JP4621908B2 - Surface state measuring method, surface state measuring device, microscope, information processing device - Google Patents

Description

  In the present invention, in order to stably control the positions of two or more probes (multi-probes), the displacement detection circuit and the probe holder are used to control the distance between the multi-probes with a small size and high accuracy, and to measure them. The present invention relates to a surface state measuring method, a surface state measuring device, a microscope using the same, and an information processing device that can measure the surface state of an object at a molecular level.

  In storage devices such as memory, in order to achieve recording at the molecular level for high-density recording, each characteristic of the molecule used in the molecular material of the device (electrical characteristics, optical characteristics, magnetic characteristics, as well as mechanical rigidity) Etc.) is necessary.

  Therefore, conventionally, as a method for measuring the characteristics of the molecule, it is known that an electrode having a gap of about several microns can be produced by a microfabrication technique and various characteristics of the molecule accidentally crosslinked in the gap can be measured. Yes.

  However, in the above method, there is a limit to the measurement of molecular characteristics at the nanometer scale such as the molecular level because the microfabrication is limited by the “light diffraction limit”.

  On the other hand, an atomic force microscope which is a kind of probe microscope having atomic level resolution is expected as a fine shape evaluation method.

  Atomic force microscopy (AFM) is expected as a new means for observing the surface shape of insulating materials, and research is ongoing. The principle is that the atomic force acting between a probe with a sufficiently sharp tip and the sample is measured as the displacement of the spring element to which the probe is attached, and the amount of displacement of the spring element is kept constant. The sample surface is scanned while the shape of the sample surface is measured using shape information as a control signal for keeping the amount of displacement of the spring element constant.

  As the spring element displacement detection means, there are an optical method (optical interference method, optical lever method) and a self-detection method (piezoresistance detection method, piezoelectric detection method) for detecting deformation distortion of the spring element as an electric signal.

  The probe used in the atomic force microscope is formed at the tip of a cantilevered support member called a cantilever, and has a quadrangular shape mainly. An example of the material of the probe is silicon. When silicon is used for the probe, the probe is processed using an anisotropic etching technique.

  By using the cantilever of such an atomic force microscope (G. Binnig, CF Quate, Ch. Gerber: Phys. Rev. Lett. 56 (1986) 930.) as a characteristic measurement probe, memory (storage device) etc. It is expected to be able to measure the characteristics of various molecular devices such as information processing equipment.

In Patent Document 1, a probe control circuit of such an information processing apparatus detects a signal generated from a physical phenomenon between a probe and a medium facing the probe as a detection signal, and detects the position of the probe by a position control signal based on the detection signal. It has been proposed to perform control.
JP-A-8-249732 (Publication date: September 27, 1996)

  However, the above-described conventional configuration and method are not a method for stably controlling the relative positions between a plurality of probes, but in measurement with a plurality of probes, various characteristics (such as the above-mentioned electrical characteristics and optical characteristics) of molecular materials, etc. , Magnetic characteristics, mechanical rigidity, etc.) cannot be measured with high accuracy.

  The present invention has been made in view of the above-mentioned problems, and its purpose is not to control the distance between the probe and the sample, which is important in the conventional atomic force microscope, but to two or more probes. By controlling the distance between each probe, the position control can accurately measure various nanoscale characteristics (such as electrical characteristics, optical characteristics, magnetic characteristics, mechanical rigidity, etc.) of molecular materials. An object of the present invention is to provide a surface state measurement method, a surface state measurement device, a microscope and an information processing device using the method.

  In order to solve the above problems, a surface state measurement apparatus according to the present invention includes a plurality of probes facing a measurement object, a probe driving unit that moves each of the probes with respect to the measurement object, and the measurement object. A detection unit for detecting and outputting a detection signal resulting from a physical phenomenon between the object and each probe, a first control unit for controlling a relative position between the probes by a position control signal based on the detection signal, and And a measuring unit that measures the surface state of the measurement object from a detection signal.

  According to the above configuration, each probe is moved relative to the surface of the measurement object by the probe driving unit, that is, the detection signal associated with the scanning can be obtained by the detection unit, and the detection signal associated with the scanning is detected. From the measurement unit, the surface state (for example, surface shape) of the measurement object can be measured.

