JP2011215168A - Method for detecting displacement of scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a displacement detection method that increases the amount of light incident on a light-receiving surface of a photodetector by raising the efficiency in transmission of light on a light path by increasing an output from a light source and thereby reduces the proportion of shot noise or Johnson noise to detection sensitivity.SOLUTION: An optical displacement detection mechanism 9 consists of: a light source 10, which irradiates a measuring object 6 with light; a light source drive circuit 21, which drives the light source 10; a photodetector 16, constituted by a semiconductor, which receives the light with which the light source 10 has irradiated the measuring object 6, converts the light into an electrical signal, and detects light intensity; and an amplifier 22 including a current/voltage conversion circuit which makes a current/voltage conversion of a signal detected by the photodetector 16 at a certain gain. In such an optical displacement detection mechanism 9, a light source 10 whose spectrum has a half width of 10 nm or greater is used to suppress the occurrence of mode-hopping noise or return light noise even when the light source 10 is driven at 2 mW or greater.

Description

  The present invention is used in a scanning probe microscope, a surface shape measuring device using a probe, etc., and irradiates a measurement target with light from a light source, and detects the intensity of the light after irradiation with a photodetector made of a semiconductor. The present invention relates to a displacement detection method for detecting the displacement of a measurement object such as a cantilever for a scanning probe microscope.

  A scanning probe microscope (SPM) is a device for measuring samples such as metals, semiconductors, ceramics, resins, polymers, biomaterials, insulators, etc. in a micro area and observing uneven images and physical property information on the sample surface. Scanning Probe Microscope) is known.

  In these scanning probe microscopes, those having a sample holder on which a sample is placed and a cantilever that has a probe at the tip and is brought close to the surface of the sample are well known. Then, the sample and the probe are relatively scanned in the sample plane (XY plane), and the displacement of the cantilever is measured by the displacement detection mechanism during the scanning, while the sample or the probe is orthogonal to the sample surface ( By operating in the Z direction) and controlling the distance between the sample and the probe, the surface shape and various physical property information are measured.

  Here, FIG. 6 shows a schematic configuration diagram of a scanning probe microscope related to a displacement detection method of a conventional typical optical displacement detection mechanism (see, for example, Patent Document 1).

  A scanning probe microscope 201 in FIG. 6 has a sample stage 212 on which a sample 211 is placed at the tip, and a three-axis fine movement mechanism (scanner) 213 constituted by a cylindrical piezoelectric element whose end is fixed on a base 215. The sample is finely moved in the direction (Z direction) perpendicular to the sample surface while being scanned in the sample surface (XY plane).

  Further, a cantilever 207 having a probe 209 at the tip is held by a column 203 fixed to the base 215 via a highly rigid arm 205. The probe 209 is formed on the lower surface of the tip of the cantilever 207 so as to protrude downward, and the tip of the probe 209 is brought close to the surface of the sample 211 by a coarse movement mechanism (not shown) operable in the Z direction. It is a configuration.

  Above the cantilever 207, a semiconductor laser (LD) 221 and a photodetector 235 made of a semiconductor material are provided, and an optical displacement detection mechanism generally called an optical lever method is provided.

  Here, the operation principle of the optical lever type optical displacement detection mechanism will be described in detail.

  7A is a schematic configuration diagram of the optical displacement detection mechanism 200, and FIG. 7B is an electric circuit diagram connected to the photodetector 235 made of a semiconductor. In the optical displacement detection mechanism 200, laser light (incident light 231) is collected and irradiated on the back surface of the cantilever 207 from a light source 221 that is installed above the cantilever 207 and is made of a semiconductor laser. The incident light 231 is reflected from the back surface of the cantilever 207, and the reflected light 233 strikes a photodetector 235 that is installed obliquely above the cantilever 207 and is made of a semiconductor. The light detector 235 can detect the incident position of the reflected light 233 with a structure in which the light receiving surface is vertically divided into two.

When light strikes the light receiving surfaces (A, B) of the photodetector 235, currents i _A , i _B are generated from the light receiving surfaces (A, B). Current / voltage conversion circuits 242a and 242b are connected to the rear side of the light receiving surface for each light receiving surface, and the current signals i _A and i _B are converted to the voltage signal v _A by the amplification factor defined by the feedback resistance value R _IV. , V _B and a voltage signal is input to a differential amplifier circuit 243 described later.

Here, in FIGS. 6 and 7, when the probe 209 and the sample 211 are brought close to each other, an interatomic force acts first, and when further brought closer, a contact force acts, causing the cantilever 207 to bend. When the cantilever 207 is bent, the spot 241 on the light receiving surface of the photodetector 235 moves up and down. Here, the amount of deflection of the cantilever 207 can be measured by detecting the voltage signal v _AB of the difference between the upper and lower light receiving surfaces by the differential amplifier circuit 243. A normal band pass filter 244 is provided behind the differential amplifier circuit 243 in order to cut frequency components other than the band used for measurement and suppress noise, and a signal passing through the band pass filter 244 is It is sent to the Z feedback circuit 251.

Since the deflection amount of the cantilever 207 depends on the distance between the probe 209 and the surface of the sample 211, the deflection amount of the cantilever 207 is detected by the output voltage v _AB of the photodetector 235 and input to the Z feedback circuit 251. Is constant, that is, the output voltage v _AB is constant, the distance between the probe 209 and the surface of the sample 211 is controlled by the Z fine movement mechanism of the three-axis fine movement mechanism 213, and the sample is scanned by the XY scanner of the three-axis fine movement mechanism 213. By doing so, an uneven image on the sample surface is obtained. These controls are performed by the control unit 257, and the three-axis fine movement mechanism 213 is driven by the XYZ scanner driver 253. The obtained uneven image is displayed on the display unit 255.

  In this optical displacement detection mechanism, the height of measurement data depends on the detection sensitivity of the displacement detection mechanism (the amount of output voltage per unit length) and the magnitude of the noise component mixed in the signal of the optical displacement detection mechanism. Resolution is determined.

  Here, there are several possible reasons for noise in the optical displacement detection mechanism.

(1) Photo detector shot noise (2) Photo detector Johnson noise (thermal noise)
(3) Light source quantum noise (4) Light source return light noise, mode hop noise (5) Cantilever thermal fluctuation (6) Light interference noise Among these, the frequency band most used in normal scanning probe microscopes The high degree is the shot noise of the photodetector (1), and the ratio of the shot noise to the detection sensitivity becomes smaller in inverse proportion to the square root of the light amount P on the light receiving surface.

  In addition, when the frequency at the time of measurement is high, the dependence of Johnson noise in (2) also increases, and the ratio of Johnson noise to detection sensitivity decreases in inverse proportion to the amount of light P on the light receiving surface.

  Here, the light amount P on the light receiving surface is expressed by P = αP0, where α is the output P0 of the light source, and α is the light transmission efficiency on the optical path from the light source through the measurement object to the photodetector.

  As described above, as the shot noise and Johnson noise increase in intensity P on the light receiving surface of the photodetector, the amount of noise with respect to the detection sensitivity decreases, and as a result, the resolution of the measurement data improves. That is, increasing the output P0 of the light source or improving the transmission efficiency on the optical path is effective in reducing the ratio of noise to detection sensitivity.

  On the other hand, when considering the noise on the light source side of the semiconductor laser, which is the most commonly used light source in the conventional optical displacement detection mechanism, the semiconductor laser emits spontaneously emitted light in the element in the low power region. The ratio of (3) increases and noise called quantum noise (3) occurs. As the power increases, the ratio of stimulated emission light becomes dominant and the ratio of quantum noise decreases. However, the semiconductor laser reduces the quantum noise as the output is increased. On the other hand, when it is driven at a high output, it is reflected by a cantilever, a sample, or an optical element arranged in the optical path as shown in (4). Return light noise that returns to the semiconductor laser and mode hop noise that occurs when temperature and light output fluctuate. For this reason, there is an optimum value for the output on the light source side, and in the prior art, driving was performed at 2 mW or less. As described above, in order to reduce the quantum noise level of the photodetector, it is necessary to increase the output on the light source side. However, the output is limited in order to suppress the generation of return light noise and mode hop noise on the light source side. It was.

  In order to reduce mode hop noise and return light noise, it is effective to reduce the coherency of the light source. In other words, in the spectrum of the intensity with respect to the wavelength of the light source, it is preferable to use a light source having a wide spectrum width at the portion where the intensity is maximum. For this purpose, the semiconductor laser has been subjected to high frequency modulation. In addition, in order to prevent return light due to a measurement target or a member in the optical path, the optical state in which reflected light does not return to the semiconductor laser has been changed by changing the polarization state of incident light and reflected light. .

  In addition, since a semiconductor laser is a light source with high coherency and excellent coherence, for example, in a scanning probe microscope, the reflected light from the cantilever interferes with the light reflected from the sample that protrudes from the cantilever, resulting in an uneven image. In addition, (6) interference noise may occur in data when measuring physical properties with respect to the distance between the probe and the sample.

JP-A-10-104245

Takeshi Fukuma et al, Development of low noise cantilever deflection sensor for multienvironment frequency-modulation atomic force microscopy ・ REVIEW OF SCIENTIFIC INSTRUMENTS, 76,053704 (2005)

  However, even if high frequency modulation or polarization of an optical system is used, mode hop noise and return light noise cannot be completely suppressed. Therefore, in the conventional technique, the output from the semiconductor laser is set to 2 mW or less, and the driving is performed in a region where mode hop noise and return light noise hardly occur.

  In addition, in order to use high-frequency modulation or a polarization optical system, it is necessary to prepare special circuits and optical elements, which complicates the system and increases the cost.

  Accordingly, an object of the present invention is to provide a displacement detection method using an optical displacement detection mechanism used in a scanning probe microscope or the like, which is simpler than the conventional displacement detection method in which the ratio of noise to detection sensitivity is reduced. Is to provide in the system.

  Furthermore, in order to suppress the ratio of noise to the detection sensitivity, it is necessary to increase the amount of light incident on the photodetector. For this purpose, the light output from the light source passes through the measurement object from the light source. It is necessary to increase the light transmission efficiency α in the process of reaching the detector. Accordingly, an object of the present invention is to provide a displacement detection method that increases the amount of incident light on the light receiving surface of the photodetector by increasing the transmission efficiency of light from the light source and reduces the ratio of noise to detection sensitivity. .

  Light detection comprising a light source for irradiating light to a measurement object, a light source driving circuit for driving the light source, and a semiconductor for detecting light intensity by receiving light after irradiating the measurement object from the light source and converting it into an electrical signal In a displacement detection method using an optical displacement detection mechanism comprising a detector and a current / voltage conversion circuit for current / voltage converting a detection signal of the photodetector at a predetermined amplification factor, an intensity spectrum with respect to the wavelength of the light source When the light source is measured, a light source having a half-width of the spectrum where the intensity is maximum is 10 nm or more, preferably 25 nm or less, and the intensity (output) of the light source is driven at 2 mW or more. The displacement detection method thus configured is used for detecting the displacement of a cantilever or a probe of a scanning probe microscope.

  In this way, in the spectrum of the intensity with respect to the wavelength of the light source, mode hop noise and return light noise are not generated by using a low-coherent light source and widening the spectrum width of the portion where the intensity is maximum. In addition, since the output of the light source can be increased, the amount of light incident on the light receiving surface of the photodetector can be increased, and the ratio of shot noise and Johnson noise to the detection sensitivity can be reduced. As a result, the resolution of the optical displacement detection mechanism can be increased.

  In the displacement detection method of the present invention, the cantilever or probe of the scanning probe microscope is driven in the solution. In this case, a transparent substrate having an arbitrary transmittance with respect to the light used for the light source is inserted in the optical path between the light source and the cantilever or the probe to be measured, and the substrate and the measurement target are The solution was filled so that the interface was in contact, and a cantilever or a probe was placed in the solution.

  With this configuration, even if reflected light from the surface of the substrate or the interface between the solution and the substrate is generated, no return light noise or mode hop noise is generated, so the output of the light source can be increased, and light detection The amount of light incident on the light receiving surface of the detector can be increased, and the ratio of shot noise and Johnson noise to the detection sensitivity can be reduced. As a result, the resolution of the optical displacement detection mechanism can be increased.

  In the displacement detection method of the present invention, the light receiving surface of the photodetector is divided into four or two parts, the light from the light source is irradiated onto the measurement target, and the reflected light from the measurement target is received by the light receiving surface. It was configured as follows. Alternatively, the measurement object is irradiated with light from the light source, and a shadow of the measurement object is projected onto the light receiving surface of the photodetector.

  With such a configuration, it is possible to increase the measurement resolution of the scanning probe microscope.

  In the present invention, a super luminescence diode (SLD) is used as the light source. SLD has a spectrum half-width of about 10 nm to about 25 nm, and has a spectrum width wider than that of a semiconductor laser, and is a low-coherent light source. Therefore, even when driven at a high output, no return light noise or mode hop noise occurs. In addition, since the spectrum width is narrower than the half-value width (approximately 20 to 70 nm) of the spectrum of the light-emitting diode, the spot can be condensed on the measurement target.

For example, in a cantilever for a scanning probe microscope, the width of the cantilever is generally 30 μm or less. If the spot becomes larger than this, the spot protrudes from the object to be measured, and as a result, the loss of light on the optical path increases and is transmitted. Although the efficiency is reduced, the spot can be narrowed down, so that the transmission efficiency can be increased.
In addition, since the coherence is inferior to that of a semiconductor laser, interference noise caused by reflected light from the cantilever and light that protrudes from the cantilever and reflects from the sample is also suppressed.

  In the present invention, an optical member having a reflecting surface having an arbitrary reflectivity and having a polarization dependency on the optical path from the light source through the measurement object to the photodetector is inserted to make the polarization dependency. The light source and the optical member are arranged so that the reflectance of the optical member according to the polarization direction of the light source is high, and the optical path is bent by reflecting the light by the optical member.

  Further, an optical member provided with a coating having a reflection surface having an arbitrary reflectance on the optical path from the light source through the measurement object to the photodetector and having a wavelength dependency on the reflectance is inserted, and The characteristics of the coat were set so that the reflectance of the optical member at a wavelength at which the intensity of the light source is maximum was increased, and the optical path was bent by reflecting light by the optical member.

  In addition, a light source having a wavelength of 700 nm or more, a reflecting member coated with gold or a gold alloy is disposed on the optical path from the light source to the measurement object and reaching the photodetector, and the light is reflected by the reflecting member to cause an optical path. Was bent.

  With this configuration, it is possible to increase transmission efficiency even with a compact displacement detection mechanism.

  Furthermore, in the present invention, the object to be measured is a cantilever, and both surfaces of the cantilever are coated with the same material and thickness. Further, the wavelength of the light source was set to 700 nm or more, the measurement object was a cantilever, and gold or a gold alloy coat was applied to one side or both sides of the cantilever.

  By configuring in this way, the cantilever itself functions as a reflecting member, the reflectance on the reflecting surface of the cantilever can be increased, and the transmission efficiency can be increased. When the cantilever is coated, the cantilever warps due to the heat of light from the light source irradiated to the cantilever due to the difference in linear expansion coefficient between the cantilever base material (usually silicon or silicon nitride) and the coated material. However, by applying coating on both sides of the cantilever, the difference in linear expansion coefficient is offset by the coating on both sides, and even if the amount of incident light is increased, the cantilever is not warped.

  In the present invention, the light from the light source is propagated by the optical fiber to irradiate the measurement object. Thus, by guiding light to the measurement target with the optical fiber, the displacement of the measurement target can be detected even in a narrow place. When the light enters the optical fiber, the reflected light from the end face causes return light noise and intensity fluctuations. However, these noises can be prevented by using a light source having a wide spectrum width. In particular, when an SLD is used, the coupling efficiency to the optical fiber is increased and the transmission efficiency can be increased.

  As described above, in the present invention, by using a low-coherence light source having a spectrum half-width of 10 nm or more, preferably 25 nm or less, the output of the light source can be reduced to 2 mW without generating mode hop noise or return light noise. Since it can be increased as described above, the amount of light incident on the light receiving surface of the photodetector can be increased, and the ratio of shot noise and Johnson noise to detection sensitivity can be reduced. As a result, the resolution of the optical displacement detection mechanism can be increased.

  Also, by configuring the reflection mirror on the optical path and the reflectivity of the measurement target according to the polarization and wavelength characteristics of the light source, it is possible to improve the light transmission efficiency from the light source to the photodetector through the measurement target. It is possible to increase the amount of light incident on the light receiving surface of the photodetector, and to reduce the ratio of shot noise and Johnson noise to the detection sensitivity. As a result, the resolution of the optical displacement detection mechanism is increased. It becomes possible to do.

  Furthermore, by using an SLD with a half-width of the spectrum of 10 nm or more and 25 nm or less as the light source, the diameter of the spot irradiated to the measurement object can be reduced, and the loss of light due to the light protruding from the measurement object can be prevented. . Furthermore, when propagating by an optical fiber, the coupling efficiency to the optical fiber can be increased. For this reason, it is possible to increase the transmission efficiency and increase the amount of light incident on the light receiving surface of the photodetector. The ratio of shot noise and Johnson noise to the detection sensitivity can be reduced, and the resolution of displacement detection can be increased. It becomes.

It is a general-view figure of the mechanism concerning the displacement detection method for scanning probe microscopes concerning the 1st example of the present invention. FIG. 2 is a circuit diagram of an amplifier including the current / voltage conversion circuit of FIG. 1. It is a general-view figure of the mechanism concerning the displacement detection method for scanning probe microscopes for measuring the sample in the solution concerning the 2nd example of the present invention. It is a general-view figure of the mechanism concerning the displacement detection method for scanning near field microscopes concerning the 3rd example of the present invention. It is a general-view figure of the mechanism concerning the displacement detection method for scanning probe microscopes of an optical fiber propagation system concerning the 4th example of the present invention. It is a general-view figure of the mechanism concerning the displacement detection method for the conventional scanning probe microscope. It is a general-view figure of the mechanism concerning the displacement detection method for the conventional scanning probe microscope.

  Hereinafter, the scanning probe microscope of the present invention will be described with reference to the drawings.

  A mechanism relating to the displacement detecting method of the first embodiment according to the present invention is shown in FIGS. FIG. 1 is a schematic view of a mechanism when the displacement detection method of the present invention is applied to a scanning probe microscope. Although FIG. 1 shows a front view, the photodetector portion is shown in a perspective view. FIG. 2 is a circuit diagram of the amplifier 22 including the current / voltage conversion circuit described in FIG.

  In this embodiment, a sample holder 1 is fixed at the tip, and a three-axis fine movement mechanism 4 made of a cylindrical piezoelectric element having a terminal fixed on the coarse movement mechanism 2 is provided. The triaxial fine movement mechanism 4 includes an XY scanner unit 4a that scans the sample 5 placed on the sample holder 1 in a sample plane (XY plane) direction, and a Z that finely moves in a direction perpendicular to the sample plane (Z direction). A fine movement mechanism 4b is provided.

  Above the sample 5 is a cantilever 6 having a sharpened probe 6b at the tip of the cantilever portion 6a, the base material being made of silicon, 10 nm of chromium as a base, and 100 nm of gold coated on both sides with the same thickness. Is fixed to the base 8 via the cantilever holder 7. An optical displacement detection mechanism 9 is disposed above the cantilever 6.

  Here, the principle of operation of the scanning probe microscope in the present embodiment will be described. The present embodiment is an atomic force microscope which is a kind of scanning probe microscope, and is used for measuring a concavo-convex image on a sample surface. In this embodiment, a method generally called a contact type atomic force microscope is used.

  When the sample 5 is moved closer to the probe 6b by the coarse movement mechanism 2, an atomic force acts between the probe 6b and the sample 5, and the probe 6b receives an attractive force. As the probe 6b further approaches, the probe 6b receives a repulsive force, and finally the probe 6b and the sample 5 come into contact with each other. At this time, the cantilever 6a bends according to the force received by the probe 6b. The force received by the probe 6 b, that is, the amount of deflection of the cantilever 6 a depends on the distance between the probe 6 b and the surface of the sample 5.

  Accordingly, the sample 5 is raster-scanned by the XY scanner unit 4a while the distance between the probe 6b and the sample 5 is changed by the Z fine movement mechanism 4b so that the deflection amount of the cantilever 6a becomes constant. An uneven shape can be obtained.

  Next, the configuration and operation principle of the optical displacement detection mechanism 9 related to the displacement detection method of this embodiment will be described.

  This optical displacement detection mechanism 9 is generally called an optical lever method, and uses a super luminescence diode (SLD), which will be described later, as a light source 10, and condenses light emitted from the light source 10 with a condenser lens 11. Then, the optical path of the incident light 13 is bent by the beam splitter 12 and irradiated to the back surface of the cantilever 6a to be measured from directly above (Z direction). The light intensity of the light source 10 is set by the light source driving circuit 21.

  The cantilever 6 is disposed to be inclined with respect to the XY plane, and the reflected light 14 is reflected in a direction different from the optical axis of the incident light 13. The reflected light 14 is bent by a mirror 15 and is incident on a photodetector (photodetector) 16 made of a semiconductor.

  The optical path of the light is temporarily formed on the back surface of the cantilever 6a, and is configured to form a spot 20 having a finite size on the light receiving surface of the photodetector 16. The photodetector 16 is manufactured using a semiconductor as a material, and has a configuration in which the light receiving surface is divided into two (A, B).

  When light enters the photodetector 16, a current signal is generated from the semiconductor constituting the photodetector 16, and is provided at the rear end of the photodetector 16. The current / voltage conversion circuit 30 and the differential amplifier circuit 33 constitute the current signal. The amplifier 22 is converted into a voltage signal with a predetermined amplification factor for each light receiving surface. The output at this time is displayed on the voltage monitor 23.

  Here, when the cantilever 6a bends in the Z direction, the spot 20 on the photodetector 16 moves up and down on the light receiving surface. The flow of the light detection signal at this time will be described with reference to the circuit diagram of the amplifier 22 including the current / voltage conversion circuit of FIG.

  The amount of deflection of the cantilever 6a can be measured by measuring the intensity Pa-Pb of light incident on the region A of the upper light receiving surface and the region B of the lower light receiving surface of the photodetector 16. When light of Pa and Pb intensity is incident, the optical signal is converted into an electric signal by the photodetector 16, and currents Ia and Ib are generated from the light receiving surfaces A and B, respectively. This current is converted into voltage signals Va and Vb by a current / voltage conversion circuit 30 including an operational amplifier 31 and a resistor R1 connected to each light receiving surface. At this time, assuming that the feedback resistance value of the current / voltage conversion circuit 30 is R1, there is a relationship of Va = R1 × Ia and Vb = R1 × Ib. As described above, the current / voltage conversion circuit 30 in the first stage is amplified with the amplification factor R1, and the current signal is converted into the voltage signal. These voltage signals Va and Vb are sent to a differential amplifier circuit 33 composed of an operational amplifier 32 and resistors R2 and R3, and a voltage difference signal Va-b is detected. Here, when the differential amplifier circuit is configured with the operational amplifier and the resistance values R2 and R3 as shown in the figure, the relationship Va−b = (R3 / R2) × (Va−Vb) holds, and the differential amplifier circuit amplifies. Amplified at a rate R3 / R2, Va-b is output. By detecting this Va-b, the deflection amount of the cantilever can be measured.

  In this embodiment, the photodetector 16 having a light receiving sensitivity of 0.65 A / W is used, and the feedback resistance value R1 of the current / voltage conversion circuit 30 is 45 kΩ. The resistance values of the differential amplifier circuit 33 are R2 = 10 kΩ and R3 = 20 kΩ. Although the absolute amount of shot noise is proportional to the feedback resistor R1, the detection sensitivity is also proportional to R1, so that it is canceled when the ratio of the shot noise to the detection sensitivity is obtained. Further, when the amount of light incident on the photodetector 16 is increased, if the amplification factor is set to be the same as in the conventional case, the detection sensitivity is too high and the control circuit 24 is likely to oscillate. The system oscillation was suppressed by reducing the size.

  The Va-b voltage signal is sent to the control circuit 24 shown in FIG. 1, and the Z fine movement mechanism 4b is operated from the scanner drive circuit 25 by a signal corresponding to the difference compared with the preset operating point, and the sample Control is applied to keep the distance between the probe 5 and the probe 6b constant. Further, the scanner driving circuit 25 operates the XY scanner unit 4a to raster scan the sample 5.

  At this time, by displaying the voltage signal applied to the triaxial fine movement mechanism 4 on the display unit 26, an uneven image on the surface of the sample 5 is obtained.

