JPH0961441A - Scanning probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning probe for realizing an improved scanning-type probe microscope for measuring even a large sample. SOLUTION: One edge of a tube scanner 2 is fixed to a post (not shown here) and a housing 101 is mounted to a free edge. An objective lens 8 with a light axis 104 which matches a center axis 103 of the tube scanner 2 when it is neutral and a reflection mirror 102 which is fixed to the optical axis 104 at an angle of 45 deg. are provided at the housing 101. The cross point between the reflection mirror 102 and the light axis 104 is located near a side focusing surface at the rear of the objective lens 8. A cantilever 6 with a tip 7 at the tip is fixed to the housing 101 vertically to a paper surface on the front focusing surface of the objective lens 8. A member for constituting a critical angle focusing detection optical system is fixed to a fixing position for the base along with the objective lens 8 outside the housing 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe used in a scanning probe microscope, that is, a cantilever having a tip at its free end that interacts with quantum mechanical elements such as tunnel electrons and atomic molecules, and a cantilever. The present invention relates to a scanning probe including a scanning unit and a detection optical system that detects vertical movement and twist of a cantilever.

[0002]

2. Description of the Related Art A scanning probe microscope (SPM) is a device for observing and measuring an ultrafine structure of a substance, and includes a scanning tunneling microscope (STM) and an atomic force microscope (AF).
M), a lateral force microscope (LFM) and the like.

As an example of SPM, a device shown in FIG. 6 is known. The sample stage 4 is fixed to the free end of the tube scanner 2 fixed to the base 1, and the sample 5 is placed on the sample stage 4.
The tube scanner 2 is an actuator configured by providing one common electrode on the inside of a cylindrical piezoelectric body and four drive electrodes 3 on the outside thereof, and independently applying a voltage to each drive electrode. By controlling, the free end can be moved like a pendulum in any direction.
As a result, the sample 5 is raster-scanned in a plane substantially perpendicular to the optical axis of the detection optical system 100.

Above the sample 5, there is a tip 7 having a sharp tip at the molecular level for quantum mechanical interaction with the sample 7.
Is arranged. The tip 7 is provided at the tip of the cantilever 6 and is supported in a cantilever shape. In addition, a detection optical system 100 using the critical angle method for detecting the movement of the cantilever 6 is provided. This detection optical system 10
0 checks the movement of the cantilever 6 by checking the in-focus state with respect to the back surface of the cantilever 6. The cantilever 6 and the detection optical system 100 are provided independently of the above-mentioned scanning mechanism.

When the sample 5 is raster scanned,
The free end of the cantilever 6 is slightly displaced by the quantum mechanical interaction force generated between the tip of the chip 7 and the surface of the sample 5 in accordance with the minute unevenness (micron order to Angstrom order) on the surface of the sample 5. .

By examining the displacement of the free end of the cantilever 6, that is, the displacement of the tip 7, for example, from a submicron surface structure such as a pit shape of a CD to a structure of less than angstrom such as an atomic arrangement of graphite or mica. Up to and can be imaged and observed.

Now, the operation of the detection optical system 100 will be described. The laser light emitted from the laser diode (LD) 9 is collimated by the collimator lens 10, reflected by the polarization beam splitter (PBS) 11, and circularly polarized by the λ / 4 plate 12, and then cantilevered by the objective lens 8. It is focused on the back surface of 6. The reflected light from the cantilever 6 is incident on the objective lens 8 and is linearly polarized by the λ / 4 plate 12 so as to be orthogonal to the first one.
1 is transmitted, and is divided into two by the half mirror 13. One is incident on the two-divided detector 15 via the critical angle prism 14 and the other is incident on the two-divided detector 17 via the critical angle prism 16.

