JPH0545157A - Interatomic force microscope and its control method - Google Patents

Abstract

PURPOSE:To prevent a noise due to scanning from being generated and a probe from being damaged and to enable a sample with minute recessed and projecting portions and a groove shape to be measured with a high accuracy by iterating approaching, separation and movement between the sample and the probe within a specified position of a cantilever. CONSTITUTION:A displacement of a cantilever 6 is detected by an optical lever by allowing a lens 8 to focus light which is emitted from a semiconductor laser 7 on the lever 6 and then the reflection light to be detected by a bisected photodiode 9. A sample 5 is installed at a position directly below a probe 12, a voltage is applied to a piezoelectric body 3 by a piezoelectric driving body 11, and a diode 9 allows a repulsive force which the lever 6 receives from the sample 5 to be measured while the sample 5 is brought closer to the probe 12. When the repulsive force reaches a specified value, approaching is stopped and then the application voltage is stored into a CPU 13 and is used as information on recessed/projecting portions. Then, the sample 5 is separated until no repulsive force remains, the piezoelectric body 1 is driven, the sample 5 is moved in a direction of X, and then similar procedures are iterated. The same applies to a direction of Y. Also, when a pillarshaped or needle- shaped whisker is mounted, a groove-shaped surface can be observed easily.

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 for stably and accurately measuring extremely small irregularities of 0.1 nm or less and deep groove shapes, and a control method thereof.

[0002]

2. Description of the Related Art In recent years, an atomic force microscope (hereinafter referred to as AFM) has been developed as an apparatus for observing a solid surface on the atomic order. The AFM and its control method will be described with reference to FIG. In AFM, a cantilever having a probe and having a length of about 100 μm is used to detect a minute force. When the sample 5 is brought closer to the probe 12, the cantilever 6 is bent by the atomic force acting between the probe and the sample. The surface of the sample is scanned while controlling the Z-direction piezoelectric body 3 by the piezoelectric body driving device 11 through the control signal generating circuit 10 so as to keep this amount of deflection constant. The scanning is performed by the piezoelectric body driving device 11 and the piezoelectric bodies 1 and 2 in the X and Y directions. The controlled variable in the feedback corresponds to the unevenness of the sample surface. Therefore, this controlled variable is calculated by the computer 1.
An AFM image can be obtained by imaging with 3 or the like. The amount of deflection of the cantilever is measured by the displacement measuring section 19. The displacement measuring unit 19 uses a method such as an optical lever, laser interference, or tunnel current. The resolution of the AFM depends on the radius of curvature of the tip of the probe, and the smaller the radius of curvature, the higher the resolution. At present, a probe with a curvature of 200 to 300 Å has been manufactured. Using this cantilever, MI
Atomic images such as CA have been observed. On the other hand, a sample having a deep groove shape such as a grating is also measured by using AFM. For such measurement, it is necessary to use an elongated probe that reaches the bottom of the groove while having a small tip curvature.

[0003]

When the sample surface is scanned by the probe, in addition to the displacement of the cantilever due to the unevenness of the sample surface, the displacement of the cantilever due to the difference in the friction coefficient of the sample surface or the displacement due to the torsion of the cantilever, etc. Occurrence occurs, and these become noise, and it may not be possible to measure an extremely fine surface shape. Further, in the case of a sample in which the wall surface of the groove is close to vertical, the side surface of the probe collides with the wall surface of the groove during scanning. In this state, the deflection of the cantilever hardly occurs, and the scanning can be continued with the distance between the sample and the probe unchanged. As a result, not only an accurate AFM image cannot be obtained, but also the probe and the cantilever may be destroyed.

In consideration of the problems of the conventional control method of the atomic force microscope, the present invention is capable of accurately observing even a sample having extremely small unevenness or a side surface shape close to vertical. An object of the present invention is to provide a force microscope and a control method thereof.

[0005]

In an atomic force microscope having a cantilever, a cantilever displacement detection device, a sample or a three-dimensional fine movement device of the cantilever, and an imaging device, the cantilever and the sample are brought close to each other at one point on the sample surface. Then, when the displacement of the cantilever reaches a predetermined value, the cantilever and the sample are separated, and then the same operation is repeated at another point on the sample surface, or a method for controlling an atomic force microscope, or a columnar or It has a cantilever with a needle-shaped protrusion, a displacement detection device for the cantilever, a three-dimensional fine movement device for the sample or cantilever, and an imaging device. The cantilever and the sample are brought close to each other at one point on the sample surface, When the displacement reaches a specified value, separate the cantilever and the sample, and then at another point on the sample surface. Flip By repeating the operation, measure the irregularity on the surface of the sample points, atomic force microscope, wherein imaging the shape of the sample surface.

