JP4500033B2 - Near-field optical microscope - Google Patents

Description

  The present invention relates to a near-field optical microscope that measures optical characteristics of a micro area on a sample surface using near-field light.

  As a first conventional technique of a near-field optical microscope, as shown in FIG. 5, for example, a scattering type is used in which a probe is inserted into evanescent light localized on the sample surface and the evanescent light scattered by the probe is detected. A near-field optical microscope has been proposed (see, for example, Patent Document 1).

  In this prior art, the sample S is placed on an XY axis piezo stage 101 that can be moved minutely in the two-dimensional plane XY direction. Further, the probe is installed on a Z-axis piezo stage 105 that can be moved minutely in the vertical Z direction.

  In this scattering-type near-field optical microscope, the probe 103 made of a dielectric or metal with a sharpened tip is inserted into the evanescent light generated on the surface of the sample S, and the light scattered at the tip of the probe 103 is collected. Then, by measuring the scattered light intensity, the optical information of the sample S is measured with a high resolution exceeding the diffraction limit.

  The intensity of the evanescent light generated on the surface of the sample S decreases exponentially with respect to the distance from the sample S. For this reason, the evanescent light generated on the surface of the sample S includes shape information and optical information on the surface of the sample S.

  Therefore, usually, the sample S and the probe 103 are relatively scanned while keeping the distance between the probe 103 and the surface of the sample S constant, and the shape information and the optical information are separated to perform measurement. In the above prior art, the probe 103 is vibrated parallel to the surface of the sample S, and the amplitude of the probe 103 at that time is measured by a displacement detector comprising the semiconductor laser 110, the lenses 111, 112, and the two-divided photodetector 113. Thus, control is performed so that the distance in the height direction between the probe 103 and the sample S is constant.

  When the probe 103 and the sample S are brought close to each other, shear force acts on the probe tip 103a. Due to this shear force, the amplitude and phase of the probe 103 change. Since this shear force depends on the distance from the surface of the sample S, the distance between the probe 103 and the sample S can be controlled by measuring the amplitude or phase of the probe 103.

  As a second conventional technique, a near-field optical microscope using an illumination reflection mode in which near-field light is irradiated on the sample surface from the probe tip and the reflected light from the sample is detected has been proposed (for example, Patent Documents). 2).

  In this near-field optical microscope, as shown in FIG. 6, as a probe, the tip of the optical fiber is sharpened by heat drawing or etching, and bent to the major axis direction of the optical fiber by melting. A type of probe 201 is used.

  A minute opening with a diameter of about 5 nm to 200 nm is provided at the tip of the probe 201, and an aluminum film is deposited on the area other than the opening. The back surface of the probe 201 is mechanically polished to provide a reflective surface. The probe 201 is fixed to a probe holder 203 having a vibration function by the piezoelectric element 202. For detection of the amplitude of the probe 201, an optical lever type displacement meter 206 is used in which the laser light from the semiconductor laser 204 is applied to a reflection surface provided on the back surface of the probe 201 and the reflected light is detected by a quadrant detector 205. Yes.

  When laser light is introduced from the end of the probe 201, evanescent light is locally generated in the vicinity of a minute opening provided at the tip of the probe 201. The evanescent light existence region is about the diameter of the opening. Then, the tip of the probe 201 is brought close to the surface of the sample S to the evanescent light existing region, the sample S is irradiated with the evanescent light, and the reflected light is collected by the objective lens 210 provided on the same side as the probe 201 with respect to the sample S. The optical characteristics of the surface of the sample S can be known by illuminating and guiding the light to the light detection unit 214 composed of photomultipliers. The optical resolution at this time is about the aperture diameter provided at the tip of the probe 201, and the resolution exceeding the diffraction limit of light can be obtained by miniaturizing the aperture diameter.

  As a third conventional technique, a scattering near-field spectroscopy system has also been proposed (see, for example, Patent Document 3).

  In this prior art, as shown in FIG. 7, a probe 301 in which silver is coated on a cantilever with a probe for an atomic force microscope is used. In this technique, an oil immersion objective lens 303 having an NA of 1.4 is arranged on the back surface of a transmissive sample S, and laser light 304 having a wavelength of 488 nm serving as an excitation source from the back surface of the sample S is sampled through the objective lens 303. S is irradiated. At this time, a mask (not shown) is inserted on the optical path so as to cut the laser light incident on the portion of the objective lens 303 where the NA is 1 or less. Further, only light having an NA of 1 or more is incident on the sample S, and this light is totally reflected by the surface portion of the sample S, and evanescent light is formed on the surface of the sample S.

