JPH0579834A - Interatomic-force microscope - Google Patents

Abstract

PURPOSE:To obtain an interatomic-force microscope which can measure roughness highly accurately without the effect of disturbance vibration. CONSTITUTION:The deflecting amount of a cantilever 26, which is caused by the interatomic force between a probe 28 that is attached to the tip of the cantilever 26 and the surface of a material to be measured 30, is measured with laser light. The laser light ray is divided into two beams by using a double- focal-point lens 22. One beam is cast on the rear surface of the cantilever 26, and the other is cast on the surface of the material to be measured 30. The vibration component in measurement is removed. Thus, the highly accurate measurement of the surface roughness can be performed.

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 for measuring the surface roughness of an object to be measured. More specifically, the present invention relates to an atomic force microscope that optically detects deflection of a cantilever beam caused by an atomic force.

[0002]

2. Description of the Related Art An atomic force microscope has been proposed which measures the surface shape of an object by detecting the force acting on the atoms when the objects are brought close to each other to the atomic level.

When a sharply pointed probe is attached to the tip of a minute cantilever and the probe is brought close to or in contact with the surface of the object to be measured, atoms between the tip of the probe and the surface of the object to be measured are attached. The interatomic force acts between and the cantilever bends. The surface roughness or surface shape of the measured object can be measured by scanning the measured object and detecting the change in the deflection amount of the cantilever. As examples of such an atomic force microscope, Japanese Patent Laid-Open Nos. 62-130302 and 2
No. 281103 is cited.

In Japanese Patent Laid-Open No. 62-130302, a tunnel microscope is used to detect the deflection of a cantilever beam. This is shown in FIG. On the back surface of the cantilever 26, a tunnel chip 64 is arranged below the tunnel distance. When the cantilever 26 is deflected, the tunnel current changes according to the amount of deflection, so the amount of deflection of the cantilever 26 can be detected by detecting this tunnel current.

Further, in Japanese Patent Application Laid-Open No. 2-281103, a so-called critical angle focus error detection method using light is used. This is shown in FIG. The mirror surface 74 on the back surface of the cantilever 26 is irradiated with laser light. When the deflection amount of the cantilever beam 26 changes, the reflected light from the mirror surface 74 entering the critical angle prisms 76 and 77 changes to a divergent light beam or a convergent light beam. As a result, a difference in output occurs between the two detectors in the photodetectors 78 and 79,
The amount of cantilever deflection can be detected.

[0006]

However, since the deflection amount of the cantilever beam due to the interatomic force is extremely small, the above conventional method is easily affected by external vibration between the probe and the surface of the object to be measured. However, there is a drawback that the measurement result includes a component of external vibration.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to realize an atomic force microscope capable of performing measurement without the influence of external vibration.

[0008]

In order to achieve this object, the atomic force microscope of the present invention comprises:
A laser light source device that outputs laser light containing two types of linearly polarized light having slightly different frequencies, and one that makes one of the two types of linearly polarized light output by the laser light source device parallel light and the other one convergent light. Including a multifocal lens, one linearly polarized light is condensed on the back surface of the cantilever, the other linearly polarized light is made into parallel light, and the irradiation diameter of the one linearly polarized light on the surface of the object to be measured. An optical system for irradiating with a radiation diameter sufficiently larger than the above, and a detection means for causing the reflected light of the two types of linearly polarized light to interfere with each other by the optical system and detecting the amount of deflection of the cantilever from the beat frequency of the interference. , Are provided.

[0009]

According to the atomic force microscope of the present invention having the above-mentioned structure, the deflection amount of the cantilever beam is detected by the optical heterodyne method by the optical system using the bifocal lens.

One of the two types of linearly polarized light output from the laser light source device is converged on the back surface of the cantilever as the measurement light by the optical system including the bifocal lens, and the other on the surface of the object to be measured. The irradiation is performed as parallel light with an irradiation diameter that is sufficiently larger than the irradiation diameter of the linearly polarized light. The light reflected from the back surface of the cantilever beam undergoes a frequency change because the optical path length changes with the deflection amount of the cantilever beam. The reflected light from the back surface of the cantilever and the surface of the object to be measured is detected by the detection means, and the deflection amount of the cantilever is calculated from the beat signal of the interference.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the same members as those of the conventional device shown in FIGS. 3 and 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

1 and 2 are block diagrams for explaining an embodiment of the present invention. As the laser light source device 10, a Zeeman laser that outputs laser light L including two types of linearly polarized light whose polarization planes are orthogonal to each other and whose frequencies are slightly different, for example, P polarized light LP and S polarized light LS is used. The laser light source 10, the non-polarization beam splitter 12, the analyzer 14, and the reference optical sensor 16 are arranged on a straight line parallel to the Z axis. The laser light L output from the laser light source device 10 is divided into two by the non-polarization beam splitter 12, and the laser light transmitted through the non-polarization beam splitter 12 is detected by the reference optical sensor 16 and the reference beat. The signal FB is output. When the frequencies of the P-polarized light LP and the S-polarized light LS are fP and fS, respectively, the frequency fB of the reference beat signal FB is | fP-fS |.

