JPH075181A - Atomic force microscope - Google Patents

Abstract

PURPOSE:To provide an optical lever type atomic force microscope which can detect the movement of a cantilever at a specific position accurately. CONSTITUTION:The incident angle of a detection light 203 impinging on a cantilever 102 having a probe 103 is set such that the reflection loss of p- polarized component on the reflective surface 109 of the cantilever is substantially maximized. A reflector 204 having the reflectance of p-polarized component at such incident angle higher than that of the reflective surface 109 of the cantilever is provided at the forward end of the cantilever. A polarizing plate 202 for producing p-polarized light from the detection light impinging on the reflective surface 109 of the cantilever is also provided.

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 a sample surface with high resolution.

[0002]

2. Description of the Related Art In recent years, a scanning tunneling microscope (hereinafter referred to as "S
"TM") was developed (G. Binnig et al., P.
Physical Review Letters, Vol. 49, p. 57 (1982)), real-space images can be measured with extremely high resolution (nanometer or less) regardless of 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 close to a distance of about 1 nm. This current is very sensitive to changes in the distance between the two and changes exponentially.Therefore, by scanning the sample surface with the probe so as to keep the tunnel current constant, the surface structure in real space can be resolved with atomic order resolution. Can be observed.

However, the STM analysis is limited to conductive samples, and it is difficult to observe insulating samples. Therefore, an atomic force microscope (hereinafter referred to as “AFM”) that detects the force acting between two substances and observes the shape of the sample surface
Has been developed (G. Binnig et al., Phys.
ical Review Letters, Vol. 56, p. 930 (1986)).

Such an AFM has a cantilever portion having a probe having a small tip diameter, and a bending of the cantilever caused by an atomic force generated between the probe and the sample surface when the probe is brought close to a sample. It consists of the part to measure. This probe may be formed at the free end of the cantilever separately from the cantilever body, or the free end of the cantilever itself may be used as the probe.

Generally, between the material surfaces, a weak attractive force due to the dispersion force is exerted at a relatively long distance, while a repulsive force is exerted at a short distance. Since the bending of the cantilever is proportional to the acting force, it is necessary 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 by measuring the degree of this bending. Is possible.
Further, by relatively two-dimensionally scanning the sample surface on the sample surface, two-dimensional information of the force on the sample surface can be obtained.

Further, by scanning while feeding feedback so that the bending of the cantilever is constant,
It is possible to observe minute irregularities on the sample surface. Here, when enumerating the methods for detecting the bending of the cantilever, STM
, A method of detecting the electrostatic capacitance between the sample and the cantilever, a method of using the interference of light, an optical lever method of detecting the bend from the change in the reflection angle by injecting light into the cantilever. However, the optical lever method is generally used from the viewpoint of operability, detection sensitivity, and the like.

The resolution by AFM is 1n in the in-plane direction of the sample.
Since it is less than or equal to m, for example, minute irregularities are formed on the sample surface at intervals of about 10 nm, and the fine irregularities are read by using the AFM to manufacture an ultrahigh-density memory close to 10 ¹² bits / cm ^2. It is also possible.

[0009]

However, the optical lever type AFM has the following problems.

FIG. 1 shows a cantilever portion of a conventional optical lever type AFM. A cantilever 102 (length L ₁ ) projects from a substrate 101 that serves as a support, and a probe 103 is provided at the tip of the cantilever 102. On the other hand, the detection light 106 causes the tip of the cantilever 102 (usually,
As shown in FIG. 1, the back surface is irradiated with light (around the position where the probe 103 is arranged). The surface of the cantilever 102 on which the detection light 106 is irradiated is the cantilever reflecting surface 1
I will call it 09.

Here, the probe 103 is brought close to the surface of the sample 104 to such an extent that an atomic force is generated, and then the surface of the sample is moved to 2
When scanning is relatively performed in the in-plane direction, the cantilever 102 is bent by the unevenness 105 (height h) on the sample surface. Due to this bending, the reflected light 107 reflected by the cantilever reflecting surface 109 has a change in the reflection angle, Δθ = 2h / L ₁ Formula (1). When the reflected light 107 reflected by the cantilever reflection surface 109 is detected by using the photodetector 108 installed at a position at a distance L ₂ from the cantilever reflection surface 109, the photodetector is detected according to the change in the reflection angle. The position of the reflected light 107 incident on 108 is shifted by d = L ₂ Δθ = 2L ₂ h / L ₁ formula (2). This shift amount is calculated by the photodetector 108, for example, a two-division photodetector (hereinafter, BPD; Bi-cell).
It can be detected using a Photo Detector).