  When the probe 301a of the probe 301 is finely aligned with the evanescent light and the probe 301a of the probe 301 is inserted, the evanescent light is scattered. At this time, the scattered light is enhanced by the action of silver coated on the probe 301a. Further, the scattered light 305 is collected by the same objective lens 303 as the one that condensed the excitation light, the excitation light is removed by a notch filter (not shown), and the scattered light is separated into a spectrum with a cooled CCD camera. By performing spectroscopic analysis with a device (not shown), Raman spectroscopic analysis is performed with a resolution exceeding the diffraction limit. In this conventional technique, the distance between the probe 301a and the sample S is controlled by the atomic force acting between the probe 301a and the sample S, and the shape information included in the evanescent light is the same as in the second conventional technique. And optical information can be measured separately.

In each of the above prior arts, a shape image and a surface property image of the sample surface are simultaneously obtained, and these measurements are performed by raster scanning or the like.
Japanese Patent Laid-Open No. 9-28112 (Section 3-7, FIG. 4) Japanese Patent Laying-Open No. 2002-243618 (FIG. 1) Japanese Patent Laid-Open No. 2000-81383 (FIG. 3)

  However, the following problems remain in the conventional near-field optical microscope. In each of the above prior arts, it is necessary to align the tip of the probe with the center of the optical axis of the evanescent light generation region or the objective lens for collecting the evanescent light. In general, evanescent light has a very low intensity, and in order to improve the light collection efficiency and increase the S / N ratio, it is necessary to collect light with an objective lens having a high numerical aperture (NA). As the size of the probe increases, the probe and objective lens must be positioned using a highly accurate micropositioning mechanism such as a piezo stage. However, during measurement, there may be a positional shift due to the influence of the creep characteristics of the piezo element and the drift caused by the temperature change. This effect is noticeable when the measurement takes a long time. In particular, when Raman spectroscopy is performed with a scanning near-field microscope, the detection light is extremely weak, and thus it is necessary to perform measurement over a long period of time from several minutes to several hours. At this time, if a positional shift occurs, the measurement location is shifted and local spectroscopic measurement becomes impossible. As described above, the conventional technique is not suitable for highly accurate measurement because the sample and the probe are relatively moved under the influence of the drift of the fine movement mechanism.

  In each of the above conventional techniques, a shape image and a surface property image are simultaneously acquired by raster scanning or the like. However, since measurement is affected by drift during measurement, simultaneous measurement of a highly accurate shape image and property image is performed. It was difficult. In particular, it is essential to obtain a shape image for Raman scattering spectroscopy using a near-field optical microscope. However, since measurement at each pixel takes a long time to obtain a Raman spectrum, it is greatly affected by drift and other factors. The above simultaneous measurement was very difficult.

  The present invention has been made in view of the above-described problems, and provides a near-field optical microscope capable of suppressing the influence of drift and the like, enabling high-precision measurement, and further obtaining high measurement efficiency. The purpose is to do.

  The present invention employs the following configuration in order to solve the above problems. That is, the near-field optical microscope of the present invention includes a stage on which an object to be measured is placed, a probe that is brought close to or in contact with the object to be measured, and the probe that is relatively relative to the object to be measured in a three-dimensional direction. A scanning mechanism that moves, a shape measuring mechanism that measures the shape of the object to be measured via the probe that is relatively moved by the scanning mechanism, an evanescent light generating mechanism that generates evanescent light on the surface of the object to be measured, and A near-field optical microscope comprising a light detection mechanism for detecting light from the object to be measured by evanescent light, and a control unit for controlling each mechanism, wherein the scanning mechanism includes at least the stage and the probe. Displacement measuring means for measuring at least a displacement in a horizontal two-dimensional plane among the one displacement is provided, and the control unit detects the light based on the measured displacement. And performing servo control for adjusting the detection position for at configuration.

  In this near-field optical microscope, the control unit performs servo control to adjust the detection position performed by the light detection mechanism based on the displacement measured by the displacement measuring means, so that the influence of the drift of the scanning mechanism is suppressed / removed by servo control. In addition, measurement over a long period of time can be stably performed with high accuracy.

  In the near-field optical microscope of the present invention, the displacement measuring unit measures a vertical displacement of at least one of the stage and the probe, and the control unit is based on the vertical displacement. Servo control for adjusting the distance between the probe and the object to be measured is performed. That is, in this near-field optical microscope, the control unit also performs servo control to adjust the distance between the probe and the object to be measured based on the vertical displacement, so that the linearity in the vertical direction is maintained and the influence of drift is suppressed. Further reduction is possible, and measurement over a long time is possible. Further, it is possible to reduce interference in the vertical direction (Z direction) that occurs when scanning in the two-dimensional plane direction (XY direction).