Now, the relationship between the position of the cantilever 6 and the output of the two-divided detector will be described with reference to FIG. First, it is considered that the free end of the cantilever 6 is displaced in the vertical direction while maintaining the horizontal state. When the cantilever 6 is in the in-focus position, the two-divided detector 1
The beam incident on 5 is, as shown in FIG.
The intensity distribution is uniform, and the outputs A and B of the light receiving portions of the two-divided detector 15 are equal. On the other hand, when the cantilever 6 is in the out-of-focus position, the beam incident on the critical angle prism 14 is not a parallel light beam but a converging light beam or a divergent light beam. However, as shown in FIG. 5 (b) or FIG. 5 (c), the intensity distribution becomes non-uniform, and the outputs A and B of the respective light receiving portions become unequal. Therefore, the vertical displacement of the cantilever 6 can be obtained by examining AB. Although this description relates to the two-divided detector 15, the same applies to the two-divided detector 17.

Up to now, the free end of the cantilever 6 has always been horizontal, but in reality, its inclination also changes with the vertical displacement. When the free end of the cantilever 6 is tilted, the beam incident on the two-divided detector 15 is shown in FIG. 5D because the reflected light deviates from the optical axis even if the position of the cantilever is in focus. As described above, it is displaced from the center position. Therefore, even if the cantilever 6 is at the in-focus position, AB does not become 0.

In order to correct the error due to the movement of the beam with respect to this inclination, the detection optical system 100 includes two critical angle prisms 14 and 1 arranged in the positional relationship shown in FIG.
6, the displacement of the free end of the cantilever 6 is (A−B) + (C−D) where the outputs of the light receiving portions of the two-divided detectors 15 and 17 are A, B, C, and D, respectively. Required by. The beams incident on the two-divided detectors 15 and 17 when the cantilever 6 is tilted and in the in-focus position are shown in FIGS. 5 (d) and 5 (e). Even if it is tilted, if it is in the in-focus position, (AB) + (CD) becomes 0, and the cantilever 6
The error caused by the movement of the beam due to the inclination of is automatically corrected.

From the description of this inclination correction, it can be easily considered to be applied to LFM. That is, if the cantilever 6 is arranged so as to extend in the direction perpendicular to the paper surface, not in the in-plane direction as shown in the drawing, the torsion of the cantilever 6 due to the lateral force will not occur in FIGS. 5D and 5E. Appears as a beam shift of. Therefore, while controlling the Z direction of the tube scanner 2 so that (A−B) + (C−D) becomes 0, (A−B) + (D−
If C) is calculated, the torsion angle of the cantilever can be measured. Either AB or DC may be used, but the sensitivity is improved by integrating both.

[0012]

The device shown in FIG.
By combining a tube scanner and a focus detection optical system based on the critical angle method, it is possible to simultaneously measure extremely small vertical displacement and twist angle of the cantilever. AFM and LFM
Is very useful.

However, the apparatus of FIG. 6 has the following problems. The need for the study of such an ultrafine structure is spreading to the manufacturing fields of semiconductors and liquid crystal panels, and thus observation and measurement of large samples are inevitably desired. On the other hand, in the apparatus shown in FIG. 1, the sample scanning mechanism is extremely small and does not have the ability to mount an 8-inch wafer or a large liquid crystal panel.

If an attempt is made to scan a sample by using a large scanning stage instead of the tube scanner, the resolution of stage movement will be insufficient due to the order of magnitude. That is, as described above, the purpose of this type of device is to measure a fine structure from the micron order to the angstrom order, and the lateral resolution for the measurement also requires a similar level. In a stage where a liquid crystal panel can be mounted, it is difficult to achieve this accuracy, and the scanning speed is drastically reduced.

If the detection optical system 100 is supported by a tube scanner and an attempt is made to scan it, the load of the detection system 100 becomes excessive with respect to the mechanical capacity of the piezoelectric element, and the vibration characteristics of the tube scanner. Deteriorates and cannot withstand high-speed scanning.

Further, if only the cantilever 6 is to be scanned, the scanning range is desired to be about 100 μm × 100 μm at maximum, so that the measurement beam may deviate from the cantilever 6 or the amount of movement of the beam position on the cantilever 6 may be increased. If it becomes large, a fatal measurement error may occur. It is an object of the present invention to provide a scanning probe for realizing a scanning probe microscope that can handle a large sample.

