JP2007322159A - Optical fiber probe, photodetector, and photodetection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber probe capable of measuring a phase object sample and capable of enhancing the S/N ratio, without the accompaniment of a complex optical system constitution, and to provide a photodetector provided therewith. <P>SOLUTION: This optical fiber probe 13 concentrically has the first emitting face 20a for normal propagation light and the second exiting face 20b for making a near-field light exude, is formed with an exuding coated layer 33 on the face for exuding the near-field light, and is provided with the coated layer 33 for reflecting one part of the light incident to the exiting face and for transmitting another one part, on the emitting face for emitting normal propagation light. The coated layer 33 is provided to make the intensity of the light return-propagated again in the optical fiber reflected on the emitting face equal to the intensity of the light return-propagated again in the optical fiber, after being emitted from the emitting face and after being reflected by a measured face 2a to be transmitted through the emission face, out of the lights incident into the emitting face for emitting normal propagation light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical fiber probe, a photodetection device, and a photodetection method for the purpose of nano-order measurement and processing.

  In recent years, nano-order measurement and processing have been performed by SPM (scanning probe microscope) technology including STM (scanning tunneling microscope) and AFM (scanning atomic force microscope). A near-field optical microscope that is capable of detecting optical characteristics in a very small region below the diffraction limit in this SPM is used as a measurement / evaluation apparatus in various fields such as biotechnology. Research and development of optical recording devices and microfabrication devices applying the above-mentioned near-field optical microscope technology are also underway.

  In the near-field optical microscope, a fine structure having a size equal to or smaller than the diffraction limit is used as a probe, and near-field light is generated in the vicinity thereof by illuminating the probe tip. By scanning the probe on the sample surface in this state, the near-field light scattered or transmitted through the sample surface can be detected by the electromagnetic interaction between the near-field light localized near the probe and the sample surface. Thus, optical information (light intensity, spectrum, polarization, etc.) of the sample surface can be obtained.

  A near-field optical microscope generally has a protruding portion in which a sharpened core is protruded at one end of an optical fiber provided with a cladding around the core, and the protruding portion has, for example, gold (Au) or silver (Ag). An optical image having a resolution exceeding the wavelength of light can be obtained by providing an optical probe coated with a metal such as.

  When measuring the physical properties of a sample in a micro area using the near-field optical microscope, the shape of the sample is measured by detecting evanescent light localized in an area smaller than the wavelength of light on the sample surface. Then, the evanescent light generated by irradiating the sample with light under the total reflection condition is scattered by the above-described optical probe and converted into scattered light. The scattered light is guided to the core of the optical fiber through the protruding portion where the optical probe is formed, and is detected by a detector connected to the other exit end of the optical fiber. That is, this near-field optical microscope can perform both scattering and detection by an optical probe.

Although the conventional near-field optical microscope can measure with high resolution, there is a demerit that the measurement range is as narrow as about several tens of μm.
In recent years, in applications such as silicon wafer defect inspection, it has been required to switch to high-resolution measurement using near-field light after the low-resolution measurement described above, and continue to measure and inspect the same sample. In response to such a demand, an apparatus having a configuration in which an optical probe for detecting near-field light is incorporated in a normal optical microscope apparatus including an observation system using an objective lens has been proposed (for example, see Patent Document 1). ).
In the prior art described in Patent Document 1, the near-field light measurement (after the optical probe for near-field light detection is positioned with respect to a minute region for which physical property measurement is desired, which is specified by a wide range measurement using an objective lens ( However, the alignment described above is very difficult and takes a long time.

JP 2000-55818 A JP 2006-29831 A

  In the prior application technology 1 (Patent Document 2 and Prior Application 1 (Japanese Patent Application No. 2005-29652)) by the present inventors for the above-mentioned problems, a solution is provided. That is, the prior application technique 1 uses an optical probe having an exit surface capable of emitting each of a light spot necessary for wide-range measurement using normal propagation light and a near-field light spot necessary for high-resolution measurement. By adopting a configuration for performing the measurement, a difficult optical probe alignment process is not required, so that the measurement / inspection process can be speeded up.

  In addition, in another prior application technique 2 (prior application 2 (Japanese Patent Application No. 2005-380273)) by the present inventor, a further higher S / N ratio of measurement using normal propagation light is realized. In the measurement using the normal propagation light in the prior application technique 1 described above, a change in reflection, scattering, and transmitted light amount of the light emitted to the sample is detected. In particular, a phase object such as a bio sample is measured. In some cases, it may be difficult to ensure the S / N ratio. On the other hand, in the prior application technique 2 (preceding application 2), by introducing an interference optical system, the phase change of the sample transmitted light can be detected, so that reflection, scattering, and transmission can be performed in the measurement using the normal propagation light. It is possible to provide a photodetector that can perform measurement even when the phase object sample is less likely to cause a change in the amount of light and can improve the S / N ratio.

  The present invention is a further improvement of the photodetection device in the prior application 2. However, the optical system in the above-mentioned prior application technique 2 is a multipath interference optical system composed of a large number of components, and in order to realize a high S / N ratio measurement, optical adjustment errors, vibrations, and environmental fluctuations are required. This is a factor in increasing costs because it is necessary to take careful measures against air turbulence.

The present invention has been made in view of the above circumstances, and further improves the light detection device in the above-mentioned prior application technique 2 to realize an interference optical system that is simple and strong against environmental fluctuations, and is low-cost light detection. The object is to provide a device.
More specifically, the present invention involves the measurement of a phase object sample in which reflection, scattering, and transmitted light amount change are unlikely to occur and the improvement of the S / N ratio with a complicated optical system configuration when measuring with normal propagation light. In addition, by using the above-mentioned optical fiber probe, it is possible to obtain a phase object sample in which reflection, scattering, and transmitted light amount change are unlikely to occur during measurement using normal propagation light. An object of the present invention is to provide a photodetection device and a photodetection method that enable measurement and improvement of the S / N ratio with a simple optical system configuration.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention has an exit surface for emitting normal propagation light and an exit surface for leaching near-field light concentrically in an optical fiber having a core for propagating light emitted from a light source, A coating layer for the exudation is formed on the exit surface from which the near-field light is exuded, and a part of the light incident on the exit surface is reflected on the exit surface from which the normal propagation light is emitted. In the optical fiber probe provided with a coating layer that partially transmits, the intensity of the light that is reflected by the exit surface out of the light that is incident on the exit surface that emits the normal propagation light and propagates back to the optical fiber, and The coating layer is provided so that the intensity of the light emitted from the exit surface, reflected by the surface to be measured, transmitted through the exit surface, and returned to the optical fiber again is the same. And

  According to a second means of the present invention, in the optical fiber probe of the first means, the exit surface for emitting the normal propagation light and the exit surface for exuding the near-field light are concentrically arranged, and the proximity A coating layer for the exudation is formed on the exit surface from which the field light is leached, and a part of the light incident on the exit surface is reflected on the exit surface from which the normal propagation light is emitted. And the normal surface has an emission surface that emits normal propagation light, and the normal surface has an inclination angle different from each other on the optical axis along which the light propagates.

A third means of the present invention is characterized in that, in the optical fiber probe of the first or second means, the covering layer on the exit surface for emitting the normal propagation light is formed of a metal thin film.
According to a fourth means of the present invention, in the optical fiber probe of the first or second means, the covering layer on the exit surface for emitting the normal propagation light is formed of a dielectric single layer film or a multilayer film. It is characterized by comprising.

  According to a fifth means of the present invention, there is provided an optical fiber comprising: a “light source that emits light”; and an “optical probe that emits light at the tip of the core of an optical fiber having a core that propagates the emitted light”. Probe "and" the optical fiber probe is placed on the surface to be measured so that a spot based on either the propagating light propagated through the core of the optical fiber or the near-field light leached from the tip of the core is formed on the surface to be measured. " A movement control means for moving in a direction approaching / separating from the measurement surface, or a movement control means for moving the measurement surface in a direction approaching / separating from the optical fiber probe; A detecting means for detecting the return light of the optical fiber probe, wherein the optical fiber probe has a concentric surface that emits normal field light and an exit surface that exudes near-field light. A coating layer for the exudation is formed on the exit surface from which the near-field light is exuded, and a part of the light incident on the exit surface is reflected on the exit surface from which the normal propagation light is emitted. An optical fiber probe having a coating layer that transmits another part of the optical fiber probe, wherein “of the light incident on the exit surface that emits the normal propagation light, is reflected by the exit surface and is again reflected on the optical fiber. The intensity of the light that propagates back and the intensity of the light that is emitted from the exit surface, reflected by the measured surface, transmitted through the exit surface, and then propagates back to the optical fiber again are the same. It is an optical fiber probe provided with the above coating layer.

  According to a sixth means of the present invention, in the light detection apparatus according to the fifth means, the optical fiber probe may be configured such that “the exit surface that emits the normal propagation light and the exit surface that exudes the near-field light are concentric. A coating layer for the exudation is formed on the exit surface from which the near-field light is exuded, and a part of the light incident on the exit surface is formed on the exit surface from which the normal propagation light is emitted. A coating layer that reflects and transmits another part is provided, the exit surface that emits the normal propagation light is on the outer peripheral side, and the inclination angle of the normal line on the exit surface with respect to the optical axis through which the light propagates is It is an optical fiber probe having a different configuration.

  According to a seventh means of the present invention, in the photodetector of the fifth means, the light emitted from the light source is propagated to the core of the optical fiber probe, and the spot based on the propagated light propagated through the core is a surface to be measured. The movement control means moves the optical fiber probe toward or away from the surface to be measured, or moves the surface to be measured toward or away from the optical fiber probe. It moves to the direction which separates, The interference light intensity change in said two lights is detected, It is characterized by the above-mentioned.

  According to an eighth means of the present invention, in the light detection device of the sixth means, the light emitted from the light source is propagated to the core of the optical fiber probe, and the spot based on the propagated light propagated through the core is a surface to be measured. The movement control means moves the optical fiber probe toward or away from the surface to be measured, or moves the surface to be measured toward or away from the optical fiber probe. It moves to the direction which separates, The interference light intensity change in said two lights is detected, It is characterized by the above-mentioned.

According to a ninth means of the present invention, in the photodetector of the seventh or eighth means, the optical fiber probe is moved closer to or away from the surface to be measured so that the interference light intensity becomes a constant value. The optical fiber probe and the surface to be measured are moved relative to each other in the surface direction of the surface to be measured while moving the surface to be measured toward or away from the optical fiber probe. It is made to move.
According to a tenth means of the present invention, in the photodetector of the ninth means, the fixed value is relatively moved in a direction in which the optical fiber probe and the surface to be measured are moved toward and away from each other. It is characterized in that it is set to the intermediate value / median value of the minimum value and maximum value of the generated interference light intensity signal change.

  The eleventh means of the present invention is a light detection method, wherein the light emitted from the light source is propagated to the core of the optical fiber probe using the light source emitting light and the optical fiber probe of the first means, The optical fiber probe is moved in a direction approaching / separating from the surface to be measured so that a spot based on the propagation light propagated through the core is formed on the surface to be measured, or the surface to be measured is moved to the light It is moved in the direction approaching / separating from the fiber probe, and the interference light intensity change in the two lights is detected.

  The twelfth means of the present invention is a light detection method, wherein the light emitted from the light source is propagated to the core of the fiber optic probe using the light source emitting light and the optical fiber probe of the second means, The optical fiber probe is moved in a direction approaching / separating from the surface to be measured so that a spot based on the propagation light propagated through the core is formed on the surface to be measured, or the surface to be measured is moved to the surface to be measured The optical fiber probe is moved toward and away from the optical fiber probe, and the interference light intensity change in the two lights is detected.

According to a thirteenth means of the present invention, in the light detection method of the eleventh or twelfth means, the optical fiber probe is moved closer to or away from the surface to be measured so that the interference light intensity becomes a constant value. The optical fiber probe and the surface to be measured are moved relative to each other in the surface direction of the surface to be measured while moving the surface to be measured toward or away from the optical fiber probe. It is made to move.
According to a fourteenth means of the present invention, in the light detection method of the thirteenth means, when the fixed value is relatively moved in the direction of approaching / separating the optical fiber probe and the surface to be measured. It is characterized in that it is set to the intermediate value / median value of the minimum value and maximum value of the generated interference light intensity signal change.

In the optical fiber probe of the present invention, after being emitted from the probe, the light reflected by the sample and collected again by the probe, and the light reflected by the inner surface (coated thin film) of the probe without being emitted from the probe By providing a coating layer that can detect a change in the intensity of interference light with respect to a phase object sample that is unlikely to undergo reflection, scattering, or transmitted light amount change during measurement with normal propagation light, and S / N The ratio can be improved without a complicated optical system configuration.
According to the present invention, there is provided an optical fiber probe capable of realizing a coating layer having desired reflection / transmission characteristics with a simple film configuration of a single layer film by forming the coating layer from a metal film. it can.
Further, according to the present invention, it is possible to provide an optical fiber probe capable of realizing a coating layer having desired reflection / transmission characteristics without absorption loss by forming the coating layer with a dielectric.

In the light detection device of the present invention, after being emitted from the probe, the light reflected by the sample and collected again by the probe, and the light reflected from the inner surface (coated thin film) of the probe without being emitted from the probe Measurement of a phase object sample that is less likely to cause reflection, scattering, and transmitted light intensity changes when measuring with normal propagating light by providing an optical fiber probe with a coating layer that can detect changes in interference light intensity And the S / N ratio can be improved with a simple optical system configuration.
In the present invention, the shape of a sample having a height difference exceeding the dynamic range of the interference signal can be measured by relatively moving the optical fiber probe and the measurement surface so that the interference light intensity becomes a constant value. (The interference light signal is a sine wave signal whose probe-sample distance is a period of 1/2 of the incident light wavelength. Therefore, in interference signal measurement, the interference light signal is 1/4. The change in distance for the wavelength is the measurement dynamic range).
In the present invention, the “fixed value” is the intermediate value between the minimum value and the maximum value of the interference light intensity signal change that occurs when the optical fiber probe and the measurement surface are moved relative to each other in the approaching / separating direction. -By setting the median value, the sensitivity of the interference signal with respect to the change in the distance between the probe and the sample is maximized, so that it is possible to provide a photodetection device capable of measuring with higher sensitivity.

In the light detection method of the present invention, after being emitted from the probe, the light reflected by the sample and collected again by the probe, and the light reflected from the inner surface (coated thin film) of the probe without being emitted from the probe By using an optical fiber probe with a coating layer that can detect changes in the intensity of interference light, measurement of a phase object sample that is less likely to cause reflection, scattering, or transmitted light intensity changes during measurement with normal propagation light And the S / N ratio can be improved with a simple optical system configuration.
In the present invention, the shape of a sample having a height difference exceeding the dynamic range of the interference signal can be measured by relatively moving the optical fiber probe and the measurement surface so that the interference light intensity becomes a constant value. A simple light detection method can be realized.
In the present invention, the “fixed value” is the intermediate value between the minimum value and the maximum value of the interference light intensity signal change that occurs when the optical fiber probe and the measurement surface are moved relative to each other in the approaching / separating direction. -By setting the median value, the sensitivity of the interference signal with respect to the change in the probe-sample distance is maximized, so that it is possible to realize a photodetection method capable of measuring with higher sensitivity.

  Hereinafter, the configuration, operation and action of the present invention will be described in detail based on the embodiments shown in the drawings.

First, the outline and measurement process (light detection method) of the optical fiber probe of the present invention and the light detection apparatus including the optical fiber probe will be described based on the schematic configuration diagram of the light detection apparatus in FIG.
A photodetection device 1 shown in FIG. 1 is applied to, for example, a near-field optical microscope that measures optical properties in a minute region of a sample, and is arranged in a light source 11 that emits light and an optical path of light emitted from the light source 11. Beam splitter 12, half-wave plate 18 a and quarter-wave plate 18 b, half-wave plate 18 a and quarter-wave plate 18 b disposed in the optical path of the light transmitted through beam splitter 12. The optical fiber probe 13 which condenses the light which passed and irradiates the to-be-measured surface 2a in the sample 2 and the photodetector 14 which detects the return light from the to-be-measured surface 2a are provided.

  The light source 11 oscillates light based on a driving power received via a power supply device (not shown). The light wavelength conversion unit 17 can switch the wavelength of light emitted from the light source 11 and is used for controlling the light spot diameter by changing the wavelength, as will be described later.

  The beam splitter 12 transmits the light emitted from the light source 11 and guides it to the surface to be measured 2 a, and reflects the return light from the surface to be measured 2 a and guides it to the photodetector 14. The light transmitted through the beam splitter 12 is incident on the half-wave plate 18a and the quarter-wave plate 18b.

  The linearly polarized light emitted from the light source 11 passes through the half-wave plate 18a and the quarter-wave plate 18b, is adjusted in polarization state, and enters the core 31 of the optical fiber probe. Here, the wavelength plates 18a and 18b adjust the polarization disturbance (ellipticalization and rotation) of the guided light that occurs when the optical waveguide 21 in the optical probe 31 has a curvature, and linearly guide the light incident on the protrusion 22. Plays the role of polarization. The half-wave plate 18a and the quarter-wave plate 18b are both used for near-field light measurement described later.

  A part of the light incident on the optical fiber probe 13 is reflected by the probe exit surface, and another part is emitted from the probe and reflected by the sample surface 2a. Returning to the inside of 13, the two lights are combined in the fiber core 31, enter the photodetector 14 together with interference, and form interference fringes. In normal propagation light, a change in interference intensity signal due to the formation of interference fringes is detected. Details of the measurement will be described later.

  The optical fiber probe 13 includes an optical waveguide portion 21 and a protruding portion (optical probe portion) 22 covered with a light-shielding coating layer 33. The optical waveguide unit 21 is configured by an optical fiber in which a clad 32 is provided around a core 31. The core 31 and the clad 32 are each made of silicon dioxide glass, and the structure is controlled so that the refractive index of the clad 32 is lower than that of the core 31 by adding germanium, phosphorus, or the like.

  The protruding portion (optical probe portion) 22 is composed of a conical core protruding from the clad at one end of the optical waveguide portion 21, and includes a first taper portion 20 a (an exit surface for emitting normal propagation light) and a second taper portion. 20b (exit surface which exudes near-field light) is comprised.

  The optical fiber probe 13 is attached to the probe control unit 15 of the light detection device 1. The probe control unit 15 is constituted by, for example, a three-axis actuator as a movement control means, and moves the optical fiber probe 13 in a direction in which the optical fiber probe 13 approaches or separates from the measurement surface 2a, or scans in the horizontal direction. The probe control unit 15 moves the measured surface 2a toward and away from the optical fiber probe 13 instead of moving the optical fiber probe 13 toward and away from the measured surface 2a. It is good also as a structure to which it moves.

  The photodetector 14 receives the return light from the measurement surface 2a (for example, the phase object to be measured is mounted) and the reflected light from a reference mirror (not shown), and the interference fringe intensity. Get information. This is subjected to photoelectric conversion to generate an interference light intensity distribution signal. An image created based on the interference light intensity distribution signal generated by the photodetector 14 is displayed on a display device (not shown). The user can measure and observe details of the phase object on the measurement target surface 2a based on an image displayed on a display device (not shown).

Next, the configuration of the optical fiber probe 13 will be described in more detail.
FIG. 2 is an enlarged explanatory view of the optical fiber probe 13 of the light detection apparatus 1 shown in FIG. First, based on FIG. 2A, the configuration of the first tapered portion 20a of the optical fiber probe 13 (the exit surface from which the normal propagation light is emitted), the light spot characteristics formed by the propagation light, and the interference light by the propagation light. The signal characteristics will be described.

First, the light spot characteristics will be described. Light 41 propagating in the core 31 (hereinafter referred to as propagating light) reaches the optical fiber probe 13 and is then emitted outside the optical fiber probe through the first tapered portion 20a. Here, the surface of the first taper portion 20a of the optical fiber probe 13 has a conical taper shape, and an angle θ ₁ (hereinafter, referred to as the normal line 43 of the surface of the first taper portion 20a and the optical axis 42 of the propagating light). The inclination angle θ ₁ ) is less than the total reflection angle in propagating light and greater than 0 degrees. As a result, most of the propagating light incident on the optical fiber probe 13 passes through the light-shielding coating layer 33 and is then emitted as refracted light to the outside of the optical fiber probe 13. The light is condensed at a position several hundred nm to several μm away from the tip of 13 to form a light spot having high light intensity.

  Incidentally, as an alternative to the optical fiber probe 13 in which the first taper portion 20a has a conical taper shape as shown in FIG. 2 (a), the first taper portion 20a has a curved surface shape as shown in FIG. 2 (b). An optical fiber probe 13 may be used. Moreover, it does not have a near-field light exudation surface as disclosed in Patent Document 2 of the prior application technique 1, or the near-field light exudation surface and the normal propagation light emission surface are configured by tapered surfaces having the same angle. A similar light spot forming function can be obtained with the configuration.

  The phenomenon of condensing light at a position away from the tip of the optical fiber probe 13 to form a light spot having a high light intensity is an inherent phenomenon when the tilt angle θ is less than the total reflection angle in propagating light. In the conventional optical fiber probe in which the tilt angle θ is formed to be greater than the total reflection angle, it is the highest near the tip of the probe, and the light intensity decreases rapidly as it moves away from the probe tip, forming only a light spot with a low light intensity. I can't.

The distance between the tip of the optical fiber probe and the focused spot can be controlled by the inclination angle of the first taper portion 20a.
FIG. 6 shows an example of the transition of the distance between the tip of the optical probe and the focused spot for each inclination angle of the first taper portion. The figure shows a case where the refractive index of the first taper portion 20a is 1.53 and the emission medium is air. At an incident angle lower than that at the total reflection angle of 40 °, it is several hundred nm from the tip of the optical fiber probe 13. This means that light is condensed at a position about several μm apart.
Further, in order to form the focused spot at a position away from the tip of the optical fiber probe 13, the first taper portion 20a (the exit surface from which the normal propagation light is emitted) and the second taper portion 20b (the near-field light is exuded). It is necessary to keep the diameter ratio of the exit surface (A divided by A in FIG. 2A) to a relatively small value. FIG. 7 shows an example of transition of the distance between the tip of the optical fiber probe and the focused spot when the diameter ratio (B / A) is changed. From FIG. 7, it can be seen that by setting the diameter ratio to 0.25 or less, the focused spot can be formed at a position away from the tip of the optical fiber probe.

The light spot diameter can be controlled by the diameter D of the base of the first taper portion 20a, the inclination angle θ, and the wavelength of the propagation light. Utilizing this fact, the diameter D of the root of the first taper portion 20a, the inclination angle θ, and the wavelength of the propagation light are determined so as to obtain a light spot diameter comparable to the required measurement resolution.
The light spot diameter can be reduced by reducing the base diameter D of the first taper portion 20a, increasing the inclination angle θ, and using light having a short wavelength for propagating light. On the contrary, when the light spot diameter is increased, the base diameter D of the first taper portion 20a is increased, the inclination angle θ is decreased, and light having a long wavelength may be used as the propagation light.