  Here, the characteristics of the SLD used for the light source 10 will be described. The SLD used in this example was an SLD with a center wavelength of 830 nm, a half-width of the spectrum of intensity with respect to the wavelength of 17 nm, and a maximum rated output of 6 mW. In general, commercially available SLDs have a spectrum half-width in the range of 10 to 25 nm, and the half-width of the spectrum of a semiconductor laser (LD) is narrower than that of several nm. Light source. For this reason, it is a light source that has low coherence compared to an LD, and has little return light noise due to reflected light from an optical member in a measurement object or an optical path. Also, mode hop noise does not occur. When high output drive is performed with an LD, these return light noise and mode hop noise are remarkably generated. Therefore, it is necessary to cut the return light using high frequency drive or a polarizing plate. In some cases, it is possible to increase the output without performing these measures. In addition, light emitting diodes (LEDs) typically have a spectrum half-width of 20 to 70 nm and have low coherence, but LEDs are difficult to squeeze with a lens, making small spots on the back of cantilevers and on photodetectors. However, the coupling efficiency to the optical fiber is poor, but the SLD can also secure the light collecting property. Thus, in the LD used in the conventional scanning probe microscope, the power of the original light source is limited to 2 mW. However, in the present invention, the light source 10 is not affected by mode hop noise or return light noise. It was possible to drive with an output of 2 mW or more. In this embodiment, driving was performed at 3 mW.

  Thus, since the light output of the light source can be made higher than before, the amount of light incident on the photodetector is also increased, and shot noise and Johnson noise can be suppressed. As a result, the ratio of noise to detection sensitivity is reduced, and the resolution can be increased.

  In addition, when considering interference between the reflected light from the cantilever and the light reflected from the sample that protrudes from the cantilever, if the SLD is used, the spot light irradiated to the measurement target can be reduced, so that the light protruding from the cantilever is reduced. In addition, since the light source itself has low coherence, interference noise is also suppressed.

  In the present invention, it is preferable to use SLD as the light source 10. However, if the light source has a spectrum half-width of 10 nm or more, such as an LED, it is driven at a high output of 2 mW or more without being affected by mode hop noise or return light noise. Is included in the present invention.

  Further, in the present invention, in addition to increasing the light amount of the light source 10, the configuration is made such that the transmission efficiency α of the optical system is increased, and the incident light to the photodetector 16 is made larger.

  First, the reflective surface of the beam splitter 12 in the optical path is coated with a dielectric that makes the near-infrared reflectance of the wavelength 830 nm higher than that in the visible region, and the beam splitter 12 is made to have polarization dependency. , S-polarized light (perpendicular to the paper surface) was incident to increase the reflection efficiency. Since the light from the SLD 10 is polarized, the SLD 10 is arranged so that the S-polarized light is incident on the reflecting surface of the beam splitter 12 in parallel. When a beam splitter that does not depend on polarization was used, the reflectivity was 0.5. However, by using a polarization-dependent type and increasing the reflectivity in the near infrared region, the reflectivity can be improved. Improved to 0.7.

  Next, the cantilever 6 is usually coated with aluminum in order to function as a reflecting member that reflects light, but gold is used to increase the reflectance in the near infrared region of 830 nm, which is the oscillation wavelength of the SLD 10. Coated. The reflectance with respect to 830 nm was able to be increased to 0.95 by using gold as opposed to 0.88 for aluminum. In order to improve the adhesion between silicon and gold as a base material, both surfaces are coated with chromium as a base.

  Here, when the cantilever 6 is irradiated with light at a high output, the temperature of the cantilever 6 is increased by the light. At this time, the cantilever 6 is warped due to a difference in linear expansion coefficient between the base material of the cantilever 6 and the coated metal. In order to prevent this, in the present embodiment, the same gold and chromium are deposited on both sides of the cantilever 6 by the same thickness by sputtering, and the difference in linear expansion coefficient is canceled by the metal on both sides to prevent warpage. I tried to do it. Note that the reflectance is slightly sacrificed, but when the influence of warping is large, it is not necessary to coat. In this case, the amount of incident light of the photodetector can be secured by increasing the power of the light source 10 by the amount that the reflectance of the cantilever 6 has decreased. In addition, when warping does not become a problem in measurement, there is no problem with a single-sided coating alone.

  Further, when the light irradiating the cantilever 6a cannot be narrowed, the spot diameter can be narrowed down to about 10 μm by using the SLD although the optical loss occurs from the cantilever 6a. In a general cantilever, since the width of the cantilever is 10 to 30 μm, the protrusion from the cantilever can be almost eliminated. The mirror 15 that functions as a reflecting member for bending the optical path in the direction of the photodetector 16 after the reflection of the cantilever has been conventionally coated with aluminum, but has been changed to a gold-coated mirror. As a result, the reflectivity of aluminum with a protective film was increased to 0.95 for gold compared to the reflectivity of 0.79.

  Using the optical system as described above, in the present invention, the output of the light source was 3 mW, the irradiation power to the cantilever was 1.05 mW, and the incident power to the photodetector was 0.87 mW.

  By performing the above-described measures, it becomes possible to increase the transmission efficiency α of the optical system, further increase the amount of incident light to the photodetector, and reduce the ratio of noise to the detection sensitivity of the photodetector. As a result, the resolution can be increased.

  In the present embodiment, the photodetector 16 has a light receiving surface that is divided into upper and lower parts. However, a four-part photodetector having a light receiving surface that is divided into left and right is also applicable. In this case, by providing a current / voltage conversion circuit for each light receiving surface, in addition to detecting the deflection amount of the cantilever 6a from the difference signal between the upper and lower light receiving surfaces, the twist amount of the cantilever can be calculated from the difference signal between the left and right light receiving surfaces. It is also possible to detect.

  Further, in this embodiment, the beam splitter 12 is used when changing the optical path of the incident light 13 in order to observe the sample 5 and the cantilever 6 directly above with the optical microscope 29, but the reflection instead of the beam splitter 12 is used. As the member, a total reflection mirror or a dichroic mirror may be used. Moreover, you may irradiate light to a cantilever directly, without using a reflection member. In this case, the transmission efficiency can be further increased.

  A second embodiment according to the present invention will be described with reference to FIG. FIG. 3 is a schematic view of a mechanism related to a displacement detection method for a scanning probe microscope operated in a solution. Since the basic configuration is the same as that of the first embodiment, the description of the overlapping parts is omitted.

In this embodiment, the cantilever 6a is vibrated in the vicinity of the resonance frequency and is brought close to the sample 45, and the amount of decrease in amplitude and the change in phase due to the atomic force and intermittent contact force when close to the sample 45 are measured. It is detected by the optical displacement detection mechanism 9 of the same optical lever system. Since the amount of decrease in amplitude and the amount of change in phase depend on the distance between the sample 45 and the probe 6b, the distance between the probe 6b and the sample 45 can be controlled. Thus, in this embodiment, a vibration type atomic force microscope is used.
Further, the cantilever holder 35 of the present embodiment has a structure composed of a metal base block 36 and a glass base block 37. A vibrator 41 made of a piezoelectric element for cantilever vibration and a cantilever fixing portion 42 are bonded and fixed to the glass base block 37. The cantilever 6 is fixed to the cantilever fixing portion 42. Since the vibrator 41 is used in a solution, the periphery is waterproofed with a silicon sealant to prevent electrical short-circuiting.