[0017]

A scanning probe according to the present invention comprises a cantilever having a sharp tip at its tip, an objective lens arranged so that the cantilever is positioned at its front focal plane, and an optical axis of the objective lens. It is a plane mirror that is tilted with respect to the objective lens. The plane mirror whose intersection with the optical axis of the objective lens is located near the back focal plane of the objective lens, the cantilever, the objective lens, and the plane mirror are housed. It has a housing that holds it in a predetermined positional relationship, a scanner that movably supports the housing, and a detection optical system that is provided independently of the housing and that optically detects displacement and twist of the cantilever.
The detection optical system emits a parallel light beam toward the plane mirror, and the parallel light beam is reflected by the plane mirror and focused on the cantilever by the objective lens. The light reflected by the cantilever is reflected by the plane mirror toward the detection optical system through the objective lens, and the detection optical system receives the reflected light and detects displacement and twist of the cantilever based on the reflected light.

For example, the detection optical system has means for detecting the position of the beam of reflected light and means for detecting the in-focus state by the critical angle method. Alternatively, the detection optical system has means for detecting the position of the reflected light beam and means for detecting the in-focus state by the confocal method.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The first embodiment will be described with reference to FIG. In the figure, the same members as in the conventional example are indicated by the same reference numerals.

The sample 5 is placed on an XY stage (not shown), and the measurement site in the relatively large sample 5 is placed near the central axis 103 of the tube scanner 2 using the XY stage. It

The tube scanner 2 has one end fixed to a column (not shown), and the housing 101 at the free end.
Is attached. In the housing 101, the objective lens 8 having an optical axis 104 which coincides with the central axis 103 when the tube scanner 2 is in a neutral state
And a reflection mirror 102 fixed to the optical axis 104 at an angle of 45 °. Reflection mirror 102 and optical axis 1
The intersection of 04 is located near the back focal plane of the objective lens 8.

On the front focal plane of the objective lens 8, the chip 7 is placed.
A cantilever 6 having a tip is fixed to the wall surface of the housing 101 in a direction extending in a direction perpendicular to the paper surface. Similar to the conventional example, the tube scanner 2 has four drive electrodes (not shown) on the outside, and by controlling the voltage applied thereto, the free end can be moved like a pendulum in any direction. As a result, the chip 7 is raster-scanned on the surface of the sample 5.

On the outside of the housing 101, members other than the objective lens 8 constituting the same critical angle focusing detection optical system 100 as in the conventional example are arranged at a fixed position with respect to the base.

Incident light from the LD 9 (the principal ray of which is designated by reference numeral 1)
(Indicated by 05) is collimated by the collimator lens 10 into a parallel light beam, reflected by the polarization beam splitter 11, and
It passes through the / 4 plate 12 and enters the reflection mirror 102. The incident light 105 is incident on the intersection of the optical axis 104 of the objective lens 8 and the reflection mirror 102 when the tube scanner 2 is in the neutral position. However, as shown in FIG. 1, when the tube scanner 2 is moved, the incident light 105 is incident slightly below the above-mentioned intersection. The angle formed by the incident light 105 reflected by the reflection mirror 102 with respect to the optical axis 104 is equal to the angle θ formed by the optical axis 104 and the central axis 103 and is θ. Therefore, the incident light 105 is condensed at a point distant from the optical axis 104 by ftan θ with respect to the back surface of the cantilever 6 with the focal length of the objective lens 8 as f.

Detection light 106 reflected by the cantilever 6
Enters the reflecting mirror 102 through the objective lens 8. The incident position is located slightly above the intersection of the reflection mirror 102 and the optical axis 104. Therefore, the detection light 106 reflected by the reflection mirror 102 shifts upward by δy with respect to the incident light 105 and travels toward the λ / 4 plate 12. The detection light 106 that has passed through the λ / 4 plate 12 passes through the polarization beam splitter 11, is divided into two by the half mirror 13, and enters the two-divided detectors 15 and 17 via the critical angle prisms 14 and 16, respectively.

When this scanning probe is used in a lateral force microscope (LFM), the incident light 105
The deviation δy of the detection light 106 with respect to is overlapped as a measurement error with respect to the torsion angle of the cantilever 6, as can be easily understood from the description of the conventional example. (Note that, when this scanning probe is used for an AFM, since the vertical movement of the tip 7 is simply measured, an error due to the tilt is corrected by the two critical angle prisms as described above, so there is no problem). Therefore, if the deviation δy between the incident light 105 and the detection light 106 is so small as to be negligible to the LFM, the twist angle of the cantilever 6 can be accurately measured in the entire scanning region without any correction to the detection signal of the LFM. Can be measured.