On the other hand, the laser beam L reflected by the non-polarizing beam splitter 12 in the negative direction of the X-axis is incident on the mirror 20 after the beam diameter is expanded by the beam expander 18 arranged on the optical axis. To do.

The laser light L is reflected by the mirror 20 in the negative direction of the Z-axis and is incident on the bifocal lens 22 and the objective lens 24 arranged below the mirror 20.

The bifocal lens 22 and the objective lens 24
As shown in FIG. 2, the support 25 holds the double focus lens 22 so that the rear focus of the double focus lens 22 and the front focus of the objective lens 24 coincide with each other. A cantilever beam 26 is attached below the support 25, and a probe 28 is attached to the tip of the cantilever beam 26. Cantilever 26
The mounting position is determined so that the back surface of the is approximately at the focal position of the objective lens 24.

Below the objective lens 24, the Z drive device 5 is provided.
6 to drive the piezoelectric element 42 to drive the objective lens 24
Z stage 40 that can be moved in the optical axis direction (Z direction) of
An XY stage 44 is arranged which can be moved by an XY drive device 58 in an XY plane perpendicular to the optical axis direction of the objective lens 24. The DUT 30 is the Z stage 40.
Mounted on. The Z stage 40 is moved in the positive direction of the Z axis via the Z drive device 56 to bring the object to be measured 30 close to the vicinity so that the atomic force acts between the object 30 and the probe 28, or the cantilever 26 is moved. Touch it so that it flexes lightly.

Further, the analyzer 34 and the measurement optical sensor 36 are arranged in the positive direction of the X axis of the non-polarizing beam splitter 12 and on the same straight line as the optical axis of the beam expander 18.

The laser light L from the mirror 20 enters a bifocal lens 22. The bifocal lens 22 is composed of optical glass and a birefringent material, and has a property that the refractive index differs depending on the direction of the plane of polarization of the incident light. Therefore, of the laser light L entering the bifocal lens 22, the P-polarized light LP becomes parallel light and the S-polarized light LS becomes convergent light and enters the objective lens 24. Further, as described above, the objective lens 24 is configured such that its front focus is located at the rear focus of the bifocal lens 22. For this reason, the S-polarized light LS that has entered as convergent light is converted into parallel light and is applied to a relatively wide range on the surface of the DUT 30. On the other hand, the P-polarized light LP that has entered the objective lens 24 as parallel light is on the back surface of the cantilever 26 as convergent light, and the probe 28
It is focused on a point directly above.

When the laser light L is a HeNe laser and the magnification of the objective lens is 150 times, the diameter of the P-polarized light LP condensed on the back surface of the cantilever 26 is about 0.8 μm, and the diameter of the object 30 to be measured is 30 μm. The diameter of the S-polarized light LS irradiated on the surface is about 6
It is 0 μm.

The object 30 to be measured is the Z stage 40, X
The Y stage 44 is mounted on a moving stage. When the DUT 30 is scanned by the XY stage 44, the probe 28 moves up and down corresponding to the minute irregularities on the surface, and the cantilever 26 bends.

The reflected light of the P-polarized light LP focused on the back surface of the cantilever beam 26 has its optical path length changed as the cantilever beam 26 moves up and down, and thus receives a frequency shift Δfs. ing. Further, the frequency shift Δfd due to the vibration of the XY stage 44 and other disturbances at the time of measurement
Therefore, the frequency of the reflected light of P-polarized light LP is fP + Δ
It becomes fd + Δfs. On the other hand, in the S-polarized light LS which is irradiated in a relatively wide range on the surface of the DUT 30 in the state of the circular parallel beam, the influence of the fine irregularities on the surface of the DUT 30 is averaged and canceled as a whole. Therefore, the frequency of the reflected light becomes fS + Δfd only by the influence of the frequency shift Δfd due to the disturbance. The P-polarized light LP is measurement light and the S-polarized light LS is reference light.

The P-polarized light LP reflected on the back surface of the cantilever 26 and the S-polarized light LS reflected on the surface of the DUT 30.
Are incident on the non-polarizing beam splitter 12 following the optical paths opposite to the incident paths, transmitted through the non-polarizing beam splitter 12, received by the measurement optical sensor 36, and output the measurement beat signal FD. This measurement beat signal FD is P-polarized LP and S-polarized L
It corresponds to a beat due to interference with S, and its frequency fD is | (fP + Δfd + Δfs) − (fS + Δf
d) | = | fP−fS + Δfs |, and the frequency shift Δfd due to the disturbance is canceled.

