JP2008051690A - Optical displacement detecting mechanism, and surface information measuring device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical displacement detecting mechanism capable of performing alignment readily and surely, when aligning light from a light source with a measuring object or the light-receiving surface of a photodetector. <P>SOLUTION: In this optical displacement detection mechanism, constituted of the light source 10 for irradiating light to a cantilever 6 which is a measuring object, a light source drive circuit 21 for driving the light source 10, the photodetector 16 for receiving the light irradiated from the light source 10 to the cantilever 6 and detecting the light intensity, and an amplifier 22 for amplifying a detection signal by the photodetector 16 at a prescribed gain, detection sensitivity used for detection by the photodetector 16 is set at a value smaller than the case when actually measuring the measuring object, by using a gain (amplification factor) adjusting unit, and a light spot 20 is positioned at a prescribed position of the photodetector 16 by a positioning mechanism 18 for the photodetector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates 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, and in particular, a sample surface using this optical displacement detection mechanism. Surfaces such as scanning probe microscopes, surface roughness meters, hardness meters, and electrochemical microscopes that measure shape information and various physical information (for example, dielectric constant, magnetization state, transmittance, viscoelasticity, friction coefficient, etc.) The present invention relates to an information measuring device.

  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. 5 (refer patent document 1).

  A scanning probe microscope 201 in FIG. 5 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, an optical displacement detection mechanism generally called an optical lever method is provided.

  This optical displacement detection mechanism is configured to irradiate laser light (incident light 231) from a light source 221 made of a semiconductor laser, which is installed above the cantilever 207, on the back surface of the cantilever 207 with a condenser lens (not shown). . 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 has a light receiving surface that is divided into two parts in the vertical direction, and can detect the incident position of the reflected light 233.

Here, the operation principle of the optical lever type optical displacement detection mechanism will be described. Before performing measurement with the scanning probe microscope, first, incident light from the light source 221 is positioned on the back surface of the cantilever 207. At this time, the light source 221 is usually provided with a biaxial positioning stage (not shown) in which the spot of the incident light 231 can move in the plane of the cantilever 207, and is irradiated on the back surface of the cantilever 207 and the sample 211. Positioning is performed while viewing an image of an optical microscope (not shown) in which the state of the spot light can be observed.

  Next, the reflected light reflected by the back surface of the cantilever 207 is aligned with the light receiving surface of the photodetector 235. The photodetector 235 is also provided with a biaxial positioning stage (not shown) that is normally movable within the light receiving surface. The photodetector 235 is made of a semiconductor material, and an electric current is generated when light strikes the light receiving surface. A current / voltage conversion circuit (not shown) is connected to the rear side of the light receiving surface, and the current signal is converted into a voltage signal with a predetermined amplification factor, and a voltage is applied to a Z feedback circuit 251 described later. A signal is input.

In order to align the spot of the reflected light 233 within the light receiving surface, first, the sum (A + B) of the light amounts of the upper light receiving surface (A) and the lower light receiving surface (B) divided into two is obtained. Align while observing the voltage signal from the current / voltage conversion circuit so as to maximize. In this state, the spot of the reflected light is aligned with an arbitrary position in the light receiving surface. Next, alignment is performed more precisely so that the spot light comes to the center of the light receiving surfaces above and below the light receiving surface. At this time, the positioning mechanism provided also to the photodetector 235 is finely adjusted so that the voltage signal of the difference (A−B) between the upper and lower light receiving surfaces is substantially zero. By aligning in this way, it becomes possible to precisely align the irradiation position of the spot light with the centers of the upper and lower light receiving surfaces.

  Next, 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, and the cantilever 207 is bent by these actions. When the cantilever 207 is bent, the position of the spot light 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 of the difference (A−B) between the upper and lower light receiving surfaces.

Since the amount of deflection of the cantilever 207 depends on the distance between the probe and the sample surface, the amount of deflection of the cantilever 207 is detected by the output voltage (AB) of the photodetector 235 and input to the Z feedback circuit 251 to bend. The distance between the probe and the sample surface is controlled by the Z fine movement mechanism 213 so that the amount is constant, that is, the output voltage (A-B) is constant, and the sample is scanned by the XY scanner 213, thereby causing unevenness of the sample surface. 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.
JP-A-10-104245

The detection sensitivity S in such an optical displacement detection mechanism, that is, the output of the difference between the signals of the upper and lower light receiving surfaces of the photodetector per unit displacement of the cantilever to be measured is the amount of light to the light receiving surface of the photodetector. P, the light / current conversion coefficient of the photodetector is α, the area of the spot light on the light receiving surface of the photodetector is A, and the spot light moves on the upper and lower light receiving surfaces when the cantilever operates per unit length. When the difference in area is Δa and the gain (amplification factor) of the current / voltage conversion circuit is G, it is expressed as follows.

