JP2006038774A - Apparatus for evaluating near-field light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for evaluating near-field light, capable of accurately discriminating the near-field light from other light (especially interference light) in the vicinity of a near-field light generating element. <P>SOLUTION: The apparatus for evaluating the near-field light is equipped with a scatterer 10 for scattering light; a photodetector 14 which detects the light being scattered by the scatterer 10; a position-changing mechanism 12 which changes the position of the scatterer 10 vertically, in relation to the near-field light 60; and a control section 15 calculating the difference between a first photo detection data which are obtained, by detecting the scattered light in the case the scatterer is arranged on the surface of the near-field light 60; and a second photodetection data which are obtained by detecting the scattered light in the case the scattering means is heightened by a distance Z from a position of the scattering means where above first photodetection data are obtained. According to the apparatus for evaluating the near-field, the distance Z makes the near-field light attenuated, but the other lights are not attenuated, and light can accurately discriminate the near-field light from the other light (especially interference light). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a near-field light evaluation apparatus that evaluates a near-field light generating element for generating near-field light, and more particularly, a distribution (for example, in-plane) of near-field light generated by a near-field light generating element. The present invention relates to a near-field light evaluation apparatus for evaluating distribution.

  In recent years, a near-field microscope based on a principle different from a general optical microscope or electron microscope has been developed, and its application is expected. This near-field microscope detects so-called near-field light. This near-field light will be briefly described below.

  When light is applied to a particle with a diameter much smaller than the wavelength of the light, a localized electromagnetic field is generated around the particle. This is called near-field light.

  Both scattered light and near-field light are electromagnetic fields generated by electric dipoles induced inside the sphere when incident light hits the sphere. However, while the scattered light travels far away, the energy of the near-field light concentrates along the spherical shape and cannot be observed at a position away from the sphere. Moreover, it is said that the near-field light is distributed only from the particle at a distance that is about the diameter of the particle. Therefore, even if a photodetector is installed at a distant location, it is impossible to know the presence of near-field light that has clung to particles.

  Therefore, in order to detect the near-field light, the near-field light can be detected by placing another particle near the particle emitting the near-field light and scattering the near-field light. That is, since the scattered near-field light can propagate far away, a part of it is observed by the photodetector. Here, the shape of the particles emitting near-field light can be known by scanning the particles as the scattering means around the particles emitting near-field light and observing the scattered near-field light. In other words, the particles as the scattering means play a role as a probe, and if this principle is used, a microscope using a near-field light, “near-field optical microscope (SNOM; Scanning Near-field Optical Microscopy, NSOM; Near-field Scanning Optical Microscopy, NOM; also referred to as Near-field Optical Microscopy) ”.

  For example, in Patent Document 1, a probe having a sharp tip is inserted in the field of evanescent light (near-field light) generated by the fine structure of the sample, and scattered light generated by the interaction between the evanescent light and the probe is detected. Discloses a scanning optical microscope apparatus capable of measuring the fine structure of a sample.

  Here, a near-field light generating element that generates near-field light is used for SNOM. This near-field light generating element has a configuration in which, for example, light enters a fine structure (such as an opening) and near-field light is generated around the structure. However, in such a near-field light generating element, not all of the incident light becomes near-field light, but most of the incident light becomes reflected light, transmitted light, and heat, and the near-field light is part of the incident light. Only.

Therefore, in the vicinity of the near-field light generating element, there is not only near-field light but also extra light composed of reflected light or transmitted light of incident light, so-called “light noise”. In order to remove such light noise, for example, Patent Document 2 includes a probe, a light irradiation means including a light source, a light sampling means, and a calculation means, and near-field light generated by light irradiation. The sample or probe is isolated from the field or placed at a shallow position in the near-field light field, noise is detected by the light sampling means, and the sample or probe is inserted deeply into the near-field light field generated by the light irradiation. Then, a near-field microscope is disclosed in which the light intensity is detected by the light sampling means, and the measurement result is calculated by subtracting noise from the light intensity by the calculation means. According to such a near-field microscope, it is reported that the influence of noise can be removed from the measurement result.
JP-A-6-137847 (published on May 20, 1994) JP 2002-148172 A (published on May 22, 2002)

  The near-field microscope disclosed in Patent Document 2 can remove “noise” mainly including a background composed of reflected light. However, the “noise” present in the vicinity of the near-field light generating element is not only the background noise composed of reflected light. There is also noise such as interference light generated by reflected light or transmitted light of incident light.

  However, until now, no consideration has been given to noise problems such as interference light in a near-field light generating element used in a near-field microscope or the like. For example, the near-field microscope disclosed in Patent Document 2 can remove background noise due to reflected light, but cannot remove the spatial distribution of noise that occurs when a probe is inserted in the vicinity of near-field light.

  The noise spatial distribution described above is due to interference fringes standing on the sample surface. If the probe is only a sphere having a diameter of about 10 nm, the interference fringes are not so much a problem. However, since the probe is actually a polygonal pyramid having a length of about several hundred nm, the interference fringes are reflected and scattered in a wide area. As a result, noise due to interference light occurs. In particular, since interference fringes due to interference light have a spatial distribution, noise changes when scanning, and it is difficult to distinguish between near-field light and interference light.

  As described above, the inventor has a large influence of interference light in the vicinity of the near-field light generating element, and it has been difficult to distinguish between near-field light and other light (particularly noise due to interference light). I found a new problem that had not been considered at all.

  The present invention has been made in view of the above problems, and its purpose is to accurately distinguish near-field light and other light (especially interference light) in the vicinity of the near-field light generating element. The object is to provide a near-field light evaluation apparatus.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has made use of the property that the intensity of the near-field light “expands exponentially when it is separated from the source”, and the proximity Finding that noise such as interference light and near-field light can be separated by measuring the scattered light twice by changing the distance from the source of the field light and calculating the difference between them to complete the present invention It came.

  That is, the near-field light evaluation apparatus according to the present invention is a scattering means for scattering light in a near-field light evaluation apparatus for evaluating near-field light generated by a near-field light generating element in order to solve the above-described problem. A light detecting means for detecting the light scattered by the scattering means, a position changing means for moving the position of the scattering means by a distance Z in the vertical direction with respect to the near-field light, and the position changing means Measuring means for measuring scattered light before and after moving the position of the means by a distance Z, and calculating a difference between the two light detection data before and after the movement, wherein the distance Z attenuates near-field light, Other light is a distance that does not attenuate.

  According to the above configuration, the scattered light can be measured twice by changing the distance from the near-field light generation source (near-field light generating element). The near-field light decreases rapidly as it moves away from its source, while the noise of other light is hardly attenuated. Therefore, the difference (attenuation) from the interference light is obtained by obtaining the difference between the two obtained light detection data. A large near-field light is emphasized.

  Therefore, the near-field light evaluation apparatus according to the present invention can accurately distinguish near-field light and other light (particularly interference light) in the vicinity of the near-field light generating element. Thereby, for example, information such as how much near-field light is attenuated when it is separated from the near-field light generating element, evaluation of measurement of the distribution of near-field light, and the like can be performed.

  Moreover, in the near-field light evaluation apparatus according to the present invention, the calculation means further includes the scattering means when arranged on the surface of the near-field light generating element where the near-field light is generated or in the very vicinity thereof. First light detection data that detects scattered light, and light that is scattered when the scattering means is arranged by moving the distance Z from the position of the scattering means when acquiring the first light detection data. It is preferable to calculate a difference from the second photodetection data in which is detected.

  According to the above configuration, first photodetection data is first obtained on the surface where near-field light is generated or in the very vicinity thereof. Next, second light detection data is obtained at a position away from the near-field light source by a distance Z. And by calculating | requiring the difference of these 1st optical detection data and 2nd optical detection data, a near field light and other lights (especially interference light) can be distinguished correctly and easily. As used herein, the “surface on which near-field light is generated or the vicinity thereof” refers to a generation source that generates near-field light on the surface of the near-field light generating element that generates near-field light, and its source A nearby area. For example, when the near-field light is generated by condensing the light on the minute opening, the minute opening and the area in the vicinity thereof on the surface where the near-field light is generated in the near-field light generating element. .

  In the near-field light evaluation apparatus according to the present invention, the near-field light evaluation apparatus includes scanning means for scanning the scattering means in a horizontal direction with respect to the surface of the near-field light element where the near-field light is generated. The position changing means detects the light scattered when the scattering means is scanned before and after moving the position of the scattering means by the distance Z, and calculates the difference between the two light detection data. preferable.

  According to the above configuration, since the scanning unit is provided, the near-field light generated in the vicinity of the near-field light generating element can be evaluated by scanning one-dimensionally or two-dimensionally. For this reason, the in-plane distribution of near-field light can be measured. The scanning unit may be a single-axis scanning unit that enables at least one-axis (for example, x-axis) scanning, but further, two-axis scanning that enables two-axis (x-axis, y-axis) scanning. More preferably, it is scanning means.

  Moreover, in the near-field light evaluation apparatus according to the present invention, the scanning unit is the same as the scanning line for acquiring the first light detection data as the scanning line for acquiring the second light detection data. It is preferable that scanning is performed at a position that is a distance Z moved in the vertical direction with respect to the near-field light generating element.

  According to the above configuration, a so-called “two-pass method” in a scanning probe microscope in which the surface is scanned in the first scan or the vicinity thereof, and the second scan is performed with a certain amount of offset from the first operation. Can be scanned. For this reason, the in-plane distribution of near-field light can be reliably measured.

  In the near-field light evaluation apparatus according to the present invention, the near-field light evaluation apparatus further includes a vibration means for vibrating the scattering means, an oscillation means, and a minute signal measurement means, The exciting means vibrates the scattering means with a signal synchronized with the oscillating means, and the minute signal measuring means only detects a signal synchronized with the oscillating means among signals detected by the light detecting means. It is preferable to selectively detect and output only the selectively detected signal to the calculating means.

  According to the above configuration, scanning can be performed in a so-called “tapping mode” in the scanning probe microscope. In addition, since the tapping period of the scattering means and the signal detected by the minute signal measuring device (lock-in amplifier) are synchronized, the effects of stationary noise (fluorescent light, etc.) and transmitted light are surely removed. Can do.

  In the near-field light evaluation apparatus according to the present invention, it is preferable that the distance Z is smaller than the wavelength of incident light emitted from a light source included in the near-field light generating element.

  This is because the region where the near-field light exists is considered to be a distance equal to or shorter than the wavelength of the light emitted from the light source from the generation source of the near-field light.

  In the near-field light evaluation apparatus according to the present invention, the distance Z is preferably smaller than ½ of the wavelength of incident light emitted from the light source included in the near-field light generating element.

  In the present invention, the noise most desired to be distinguished from near-field light is interference light. Such interference light is present in the vicinity of the minute aperture of the near-field light generating element, and changes in the order of the light source wavelength. Specifically, repeated light and dark interference fringes are generated for each half wavelength of the light source wavelength.

  Therefore, by setting the distance Z to be equal to or less than ½ wavelength of the light source wavelength, which is the light / dark repetition interval of the interference fringes, the scattering means does not cross the border between the light and darkness of the interference fringes due to movement in the vertical direction. . For this reason, there is no confusion between the change in the border between the bright and dark interference fringes and the attenuation change in the near-field light. Therefore, by setting the distance Z as in the above configuration, the near-field light and the interference light can be accurately distinguished.

  In the near-field light evaluation apparatus according to the present invention, the distance Z is preferably smaller than the diameter of the circular opening when the near-field light generating element has a circular shape.