  In addition, the above configuration includes the first control unit for controlling the relative positions between the probes by moving the plurality of probes facing the measurement object, respectively, so that the position control of the plurality of probes can be performed. The gap length, which is the distance between each probe and between each probe and the measurement object, can be controlled stably so that measurement at the molecular level or atomic level can be performed. The surface state of an object can be stably measured on a nanometer scale.

  As a result, since the above configuration can stably measure the surface state of the measurement object on the nanometer scale, the resolution of the microscope can be obtained when used in an information processing apparatus that is a microscope such as an atomic force microscope or a storage device such as a memory. And the amount of information processing of the information processing apparatus can be improved.

  In the surface state measuring apparatus, it is preferable that the first controller is configured to bring the probes close to each other.

  In the surface state measuring apparatus, it is preferable that the probes are arranged so that the tip portions of the probes are close to each other.

  The surface state measuring apparatus may further include a cantilever having the probe at the tip.

  In the surface state measuring apparatus, it is preferable that the tip of each probe is formed so as to extend in a direction facing the measurement object.

  In the surface condition measuring apparatus, it is preferable that each probe is formed with a sharp tip.

  In the surface state measuring apparatus, a protrusion extending along the longitudinal direction of each probe may be formed at the tip of each probe.

  In the surface condition measuring apparatus, the protruding portion may be formed with a pointed tip.

  In the said surface state measuring device, the said protrusion part may be equipped with the bending part by which the front end side bends toward the said measurement target object.

  In the surface state measuring apparatus, the physical phenomenon is preferably at least one selected from the group consisting of an atomic force, a tunnel current, and static electricity.

  In the surface state measurement apparatus, the apparatus further includes a second control unit that controls each probe driving unit so that the interval between each probe and a measurement object is constant based on the detection signal, You may provide the probe position detection part which detects the position of a probe.

  The microscope of the present invention is characterized by having any one of the above-described surface state measuring devices.

  An information processing apparatus according to the present invention includes any one of the above-described surface state measurement apparatuses.

  In order to solve the above problems, the surface state measurement method of the present invention moves a plurality of probes facing a measurement object to each of a relative position between the measurement object and a relative position between the probes, A detection signal generated from a physical phenomenon between the measurement object and each probe is detected, and the surface state of the measurement object is measured from the detection signal.

  In the surface state measurement method, the physical phenomenon is preferably at least one selected from the group consisting of an atomic force, a tunnel current, and static electricity.

  In the surface state measuring method, it is preferable that the probes are moved so that the tips of the probes are close to each other.

  As described above, the surface state measurement apparatus according to the present invention includes a plurality of probes facing the measurement object, a probe driving unit that moves each of the probes with respect to the measurement object, the measurement object, and each of the measurement objects. From the detection signal, a detection unit that detects and outputs a detection signal generated from a physical phenomenon between the probes, a first control unit for controlling the relative position between the probes by a position control signal based on the detection signal, and And a measurement unit that measures the surface state of the measurement object.

  Therefore, the above-described configuration includes the first control unit for moving the plurality of probes facing the measurement object and controlling the relative position between the probes. Each can be performed, and the gap length leading to measurement at the molecular level or atomic level can be controlled stably, so that the surface state of the measurement object can be stably measured at the nanometer scale.

  As a result, since the above configuration can stably measure the surface state of the measurement object on the nanometer scale, the resolution of the microscope can be obtained when used in an information processing apparatus that is a microscope such as an atomic force microscope or a storage device such as a memory. And the amount of information processing of the information processing apparatus can be improved.

  An embodiment of the surface state measuring apparatus according to the present invention will be described below with reference to FIGS. That is, in the surface state measuring apparatus, as shown in FIG. 2, a plurality of probes 2 (only one is shown in FIG. 2) are provided so as to face the measurement object 1. The measurement object 1 is mounted on a mounting table 3 that moves two-dimensionally in the xy direction shown in FIG. 2 (that is, a horizontal direction substantially parallel to the surface of the measurement object 1).

