JPH08313542A - Scanning probe microscope - Google Patents

Abstract

PURPOSE: To provide a scanning probe microscope which can measure a sample with high resolution by only detecting the vibrational component of a probe with high accuracy. CONSTITUTION: A scanning probe microscope is provided with a displacement detector 4 which optically detects the displacement of the front-side measuring point 2a and base-side measuring point 2b of a cantilever 2 at the same time and signal processing circuit 48 which performs differential calculation on the detected signals of the detector 4 so as to only measure the vibrational component of the cantilever after separating the component from the vibration component of a whole system. The detector 4 is provided with an illuminating optical system which simultaneously projects first and second laser beams 28a and 28b for measurement upon the measuring points 2a and 2b, first and second critical-angle prisms 42a and 42b which change the propagated quantities of first and second reflected beams 38a and 38b from the measuring points 2a and 2b in accordance with the angles of incidence of the reflected beams 38a and 38b, and first and second four-divided photodiodes 46a and 46b which output signals corresponding to the variation of the received quantities of the reflected beams 38a and 38b propagated through the prisms 42a and 42b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope used for observing a sample with atomic resolution.

[0002]

2. Description of the Related Art Conventionally, a scanning probe microscope (SPM; SPM) has been used as an apparatus for observing a sample with atomic resolution.
canning probe microscope) is known. As an example of such an SPM, a scanning tunneling microscope (STM; Sc; Sc) using a Binnig or a roller (Rohrer) is used.
anning Tunneling Microscope) was invented. But,
In this STM, the samples that can be observed are limited to conductive samples. Therefore, atomic force microscope (AFM; AtomicFo) is used as a device that can observe an insulating sample with atomic resolution using STM element technology such as servo technology.
rce Microscope) has been proposed (JP-A-62-1303).
No. 02).

The AFM structure is similar to the STM and is positioned as one of scanning probe microscopes. Such an AFM includes a probe having a sharply pointed protrusion (probe) at its free end. When the probe is brought close to the sample, the free end of the probe is displaced by the interaction force (atomic force) acting between the atom at the probe tip and the atom on the sample surface. While measuring the change in vibration amplitude generated at the free end electrically or optically, the XY probe is moved along the sample surface.
By scanning in the direction, it is possible to three-dimensionally capture the unevenness information of the sample and the like (hereinafter referred to as prior art 1).

As a technique for detecting the vibration of the probe at the time of such AFM measurement, for example, Japanese Patent Laid-Open No. 4-1 is used.
As disclosed in Japanese Patent No. 618088, a method applying a defocus detection method using a critical angle prism (hereinafter referred to as prior art 2), or a probe as disclosed in, for example, Japanese Patent Laid-Open No. 6-26852. It is also possible to apply a method of optically detecting the displacement of the front end and the base end (hereinafter referred to as prior art 3).

[0005]

By the way, the vibration component generated in the probe includes the vibration component of the system of the scanning probe microscope other than the probe. However, in the detection method combining the conventional techniques 1 to 3,
Since it is not possible to separately detect the vibration component of the entire system of the scanning probe microscope and the vibration component of the probe itself, it is not possible to detect only the vibration component of the probe with high accuracy, and the high resolution sample It was difficult to measure.

The present invention has been made to solve such a problem, and an object thereof is to detect a sample with a high resolution by detecting only a vibration component of a probe with high accuracy. Type probe microscope.

[0007]

In order to achieve such an object, the present invention provides a scanning probe microscope including a probe having a base end supported and a tip displaceable. Displacement detection means for optically detecting the displacement of the tip end side and the base end side of the probe simultaneously, so that only the vibration component of the probe is separated and measured from the vibration component of the entire system of the scanning probe microscope, And a calculation unit that performs a predetermined calculation on the detection signal detected by the displacement detection unit.

Further, in the scanning probe microscope of the present invention, the displacement detecting means includes a first displacement detecting optical system for optically detecting a displacement of the probe on the tip end side, and a displacement on the base end side of the probe. And a second displacement detecting optical system for optically detecting the difference between the output signals from the first and second displacement detecting optical systems. An arithmetic processing circuit for performing at least one of the above is provided.

Further, in the scanning probe microscope of the present invention, the first and second displacement detection optical systems include an illumination optical system for irradiating the distal end side and the proximal end side of the probe with measuring light at the same time. First and second critical angle prisms that change the amount of transmitted light of each reflected light corresponding to the incident angle of each reflected light from the tip end side and the base end side of the probe, and the first and second critical angle prisms. It is provided with first and second light receiving elements that receive each of the reflected lights transmitted through the prism and output a signal corresponding to a change in the amount of received light.

[0010]

The displacement detecting means optically detects the displacements of the probe on the distal end side and the proximal end side at the same time. At this time, the detection signal output from the displacement detection means is subjected to a predetermined calculation by the calculation means. As a result, only the vibration component of the probe is separated and measured from the vibration component of the entire system of the scanning probe microscope.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning probe microscope according to an embodiment of the present invention will be described below with reference to the accompanying drawings. FIG.
As shown in FIG. 3, the scanning probe microscope of the present embodiment is separated from the tip end side of the cantilever 2 in order to separate and detect only the vibration component of the probe, that is, the cantilever 2 from the vibration component of the entire system of the scanning probe microscope. A displacement detector 4 that simultaneously optically measures the displacement on the base end side is provided.

In such a scanning probe microscope, the sample 6 is placed on a tube type piezoelectric scanner 8 which is capable of scanning in the X and Y axis directions, and the tube type piezoelectric scanner 8 has a Z axis. Mirror body 12 through the stage 10
It is attached on the base 12a.

The displacement detector 4 is attached to the upper side of the mirror body 12 and is configured to emit a measuring laser beam in the field of view of the objective lens 14. The cantilever 2 has a holder portion 18 at the base end portion thereof via the support portion 16.
The holder portion 18 is fixed to the laminated piezoelectric body 20 supported by the mirror body 12, while being positioned within the observation visual field of the objective lens 14 while being supported by the mirror body 12. As a result, by applying a predetermined voltage to the laminated piezoelectric body 20,
The cantilever 2 can be made to approach the sample 6 roughly and finely.

The displacement detector 4 also includes an observation optical system 22.
CCD camera 24 is optically connected via
With these observation optical system 22 and CCD camera 24,
The relative position of the cantilever 2 with respect to the sample 6 and the spot position of the measuring laser beam with which the cantilever 2 is irradiated can be optically observed, and the state of the surface of the sample 6 can be optically observed. .

FIG. 2 schematically shows the internal structure of the displacement detector 4 applied to the scanning probe microscope of this embodiment and the arrangement of the objective lens 14 and the cantilever 2. As shown in FIG. 2, the first and second semiconductor lasers 2
The first and second measurement laser beams 28a and 28b emitted from 6a and 26b are converted into parallel light beams by the first and second collimating lenses 30a and 30b, and thereafter,
The prism 32 is irradiated.

The first and second measuring laser beams 28a and 28b irradiated on the prism 32 are converted into parallel beams and propagated in the same plane, and then the objective is converted by the polarization beam splitter 34 which functions as an optical isolator. Lens 1
It is reflected in four directions.

The first and second measurement laser beams 28a and 28b reflected from the polarization beam splitter 34 are λ /
After being converted from linearly polarized light to circularly polarized light by the 4 plate 36, a crossing angle θ is formed at the principal point 14a of the objective lens 14 and light is focused on the tip side measurement point 2a and the base end side measurement point 2b of the cantilever 2, respectively. To do. Specifically, the first measurement laser beam 2
8a is focused on the tip side measurement point 2a, and the second measurement laser beam 28b is focused on the base side measurement point 2b. The optical axis (generally, the crystal axis) of the λ / 4 plate 36 applied to this embodiment has the first and second measurement laser beams 28.
It is assumed that they are arranged so as to form an angle of 45 ° with respect to the optical axes of a and 28b.

In the present embodiment, the crossing angle θ is tan (θ / 2) = (, where L is the distance between the distal measurement point 2a and the proximal measurement point 2b and f is the focal length of the objective lens 14. L / 2) / f.

Therefore, the first and second semiconductor lasers 26
a and 26b are arranged so as to satisfy the above relationship. The principal point 14a of the objective lens 14 means the intersection of the principal plane of the objective lens 14 and the optical axis,
The distance between the principal point 14a and the focal point of the objective lens 14 is called the focal length f.

The first and second reflected lights 38 reflected from the tip side measurement point 2a and the base side measurement point 2b of the cantilever 2.
a and 38b are again from the objective lens 14 to the λ / 4 plate 36.
Is transmitted to the polarization beam splitter 34 via.

In this case, the first wave transmitted to the λ / 4 plate 36
The second reflected light 38a and the second reflected light 38b are circularly polarized light, but once again transmitted through the λ / 4 plate 36, the first and second reflected lights 38a and 38b are transmitted.
The reflected light 38a, 38b of
The light is transmitted to the polarization beam splitter 34 after being converted into linearly polarized light having different polarization planes.

Therefore, the first and second reflected lights 38a and 38b transmitted to the polarization beam splitter 34 are transmitted to the beam splitter 40 after passing through the polarization beam splitter 34.

The first and second reflected lights 38a and 38b transmitted to the beam splitter 40 are transmitted to the first critical angle prism 42a after a part of the light is transmitted through the beam splitter 40, The remaining light is reflected from the beam splitter 40 and then propagated to the second critical angle prism 42b.

As shown in FIGS. 3 (a) and 3 (b), the first and second critical angle prisms 42a and 42a applied to the present embodiment.
The apex angle φ of 42b is equal to that of the first and second reflected lights 38a, 38.
b is designed to be totally reflected in the first and second critical angle prisms 42a and 42b. Specifically, when the incident angle (that is, the critical angle) of the first and second reflected lights 38a and 38b at the time when the total reflection starts in the first and second critical angle prisms 42a and 42b is θc, The vertical angle φ is φ> θc
Is designed to satisfy the relationship.

In this case, the apex angle φ, the critical angle θc, and the crossing angle θ
The relationship with and satisfies the following relationship: tan φ = (sin2θc) / {cos (θ / 2)}.

According to this relationship, for example, the 20 × objective lens 14 (focal length f = 9 mm) is used to measure the tip side measurement point 2a and the base end side measurement point 2b with a mutual interval of 180 μm. In this case, the first and second critical angle prisms 4
BK7 (wavelength 656.3 nm) as a material for 2a and 42b
, The critical angle θc
Is 1.3 degrees. As a result, the apex angle φ of the first and second critical angle prisms 42a and 42b is 44.76 degrees.

As shown in FIG. 2, the first and second reflected lights 38a and 38b transmitted to the first and second critical angle prisms 42a and 42b have first and second critical angles. After being reflected in the prisms 42a and 42b, they are reduced and projected onto the first and second four-division photodiodes 46a and 46b by the first and second condenser lenses 44a and 44b.

The first and second four-division photodiodes 46a and 46b are arranged closer to the lens side than the focal positions of the first and second condenser lenses 44a and 44b, respectively.

A method for detecting the displacement of the tip side measurement point 2a and the base end side measurement point 2b of the cantilever 2 by the above displacement detector 4 will be described below. The displacement detection method used in this embodiment is disclosed in, for example, Japanese Patent Laid-Open No. 59-9000.
The method disclosed in JP-A No. 7 and JP-A-60-38606 is adopted.

When the tip side measurement point 2a and the base end side measurement point 2b of the cantilever 2 are located at the focal point of the objective lens 14, the tip side measurement point 2a and the base end side measurement point 2b are moved to the objective lens 14. The first and second reflected lights 38a and 38b propagated through the light beams become parallel light beams. Further, when the tip end side measurement point 2 a and the base end side measurement point 2 b of the cantilever 2 are positioned closer to the lens side than the focal position of the objective lens 14, the tip end side measurement point 2
The first and second reflected lights 38a and 38b transmitted from a and the measurement point 2b on the base end side via the objective lens 14 become divergent light fluxes. Also, the measurement point 2a on the tip side of the cantilever 2
And the proximal measurement point 2b is located away from the lens with respect to the focal position of the objective lens 14, the objective lens 14 is measured from the distal measurement point 2a and the proximal measurement point 2b.
First and second reflected lights 38a, 38 transmitted through the
b is a condensed light flux.