  FIG. 8 shows the transition of the light spot diameter when the wavelength of the propagating light is changed when the inclination angle of the first tapered portion 20a is 10 °. A specific example of a numerical value is shown as an example of forming an arbitrary spot diameter. When light is emitted from the first tapered portion 20a having a refractive index of 1.53 into the air, the light spot diameter is set to 0.4 μm (half value). When controlling to the full width), the root diameter D of the first taper portion 20a may be 2 μm, the inclination angle 20 degrees, and the wavelength of the propagation light may be 0.4 μm. Incidentally, in this case, the distance between the tip of the optical fiber probe and the focused spot is 1.2 μm.

Next, characteristics of the optical probe interference optical signal will be described.
The optical fiber probe of the present invention utilizes the fact that optical interference occurs on the principle as shown in FIG. The light incident on the optical fiber probe is separated into (1) probe internal reflected light and (2) sample surface reflected light by the coating film attached to the normal propagation light exit surface 20a. The light of (2) is collected as described above, forms a light spot on the sample surface, is reflected by the sample, passes through the coating film again, and is guided through the fiber together with the light of (1). Then go back. At this time, the lights of (1) and (2) taking the same optical path interfere with each other, and the above-described photodetector 14 in FIG. 1 detects the interference light signal. This interference light signal is a signal that changes in a sine wave shape with a half period of the incident light wavelength with respect to the change of WD in FIG. 3A, and is represented as I in the equation of FIG. It can be detected as a change in I by changing φ2 in the equation depending on a minute change in WD or the presence or absence of a minute phase object arranged on the sample surface.

  Here, in order to implement the measurement method of the present invention, it is necessary to set the contrast of the interference light intensity change to a high value. From the equation of FIG. 3B, the condition for maximizing the contrast is I1 = I2. Considering this, for example, if the coating layer of the emission surface 20a in FIG. 3A is a metal single layer film, the above condition can be realized by adjusting the film thickness. As an example, FIG. 4 shows a difference between I1 and I2 with respect to the thickness of the coating layer when the reflectance of the surface to be measured is 100%, the probe tilt angle is 15 deg, and the coating layer material is Au. The change of contrast of interference light intensity is shown. FIG. 4 shows that when the film thickness is about 18 nm, the difference in light intensity is zero and the contrast has a maximum value. Based on this figure, for example, by selecting a film thickness in a film thickness range (about 10 to 26 nm from the figure) with a contrast of 0.5 or more, measurement with high sensitivity and high S / N ratio becomes possible.

  By the way, the material of the coating layer of the emission surface 20a is not a metal as described above, but a dielectric film, so that there is no absorption loss in the film, so that the same high contrast as in the case of metal can be obtained. Can do. In this case, the dielectric film can be a multilayer film, and can be realized by appropriately selecting the number of layers and the laminated material.

Although it has been described that an absorption loss occurs when the coating layer is made of metal, in this case as well, the light transmittance is set to a maximum value or a value in the vicinity thereof in consideration of the dispersion characteristics of the complex refractive index of the light-shielding coating layer 33. By selecting the wavelength to be selected, the light intensity of the light emitted from the optical fiber probe 13 can be improved, and the decrease in the light interference intensity due to the absorption loss can be minimized. In general, the light transmittance distribution has a convex shape as shown in FIG. Here, the “wavelength with light transmittance in the vicinity of the maximum value” according to the light detection apparatus and the light detection method of the present invention means that the light transmittance is a value half the maximum value T ₀ (T ₁₁ wavelengths when taking ₁₎ lambda, lambda _12, and in the case of, refers to a wavelength fit into lambda ₁₁ or lambda ₁₂ or less in the wavelength range (the shaded portion in gray in FIG. 9). For example, in the case of Au, it is desirable to select light having a wavelength that falls within a wavelength band of about 480 to 700 nm.

  By adjusting each parameter (incident light wavelength, taper angle, film thickness, etc.) of the optical fiber probe 13 in consideration of the above-mentioned light spot characteristics and interference light signal characteristics, high lateral resolution and high sensitivity, Measurement of propagating light (wide range) with a high S / N ratio is possible.

Next, based on FIG. 2A, the configuration of the second tapered portion 20b of the optical fiber probe 13 (exit surface on which the near-field light is oozed) will be described.
Of the light 41 propagating in the core 31 (hereinafter referred to as propagating light), the component in the vicinity of the fiber optical axis reaches the optical fiber probe 13 and then enters the second tapered portion 20b. Here, the surface of the second taper portion 20b of the optical fiber probe 13 has a conical taper shape, and an angle θ ₂ (hereinafter, referred to as the normal line 43 of the surface of the second taper portion 20b and the optical axis 42 of the propagating light). The inclination angle θ ₂ ) is not less than the total reflection angle in propagating light and less than 90 degrees. As a result, most of the propagating light incident on the optical fiber probe 13 is reflected at the interface between the light-shielding coating layer 33 and the core 31 of the optical fiber probe 13. At this time, some of the light is shielded. It exudes to the surface of the layer 33, propagates along the light-shielding coating layer 33 toward the tip of the optical fiber probe 13, and becomes surface plasmon localized at the tip. A near-field light spot can be formed in the vicinity of the tip of the optical fiber probe 13 by the surface plasmon obtained in the above process.
Here, the light-shielding coating layer 33 may be made of any material, but it is desirable that the light-shielding coating layer 33 be an Au thin film because the effect of enhancing near-field light by surface plasmons can be obtained and the chemical stability is excellent.

For example, in the case of an Au thin film, as shown in FIG. 10, there is wavelength dependence of near-field light intensity. Therefore, the light intensity of the light emitted from the optical fiber probe 13 can be improved by selecting the incident light wavelength based on the above dependency. In general, the light transmittance distribution has a convex shape as shown in FIG. Here, the “wavelength having the light transmittance near the maximum value” according to the light detection apparatus and the light detection method of the present invention means that the light transmittance is a value half of the maximum value P ₀ (P ₁ ) A wavelength that falls within a wavelength band of λ _{11 to} λ ₁₂ (gray shaded portion in FIG. 10) when λ ₁₁ and λ ₁₂ are used. For example, in the case of Au, it is desirable to select light having a wavelength that falls within a wavelength band of about 480 to 700 nm.

