JPH0424501A - Shape measuring apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for measuring the surface shape of an object with high resolution.

[Prior Art] Conventionally, as a shape measuring device using an optical microscope such as an atomic force microscope of this type, there is one described in Japanese Patent Application Laid-Open No. 130302/1983, which is shown in FIG. In this conventional shape measuring device, the cusp 5 is placed on a cantilever beam 7.
The surface of the sample 4 approaches the cusp 5 (as a result, the cantilever beam 7 is deflected by a small amount due to the action of atomic force. The amount of this deflection is detected by the tunneling tip 8, and the amount of deflection is kept constant. The XYZ drive device 3 is controlled to control the XYZ drive device 3.Furthermore, this XYZ drive device 3 has the function of scanning within the plane of the sample 4.Changes in the drive amount in these XYZ directions represent the surface shape of the sample 4, and therefore, based on this, In addition, in the prior art embodiment of the above-mentioned publication, the XYZ drive device 3 is vibrated in the Z direction at the natural frequency of the cantilever beam 7, and the natural vibration caused by the approach of the surface of the sample 4 is measured. It is also shown that the XYZ drive device 3 is controlled using phase changes.

[Problems to be Solved by the Invention] In the above-mentioned prior art, (1) the amount of deflection of the cantilever beam is detected by a tunnel tip; therefore, in addition to the atomic force acting between the sample and the cantilever beam, The atomic force between the beam and the tunnel tip also acts, making it impossible to accurately detect the force between the sample and the cantilever beam.

(2) The distance between the cantilever beam and the tunnel tip is approximately ln.
Therefore, it is difficult to adjust the distance.

[3] Since the amount of deflection is detected only by the action of the free end of the cantilever beam, fluctuations at the fixed end will affect the amount of deflection detected, and mechanical fluctuations around this will greatly affect the measurement accuracy. Become.

The present invention eliminates the above-mentioned drawbacks and accurately detects the amount of deflection of a cantilever beam without being affected by external forces or fluctuations. a cantilever beam, and a scanning mechanism unit that scans the sample surface by bringing the apex and the sample surface close together, and the deflection of the cantilever beam that occurs when the apex and the sample surface are brought close together A device for measuring shape by quantity, comprising a light source having two different frequencies, projecting light of one of the two frequencies onto the free end of the cantilever beam, and projecting light of the other frequency onto the fixed end of the cantilever beam; an optical section that combines the reflected light; a measurement beat detection section that detects the beat light of the combined light;
a basic beat detection unit that detects a beat signal based on two frequencies of the light source; a phase difference meter that measures the phase difference between the beat signals produced by the basic beat detection unit and the measurement beat detection unit; and a phase difference meter that controls the scanning mechanism unit and The present invention is characterized by comprising a control section that controls the phase difference to a constant amount, and an output section that outputs position information of the scanning mechanism section as a shape of a sample surface.

FIG. 1 shows a conceptual diagram of the shape measuring device of the present invention.

A light source 6 having two frequencies outputs coherent light consisting of slightly different frequencies f1 and [2. Hetero gain interferometric length measurement is performed using the lights of frequencies fl and f2. The lights of frequencies f1 and f2 are input to the basic beat detection section 2 in order to detect a beat signal generated by their interference. The detected basic beat signal is input to the phase difference meter 10. The light having frequencies f6 and f2 emitted from the basic beat detection section is branched by the first optical section 12 into light having frequencies f1 and f2, respectively, and the light having frequencies f,
The light is projected onto the free end of the cantilever beam 7 and reflected.

The other light having the frequency f2 is projected onto the fixed end of the cantilever beam 7 by the second optical section 13 and is reflected. The two reflected lights of frequencies f1' and f2' are combined by the first optical section 12 and enter the measurement beat detection section 9. The measurement beat detection section 9 detects a measurement beat signal generated by interference of the lights f1 and f2 reflected from the free end and the fixed end of the cantilever beam 7, respectively. The phase of this measurement beat signal changes in accordance with the change in the optical path length of the light f1 and the optical path length of the light f2 due to the deflection of the cantilever beam 7. This measured beat signal is input to a phase difference meter 10, which detects the phase difference with the basic beat signal. The cantilever beam 7 is held by a fixed end holder 14, and furthermore, the free end of the cantilever beam 7 forms a cusp 5 that receives a force from the surface of the sample 4. The force caused by the sample 4 approaching the cusp 5 causes the cantilever beam 7 to deflect. This amount of deflection is proportional to the output of the phase difference meter 10, and by controlling the XYZ drive device 3 with the control section 11 so that the output of the phase difference meter 10 is constant,
The force acting between the sample 4 and the cusp 5 can be made constant.