At this time, there is a concern that the reflected light of the S-polarized light LS reflected on the back surface of the cantilever 26 may enter the optical sensor for measurement and cause measurement noise. Is slightly inclined with respect to the optical axis (Z axis), the reflected light from the back surface of the cantilever beam 26 is also inclined with respect to the optical axis and does not enter the measurement optical sensor.

The measurement beat signal FD and the reference beat signal FB are supplied to the measuring circuit 50, and the frequency fD (= | fP-fS + Δfs |) of the measurement beat signal FD to the frequency fB (= | fP- of the reference beat signal FB). fS |)
By subtracting from, only the frequency shift Δfs due to the unevenness of the surface of the DUT 30 is extracted, and the signal representing this frequency shift Δfs is supplied to the control circuit 52.
The control circuit 52 is composed of, for example, a microcomputer, and while sequentially moving the XY stage 44 in the XY directions by the XY drive device 58, based on the following expression 1 from the signal (Δfs) supplied from the measurement circuit 50. The displacement Zs at each position is calculated.

The displacement Zs calculated over the entire XY scanning plane is plotted by the display 54 and the surface roughness is three-dimensionally displayed.

[0026]

[Equation 1]

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above embodiment, the cantilever 2 is simply used.
Although the deflection amount of 6 was only detected by using the heterodyne method, the deflection amount of the cantilever 26 is always made constant by giving the displacement Zs obtained by the control circuit 52 to the Z drive device 56 as a feedback signal. You may measure it.

Also, for example, in the above embodiment, the cantilever 2
Although the probe 28 is attached to the tip of 6, the tip of the cantilever 26 may be sharpened so that the cantilever 26 itself also has the function of the probe.

In the above embodiment, the laser light source device 3 is used.
A quadrature dual-frequency Zeeman laser was used as 0, but a laser light source device of a type that forms a desired frequency difference between two linearly polarized lights by using a frequency shifter including an acousto-optic modulator is used. Is good. In this case, the reference beat signal FB can also be detected from the drive frequency signal of the acousto-optic modulator.

Further, for example, the mirror 20 is replaced with a semi-transparent mirror, and a microscope lens barrel is provided above it so that the measurement state can be monitored, or an optical isolator is inserted between the laser light source device 10 and the non-polarizing beam splitter 12. The present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[0032]

As is apparent from the above description, when the atomic force microscope of the present invention is used, since there is no optical path difference between the measurement light and the reference light, it is highly accurate without being affected by disturbance such as external vibration. The surface shape can be measured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment embodying the present invention.

FIG. 2 is a configuration diagram in the vicinity of an objective lens in an embodiment embodying the present invention shown in FIG.

FIG. 3 is a configuration diagram of a conventional atomic force microscope.

FIG. 4 is a block diagram of a conventional atomic force microscope.

[Explanation of symbols]

 10 Laser Light Source Device 12 Beam Splitter 14 Analyzer 16 Optical Reference Sensor 18 Beam Expander 20 Mirror 22 Dual Focus Lens 24 Objective Lens 26 Cantilever 28 Probe 30 Measured Object 32 Support 34 Analyzer 36 Measurement Light Sensor 40 Z stage 42 Piezoelectric element 44 XY stage 50 Measurement circuit 52 Control circuit 54 Indicator 56 Z drive device 58 XY drive device

Claims (1)

[Claims] 1. A probe for bringing atomic force close to the surface of the object to be measured to generate an atomic force between the surface of the object and the surface of the object to be measured, and an interatomic distance between the probe and the surface of the object to be measured. A cantilever beam that is supported within a distance where a force can be generated and supported, and a scanning unit that scans the object to be measured, and the interatomic distance that optically detects the deflection of the cantilever caused by the interatomic force In a force microscope, one of the two types of linearly polarized light output by the laser light source device, which outputs laser light containing two types of linearly polarized light whose polarization planes are orthogonal to each other and whose frequencies are slightly different Includes a bifocal lens for making the parallel light and the other the convergent light, and condensing one linearly polarized light on the back surface of the cantilever, and making the other linearly polarized light parallel light, and the object to be measured. Linear polarization of the one on the surface An optical system that irradiates with an irradiation diameter sufficiently larger than the irradiation diameter, and a detection that causes the reflected light of the two types of linearly polarized light to interfere with each other by the optical system and detects the deflection amount of the cantilever from the beat frequency of the interference. An atomic force microscope, comprising: