JP5140179B2 - Displacement detection method of scanning probe microscope - Google Patents

Description

  The present invention relates to a displacement detection method related to an optical displacement detection mechanism that irradiates a measurement target with light from a light source and detects the intensity of the light after irradiation with a photodetector. Of surface information measuring devices such as scanning probe microscopes, surface roughness meters, hardness meters, and electrochemical microscopes that measure various physical information (for example, dielectric constant, magnetization state, transmittance, viscoelasticity, friction coefficient, etc.) The present invention relates to a displacement detection method.

  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, the schematic block diagram of the scanning probe microscope using the conventional typical optical displacement detection mechanism is shown in FIG. 6 (for example, refer 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. (For example, see Non-Patent Document 1)
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.

  By measuring the difference in intensity between the light incident on the region A of the upper light receiving surface of the photodetector 235 and the region B of the lower light receiving surface, the amount of deflection of the cantilever 207 can be measured. When light enters the photodetector 235, the optical signal is converted into an electrical signal, 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 242 configured by an operational amplifier 245 and a feedback resistor RIV connected to each light receiving surface. At this time, if the feedback resistance value of the current / voltage conversion circuit 242 is RIV, there is a relationship of vA = RIV × iA and vB = RIV × iB. In this manner, the current / voltage conversion circuit 242 functions as a first-stage amplifier that converts a current signal into a voltage signal with an amplification factor RIV.

  These voltage signals vA and vB are sent to a differential amplifier circuit 243 including an operational amplifier 246 and resistors R2 and R3, and a voltage difference signal vA-B is detected. Here, when the differential amplifier circuit is configured by the operational amplifier and the resistance values R2 and R3 as shown in FIG. 7, the relationship of vA−B = (R3 / R2) × (vA−vB) is established, and the differential amplifier circuit 243 is established. Acts as an amplifier that amplifies the voltage signal at an amplification factor R3 / R2, and outputs a voltage signal vA-B.

  Here, when the probe 209 and the sample 211 are brought close to each other in FIGS. 6 and 7, an interatomic force acts first, and when the probe 209 is further brought closer, a contact force acts and the cantilever 207 is bent. 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 vA-B 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 vA-B of the photodetector 235 and input to the Z feedback circuit 251. The Z fine movement mechanism 213 controls the distance between the probe 209 and the surface of the sample 211 so that the amount is constant, that is, the output voltage vA-B is constant, and the XY scanner 213 scans the sample. An image 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. . However, even if these devices are used, mode hop noise and return light noise cannot be completely eliminated. Therefore, the light intensity on the light source side is driven at 2 mW or less.

  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, mud evolution of low noise cantilever deflection sensor for multienvironment frequency-modulation atomic force microscopy ・ REVIEW OF SCIENTIFIC INSTRUMENTS, 76,053704 (2005)

As described above, the output of the light source is optimized so that the ratio of noise to the detection sensitivity of the optical displacement detection mechanism is reduced, but the conventional optical displacement detection mechanism uses a light source. Since the light intensity on the side and the amplification factor of the amplifier on the photodetector side were fixed, there were the following problems. (1) Since the light intensity on the light receiving surface of the photodetector changes depending on the optical characteristics such as the reflectance of the measurement object and the shape of the measurement object, the detection sensitivity and the ratio of noise differ depending on the measurement object.
(2) The measurement object may be heated by the irradiation light from the light source to the measurement object, and the measurement object may be deformed.
(3) In an optical lever type optical displacement detection mechanism or the like, the detection sensitivity changes depending on the shape such as the length of the object to be measured and the mechanical characteristics such as the spring constant.

  In particular, scanning probe microscopes have been devised to increase reflectance by coating aluminum or gold on the silicon or silicon nitride cantilever to be measured in order to prevent a decrease in detection sensitivity or an increase in noise. . When measuring the electrical characteristics of a sample with a scanning probe microscope, the cantilever is made conductive by coating the cantilever with a conductor such as gold or rhodium. Further, cantilevers having different mechanical characteristics and shapes such as spring constant and resonance frequency are selected depending on the sample to be measured.

  Therefore, in the scanning probe microscope, the reflectance varies greatly depending on the cantilever, and the detection sensitivity and the ratio of noise vary depending on the measurement target.

  Further, the temperature of the cantilever rises due to the irradiation light from the light source due to the difference in the linear expansion coefficient between the material of the film coated on the cantilever and the base material of the cantilever, and the cantilever is bent and deformed. Considering the ratio of noise to detection sensitivity, the cantilever is irradiated with light at a high intensity. Therefore, a cantilever with a small spring constant is greatly affected by thermal deformation.

  Further, when cantilevers having different shapes are selected, since the lever ratio of the light lever changes, the detection sensitivity changes.

  Due to the above problems, the measurement accuracy may be deteriorated in the displacement detection method using the conventional optical displacement detection mechanism.

  Therefore, the object of the present invention is to adjust the detection sensitivity and the ratio of noise without depending on the reflectance, shape and mechanical characteristics of the measurement object even if the measurement object changes, and the measurement object by the irradiation light to the measurement object It is an object of the present invention to provide a displacement detection method and a scanning probe microscope employing the displacement detection method that can reduce the influence of thermal deformation of the material and ensure measurement accuracy under optimum conditions.

  In order to solve the above-mentioned problems, the present invention has the following displacement detection method in the optical displacement detection mechanism.

A light source that irradiates light to the measurement target, a light source driving circuit that drives the light source, a light detector that receives light after irradiating the measurement target from the light source and detects the light intensity, and a detection signal of the light detector is predetermined. In a displacement detection method related to an optical displacement detection mechanism including an amplifier that amplifies at an amplification factor of, the light intensity is adjusted by means (light intensity variable means) that arbitrarily changes the light intensity irradiated from the light source to the measurement object ; By performing an intensity adjustment for adjusting the detection signal intensity by means of adjusting the light intensity again for the trouble caused by the adjustment of the light intensity and means for arbitrarily changing the amplification factor of the amplifier (amplification factor variable means) The light detector can detect light with a certain accuracy regardless of the measurement object.

  Light from the light source is irradiated onto the measurement target, the reflected light from the measurement target is received by the photodetector, the light intensity irradiated to the measurement target is adjusted according to the reflectance of the measurement target, and the measurement target is reflected The reflected light intensity later was set to a predetermined value.

  Further, the detection signal is amplified so that the detection sensitivity at the photodetector becomes a predetermined value in accordance with the difference in the received light intensity due to the difference in the reflectance of the measurement object.

  By adopting the above displacement measurement method, the intensity at the light receiving surface of the photodetector can be adjusted regardless of the shape and reflectance of the measurement target. As a result, it is possible to arbitrarily set the detection sensitivity and the noise ratio to an optimum state.

In the present invention, the light from the light source upon irradiating the measurement object, wherein by irradiating light measured is heated, if caused a problem that the measurement target is deformed, the deformation amount is a predetermined value to fit, by lowering the intensity of light irradiating the measurement target, it was Unishi by increasing the amplification factor.

Further, in the present invention, when the measurement object is irradiated with light from the light source, the measurement result is caused by the influence of stray light other than the light that reflects the cantilever that is a part of the measurement object and enters the photodetector. In order to suppress the problem, the intensity of light applied to the measurement object is lowered to increase the amplification factor .

With such a configuration, the influence of the measurement accuracy due to thermal deformation and impact of stray light to be measured it is possible to perform readjustment of the light intensity so as not to.

The light source was either a super luminescence diode, a light emitting diode, or a semiconductor laser whose return light was prevented by high frequency modulation or polarization by an optical system.

The present invention, as above, the scanning probe microscope and the surface information measuring apparatus optical characteristics and shape and that by the influence of the mechanical properties detection sensitivity and noise deterioration or heat, such as a cantilever or reflectance probes used for Defects such as deformation can be prevented, and detection can be performed with an optimal light intensity and amplification factor. Therefore, measurement with a scanning probe microscope or a surface information measuring device can be performed under optimal conditions.

As described above, the displacement detector structure of the present invention adjusts the more light intensity in the optical intensity varying means to adjust the intensity of light irradiated on the measurement object, also provided to an amplifier provided on the light detector By adjusting the intensity of the detection signal using the variable amplification factor means, even if the measurement target changes, the detection sensitivity and the optical characteristics such as the reflectance of the measurement target or the mechanical characteristics such as the shape and the spring constant are not affected. The ratio of noise can be adjusted, the influence of defects such as thermal deformation of the measurement object due to the irradiation light on the measurement object can be reduced, and measurement accuracy can be ensured under optimum conditions.

  In particular, by applying the optical displacement detection mechanism of the present invention to a scanning probe microscope and a surface information measuring device, it becomes possible to perform measurement of the scanning probe microscope and the surface information measuring device under optimum conditions, and high accuracy. Measurement at can be performed.

It is a general-view figure which shows 1st Example and 2nd Example of the displacement detection method for scanning probe microscopes which concern on this invention. FIG. 2 is a circuit diagram of an amplifier described in FIG. 1. It is a general-view figure which shows 2nd Example of the displacement detection method for scanning probe microscopes used in the solution which concerns on this invention. It is a general-view figure which shows 3rd Example of the displacement detection method for the scanning near-field microscope which concerns on this invention. It is a general-view figure which shows 4th Example of the displacement detection method for the scanning probe micromirrors which concerns on this invention. It is a general-view figure of the conventional scanning probe microscope. It is a general-view figure of the optical displacement detection mechanism for the conventional scanning probe microscope.

  Hereinafter, a case where the optical displacement detection mechanism of the present invention is applied to a scanning probe microscope will be described with reference to the drawings.

  A schematic diagram of the displacement detection method of the first embodiment according to the present invention is shown in FIGS. FIG. 1 is a schematic view when an optical displacement detection mechanism 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 schematic diagram of a circuit diagram of the amplifier 22 of 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, the cantilever 6 having a sharpened probe 6 b at the tip of the cantilever portion 6 a is fixed to the base 8 via a 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 and a vibration-type atomic force microscope can be used in combination.

  In the case of the contact method, 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.

  In the case of the vibration method, the cantilever 6 is vibrated in the vicinity of the resonance frequency by a vibrator 41 made of a piezoelectric element. When the probe 6b is moved closer to the sample 5 while measuring the amplitude and phase of the cantilever 6a by the optical displacement detection mechanism 9, the atomic force and intermittent contact amount act to change the amplitude and phase. Since this amount of change depends on the distance between the probe 6b and the sample 5, the distance between the probe 6b and the sample 5 is controlled by controlling the distance between the probe 6b and the sample 5 so that the amplitude and phase are constant. It can be kept constant.

  Next, the configuration and operating principle of the optical displacement detection mechanism 9 of this embodiment will be described.

  This optical displacement detection mechanism 9 is generally called an optical lever system, and a semiconductor laser having a wavelength of 670 nm and a maximum output of 5 mW is used as the light source 10, and the laser light emitted from the light source 10 is collected by the condenser lens 11. Then, the optical path of the incident light 13 is bent by the beam splitter 12 and irradiated onto 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 the mirror 15 and enters the photodetector 16.

  The optical path of the light is configured to form an image at one end on the back surface of the cantilever 6a and form a spot 20 having a finite size on the light receiving surface of the photodetector 16. The photodetector 16 is a photodiode manufactured using a semiconductor as a material, and has a configuration in which the light receiving surface is divided into four (A1, A2, B1, B2).

  When light enters the photodetector 16, a current signal is generated from the semiconductor constituting the photodetector 16, and four amplifiers 22 each having a current / voltage conversion circuit provided at the rear end of the photodetector 16 are used. Each light receiving surface is converted into a voltage signal with a predetermined amplification factor. 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.

  Therefore, of the four divided light receiving surfaces (A1, A2, B1, B2), light incident on the upper two light receiving surface regions A (A1 + A2) and the lower two light receiving surface regions B (B1 + B2) It is possible to measure the amount of deflection of the cantilever 6a by measuring the intensity difference AB.