The above behavior is the most ideal case,
If the entire cantilever is warped or warped when the cantilever is bent, the reflected light 107 is reflected on the cantilever 102 at various reflection angles, and the amount of deviation detected by the photodetector 108 is exceeded. The error will be included. In order to reduce such an influence as much as possible and improve the measurement accuracy, the detection light is sufficiently narrowed to reduce the incident area of the detection light on the cantilever reflection surface 109, and the movement of the probe 103 is most sensitively reflected. It is necessary to make the detection light 106 incident on the position, that is, in the case of FIG. 1, the tip of the cantilever 102 (the back surface of the cantilever 102 where the probe 103 is located). However, it takes a lot of labor and time to adjust the optical system so that the detection light can be condensed to a diameter of several μm, for example, at the tip of a cantilever having a length of several hundred μm.

In order to solve such a problem, a reflection barrier is provided on the cantilever reflecting surface around the light reflecting portion and the light reflecting portion, and even if the beam diameter of the detection light is equal to or larger than the area of the light reflecting portion, A method for preventing the detection light reflected by a portion other than the reflecting portion from reaching the photodetector is disclosed in Japanese Patent Laid-Open No. 4-206.
No. 285810. Japanese Patent Application Laid-Open No. 4
In No. 285810, as a first embodiment, a zigzag structure having a pitch of 1 μm is constructed as the reflection barrier. In addition, in the second embodiment, a diameter of 1 μm is used as a light reflecting portion on a cantilever made of silicon nitride.
In order to improve the measurement sensitivity, it is possible to vapor-deposit m gold and utilize the fact that the reflectance of the gold is higher than that of silicon nitride to detect the reflected light from the light reflecting portion in a focused manner and improve the measurement sensitivity. It is disclosed.

When the above-mentioned conventional method is used, for example,
In order to construct some kind of reflective barrier on the cantilever as in the first embodiment described above, the number of manufacturing steps is increased and becomes complicated, and the reflected light of the detection light at this portion does not reach the photodetector. In order to do so, there is a problem that labor is required for the morphological design of the reflective barrier, its manufacturing process, and adjustment of the AFM optical system. Further, although the method shown in the second embodiment is simple, as will be described later, the influence of the reflected light reflected by the portion other than the light reflecting portion on the reflected light detected by the photodetector is In some cases, it cannot be ignored.

In view of the above-mentioned problems of the prior art, an object of the present invention is to provide, in an optical lever type AFM, a detection light reflected by a cantilever, particularly a reflected light from a specific position on the cantilever. (EN) Provided is a device capable of relatively significantly increasing the intensity of reflected light reflected by other portions, and capable of accurately detecting movement of a specific position of a cantilever during surface shape measurement. It is in.

[0016]

SUMMARY OF THE INVENTION The present invention, which has been made to achieve the above object, provides a cantilever portion having a sharp probe and a means for controlling the distance between the probe and the sample surface. , A means for relatively two-dimensionally scanning the probe on the sample surface, and a change in the bending of the cantilever due to the vertical movement of the probe caused by the atomic force generated between the probe and the sample surface. In order to do so, in an optical lever type atomic force microscope having a photodetector that detects a change in the reflection angle of the detection light incident on the cantilever on the cantilever reflection surface, the detection light to the cantilever reflection surface The incident angle is set so that the reflection loss of the p-polarized light component on the cantilever reflection surface becomes substantially maximum, and it is interlocked with sensitivity to the movement of the probe on the cantilever reflection surface. In A reflection plate having a reflectance of the p-polarized component larger than that of the cantilever reflection surface at the detection light incident angle set as described above, and further reflected by the cantilever reflection surface and incident on the photodetector. The detected light is a p-polarized component, which is an atomic force microscope.

The mechanism and principle of the present invention will be described in detail below. FIG. 2 is a schematic view showing an example of the configuration of the main part that characterizes the atomic force microscope of the present invention.