That is, the measurement point 2 on the tip side of the cantilever 2
When a and the measurement point 2b on the base end side are deviated from the focal position of the objective lens 14, in both cases, the non-parallel light flux enters the first and second critical angle prisms 42a and 42b.

The first and second critical angle prisms 42a, 4
2b is designed to totally reflect the parallel light flux. Therefore, when the non-parallel light flux is incident on the first and second critical angle prisms 42a and 42b, the central ray thereof is incident at the critical angle θc, but the luminous flux deviated to one side from the central ray is incident on the incident light. The angle is smaller than the critical angle. Therefore, a part of the light flux is emitted to the outside of the prism, and the remaining light is reflected. On the contrary, the incident angle of the light beam shifted from the central ray to the other becomes larger than the critical angle. Therefore, all the luminous fluxes are totally reflected.

Such optical transmission process is the first and second
In the critical angle prisms 42a and 42b of (1), a light beam incident at an incident angle smaller than the critical angle and a light beam incident at an incident angle larger than the critical angle are repeated by being repeated several times (two times in this embodiment). The difference in the amount of transmitted light (the amount of light flux transmitted in the first and second critical angle prisms 42a and 42b) between the two is enlarged.

Moreover, in this case, the tip side measurement point 2a and the base end side measurement point 2b of the cantilever 2 are close to the lens side with respect to the focal position of the objective lens 14, and are separated from the lens. Then, the magnitude of the transmitted light amount difference is reversed.

In the present embodiment, the first reflected light 3 from the measurement point 2a on the tip side of the cantilever 2 among such luminous flux 3 is reflected.
8a is reduced and projected onto the light-receiving surfaces A and B of the first 4-division photodiode 46a and the light-reception surfaces E and F of the second 4-division photodiode 46b, and from the base end side measurement point 2b of the cantilever 2. The second reflected light 38b is reflected by the first 4
The images are reduced and projected onto the light receiving surfaces C and D of the divided photodiode 46a and the light receiving surfaces G and H of the second four-divided photodiode 46b.

In this case, the displacement state of the vibration amplitude generated at the tip end and the base end of the cantilever 2 is reflected on the first and second four-division photodiodes 46a and 46b as a light quantity distribution. .

Here, the light-receiving surfaces A, B, C, D, E, of the first and second four-division photodiodes 46a, 46b.
The signals photoelectrically converted via F, G, and H are V _A , V _B ,
If V _C , V _D , V _E , V _F , V _G , and V _H are set, the above-mentioned signals are subjected to predetermined arithmetic processing via the signal processing circuit 48, whereby the displacement of the tip end and the base end of the cantilever 2 is calculated. It is possible to detect at the same time.

Specifically, as shown in FIG. 1, between the sample 6 and the cantilever 2 in a state where the cantilever 2 is excited by vibrating the laminated piezoelectric body 20 of the scanning probe microscope of the present embodiment. The displacement of the vibration amplitude of the tip end and the base end of the cantilever 2 caused by the interaction is measured.

As a result, the displacement signal Z of the tip side measuring point 2a of the cantilever 2 detected by the signal processing circuit 48 is detected.
_{1, Z 1 = {(V A} -V B) + (V E -V F)} / (V A +
_{V B + V E + V F} ) , and the displacement signal Z ₂ proximal measuring point 2b of the cantilever _{2, Z 2 = {(V C} -V D) + (V G -V H)} / (V C +
V _D + V _G + V _H ).

Then, in the signal processing circuit 48, only the displacement of the vibration amplitude at the tip and the base end of the cantilever 2 is detected by calculating the difference Z ₁ -Z ₂ of the displacement signals.

As described above, according to the present embodiment, the difference between the displacement signal Z ₁ of the measuring point 2a on the tip side of the cantilever 2 and the displacement signal Z ₂ of the measuring point 2b on the base side of the cantilever 2 is simply executed to perform the scanning type operation. Only the displacement component of the vibration amplitude of the cantilever 2 can be accurately and easily separated and detected from the vibration component of the entire system of the probe microscope. In addition, according to the present embodiment, since the displacement measurement of the tip end and the base end of the cantilever 2 is performed by the same displacement detector 4, the displacement signal difference Z ₁ -Z is simply executed without executing complicated signal processing. It is possible to easily measure only the deflection of the cantilever 2 with high accuracy simply by calculating ₂ .

As another calculation method, it is also possible to perform signal processing by the following division calculation. The displacement signal (vibration) Z _{1 at} the tip side measurement point 2a of the cantilever 2 when the cantilever 2 vibrates at the angular frequency ω is

[0043]

[Equation 1] It is expressed as

Where i is an imaginary unit, t is time, and | Z ₁
| Is the amplitude of vibration, and φ ₁ is the phase of vibration. Similarly, the displacement signal (vibration) Z ₂ at the measurement point 2b on the base end side of the cantilever ₂ is

[0045]

[Equation 2] It is expressed as

Where i is an imaginary unit, t is time, and | Z ₂
Is the amplitude of vibration and φ ₂ is the phase of vibration. Displacement signals Z ₁ , Z calculated from these equations (1) and (2)
_When the division operation of Z ₁ / Z ₂ is performed based on ₂ ,

[0047]

(Equation 3) Therefore, the shift amount of the phase φ ₁ with respect to the phase φ ₂ is known.
That is, the vibration and phase of the tip portion with respect to the base end portion of the cantilever 2 can be obtained.

Therefore, by performing such division operation,
Measurement point 2a on the tip side of cantilever 2 and measurement point 2b on the base end side
Since the vibration amplitude ratio of the cantilever 2 can be known, it becomes possible to separate and obtain only the deflection of the cantilever 2 with higher accuracy.
It is possible to measure the sample 6 with high resolution.

[0049]

According to the present invention, it is possible to detect the displacement of the probe on the distal end side and the proximal end side and to perform at least one of the difference calculation and the division calculation of the detection signals. Only the vibration component of the probe can be separated from the vibration component for measurement. As a result, it becomes possible to provide a scanning probe microscope capable of measuring a sample with high resolution.

[Brief description of drawings]

FIG. 1 is a side view schematically showing the configuration of a scanning probe microscope according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing an internal configuration of a displacement detector applied to the scanning probe microscope of the present invention and an arrangement of an objective lens and a cantilever.

FIG. 3A is a perspective view showing a state in which reflected light is totally reflected in a critical angle prism applied to the scanning probe microscope of the present invention, and FIG. 3B is a perspective view of FIG. The longitudinal cross-sectional view of the critical angle prism shown.

[Explanation of symbols]

2 ... Cantilever, 2a ... Tip side measurement point, 2b ... Base end side measurement point, 4 ... Displacement detector, 28a ... 1st measurement laser beam, 28b ... 2nd measurement laser beam, 38a ... 1st
Reflected light, 38b ... second reflected light, 42a ... first critical angle prism, 42b ... second critical angle prism, 46a ...
First 4-division photodiode, 46b ... Second 4-division photodiode, 48 ... Signal processing circuit.

Claims (3)

[Claims] 1. A scanning probe microscope including a probe having a base end supported and a distal end freely displaceable, wherein the displacement for optically detecting the displacement of the probe at the front end side and the base end side at the same time. A detection means, and an operation means for performing a predetermined operation on the detection signal detected by the displacement detection means so that only the vibration component of the probe is separated and measured from the vibration component of the entire system of the scanning probe microscope. And a scanning probe microscope. 2. The displacement detecting means comprises a first displacement detecting optical system for optically detecting a displacement of the probe on the tip end side, and a second displacement detecting optical system for optically detecting a displacement of the probe on the base end side. A displacement detection optical system, and the arithmetic means includes an arithmetic processing circuit for performing at least one of a difference arithmetic operation and a division arithmetic operation on each output signal from the first and second displacement detection optical systems. The scanning probe microscope according to claim 1, wherein the scanning probe microscope is provided. 3. The first and second displacement detection optical systems include an illumination optical system that irradiates measurement light to the tip end side and the base end side of the probe at the same time, and a tip end side and a base end side of the probe. Of the first and second critical angle prisms that change the amount of transmitted light of the respective reflected lights according to the incident angle of each of the reflected lights, and the waves are transmitted through the first and second critical angle prisms. The scanning probe microscope according to claim 2, further comprising first and second light receiving elements that receive each of the reflected lights and output a signal corresponding to a change in the amount of received light.