JP3002221B2 - Scanning probe microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an electron microscope, and more particularly to a scanning probe microscope capable of measuring a surface state of a substance with a microscopic spatial resolution.

[Prior art]

Scanning Tunnel Micros
cope) is to bring a very thin needle-shaped electrode with a tip of one or several electrons close to the surface of a conductive sample and apply a tunnel current flowing when a low voltage is applied between the electrode and the sample. The sample surface image is obtained at a spatial resolution of the atomic order by measuring and scanning this needle-shaped electrode in a two-dimensional direction along the sample surface using a piezoelectric element. That is, the needle electrode with the applied voltage is brought close to the sample surface until the tunnel current flows, and then the tip of the needle electrode is scanned along a predetermined pattern.
Since the tunnel current changes when the sample surface has irregularities,
The needle mechanism moves the needle electrode up and down according to the unevenness by the feedback mechanism, and the movement of the tip of the needle electrode at this time is converted into a sample surface image.

[Problems to be solved by the invention]

In general, the electrons emitted from the sample surface are not only the magnitude of the amount, but also, for example, the potential of the sample surface, the initial velocity distribution of the electrons when emitted (the distribution of the absolute value of the angle and the velocity),
It has information such as spin. However, in the above-described conventional scanning tunneling electron microscope (hereinafter referred to as STM), since only the magnitude of the tunnel current is measured, other information inherent in electrons cannot be observed. Even when only the tunnel current is measured, even if the state of the sample surface changes on the order of picoseconds and the electron current emitted from this surface changes temporally on the order of picoseconds, There is a problem in that a picosecond response characteristic cannot be obtained because there is a limit in the frequency characteristic of the amplifier circuit when detecting a current from the amplifier. Furthermore, even when the number of electrons emitted from the sample surface is very small, ie, within several tens, there is a problem in that the detection is buried in the noise of the detection unit and the amplifier and cannot be detected. As shown in FIG. 13, when the surface of the sample 1 is irradiated with light 2 or when the current emitted when the sample 1 is heated is measured, the needle electrode 3 forming the anode is used. There is also a problem that a spatial resolution in the size of the needle tip cannot be obtained because a current flows through the whole. The present invention has been made in view of the above-mentioned conventional problems, and can observe information other than the amount of current of electrons emitted from the sample surface, can detect the amount of current in picosecond order, and Even when the number of electrons emitted from the surface is small, it can be detected with a good SN ratio, and high spatial resolution can be obtained even when the emission current is measured by irradiating or heating the sample surface with light. It is an object of the present invention to provide a scanning probe microscope as described above.

[Means for Solving the Problems]

The present invention is a member for scanning the surface of a sample at a position slightly away from the sample in a vacuum, and inside the member,
A probe having a through-hole formed in the output direction from the tip, and disposed behind the through-hole, emitted from the sample, and for obtaining information of the electron beam after passing through the through-hole. The above object is achieved by a scanning probe microscope having an electron beam detector. According to a second aspect of the present invention, the probe is a needle-like electrode, and the through-hole penetrates the center of the needle-like electrode in the axial direction to achieve the above object. According to a third aspect of the present invention, the above object is achieved by covering the tip of the through hole of the probe with a thin film orthogonal to the through hole, and forming at least one hole in the thin film. According to a fourth aspect of the present invention, the above-mentioned object is achieved by configuring the electron beam detecting device to include an accelerating electrode for electrons emitted from the sample and an electron multiplier. According to a fifth aspect of the present invention, the above-mentioned object is achieved by configuring the electron beam detecting device to include an accelerating electrode for electrons emitted from the sample, a microchannel plate, and an output anode. According to a sixth aspect of the present invention, the above-mentioned object is achieved by configuring the electron beam detecting device to include an accelerating electrode for electrons emitted from the sample and an electron implanted semiconductor. According to a seventh aspect of the present invention, the above object is achieved by configuring the electron beam detection device to include an acceleration electrode, a focusing electrode, a deflection electrode, and an electron beam detection unit having positional resolution. In claim 8, the electron beam detection device is
The above object is achieved by including an acceleration electrode, a focusing electrode, a deflection electrode, and an aperture electrode for electrons emitted from a sample. According to a ninth aspect of the present invention, the above object is achieved by configuring the electron beam detection device to include an electron optical system that captures an electron beam passing through the through hole and performs electron spectroscopy. According to a tenth aspect of the present invention, the above object is achieved by configuring the electron beam detection device to include an electron optical system that detects a spin direction of an electron passing through the through hole. Further, in claim 11, the above object is achieved by controlling the distance between the probe and the sample based on a current flowing into a portion of the tip of the probe different from the through hole. According to a twelfth aspect of the present invention, a needle-shaped electrode is further provided at the tip of the probe, and the distance controlling current flows into the needle-shaped electrode to achieve the above object.

