JPH0626853A - Interatomic force microscope - Google Patents

Abstract

PURPOSE:To obtain an interatomic force microscope which can observe a large sample. CONSTITUTION:A cantilever 32 is fixed to a supporting member 36, which is supported with an x-y-z scanner 34. A probe 28 and a reflecting surface 40 are provided at the free end of the cantilever. The supporting member 36 has a horizontally extending arm part 36a. A light source 42, which emits a laser beam, is attached to the tip part of the arm part. An objective lens 44 is arranged at a position where the focal point is located at the reflecting surface 40. A relay lens 52, whose magnificaion is equal to that of the objective lens 44, is arranged at a position where the focal point is located at the light source 42. A half mirror 48 and a mirror 50 are arranged at the upper side of the objective lens 44 and the relay lens 52, respectively, at the inclination of 45 deg. with respect to the optical axis. A mirror 54, which reflects the laser beam transmitted through the half mirror rightward, is provided at the upper side of the half mirror 48. A focusing detector 58 is arranged at the rear focal- point position of a lens 56, which is arranged at the right side of the mirror 54.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an atomic force microscope (AF
M). More specifically, the present invention relates to a cantilever displacement detection system that detects displacement of a cantilever.

[0002]

2. Description of the Related Art A cantilever displacement detection system of AFM includes
Interferometry, optical lever method, focus detection method, etc. are available. Interferometry is
A laser beam is applied to a mirror provided on the surface of the free end of the cantilever opposite to the probe, and the change in the intensity of reflected light caused by the displacement of the cantilever is detected using an interferometer. In the optical lever method, a change in the incident angle of a laser beam on a mirror caused by displacement of a cantilever is detected by the principle of optical lever as expansion of beam displacement on a beam receiver surface. The focus detection method detects displacement based on the focus state of the beam projected onto the detector from the mirror surface of the cantilever through an optical element such as a critical angle prism, a cylindrical lens, or a knife edge.

In the critical angle method, the laser beam incident on the prism is set so as to emerge from and enter the prism surface at a substantially critical angle. This laser beam is transmitted through the prism surface or reflected inside the glass with a slight change in the incident angle. That is, the transmittance and the reflectance change sharply with respect to the deviation angle. FIG. 2 shows a reflectance curve when the refractive index n of the glass material is 1.5. Here, the observation optical system integrated AFM disclosed in Japanese Patent Laid-Open No. 3-71001, in which the critical angle method is applied to a cantilever displacement detection system, will be described with reference to FIG.

The laser light emitted from the laser diode 87 is shaped into parallel light by the collimator lens 90 and is incident on the polarization beam splitter 86. The laser light reflected by the polarization beam splitter 86 is
Further, it is reflected by the half mirror 85, and the quarter wavelength plate 84
Incident on.

On the other hand, the illumination light emitted from the light source 96 of the observation illumination device is collimated by the lens 97 and reflected by the half mirror 92. The illumination light reflected by the half mirror 92 passes through the filter 91 and the half mirror 85 and enters the quarter wavelength plate 84.

The laser light and the illumination light passing through the quarter-wave plate 84 have different chief rays and enter the objective lens 83. When passing through the quarter-wave plate 84, the laser light is converted from linearly polarized light into circularly polarized light, and is condensed by the objective lens 83 on the upper surface of the cantilever 22 having the probe at the free end. On the other hand, the illumination light is condensed near the tip of the probe and illuminates the entire field of view.

The illumination light reflected from the sample 26 passes through the objective lens 83, the quarter-wave plate, the half mirror 85, the filter 94, and the half mirror 92, and the imaging lens 9
An image is formed by 3 and enters the prism 94. Part of the light incident on the prism 94 is reflected by the interface of the prism 94 and reaches the eyepiece lens 95. The light passing through the prism 94 is the video camera 2 including a CCD image element and the like.
It is incident on 7, converted into an image signal, and then the video monitor 2
It is sent to 8 and displayed. The quarter-wave plate 84 is arranged slightly inclined with respect to the optical axis so that the reflected light of the illumination light does not directly enter the observation optical system, and provides a clear visual field observation image without flare.