  The glass base block 37 is provided with a protrusion 38 whose tip is processed into a flat surface. On the other hand, a petri dish 44 is placed on the sample holder 1 of the three-axis fine movement mechanism 4 composed of a cylindrical piezoelectric element, and a living body such as a cell immersed in a solution 46 in the petri dish 44 or a sample of an organic thin film or the like. 45 is fixed.

  As the sample 45 and the probe 6b are brought closer to each other, the flat portion 39 of the projection 38 comes into contact with the liquid surface in the petri dish by surface tension, and the liquid layer 46 is formed so that the cantilever 6 and the sample 45 are immersed in the solution. It becomes a state.

  In the optical displacement detection mechanism 9, an SLD is used as the light source 10 as in the first embodiment. Light from the SLD is collected by the condenser lens 11, and the optical path of the incident light 13 is made by the beam splitter 12. Bend and irradiate the back surface of the cantilever 6a to be measured from directly above (Z direction). The light intensity of the light source 10 is set by the light source driving circuit 21. The glass base block 35 of the cantilever holder 35 is made of quartz glass and transmits 830 nm which is the wavelength of the SLD. The incident light is bent by the beam splitter 12 in the air layer, then passes through the glass base block 37, proceeds to the liquid layer 46, and is irradiated on the back surface of the cantilever 6a. The laser light reflected by the back surface of the cantilever 6 a passes through the glass base block 37 from the liquid layer 46 and then enters the photodetector 16 having a light receiving surface divided into two via the mirror 15. The photodetector 16 is connected to an amplifier circuit 22 including a current / voltage conversion circuit. The amplifier circuit 22 including the current / voltage conversion circuit is the same as the circuit shown in FIG. 2 of the first embodiment. Here, especially when the cantilever 6a is vibrated in the solution, the amplitude detection signal is affected by the viscous resistance that the cantilever 6a described later receives from the solution and the influence of scattered light from a member through which light passes. In many cases, noise other than the resonance frequency is placed and the measurement accuracy is deteriorated. For the purpose of removing this noise, a band pass filter that removes frequency components other than the vicinity of the resonance frequency of the cantilever 6a may be provided behind the differential amplifier circuit 33 of the amplifier 22.

  Here, since the incident light 13 is reflected at the interface 40 between the glass base block 37 and the air layer 43 and at the interface 39 between the glass base block 37 and the liquid layer 46, the measurement is performed in the air of the first embodiment. The return light to the light source 10 side becomes larger than the case. In the semiconductor laser used as the light source in the conventional optical displacement detection mechanism, this return light generates return light noise and mode hop noise, so that the output of the light source cannot be increased. The noise could not be reduced. Although it is possible to reduce mode hop noise and return light noise by harmonically modulating the light source 10, it cannot be completely removed, and the light source driving circuit 21 becomes complicated when using high frequency modulation. The cost was also high. In particular, when the cantilever 6a is vibrated in a solution, the viscosity resistance is larger and the vibration becomes weaker than in the atmosphere. Therefore, unless the noise with respect to the detection sensitivity is reduced, the vibration detection accuracy deteriorates and the measurement accuracy deteriorates. To do.

  However, since an SLD that is a low-coherent light source is used as the light source 10, return light noise and mode hop noise can be suppressed without using a special technique such as harmonic modulation, and the output of the light source 10 is increased. It became possible. In this embodiment, considering the loss when light passes through the glass base block 37, the output of the light source 10 is set higher than the air layer and driven at 4 mW. For this reason, it is possible to reduce the ratio of shot noise and Johnson to the detection sensitivity of the photodetector 16, and to accurately detect the vibration of the cantilever 6a even in the solution. As a result, it is possible to increase the resolution. .

  A third embodiment of the present invention is shown in FIG. FIG. 4 is a schematic view of a mechanism relating to a displacement detection method for probe displacement detection used in a scanning near-field microscope which is a kind of scanning probe microscope. Detailed configuration other than the main part is omitted.

  The probe 50 used in the present embodiment has a configuration in which the tip of an optical fiber is sharpened, an opening is provided at the tip, and portions other than the opening are coated with aluminum. This probe 50 is fixed to a probe holder 52 to which a piezoelectric element 51 for vibration is attached by a leaf spring 53, and is arranged so that the major axis direction of the probe 50 is orthogonal to the surface of the sample 54.

  The probe 50 arranged in this manner is vibrated in the vicinity of the resonance frequency of the probe 50 in the direction parallel to the surface of the sample 54 (Y-axis direction in the figure) by the vibrating piezoelectric element 51. At this time, when the tip of the probe 50 and the surface of the sample 54 are brought close to each other, the probe tip receives a resistance force, a frictional force, an atomic force, or the like of the adsorption layer on the surface of the sample 54. These forces are collectively called shear force. When the shear force is applied, the amplitude of the probe 50 decreases. The amount of decrease in amplitude depends on the distance between the tip of the probe 50 and the surface of the sample 54. Therefore, the sample 54 and the probe 50 are kept at a constant distance by controlling the distance between the sample 54 and the probe 50 so that the amplitude and phase are constant while measuring the amplitude amount and phase change of the probe 50. Is possible. Similar to the first embodiment, it is possible to measure a concavo-convex image on the surface of the sample by relatively raster-scanning the sample 54 and the probe 50 in this state. In the scanning near-field microscope, light is incident on the probe 50, evanescent light is generated near the opening at the tip of the probe, irradiated on the sample 54, scattered on the sample surface, and the scattered light is detected by a detector. As a result, the optical characteristics of the surface of the sample 54 can be measured simultaneously.

  Here, a method for measuring the amplitude of the probe 50 in this embodiment will be described. The optical displacement detection mechanism 55 of the present embodiment includes a light source unit 56 in which a condenser lens and a light source are incorporated, and a photodetector 57 whose surface is divided into two and made of a semiconductor. Light from the light source unit 56 is applied to the probe 50 from the lateral direction (X direction in the figure). At this time, the light from the light source unit 56 is imaged, but the irradiation point on the probe 50 is irradiated at a position shifted from the imaging point to the extent that the probe 50 does not block all the light.