[Action and effect]

In the present invention, an electron beam emitted from the sample surface by a probe having a through hole formed in the output direction from the tip on the inner side is guided to an electron beam detection device behind it through the through hole. Here, since various characteristics of the electron beam can be detected, not only the magnitude of the current amount but also the electron beam, for example, the potential of the sample surface, the initial velocity distribution of the emitted electrons, the spin, etc. Can detect various characteristics of the sample, and can detect changes in the emission current on the order of picoseconds.Furthermore, even when electrons are emitted from the entire surface of the sample due to light irradiation or the like, it has passed through the through-hole. Since only electrons are guided to the electron beam detector, an excellent high spatial resolution can be obtained even in this case.

【Example】

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The scanning probe microscope 10 according to this embodiment includes a probe 12, a holding table 14 for holding the probe 12, a piezoelectric fine movement scanning element 16 for finely moving the holding table 14 in the XYZ directions,
A drive circuit 18 for driving the piezoelectric fine movement scanning element 16 and an electron beam detection device 20 provided behind the probe 12 are provided. The probe 12 is configured to scan the surface of the sample 22 at a position where its tip is slightly away from the sample 22 by the piezoelectric fine movement scanning element 16. Further, as shown in the drawing, the probe 12 has a through hole 24 formed from the tip toward the output direction. In this embodiment, the probe 12 forms a through hole 24 by etching the SiO ₂ film 12B provided on the Si substrate 12A, and forms a gold vapor-deposited film 12C having a thickness of, for example, about 100 mm on the surface. It is configured. The electron beam detection device 20 includes an electron optical system 20A and an electron beam detection unit 20B that detects electrons processed or amplified by the electron optical system 20A. In the figure, reference numeral 21 denotes an output signal processing unit, and 26 denotes a piezoelectric fine movement scanning element.
An X-direction scanning voltage generation circuit 16 for controlling the X-direction 16; a Y-direction scanning voltage generation circuit 28 for the Y-direction control; and 30, a position control in the Z-direction, that is, the tip of the probe 12 and the surface of the sample 22. Z-axis servo amplifier for controlling the distance of
Reference numeral 31 denotes a power supply for applying a bias voltage between the sample 22 and the probe 12. The Z-axis servo amplifier 30 is the same as the conventional one, detects a tunnel current and
Is used to adjust the distance between the surface of the sample 22 and the tip of the probe 12. The electron optical system 20A includes an accelerating electrode 32 having an aperture formed at the center for accelerating electrons passing through the through-hole 24, as shown in an enlarged view in FIG. And an electron multiplier (electron multiplier) 34 into which the accelerated electrons enter. Here, the electron beam detector 20 includes an anode 34A in the electron multiplier 34 and a pulse counter 36 for counting pulses generated for each signal electron input thereto.
It is composed of In this embodiment, the outer diameter of the tip of the needle electrode of the probe 12 is 0.2 μm, the diameter of the through hole 24 is 0.1 μm, the length of the through hole 24 is 2 μm, and the exit side of the through hole 24 (electron beam detection The inner diameter of the device 20) is 1 μm. Next, the operation of the above embodiment will be described. The distance between the tip of the probe 12 and the surface of the sample 22, that is, the distance in the Z-axis direction, is set so that an appropriate tunnel current is emitted from the sample 22. For example, in FIG. 1, if the distance between the sample 22 and the tip of the probe 12 is made close to 500 ° and a voltage of several volts is applied between the two, electrons are emitted from the surface of the sample 22 by field emission. It is guided into the through hole 24. The emitted electrons guided into the through-hole 24 are accelerated by, for example, several hundred volts by the acceleration electrode 32, pass through an aperture at the center of the acceleration electrode 32, and enter the electron multiplier 34. In the electron multiplier 34, the electrons are multiplied, and the
