JPH03123805A - Interatomic force microscope - Google Patents

Abstract

PURPOSE:To obtain the accurate image of the surface of a sample and to improve stability to an external noise such as vibration, etc., by utilizing the interference of light so that the displacement of a cantilever may be detected and arranging a reference mirror surface which is a standard in the same vibration system as the sample. CONSTITUTION:A luminous flux L emitted from a light source 12 is converted into circularly polarized light by a 1/4 wavelength plate 14 and made incident on a polarizing beam splitter 16. Then, it is separated to a reference luminous flux Lr and a test luminous flux Lt on the beam splitting surface of the splitter 16 so that the reference mirror surfaces 20 and 30 may be irradiated with one of them and the reflection surface of the cantilever 44 may be irradiated with the other. The reference surfaces 20 and 30 and the reflection surface are positioned on the same plane and, desirably, the reference mirror surfaces 20 and 30 are made to closely contact with the cantilever 44. The two luminous fluxes Lr and Lt reflected by the reference mirror surfaces 20 and 30 and the reflection surface are synthesized and the displacement of the cantilever 44 is detected from interference fringe occurring at such a time by an interference fringe counting part 34. Then, the image of the surface of the sample 48 is formed based on the detected displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an atomic force microscope, and more particularly to an atomic force microscope that uses an interferometer to detect the displacement of a cantilever that supports a probe.

[Prior art] When a probe with a sharp tip and supported by a cantilever is brought close to the sample surface, a slight attractive or repulsive force (interatomic force) is created between the atoms at the tip of the probe and the atoms on the sample surface. ) occurs. The force applied to the probe deforms the cantilever, causing displacement.

By scanning the tip along the sample surface while detecting the displacement of the cantilever and measuring the interatomic force acting between the atoms at the tip of the tip and the atoms on the sample surface, we can measure the force on the sample surface. An atomic force microscope has been proposed that obtains dimensional information and uses this information to construct the surface structure of a sample with atomic-level resolution. An example is G. Binnig, C.F. Quate, Phys, Rev. Letters, Vol. 56, No. 9, March 1986, pp. 930-933. , Ch. Gerber
It is described in the paper by et al.

[Problems to be Solved by the Invention] Methods for detecting displacement of a cantilever include a method using tunnel current and a capacitance method.

In a method using tunnel current, a tunnel tip is placed above the cantilever at a distance where tunnel current can flow, biased, and the displacement of the cantilever is detected using the tunnel current flowing between the two.

Further, in the capacitance method, a flat plate capacitor is provided with the upper surface of the cantilever as an electrode plate, and the displacement of the cantilever is detected by measuring the change in capacitance caused by the displacement of the cantilever.

The displacement of the cantilever caused by the atomic force is extremely small. Therefore, the cantilever displacement detection system is required to be highly sensitive and resistant to external noise.

However, all of the above-mentioned methods are susceptible to external noise such as vibration, and the measurement results include the influence of external noise and are unstable.

An object of the present invention is to provide an atomic force microscope that has high sensitivity and excellent resistance to external noise such as vibrations.

[Means for Solving the Problems] The atomic open force microscope of the present invention includes a probe for generating atomic force and a reflective surface with a high reflectance on the upper surface, and the probe is configured to generate atomic force. a cantilever supported at a distance closer to the sample than possible; a means for scanning the probe along the sample surface; a light source that generates coherent light; a means for separating the light beam into a light beam, a reference mirror surface provided on the same plane as the reflecting surface, a means for irradiating one of the separated light beams onto the reference mirror surface, and a means for irradiating the other separated light beam onto the reflection surface of the cantilever. means for irradiating; and 2 reflected from the reference mirror surface and the reflective surface.
A means is provided for forming an image of the sample surface by interfering with the light flux of the book and detecting the displacement of the cantilever.

[Function] In the atomic force microscope of the present invention, the light beam emitted from the light source is separated into two beams, one of which is applied to the reference mirror surface and the other to the reflective surface of the cantilever. The reference mirror surface and the reflective surface are located on the same plane, and preferably the reference mirror surface and the cantilever are close to each other. The two beams reflected by the reference mirror surface and the reflecting surface are combined, and the displacement of the cantilever is detected from the interference fringes generated at this time using an interferometer or the like, and an image of the sample surface is formed based on this.