In the present invention, the cantilever reflecting surface 1
Detection light 20 that is reflected at 09 and enters the photodetector 108
5 is a p-polarized component for the reason described later. Therefore, in the present configuration example, the detection light 2 emitted from the light source 201
03 is incident on the cantilever reflecting surface 109 as p-polarized light by the polarizing plate 202. When the dependence of the reflectance on the cantilever reflecting surface 109 at this time on the incident angle (θ in FIG. 2) is examined, there is θ _{p at} which the reflectance is minimum. That is, at this time, the reflection loss on the cantilever reflection surface 109 becomes maximum.

In the present invention, the incident angle of the detection light 203 on the cantilever reflecting surface 109 is set to the vicinity of θ _p , and generally, at the dielectric interface, the medium 1 to the medium 2 are set.
When p-polarized light is incident on the
Assuming ₁ and n ₂ , θ _p is the Brewster angle (θ _B ) defined by the equation (3), where θ _B = tan ⁻¹ (n ₂ / n ₁ ). Becomes zero. However, when the material forming the cantilever reflection surface 109 is a thin film deposited on another material and the film thickness is equal to or less than the wavelength of the detection light 203 (particularly, equal to or less than ¼ of the wavelength), the formula (3 It is necessary to use the equation of the multilayer film system instead of), but there is an incident angle θ _p that maximizes the reflection loss, so that it can be used.
Since the refractive index has dispersion with respect to the wavelength of incident light, it is desirable to use a single wavelength light such as a laser light as the detection light 203.

In the present invention, as described above, the incident angle of the detection light 203 on the cantilever reflecting surface 109 is set to the incident angle θ _p at which the reflection loss becomes maximum (the reflectance is minimum).
Further, on the cantilever reflection surface 109, the detection light 203
Reflection plate as larger than that in the reflectance cantilever reflecting surface 109 when is incident at an incident angle theta _p 20
4 is provided. As described above, even when the beam diameter of the detection light 203 is larger than the area of the reflection plate 204,
Detection light 205 due to reflection from a portion other than the reflection plate 204
It is possible to minimize the influence on. That is, when the above optical system is used, the reflected light from the reflection plate 204 can be selectively detected, and the detection accuracy of the surface state of the sample 104 can be improved. Furthermore, the reflector 2
The sample 04 is formed at a position that most interlocks with the movement of the probe 103 (a position on the cantilever reflection surface 109 where the probe 103 is located on the back surface in the example of FIG. 2). It is possible to increase the detection sensitivity of the uneven shape of the surface.

In the present invention, the detection light 205 incident on the photodetector 108 is made to have a p-polarized component so that the reflection light from the reflection plate 204 can be detected more selectively. The reason will be described below.

Unpolarized light or s-polarized light has a higher reflectance than p-polarized light at the same incident angle (incident angle of 0 ° or 90 °).
This is shown in FIG. 3).

In FIG. 3, He of wavelength 6328Å is added to silicon.
The reflectance on the silicon surface when -Ne laser light is incident is plotted against the incident angle. When the incident angle is around 0 °, seven curves are drawn. These are, in order from the one with the smallest reflectance, gold with 0,10 on silicon.
The relationship is shown when 0, 200, 300, 400, 500 and 700 Å are deposited. Also, each curve is
It is divided into two near the incident angle of 10 °. Regardless of the deposited gold film thickness, the one with the same incident angle has a large reflectance corresponds to the s-polarized light incident, and the smaller one has the p-polarized light incident. It corresponds to.

From FIG. 3, for example, the cantilever 102 is made of silicon, and the light source 201 has a wavelength of 6328.
If a He-Ne laser of Å is used, when the detection light incident angle θ is, for example, 40 °, the film thickness of the reflection plate 204 is 70
Even if 0 Å gold is provided, the reflectance on the reflecting plate 204 is 90 to 95%, whereas the reflectance on the cantilever reflecting surface 109 (that is, the silicon surface) not including the reflecting plate 204 is. , 25% when p-polarized light is incident and about 43% when s-polarized light is incident, and when the beam diameter of the detection light 203 is larger than the area of the reflection plate 204, the detection light 205
Contains a large amount of light reflected on the silicon surface. On the other hand, when the incident angle θ is brought to around 75 ° (75.5 °), the reflecting plate 204 (gold) is incident upon p-polarized light incidence.
Although the reflectance above is relatively small, the reflectance on the cantilever reflecting surface 109 (silicon) that does not include the reflector 204 is substantially zero. For example, the thickness of the reflector 204 (gold) is 200Å. However, the reflectance is 36%, and only the detection light reflected by the reflection plate 204 is selectively detected.
It is possible to detect at 08. However, at this time, if s-polarized light is used as the detection light 203, the reflectance from each point is 7
Since it exceeds 0%, it is understood that it is not suitable for use in the present invention.

