JPH0571951A - Interatomic power microscope and information processor - Google Patents

Abstract

PURPOSE:To enhance detection accuracy and sensitivity by preventing the diffusion of the reflected beam of laser beam in an optical lever type interatomic power microscope. CONSTITUTION:An optical lever type interatomic power microscope is provided to one end part of a light reflecting flat plate 105 having a probe 103 for measuring the surface shape of a sample supported thereon by a hinge 106. A change in the surface shape of the sample is detected on the basis of the angle of rotation of the light reflecting flat plate 105 corresponding to the twist angle of the hinge 106 generated by the movement of the probe 103 moved up and down by interatomic power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic force microscope capable of observing the surface of a substance with high resolution and an information processing apparatus using the principle thereof.

[0002]

2. Description of the Related Art In recent years, a scanning tunneling microscope (hereinafter referred to as ST
Abbreviated as M) was developed (G. Binnig eta
l. ． Phys. Rev. Lett. 49 (1982)
57), it has become possible to measure a real space image with extremely high resolution (nanometer or less) regardless of whether it is single crystal or amorphous.

Such an STM utilizes that a tunnel current flows when a voltage is applied between a metallic probe and a conductive substance to bring them closer to a distance of about 1 nm. Since this current is very sensitive to changes in the distance between the two and changes exponentially, it is possible to observe the surface structure in real space with atomic order resolution by scanning the probe so that the tunnel current is kept constant. it can.

However, the STM analysis is limited to conductive samples and is not suitable for observing insulating samples. Therefore, a new atomic force microscope (Atomic Force Microscope)
e; hereinafter abbreviated as AFM) was proposed (Binnig et al. Phys. Rev. Lett. 56).
(1986) 930).

The AFM is for observing the shape of the surface of a material two-dimensionally by the force acting between the materials.
Unlike STM, it can be observed on a nanometer scale on the surface of materials and organic molecules that do not have electrical conductivity, so it is expected to have a wide range of applications.

This AFM is composed of a cantilever portion having a probe with a small tip diameter and a displacement measuring portion for measuring the bending of the cantilever. This probe may be manufactured at the free end of the cantilever separately from the cantilever body, or may be used by tilting the cantilever itself with respect to the sample surface to use the free end of the cantilever as a probe.

Generally, a weak attractive force due to the dispersive force is exerted between the material surfaces at a relatively long distance, while a locomotive force is exerted at a short distance. Since the bending of the cantilever is proportional to this acting force, by measuring this bending, it is possible to detect the weak and local force acting between the tip of the probe and the sample surface that is close to it within a few nm. Becomes further,
By scanning the sample, two-dimensional information of the force on the sample surface can be obtained.

Further, by scanning while feeding the cantilever so that the bending of the cantilever is constant, it is possible to observe minute irregularities on the sample surface. here,
The method for detecting the bending of the cantilever is ST.
There is a method that applies M, a method that detects the capacitance between the sample and the cantilever, a method that uses light interference, and an optical lever method that reads the bend from the change in the reflection angle of the laser light incident on the cantilever. The optical lever method is generally used in consideration of the characteristics and detection sensitivity.

Since the resolution by the AFM is 1 nm or less in the direction parallel to the sample surface, unevenness is formed on the sample surface at intervals of about 10 nm, and by reading the unevenness with the AFM, it is over 10 ¹² bits / cm ^2. It is also possible to manufacture a high-density memory.

[0010]

However, the above-mentioned conventional example has the following problems.

First, FIG. 5 shows a cantilever portion of a conventional optical lever type AFM. From the substrate 201, the cantilever 2
02 (length 1) is projected, and the probe 203 is provided at the tip of the cantilever 202. If the sample surface 204 is two-dimensionally scanned by the probe 203, the cantilever 202 is bent by the unevenness 205 (height h) on the surface. This bend is the laser light 206,
The change is detected as a change in the reflection angle of 207 (Δθ = 2h / L).

In FIG. 5, the laser beams 206 and 207 are drawn as a single line, but actually, they are beams having a diameter of about 10 μm. Therefore, when the size of the cantilever is about this laser beam diameter, the reflection angle of the light in the laser beam deviates. This state is shown in FIG. 6 (cross-sectional view). Lights 301, 302, and 303 projecting from the substrate 201 and incident on the cantilever 202 are reflected at different positions on the cantilever, and the reflected lights are 304, 30 respectively.
It becomes 5,306. That is, the reflected light is not fixed in one direction, and it becomes difficult to accurately measure the bend of the cantilever 202.

In particular, when the AFM is used in an information processing apparatus that records and reproduces information by using a tunnel current, it is necessary to arrange a plurality of probes from the viewpoint of speeding up reading and writing of recording bits. The size of the cantilever must be reduced for integration, and the above-mentioned problems become more prominent. Further, in order to increase the sensitivity of the AFM, the cantilever must be thin, and when a metal or other film is laminated on the cantilever, there is a problem that the cantilever warps due to residual stress.