  It is considered that the region where the near-field light is distributed in the near-field light generating element is limited to a region about the diameter of the minute opening from the circular minute opening included in the near-field light generating element. Therefore, by setting the distance Z to be smaller than the diameter of the minute opening as in the above configuration, the near-field light is attenuated, but other optical noise (interference light, etc.) is not attenuated. Can be suitably set.

  Further, in the near-field light evaluation apparatus according to the present invention, the distance Z is smaller than the distance of the narrowest portion of the opening when the shape of the minute opening included in the near-field light generating element is a shape other than a circle. Small is preferable.

  Further, when the shape of the minute opening is a shape other than a circle, the region where the near-field light is distributed in the near-field light generating element is from the minute opening of the near-field light generating element to the most of the minute opening. There is a theory that the area is limited to a distance of a narrow portion. For this reason, as in the above configuration, by setting the distance Z, near-field light is attenuated, but other optical noise (interference light or the like) can be suitably set to a distance that is not attenuated.

  In the near-field light evaluation apparatus according to the present invention, the distance Z is preferably 1 nm or more and 100 nm or less.

  By setting the distance Z as in the above configuration, near-field light is attenuated reliably and simply, but other optical noise (interference light or the like) can be suitably set to a distance that does not attenuate. .

  The calculation means may be realized by a computer. In this case, the calculation control program of the calculation means for causing the calculation means to be realized by the computer by operating the computer as each of the means, and recording the program. Such computer-readable recording media also fall within the scope of the present invention.

  According to the near-field light evaluation apparatus of the present invention, there is an effect that near-field light and other light (especially interference light) can be accurately distinguished in the vicinity of the near-field light generating element. For this reason, when it leaves | separates from a near-field light generating element, information, such as how much near-field light attenuate | damps, measurement of distribution of near-field light, etc. can be performed.

[Embodiment 1]
One embodiment of the present invention is described below with reference to FIGS. FIG. 1 is a diagram schematically showing a configuration of a near-field light evaluation apparatus according to an embodiment of the present invention. As shown in the figure, the near-field light evaluation apparatus 100 according to the present embodiment includes a scatterer 10, a scanning mechanism 11, a changing mechanism 12, a probe 13, a photodetector 14, a control unit 15, and a monitor 16. . The near-field light evaluation apparatus 100 evaluates the near-field light 60 generated by the near-field light generating element 50 as an evaluation target. The term “evaluation of near-field light (near-field)” in this specification means near-field light and other light (incident light, transmitted light, reflected light, interference from the light source of the near-field light generating element). And light near the near-field light generating element such as light) and the distribution of near-field light is measured. The word “near field” is a near (electromagnetic) field as the name implies, and the word “near field light” is light (electromagnetic wave) existing in the near field. For this reason, in this specification, there is no clear difference in meaning between the terms “near field” and “near field light”, and the terms are synonymous. In this specification, the term “near field light” is mainly used. And

FIG. 2 is a diagram schematically showing the structure of the near-field light generating element 50. The structure of the near-field light generating element 50 will be described with reference to FIGS. As shown in FIGS. 1 and 2, the near-field light generating element 50 functions as a near-field light generating device that generates near-field light, and is provided with a light source 51, a condensing lens 53, and a minute opening 54. A substrate 55 is provided. The light source 51 is a light irradiation unit that irradiates a laser beam 52. In general, a laser beam that can be condensed well is generally used for the near-field light generating element in order to efficiently generate near-field light. Note that the manner in which near-field light is generated varies depending on the polarization direction. The condensing lens 53 functions as light condensing means for condensing the laser light 52 with respect to the minute opening 54.
The substrate 55 is covered with a metal film such as Al, Au, Ag, Pt. The thickness of this metal film is about 10 to 100 nm. When a metal thin film is used, surface plasmon polarin is generated near the substrate surface, and enhancement of near-field light can be expected. Further enhancement may be performed by providing a periodic structure around the minute opening 54. Further, although the minute opening 54 is provided in the substrate 55, the substrate 55 is not particularly limited as long as it only generates near-field light as long as it has a minute shape with transmittance and refractive index change. For example, even if an opening is not provided, near-field light is generated around the ball when light is applied to a small glass ball.

  The minute opening 54 is circular in the present embodiment, but is not limited to this shape, and may be a special shape such as a polygon or a combination of a circle and a polygon. It is known that the near-field light output from the near-field light generating element 50 has the same size as the minute opening 54 and the shape varies depending on the shape of the minute opening 54. Since the near-field light generating apparatus 100 is mainly used to obtain a light spot that exceeds the diffraction limit, the diameter of the minute opening 54 is generally equal to or less than the wavelength of the laser light 52. For example, if the laser light emitted from the light source 51 is red light, the wavelength is about 600 nm, and if the laser light emitted from the light source 51 is blue light, the wavelength is smaller than about 400 nm. The diameter of the minute opening 54 is set. Therefore, for example, the diameter of the minute opening 54 is preferably about several nm to several hundred nm. The minute opening 54 can be said to be a source of near-field light.

  When the laser beam 52 is condensed on the minute opening 54 by the condenser lens 53, near-field light 60 is formed in the vicinity of the minute opening 54. Although it is ideal that only the near-field light is output from the minute opening 54, actually, a combination of transmitted light and near-field light is output. Further, the transmitted light is scattered and diffracted at a number of locations around the microscopic aperture 54, and they overlap and interfere. Interference fringes generated by the interference light are present around the microscopic aperture 54 and become noise.

  Note that the near-field light to be evaluated by the near-field light evaluation apparatus 100 according to the present invention may be near-field light generated by any near-field light generating element, and is not particularly limited. I will add a note.

  Next, the configuration of the near-field light evaluation apparatus 100 will be described in detail. The scatterer 10 shown in FIG. 1 functions as a scattering unit that scatters light. Since the near-field light is present in the vicinity of the minute opening 54, it is not detected by the photodetector 14 as it is. Therefore, it is necessary to scatter the near-field light 60 using this scatterer 10 and convert the near-field light into propagating light. Here, the “light” is present in the vicinity of the near-field light generating element 50 such as incident light, transmitted light, reflected light, and interference light from the light source 51 of the near-field light and the near-field light generating element 50. Includes all light.

  The scanning mechanism 11 functions as a scanning unit for causing the scatterer 10 to scan the vicinity of the near-field light 60 (the surface where the near-field light 60 in the near-field light generating element 50 is generated). That is, the scanning mechanism 11 scans the vicinity of the near-field light 60 in the horizontal direction with respect to the surface of the near-field light generating element 50 where the near-field light 60 is generated. The scanning mechanism 11 may be a uniaxial scanning mechanism that causes the scatterer 10 to scan one-dimensionally along the surface of the near-field light generating element 50, but preferably two-dimensionally scanning 2. An axial scanning mechanism is preferred. In the present embodiment, the scanning mechanism 11 is a uniaxial scanning mechanism.

  The changing mechanism 12 is perpendicular to the near-field light 60, that is, perpendicular to the surface of the near-field light generating element 50 where the near-field light 60 is generated (away from the source of the near-field light 60). In the direction), it functions as a position changing means for moving the position of the distance Z scatterer 10. For the purpose of the present invention, the changing mechanism 12 determines at least the distance (position in the height direction) between the surface of the near-field light generating element 50 where the near-field light 60 is generated and the scatterer 10 as the distance Z. For example, the distance between the scatterer 10 and the near-field light 60 may be changed to a distance Z or more.

  The probe 13 is a member for connecting the scatterer 10, the scanning mechanism 11, and the changing mechanism 12, and is for transmitting the operations of the scanning mechanism 11 and the changing mechanism 12 to the scatterer 10.

  The photodetector 14 functions as a light detection unit that detects the scattered light 17 scattered by the scatterer 10.