  Here, the circuit configuration of the amplifier 22 will be described with reference to FIG. In the optical displacement detection mechanism 9 of the present embodiment, the photodetector 16 is used to calculate the intensity difference between 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. By measuring, the amount of deflection of the cantilever 6a can be measured. Here, the intensity of light incident on each light receiving surface is Pa1, Pa2, Pb1, and Pb2. When light having an intensity of Pa1, Pa2, Pb1, and Pb2 is incident on each light receiving surface, the optical signal is converted into an electrical signal by the photodetector 16, and the currents Ia1, A2, Ia2, Ib1, and Ib2 are generated. The light receiving sensitivity of the photodetector of this embodiment is 0.65 A / W. This current is converted into voltage signals Va1, Va2, Vb1, and Vb2 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 are relationships Va1 = R1 × Ia1, Va2 = R1 × Ia2, Vb1 = R1 × Ib1, and Vb2 = R1 × Ib2. 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 are input to the adder circuit 34, and the sum of the light amounts Va = Va1 + Va2 of the upper two light receiving surfaces and the sum Vb = Vb1 + Vb2 of the lower two light receiving surfaces are output. These signals 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 by the operational amplifier and the resistance values R2 and R3 as shown in the figure, the relationship Va−b = (R3 / R2) × (Va−Vb) is established, and the amplification factor is obtained by the differential amplifier. It is amplified by R3 / R2 and Va-b is output. Thus, the current / voltage conversion circuit 30 and the differential amplifier circuit 33 function as an amplifier. The amount of deflection of the cantilever 6a can be measured by detecting this Va-b.

  The A-B voltage signal Va-b is sent to the control circuit 24, and compared with a preset operating point, the Z fine movement mechanism 4b is operated from the scanner driving circuit 25 by a signal corresponding to the difference. And control is performed so as to keep the distance between 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.

  In this embodiment, the light intensity adjuster 28 is provided in the light source driving circuit 21 to adjust the current value to the semiconductor laser used in the light source 10 so that the output of the light source can be adjusted.

  The amplifier 22 is provided with an amplification factor adjuster 27. The amplification factor adjuster 27 adjusts the resistance value R3 of the differential amplifier circuit 33 so that the amplification factor can be adjusted.

  Here, the light intensity adjuster 28 and the amplification factor adjuster 27 optimize the conditions according to the cantilever to be measured.

  First, when observing the surface of a silicon wafer or the like with a vibration-type atomic force microscope, silicon is used as a material, and the back surface of the cantilever 6a is coated with aluminum in order to increase reflectivity. The length is 125 μm, the width is 30 μm, A cantilever having a thickness of 4 μm and a spring constant of about 40 N / m is used. In this case, since the spring constant is relatively hard and the vibration method is used, the influence of the thermal deformation caused by heating of the cantilever 6a does not greatly affect the measurement accuracy when the laser is irradiated. Therefore, in order to reduce the ratio of noise to detection sensitivity, the light intensity of the light source 10 is increased using the light intensity adjuster 28 within a range where mode hop noise and return light noise are not generated, and strong light is transmitted to the cantilever 6a. Irradiation was performed to increase the amount of light incident on the photodetector 16 to increase the measurement accuracy. In this embodiment, the output of the light source 10 is 1.5 mW, and the feedback resistance value R1 of the current / voltage conversion circuit 30 is set to 100 kΩ. The resistance values of the differential amplifier circuit 33 were set to R2 = 10 kΩ and R3 = 20 kΩ. That is, the amplification factor of the amplifier was set to 100000 times in the first-stage current / voltage conversion circuit 30 and doubled in the differential amplifier circuit 33 at the rear end.

  Next, the atomic force of the vibration method is used by using the cantilever 6 having the same shape, which is not coated in order to reduce the manufacturing cost or prevent the coating film from adhering to the probe 6b at the tip and reducing the resolution. Measurements were taken with a microscope. In this case, since the reflective film made of aluminum is not coated, the reflectivity of the cantilever 6b to be measured decreases, the light intensity incident on the light receiving surface of the photodetector 16 decreases, and the detection sensitivity decreases and noise increases. cause. Therefore, in this embodiment, a semiconductor laser is used as the light source 10, the current value for driving the light source 10 is increased by the light intensity adjuster 28, and the decrease in reflectance is compensated by the increase in the amount of incident light to the cantilever 6a. The amount of light incident on the light receiving surface of the photodetector 16 was adjusted in the same manner as when the cantilever 6a was coated with aluminum. As a result, it was possible to ensure the same detection sensitivity and noise ratio as those with a coat.

  Next, aluminum is coated on the back surface of the cantilever 6a by using silicon, and a cantilever having a length of 225 μm, a width of 30 μm, a thickness of 5 μm and a spring constant of about 13 N / m is used. Also in this case, since the spring constant is relatively hard and the vibration method is used, when laser irradiation is performed, the influence that the cantilever 6a is heated to cause thermal deformation does not greatly affect the measurement accuracy. Therefore, in order to reduce the ratio of noise to detection sensitivity, the light intensity of the light source 10 is increased using the light intensity adjuster 28 within a range where mode hop noise and return light noise are not generated, and strong light is transmitted to the cantilever 6a. Irradiated to improve measurement accuracy.

  However, in the case of an optical lever type displacement detection mechanism, the detection sensitivity varies depending on the lever ratio determined by the length of the cantilever 6a and the distance from the light irradiation position of the cantilever 6a to the photodetector 16, and the detection sensitivity is the length of the cantilever. Inversely proportional. Therefore, when compared with a cantilever having a spring constant of 40 N / m in the above example, the length of the cantilever 6a is 1.8 times longer, so that the detection sensitivity is 0.56 times that in the case of a cantilever with 40 N / m. To drop. Therefore, the output of the light source 10 may be increased in order to increase the detection sensitivity. However, since a semiconductor laser is used as the light source 10, generation of mode hop noise and return light noise is a problem. Then, the amplification factor adjuster 27 adjusts the amplification factor of the amplifier provided in the photodetector to compensate for the decrease in detection sensitivity.

  In the unlikely event that thermal deformation will occur, both surfaces of the cantilever 6a are coated with the same material and with the same film thickness so that the linear expansion coefficients of both surfaces become equal, so that thermal deformation hardly occurs. .

  Next, the case of measuring with a contact-type atomic force microscope will be described. When the contact mode is performed, a cantilever having a small spring constant is used in order to reduce the influence of wear on the probe tip. In this example, a cantilever made of silicon nitride, having a length of 200 μm, a thickness of 0.4 μm, and having a spring constant of 0.02 N / m coated with gold on one side and coated with chromium is used. In this cantilever 6a, since the spring constant is small, the temperature of the cantilever 6a is increased by light irradiation, and the cantilever 6a warps due to the difference between the linear expansion coefficient of the metal coat portion and the linear expansion coefficient of the silicon nitride base material portion. Measurement accuracy will deteriorate. Therefore, in this embodiment, the current value for driving the semiconductor laser 10 by the light intensity adjuster 28 is reduced to 0.5 mW, which is 1/3 of the value when the aluminum coating of 40 N / m is applied by the vibration method. Reduced the heat generation. Further, in order to compensate for a decrease in detection sensitivity due to a decrease in light output, the amplification factor of the amplifier provided in the photodetector is increased three times by the amplification factor adjuster 27.

  As described above, by optimizing the light intensity and gain applied to the cantilever 6a by the light intensity adjuster 28 and the gain adjuster 27, the shape, reflectivity, spring constant, etc. of the cantilever to be used are optimized. Appropriate detection sensitivity and noise ratio can be ensured regardless of the difference in characteristics. In addition, the influence of thermal deformation due to the difference in the coefficient of linear expansion between the base material and the coated thin film can be reduced, and measurement with a scanning probe microscope can be performed under optimum conditions.

  A second embodiment according to the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram 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, a vibration-type atomic force microscope is used in this embodiment, and the cantilever holder 35 for measuring a solution according to this embodiment is a cantilever holder used for measurement in the atmosphere of the first embodiment. 7 and replaceable configuration.

  The solution measuring cantilever holder 35 is 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, a super luminescence diode (SLD) having a peak wavelength of 830 nm and a spectral width of light intensity with respect to the wavelength of 17 nm is used as the light source 10. The light from the SLD is collected by the condenser lens 11, and the optical path of the incident light 13 is bent by the beam splitter 12 and irradiated from right above (Z direction) to the back surface of the cantilever 6a to be measured. 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 whose light receiving surface is divided into four through the mirror 15. The photodetector 16 is connected to the amplifier 22. The amplifier 22 is the same as the circuit of the first embodiment shown in FIG. Here, especially when the cantilever 6a is vibrated in the solution, the cantilever 6a described later is affected by the viscous resistance received from the solution, the influence of scattered light from the member through which light is transmitted, and the cantilever 6a is vibrated. In many cases, noise other than the resonance frequency of the cantilever 6a is placed on the amplitude detection signal due to the liquid layer 46 and the glass base block 37 shaking accompanying the above, and the measurement accuracy is deteriorated. In order to remove 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.

  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. When a semiconductor laser is used as the light source 10 as in the first embodiment, the 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. By using an SLD that is a light source having a large spectrum half-value width and a low coherence as in the present embodiment, return light noise and mode hop noise can be suppressed, and the output of the light source 10 can be increased.

  When light passes through the glass base block 37 and the liquid layer 46 as in the present embodiment, light loss occurs, and light enters the cantilever 6a at the same output as that measured in air. As a result, the intensity of the incident light decreases, leading to a decrease in detection sensitivity and an increase in noise. In the present embodiment, the light intensity adjuster 28 increases the intensity of the light source 10 to 4 mW to compensate for the loss of these lights, ensuring the same incident light intensity as in the air, and suppressing a decrease in detection sensitivity and an increase in noise. I did it.

  When the cantilever holder 35 for solution is replaced with the cantilever holder 7 in the atmosphere and the measurement is performed in the atmosphere, the loss of light in the glass base block 37 and the liquid layer 46 is eliminated. The current value for driving is lowered and the light intensity of the light source is returned to 1.5 mW for use.

  Note that a semiconductor laser may be used instead of the low-coherent light source, and high-frequency modulation may be performed, or an optical system may be assembled so as to reduce return light using polarized light. In this case, it is possible to slightly increase the output limit of the light source in which mode hop noise or return light noise occurs.

  A third embodiment of the present invention is shown in FIG. FIG. 4 is a schematic diagram of a probe of a scanning near-field microscope, which is a kind of scanning probe microscope, and an optical displacement detection mechanism for detecting the displacement of the probe. 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 emitting diode (LED) 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 LED used had a wavelength of 700 nm and a spectrum half width of 35 nm. 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.

  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 arranged at a position facing the light source unit 56 with respect to the probe 50. Incidently enter.

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

  When the probe 50 vibrates in the optical displacement detection mechanism 55 configured as described above, the area difference of the portion not blocked by the shadow 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.

  Also in this embodiment, as in the first and second embodiments, the light intensity of the light source 56 can be adjusted by the light intensity adjuster 65 provided in the light source driving circuit 64.

  The amplifier 61 is provided with an amplification factor adjuster 62 so that the amplification factor can be adjusted.

  The probe used in the scanning near-field microscope usually has a diameter of 125 μm. However, depending on the sample 54, a probe having a small diameter may be used, or a glass pipette having a large diameter may be used. In addition, a sharpened metal wire is also used as the probe 50. In this case, an evanescent field is generated on the surface of the sample 50, the evanescent field is scattered at the probe tip made of the metal wire, and the scattered light is analyzed. Measurement of the optical characteristics is performed. Thus, when the diameter of the probe 50 changes, the size of the shadow on the light receiving surface of the photodetector 57 also changes, and as a result, the detection sensitivity changes. Therefore, the light intensity converter 65 changes the current value to change the light emission intensity of the LED to compensate for the difference in detection sensitivity. Note that supplementation may be performed on the amplification factor adjuster 62 side.

  As described above, by optimizing the irradiation light intensity and amplification factor to the probe 50 by the light intensity adjuster 65 and the amplification factor adjuster 62, the influence of the difference in the shape of the probe used can be reduced, and appropriate detection sensitivity can be obtained. Thus, it is possible to measure with a scanning near-field microscope.

  FIG. 5 is a schematic diagram of an optical displacement detection mechanism used in a scanning probe microscope according to the fourth embodiment of the present invention. Since the basic configuration of this embodiment is the same as that of the optical lever type optical displacement detection mechanism described in the first embodiment with reference to FIGS. 1 and 2, the description of overlapping portions is omitted. The difference from FIG. 1 is that the light source drive circuit 21 does not have a light intensity adjuster.

  In this embodiment, the optical filter 40 for adjusting the light intensity is inserted in the optical path between the light source 10 and the cantilever 6a so that the intensity of the light incident on the cantilever 6a can be adjusted. As the optical filter 40, a neutral density filter (ND filter) that reduces the intensity of light was used.

  Thereby, the same effect as adjusting the intensity of incident light on the cantilever with the light intensity adjuster 28 of the first embodiment can be obtained.

  As mentioned above, although the Example of this invention was described, this invention is not limited to these Examples.

  For example, in this embodiment, a semiconductor photodetector having a light receiving surface divided into four or two is used, but any detector that detects the intensity of light or the position of a spot can be applied. 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 is commercially available.

  In addition, the light source has relatively stable output and excellent response when adjusting the light intensity. When the object to be measured is a very small probe, the light spot can be narrowed down with an optical lens. Are preferably a semiconductor laser (LD), a super luminescence diode (SLD), or a light emitting diode (LED), which is excellent in coupling efficiency to a fiber, but other light sources such as a white light source are also included in the present invention. In particular, the SLD has a feature that even if it is used at a high output, the influence of mode hop noise and return light noise can be reduced without using a special device like the LD. For example, in the case of a scanning probe microscope, the light reflected by the cantilever to be measured and the light reflected from the cantilever interfere with each other, and the relationship between the force applied to the probe with respect to the distance between the probe and the sample (generally, When measuring a force curve), the force curve may swell. In addition, interference fringes may also occur when the concavo-convex image is measured. In this way, interference sometimes adversely affects measurement data. However, since SLD is low coherent and has low coherence, the influence of interference can also be prevented. Further, when the influence of interference appears greatly due to the intensity of light irradiated to the measurement object, it is possible to suppress the influence of interference by lowering the intensity with the light intensity variable means.

In addition, when a force curve or a concavo-convex image is measured with a scanning probe microscope, a defect may appear in the force curve or the concavo-convex image due to the influence of stray light other than the light reflected from the cantilever and incident on the photodetector. . In general, the influence of stray light increases as the intensity of light applied to the measurement object increases. Therefore, when the influence of stray light is large, the above-mentioned problem can be suppressed by reducing the intensity with the light intensity variable means. .

  Also, the optical system is not limited to this embodiment, and the measurement object is irradiated with light, the light passing through the measurement object is received by a photodetector, and the displacement of the measurement object is measured by a signal from the photodetector. If so, it can be applied to any optical displacement detection mechanism. For example, light from a light source may propagate through an optical fiber and irradiate the measurement target.

  Arbitrary methods can be used for the light intensity adjuster of the light source and the gain adjuster on the light detector side.For example, a method of continuously adjusting using a volume knob may be used. A method may be used in which the setting is made using a changeover switch.

  In order to change the amplification factor, the resistance value R3 of the differential amplifier circuit of FIG. 2 is changed. However, even if the resistance value R1 of the current / voltage conversion circuit 30 may be changed, the resistance value R2 may be changed. Good. Further, it may be changed by adjustment in the electric circuit in the control circuit after the differential amplifier circuit 33 or setting of software in the signal processing system.

  As the optical filter used for adjusting the light intensity of the light source, any filter can be used as long as it is used for the purpose of adjusting the amount of light.

  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, the present invention includes everything that measures the physical properties of the sample surface by controlling the distance between the probe and the sample surface or detecting the force or interaction applied to the probe. Also, the present invention includes all processing of the sample surface with a probe and manipulation of a material on the sample surface. Further, it is not always necessary to scan with an XY scanner, and those having only a function of detecting an interaction in the height direction using the Z fine movement mechanism are also included in the present invention. In addition to detecting the amount of deflection of the cantilever using the difference signal between the upper and lower light receiving surfaces using the left and right light receiving surfaces of the quadrant photodetector, the amount of torsion of the cantilever is detected from the difference signal between the left and right light receiving surfaces. It is also possible to measure the frictional force. In this case, the amplification factor is changed with respect to the light intensity difference signal between the left and right light receiving surfaces.

  In addition, prior to measurement, when aligning the spot light of the light source to the measurement object, the light source is moved while usually observing the spot light and the measurement object with an optical microscope. The spot light of the observation image is scattered and the center position of the spot light cannot be recognized. In such a case, by adjusting the light intensity by reducing the light intensity using the light intensity adjuster of the present invention, the visibility can be improved, and the spot light can be reliably aligned with the measurement object.