  The shape of each probe 2 may be any shape as long as it has a tapered shape that gradually decreases toward the tip and can detect the interaction described later. For example, a triangular pyramid shape, a quadrangular pyramid shape, a cone shape, etc. Shape. Moreover, as a raw material of each said probe 2, although the interaction mentioned later can be detected and what is easy to shape | mold into the said shape, silicon | silicone is mentioned, for example. When silicon is used for each probe 2, an anisotropic etching technique is suitable for forming the probe.

  A scanning unit 4 for driving the mounting table 3 is attached as a probe driving unit. A scan system 5 that generates a control signal for controlling the scan unit 4 is provided.

  On the other hand, in the surface state measuring apparatus, the cantilever 6 having the probe 2 at the tip is attached in the shape of a single cantilever pipe with a length of 0.1 mm to 1 mm. The probe 2 is provided at the tip of the cantilever 6 so that the tip of the probe 2 faces the surface of the measurement object 1. Each cantilever 6 is attached so that the tips of the tips provided with the probes 2 are in contact with each other, and the longitudinal direction of each cantilever 6 is substantially parallel to the surface of the measurement object 1. . The cantilever 6 may be made of aluminum, copper, an alloy thereof, carbon, or the like as long as it has conductivity for detecting an interaction and has rigidity enough to withstand excitation described later.

  On the proximal end side of the cantilever 6, a first drive unit 7 for reciprocating the probe 2 in the vertical direction (z direction in FIG. 2), and a horizontal direction orthogonal to the longitudinal direction of the cantilever 6 ( A second drive unit 8 for reciprocating in the y direction in FIG. 2; a third drive unit 9 for reciprocating the probe 2 in the direction along the longitudinal direction of the cantilever 6 (x direction in FIG. 2); Are each formed as a probe driving section.

  The first drive unit 7, the second drive unit 8, and the third drive unit 9 may be any devices that can drive the probe 2 on the micron order (maximum driving distance is 0.1 μm to 10 μm). Examples thereof include an automatic drive by a stepping motor or an impact stage, or a fine movement drive mechanism using a manual screw type. Of the above-described fine movement driving mechanisms, those composed of piezoelectric elements are particularly suitable. Therefore, the first drive unit 7, the second drive unit 8, and the third drive unit 9 change the relative positions of the plurality of probes 2 to each other and relative to the surface of the measurement object 1. Each can be moved to change.

  In the surface state measuring apparatus, a semiconductor laser 10, a mirror 11, and a photodiode 12 are mounted for optically detecting the position of the probe 2 (especially in the z direction) (optical lever method). For this optical detection, it is preferable that the surface (back surface) opposite to the mounting position of the probe 2 at the tip of the cantilever 6 has a mirror finish. The semiconductor laser 10 irradiates the opposite surface with laser light. The mirror 11 guides the reflected light of the laser beam from the opposite surface to the light receiving surface of the photodiode 12. The photodiode 12 converts the received light into an electrical signal including the position information signal of the probe 2 by, for example, a push-pull method and outputs the electrical signal.

  Furthermore, in the surface state measuring device, the shape signal is calculated by inputting the electric signal and calculating the surface shape (surface state) of the measurement object 1 from the position information signal of the probe 2 from the electric signal. A measurement unit 13 for outputting, a display 14 for displaying the surface shape based on the shape signal, and a memory 15 as a video RAM for the display 14 are provided.

  And in the said surface state measuring device, each probe 2 is detected by the detection part 16 which detects and outputs the detection signal which arises from the physical phenomenon between the said measurement object 1 and each probe 2, and the position control signal based on the said detection signal. A control unit 17 is provided for controlling the relative position between them. Examples of the physical phenomenon include interactions such as atomic force, tunnel current, and electrostatic force.

  When detecting the tunnel current, the detection unit 16 applies a voltage between the measurement object 1 and the probe 2 through the wirings A and B, and when the interval approaches about 1 nanometer (nm). The generated tunnel current can be detected. Further, the detection unit 16 applies a voltage between the adjacent probes 2 through the wirings B and B so that the tunnel current generated when the distance approaches about 1 nanometer (nm) can be detected. It has become. Since these tunnel currents change with high accuracy in response to the change in the interval, the intervals can be controlled with a resolution of at least 0.1 nm.