A pulse counter that counts the pulses that are incident on 34A and that are generated for each signal electron
Counted by 36. Therefore, even if the emission current from the surface of the sample 22 is very weak, it can be detected. Furthermore, if the tip of the probe 12 is scanned along the sample surface in the XY direction by the piezoelectric fine movement scanning element 16, the spatial distribution of the emission current can be obtained with a spatial resolution substantially equal to the inner diameter of the tip of the through hole of 0.1 μm. Can be. In the above embodiment, the probe having the through hole 24 is used.
Numeral 12 is obtained by processing the SiO ₂ film 12B by etching, but the present invention is not limited to this, and a through hole may be formed by other means. Therefore, for example, a hollow glass tube is melted and pulled to form a hollow needle shape, or a glass that is easily etched as a core, and a glass that is hard to be etched is used as a clad. Alternatively, the core glass may be removed by etching to form a through-hole therein, and a thin metal may be further evaporated on the surface. Further, in the above-described embodiment, the probe 12 is formed in a hollow needle shape. This is, for example, as shown in FIG. 3, the tip of the through hole 24 in the tapered probe 38 having an inner diameter of 0.2 μm. A thin film 38A about 500 mm thick in the opening
To form a hole 38B of, for example, about 500 mm,
Further, a thin metal film of about 100 ° may be deposited on the surface of the thin film 38A. In this way, a more uniform electric field can be formed between the surface of the sample 22 and the tip of the probe 38, and higher resolution can be obtained. As another configuration of forming a thin film and providing a hole in the thin film as described above, for example, an organic film is attached to the tip opening of the probe 38, and about 100 mm of aluminum is vapor-deposited thereon,
After heating, the organic film is removed, an aluminum thin film is formed, a resist film is formed on the aluminum thin film, and the resist is etched by electron beam exposure so that a hole of about 50 mm is formed by an electron beam. You may make it. Here, the probe 38 has a tapered shape, but is not limited to this shape. For example, as shown in FIG.
A configuration covered with a thin film 38A having 8B may be used. Further, as shown in FIG. 4 (B), the through hole 2 of the flat probe 13B is formed.
4 may be covered with a similar thin film 38A. Further, as shown in FIG. 5, for example, as shown in FIG. 5, a thin metal film 38C is provided at the tip of the through hole 24 of the probe 38, and many holes 38D are formed therein.
To make the electric field between
You may lead to D. In each of the above embodiments, the probe is moved by the piezoelectric fine scanning element 16, but the present invention is not limited to this.
You may make it move by 16. Next, another embodiment of the electron beam detector 20 disposed at the rear of the probe 12, 13A, 13B or 38 will be described. The embodiment of FIG. 6 uses a microchannel plate (hereinafter referred to as MCP) 40 as an electron multiplier in addition to the accelerating electrode 32, and the current connected to the anode 40A where the electrons multiplied by the microchannel plate 40 are incident. The output is measured by a total 42. In this case, a pulse counter may be provided instead of the ammeter 42 as in the embodiment of FIG. Further, when there is a distribution in the number of emitted electron streams, the emission distribution of electrons can be obtained by inputting an output signal pulse to a pulse height analyzer. In the embodiment shown in FIG. 7, an electron implanted semiconductor 44 into which electrons passing through the accelerating electrode 32 are implanted is provided. The electron-implanted semiconductor 44 is a reverse-biased pn junction, and generates many electron-hole pairs by implanting electrons accelerated to about 10 KV by the acceleration electrode 32,
The multiplied signal can be obtained as an output pulse. Next, the embodiment shown in FIG. 8 will be described. In this embodiment, even when the surface state of the sample 22 changes in the order of picoseconds, this can be detected. For example, when the sample 22 is an LSI, when the LSI is driven,
The voltage of a part of the circuit forming I changes on the order of picoseconds, and the change over time can be obtained by this embodiment. The electron beam detection device of this embodiment has a mesh-shaped acceleration electrode 46, a focusing electrode 48, an anode 50,
The deflection electrode 52, the MCP 40, and the fluorescent screen 54 are arranged in this order. A sweep voltage is applied to the deflection electrode 52 from an oblique sweep voltage generation circuit 56, and a synchronization signal pulse output from an LSI drive power supply 58 is supplied to the oblique sweep voltage generation circuit 56 by a delay circuit 60. Is to be entered. In this embodiment, the electron beam emitted from the surface of the sample 22 is focused by the focusing electrode 48 so as to pass between the deflection electrodes 52 after being accelerated by the acceleration electrode 46. At this time, if a sweep voltage is applied from the LSI drive power supply 58 to the deflection electrode 52 from the oblique sweep voltage generation circuit 56 in synchronization with the drive of the LSI (sample 22), the change in the picosecond order of the emitted electron current is detected by the fluorescence. The information can be obtained by converting into a luminance distribution in the sweep direction on the surface 54. Therefore, if the relationship between the tunneling current value and the voltage between the sample 22 and the tip of the probe 12 is determined in advance, it is possible to obtain a picosecond-order voltage change waveform of a point of current interest from the obtained luminance distribution. . In this case, if the magnitude of the electron current is sufficient, the MCP40
Is unnecessary. Further, for example, an electron-implanted CCD may be used in place of the phosphor screen 54 in the above embodiment. In this way, by sequentially obtaining the voltage change waveform at the required locations, the voltage distribution on the entire surface of the sample 22 and the change state thereof can be known. The electron beam detector in the embodiment of FIG.
It is equivalent to an electron lens system and an electron beam detector used in a so-called streak tube, but instead of the above, is provided in front of an electron optical system used in a sampling streak tube, that is, an output electron beam detector. Using the aperture electrode, only the electron beam at a certain time among the swept electron beams may be extracted to the output side, the fluorescent screen may be illuminated, and the PMT may be detected. In this case, the entire voltage waveform can be obtained by gradually shifting the sweep timing with respect to the driving of the LSI. In the embodiment shown in FIGS. 5 to 7, similarly, a pulse voltage waveform can be obtained by detecting the time difference between the pulse generated at the output unit and the drive timing of the LSI. Next, the embodiment of FIG. 9 will be described. In this embodiment, the surface of the sample 22 is irradiated with light, and of the photoelectrons emitted from the surface of the sample 22 at this time, only the photoelectrons that have passed through the through hole 24 of the probe 12 are transmitted to an electron optical system 62 that performs electron spectroscopy. The energy distribution of the emitted photoelectrons is measured by conducting electron spectroscopy. This electron optical system includes the MCP 40 and the anode 40A. Next, the embodiment shown in FIG. 10 will be described. In this example, the probe 12
After the photoelectrons that have passed through are accelerated by the acceleration electrode 46, they collide with the metal thin film 64, and the angular distribution of the reflected electrons is
An angle distribution of electrons is obtained by capturing the metal thin film 64 with an anode 66 whose angle is variable, whereby information on the spin direction of electrons is obtained. Next, the embodiment of FIG. 11 will be described. In this embodiment, a tunnel current from a point to be measured on the surface of the sample 22 is guided to the through-hole 24, and a probe other than the through-hole 24 is used.
The position of the probe 12 in the Z-axis direction is controlled by capturing a tunnel current guided to the tip 12 and measuring the tunnel current. In the case where the surface of the sample 22 is irradiated with light as in the case of the embodiment shown in FIG. 9, when positioning the probe, the irradiation of light is stopped once and the tunnel current in that state is used. Is performed in the Z-axis direction. Next, the embodiment of FIG. 12 will be described. In this embodiment, a needle-shaped electrode 68 is attached to the tip of the probe 12 at a position slightly away from the through-hole 24, and the position of the probe 12 in the Z-axis direction is controlled by a tunnel current flowing therethrough. It is.