  Further, in the near-field optical microscope of the present invention, the control unit performs the detection by the light detection mechanism at an arbitrary designated position where the shape measurement is performed after the surface shape of the object to be measured is measured by the shape measurement mechanism. Control is performed as described above. That is, in this near-field optical microscope, the surface shape of the object to be measured is measured and then detected by an optical detection mechanism at an arbitrary designated position where the shape is measured. Therefore, the target local area on the shape image acquired in advance is detected. Only the area can be selectively measured for physical properties. Therefore, it is not necessary to measure the optical characteristics of all the points in the two-dimensional plane, and the target portion can be positioned and measured with high accuracy, so that the measurement efficiency is improved.

  Moreover, the near-field optical microscope of the present invention is characterized in that the control unit performs control so that the detection is automatically performed in a specified order for a plurality of the specified positions. That is, this near-field optical microscope automatically detects a plurality of designated positions in a designated order, so that more efficient measurement is possible.

  The near-field optical microscope of the present invention includes a spectroscopic system in which the light detection mechanism includes a light detector that receives light from the object to be measured and a spectroscope, and measures the spectrum of the detection light. It is characterized by that. That is, this near-field optical microscope is equipped with a spectroscopic system that measures the spectrum of the detection light, so that it is possible to perform Raman scattering spectroscopic analysis that requires long-time measurement with high accuracy and efficiency. .

  The present invention has the following effects.

  That is, according to the near-field optical microscope according to the present invention, the control unit performs servo control for adjusting the detection position performed by the light detection mechanism based on the displacement measured by the displacement measurement unit, and thus the influence of the drift of the scanning mechanism. It is possible to stably and accurately measure the transmittance, reflectance, fluorescence characteristics, or spectral spectrum of the sample surface over a long period of time.

  In addition, since the optical characteristics are measured locally at the specified position after the shape measurement, it is not necessary to measure the optical characteristics of all points on the two-dimensional plane, and the target part is measured with high accuracy. Measurement efficiency can be improved.

  Hereinafter, a first embodiment of a near-field optical microscope according to the present invention will be described with reference to FIG.

  The near-field optical microscope of the present embodiment includes a scattering near-field Raman spectroscopic system for performing structural analysis at the molecular level using Raman scattered light from a sample.

  In this near-field optical microscope, an objective lens 22 having a numerical aperture of 1 or more (here, an oil immersion lens having a numerical aperture of 1.4) is placed on a transparent sample holder (stage) 21 on which a sample (object to be measured) S is placed. It is arranged below. A laser beam from a laser source 23 is introduced into the objective lens 22. In other words, the diameter of the parallel light beam is expanded by the beam expander 24, the laser light is bent by 90 ° by the half mirror 25 and guided to the objective lens 22.

  In addition, on the optical path between the beam expander 24 and the half mirror 25, a disk-shaped light shielding plate 26 is provided so as to cut light of a portion having a numerical aperture of 1 or less out of light incident on the objective lens 22. Has been inserted. With such an optical system, light having a numerical aperture of 1 or more is incident on the sample S from the objective lens 22, so that the light is incident at a total reflection angle, and evanescent light is formed on the surface of the sample S. That is, the laser source 23, the beam expander 24, the half mirror 25, the objective lens 22, and the like function as an evanescent light generation mechanism Y2 that generates evanescent light on the surface of the sample S.

The sample holder 21 is attached to a sample triaxial fine movement mechanism (scanning mechanism) 28. The sample triaxial fine movement mechanism 28 includes a piezoelectric element and an XY fine movement mechanism (not shown) for fine movement in a two-dimensional XY plane and a Z fine movement mechanism (not shown) for fine movement in the vertical Z direction. ing. Here, a capacitance displacement meter (displacement measuring means) 37 is attached to the sample triaxial fine movement mechanism 28, and the displacement amount of all three axes is always measured by the capacitance displacement meter 37. Has been. Further, the measured displacement amount is sent to the control device C connected to the capacitance type displacement meter 37 and the sample triaxial fine movement mechanism 28, and the control device C reduces the displacement amount to a predetermined value or less. Thus, the sample triaxial fine movement mechanism 28 is set to be servo-controlled by a closed loop. The control device C is connected to each mechanism of the microscope, and includes a CPU and the like for controlling these in an integrated manner.

  On the other hand, a cantilever holder 29 is disposed above the sample holder 21. The cantilever holder 29 is made of a silicon substrate, and a cantilever 30 having a sharpened probe portion 30a is attached to the tip. A metal is deposited on the probe portion 30a. In this embodiment, silver is used as the vapor deposition metal. An optical lever optical system 31 is disposed above the cantilever 30, and the deflection of the cantilever 30 is detected by the optical lever optical system 31.

  The optical lever optical system 31 has a configuration in which the light of the laser diode 32 is condensed on the back surface of the cantilever 30 by the lens 33 and the reflected light from the cantilever 30 is detected by the photodetector 34 in which the light receiving surface is divided into four. Yes. That is, when the cantilever 30 bends, the spot on the photodetector 34 moves up and down, and the bend of the cantilever 30 is measured by detecting the difference in light intensity at each divided surface at this time. The wavelength of the laser diode 32 is different from the wavelength to be measured.

  The cantilever holder 29 is attached to an optical head 35 having a built-in optical lever optical system 31. Further, the optical head 35 is attached to a probe three-axis fine movement mechanism (scanning mechanism) 36 that can perform a scanning operation on a two-dimensional XY plane constituted by piezoelectric elements and a servo operation in the vertical Z direction. The probe triaxial fine movement mechanism 36 has a configuration in which a scanner movable in one axial direction is combined in three directions of X, Y, and Z.

  A capacitance displacement meter (displacement measuring means) 37 is attached to the probe triaxial fine movement mechanism 36, and the displacement amount of all three axes is always measured by the capacitance displacement meter 37. Yes. Further, the measured displacement amount is sent to the control device C connected to the capacitance type displacement meter 37 and the probe triaxial fine movement mechanism 36, and the displacement amount of the control device C is below a predetermined value. The probe triaxial fine movement mechanism 36 is set to be servo-controlled in a closed loop.

  The probe triaxial fine movement mechanism 36 is mounted on a coarse movement stage 38 for bringing the probe portion 30a and the surface of the sample S close to each other. The coarse movement stage 38 has a configuration in which the coarse movement stage 38 is brought close to the sample S by using the mechanism of the stepping motor 39 and the feed screw 40 with the leg of the micrometer head 41 as a fulcrum.

  A half mirror 25 that transmits the optical signal collected by the objective lens 22 is disposed below the objective lens 22. A total reflection mirror 43 is disposed on the optical axis of the light that has passed through the half mirror 25.

  An imaging lens 44, notch filters 45 and 42, and a spectroscope 46 are arranged in this order on the optical axis of the light bent at 90 degrees by the total reflection mirror 43. The notch filter 45 has an optical characteristic of cutting the laser diode light component of the optical lever optical system 31 from the light imaged by the imaging lens 44, and the notch filter 42 cuts the excitation laser light component. To do. The spectroscope 46 is provided with a cooled CCD camera or the like as a photodetector.

  Next, a case where measurement is performed with the near-field optical microscope of the present embodiment will be described with reference to FIGS.

  In the near-field optical microscope of the present embodiment, when the probe unit 30 a and the sample S are brought close to the region where the atomic force acts, the cantilever 30 is bent by the atomic force acting on the tip of the cantilever 30. Since the amount of deflection depends on the distance between the probe portion 30a and the sample S, the sample three-axis fine movement mechanism 28 is servo-operated by the control device C so that the amount of deflection is constant. It becomes possible to keep the distance from the probe portion 30a constant.

Then, the control device C controls each fine movement mechanism so that the distance between the probe portion 30a and the surface of the sample S is kept constant, and the surface of the sample S is raster scanned (see FIG. 2A). A solid line in the figure), and an uneven image (shape image) on the surface of the sample S is measured in advance. In other words, the optical lever optical system 31, the control device C, and the like measure the shape of the sample S through the probe portion 30a that is relatively moved by the sample triaxial fine movement mechanism 28 and the probe triaxial fine movement mechanism 36. It functions as the mechanism X2. In this way, by mapping the servo signal used for controlling the distance between the sample S and the probe portion 30a, the uneven image on the surface of the sample S can be measured.

  In this embodiment, the Z-direction servo operation for keeping the distance between the cantilever 30 and the sample S constant is performed by the sample triaxial fine movement mechanism 28. Instead, the probe triaxial fine movement mechanism is used. 36 may be used.

  Next, as shown in FIG. 2 (b), several measurement points (designated positions) P for measuring surface physical properties (optical characteristics) are determined and controlled from the concavo-convex image of the surface of the sample S obtained by the above measurement. The position coordinates of the measurement point P and the measurement order are input to the apparatus C, and measurement of the optical characteristics is started. The position of the measurement point P and the measurement order of the optical characteristics may be determined in advance before measuring the shape of the surface of the sample S. Further, as shown in FIG. 3A, an arbitrary straight line L may be designated as the designated position instead of a point, and the optical characteristics on the designated straight line L may be measured. Furthermore, as shown in FIG. 3B, an arbitrary area A may be specified as the specified position, and the optical characteristics may be measured in the specified area A.