While keeping this force constant, the sample 4 is moved by the XYZ drive device 3.
scan over the surface. The control information in these three directions is used as the position information of the XYZ drive device 3, and the surface shape of the scanning plane is outputted to the output unit 15.
Output to.

[Example] A first embodiment of the shape measuring device of the present invention is shown in FIG.

A light source 6 having two frequencies of laser light using a frequency shifter using a Zeeman laser or an acousto-optic device outputs linearly polarized light of frequencies f1 and f2 with polarization planes different by 90 degrees from each other. fl and f2 represent light of slightly different frequencies. The lights fI and f2 are split by a beam splitter 16 and incident on a linear polarizer 17 whose polarization direction is tilted by 45 degrees, and the light is received by a basic beat light receiving element 18.

The beam splitter 16 can be composed of a half prism or the like,
The linear polarizer 17 can be composed of a Durham-Thomson prism, a dichroic polarizing plate, a polarizing prism, or the like.

The basic beat light receiving element 18 is composed of a pin photodiode or the like. The other light split by the beam splitter 16 enters the polarizing beam splitter 19, and is split into lights of frequencies f and f2 depending on the polarization direction of the light. The transmitted light f1 passes through the λ/4 wavelength plate 20, is reflected at the free end of the cantilever beam 7, enters the λ/4 wavelength plate 20 again, the light is reflected by the polarizing beam splitter 19, and is reflected by the linear polarizer. 23 and is received by the measurement beam splitter light receiving element 24. On the other hand, polarized beam splitter 19
The light f2 reflected at The beam is incident on the measurement beat light receiving element 24. The cantilever beam 7 is made of an elastic material such as gold, copper, tungsten, or iron, and has one end attached to the fixed end holding portion 14.
and a cusp 5 pointed toward the sample is formed at the other end.

The point is formed by processing metal or a non-metal such as diamond to make the tip sharp. The sample 4 is placed facing the cusp 5, and is movable in three directions, X1Y, and Z, by a Z drive device 25, a Y drive device 26, and an X drive device 27. This X,
Y.

The Z drive device is controlled by a control section 11, and its control amount is inputted to an output section 15. Basic beat light receiving element 1
8 and the measurement beat light receiving element 24 are respectively input to a phase difference meter 10, and the output of the phase difference meter 10 is input to a control section 11. The X drive device 27, the Y drive device 26, and the Z drive device 25 are constituted by fine movement mechanisms constituted by piezo elements.

The control section 11 can be constructed from simple electric elements.

(Function) Linearly polarized light having frequencies f1 and f2 with polarization planes different from each other by 90 degrees is output from the light source 6 having two frequencies, and a beam splitter is used to split this light into basic beat detection light and measurement beat detection light. The light enters the printer 16. The basic beat detection light is received by the basic beat light receiving element 18, which constitutes a linear polarizer 17 to obtain beat light by interference of frequencies f1 and f2 on the basic beat light receiving element 18, and photoelectrically converts the intensity change. Using the fact that the measurement beat detection lights have different polarization planes by 90°, the polarization beam splitter 19
The light is divided into light having a frequency of fl and light having a frequency of f2. The light thus divided is projected onto the free end and the fixed end of the cantilever beam 7, respectively. Mirror 22 is used for this purpose. The λ/4 wavelength plate 20 rotates the plane of polarization of the light f transmitted by the polarizing beam splitter 19 and the light f, - which is reflected at the free end and enters the polarizing beam splitter 19 by 90 degrees.

As a result, the light f1 is reflected by the polarization beam splinter 19 and enters the linear polarizer 23. The λ/4 wavelength plate 20 converts the linearly polarized light [1 into circularly polarized light, and converts the light f1' reflected at the free end into linearly polarized light f2 whose plane of polarization is rotated by 90 degrees again. The λ/4 wavelength plate 21 functions similarly to the λ/4 wavelength plate 20, and serves to guide the light f2'' reflected at the fixed end of the cantilever beam 7 to the linear polarizer 23. Beat light receiving element 24 is linear polarizer 17
It functions similarly to the basic beat light receiving element 18 and detects the measurement beat signal.

The phase difference meter 10, the control section 11, and the output section 15 have the same functions as shown in the conceptual diagram. The X drive device 27, Y drive device 26, and Z drive device 25 correspond to the XYZ drive device shown in the conceptual diagram, and the Z drive device 25 makes the force acting between the sample 4 and the cusp 5 constant. make it work like this.