[Example] An example of the present invention will be described with reference to FIG. In the figure, only the central ray of the propagating beam is shown. A linearly polarized light beam emitted from a light source 12 such as a laser diode is converted into circularly polarized light by a 174-wave plate 14, enters a polarizing beam splitter 16, and is divided into a reference light beam Lr and a test light beam Lt at the beam splitting surface. It can be divided into

Reference light beam Lr reflected by polarizing beam splitter 16
The (S-polarized light) passes through the quarter-wave plate 18, is converted into circularly polarized light, and is irradiated onto the reference mirror 20. The reference light beam Lr reflected by the reference mirror 20 passes through the quarter-wave plate 18 again, is converted into P-polarized light, passes through the polarization beam splitter 16, and is reflected by the prism 22. The reference light beam L'' reflected by the prism 22 is further reflected by the prism 24, passes through the polarizing beam splitter 26 and the quarter-wave plate 28, is converted into circularly polarized light, and is irradiated onto the reference mirror 30.

Although the reference mirrors 20 and 30 are described as different members with different reference numerals in the drawings, they may be a common reference mirror provided in a ring shape on the aluminum block 32. The reference light beam Lr is reflected by the reference mirror 30, passes through the quarter-wave plate again, becomes S-polarized light, is reflected by the polarization beam splitter 26, and enters the interference fringe counting section 34.

On the other hand, the test light beam Lt (P-polarized light) transmitted through the polarizing beam splitter 16 is converted into S-polarized light by the 172-wave plate 36, reflected by the polarized beam splitter 38, and 1/
It passes through a four-wavelength plate 40 and is converted into circularly polarized light, which is then passed through a lens 42.
The optical path is bent and focused, and the cantilever 4
A beam spot is irradiated onto the top surface of the tip of the pointer 4. The cantilever 44 has a probe 4 acting on the surface of the sample 48.
6 on the lower surface of the tip, and is fixed to the aluminum block 32 via a piezoelectric body 50. Furthermore, the cantilever 44
The top surface is coated with a high reflectance coating such as gold, and
It is arranged in the same plane as the reference mirrors 20 and 30. In addition,
The sample 48 is placed on the XYZ scanner 51 and is provided so as to be movable in three-dimensional directions. The test light beam Lt irradiated onto the cantilever 44 is reflected, passes through the lens 42 and the quarter-wave plate 40, is converted into P-polarized light, and passes through the polarizing beam splitter 52. The test light beam Lt is reflected twice within the prism 54 and enters the polarizing beam splitter 38 again. The test light beam Lt enters the cantilever 44 via the quarter-wave plate 40 and the lens 42, is reflected, and enters the polarizing beam splitter 52 via the lens 42 and the quarter-wave plate 40. Test luminous flux Lt
is converted into S-polarized light by passing through the quarter-wave plate 40 twice, and is reflected by the polarizing beam splitter 52. The test light beam Lt reflected by the polarizing beam splitter 52 is converted into P-polarized light by the quarter-wave plate 56, passes through the polarizing beam splitter 26, and enters the interference fringe counting section 34.

The prism 54 is positioned so that when the cantilever 44 is in the reference position, that is, when the reference mirrors 20 and 30 and the top surface of the cantilever 44 are located on the same plane, the optical path lengths of the reference light beam Lr and the test light beam Lt are equal. is adjusted. The reference light beam Lr and the test light beam Lt are incident on the interference fringe counting section 34, and the displacement of the cantilever 44 is detected from the optical path difference between these light beams. Note that the interference fringe counting section 34 uses an interferometer capable of reversible counting of a polarization interferometer.

According to this embodiment, the reference mirrors 20 and 30, which serve as standards for detecting the displacement of the cantilever 44, are placed in the same vibration system as the sample 48, so stability against external noise such as vibration is improved. .

Another embodiment of the invention is shown in FIG. Only the central ray of the propagating light beam is illustrated.