The laser light reflected on the upper surface of the cantilever 22 passes through the objective lens 83 and the quarter-wave plate, is reflected by the half mirror 85, and is guided to the polarization beam splitter 86. When passing through the quarter-wave plate 84,
The laser light is converted into linearly polarized light whose vibrating surface is rotated by 90 ° with respect to the time of incidence. The laser light incident on the beam splitter 86 is divided into two, one of which is radiated to the first two-divided light receiving element 89a through the first critical angle prism 88a, and the other of which is second light through the second critical angle prism 88b. The two-divided light receiving element 89b is irradiated. The critical angle method is used to detect the position of the cantilever. The principle of the critical angle method will be briefly described with reference to FIG. In the critical angle method, the critical angle prism c is arranged so that the angle formed by the parallel light flux and the reflecting surface of the prism becomes the critical angle when the parallel light flux enters from the lens b.

When the reflecting surface a is at the focal position of the objective lens b (the position shown by the solid line B), that is, when the beam is in focus, the reflected light from the reflecting surface a is collimated by the lens b. It is incident on the critical angle prism c. At this time, all the light flux is totally reflected by the reflecting surface of the prism, and 2
An equal amount of light is supplied to each photodiode of the divided light receiving element.

On the other hand, when the reflecting surface a is at a position closer to the focal point of the lens b (the position shown by the dotted line A), the light passing through the lens b becomes a divergent light beam and enters the critical angle prism c. On the contrary, when the reflecting surface a is at a position far from the focal point of the lens b (position shown by the dotted line B), the light passing through the lens b becomes a focused light flux and enters the critical angle prism c. In either case, the non-parallel light flux is incident on the critical angle prism c. In these cases, only the central ray is incident at the critical angle,
Since the incident angle of the light beam on one side from the center is smaller than the critical angle, part of the light is emitted outside the refraction prism and only the remaining light is reflected. On the contrary, the light beam on the opposite side of the center is totally reflected because the incident angle becomes larger than the critical angle. As a result, the amount of light incident on the two-divided light receiving element differs between the left and right photodiodes, and a signal corresponding to the difference in light amount is output from the output terminal f via the differential amplifier e. That is, the position of the reflection surface a is detected as the light amount difference on the detection surface of the two-divided light receiving element d.

As described above, since the light incident at an angle smaller than the critical angle is partially emitted to the outside of the critical angle prism every time it hits the reflecting surface, the light amount of the refraction component is significantly reduced. Therefore, the difference in the amount of light between the light incident at an angle smaller than the critical angle and the light incident at the angle larger than the critical angle is greatly expanded. Therefore, in order to improve the measurement accuracy, it is desirable that the reflection be repeated several times in the critical angle prism. In this embodiment, the detection light is reflected twice in the critical angle prism. The output of the photodiode PD1 of the first two-divided light receiving element is input to the inverting input terminal of the comparator 102, and the output of the photodiode PD2 is input to the non-inverting input terminal of the comparator 102, as shown in FIG. The difference between the outputs of the photodiode PD1 and the photodiode PD2 that is input is output from the comparator 102. On the other hand, the photodiode P of the second two-divided light receiving element
The output of D3 is input to the inverting input terminal of the comparator 104, the output of the photodiode PD4 is input to the non-inverting input terminal of the comparator 104, and the difference between the outputs of the photodiode PD1 and the photodiode PD2 is the comparator 104. Is output from. The outputs of the comparators 102 and 104 are added and input to one terminal of the comparator 106, and the result of comparison with the reference value is output. Therefore, a signal indicating the difference in the amount of light in the area divided into two parts with the center line of the beam spot applied to the two-divided light receiving element, that is, the position of the cantilever 22 is output from the terminal 108.

In this apparatus, the sample 26 is placed on an xyz driving device (for example, a cylindrical actuator) not shown, and the sample 26 is raster-scanned on the xy plane for several tens of cycles, and directly obtained during that period. AFM by processing the signal indicating the displacement of the cantilever or the servo signal obtained when servo is applied in the z direction so as to keep the displacement of the cantilever constant in synchronization with the scanning signal.
I'm getting a statue.