  The light irradiated to the probe 50 forms an image at one end, and then spreads again to produce a finite spot 58 in the plane of the photodetector 57 disposed at a position facing the light source unit 56 with respect to the probe 50. So that it is incident.

  At this time, the portion blocked by the probe 50 appears as a shadow in the spot 58.

  In the measurement, first, the light source unit 56 is moved by the biaxial light source positioning mechanism 59 provided in the light source unit 56 so that the probe 50 is irradiated with light. Next, the single-axis photodetector positioning mechanism 60 provided on the photodetector 57 side is used to move the photodetector 57 in the left-right direction (Y direction in the figure), and a current disposed behind the photodetector 57. While observing the output of the voltage / voltage conversion circuit 61 with the voltage monitor 63, alignment is performed so that the spot 58 hits approximately the center of the photodetector 57.

  When the probe 50 vibrates in the optical displacement detection mechanism 55 configured in this way, the area difference between the portions where the shadow is not obstructed on the light receiving surface of the two-divided photodetector 57 changes. It is possible to measure the amplitude amount or phase of the probe 50 by detecting the difference in the optical output of.

  In this example, a light emitting diode (LED) having a wavelength of 700 nm and a spectral half width of 35 nm was used as a light source. The light source 56 was driven by a light source driving circuit 64 and used at an intensity of 3 mW.

  LED cannot narrow down the spot like a semiconductor laser or SLD, but the optical fiber probe used in this example has a diameter of φ125μm, which is larger than the cantilever. Is possible.

  When a semiconductor laser is used as a conventional light source, mode hop noise or reflected light noise is generated by reflected light from a probe or a photodetector, so that the light source can be driven with a large intensity of 2 mW or more. However, in this embodiment, an LED which is a light source having a wide spectrum width and a low coherence is used, so that mode hop noise and return light noise do not occur, and the light source can be driven with high output. For this reason, the intensity of the spot on the light receiving surface to the photodetector can be increased, and the ratio of the noise of the photodetector to the detection sensitivity can be reduced, and as a result, the resolution can be increased.

  A fourth embodiment of the present invention is shown in FIG. FIG. 5 is a schematic view of a mechanism related to a displacement detection method for a scanning probe microscope in which light is propagated by an optical fiber, irradiated to the cantilever, and the displacement of the cantilever is detected by an optical lever method. Also in this embodiment, the detailed configuration other than the main part is omitted.

  In this embodiment, a cantilever holder 72 to which a piezoelectric element 73 for cantilever excitation is attached is fixed to the tip of a cylindrical three-axis fine movement mechanism 71 whose end is fixed to a base 70, and a cantilever 74 is attached to the cantilever holder 72. It is fixed. A sample 85 is placed at a position facing the probe 74b provided on the cantilever 74.

  A light source unit 76 including a light source 75, a condenser lens 77, and an optical connector 78 is provided at a position away from the triaxial fine movement mechanism 71. An SLD is used for the light source 75, and the SLD is driven by a light source driving circuit 79. A single mode optical fiber 80 for 830 nm which is the wavelength of SLD is connected to the optical connector 78, and the light of the SLD 75 is coupled to the end of the optical fiber by a condenser lens 77.

  The optical fiber 80 passes through the inside of the cylindrical triaxial fine movement mechanism 71, and the distal end is fixed to the distal end of the triaxial fine movement mechanism. A condensing lens 81 is fixed to the tip of the triaxial fine movement mechanism 71. The light propagated to the tip of the optical fiber is collected again by the condensing lens 81 and collected on the back surface of the cantilever 74a. Here, since the tip of the optical fiber 71, the condensing lens 81, and the cantilever 74 are all fixed to the tip of the triaxial fine movement mechanism 71, even if the triaxial fine movement mechanism 71 is driven, it is condensed on the back surface of the cantilever 74a. The spot position of the light does not deviate.

  The light reflected by the back surface of the cantilever 74a is condensed by the lens unit 82 onto the semiconductor photodetector 83 whose light-receiving surface is divided into four to create a spot. The semiconductor photodetector 83 is connected to an amplifier 84 including a current / voltage conversion circuit, and the displacement of the cantilever 74a is detected. Here, the lens unit 82 is fixed independently of the triaxial fine movement mechanism 71, but the spot on the photodetector 83 does not move even when the cantilever 74 is scanned by driving the triaxial fine movement mechanism 71. The tracking lens structure is as follows.

  In this embodiment, measurement is performed based on the principle of the vibration type atomic force microscope having the above-described configuration. In the first to third embodiments, the sample side is scanned, but in this embodiment, since the cantilever 74 side is scanned, it is possible to measure a large sample. In such a cantilever scan, it is necessary to reduce the weight of components driven by the triaxial fine movement mechanism 71 as much as possible to increase the resonance frequency of the triaxial fine movement mechanism 71 in order to perform high-speed driving. The mechanism attached to the tip of the triaxial fine movement mechanism 71 can be reduced in weight by being separated from the triaxial fine movement mechanism 71 and independently arranged outside and transmitting light through the optical fiber 80.

  Here, when the conventional semiconductor laser was used as the light source, the output of the light source could not be increased due to the return light noise caused by the reflected light at the end face of the optical fiber 80 or the mode hop noise of the LD. By adopting it, it is possible to suppress the generation of these noises and increase the output of the light source. In addition, the SLD can focus light with a lens compared to an LED, etc., so that the coupling efficiency to the optical fiber can be increased, the coupling loss is suppressed, and the light transmission efficiency to the photodetector is increased. It is also possible.

  In this embodiment, the output of the light source can be increased and the transmission efficiency can be increased with the above configuration, so that the intensity of the spot on the light receiving surface to the photodetector can be increased, and the noise of the photodetector with respect to the detection sensitivity. As a result, the resolution can be increased.

  The present invention is not limited to the embodiments described above.

  For example, the light source has a relatively stable output, and when the object to be measured is a very small probe, the optical lens can reduce the light spot to a small size, and when propagating through an optical fiber, it is a superluminescent diode with excellent coupling efficiency to the fiber. (SLD) is preferable, but any light source having a half-width of the spectral intensity of 10 nm or more, such as a light emitting diode (LED) or a white light source, can be applied.