  When starting these optical characteristics, control is performed so that a trigger signal is sent to the spectroscope 46 side for each pixel at the measurement position to start spectroscopy.

In accordance with the above measurement sequence, the control device C causes the sample triaxial fine movement mechanism 28 to position the predetermined measurement point P at the tip of the probe portion 30a and starts optical measurement.

  The evanescent light generated on the surface of the sample S generally exists between 100 nm and 200 nm, and attenuates along an exponential function curve as the distance from the surface of the sample S increases. By positioning the probe portion 30a and the sample S in this area while performing servo operation, the evanescent light is scattered at the tip of the probe portion 30a, and the light scattered at the tip of the probe portion 30a It is enhanced by the electric field enhancing action and converted to propagating light.

  This scattered light is collected by the same objective lens 22 as the objective lens 22 used for incidence of excitation light. When the light is condensed, the light is collected by the entire objective lens 22 including a portion having a numerical aperture of 1 or less. At this time, the probe portion 30 a needs to be aligned with the center of the optical axis of the objective lens 22. This requires higher precision alignment as the objective lens 22 has a higher magnification. In particular, since the optical signal intensity is weak in the near-field optical microscope, more precise positioning is required in order to improve the excitation efficiency and condensing efficiency of the evanescent light.

  Here, by using the probe triaxial fine movement mechanism 36, the probe portion 30a can be finely positioned in the two-dimensional plane XY direction. The collected optical signal is transmitted through the half mirror 25, bent at 90 degrees by the total reflection mirror 43 and imaged by the imaging lens 44, and then the laser diode component of the optical lever optical system by the notch filter 45. And the laser component of the excitation light is cut by the notch filter 42 and guided to the spectroscope 46. That is, the half mirror 25, the total reflection mirror 43, the imaging lens 44, the notch filters 42 and 45, the spectroscope 46, and the like function as a light detection mechanism Z2 that detects light from the sample S by evanescent light.

  In this way, while the height of the sample S and the probe portion 30a is kept constant by the sample triaxial fine movement mechanism 28, the probe portion 30a is raised to an arbitrary designated position where the shape is measured in advance by servo control. By positioning accurately, Raman spectroscopic analysis can be performed with a resolution exceeding the diffraction limit.

  Since the detection light is very weak, the scanning speed of the sample S is slowed down, or measurement is performed at a specific point on the sample S for a long time. In the conventional near-field optical spectroscopic system, the longer the measurement is, the greater the influence of the drift due to the creep characteristics of the fine movement mechanism and the temperature change. There was the inconvenience of moving to.

  However, in the near-field optical microscope of the present embodiment, both the sample triaxial fine movement mechanism 28 and the probe triaxial fine movement mechanism 36 always measure the displacement in the two-dimensional XY plane to obtain a predetermined displacement amount. Since the servo control is applied, it is possible to suppress the drift of the fine movement mechanism, perform stable measurement for a long time, and improve positioning reproducibility.

  Also, since the vertical Z scanners of both the sample triaxial fine movement mechanism 28 and the probe triaxial fine movement mechanism 36 are provided with displacement meters and servo-operated by the control device C, linearity in the height direction is maintained. Therefore, the effect of drift can be further reduced, and measurement over a long period of time can be performed. In addition, it is possible to reduce interference in the Z direction that is caused by scanning in the two-dimensional plane XY direction.

  Further, since the control device C performs control so as to measure the optical characteristic at an arbitrary measurement point P whose shape is measured after measuring the surface shape of the sample S by raster scanning, the shape acquired in advance. Only the desired local region on the image can be selectively measured. Therefore, since it is not necessary to measure the optical characteristics of all points on the surface of the sample S, the target portion can be measured efficiently and with high accuracy in the minimum necessary time.

  Next, a second embodiment of the near-field optical microscope according to the present invention will be described with reference to FIG. In the following description, the same components described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The near-field optical microscope of the second embodiment generates evanescent light at the tip of the optical fiber probe 1, irradiates the sample S with the evanescent light, and detects the light transmitted through the sample S, thereby detecting the optical characteristics of the sample S. An illumination transmission mode for obtaining information is adopted. The optical fiber probe 1 used in this microscope is a bent type optical fiber probe in which the tip of the optical fiber is sharpened by heat drawing or etching and further bent to be melted.

  The surface of the optical fiber probe 1 is coated with aluminum, and an opening having a diameter of about 50 to 200 nm is provided at the tip. In addition, a reflection surface for reflecting the laser for the optical lever by mechanical polishing is provided on the back surface of the probe 1.

  This probe 1 is fixed to a probe holder 2. The probe holder 2 is provided with a piezoelectric element 3 for probe vibration.