For the above reasons, in the present invention, the detection light 205 entering the photodetector 108 is the p-polarized component. In the example shown in FIG. 2, a polarizing plate 202 is provided between the light source 201 and the cantilever 102 to detect the detection light 20.
3 uses p-polarized light itself, for example, the polarizing plate 2
Instead of 02, p-polarized light may be extracted using a polarizing plate installed between the cantilever 102 and the photodetector 108. In this case, the detection light 203 may be a light ray containing a p-polarized component.

In the configuration of the present invention as shown in FIG. 2, when the detection light 203 is irradiated from the light source 201 to the cantilever reflection surface 109 including the reflection plate 204, the reflection plate 2
Since the reflectance of the detection light 203 irradiated on the portion other than 04 can be made negligibly smaller than that on the reflection plate 204, the substantial beam size is the reflection plate 204.
Is the size of. Therefore, even if the detection light is not focused on the tip of the cantilever, the displacement of the tip of the cantilever can be detected with high sensitivity as long as the detection light is applied to the reflecting surface of the cantilever including the reflection plate 204. However, detection light 2
It is not preferable that the beam diameter of 03 is too large as compared with the size of the reflection plate 204.

The reflecting plate 204 is not limited to the above-mentioned gold, but the reflectance of the p-polarized component at the detection light incident angle set as described above has the underlying cantilever reflecting surface 1.
Any material larger than 09 may be used, and in addition to gold, metals such as silver, aluminum and platinum, and alloys thereof can be used. The manufacturing method thereof may be based on a conventionally known method such as vapor deposition, and in order to limit the size and position thereof, also conventionally known mask vapor deposition or photolithography technology may be used. The size of the reflection plate 204 is preferably about 1 μm to 30 μm in diameter, and more preferably 1 μm to 10 μm. The shape is not limited to the disk shape, and may be another shape.

The arrangement of the optical components such as the light source, the polarizing plate and the photodetector is not limited to that shown in FIG. 2, and if the basic operation is the same, other geometrical arrangements may be selected. Not to mention good things.

As described above, according to the present invention, since the change in the reflection angle of the detection light at a specific position (reflector plate) on the cantilever can always be accurately obtained, the sample surface state can be measured accurately and stably. You can

Furthermore, by using the AFM of the present invention in an information processing apparatus using the AFM, it is possible to improve the accuracy of recording / reproducing information.

[0031]

EXAMPLES Examples of the present invention will be described below.

Example 1 An experiment was conducted using the optical leverage AFM of the present invention having the configuration shown in FIG. A mechanism for bringing the probe 103 close to the surface of the sample or relatively two-dimensionally scanning is omitted in this drawing because it is a conventionally known method.

As the cantilever 102, one side is 100 μ
A triangular Si cantilever (thickness: about 1 μm) of m was used. At the tip of the cantilever 102, there is a probe 103 formed by anisotropically etching Si, and at the tip of the cantilever on the back surface of the cantilever 102, photolithography is used to form gold with a size of about 5 μm. , Thickness 20
The reflection plate 204 was formed by depositing so as to be 0Å.

The detection light source 201 has a wavelength of 6328.
Å, He-Ne laser light with a beam diameter of 20 μm was used. The Glan-Thomson polarization prism was used as the polarizer 202, and the laser light (detection light 203) was incident on the cantilever reflection surface 109 as p-polarized light. The position of the light source 201 was roughly adjusted so that the incident angle at this time was around 75 °. As the photodetector 108, a conventionally known two-split photodetector (BPD) was used. After the distance between the probe 103 and the sample is set to a distance required for surface observation, the detection light 203 is irradiated onto the Si surface in the vicinity of the reflection plate 204, and the reflected light intensity detected by the photodetector 108 under this condition is changed. The incident angle was adjusted so that the total amount was the smallest. The position of the light source 201 was slightly adjusted so that the detection light 203 was incident on the entire reflection plate 204 while maintaining the incident angle (75.5 °).