[0006]

Function: With the cantilever receiving a constant force from the sample surface, instead of scanning the sample surface with the probe, it is as if the cane is used to examine the surface shape of the road. The travel distance of the sample (or probe),
By measuring the relationship between the force acting between the sample and the probe and imaging the surface shape, it is possible to remove noise components such as cantilever displacement due to differences in the friction coefficient of the sample surface and displacement due to torsion of the cantilever. You can Also, when using an elongated probe to observe a sample whose wall surface such as a groove is nearly vertical, the side surface of the probe collides with the wall surface during scanning, and the probe and cantilever are destroyed. It is possible to observe the surface shape without any need.

[0007]

【Example】

(Example 1) Hereinafter, a specific example will be described in detail. Figure 1
The first aspect of the atomic force microscope and the control method thereof according to the present invention.
It is the schematic which shows an Example. The sample is set on a tripod-type fine movement mechanism formed of piezoelectric bodies 1, 2, and 3 in three directions of X, Y, and Z. The scanning of the sample 5 in the horizontal plane was performed by applying the voltage generated by the piezoelectric body driving device 11 to the piezoelectric bodies in the X and Y directions. The force acting between the sample and the probe, that is, the displacement of the cantilever 6, outputs 5 mW.
The laser light emitted from the semiconductor laser 7 was focused on the cantilever by the lens 8, and the reflected light was detected by the optical lever detected by the two-divided photodiode 9. The control of the distance between the sample and the cantilever was performed by applying the control voltage to the piezoelectric body 3 in the Z direction by the control signal generation circuit 10 and the piezoelectric body drive device 11. A specific control method when observing the Au sputtered film will be described below.

A sample 5 having an Au thin film formed on a Si substrate was placed on the sample table 4 so that the central portion of the sample was located below the probe 12. A voltage was gradually applied to the piezoelectric body 3 in the Z direction by the piezoelectric body driving device 11, and the force applied to the cantilever 6 from the sample 5 was simultaneously measured by the two-divided photodiode 9 while the sample 5 was approaching the probe 12. .. When the cantilever 6 receives a repulsive force of a predetermined magnitude, the approach of the sample to the probe is stopped, and the voltage applied to the piezoelectric body 3 in the Z direction at that time is stored in the computer 13. This voltage value becomes unevenness information at each point on the substrate surface. In the measurement of this sample, the magnitude of the repulsive force was 1 × 10 ⁻⁸ N. Next, the sample 5 was separated from the probe 12 until the cantilever 6 received a force from the sample 5. Next, by using the piezoelectric body driving device 11, the sample 5 is moved by the piezoelectric body 1 in the X direction.
Was moved to the left by 2 nm. Thereafter, a voltage is gradually applied to the piezoelectric body 3 in the Z direction, and the sample 5 is moved closer to the probe 12 until the cantilever 6 receives a repulsive force of 1 × 10 ⁻⁸ N. The voltage applied to the computer 13 was stored in the computer 13. Next, the sample 5 is formed by the piezoelectric body 1 in the X direction.
Was further moved to the left by 2 nm. Such measurement was repeated 256 times in the X direction to complete scanning for one line. Then Y
The sample 5 was moved downward by 2 nm by the piezoelectric body 2 in the direction, and one line was scanned by the same operation. After 256 scans, 256 × 256 pieces of unevenness information on the sample surface were obtained.

By controlling the AFM as in the present invention, the noise level is low and a high resolution image can be obtained as compared with the conventional case where the cantilever continuously scans the sample surface while receiving a constant repulsive force. Was obtained. As one of the causes of this, it is considered that the noise due to the torsion component of the cantilever, which is generated when the surface of the sample is scanned in the X direction, is completely eliminated.