  The probe holder 2 is attached to a probe biaxial fine movement mechanism (scanning mechanism) 7 capable of fine movement on a two-dimensional XY plane composed of piezoelectric elements. A capacitance displacement meter (displacement measuring means) 8a is attached to the probe biaxial fine movement mechanism 7, and the displacement amount is always measured by the capacitance displacement meter 8a. Further, the measured displacement amount is sent to a control device (control unit) C connected to the capacitance type displacement meter 8a and the probe biaxial fine movement mechanism 7, and the control device C has the displacement amount. The probe 2-axis fine movement mechanism 7 is set to be servo-controlled so as to be below a predetermined value.

  On the other hand, a sample holder (stage) 5 on which the sample S is placed is attached to a sample triaxial fine movement mechanism (scanning mechanism) 6. The sample triaxial fine movement mechanism 6 includes a piezoelectric element and an XY fine movement mechanism (not shown) for fine movement in a two-dimensional XY plane and an X fine movement mechanism (not shown) for fine movement in the vertical Z direction. ing. Here, the XY fine movement mechanism of the sample triaxial fine movement mechanism 6 is provided with a capacitance displacement meter (displacement measuring means) 8b, and the displacement amount is always measured by the capacitance displacement meter 8b. Has been. Further, the measured displacement amount is sent to the control device C connected to the capacitance type displacement meter 8b and the sample triaxial fine movement mechanism 6, and the control device C reduces the displacement amount to a predetermined value or less. Thus, the XY fine movement mechanism of the sample triaxial fine movement mechanism 6 is set to be servo-controlled. That is, the control device C controls the fine movement mechanisms 6 and 7 by a so-called closed loop.

  The capacitance displacement gauges 8a and 8b measure the position by detecting a change in capacitance due to a change in position between the opposing electrodes arranged in the drive unit and the fixed unit in the fine movement mechanism. Is.

  Also, a capacitive displacement meter (not shown) for measuring the amount of movement in the Z direction is attached to the Z fine movement mechanism of the sample triaxial fine movement mechanism 6.

  Above the optical fiber probe 1, a semiconductor laser 9 and a four-divided photodetector 10 are disposed as an optical lever type displacement meter that detects the attenuation amount of the amplitude of the optical fiber probe 1. In this optical lever system, a laser is irradiated from the semiconductor laser 9 to the reflection surface on the back surface of the probe, and this reflected light is detected by a four-divided photodetector 10. Further, the control device C servo-drives the sample triaxial fine movement mechanism 6 in the vertical Z direction so that the attenuation amount becomes equal to a preset target value, whereby the sample S and the optical fiber probe 1 are moved. It is set to keep the distance constant.

  Further, an objective lens 13 (NA 1.4, oil immersion lens) is disposed below the sample holder 5 so as to be directly below the sample S.

  Further, an Ar laser 12 that is a laser source for introducing laser light through a condenser lens 11 is provided on the distal side of the optical fiber probe 1.

  A total reflection mirror 14 that reflects the detection light collected by the objective lens 13 is disposed below the objective lens 13, and is on the optical axis of the detection light reflected by the total reflection mirror 14. The imaging lens 15, the short pass filter 17, and the photodetector 16 are arranged in this order.

  The photodetector 16 uses an avalanche photodiode having a light receiving surface φ250 μm, and adopts a method of measuring light intensity by photon counting detection. The short pass filter 17 has an optical characteristic of cutting a laser diode light component of the optical lever optical system.

  Next, a case where measurement is performed with the near-field optical microscope of the present embodiment will be described below.

  First, it is necessary to align the tip of the optical fiber probe 1 with the center of the optical axis of the objective lens 13 disposed immediately below the sample S. In the near-field optical microscope, since the detected optical signal is weak, an objective lens having a large numerical aperture is used for the purpose of improving the light collection efficiency. As the numerical aperture of the objective lens increases, higher precision alignment is required. However, by using the probe biaxial fine movement mechanism 7, the optical fiber probe 1 can be finely positioned in the two-dimensional plane XY direction. Is possible.

  Furthermore, it is necessary to align the light to be detected with the light receiving surface of the avalanche photodiode that is the light detector 16, but since the light receiving area of the light detector 16 is very small, highly accurate positioning is required. . At this time, the optical fiber probe 1 is finely positioned using the probe biaxial fine movement mechanism 7, whereby the detected light can be aligned with the light receiving surface of the photodetector 16 with high accuracy.

  After aligning the optical axes of the optical fiber probe 1 and the objective lens 13, the sample S is brought closer to the optical fiber probe 1 while vibrating the optical fiber probe 1 near the resonance frequency. At this time, the amplitude is attenuated by an atomic force acting between the optical fiber probe 1 and the sample S or intermittent contact. The amount of attenuation at this time depends on the distance between the optical fiber probe 1 and the sample S.

  Then, the control device C controls each fine movement mechanism, performs a raster scan on the surface of the sample S as in the first embodiment, while keeping the distance between the optical fiber probe 1 and the surface of the sample S constant. An uneven image on the S surface is measured in advance. That is, the optical lever optical system such as the piezoelectric element 3, the semiconductor laser 9, and the four-divided photodetector 10, the control device C, and the like are moved by the probe triaxial fine movement mechanism 6 and the probe biaxial fine movement mechanism 7. Functions as a shape measuring mechanism X1 that measures the shape of the sample S via

  In this way, by mapping the servo signal used for controlling the distance between the sample S and the optical fiber probe 1, it is possible to measure the uneven image on the surface of the sample S.

  Next, from the concavo-convex image of the surface of the sample S obtained by the above measurement, several measurement points (designated positions) P for measuring the surface physical properties (optical characteristics) are determined in the same manner as in the first embodiment. The position coordinates of the measurement point P and the measurement order are input, and measurement of optical characteristics is started.

In accordance with the above measurement sequence, the control device C uses the sample biaxial fine movement mechanism 6 to place a predetermined measurement point P at the tip of the optical fiber probe 1 and starts optical measurement. First, an Ar laser 12 is introduced into the end of the optical fiber probe 1 through the condenser lens 11 to form evanescent light in the vicinity of a minute opening at the tip of the optical fiber probe 1. That is, the Ar laser 12, the condensing lens 11, the optical fiber probe 1, and the like function as an evanescent light generation mechanism Y1 that generates evanescent light on the surface of the sample S.

  Further, the evanescent light is irradiated onto the sample S by positioning in the evanescent light existing region while controlling the distance between the optical fiber probe 1 and the sample S. The irradiation light passes through the sample S, is collected by the objective lens 13 disposed immediately below the sample S, is bent by 90 degrees by the total reflection mirror 14, and then passes through the imaging lens 15 and the short pass filter 17. An image is formed on the photodetector 16. That is, the objective lens 13, the total reflection mirror 14, the imaging lens 15, the short pass filter 17, the photodetector 16, and the like function as a light detection mechanism Z1 that detects light from the sample S by evanescent light.

  After measuring the optical characteristics in this way, the optical fiber probe 1 is automatically moved to each measurement point P in the set measurement order, and the optical characteristics are measured after positioning in the same manner as described above.

  In the near-field optical microscope of the present embodiment, both the sample triaxial fine movement mechanism 6 and the probe biaxial fine movement mechanism 7 always measure the displacement in the horizontal two-dimensional plane to obtain a predetermined displacement amount. Since the servo control is applied, the drift of these fine movement mechanisms is suppressed, the positional deviation between the optical axis and the sample S and the probe 1 is suppressed, and stable measurement can be performed for a long time. Accuracy is also improved.

  In addition, since the control device C performs servo control for adjusting the distance between the probe 1 and the sample S based on the vertical displacement, the linearity in the vertical direction is maintained, and the influence of drift can be further reduced. Measurements up to can be made. In addition, it is possible to reduce vertical interference caused by scanning the surface of the sample S.

  Further, since the control device C performs control so as to measure the optical characteristic at an arbitrary measurement point P whose shape is measured after measuring the surface shape of the sample S, the object on the shape image acquired in advance is determined. It is possible to selectively measure physical properties of only the local region. Therefore, it is not necessary to measure the optical characteristics of all the points on the surface of the sample S, and it becomes possible to position and measure the target portion with high accuracy, thereby improving the measurement efficiency.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in each of the above embodiments, closed-loop control is performed using a displacement meter for the fine movement mechanism in the Z direction, but control is performed so that the distance between samples is always constant by measuring the probe amplitude. Alternatively, the displacement meter may be used only for the purpose of simply measuring the displacement as a so-called open loop and increasing the length measurement accuracy in the Z direction. In this case, the above-described embodiment in which the detection of the displacement of the fine movement mechanism in the Z direction is a closed loop cannot provide the above-described advantage of the closed loop, but the overall system response is improved. A configuration in which a displacement meter is not provided in the Z direction is also conceivable. In this case, the hysteresis characteristic of the piezoelectric element may be corrected by calculation in order to ensure the measurement accuracy.

Moreover, although the illumination transmission mode and the scattering near-field optical microscope have been described in the above embodiment, the present invention is not limited to these measurement modes, and for example, the following measurement modes may be adopted.