In order to examine whether or not this condition can be satisfied, the formula for δy was derived using the optical path diagram of FIG. An intersection 102c of the optical axis 104 of the objective lens 8 and the reflection mirror 102 from the fulcrum of the tube scanner 2
Up to 1 and the tube scanner 2 scans, the angle formed by the optical axis 104 with respect to the central axis 103 is θ, and the swing width of the intersection 102c is w.
The increase amount Δ of is given by the following equation.

[0028]

[Equation 1]

The intersection 10 of the reflecting mirror 102 and the optical axis 104
When the distance from 2c to the rear focal point of the objective lens 8 is z and the focal length of the objective lens 8 is f, the angle Φ at which the incident light 105 enters the cantilever 6 is given by the following equation.

[0030]

[Equation 2]

After that, the formula of the reflection mirror 102 with respect to the appropriate xy coordinate axes and the formula of the detection light 106 from the objective lens 8 to the reflection mirror 102 are derived, and the intersection point coordinates (x, y).
Finally, the deviation δy is obtained by the following equation through the work of obtaining

[0032]

(Equation 3)

The simulation result based on the equation (3) is shown in FIG. The horizontal axis represents the inclination θ (w) of the optical axis 104 with respect to the scanning width w, and the vertical axis represents δy. The manner in which δy changes with the position of the reflection mirror 102 can be well understood.

As an example of numerical values, l = 80 mm, f
= 5 mm, θ = 0.0358 °, w = 50 μm, z = 0
In this case, δy = 0.0287 μm. As LFM, δy with respect to the torsion angle of the cantilever 6 is also given by the formula (3).
Can be calculated using. However, the twist angle is φ
Then, Φ + 2φ must be used instead of Φ in equation (3).

As a numerical example of δy with respect to φ, θ = 0,
If φ = 2 ° and other conditions are the same as the above numerical example,
δy = 349.634 μm. Therefore, the S / N is
It is 0.8 × 10 -4, which can be considered as a level that does not require correction.

Since the shift amount between the focal point on the cantilever 6 and the optical axis 104 is ftan θ as described above, ± 3.1 μ
m, the measurement beam is out of the cantilever 6,
A large error does not occur in the measurement of the vertical movement of the cantilever 6.

Further, as a secondary advantage, the cantilever 6
When the beam is defocused in a tilted state, the beams incident on the two-divided detectors 15 and 17 have the beams shown in FIGS.
As shown in (g), it is general that the boundary between the dark part (the part shown by the dots) and the bright part of the intensity distribution deviates from the dividing line of the detector. Therefore, in the tilt correction described in the conventional example, the focusing point is not erroneous, but the linearity of the signal with respect to the defocus amount slightly changes. However, in the present invention, since z is zero or extremely small, the above deviation may be considered to be approximately Δ. Because the boundary line of the change of the intensity distribution corresponds to the alternate long and short dash line perpendicular to the objective lens 8 in FIG.
This always intersects the optical axis 104 at FB. Therefore, if there is an intersection 102c of the optical axis 104 of the reflection mirror 102 here, the deviation from the incident light 105 is Δ.

Incidentally, Δ under the conditions in the above-mentioned numerical example is only 15.6 nm if z = 0. Therefore,
The beam on the two-divided detectors 15 and 17 is shown in FIG.
As shown in (h) and FIG. 5 (i), the tilt correction exhibits an almost ideal effect.

Up to now, an optical system using the critical angle method has been described as an example of the optical system for detecting the movement of the cantilever, but the optical system for detection is not limited to this.
Next, another example of the detection optical system will be described with reference to FIG.

This detection optical system is the same as the optical system of FIG. 1 up to the half mirror 13, and in the subsequent parts, means for detecting the position of the beam and means for detecting the focused state by the confocal method. And have.