  The control unit 17 generates a two-dimensional surface shape from the shape signal from the measurement unit 13 and outputs the two-dimensional surface shape to the memory 15, and also maintains a constant interval between the probe 2 and the measurement object 1 from the detection signal. Thus, the first drive unit 7, the second drive unit 8 and the third drive unit 9 can be controlled so as to feedback control the position of the probe 2 (that is, the cantilever 6). As shown in FIG. 3A, when the probe 2 at the tip of the cantilever 6 approaches the surface of the measurement object 1 on the nanometer scale, the feedback control is performed as shown in FIG. This utilizes the fact that the amplitude of the detection signal in the unit 16 increases or decreases (or the frequency increases or decreases).

  In addition, the control unit 17 can control the scan system 5 so that the surface of the measurement object 1 is scanned two-dimensionally by the probes 2. Further, the control unit 17 can control the first driving unit 7 to reciprocate the probe 2 at the tip of the cantilever 6 in the vertical direction (z direction), preferably at the resonance frequency of the cantilever 6. ing.

  Next, a surface state measuring method using the surface state measuring apparatus will be described. As shown in FIG. 1A, in the surface state measurement method described above, detection is a displacement detection mechanism provided on at least one of the probes 2 while exciting the probes 2 in order to control the interval between the probes 2. The third drive unit 9 made of a piezoelectric element, which is a fine movement drive mechanism, reduces the distance between the unit 16 and the control unit 17. At that time, due to the interaction (tunnel current) between the probes 2 adjacent to each other, the displacement is detected in the signal on the probe 2 side having the displacement detection mechanism as shown in FIG. . When the displacement reaches the set value, stable probe position control is performed. For example, in the case of visual inspection, the probe may come into contact with the probe, or may collide and break, but there is no such reason when the displacement detection mechanism is used.

  Since the present invention can control the relative position between a plurality of probes 2 with a simple apparatus configuration, and can stably control the gap length to molecules and atoms, In addition to the dramatic improvement, it is possible to increase the resolution of the scanning tunneling microscope and increase the storage capacity by applying it to a storage device such as a memory.

  As a modification of the present embodiment, as shown in FIG. 4, the tunnel current between the probes 2 may be monitored without exciting each probe 2. As another modification of the present embodiment, as shown in FIG. 5, the atomic force between the probes 2 may be monitored while exciting one of the probes 2 and not the other. . As yet another modification of the present embodiment, the atomic force between the probes 2 may be monitored while exciting both of the probes 2 as shown in FIG.

  In the present embodiment, the probe 2 has a quadrangular pyramid shape whose tip is directed to the surface of the measurement object 1. However, for position control between the probes 2, FIG. As shown to a), it is desirable to form the rod-shaped protrusion part 18 extended in the longitudinal direction of the cantilever 6 in the probe 2. FIG. The protrusion 18 is more preferably formed on the probe 2 on the distal end side of the cantilever 6, and more preferably on the proximal end side of the probe 2. Moreover, it is preferable that the protrusion part 18 is formed so that the shape may become thin toward the front-end | tip, and a taper shape with a pointed tip is more preferable.

  Further, as shown in FIG. 7B, the protrusion 18 includes a bent portion 18 a where the tip end side of the protrusion 18 is bent in the direction of the surface of the measurement object 1. Desirable for position control. The bent portion 18a is preferably formed so that its shape becomes narrower toward the tip, and more preferably a tapered shape with a sharp point.

  Further, in the present embodiment, as shown in FIG. 8 (a), two probes 2 are provided so as to be in contact with each other, but as shown in FIG. 8 (b), three probes are provided. These tip sides may be provided so as to touch each other, as shown in FIG. 8 (c), even if four tips are provided so as to touch each other, as shown in FIG. 8 (d), Eight of them may be provided so that their tip sides are in contact with each other.

  Hereinafter, the interactions such as interatomic force and electrostatic force as the physical phenomenon will be described. First, the atomic force will be described. As shown in FIG. 9, in the surface state measurement apparatus of the present invention, the atomic force acting between the probe 2 and the surface of the measurement object 1 is attached to the probe 2. By detecting the deflection of the cantilever 6 and controlling the position of the probe 2 so as to make the deflection constant and scanning the surface shape two-dimensionally, the surface shape can be measured and imaged.