That is, the evanescent light generated at the tip of the probe is irradiated onto the sample , the light reflected by the sample is collected by an objective lens, etc., and guided to a photo detector such as a photomultiplier, thereby knowing the optical characteristics of the sample surface. Illumination reflection mode that can
A collection mode in which the evanescent light generated in the sample is collected by an optical fiber probe with a small opening at the tip and guided to a photo detector such as a photomultiplier, and the optical characteristics of the sample surface can be known.
A laser is introduced from the end of an optical fiber probe, the evanescent light is localized in the vicinity of a minute opening provided at the tip of the optical fiber probe, the tip of the optical fiber probe is brought close to the sample surface to the near-field existence region, and the evanescent light is emitted. Illumination, collection mode, etc. that can know the optical characteristics of the sample surface by irradiating the sample, collecting the reflected light from the sample with the same optical fiber probe, and guiding it to a photo detector such as a photomultiplier. It may be adopted.

1 is a schematic diagram illustrating an overall configuration of a near-field optical microscope according to a first embodiment of the present invention. In the near-field optical microscope of 1st Embodiment which concerns on this invention, it is explanatory drawing which shows the measurement position of a shape measurement and an optical characteristic measurement. In the near-field optical microscope of 1st Embodiment which concerns on this invention, it is explanatory drawing which shows the other measurement position of a shape measurement and an optical characteristic measurement. It is a schematic diagram which shows the whole structure of the near-field optical microscope of 2nd Embodiment which concerns on this invention. 1 is a schematic diagram showing an overall configuration of a near-field optical microscope in the first prior art according to the present invention. It is a schematic diagram which shows the whole structure of the near-field optical microscope in the 2nd prior art which concerns on this invention. It is a schematic diagram for demonstrating the principal part structure of the near-field optical microscope in the 3rd prior art which concerns on this invention.

Explanation of symbols

1 Bent type optical fiber probe 2 Probe holder 5, 21 Sample holder (stage)
6, 28 Three-axis fine movement mechanism (scanning mechanism) for sample
7, 36 Triaxial fine movement mechanism for scanning (scanning mechanism)
8a, 8b, 37 Capacitive displacement meter (displacement measuring means)
12 Ar laser 13, 22 Objective lens 14 Photo detector 23 Laser source 24 Beam expander 26 Light shield plate 29 Cantilever holder 30 Cantilever 30a Probe unit 31 Optical lever optical system 35 Optical head 38 Coarse moving stage 46 Spectrometer C Control device ( Control part)
S sample (object to be measured)
X1, X1 Shape measurement mechanism Y1, Y2 Evanescent light generation mechanism Z1, Z2 Light detection mechanism

Claims (5)

A stage for placing an object to be measured;
A probe in proximity to or in contact with the object to be measured;
A scanning mechanism for moving the probe relative to the object to be measured in a three-dimensional direction;
A shape measuring mechanism that measures the shape of the object to be measured via the probe that is relatively moved by the scanning mechanism;
An evanescent light generating mechanism for generating evanescent light on the surface of the object to be measured;
A light detection mechanism for detecting light from the object to be measured by the evanescent light;
A control unit that controls each of the mechanisms, a near-field optical microscope comprising:
The scanning mechanism has an XY fine movement mechanism with each means of movement and displacement measurement in a horizontal two-dimensional plane, and the XY fine movement mechanism is provided on both sides of the probe side and the stage side,
The evanescent light generation mechanism includes excitation means, and the light detection mechanism includes light collection means,
The probe-side XY fine movement mechanism aligns the probe tip with respect to at least one of an excitation position excited by the excitation means and a light collection position condensed by the light collection means,
Said stage-side XY fine movement mechanism is, any designated position of a sample placed on the stage, aligns against the probe tip,
Wherein the control unit is configured to perform a servo control for holding the position of each XY fine movement mechanism is specified in the probe side and the stage side of the measured displacement by the displacement measuring means, wherein the XY fine movement mechanism having,
A near-field optical microscope. The near-field optical microscope according to claim 1,
A near-field optical microscope provided with at least one of the stage side and the probe side, wherein the scanning mechanism has a Z fine movement mechanism with a displacement measuring means for measuring displacement in the vertical direction. The near-field optical microscope according to claim 1 or 2,
The controller is excited by at least one of the evanescent light generation mechanism and the light detection mechanism at an arbitrary designated position where the shape is measured after measuring the surface shape of the object to be measured by the shape measurement mechanism. And a near-field optical microscope that performs control to execute at least one of light collection and light collection. The near-field optical microscope according to claim 3,
A near-field optical microscope in which the control unit performs control to automatically execute at least one of the excitation and condensing in a designated order at a plurality of the designated positions. The near-field optical microscope according to any one of claims 1 to 4,
A near-field optical microscope provided with a spectroscopic system in which the light detection mechanism includes a light detector that receives light from the object to be measured and a spectroscope, and that measures a spectrum of detection light.

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