[0013]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention A displacement detection system for a cantilever to which the above-mentioned interferometry method, optical lever method, or focus detection method is applied is a cantilever, a laser light source for emitting a laser beam for irradiating the cantilever, and a reflected laser. It has a detector that receives the beam, and includes an adjustment unit that accurately directs the laser beam.

When measuring the surface roughness on the order of nm or when observing the structure of a semiconductor during processing, it has become necessary to directly measure components such as an 8-inch wafer. Therefore, if the stage on which the sample is placed is made large and the rigidity is increased, the weight is inevitably increased. Therefore, when the sample is moved to perform the raster scanning, the weight of the sample and the stage combined is large and the inertia becomes large, which makes control very difficult. An object of the present invention is to provide an atomic force microscope capable of observing a large sample.

[0015]

The atomic force microscope of the present invention comprises a cantilever having a reflecting surface at the free end of the surface opposite to the probe, a laser light source for emitting a laser beam, and a cantilever. The irradiation means for irradiating the reflection surface of the cantilever with the laser beam from the laser light source so that the vicinity of the reflection surface of the cantilever becomes the focusing surface, and the support for supporting the fixed end of the cantilever and the laser light source so that their relative positions do not change. The member and the scanning means for moving the supporting member parallel to the surface of the sample to scan the probe along the surface of the sample, and the displacement of the free end of the cantilever from the focusing surface by the reflected light from the reflecting surface of the cantilever. And a focus detector that detects the shift as a deviation.

[0016]

In the present invention, the laser light source and the fixed end of the cantilever are attached to the support member so that their relative positional relationship does not change. This support member is moved parallel to the surface of the sample. As a result, the probe is scanned along the sample surface. The laser beam emitted from the laser light source is guided to the reflecting surface of the cantilever by the irradiating means, and is irradiated so that the reflecting surface becomes the focus position. The irradiating means and the reflecting surface are arranged, for example, at positions conjugate with each other. The laser beam is irradiated so that the reflection surface is always focused. The laser beam reflected by the reflecting surface enters a focus detector that detects the amount of defocus that occurs according to the displacement of the probe, that is, the displacement of the reflecting surface.

[0017]

EXAMPLE An example of the atomic force microscope of the present invention will be described with reference to FIG.

The cantilever 32 is an xyz scanner 3
The probe 38 is fixed to a support member 36 supported by the No. 4, and a probe 38 is provided on the lower surface and a reflective surface 40 is provided on the upper surface at its free end. The support member 36 has a horizontally extending arm portion 36a, and a laser light source 42 that emits a laser beam upward is attached to the tip end portion thereof. An objective lens 44 supported by a mirror body 46 is arranged above the reflecting surface 40 of the cantilever 32 so that the reflecting surface 40 has a substantially focal length. Above the objective lens 44,
A half mirror 48 whose normal is inclined by 45 ° with respect to the central axis of the objective lens 44 is provided. The half mirror 48 reflects the laser beam from the laser light source 42 and transmits the laser beam from the reflecting surface 40. The objective lens 4 is provided above the laser light source 42.
A relay lens 52 having the same size as that of the lens 4 is supported by the mirror body 46, and the laser light source 42 is arranged so as to have a focal length. Above the relay lens 52, a mirror 50 for reflecting the laser beam from the lens 52 toward the half mirror 48 is arranged with its normal line inclined by 45 ° with respect to the central axis of the relay lens 52. As described above, the objective lens 44 and the relay lens 52 are optically connected to each other via the half mirror 48 and the mirror 50, and the two lenses 44 and 52 are formed by the reflecting surface 40 and the xyz scanner 34 of the laser light source. The raster scan planes are arranged so as to maintain a conjugate relationship. Further, above the half mirror 48, a mirror 54 for reflecting the laser beam transmitted therethrough to the right is provided. A lens 56 is arranged on the right side of the mirror 54, and at the rear focal position of the lens 56 at a position conjugate with the focusing surface of the objective lens 44, the reflecting surface 40 is adjusted based on the incident laser beam. A focus detector 58 that detects the amount of deviation from the focal plane is provided.