A coherent beam emitted from the light source 62 enters a polarizing beam splitter 66 via a beam expander 64, where it is separated into a reference beam Lr and a test beam Lt. The reference light beam Lr reflected by the polarizing beam splitter 66 is reflected by the prism 68 and passed through the 1/2 wavelength plate 7.
0, it is converted into P polarized light. The light beam Lr passing through the half-wave plate 70 is refracted and condensed by a hologram lens 72 that has a circular opening in the center and a lens surface in the periphery. A polarizing film 74 is placed at the focal point of the hologram lens 72, and at the focal point of an objective lens 76 provided below. Reference light flux L
The light r passes through the polarizing film 74, is refracted by the objective lens 76, and is converted into a parallel beam of light, which is then irradiated onto the reference mirror 80 via the quarter-wave plate 78 and reflected. The reference light beam Lr reflected by the reference mirror 80 passes through the 174-wave plate 78 again, is converted into S-polarized light, and is focused onto the polarizing film 74 by the objective lens 76 . The reference light beam Lr converted into S-polarized light is reflected by the polarizing film 74 and reaches the opposite side of the objective lens 76 , where it is converted into a parallel light beam and refracted, and passes through the quarter-wave plate 82 to the reference mirror 84 . irradiated.

The light beam Lr is reflected by the reference mirror 84, passes through the 174-wave plate 82 again, is converted into P-polarized light, is refracted by the objective lens 76, and is focused onto the polarizing film 74. The reference light beam Lr converted into P-polarized light is passed through the polarizing film 7
4 and reaches the hologram lens 72 , where the optical path is bent and converted into a parallel beam, which passes through the polarizing beam splitter 86 and enters the interference fringe counting section 90 .

On the other hand, the test light beam Lt passing through the polarizing beam splitter 66 passes through a quarter-wave plate 92, is converted into circularly polarized light, is refracted and condensed by an objective lens 76, and is used to detect atomic force. The upper surface of a cantilever 94 equipped with a probe (not shown) is irradiated with light. The cantilever 94 has a reflective surface with a high reflectance on its upper surface, as in the above-described embodiment, and efficiently reflects the irradiated test light beam Lt. The light beam Lt reflected by the cantilever 94 is refracted by the objective lens 76, and becomes a parallel light beam and enters the lens 96. The lens 96 focuses the test light beam Lt onto a reflector 98. The reflector 98 reflects the irradiated test light flux Lt at a high rate, and the reflected light flux Lt is reflected by the lens 9.
6 and returns to the cantilever 94 via the objective lens 76. The test light flux Lt is further reflected by the cantilever 94,
It is reconverted into a parallel beam by the objective lens 76 and becomes 1/4
The light is incident on the wave plate 92. The test light beam Lt is converted into S-polarized light by the quarter-wave plate 92, reflected by the two polarization beam splitters 66 and 86, and incident on the interference fringe counting section 90. In the interference fringe counting section 90, from the interference fringes caused by the optical path difference between the reference light beam Lr and the test light beam Lt,
Displacement of cantilever 94 due to atomic force is detected.

According to this embodiment, since the cantilever 94 and the reference surfaces 80 and 84 are provided closer together, stability against vibrations is further improved.

[Effects of the Invention] According to the atomic force microscope of the present invention, since light interference is used to detect the displacement of the cantilever, a highly accurate image of the sample surface can be obtained. Furthermore, since the reference mirror surface serving as a reference is placed in the same vibration system as the sample, stability against external noise such as vibration is improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an atomic force microscope according to one embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of an atomic force microscope according to another embodiment. 12... Light source, 16... Polarizing beam splitter-2
0, 30... Reference mirror, 34... Interference fringe counting unit, 44
...Cantilever 46...Tip, 48...Sample.

Claims (1)

[Claims] A probe for generating an atomic force; a cantilever having a reflective surface with a high reflectance on its upper surface and supporting the probe close to a sample at a distance below which the atomic force can be generated; means for scanning along the sample surface, a light source that generates coherent light, means for separating the light beam generated from the light source into two light beams, and a reference provided on the same plane as the reflecting surface. a mirror surface, means for irradiating one of the separated light beams onto the reference mirror surface, means for irradiating the other separated light beam onto the reflective surface of the cantilever, and two beams reflected from the reference mirror surface and the reflective surface. an atomic force microscope comprising: means for interfering the light beams of the cantilever and detecting the displacement of the cantilever to form an image of the sample surface.