Further, the light intensity of the near-field light spot has a dependency on the inclination angle θ ₂ of the tapered portion as shown in FIG. By selecting the inclination angle θ ₂ in consideration of the above-described dependence, the generated near-field light intensity can be improved. Here, the “tilt angle that makes the near-field light intensity a value close to the maximum value” according to the light detection apparatus and the light detection method of the present invention means that the near-field light intensity is ½ of the maximum value P ₀ . This means an inclination angle that falls within the range of θ _{a to} θ _b (gray shaded portion in FIG. 11) when the inclination angle when taking the value (P ₁ ) is θ _a , θ _b . For example, when the light-shielding coating layer 33 is Au and the incident light wavelength is 532 nm, the inclination angle θ ₂ is preferably about 45 ° to 55 °.

Further, as in the optical fiber probe 13 shown in FIG. 2A and the like mentioned above, the second tapered portion 20b (the exit surface through which the near-field light oozes out) is not entirely covered by the light-shielding coating layer 33. As shown in FIG. 5, an optical fiber probe in which only the tip of the optical fiber probe 13 is not provided with the light-shielding coating layer 33 (having a minute opening 23) may be used.
With the configuration of the second tapered portion 20b described above, a high-intensity near-field light spot can be obtained, so that near-field light measurement with a high S / N ratio is possible.

Next, an outline of the measurement process in the photodetection device having the above configuration will be described.
First, a phase difference measurement process of propagation light measurement (wide range measurement) in the light detection device 1 will be described. In FIG. 1, light having a wavelength λ having a linearly polarized light component emitted from the light source 11 passes through the beam splitter 12, passes through the half-wave plate 18 a and the quarter-wave plate 18 b, and travels to the optical fiber probe 13. Incident. The light incident on the optical fiber probe 13 propagates through the core 31 as it is, and the light emitted from the protruding portion 22 of the optical fiber probe 13 is collected at a position away from the tip of the optical fiber probe 13 to obtain the light. A spot is formed.
Here, the probe control unit 15 moves the optical fiber probe 13 in the direction of approaching and separating from the surface to be measured, and the position of the surface 2a to be measured of the sample 2 at the position of the light spot formed by the above-described focusing. Match. Information on the distance between the tip of the optical fiber probe and the focused spot used at this time is obtained in advance by experiments or the like.

  Next, the probe controller 15 causes the optical fiber probe 13 to be measured against the surface 2a to be measured (here, the surface 2a to be measured of the sample 2 is sufficiently flat and the phase object to be measured is mounted). Scan horizontally. The light emitted from the optical fiber probe 13 is reflected by the surface to be measured 2a, propagates again as return light in the optical fiber probe 13, passes through the quarter-wave plate 18b and the half-wave plate 18a, The light is reflected by the splitter 12 and enters the photodetector 14. The return light is obtained by being incident on and transmitted through a phase object sample existing on the surface to be measured 2a, reflected by the surface of the surface to be measured 2a, and transmitted again through the phase object. Contains phase difference information of the object. The return light and the probe internal reflection light shown in FIG. 3 (a) are combined and detected as interference light intensity information by the photodetector 14, so that the user can detect the phase object on the measurement target surface 2a. The generated phase difference information can be obtained from an image displayed on a display device (not shown).

  In the optical detection device 1 of the present invention, when the optical fiber probe 13 is scanned in the horizontal direction with respect to the measurement surface 2a of the sample 2, the height of the optical fiber probe 13 with respect to the measurement surface 2a is fixed. (The probe-sample distance varies depending on the unevenness of the sample), and control in the approaching / separating direction becomes unnecessary during such measurement. This, combined with the length of the distance between the probe tip and the focused spot (about several hundred nm to several μm) described above, enables faster scanning and leads to a significant reduction in measurement time. Furthermore, compared with the conventional near-field light measurement, since the measurement range per measurement point is wide, a wide range of measurement can be realized with the same number of measurement points and the same number of measurement lines (scanning lines).

Furthermore, compared with the case where the light emitted from the optical fiber probe 13 is not condensed, more return light from the measurement surface 2a can be obtained, and as a result, the high contrast accompanying the improvement of the S / N ratio. It is possible to provide a user with a measurement result.
As described above, it is possible to realize a light detection apparatus and a light detection method that enable efficient light detection and high speed at the time of propagation light (wide range) measurement.

Next, an example of the shape measurement process of propagation light measurement (wide range measurement) in the light detection device 1 will be described.
In FIG. 1, light having a wavelength λ having a linearly polarized light component emitted from the light source 11 passes through the beam splitter 12, passes through the half-wave plate 18 a and the quarter-wave plate 18 b, and travels to the optical fiber probe 13. Incident. The light incident on the optical fiber probe 13 propagates through the core 31 as it is, and the light emitted from the protruding portion 22 of the optical fiber probe 13 is collected at a position away from the tip of the optical fiber probe 13 to obtain the light. A spot is formed.
Here, the probe controller 15 moves the optical fiber probe 13 in the direction of approaching / separating from the measured surface 2a of the sample 2, and the measured surface 2a is moved to the position of the light spot formed by the above-described light collection. Match the positions. Information on the distance between the probe tip and the focused spot used at this time is acquired in advance by an experiment or the like.

  Next, the probe controller 15 scans the optical fiber probe 13 in the horizontal direction with respect to the surface 2a to be measured (here, the surface 2a to be measured 2 of the sample 2 has an uneven surface). At this time, the intensity of the interference light fluctuates as the optical path length (WD in FIG. 3A) changes according to the shape distribution of the surface 2a to be measured. The WD is servoed so that this fluctuation is a constant value. Control. That is, horizontal scanning is performed while keeping WD constant. By mapping the locus of the optical fiber probe 13 at this time, the shape distribution of the measured surface 2a can be acquired.