(Effects) As described above, in this embodiment, the interval between the spot positions of the light projected onto the cantilever beam 7 can be easily changed, and therefore the apparatus can be constructed at low cost.

Next, a second embodiment of the shape measuring device of the present invention is shown in FIG.

In this example, lights of frequencies f1 and f2 outputted from a light source 6 having two frequencies of light are expanded by a beam expander 28 and enter a beam splitter 29. The beam expander 28 is commercially available as a beam expander, and can be easily constructed from a concave-convex lens. The beam splitter 29 splits the incident light, and one of the lights is made to enter the linear polarizer 17 and the other light is made to enter the Wollaston prism 30. In the Wollaston prism 30, the plane of polarization is 90°.
The lights of different frequencies f1 and f2 are separated into two lights by the separation angle of the Wollaston prism, and the lights are focused on the free end and the fixed end of the cantilever beam 7, respectively, through a condenser lens 31. The reflected light f1゛,
f2' passes through a condensing lens, is combined again at Wollaston prism 30, and guided to linear polarizer 23 by beam splitter 29. The configuration other than those described above is the same as that described for the first embodiment, so detailed explanation thereof will be omitted.

(Operation) In this example, the light flf2 outputted from the light source 6 having two frequencies of light has a small beam diameter, so it is expanded by the beam expander 28. The expanded light is branched so as to be incident on a linear polarizer 17 for detecting fundamental beats and a Wollaston prism 30 for detecting measurement beats. The light incident on the Wollaston prism 30 is separated into lights f1 and f2 whose planes of polarization differ by 90°, respectively, at angles predetermined by the Wollaston prism 30. This separated light f
1 and f2 are respectively condensed by the condenser lens 31 at positions determined by the separation angle and the focal length of the condenser lens. In order to detect the deflection of the cantilever beam 7, the separation angle and the focal length of the condensing lens are selected so that the light is focused on the free end and the fixed end of the cantilever beam 7, respectively. The reflected light is guided to the Wollaston prism 30 by a condensing lens. The reflected lights f, -1f2- are incident on the Wollaston prism 30 at the same angle as the separation angle, so that the lights f, - and f2-
are combined and polarized by a beam splitter 29, and a linear polarizer 23 and a measurement beat light receiving element 24 obtain a measurement beat signal. Since the functions other than those described above are the same as those described for the first embodiment, detailed explanation thereof will be omitted.

(Effects) According to this example, the projection mechanism to the cantilever beam 7 is simplified and is less susceptible to vibrations, thermal fluctuations, and the like. Furthermore, since the number of common optical paths for the lights f1 and f2 is increased, the influence of light fluctuations and the like is further reduced.

Next, a third embodiment of the shape measuring device of the present invention is shown in FIG.

In this example, the light expanded by the beam expander 28 is split by the beam splitter 43. The reflected light is transmitted through a polarizer 36
beam enters the beam, is deflected by the mirror 33, and is again beam splitter 4.
3 and is transmitted, enters the linear polarizer 34 and reaches the light receiving element 29. The mirror 33 can be configured with a corner cube or the like. On the other hand, the light transmitted through the beam splitter 43 is reflected by the cantilever beam 7 on the beam splitter 29 and enters the polarizer 35 as light with a frequency f and -1f2-. This light is reflected by the beam splitter 43, enters the linear polarizer 34, and reaches the light receiving element 37. The beat signal received here enters the phase meter 32 together with the basic beat signal, and its output is displayed at the output section I5. The linear polarizer 34, the polarizer 35, and the polarizer 36 can be constructed of the same material as the linear polarizer 23. Measurement beat light receiving element 24, linear polarizer 23, beam splinter 29, linear polarizer 17, basic beat light receiving element 18, Wollaston prism 30, condensing lens 31, and Z fine movement device 40 are fixed to the head 38 for Z coarse movement. The device 39 is configured to be movable.

The Z fine movement device 40 and the Z coarse movement device 39 can be controlled by the control section 11. The X position detector 41 and the Y position detector 42 are configured to be able to detect the amount of movement of the X drive device 27 and the Y drive device 26, respectively, and their outputs are input to the output section 15. The Z fine movement device can be composed of a piezo element, and the Z coarse movement device can be composed of a linear motor or the like.

(Function) In the present invention, in order to scan large irregularities of several hundred μm or more on the surface of the sample 4 at high speed, the Z fine movement device 40 and the Z coarse movement device 39 are used to move the surface between the cantilever beam 7 and the sample 4. The control unit 11 controls so that the applied force is constant. The Z fine movement device fixes only the cantilever beam in order to operate at several KHz or higher. Therefore, the entire system is driven by the Z coarse movement device 39. In order to detect the amount of movement of the free end of the cantilever beam 7 due to the Z fine movement and the Z coarse movement, the light from the beam expander 28 is transmitted through the beam splitter 43 and projected onto the free end. This reflected light f2-
returns to the beam splitter 43 again, reflects it, and makes it incident on the linear polarizer 34. The polarizer 35 selectively selects the reflected light f1' from the free end of the light components f and -f2- reflected by the cantilever beam 7. At the same time, the light f1 and f2 reflected by the beam splitter 43 and incident on the polarizer 36 are selectively selected from the light f1 by the polarizer 36, deflected by the mirror 33, transmitted through the beam splitter 43, and become linearly polarized light. The light is incident on the child 34. This light with a frequency f always has a constant optical path length, and is combined with the light f2- from the free end 5 of the cantilever beam 7, and is sent to the light receiving element 37 as beat light.
As a result, a change in phase corresponding to a change in the position of the free end portion 5 can be caused. By detecting this phase change as a phase difference with the basic beat signal using a phase difference meter, the amount of movement of the free end portion 5 can be detected. The linear polarizer 34, like the linear polarizer 23,
and f2' interference to obtain a beat signal. The output unit 11 includes an X position detector 41 installed to detect the amount of movement of the free end portion 5 and the amount of movement of the X drive device.
The surface shape of the sample 4 can be output based on the signal from the Y position detector 42 and the output of the Y position detector 42 attached to detect the amount of movement of the Y drive device.

(Effects) According to this example, since the cantilever beam 7 is directly controlled, high-speed scanning is possible, and when used in conjunction with the Z coarse movement device, it is possible to measure samples with large irregularities. Therefore, by directly measuring the movement of the sample and the cantilever beam 7, it is possible to output an accurate surface shape without relying on control information from the control unit that has mechanical errors such as hysteresis.

[Effects of the Invention] As described above, according to the present invention, the amount of deflection can be detected without being affected by the movement of the cantilever beam holding part, and the surface shape can be determined with high precision without applying extra external force to the cantilever beam. can be measured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the concept of the shape measuring device of the present invention, FIG. 2 is an explanatory diagram showing the configuration of the first embodiment of the shape measuring device of the present invention, and FIG. 3 is a second embodiment of the shape measuring device of the present invention. FIG. 4 is an explanatory diagram showing the configuration of a third embodiment of the shape measuring device of the present invention. FIG. 5 is an explanatory diagram showing the configuration of a conventional shape measuring device. 2 ... Basic beat detection section 3 ... XYZ drive device 4 ... Sample cusp Light source with light of two frequencies Cantilever beam Tunneling chimp measurement Beat detection part Phase difference meter control section First optical section Second Optical section Fixed end holding section Output section Beam splitter Linear polarizer Basic beat light receiving element Polarizing beam splinter λ/4 wave plate λ/4 wave plate mirror Linear polarizer Measurement Beat light receiving element X drive device Y drive device X drive device Beam expander Beam Splinter Wollaston Prism Condensing Lens Phase Contrast Mirror Linear Polarizer Polarizer Polarizer Light Receiving Element Haese Z Coarse Adjuster Z Fine Adjuster X Position Detector Y Position Detector Beam Splinter Figure 2 Figure 4

Claims (1)

[Claims] (1) It has a cantilever beam having a tip at its free end, and a scanning mechanism unit that scans the sample surface by bringing the tip and the sample surface closer together, and the tip and the sample surface are brought closer together. In a device that measures the shape of the cantilever beam by the amount of deflection that occurs when the beam is deflected, a light source having two different frequencies is used, and light of one of the two frequencies is emitted to the free end of the cantilever beam.
an optical section that projects light of the other frequency to the fixed end and combines the reflected lights; a measurement beat detection section that detects the beat light of the combined light; and a beat signal based on the two frequencies of the light source. a basic beat detection section; a phase difference meter that measures the phase difference between the beat signals produced by the basic beat detection section and the measurement beat detection section; and a control section that controls the scanning mechanism section and controls the initial phase difference to a constant amount. , and an output section that outputs position information of the scanning mechanism section as a shape of a sample surface.