That is, the object of the present invention is to
It is an object of the present invention to provide an atomic force microscope and an information processing device capable of solving the above-mentioned problems.

[0015]

The present invention for achieving the above object is to provide an optical lever type atomic force microscope, in which a probe for measuring the shape of a sample surface is supported by a hinge for light reflection. It is provided at one end of the flat plate and is generated by the movement of the probe that moves up and down by the atomic force.
The atomic force microscope is characterized in that the configuration change of the sample surface is detected by the rotation angle of the light reflecting flat plate corresponding to the twist angle of the hinge portion.

Further, the present invention is also characterized by an atomic force microscope in which the probe is conductive and a bias voltage can be applied between the probe and the conductive sample so that a change in tunnel current can be detected. ..

Further, an information processing apparatus for recording / reproducing information on / from a recording medium by using a tunnel current is characterized by an information processing apparatus having at least the above atomic force microscope.

That is, according to the present invention, since the laser light reflecting portion is a flat surface, the detection accuracy is improved without the reflected beam being diffused, and the detection has a change in the rotation angle about the hinge portion. For reading, the cantilever portion of the probe can be thickened, and there is an advantage that it does not warp even if a metal film is deposited on the surface of the cantilever.

[0019]

EXAMPLES Examples of the present invention will be described in detail below.

(Embodiment 1) FIG. 1 shows a probe portion of an AFM according to the present invention. 101 is a Si wafer, 102 is S
iN film, 103 is Au probe (height about 4 μm), 10
4 is a cantilever portion, 105 is a laser light reflecting surface, 10
6 is a hinge and 107 is a reflective Au film.

FIG. 2 shows a manufacturing process diagram. In addition, this shows the AA cross section of FIG. (A). A SiN film 102 having a thickness of about 2 μm was formed on a Si (100) substrate 101 by the LPCVD method. (B). An opening was provided in the SiN by photolithography and reactive ion etching with CF ₄ . (C). Membrane 108 having a thickness of 20 μm is formed by Si anisotropic etching using a KOH 27 wt% aqueous solution at 80 ° C.
Was produced. (D). Patterning of cantilevers, hinges, etc. was performed in the same manner as in (b). (E). Au probe 1 by vapor deposition and lift-off method
03 (height about 4 μm) was produced. (F). The membrane 108 was removed in the same manner as in (c). (G). The Au film 107 for reflection was prepared by vapor deposition to have a thickness of 500 liters.

Here, the thickness (sum) of the SiN film and the Au film
Is a, the cantilever length is L, the width is D, the cross section of the hinge part is a × b, the length r and Young's modulus of SiN are E, and the lateral elastic modulus is G, the elastic constant of the cantilever part (bend mode). ) Is

[0023]

[Equation 1] And the elastic constant of the rotation torque of the hinge is

[0024]

[Equation 2] Then, when converted to the relationship between the force applied to the tip of the cantilever and the displacement of the tip of the cantilever,

[0025]

[Equation 3] Becomes In the present embodiment, since a = 3 μm, b = 10 μm, r = 150 μm L = 30 μm, D = 30 μm, k _C ˜500 (N / m), k _H ˜100
(N / m). That is, the change in the surface shape is detected not as the bending deformation of the cantilever but mainly as the change in the rotation angle about the hinge portion. At that time, since the laser beam is incident on the flat surface portion like 105 in FIG. 1,
It is possible to detect a change in the rotation angle with high accuracy. Actually, when the AFM observation of the HOPG (graphite) surface and the mica surface was performed using the above probe and detection method, a good atomic arrangement image could be obtained.

(Example 2) In this example, Pd was vapor-deposited to a thickness of 100 nm on both the surface on which the probe 103 was provided and the surface on the laser light reflecting side, which were the same as in Example 1. Here, the Pd film is for increasing the reflectance of the surface on which the laser light is applied, and for allowing the bias voltage to be applied between the conductive sample and the probe 103 on the opposite surface.

Conventionally, in the AFM, the elastic constant must be lowered in order to increase the measurement sensitivity, and the cantilever must be made as thin as possible. Further, when a metal film is laminated to increase the reflectance, the cantilever may be warped due to the stress of the metal film.

In the present embodiment, since the cantilever can be made sufficiently thick, the warp of the cantilever can be suppressed to 0.5 μm or less even at the tip even after Pd vapor deposition. In addition, since the metal film is deposited on the surface facing the sample, STM observation using the conductive sample is also possible.

FIG. 3 shows a block diagram of an apparatus for AFM / STM observation. An Au probe 103 is provided on a lever that rotates around the hinge portion 106, and reflective Au films 107 and Pd films 109 are deposited on both surfaces of the lever.