  Further, a minimum value of the interference light intensity signal change generated when the optical fiber probe 13 and the surface to be measured 2a are relatively moved in the approaching / separating direction and an intermediate / median value of the maximum value. By doing so, the sensitivity of the interference signal with respect to the change in the probe-sample distance is maximized, so that more sensitive shape measurement is possible.

  When the measurement method described in the above-described phase measurement procedure “fixing the height (Z coordinate) of the optical fiber probe 13 with respect to the measured surface 2a” is applied to the shape measurement, the periodicity of the fluctuation of the interference light signal From this, the measurement dynamic range is limited to the range of phase change for the half period (1/4 of the incident light wavelength), but by using the above shape measurement method, the range of phase change of the interference light signal fluctuation A wide measurement dynamic range not limited to the above can be obtained.

  As described above, it is possible to realize a light detection apparatus and a light detection method capable of measuring a phase object distribution and a minute step shape distribution with high sensitivity and a high S / N ratio at the time of propagation light (wide range) measurement. Can do. In the above-described prior application technique 2, it is necessary to add a reference mirror or the like when constructing the interference optical system. However, according to the configuration of the present invention, the coating layer 33 of the optical fiber probe 13 is simply modified. An interference optical system can be realized by the configuration.

Next, a measurement process of near-field light measurement (high resolution measurement) in the light detection device 1 will be described.
In FIG. 1, light having a linearly polarized component emitted from a light source 11 is transmitted through a beam splitter 12, and the polarization component is controlled by a half-wave plate 18a and a quarter-wave plate 18b, and then an optical fiber. It enters the probe 13. The light incident on the optical fiber probe 13 propagates through the core 31 as it is and enters the light-shielding coating layer 33 of the optical fiber probe 19. At this time, near-field light as an evanescent wave oozes out on the exit end side of the light-shielding coating layer 33. In a state where the near-field light is exuded, the probe controller 15 moves the optical fiber probe 13 in a direction approaching the surface to be measured 2a. At this time, when the distance between the tip of the optical fiber probe 13 and the measured surface 2a of the sample 2 is equal to or less than ¼ of the wavelength λ of the light emitted from the light source 11, the proximity oozed from the optical fiber probe 13 The field light is irradiated onto the surface to be measured 2a, and a minute light spot is formed on the surface to be measured 2a by near-field light. The near-field light that forms the light spot is transmitted through the light-shielding coating layer 33, propagates through the core 31 of the optical fiber probe 13, passes through the quarter-wave plate 18b and the half-wave plate 18a, and passes through the beam splitter. 12 is reflected and guided to the photodetector 14. As described above, high-resolution measurement of the measurement target surface 2a of the sample 2 is performed.

  From the above, in the photodetecting device 1 of the present invention, the spot due to the propagating light is moved by moving one mounted optical fiber probe 13 in the direction of approaching / separating from the measured surface 2a of the sample 2. Alternatively, since the spot by the near-field light can be selectively switched and formed on the measurement surface 2a, a wide range measurement using the propagation light and high resolution using the near-field light can be performed by one optical fiber probe 13. Both measurements can be realized.

  As described above, according to the present invention, in the measurement system capable of realizing high-resolution measurement using near-field light, it is not necessary to separately arrange an optical fiber probe used only for wide-range measurement. Can be reduced, and as a result, the manufacturing cost can be greatly reduced.

It is a schematic block diagram of the photon detection apparatus which shows one Example of this invention. It is an expansion explanatory view of the optical fiber probe of the photon detection apparatus shown in FIG. It is explanatory drawing of the principle of the optical interference in the optical fiber probe of this invention. It is a figure which shows the change of the contrast of the light intensity difference with respect to the film thickness of a coating layer, and interference light intensity. It is an enlarged view which shows another example of the optical fiber probe of the photon detection apparatus shown in FIG. It is a figure which shows an example of transition of the distance between probe front-end | tips and condensing spots for every inclination-angle of the 1st taper part of the optical fiber probe of this invention. It is a figure which shows an example of transition of the distance between a probe front-end | tip and a condensing spot when changing the diameter ratio (B / A) of the 1st taper part of the optical fiber probe of this invention, and a 2nd taper part. It is a figure which shows transition of the light spot diameter at the time of changing the wavelength of propagation light in case the inclination-angle of the 1st taper part of an optical fiber probe is 10 degrees. It is a figure which shows the light transmittance distribution with respect to the light wavelength of the coating layer of the optical fiber probe of this invention. It is a figure which shows the relationship between a light wavelength and the near-field light intensity in a probe tip when the coating layer of an optical fiber probe is an Au thin film. It is a figure which shows the relationship between the inclination angle of the taper part of an optical fiber probe, and the near-field light intensity in a probe front-end | tip.

Explanation of symbols

1: Photodetector 2: Sample 2a: Surface to be measured 11: Light source 12: Beam splitter 13: Optical fiber probe 14: Optical detector 15: Probe controller 17: Optical wavelength converter 18a: 1/2 wavelength plate 18b: 1/4 wavelength plate 20a: 1st taper part (exit surface which inject | emits normal propagation light)
20b: 2nd taper part (exit surface which exudes near-field light)
21: Optical waveguide (optical fiber)
22: Protruding part (optical probe part)
31: Core 32: Clad 33: Covering layer 41: Light propagating in the core (propagating light)
42: Optical axis of propagating light 43: Normal A: Diameter of the first taper part B: Diameter of the second taper part D: Diameter of the base of the first taper part WD: Distance between probe and sample

Claims (14)