  The power of the light source can be increased within a range where the light source operates stably as long as it is 2 mW or more. The output of the light source is generally susceptible to the heat generated by the light source and the ambient temperature. However, the heat source is radiated by a heat sink, or the temperature of the light source is controlled by a Peltier element to drive the light source stably at a higher output. be able to.

  Furthermore, when measuring with a scanning probe microscope, the reflected light from the cantilever and the light reflected from the sample that protrudes from the cantilever interfere with each other, and the force applied to the probe with respect to the concavo-convex image and the distance between the probe and the sample Interference fringe noise may occur in the relationship (force curve), but the present invention uses a low-coherent light source with a half-width of the spectrum intensity of 10 nm or more. Can be reduced.

  In the present embodiment, a semiconductor photodetector having a light receiving surface divided into four or two is used. However, any detector that converts the intensity of light into an electrical signal is applicable. For example, a semiconductor element called a Position Sensitive Detector (PSD) that does not have a dividing surface and can detect a spot position on a light receiving surface made of a semiconductor is commercially available.

  Further, the scanning probe microscope is not limited to the contact-type or vibration-type atomic force microscope and the scanning near-field microscope described in the embodiments, and can detect these displacements and amplitudes using a cantilever or a probe. However, any device that controls the distance between the probe and the sample surface, and that measures the physical properties of the sample surface by detecting the force or interaction applied to the probe are all objects of the present invention. Further, the processing of the sample surface by the probe and the manipulation of the material on the sample surface are all objects of the present invention. Further, it is not always necessary to scan with an XY scanner, and the present invention includes a case where an interaction in the height direction is detected using a Z fine movement mechanism.

  Further, the displacement detection method of the scanning probe microscope of the present invention includes, for example, a surface roughness measuring instrument using an optical displacement detection mechanism, a surface information measuring device such as an electrochemical microscope, or a probe processing for processing a sample surface with a probe. The present invention can also be applied to a displacement detection method such as a device. Even in these cases, by applying the displacement detection method of the present invention, the ratio of noise to the detection sensitivity can be reduced, and the measurement accuracy is improved.

DESCRIPTION OF SYMBOLS 1 Sample stage 2 Coarse movement mechanism 4 Triaxial fine movement mechanism 5 Sample 6 Cantilever 7 Cantilever holder 9 Optical displacement detection mechanism 10 Light source 11 Condensing lens 12 Beam splitter 15 Mirror 16 Light detector 17 Light source positioning mechanism 18 Light detector positioning Mechanism 19 Light source unit 20 Spot 21 Light source drive circuit 22 Amplifier (current / voltage conversion circuit)
23 Voltage monitor 29 Optical microscope 30 Current / voltage conversion circuit 33 Differential amplification circuit 35 Cantilever holder 36 Metal base block 37 Glass base block 43 Air layer 44 Petri dish 45 Sample 46 Solution 50 Probe 52 Probe holder 54 Sample 55 Optical displacement detection mechanism 56 Light Source 57 Photodetector 58 Spot 59 Light Source Positioning Mechanism 60 Photodetector Positioning Mechanism 61 Amplifier (Current / Voltage Conversion Circuit)
64 Light source driving circuit 71 Triaxial fine movement mechanism 72 Cantilever holder 74 Cantilever 75 Light source 76 Light source unit 77 Condensing lens 78 Optical coupler 79 Light source driving circuit 80 Optical fiber 81 Condensing lens 82 Lens unit 83 Photo detector 84 Current / voltage conversion circuit 85 Sample 200 Optical displacement detection mechanism 201 Scanning probe microscope 207 Cantilever 209 Probe 211 Sample 213 Three-axis fine movement mechanism 221 Light source (semiconductor laser)
235 Photodetector 242 Amplifier (current / voltage conversion circuit)
243 Differential amplifier circuit 244 Band pass filter

Claims (10)

A cantilever having a probe at the tip or a probe of any shape;
When the spectrum of the intensity with respect to the wavelength is measured, it consists of a super luminescence diode (SLD) or a light emitting diode (LED) having a half width of 10 nm or more and 25 nm or less in the portion where the intensity is maximum, A light source for irradiating
A light source driving circuit for driving the light source;
A light detector for detecting light intensity by receiving light after irradiating the measurement target from the light source on a light receiving surface made of a semiconductor material and converting the light into an electrical signal;
In a displacement detection method of a scanning probe microscope comprising: a current / voltage conversion circuit that processes a detection signal of the photodetector with a predetermined amplification factor;
A displacement detection method for a scanning probe microscope, wherein the output of the light source is driven at an output of 2 mW or more.   The light receiving surface of the photodetector is divided into four or two, the light from the light source is irradiated onto the measurement target, and the reflected light from the measurement target is received by the light receiving surface. A displacement detection method for a scanning probe microscope.   The light receiving surface of the photodetector is divided into four or two, and the measurement object is irradiated with light from the light source, and a shadow of the measurement object is projected onto the light receiving surface of the photodetector. The displacement detection method of the scanning probe microscope described in 1. On the optical path from the light source through the measurement object to the photodetector, an optical member having a reflection surface with an arbitrary reflectivity having polarization dependency,
The light source has polarization dependence;
The displacement detection method for a scanning probe microscope according to any one of claims 1 to 3, wherein the reflectance of the optical member is increased by the arrangement of the light source and the optical member. On the optical path from the light source through the measurement object to the photodetector, an optical member having a reflection surface with an arbitrary reflectivity having wavelength dependency,
The displacement detection method of the scanning probe microscope according to claim 1, wherein the reflectance of the optical member is increased by the arrangement of the light source and the optical member. The wavelength of the light source is 700 nm or more;
The displacement of the scanning probe microscope according to any one of claims 1 to 5, wherein a reflecting member coated with gold or a gold alloy is disposed on an optical path from the light source through the measurement object to the photodetector. Detection method. The measurement object is a cantilever,
The displacement detection method of a scanning probe microscope according to any one of claims 1 to 6, wherein a coating having the same material and thickness is applied to both surfaces of the cantilever.   The displacement detection method for a scanning probe microscope according to claim 1, wherein light from the light source is propagated by an optical fiber to irradiate a measurement object.   The displacement detection method for a scanning probe microscope according to any one of claims 1 to 8, wherein the cantilever or the probe is driven in a solution.   A transparent substrate having an arbitrary transmittance for light emitted from the light source in an optical path between the light source and the cantilever or probe that is the measurement target; and between the substrate and the measurement target. The displacement detection method of the scanning probe microscope according to claim 9, wherein the solution is filled so that the interface contacts.

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