As shown in FIG. 10, the interatomic force is an interaction between nonpolar neutral atoms. The above interaction can be approximated by a Lennard-Jones type potential. is there. The relationship between the potential energy U ₀ and the interatomic distance r ₀ is expressed by the following equation (1).

Here, ε _LJ is the cohesive energy, and σ is the distance between the equilibrium atoms.

The interatomic force F ₀ acting between these atoms is expressed by the following formula (2).

  FIG. 11 shows the plotted results obtained by modifying the above equation (2) and substituting specific numerical values. From FIG. 11, it can be seen that an attractive force works when the interatomic distance is about 0.2 nm or more, and a repulsive force works when the distance is more than that (less than 0.2 nm).

  Thus, an attractive force is generated between the tip of the probe 2 and the surface of the measurement object 1 at a long distance (0.2 nm or more). This attractive force is due to the dispersion force (in other words, cohesive force). The dispersive force is a force that acts between these dipoles because a dipole is also generated in the other atom by an instantaneous dipole (a non-polar atom causes a momentary charge bias). Larger atomic molecules tend to generate instantaneous dipoles due to their weaker force to hold electrons, resulting in higher dispersion force.

  On the other hand, repulsive force acts between the tip of the probe 2 and the surface of the measurement object 1 at a short distance of less than 0.2 nm. This repulsive force is due to exchange interaction. The exchange interaction is that when two electron clouds of two atoms overlap each other, the electron cloud cannot electrostatically shield the positive charge of the nucleus, and the Coulomb force is generated between the positive charges of both nuclei. Arise. Also, due to Pauli's prohibition, electrons of the same energy level cannot occupy the same space. Therefore, when two atoms approach the short distance, the electron cloud is distorted. As a result, a repulsive force acts between the tip of the probe 2 and the surface of the measurement object 1 at the short distance.

Next, interaction such as electrostatic force as the physical phenomenon will be described. The electrostatic force, as shown in FIG. 12, the distance r ₀ away each charge was Q1, Q2 is the electrostatic force F ₀ exerted between, the electrostatic force F ₀ is expressed by the following equation (3) The

Here, k = 8.99 × 10 ⁹ (Nm ² / C ² ).

  When electrostatic force is used as a physical phenomenon, in the surface state measuring apparatus of the present invention, the electrostatic force acting between the probe 2 and the surface of the measurement object 1 is used as the deflection of the cantilever 6 to which the probe 2 is attached. The surface shape can be measured and imaged by detecting and controlling the position of the probe 2 so as to keep the deflection constant and scanning the surface shape two-dimensionally.

  As described above, in the present invention, as shown in FIG. 13, a plurality of probes 2 can be controlled on a nanoscale independently of each other, and thus formed on the surface of the measurement object 1 in the nanotechnology field. It becomes possible to directly evaluate the characteristics (how much current flows, how hard, etc.) of each functional element (including molecules) 1a, for example, pentacene molecule.

  In addition, if the distance between each of the plurality of probes 2 can be controlled stably, the surface shape can be observed with a large number of probes 2 in the atomic force microscope, so that a wide range of surfaces can be measured at one time. Speed up.

  Since the surface state measuring method and the surface state measuring apparatus of the present invention can accurately measure the surface state of a measurement object at the molecular level, the measuring field such as a surface shape measuring device such as a microscope, the semiconductor manufacturing field, and the storage such as a memory It can be suitably used in the information processing field such as devices.

