafter, experimental examples of the observation device 1 will be described, but the present invention is not limited to the following experimental examples.

[0072] In the experimental example, an image of an observation object 2 was generated using an observation device 1 shown in FIG. 1. A sunscreen containing water, oil, and fine particles of an ultraviolet reflector was used as the observation object 2. The observation object 2 was placed between a first insulating film 11 and a second insulating film 12. As the first insulating film, a 50 nm thick SiN thin film was used in which a 10 nm thick tungsten conductive film 13 was laminated on the first main surface 11a. A 200 kHz sine wave signal was applied to the electrode 14 as an input signal 101. The gain of the AC amplifier 31 was set to 10 times. The cutoff frequency of the high-pass filter 32 was set to 20 kHz. Then, the differential amplifier 34 took the difference between the output of the high-pass filter 32 and the reference signal 102, and the difference was output as an output signal 114. The output signal 114 was amplified 100 times by the AC amplifier 35, and the 200 kHz frequency component was extracted by the lock-in amplifier 36. Then, an image of the observation object 2 was generated based on the output signal 116 of the lock-in amplifier 36 .

[0073] On the other hand, in the comparative experimental example, the observation object 2 was observed using a conventional observation device. FIG. 4 is a schematic diagram of a conventional observation device 100. As shown in FIG. 4, the observation device 100 differs from the observation device 1 in that it does not include a phase amplitude adjuster 33, a differential amplifier 34, and an AC amplifier 35. In the comparative experimental example, the detection signal 113 output from the high-pass filter 32 was output to the lock-in amplifier 36, and a signal in a band of 200 kHz was extracted by the lock-in amplifier 36. Then, an image of the observation object 2 was generated based on the output signal 116 of the lock-in amplifier 36.

[0074] FIG. 5 is an impedance amplitude image generated in an experimental example, and FIG. 6 is an impedance amplitude image generated in a comparative experimental example. The image acquired in the experimental example has little noise, and the fine particles shown in white and the oil shown in black are clearly captured with high contrast. On the other hand, the image acquired in the comparative experimental example has a lot of noise, and the image of the fine particles is generally unclear. From these results, it was confirmed that the observation device 1 can generate images with higher contrast than the conventional observation device 100. It is believed that this result is due to the improvement of the SN ratio of the output signal 114 by taking the difference between the detection signal 113 and the reference signal 213.

[0075] Although the observation devices 1, 1A according to various embodiments have been described above, the present invention is not limited to the above-described embodiments and various modifications can be made without departing from the spirit and scope of the invention.

[0076] For example, in the above-described embodiment, the observation object 2 is disposed between the first insulating film 11 and the second insulating film 12, but the observation device 1, 1A does not necessarily have to include the second insulating film 12. For example, as shown in FIG. 7, the sample holder 10 may not include the second insulating film 12, and the lower part of the first insulating film 11 may be filled with the aqueous solution 3, and the observation object 2 may be disposed between the second main surface 11b of the first insulating film 11 and the electrode 14. Even when such a sample holder 10 is used, the observation object 2 can be observed based on the signal detected by the conductive film 13.

[0077] In the above embodiment, the electrode 14 has an elongated shape extending toward the first insulating film 11. However, the electrode 14 may be a plate-shaped electrode facing the first insulating film 11.

[0078] Moreover, the observation object 2 does not necessarily have to be placed in the aqueous solution 3, and may be placed in a substance having a dielectric constant different from that of the observation object 2, in a vacuum, or in air. Even in this case, an image of the observation object 2 can be generated from the difference in dielectric constant. Moreover, the observation device 1, 1A may perform a composition analysis of the observation object 2 based on the impedance acquired from the output signal 116 without generating an image of the observation object 2.

[0079] The various embodiments described above can be combined to the extent that no contradiction occurs.