In the above embodiment, the unevenness information was measured once for each point, but the measurement at each point was repeated a plurality of times,
An image with a lower noise level was obtained by imaging using the average value. Further, although the optical lever method was used as the displacement measuring means of the cantilever in the above embodiment, the same result was obtained by using the laser interferometry method or the tunnel current method.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
Figure 2 shows a schematic diagram of the cantilever part of the atomic force microscope.
Shown in. Length 100 created by photolithography
μm, thickness 1.5μm V type SiO₂Thin film cantilever 14
At the tip of the needle, the length of one needle is 2-5μm
A zinc oxide whisker 15 was attached. This whisker is CV
It was created by the D method and is 4 from the body center of the tetrahedron.
Tetrapod-shaped three-dimensional structure extending toward the apex
Since it is a crystal, using an adhesive as shown in FIG.
It could be easily attached to the cantilever. This power
Use a cantilever to keep the cantilever
With the conventional control method of continuously scanning while receiving a repulsive force,
Stable when measuring a groove shape 18 with a depth of 1 μm and a width of 1 μm
May not be able to be measured and the whisker may be damaged.
It was. In addition, Si etch pits are used as a template for Si ₃N_FourIn thin film
Measured by the conventional control method using the created cantilever
Image and the cantilever equipped with the whisker of the present invention
And compare it with the image measured by the control method of the present invention.
However, the device of the present invention can more accurately observe the groove shape.
It turned out to be possible. The reason for this is as shown in FIG.
Since the conventional probe has a pyramid shape with an apex angle of 70 degrees,
The probe 16 does not reach the bottom of the groove, so it differs from the actual sample shape.
The image shown by the broken line was obtained (Fig. 3 (a)).
However, the whisker probe 17 reaches the bottom of the groove and is shown by the broken line.
An image faithful to the surface shape was obtained (Fig. 3).
(B)).

In this embodiment, the case of using zinc oxide whiskers has been described, but tin oxide, silicon carbide, alumina,
Even if a needle crystal of a metal or an organic material is used, by using the control method of the present invention, an A image faithful to the surface shape can be stably obtained even in a groove having a vertical wall surface.

[0013]

As is clear from the above description,
According to the present invention, it is possible to stably and highly accurately measure extremely small irregularities having a low noise level of 0.1 nm or less, and further, when measuring a sample having a deep groove shape such as a grating or a wall surface close to vertical, a cantilever. Accurate measurement is possible without destroying the probe.

[Brief description of drawings]

FIG. 1 is a schematic view for explaining an atomic force microscope and a control method therefor according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a cantilever portion of an atomic force microscope according to a second embodiment of the present invention.

FIG. 3 is an explanatory view of a conventional cantilever and an AFM image of a groove shape obtained by the cantilever of the present invention.

FIG. 4 is a schematic diagram for explaining a conventional atomic force microscope and a control method thereof.

[Explanation of symbols]

 1 X-direction piezoelectric body 2 Y-direction piezoelectric body 3 Z-direction piezoelectric body 4 Sample stage 5 Sample 6 Cantilever 7 Semiconductor laser 8 Condensing lens 9 Two-divided photodiode 10 Control signal generation circuit 11 Piezoelectric body drive device 12 Probe 13 Control computer 14 cantilever 15 zinc oxide whisker 16, 17 probe 18 displacement measuring unit

Claims (5)

[Claims] 1. An atomic force microscope having a cantilever, a displacement detecting device for the cantilever, a three-dimensional fine movement device for the sample or the cantilever, and an imaging device, wherein the cantilever and the sample are brought close to each other at one point on the sample surface. A method for controlling an atomic force microscope, wherein when the displacement reaches a predetermined value, the cantilever and the sample are separated, and then the same operation is repeated at another point on the sample surface. 2. When the cantilever and the sample are brought close to each other at one point on the sample surface and when the displacement of the cantilever reaches a predetermined value, the operation of separating the cantilever and the sample is repeated a plurality of times, and then the sample surface The atomic force microscope control method according to claim 1, wherein the same operation is repeated at another point. 3. A cantilever having a columnar or needle-like protrusion formed thereon, a cantilever displacement detection device, a sample or a three-dimensional fine movement device of the cantilever, and an imaging device, and the cantilever and the sample are provided at one point on the sample surface. , And when the displacement of the cantilever reaches a predetermined value, the cantilever and the sample are separated, and then the same operation is repeated at another point on the sample surface to measure the unevenness state at each point on the sample surface. , An atomic force microscope characterized by imaging the shape of a sample surface. 4. When the cantilever and the sample are brought close to each other at one point on the sample surface, and when the displacement of the cantilever reaches a predetermined value, the operation of separating the cantilever and the sample is repeated a plurality of times, and then the sample surface The atomic force microscope according to claim 3, wherein an average unevenness state at each point on the sample surface is measured by repeating the same operation at another point. 5. The columnar or needle-shaped protrusion is a needle-shaped crystal of an organic material such as metal, zinc oxide, tin oxide, alumina, silicon carbide, or phthalocyanine, according to claim 3 or 4. Atomic force microscope.