S = GαPΔa / A (1)
That is, Δa is determined by the length of the cantilever and the lever ratio of the optical lever optical system determined by the distance from the cantilever to the photodetector, and A is determined by the characteristics of the condenser lens and the distance from the light source to the photodetector. Therefore, in order to increase the sensitivity after the lever ratio and the condensing lens are determined, the light amount P to the light receiving surface of the photodetector is increased or the gain (amplification factor) G of the current / voltage conversion circuit is increased. There is a need to.

  However, when the sensitivity S of the displacement detection mechanism is increased, the output signal of the photodetector greatly changes with a small amount of movement when the position of the spot light incident on the light receiving surface of the photodetector from the measurement object is aligned. Therefore, alignment is very difficult. In particular, a surface information measuring device that measures the shape information of the sample surface and various physical information (for example, dielectric constant, magnetization state, transmittance, viscoelasticity, friction coefficient, etc.) using such an optical displacement detection mechanism. In a scanning probe microscope which is a kind of the above, the demand for detecting a finer force is increasing, and there is a tendency to increase the detection sensitivity, which makes positioning more difficult.

  In addition, when irradiating incident light from a light source onto a cantilever to be measured, alignment is performed while observing the spot light of the irradiation light on the cantilever and the cantilever with an observation image of an optical microscope (not shown). When the light intensity is high, the intensity of the scattered light scattered on the sample surface and the cantilever also increases, the light spot is observed on the observation image of the optical microscope remarkably, and the visibility decreases, and the cantilever and It is difficult to observe the center of the spot light of the irradiation light, and it becomes difficult to accurately align the center of the spot light of the irradiation light to the cantilever, and as a result, there is a problem of causing a decrease in measurement accuracy.

  Therefore, the object of the present invention is to easily align the spot position to the photodetector and measurement object before measurement even when the detection sensitivity is increased in the optical displacement detection mechanism used in a scanning probe microscope and the like. An optical displacement detection mechanism that can be reliably performed is provided.

    In order to solve the above problems, in the present invention, an optical displacement detection mechanism and a surface information measuring device using the same are configured by the following means.

  In the optical displacement detection mechanism of the present invention, a light source that irradiates light to the measurement object, a light source drive circuit that drives the light source, and light that has been irradiated from the light source to the measurement object are received and the light intensity is detected Optical displacement comprising a photodetector, a photodetector positioning mechanism for positioning the spot light at a predetermined position of the photodetector, and an amplifier that amplifies the detection signal of the photodetector with a predetermined gain A detection mechanism that is detected by the photodetector when the spot light is positioned at a predetermined position of the photodetector by the photodetector positioning mechanism before actually measuring the measurement target. Was adjusted to be smaller than when actually measuring the measurement object.

  With the configuration described above, it is possible to easily and reliably perform alignment by the photodetector positioning mechanism by reducing the detection sensitivity.

  In addition, by returning the setting to the original gain (amplification factor) after alignment, it becomes possible to measure with high sensitivity when actually measuring the sample.

Further, in the optical displacement detection mechanism of the present invention, the gain (amplification factor) of the amplifier provided in the photodetector.
With a gain (amplification factor) adjuster so that the setting can be changed, the detection sensitivity is reduced by setting the gain to a value smaller than that during actual measurement, and the light spot is positioned at a predetermined position of the photodetector. I did it.

  In this way, by reducing the gain (amplification factor) G of the amplifier in the equation (1), as a result, the detection sensitivity S can be reduced, and the alignment by the photodetector positioning mechanism can be performed easily and reliably. Can be performed.

  In the optical displacement detection mechanism of the present invention, the light intensity variable means is provided to set the intensity of the light incident on the photodetector to a value smaller than that at the time of actual measurement, the detection sensitivity S is reduced, and the light The light spot is positioned at a predetermined position of the detector.

  As a light intensity setting method, the light spot is positioned at a predetermined position of the photodetector by setting the light emission intensity of the light source to be smaller than the actual measurement by the light source driving circuit than when actually measuring the measurement target. did.

  Another method for setting the light intensity is to insert a neutral density filter that reduces the light intensity at any position on the optical path from the light source to the light detector when actually measuring the measurement target. Thus, the light spot is positioned at a predetermined position of the photodetector.

  With the configuration described above, the amount of light P to the light receiving surface of the photodetector can be reduced in the expression (1), and as a result, the detection sensitivity S is reduced, and the alignment by the positioning mechanism of the photodetector is performed. Can be easily and reliably performed. By returning to the original light amount after the alignment, it is possible to measure with high sensitivity when actually measuring the measurement object.

  Furthermore, the present invention has a light source positioning mechanism for adjusting the irradiation position of the light of the light source to the measurement object, and before irradiating the measurement object than when actually measuring the measurement object by the light intensity varying means. The light intensity of the light source was set to a small value, and the light of the light source was positioned on the measurement object.

  With this configuration, the visibility of the measurement target and the center of the spot light is improved when the spot light is aligned with the measurement target, and the alignment of the light spot to the measurement target is accurately and easily performed. Measurement accuracy can be improved.

  Further, as a measurement object of the optical displacement detection mechanism of the present invention, a cantilever having a probe at the tip or a probe of any shape, a sample holder provided with the optical displacement detection mechanism as described above, and a probe at the tip A sample holder for holding a cantilever or a probe having an arbitrary shape, a moving means comprising one or more fine movement mechanisms for moving the cantilever or probe and the sample holder relative to at least a Z direction perpendicular to the sample surface, and an optical A scanning probe microscope including a control unit that collects observation data of the sample by controlling the moving unit based on the measurement result of the displacement detection mechanism is configured.

  In the optical displacement detection mechanism for a scanning probe microscope, the light receiving surface of the photodetector is divided into four or two parts, the light from the light source is irradiated on the back surface of the cantilever, and the reflected light from the cantilever is received by the light receiving surface. Before the measurement, the reflected light from the cantilever was positioned near the center of the dividing surface on the photodetector.

  In addition, the light receiving surface of the light detector is divided into four or two parts, the probe is irradiated with light from the light source, and the probe's shadow is projected onto the light receiving surface of the light detector. In the mechanism, the light irradiated to the probe is positioned near the center of the divided surface on the photodetector before measurement.

  Further, the measurement object by the optical displacement detection mechanism of the present invention is used as a probe for measuring surface information, and the optical displacement detection mechanism is used to detect the position information of the probe. Surface information measuring devices such as a roughness meter, a hardness meter, and an electrochemical microscope were constructed.

  By using the optical displacement detection mechanism configured in this way, it is easy and reliable to align the optical displacement detection mechanism of the cantilever and probe before measurement by a surface information measuring device such as a scanning probe microscope. Measurement accuracy is improved, and time required for measurement preparation is shortened.

  By configuring the optical displacement detection mechanism as described above, the positioning of the light detector is reduced by reducing the sensitivity of the light detector when aligning the light spot on the light receiving surface of the light detector. Positioning by the mechanism can be performed easily and reliably.

  By returning the setting to the original sensitivity after the alignment, it is possible to measure with high sensitivity when actually measuring the measurement object.

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

  The optical displacement detection mechanism 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 circuit diagram of an amplifier 22 having the current / voltage conversion circuit 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, a silicon 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 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, deflection occurs in the cantilever portion 6a according to the force received by the probe 6b. The force received by the probe 6b, that is, the amount of deflection of the cantilever portion 6a depends on the distance between the probe 6b and the surface of the sample 5.

  Therefore, the surface of the sample 5 is raster-scanned by the XY scanner unit 4a while changing the distance between the probe 6b and the sample 5 by the Z fine movement mechanism 4b so that the deflection amount of the cantilever unit 6a is constant. Can be obtained.

  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 uses a semiconductor laser as a light source 10, condenses laser light emitted from the light source 10 with a condenser lens 11, and uses a beam splitter 12. The optical path of the incident light 13 is bent to irradiate the back surface of the cantilever part 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 portion 6 a and 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 four parts (A1, A2, B1, B2).

When light is incident on 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 portion 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 part 6a by measuring the intensity difference AB.

  Here, the circuit configuration of the amplifier 22 including the current / voltage conversion circuit will be described with reference to FIG. In the optical displacement detection mechanism of this embodiment, the deflection of the cantilever portion 6a is measured by measuring the difference in intensity between the light incident on the region A of the upper light receiving surface of the photodetector 16 and the region B of the lower light receiving surface. The amount 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 electric signal by the photodetector 16, and the currents Ia1, A2, A1, and B2 are converted from the respective light receiving surfaces A1, A2, B1, and B2. Ia2, Ib1, and Ib2 are generated. 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-current 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 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) is established, and the amplification factor R3 is established by the differential amplifier. It is amplified by / R2, and Va-b is output. By detecting this Va-b, the deflection amount of the cantilever can be measured.

  In this embodiment, when using the photodetector 16 having a light receiving sensitivity of 0.65 A / W and measuring a measurement object with a scanning probe microscope, 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 during actual measurement is set to 100000 times in the first-stage current / voltage conversion circuit and 2 times in the differential amplifier.

  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.

  Here, an adjustment method of the optical displacement detection mechanism 9 before measurement will be described. The cantilever 6 is a consumable item and may need to be replaced after each measurement. In addition, the most suitable cantilevers of different materials and shapes are selected and used according to the purpose of measurement. Therefore, each time the cantilever 6 is replaced, it is necessary to align the incident light 13 with the back surface of the cantilever portion 6 a and further align the reflected light 14 with the light receiving surface of the photodetector 16.

  First, when aligning the spot light on the back surface of the cantilever portion 6a, first, the optical microscope 29 observes the spot of the incident light 13 on the surface of the cantilever 6 and the sample 5, and further on the sample surface. A light source module 19 including a light source 10 and a condensing lens 11 is attached to a light source positioning mechanism 17 including a biaxial feed screw type stage. By operating the light source positioning mechanism 17, The incident light 13 can be moved in the XY plane. While observing the spot of the incident light 13 applied to the cantilever 6 and the sample 5 from the image of the optical microscope 29, the center of the spot of the incident light 13 is positioned accurately on the back surface of the cantilever 6a.

  Next, the alignment of the spot light of the photodetector 16 will be described. The photodetector 16 is also provided with a photodetector positioning mechanism 18 composed of a biaxial feed screw type stage. When aligning the spot 20 of the reflected light on the light receiving surface of the photodetector 16, first, the total light amount (Pa1 + Pa2 + Pb1 + Pb2) of the light receiving surface divided into four is maximized while observing the signal of the voltage monitor 23. Thus, the alignment is performed by the photodetector positioning mechanism 18. In this state, the spot 20 is positioned at an arbitrary position on the light receiving surface of the photodetector 16. Next, the spot 20 is aligned with the center of the light receiving surface divided into four. Therefore, while observing the signal of the difference (Va1 + Va2) − (Vb1 + Vb2) between the upper and lower light receiving surfaces with the voltage monitor 23, the photodetector 16 is moved by the photodetector positioning mechanism 18 so that the signal becomes substantially zero. To do. Thereby, the spot 20 can be aligned with the center of the upper and lower light receiving surfaces. When detecting the deflection of the cantilever 6a, the alignment up to this point is sufficient, and even a photodetector having a light receiving surface divided into two parts can be measured. For example, the amount of twist of the cantilever 6a is measured and the probe 6b In the case of a friction force microscope that measures the friction force between the tip and the surface of the sample 5, the torsion amount is measured by the difference between the left and right signals (Va1 + Vb1) − (Va2 + Vb2). It is necessary to perform alignment by the photodetector positioning mechanism 18 so that the difference between the signals on the light receiving surface becomes zero.

Here, in order to measure the sample characteristics with high sensitivity in the scanning probe microscope, it is necessary to increase the detection sensitivity of the photodetector 16 (voltage output per unit displacement of the measurement target (here, the cantilever 6)). However, when the detection sensitivity is high, when the reflected light spot 20 is aligned on the photodetector 16, the output of the upper and lower light receiving surfaces can be output by moving the photodetector positioning mechanism 18 slightly. The difference signal varies significantly, making it very difficult to align the reflected light spot 20 to the center of the light receiving surface of the photodetector 16.

  Therefore, a gain (amplification factor) adjuster 27 is provided so that the gain (amplification factor) set by the amplifier 22 can be changed, and the spot of the reflected light 14 is spotted on the photodetector 16 by lowering the gain (amplification factor). Twenty alignments were performed. That is, by setting the gain (amplification factor) G in equation (1), the detection sensitivity S is lowered, and the fluctuation of the output voltage is set to be small even if the photodetector positioning mechanism 18 is moved. Changing the amplification factor can be realized by making any of the resistance values R1, R2, and R3 of the circuit of FIG. 2 variable. Further, it may be changed by adjustment in the electric circuit in the control circuit 24 after the differential amplifier circuit 33 or setting of software in the signal processing system.

  As a result, it is possible to easily and accurately align the spot 20 with the photodetector 16. As a result, the time required for measurement preparation for alignment is shortened, and highly accurate alignment is possible.

  After the measurement preparation of the optical displacement detection mechanism 9 is completed, the amplification factor of the gain (amplification factor) adjuster 27 is set to the original value, thereby increasing the detection sensitivity and actually measuring the sample with high accuracy. Can be performed.

  An optical displacement detection mechanism according to a second embodiment of the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, the description of the overlapping parts is omitted. In the second embodiment, a light intensity adjuster 28 is attached to the light source drive circuit 21 of the light source 10 of the optical displacement detection mechanism 9.

  When the alignment of the incident light 13 on the back surface of the cantilever portion 6a and the alignment of the spot on the light receiving surface of the photodetector 16 are performed before the measurement, the light intensity adjuster 28 is used to adjust the light source more than the actual measurement. The position is adjusted by reducing the strength of 10. In this embodiment, the intensity is reduced by lowering the current value for driving the semiconductor laser 10.

  First, when positioning the back surface of the cantilever part 6a, the optical microscope 29 observes the surface of the cantilever 6 and the sample 5, and the spot of the incident light 13 on the sample surface. A light source module 19 composed of a light source 10 and a condenser lens 11 is attached to a light source positioning mechanism 17 composed of a biaxial feed screw type stage, and this light source is observed while observing an optical microscope image 29. The positioning mechanism 17 is operated, the incident light is moved on the XY plane, and is aligned with the back surface of the cantilever portion 6a so as to be positioned at the center of the spot of the incident light 13. If the intensity of the light source 10 is large at this time, the scattered light of the incident light scattered on the surface of the sample 5 and the back surface of the cantilever part 6a increases, and the intensity of the scattered light in the observation image of the optical microscope 29 becomes strong. The visibility of the cantilever 6 and the center of the spot of the incident light 13 is remarkably deteriorated. Therefore, by reducing the intensity of the light amount of the light source 10, the intensity of the incident light 13 is reduced. As a result, the scattered light intensity is also reduced, and the scattered light is hardly observed in the observation image, and the spot of the cantilever 6 and the incident light 13 And the incident light 13 can be easily and reliably positioned on the back surface of the cantilever portion 6a.

  Further, when the spot 20 of the reflected light 14 is aligned with the center of the photodetector 16, the intensity of the spot 20 is also reduced, so that the intensity P of the equation (1) can be reduced, and the first implementation. As in the example, the detection sensitivity S decreases, and even if the detector positioning mechanism 18 is moved, fluctuations in the output voltage are reduced. As a result, it is possible to easily and accurately align the spot with the photodetector. As a result, the time required for measurement preparation for alignment is shortened, and highly accurate alignment is possible.

  Also in this embodiment, after the measurement preparation of the optical displacement detection mechanism 9 is completed, the intensity of the light source 10 is set to the original value, so that the detection sensitivity becomes higher than that at the time of alignment adjustment, and the sample is actually increased. Measurement can be performed with high accuracy.

  A third embodiment of the present invention is shown in FIG. FIG. 3 is a schematic diagram of a probe of a scanning near-field microscope, which is a type 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. As in the first embodiment, it is possible to measure the concavo-convex image on the sample surface by relatively 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 this embodiment includes a light source unit 56 in which a condensing lens and a semiconductor laser 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.

When aligning the spot light to the probe 50, 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 light strikes the probe 50. Next, the optical detector 57 is moved in the left-right direction (Y direction in the figure) by the uniaxial photodetector positioning mechanism 60 provided on the photodetector 57 side, and the current / While observing the output of the amplifier 61 having the voltage conversion circuit with the voltage monitor 63, the position is adjusted so that the spot 58 hits the vicinity of the center of the photodetector 57.

When the probe 50 vibrates in the optical displacement detection mechanism 55 configured as described above, 2
Since the area difference of the portion not blocked by the shadow on the light receiving surface of the divided photodetector 57 changes, the amplitude amount or phase of the probe 50 is measured by detecting the difference between the light outputs of the two divided surfaces. It becomes possible.

  Also in this embodiment, similarly to 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 drive circuit 64, and the laser beam is transmitted to the probe 50. By reducing the intensity of the laser when applying light, visibility is improved, and incident light can be easily and reliably positioned on the probe 50. Further, since the amplifier 61 is provided with the gain (amplification factor) adjuster 62, it is possible to easily and accurately align the spot with the photodetector 57 by reducing the measurement sensitivity. As a result, the time required for measurement preparation for alignment is shortened, and highly accurate alignment is possible.

  Also in this embodiment, after the measurement preparation of the optical displacement detection mechanism 55 is completed, the detection sensitivity becomes higher than that at the time of alignment adjustment by setting the amplification factor and the light source intensity to the original values. Measurement can be performed with high accuracy.

  FIG. 4 is a schematic diagram of an optical displacement detection mechanism used in the scanning probe microscope according to the third 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 and second embodiments with reference to FIG. The difference from FIG. 1 is that the light source drive circuit 21 does not have a light intensity adjuster, and the amplifier 22 does not have a gain (amplification factor) adjuster.

  In this embodiment, when adjusting the alignment of the optical displacement detection mechanism 9 before measurement, a neutral density filter 40 for reducing the intensity of light is inserted into the optical path between the light source 10 and the cantilever 6a to insert the cantilever 6a. The intensity of incident light was reduced. As a result, the visibility when positioning the spot of the incident light 13 on the cantilever portion 6a is improved, and the incident light 13 can be easily and reliably positioned on the back surface of the cantilever portion 6a. In addition, since the detection sensitivity is lowered, it is possible to easily and accurately align the spot of the reflected light 14 on the photodetector 16. As a result, the time required for measurement preparation for alignment is shortened, and highly accurate alignment is possible.

  Also in the present embodiment, after the preparation for alignment of the optical displacement detection mechanism 9 is completed, the intensity of the light source 10 returns to the original value by removing the neutral density filter 40 from the optical path, and the detection sensitivity is higher than that at the time of alignment adjustment. It is possible to actually measure the sample with high accuracy by increasing the height.

The neutral density filter 40 may be placed on the optical path after being reflected by the cantilever portion 6a. In this case, there is no change in the visibility of the alignment of the spot of the incident light 13 on the cantilever portion 6a. Therefore, it is difficult to observe the spot of the incident light 13 especially when the intensity of the incident light 13 is lowered with the optical microscope 29. This is advantageous in some cases. Further, since the detection sensitivity can be reduced, the alignment of the spot of the reflected light 14 to the photodetector 16 can be performed more easily and accurately.

  In the present embodiment, a so-called vibration-type atomic force microscope in which the cantilever 6 is vibrated in the vicinity of the resonance frequency by a vibrator 41 made of a piezoelectric element is used. In this embodiment, when the probe 6b is brought closer to the sample 5 while measuring the amplitude and phase of the cantilever portion 6a by the optical displacement detection mechanism 9, the atomic force and the intermittent contact amount act to cause the amplitude and phase. The phase changes. 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.

  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 photodetector made of a semiconductor having a light receiving surface divided into four or two is used. However, any detector can be used as long as it has a light receiving surface and outputs a voltage signal. Is possible. 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.

  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.

  Further, the light source is not limited to the semiconductor laser (LD), and any light source such as a super luminescence diode (SLD), a white light source, and a light emitting diode (LED) whose coherence is lower than that of the semiconductor laser can be applied.

  As a positioning mechanism provided in the photodetector or the light source, any mechanism can be used regardless of a manual type or an automatic type. The degree of freedom of positioning is not limited to one or two orthogonal axes, and may be multi-axis, and those using a tilt mechanism are also included in the present invention.

  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 varying using a volume knob, or a plurality of setting values in advance. A method may be used in which the setting is made using a changeover switch.

  The neutral density filter used for adjusting the light intensity of the light source can be any filter as long as it is used for the purpose of changing the light quantity.

  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.

  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.

It is a general-view figure which shows 1st Example and 2nd Example of the optical displacement detection mechanism for scanning probe microscopes concerning this invention. FIG. 2 is a circuit diagram of an amplifier including the current / voltage conversion circuit described in FIG. 1. It is a general-view figure which shows 3rd Example of the optical displacement detection mechanism for scanning near-field microscopes based on this invention. It is a general-view figure which shows 4th Example of the optical displacement detection mechanism for scanning probe micromirrors based on this invention. It is a general-view figure of the conventional scanning probe microscope.

Explanation of symbols

1 Sample holder 2 Coarse movement mechanism 4 Triaxial fine movement mechanism 5, 54 Sample 6 Cantilever (measurement object)
6a Cantilever portion 6b Probe 9, 55 Optical displacement detection mechanism 10, 56 Light source 16, 57 Photo detector 17, 59 Light source positioning mechanism 18, 60 Photo detector positioning mechanism 19 Light source unit 21, 64 Light source drive circuits 22, 61 Amplifiers 23 and 63 Voltage monitors 27 and 62 Gain (amplification factor) adjusters 28 and 65 Light intensity adjuster 29 Optical microscope 30 Current / voltage conversion circuit 33 Differential amplification circuit 34 Addition circuit 40 Neutral filter 50 Probe 201 Scanning probe Microscope 205 Arm 207 Cantilever 209 Probe 211 Sample 212 Sample stage 213 Three-axis fine movement mechanism (scanner)
221 Light source 231 Incident light 233 Reflected light 235 Photodetector

Claims (10)

A light source that irradiates the object to be measured;
A light source driving circuit for driving the light source;
A photodetector that receives light after irradiating the measurement target from the light source and detects light intensity;
A positioning mechanism for a photodetector that adjusts the position of the spot light at a predetermined position of the photodetector;
An optical displacement detection mechanism comprising an amplifier that amplifies the detection signal of the photodetector with a predetermined gain,
When the spot light is adjusted to a predetermined position of the photodetector by the photodetector positioning mechanism before actually measuring the measurement object, the detection sensitivity detected by the photodetector is actually measured. An optical displacement detection mechanism comprising means for setting smaller than that for measurement. A gain regulator that varies the gain setting in the amplifier,
2. The optical displacement detection according to claim 1, wherein the detection sensitivity detected by the photodetector is lowered by setting the gain of the amplifier to a value smaller than that during actual measurement by the gain adjuster. mechanism.   A light intensity variable means capable of varying the intensity of light incident on the photodetector is provided, and the intensity of light incident on the photodetector is set to a smaller value than when the measurement object is actually measured by the light intensity variable means. The optical displacement detection mechanism according to claim 1, wherein detection sensitivity detected by the photodetector is lowered.   A light source positioning mechanism for adjusting the irradiation position of the light from the light source to the measurement object, and actually measuring the measurement object by the light intensity varying means before irradiating the measurement object. 4. The optical displacement detection mechanism according to claim 3, wherein the light of the light source is positioned on a measurement object by setting to a value smaller than the time. The light intensity varying means is a light source driving circuit connected to the light source,
5. The optical displacement detection mechanism according to claim 3, wherein the light source drive circuit makes the light emission intensity of the light source before measurement smaller than that at the time of actual measurement.   6. The light intensity varying means is a neutral density filter for reducing the intensity of light provided on an optical path between the light source and the photodetector. The optical displacement detection mechanism described. The optical displacement detection mechanism according to any one of claims 1 to 6, and the measurement object is a cantilever having a probe at a tip or a probe having an arbitrary shape,
A sample holder for holding a sample, a holder for holding the cantilever or probe, and a one-axis or more fine movement mechanism for moving the cantilever or probe and the sample holder relative to each other at least in the Z direction perpendicular to the sample surface A scanning probe microscope comprising: moving means; and control means for collecting observation data of the sample by controlling the moving means based on a measurement result by the optical displacement detection mechanism. A light-receiving surface of the photodetector is divided into four or two, a scanning probe microscope that irradiates the back surface of the cantilever with light from the light source and receives reflected light from the cantilever with the light-receiving surface,
8. The scanning probe microscope according to claim 7, wherein the reflected light from the cantilever is positioned in the vicinity of the center of the dividing surface on the photodetector before measurement. The light receiving surface of the photodetector is divided into four or two parts, the light from the light source is irradiated onto a probe having an arbitrary shape, and the shadow of the probe is projected onto the light receiving surface of the photodetector,
The scanning probe microscope according to claim 7, wherein the light irradiated to the probe is positioned near the center of the divided surface on the photodetector before measurement.   The optical displacement detection mechanism according to any one of claims 1 to 6, and a probe whose surface measurement is performed by the measurement object, wherein the position information of the probe is detected by the optical displacement detection mechanism. A surface information measuring device characterized in that it performs.

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