[0080] The present disclosure includes the following: [1] An insulating film having a first main surface and a second main surface; a conductive film laminated on the first main surface of the insulating film; an electrode facing the second main surface of the insulating film across an object to be observed; a signal generator for applying an AC signal to the electrodes; a scanning device for scanning a beam along a surface of the conductive film; a reference signal generating unit that generates a reference signal based on a first detection signal derived from a signal detected at the conductive film when the AC signal is applied to the electrode without irradiating the conductive film with the beam; a differential section that outputs an output signal indicating a difference between the reference signal and a second detection signal derived from a signal detected at the conductive film when the AC signal is applied to the electrode while the beam is scanned across the conductive film; an observation unit that observes the observation object based on the output signal; An observation device comprising: [2] Further comprising another insulating film disposed between the insulating film and the electrode; The observation apparatus according to [1], wherein the object to be observed is disposed between the insulating film and the other insulating film. [3] The observation device described in [1] or [2], further comprising an AC amplifier that amplifies the output signal. [4] The observation device according to any one of [1] to [3], wherein the reference signal generating unit adjusts a phase and an amplitude of the AC signal to generate the reference signal that approximates the first detection signal. [5] The observation device according to any one of [1] to [3], wherein the reference signal generating section generates the reference signal by adjusting a phase of the first detection signal. [6] The observation device according to any one of [1] to [5], wherein the signal generator applies the AC signal containing a plurality of frequency components to the electrodes. [7] An AC amplifier for amplifying the output signal; a plurality of extractors for respectively extracting the plurality of frequency components from the amplified output signal; The observation device described in [6] further comprises: [8] An observation method for observing an observation object using an observation device, comprising: The observation device is an insulating film having a first main surface and a second main surface; a conductive film laminated on the first main surface of the insulating film; an electrode facing the second main surface of the insulating film across an object to be observed; a signal generator for applying an AC signal to the electrodes; a scanning device for scanning a beam along a surface of the conductive film; Equipped with The observation method includes: generating a reference signal based on a first detection signal derived from a signal detected at the conductive film when the AC signal is applied to the electrode without irradiating the conductive film with the beam; outputting an output signal indicating a difference between the reference signal and a second detection signal derived from a signal detected at the conductive film when the AC signal is applied to the electrode while scanning the beam with respect to the conductive film; observing the observation object based on the output signal; An observation method comprising: [Explanation of symbols]

[0081] 1,1A...observation device, 2...object to be observed, 11...first insulating film (insulating film), 11a...first main surface, 11b...second main surface, 12...second insulating film (another insulating film), 13...conductive film, 14...electrode, 21...scanning device, 22...signal generator, 36...lock-in amplifier, 38...image generating section, 40...reference signal generating section, 42...phase adjustment section, 50...observation section, 102,213...reference signal, 113...detection signal (first detection signal, second detection signal), 114...output signal, L...beam.

Claims

1. An insulating film having a first main surface and a second main surface, A conductive film laminated on the first main surface of the insulating film, Through the object being observed, the electrode facing the second main surface of the insulating film, A signal generator that applies an AC signal to the aforementioned electrode, A scanning device that scans a beam along the surface of the conductive film, A reference signal generation unit generates a reference signal based on a first detection signal derived from a signal detected in the conductive film when the AC signal is applied to the electrode without irradiating the conductive film with the beam, A differential unit that outputs an output signal showing the difference between a second detection signal derived from the signal detected in the conductive film and the reference signal when the AC signal is applied to the electrode while scanning the conductive film with the beam, An observation unit that observes the object to be observed based on the output signal, Equipped with, The reference signal generation unit is an observation device that generates a reference signal that approximates the first detection signal by adjusting the phase and amplitude of the AC signal.

2. The facility further comprises another insulating film disposed between the insulating film and the electrode, The observation apparatus according to claim 1, wherein the object to be observed is placed between the insulating film and the other insulating film.

3. The observation apparatus according to claim 1, further comprising an AC amplifier for amplifying the output signal.

4. The observation apparatus according to claim 1, wherein the signal generator applies the AC signal containing multiple frequency components to the electrode.

5. An AC amplifier that amplifies the output signal, Multiple extraction devices for extracting the multiple frequency components from the amplified output signal, The observation apparatus according to claim 4, further comprising the following:

6. An observation method for observing an object using an observation device, The observation device is An insulating film having a first main surface and a second main surface, A conductive film laminated on the first main surface of the insulating film, Through the object being observed, the electrode facing the second main surface of the insulating film, A signal generator that applies an AC signal to the aforementioned electrode, A scanning device that scans a beam along the surface of the conductive film, Equipped with, The aforementioned observation method is, The steps include generating a reference signal based on a first detection signal derived from a signal detected in the conductive film when the AC signal is applied to the electrode without irradiating the conductive film with the beam, The steps include: applying the AC signal to the electrode while scanning the conductive film with the beam, outputting an output signal that shows the difference between a second detection signal originating from the signal detected in the conductive film and the reference signal; The steps include observing the object to be observed based on the output signal, Includes, An observation method wherein the reference signal is generated by adjusting the phase and amplitude of the AC signal so as to approximate the first detection signal.

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