An optical fiber having a core for propagating light emitted from a light source has an exit surface for emitting normal propagation light and an exit surface for leaching near-field light concentrically, and the exit surface for leaching the near-field light. Further, a coating layer for the exudation is formed, and a coating layer that reflects a part of the light incident on the emission surface and transmits another part is provided on the emission surface that emits the normal propagation light. In optical fiber probe,
Of the light incident on the exit surface that emits the normal propagation light, the intensity of the light that is reflected by the exit surface and propagates back to the optical fiber, and the light that is emitted from the exit surface and reflected by the surface to be measured An optical fiber probe comprising the coating layer such that the intensity of the light transmitted through the exit surface and returning to the optical fiber is the same. The optical fiber probe according to claim 1,
The exit surface that emits the normal propagation light and the exit surface that exudes the near-field light are concentric, and a coating layer for the exudation is formed on the exit surface that exudes the near-field light. The exit surface for emitting the normal propagation light further includes a coating layer that reflects part of the light incident on the exit surface and transmits another part, and the exit surface for emitting the normal propagation light has an outer periphery. An optical fiber probe characterized in that the angle of inclination of the normal line on the exit surface with respect to the optical axis through which light propagates is different for each exit surface. The optical fiber probe according to claim 1 or 2,
The optical fiber probe according to claim 1, wherein the coating layer on the exit surface for emitting the normal propagation light is formed of a metal thin film. The optical fiber probe according to claim 1 or 2,
The optical fiber probe according to claim 1, wherein the covering layer on the emission surface for emitting the normal propagation light is formed of a single layer film or a multilayer film of a dielectric. A light source that emits light;
An optical fiber probe in which an optical probe for emitting light is formed at the tip of the core of an optical fiber having a core for propagating the emitted light;
The optical fiber probe is placed on the surface to be measured so that a spot based on either the propagating light propagated through the core of the optical fiber or the near-field light exuding from the tip of the core is formed on the surface to be measured. Movement control means for moving in the direction of approaching / separating, or movement control means for moving the measured surface in the direction of approaching / separating with respect to the optical fiber probe,
Detecting means for detecting return light from the surface to be measured;
In a photodetection device comprising:
The optical fiber probe has an exit surface for emitting normal propagation light and an exit surface for leaching near-field light concentrically, and a coating layer for leaching is formed on the exit surface for leaching the near-field light. An optical fiber probe comprising a coating layer that is formed and further reflects a part of light incident on the exit surface and transmits another part on an exit surface that emits the normal propagation light,
Of the light incident on the exit surface from which the normal propagation light exits, the intensity of the light that is reflected by the exit surface and propagates back to the optical fiber and is emitted from the exit surface, and is measured at the measured surface. An optical detection apparatus comprising: an optical fiber probe including the coating layer that has the same intensity of light that is reflected and transmitted through the exit surface and then propagates back to the optical fiber. The light detection device according to claim 5,
The optical fiber probe has an exit surface for emitting the normal propagation light and an exit surface for exuding the near-field light in a concentric plane, and the exit surface for exuding the near-field light is used for the exudation. A coating layer that reflects a part of the light incident on the exit surface and transmits another part is provided on the exit surface that emits the normal propagation light. An optical detection device comprising: an optical fiber probe having a configuration in which an exit surface to be emitted is on an outer peripheral side and a normal inclination angle of the exit surface with respect to an optical axis through which light propagates is different for each exit surface. The light detection device according to claim 5,
Propagating light emitted from the light source to the core of the optical fiber probe,
Moving the optical fiber probe in a direction approaching / separating from the surface to be measured by the movement control means so that a spot based on the propagation light propagated through the core is formed on the surface to be measured; or Moving the surface to be measured in the direction of approaching / separating from the optical fiber probe;
A photodetector for detecting interference light intensity change in the two lights. The light detection device according to claim 6.
Propagating light emitted from the light source to the core of the optical fiber probe,
Moving the optical fiber probe in a direction approaching / separating from the surface to be measured by the movement control means so that a spot based on the propagation light propagated through the core is formed on the surface to be measured; or Moving the surface to be measured in the direction of approaching / separating from the optical fiber probe;
A photodetector for detecting interference light intensity change in the two lights. The photodetection device according to claim 7 or 8,
The optical fiber probe is moved in the direction of approaching / separating from the surface to be measured so that the interference light intensity becomes a constant value, or the surface to be measured is An optical detection apparatus, wherein the optical fiber probe and the surface to be measured are moved relative to each other in the direction of the surface of the surface to be measured while moving in a direction away from each other. The light detection device according to claim 9, wherein
The fixed value is a minimum value of the interference light intensity signal change that occurs when the optical fiber probe and the surface to be measured are moved relative to each other in the approaching / separating direction, and an intermediate / median value of the maximum value. A photodetection device. Using a light source that emits light and the optical fiber probe according to claim 1,
Propagating the light emitted from the light source to the core of the optical fiber probe,
The optical fiber probe is moved in a direction approaching / separating from the surface to be measured so that a spot based on the propagation light propagated through the core is formed on the surface to be measured, or the surface to be measured is moved to the surface to be measured Move it toward and away from the optical fiber probe,
An optical detection method, comprising: detecting an interference light intensity change in the two lights. Using a light source that emits light and the optical fiber probe according to claim 2,
Propagating light emitted from the light source to the core of the optical fiber probe,
The optical fiber probe is moved in a direction approaching / separating from the surface to be measured so that a spot based on the propagation light propagated through the core is formed on the surface to be measured, or the surface to be measured is moved to the surface to be measured Move it toward and away from the optical fiber probe,
An optical detection method, comprising: detecting an interference light intensity change in the two lights. The light detection method according to claim 11 or 12,
The optical fiber probe is moved in the direction of approaching / separating from the surface to be measured so that the interference light intensity becomes a constant value, or the surface to be measured is A light detection method, wherein the optical fiber probe and the surface to be measured are moved relative to each other in the direction of the surface of the surface to be measured while moving in a separating direction. The light detection method according to claim 13.
The fixed value is a minimum value of the interference light intensity signal change that occurs when the optical fiber probe and the surface to be measured are moved relative to each other in the approaching / separating direction, and an intermediate / median value of the maximum value. A featured light detection method.

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