Next, the operation of this embodiment will be described.
At the time of measurement, the probe 38 using the xyz scanner 34
The sample 60 placed on the sample stage 62 is brought close to the distance where the atomic force is generated. In each of the optical components of this embodiment, when the free end of the cantilever 32 is displaced by a predetermined amount due to the generation of an atomic force between the probe 38 and the sample 60, the reflecting surface 40 is in the in-focus position. Have been adjusted to come. The laser beam emitted from the laser light source 42 passes through the relay lens 52, is reflected by the mirror 50, passes through the opening 36 b provided in the support portion 36, is reflected by the half mirror 48, and passes through the objective lens 44. , Is focused on the reflecting surface 40 provided at the free end of the cantilever 32. The laser beam reflected by the reflecting surface 40 passes through the objective lens 44 and the half mirror 48, is reflected by the mirror 54, passes through the lens 56, and then enters the focus detector 58. As described above, the focus detector 58 uses the critical angle prism, knife edge, or the like to detect the displacement of the reflecting surface 40 that changes according to the change in the atomic force. The output of the focus detector 58 is processed together with the position information obtained from the xyz scanner 34 to obtain an image of the sample 60.

In the present embodiment, the xy scan of the probe 38 is x
The support member 36 is attached to the sample 60 using the yz scanner 34.
By moving it parallel to the surface of. now,
The scanning points P ₁ , P ₂ , and P ₃ of the xyz scanner 34 are 10 to 200 μm in the central portion of the objective lens 44 (lens 52).
Raster scanning is performed in a range of m squares. When exaggerated to show the dimensions of the cantilever exaggerated in FIG. 1, the laser light source 42 is at the position of O ₂ as shown by the solid line. At this time, the reflecting surface 40 provided at the free end of the cantilever 32 is at the position P ₂ , and the laser beam emitted from the laser light source 42 enters the reflecting surface 40 along the optical path indicated by L ₂ . Further, as shown by the imaginary line, when the laser light source 42 is at the position of O ₃ , the reflecting surface 40
Is at the position P ₃ , and the laser beam enters the reflecting surface 40 along the optical path indicated by L ₃ . Similarly, when the laser light source 42 is at the O ₁ position, the reflecting surface 40 is at the P ₁ position, and the laser beam enters the reflecting surface 40 along the optical path indicated by L ₁ . In this way, the laser beam is always applied to the reflecting surface 40 in the same focusing relationship, and therefore goes to the focusing detector 58 under the same conditions.

As described above, the scanning of the probe 38 is performed by moving the support member 36 using the xyz scanner 34. Since the member moved at this time is relatively lightweight, scanning can be performed over a wide range with good controllability.

[0022]

According to the present invention, scanning is performed by moving a supporting member having a laser light source and a cantilever attached. At this time, the moving member is relatively lightweight, so that controllability is good, and comparison is made. The scanning can be performed over a wide range.

[Brief description of drawings]

FIG. 1 shows an example of an atomic force microscope of the present invention.

FIG. 2 shows a reflectance curve of a glass material.

FIG. 3 shows a conventional atomic force microscope integrated with an observation optical system.

FIG. 4 is a diagram for explaining the principle of the critical angle method.

5 shows a configuration of a displacement detection circuit connected to the photodiode of FIG.

[Explanation of symbols]

32 ... cantilever, 34 ... xyz scanner, 36 ...
Support part, 38 ... Probe, 40 ... Reflective surface, 42 ... Laser light source, 44 ... Objective lens, 52 ... Relay lens, 58 ... Focus detector.

Claims (1)

[Claims] 1. An inter-atom for measuring a physical property of a sample by scanning a probe provided on a free end of a cantilever along a surface of the sample and measuring a physical property of the sample based on a force acting between atoms of the probe tip and the sample surface. It is a force microscope, and it has a cantilever that has a reflecting surface at the free end of the surface opposite to the probe, a laser light source that emits a laser beam, and a focusing surface near the reflecting surface of the cantilever. Irradiation means that irradiates the reflecting surface of the cantilever with the laser beam from the laser light source, a support member that supports the fixed end of the cantilever and the laser light source so that their relative positions do not change, and the support member moves parallel to the sample surface. And scanning means for scanning the probe along the sample surface, and focus detection that detects the displacement of the free end of the cantilever as a deviation from the focusing surface by the reflected light from the reflecting surface of the cantilever. Atomic force microscope equipped with a vessel.