When the lever rotates around the hinge portion 106 due to the force acting between the probe 103 and the sample 112, the reflection angle of the laser light emitted from the laser 110 changes, which can be detected by the two-divided photodiode 111. (AFM observation).

Next, when the sample 112 is conductive, a bias voltage of 1 is applied between the Pd film 109 on the probe side and the sample 112.
13 is applied, and the tunnel current flowing at that time is measured by an ammeter 11
4 (STM observation). In addition, AFM, ST
The M signal is taken in by the controller 115, and the monitor 1
An image is displayed at 16. Further, it is also possible to control the cylindrical piezo element 117 by the controller 115 and apply feedback.

When the AFM and STM operations of this embodiment were actually carried out, the atomic images of graphite were AFM and ST.
Both M could be observed well.

Example 3 Using the AFM device of Example 2, recording bit writing and reading experiments were conducted.

FIG. 4 shows a block diagram of the apparatus. Reference numeral 118 is a display device and 119 is a microcomputer, and AFM detection using the laser 121, the photodiode 120, and the lever 125 is the same as that in the second embodiment. Cantilever 1
25 is installed on the Z direction fine movement control mechanism 124 and the XY direction fine movement control mechanism 122, and is driven and controlled by the servo circuit 126 and the XY scanning drive circuit 123.

Further, as will be described later, 130 is a substrate 129.
Is a recording medium, 128 is a recording bit, and 127 is a pulse power source used for producing the recording bit. The recording medium is installed on the XY stage 131, and can be three-dimensionally moved by the coarse movement mechanism 132 and the coarse movement drive circuit 133.

As the recording medium, Au formed on a glass substrate was used, and a pulse voltage of several V and several μsec was applied between the cantilever and the Au film to obtain a diameter of 10 mm.
A convex part having a thickness of about nm and a height of about 2 nm was formed. This became a recording bit, and a recording bit string was formed while scanning two-dimensionally in the XY directions. Next, as in the second embodiment, this bit string could be read by the AFM.

[0037]

As described above, the present invention has the following effects.

1. Since the reflected beam of laser light does not diffuse, detection accuracy and sensitivity are improved.

2. Even if a metal film or the like is vapor-deposited on the cantilever, it does not warp, so that not only the surface alignment with the sample becomes easy, but also it becomes possible to operate as an STM in the case of a conductive sample.

3. Since the probe for detecting the atomic force can be made small, a large number of probes can be integrated, and a high-density, large-capacity information processing device can be manufactured.

4. Since the sensitivity and accuracy of the AFM are improved, a highly reliable information processing device with a low error rate can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic aspect of the present invention.

FIG. 2 is a process drawing of a probe according to the present invention.

FIG. 3 is a block diagram of an AFM / STM device according to a second embodiment.

FIG. 4 is a configuration diagram of an information processing device.

FIG. 5 is a diagram showing a probe unit of a conventional optical lever type AFM.

FIG. 6 is a diagram showing a problem of a conventional optical lever type AFM.

[Explanation of symbols]

 101 Si Wafer 102 SiN Film 103 Au Probe 104 Cantilever Part 105 Laser Light Reflecting Surface 106 Hinge 107 Reflecting Au Film 108 Si Membrane 109 Pd Film 110 Laser 111 Two-Divided Photodiode 112 Sample 113 Bias Voltage 114 Tunnel Current Detecting Section 115 Controller 116 Monitor 117 Cylindrical piezo element 118 Display device 119 Microcomputer 120 Photodiode 121 Laser 122 XY direction fine movement control mechanism 123 XY scanning drive circuit 124 Z direction fine movement control mechanism 125 Cantilever 126 Servo circuit 127 Pulse power supply 128 Recording bit 129 Recording medium 130 Substrate 131 XY stage 132 Coarse movement mechanism 133 Coarse movement drive circuit 201 Substrate 202 Cantilever 20 3 probe 204 sample surface 205 surface unevenness 206, 207 laser light 301, 302, 303 incident light 304, 305, 306 reflected light

Front page continued (72) Inventor Toshihiko Miyazaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. An optical lever type atomic force microscope comprising:
A probe for measuring the shape of the sample surface is provided at one end of a light-reflecting flat plate supported by a hinge, and light corresponding to the twist angle of the hinge part generated by the movement of the probe that moves up and down by an atomic force Atomic force microscope characterized by detecting the change in shape of the sample surface by the rotation angle of the reflecting plate. 2. The probe is conductive, and a bias voltage can be applied between the probe and a conductive sample so that a change in tunnel current can be detected. Atomic force microscope. 3. An information processing apparatus for recording / reproducing information on / from a recording medium using a tunnel current, comprising at least the atomic force microscope according to claim 2.