[Brief description of the drawings]

FIG. 1 is a sectional view including a partial block diagram showing an embodiment of a scanning probe microscope according to the present invention, FIG. 2 is a schematic sectional view showing an electron beam detecting device in the embodiment, and FIGS. FIG. 5 is a cross-sectional view showing another shape of the probe according to the present invention. FIGS. 6 and 7 are schematic cross-sectional views showing another embodiment of the electron beam detector of the scanning probe microscope according to the present invention. FIG. 8 is a schematic sectional view including a partial block diagram showing still another embodiment of the scanning probe microscope according to the present invention, and FIGS. 9 and 10 show still another embodiment of the electron beam detecting device. FIG. 11 is a schematic cross-sectional view including a partial block diagram showing another embodiment of the scanning probe microscope, FIG. 12 is a cross-sectional view showing another embodiment of the probe tip shape, Fig. 13 is a cross-sectional view showing a probe in a conventional scanning probe microscope. That. 10… Scanning probe microscope, 12, 13A, 13B, 38… Probe, 16… Piezoelectric fine scanning element, 20… Electron beam detector, 20A, 62… Electronic optical system, 20B… Electron beam detection Part, 22: sample, 24: through hole, 32, 46: accelerating electrode, 34: electron multiplier, 34A, 40A: anode, 36: pulse counter, 38A: thin film, 38B, 38D ... holes, 38C ... metal film, 40 ... microchannel plate (MCP), 44 ... electron implanted semiconductor, 48 ... focusing electrode, 50 ... anode, 52 ... deflection electrode, 54 ... fluorescent screen, 56: Oblique sweep voltage generation circuit 64: Metal thin film 68: Needle electrode

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 37/00 H01J 37/28 H01J 37/244 G01B 7/34 G01B 21/30 JICST file (JOIS)

Claims (12)

(57) [Claims] A probe for scanning the surface of a sample at a position slightly away from the sample in a vacuum, the probe having a through hole formed from the tip toward the output direction inside the member. An electron beam detection device disposed behind the through hole, for obtaining information of the electron beam emitted from the sample and having passed through the through hole. 2. A scanning probe microscope according to claim 1, wherein said probe is a needle-like electrode, and said through-hole penetrates the center of said needle-like electrode in the axial direction. 3. The probe according to claim 1, wherein the tip of the through hole in the probe is covered with a thin film orthogonal to the through hole, and at least one hole is formed in the thin film. Scanning probe microscope. 4. A scanning probe microscope according to claim 1, wherein said electron beam detector comprises an accelerating electrode for electrons emitted from a sample and an electron multiplier. . 5. An electron beam detecting apparatus according to claim 1, wherein said electron beam detecting device comprises:
A scanning probe microscope comprising a microchannel plate and an output anode. 6. The scanning probe type according to claim 1, wherein the electron beam detecting device comprises an accelerating electrode for electrons emitted from the sample and an electron implanted semiconductor. microscope. 7. A scanning device according to claim 1, wherein said electron beam detecting device includes an accelerating electrode, a focusing electrode, a deflecting electrode, and an electron beam detecting section having a position resolution. Probe type microscope. 8. An electron beam detecting apparatus according to claim 1, wherein said electron beam detecting device comprises:
A scanning probe microscope comprising a focusing electrode, a deflection electrode, and an aperture electrode. 9. An electron beam detecting apparatus according to claim 1, wherein said electron beam detecting device includes an electron optical system for capturing an electron beam passing through said through hole and performing electron spectroscopy. Scanning probe microscope. 10. A scanning probe according to claim 1, wherein said electron beam detecting device includes an electron optical system for detecting a spin direction of an electron passing through said through hole. Type microscope. 11. The probe according to claim 1, wherein a distance between the probe and the sample is controlled based on a current flowing into a location different from the through-hole at the tip of the probe. A scanning probe microscope, characterized in that: 12. The scanning probe type according to claim 11, wherein a needle electrode is further provided at the tip of said probe, and said current for distance control flows into said needle electrode. microscope.