  In addition, when aligning the spot light to a predetermined position on the photodetector, the alignment is usually performed by moving the photodetector while observing the detection signal, but if the detection sensitivity is high, slight movement of the photodetector is performed. Since the detection signal varies greatly depending on the amount, alignment is difficult. By changing the intensity with the light intensity adjuster or the optical filter of the present invention, or lowering the amplification factor with the amplification factor adjuster, it is possible to easily align the spot light to the photodetector before measurement.

  The optical displacement detection mechanism of the present invention is not limited to application to a scanning probe microscope. For example, the present invention can be applied to a surface information measuring device such as a surface roughness meter using an optical displacement detection mechanism, an electrochemical microscope, or a probe processing device that processes a sample surface with a probe. Even in these devices, probes having different shapes, optical characteristics, and mechanical characteristics are used depending on the sample to be measured. Therefore, by applying the optical displacement detection mechanism of the present invention, the detection sensitivity and noise are optimized regardless of the probe. It becomes possible to adjust to the state, and the measurement accuracy of the apparatus is improved.

1 Sample stage 2 Coarse movement mechanism 4 Triaxial fine movement mechanism 5 Sample 6 Cantilever (measurement target)
7 Cantilever holder for atmospheric measurement 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 23 Voltage monitor 29 Optical microscope 30 Current / voltage conversion circuit 33 Differential amplification circuit 34 Adder 35 Cantilever holder for solution 36 Metal base block 37 Glass base block 43 Air layer 44 Petri dish 45 Solution 46 Probe 50 Probe 52 Probe holder 54 Sample 55 Optical Type displacement detection mechanism 56 Light source unit 57 Photo detector 58 Spot 59 Light source positioning mechanism 60 Photo detector positioning mechanism 61 Amplifier 64 Light source drive circuit 200 Optical displacement detection mechanism 201 Scanning probe microscope 207 Inch lever 209 Probe 211 Sample 213 Three-axis fine movement mechanism 221 Light source (semiconductor laser)
235 Photodetector 242 Current / voltage conversion circuit 243 Differential amplification circuit 244 Band pass filter

Claims (4)

A light source that irradiates light to a measuring object consisting of a cantilever having a probe at the tip or a probe of an arbitrary shape;
A light source driving circuit for driving the light source;
A photodetector in which the material of the light receiving surface that receives the light after irradiating the measurement target from the light source as a spot light at a predetermined position through alignment and detects the light intensity is a semiconductor;
An amplifier for amplifying the detection signal of the photodetector at a predetermined amplification rate;
Amplification factor variable means for arbitrarily adjusting the amplification factor of the amplifier;
In a displacement detection method of a scanning probe microscope, comprising: a light intensity varying means that arbitrarily changes the intensity of irradiation light from the light source to the measurement object;
A light intensity adjusting step measurement sensitivity and / or noise accuracy of the photodetector to adjust the light intensity of the light source to be a desired value by the strongly light level varying means,
When a problem associated with the light intensity change by the light intensity adjustment occurs, the light intensity is reduced again by the light intensity variable means to prevent the problem, and the gain variable means at the photodetector. A detection sensitivity adjustment step for adjusting the amplification factor so as to obtain a predetermined detection sensitivity;
Displacement detection method for a scanning probe microscope characterized by comprising. When the defect is thermal deformation exceeding a predetermined amount of the measurement target,
In the detection sensitivity adjustment step, the light intensity is reduced by the light intensity variable means to suppress the thermal deformation, and the amplification factor is adjusted by the gain variable means to increase the gain so that a desired sensitivity is obtained. The displacement detection method of the scanning probe microscope according to claim 1. When the defect is due to the influence of stray light other than the light that reflects the cantilever and enters the photodetector,
In the detection sensitivity adjustment step, the light intensity is reduced by the light intensity variable means to suppress the influence of the stray light, and the amplification factor is adjusted to increase the amplification factor so that a desired sensitivity is obtained. The displacement detection method of a scanning probe microscope according to claim 1 . The light source is one of a super luminescence diode (SLD), a light emitting diode (LED), or a semiconductor laser (LD) in which return light is prevented by high frequency modulation or polarization by an optical system, and the light intensity adjustment step returns 4. The displacement detection method for a scanning probe microscope according to claim 1, wherein the displacement detection method is adjusted to suppress optical noise or mode hop noise .

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