Specifically, as shown in FIG. 4, the detection optical system includes a position sensor 18 for checking the position of the beam reflected by the half mirror 13, a lens 19 for condensing the beam transmitted through the half mirror 13, A half mirror 20 that divides the beam that has passed through the lens 19 into two, a pinhole 21 that is arranged behind the focal point of the beam that has passed through the half mirror 20, and light that detects the intensity of light that has passed through the pinhole 21. The pinhole 2 arranged in front of the focal point of the beam reflected by the detector 22 and the half mirror 20.
3 and a photodetector 24 that detects the intensity of light that has passed through the pinhole 23.

The two pinholes 21 and 23 are arranged so as to be offset from each other by an equal distance from the focal point of the beam. Therefore, when the cantilever 6 is at the in-focus position, the light amounts detected by the two photodetectors 22 and 24 are equal, and the output difference between the two photodetectors 22 and 24 is zero.

When the cantilever 6 moves up and down to move out of the in-focus position, the focal point of the beam moves back and forth along the optical axis accordingly, so that the two photodetectors 22 and 24 are moved.
The amounts of light incident on are not equal. Therefore, the vertical movement of the cantilever 6 can be measured by checking the output difference between the two photodetectors 22 and 24.

When the cantilever 6 is twisted, the position of the beam incident on the position sensor 18 moves. Therefore, the twist of the cantilever 6 can be obtained by checking the incident position of the beam.

[0045]

According to the scanning probe of the present invention, a cantilever scanning type scanning probe microscope can be constructed, and a large sample such as a silicon wafer or an LCD substrate can be dealt with.

Since the detection optical system is provided independently of the housing, the load on the scanner is not significantly increased and the vibration characteristics are not significantly impaired.
Since the position of the plane mirror that intersects with the optical axis of the objective lens is located near the back focal plane of the objective lens, the deviation of the optical path caused by the scanning of the scanner is minimized and the measurement accuracy is remarkably high. It will not be damaged.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a scanning probe according to an embodiment of the present invention.

2 is a diagram showing an optical path in the scanning probe of FIG. 1. FIG.

FIG. 3 is a graph showing a relationship between an angle θ and a shift δy.

FIG. 4 is a diagram showing the configuration of another detection optical system that replaces the detection optical system of FIG.

5 is a diagram showing a beam pattern on a two-divided detector in the detection optical system using the critical angle method shown in FIG. 1 or FIG.

FIG. 6 is a diagram showing a conventional example of a scanning probe microscope.

[Explanation of symbols]

2 ... Tube scanner, 6 ... Cantilever, 7 ... Chip, 8 ... Objective lens, 9 ... Laser diode, 10 ...
Collimator lens, 11 ... Polarizing beam splitter, 1
2 ... λ / 4 plate, 13 ... Half mirror, 14 ... Critical angle prism, 15 ... Two-divided detector, 16 ... Critical angle prism, 17 ... Two-divided detector, 101 ... Housing, 1
02 ... Reflective mirror.

Claims (3)

[Claims] 1. A cantilever having a sharp tip at its tip, an objective lens arranged so that the cantilever is positioned at the front focal plane thereof, and a plane mirror arranged obliquely with respect to the optical axis of the objective lens. A plane mirror whose intersection with the optical axis of the objective lens is located near the back focal plane of the objective lens, a housing that houses the cantilever, the objective lens, and the plane mirror, and holds them in a predetermined positional relationship. It has a scanner that movably supports and a detection optical system that is provided independently of the housing and that optically detects displacement and twist of the cantilever.The detection optical system emits a parallel light beam toward a plane mirror. Then, the parallel light flux is reflected by the plane mirror and focused on the cantilever by the objective lens, and the light reflected by the cantilever passes through the objective lens to form a plane. Is reflected toward the detecting optical system by error, detection optical system detects the displacement and twisting of the cantilever on this basis it receives the reflected light, scanning probe. 2. The scanning probe according to claim 1, wherein the detection optical system has means for detecting the position of the beam of the reflected light and means for detecting the focused state by the critical angle method. 3. The scanning probe according to claim 1, wherein the detection optical system has means for detecting the position of the beam of the reflected light and means for detecting the in-focus state by the confocal method.