When the surfaces of highly oriented graphite (hereinafter referred to as "HOPG") and mica were observed using such an apparatus, a good atomic arrangement image with less noise could be stably obtained.

Comparative Example 1 After performing the experiment described in Example 1, the same apparatus and the same method as in Example 1 were used except that the polarizer 202 was removed (at this time, the incident angle was readjusted). Is not performed, and the same incident angle (75.5 °) as that of the first embodiment is set), HOP
When the surfaces of G and mica were observed, a slight instability was observed during image output as compared with Example 1, and a slight decrease in the reproducibility of the output image during repeated scanning was observed.

Second Embodiment In the first embodiment, the polarizer 202 is removed, and instead, a Glan-Thompson polarizer is used as a polarizer at the position A in FIG. 5, and only the p-polarized component of the detection light 205 is detected by the photodetector 108. It was arranged so that would be incident.

When the surfaces of HOPG and mica were observed using this apparatus, a good atomic array image with less noise could be stably obtained, as in Example 1.

Example 3 An apparatus similar to Example 1 except that the cantilever 102 using Si ₃ N _{4 in place} of Si was used in Example 1.
When the surface of HOPG and mica was observed using the method,
Similar to Example 1, a good atomic array image with less noise could be stably obtained. The incident angle at this time was 76.0 °.

[0040]

As described above, according to the present invention, in the optical lever type AFM, the fluctuation amount of a specific position on the cantilever can be controlled without being affected by the non-essential fluctuation component contained in the detection light. Since the measurement can be performed, there is an effect that the detection accuracy of the sample surface state and the detection sensitivity are improved.

[Brief description of drawings]

FIG. 1 is a view showing a peripheral portion of a cantilever of a conventional optical lever type AFM.

FIG. 2 is a diagram showing a configuration of an optical lever type AFM of the present invention.

FIG. 3 is a diagram showing a relationship between an incident angle and reflectance when p-polarized light and s-polarized light having a wavelength of 6328Å are incident on a sample in which silicon and a gold thin film are deposited on the silicon.

FIG. 4 is a diagram illustrating an example of the present invention.

[Explanation of symbols]

 101 substrate 102 cantilever 103 probe 104 sample 105 unevenness of sample surface 106 detection light (incident light) 107 detection light (reflected light) 108 photodetector 109 cantilever reflection surface 201 light source 202 polarizing plate 203 detection light (incident light) 204 reflection Plate 205 Detection light (reflected light)

Claims (6)

[Claims] 1. A cantilever portion having a sharp probe,
Means for controlling the distance between the probe and the sample surface, means for relatively two-dimensionally scanning the probe on the sample surface, and atomic force generated between the probe and the sample surface In order to detect the change in the bending of the cantilever due to the vertical movement of the probe caused by the optical lever, an optical lever having a photodetector that detects the change in the reflection angle of the detection light incident on the cantilever on the cantilever reflecting surface is detected. In the atomic force microscope of the method, the detection light incident angle on the cantilever reflection surface is set so that the reflection loss of the p-polarized light component on the cantilever reflection surface becomes substantially maximum, and the cantilever reflection surface. The reflection of the p-polarized light component at the detection light incident angle set as described above is larger than that of the cantilever reflection surface at a position where it can be interlocked with the movement of the probe with high sensitivity. The has further the cantilever is reflected by the reflecting surface detection light incident on the light detector, atomic force microscope, which is a p-polarized light component. 2. The detection light incident on the cantilever reflection surface is a p-polarized light beam so that the detection light incident on the photodetector is a p-polarized component only. The atomic force microscope described. 3. A polarizing plate is provided between the cantilever reflection surface and the photodetector so that the detection light incident on the photodetector has only a p-polarized component. The atomic force microscope described. 4. The atomic force microscope according to claim 1, wherein the detection light incident on the cantilever is a single wavelength light. 5. The reflection plate is made of a metal of gold, platinum, aluminum, silver, or an alloy thereof,
5. The atomic force microscope according to claim 1, wherein a constituent material of the cantilever reflecting surface excluding the reflecting plate is silicon, silicon oxide or silicon nitride. 6. The incident light incident angle on the cantilever reflection surface is in the vicinity of Brewster's angle with respect to the constituent material of the cantilever reflection surface excluding the reflection plate, according to any one of claims 1 to 5. Atomic force microscope.