The position control between each probe in the surface state measuring method of this invention is shown, (a) is a schematic front view of each probe which shows the said position control, (b) is the detection before and after each probe approaches each other. It is each waveform figure which shows the change of a signal. It is a block diagram of the surface state measuring device of the present invention. The position control between the measurement object and the probe in the surface state measurement method of the present invention is shown, (a) is a schematic front view of the measurement object and the probe, (b) is a measurement object and the probe each other It is each waveform figure which shows the change of the detection signal before approaching (contact) and after approaching (contact). It is a schematic front view of each probe which shows one modification of said surface state measuring method. It is a schematic front view of each probe which shows the other modification of said surface state measuring method. It is a schematic front view of each probe which shows the further another modification of said surface state measuring method. It is a front view which shows each modification of the said probe, (a) shows one modification, (b) shows another modification. It is a top view which shows each modification of each said probe, (a) shows this embodiment with each probe being two, (b) shows each modification with three each probes, (c) Each probe shows four other modifications, and (d) shows yet another modification with eight probes. It is a schematic front view of the said surface state measuring device at the time of using atomic force for a physical phenomenon. It is a schematic diagram of each atom for demonstrating the said atomic force. It is a graph which shows the relationship between the interatomic force between each said atom and interatomic distance. In order to explain the electrostatic force as a physical phenomenon, it is a schematic diagram of each charge that generates the electrostatic force. It is a schematic front view which shows an example of the surface state measuring method of this invention using the said surface state measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement object 2 Probe 6 Cantilever 7 1st drive part 9 3rd drive part

Claims (16)

A plurality of probes facing the measurement object;
A probe driving unit that moves each of the probes with respect to the measurement object and moves a relative position between the probes;
A voltage is applied between each probe and the measurement object and a voltage is applied between the probes to detect a tunnel current between the probe and the measurement object and a tunnel current between the probes. and to output, the measurement object and detector which detects and outputs a detection signal arising from the physical phenomenon between each probe,
The relative position between the probes is controlled by the tunnel current between the probes by the detection unit, and the probes and the measurement object by the tunnel current between the probes and the measurement object by the detection unit. A first control unit for controlling the probe driving unit to control the interval of
A surface state measurement apparatus comprising: a measurement unit that measures a surface state of the measurement object from the detection signal. 2. The surface state measuring apparatus according to claim 1, wherein the first controller is configured to bring the probes close to each other by a tunnel current between the probes .   3. The surface state measuring apparatus according to claim 1, wherein the probes are arranged so that tip portions of the probes are close to each other.   The surface state measuring apparatus according to any one of claims 1 to 3, further comprising a cantilever provided with the probe at a tip portion. The tip of each probe is set to extend in a direction opposite to the measurement object ,
5. The first control unit controls a distance between a tip portion of each probe and the measurement object by a tunnel current between the probes and the measurement object. Surface state measuring device.   6. The surface state measuring apparatus according to claim 5, wherein each of the probes has a sharp tip. A protrusion extending along the longitudinal direction of the cantilever is formed at the tip of the cantilever to apply a voltage between the probes and detect a tunnel current between the probes. The surface state measuring apparatus according to any one of claims 4 to 6.   The surface state measuring apparatus according to claim 7, wherein the protruding portion is formed with a pointed tip.   The surface state measuring device according to claim 7 or 8, wherein the protruding portion includes a bent portion whose front end is bent toward the measurement object.   10. The surface state measuring apparatus according to claim 1, wherein the physical phenomenon is at least one selected from the group consisting of an atomic force, a tunnel current, and static electricity. The measurement unit includes a probe position detection unit that detects the position of each probe,
Furthermore, it has a second controller for feedback controlling the Burobu driving unit so as to maintain the spacing of the physical phenomenon above probe and the measurement object a force is applied in a constant based on the detection signal The surface state measuring apparatus according to claim 1, wherein   A microscope comprising the surface state measuring device according to claim 1.   An information processing apparatus comprising the surface state measurement apparatus according to claim 1. A voltage is applied between each of the plurality of probes facing the measurement object and the measurement object and a voltage is applied between the probes, and a tunnel current between the probe and the measurement object and each of the measurement objects. Detect tunnel current between probes,
The relative positions of the plurality of probes and the measurement object are moved by the tunnel currents between the probes and the measurement object, respectively , and the relative positions between the probes by the tunnel current between the probes. Move each
Detecting a detection signal arising from the physical phenomenon between the measurement object and the respective probe,
The position of each probe is detected as a position information signal,
A surface state measurement method, wherein the surface state of the measurement object is measured by feedback controlling each probe so as to maintain a constant distance between the probe and the measurement object from the detection signal. .   15. The surface state measurement method according to claim 14, wherein the physical phenomenon is at least one selected from the group consisting of an atomic force, a tunnel current, and static electricity. The surface state measuring method according to claim 14 or 15, wherein each probe is moved so that a tip portion of each probe is close to each other.

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