  The control unit 15 controls the function of changing the height position of the scatterer 10 in the changing mechanism 12. The control unit 15 is obtained by the light detection unit 14 detecting light scattered when the scatterer 10 is scanned before and after the change mechanism 12 changes the position of the scatterer 10 in the height direction. It also functions as a calculation means for obtaining the difference between the two light detection data.

  As a method for calculating the difference between the two pieces of light detection data, for example, the intensity of the scattered light detected by the photodetector 14 is converted into an electrical signal, and the difference is calculated. In addition to this, a conventionally known calculation method or data conversion method for determining the difference in intensity between the two scattered lights can be suitably used, and is not particularly limited.

  The monitor 16 is a device that visualizes information of the control unit 15, for example, information such as a difference between two pieces of light detection data calculated by a calculation unit, and a height position at which the changing mechanism 12 has the scatterer 10 disposed. A conventionally known CRT, liquid crystal display or the like can be suitably used.

  Next, a detailed operation when the near-field light 60 generated in the near-field light generating element 50 is evaluated by the near-field light evaluation apparatus 100 will be described.

  First, the scatterer 10 performs a first scan on the surface (near the near-field light generation source) where the near-field light 60 is generated in the near-field light generating element 50 (first pass). In this case, scanning is performed in a so-called contact mode so as to contact the surface of the near-field light generating element 50. If the near-field light can be scattered, the surface of the near-field light generating element 50 may be scanned in the vicinity of the surface (distance of several nm to several tens of nm) without scanning in the contact mode. . Further, such scanning may be one-dimensional (for example, only in the x-axis direction) or two-dimensional (in the x-axis direction and the y-axis direction). This will be described as one-dimensional scanning. In the present specification, the x-axis and y-axis directions refer to the horizontal direction with respect to the plane where the near-field light 60 is generated in the near-field light generating element 50, and the z-axis direction refers to the proximity The direction perpendicular to the plane in which the near-field light 60 is generated in the field light generating element 50 is said.

  Then, the light scattered by the first pass scanning is detected by the photodetector 14. In this first pass, the light scattered when the scatterer 10 is placed on the surface of the near-field light generating element 50 where the near-field light 60 is generated or in the vicinity thereof is scanned to the light detection unit 14. The detection data detected in this way is referred to as first photodetection data.

  Next, the scatterer 10 is arranged with the distance Z raised (moved) from the height position of the scatterer 10 when the first light detection data is acquired by the changing mechanism 12. That is, when the surface of the near-field light generating element 50 where the near-field light 60 is generated is scanned in the first pass, the distance Z height is changed (offset) from the surface of the near-field light generating element 50. ), The scatterer 10 is arranged. Subsequently, the scatterer 10 is scanned in the same manner as in the first pass (second pass) while maintaining this height position.

  That is, the scanning mechanism 11 uses the scanning direction horizontal to the surface of the near-field light generating element 50 as the scanning line (so-called second pass) of the scatterer 10 when acquiring the second light detection data. Scanning is performed with the same scanning line as the scanning line (so-called first pass) for acquiring one photodetection data, and the height position of the near-field light generating element 50 from the plane is relative to the near-field light generating element. Scanning is performed at a position where the distance Z is raised (moved) in the vertical direction. In other words, this method is a means for scanning the second pass while adding a predetermined offset to the surface shape data scanned in the first pass and changing the distance from the near-field light generating element 50. . In the second pass, the scatterer 10 does not contact the surface.

  Then, the light scattered by the second pass scanning is detected by the photodetector 14. In the second pass, detection data obtained by detecting light scattered by the scatterer 10 by the light detection unit 14 is referred to as second light detection data.

  These two pieces of light detection data are sent to the control unit 15 functioning as the calculation means described above, and the difference between them is obtained. That is, the control unit 15 that functions as a calculation unit includes first light detection data that detects light scattered when the scatterer 10 is placed on the surface of the near-field light 60 (or in the vicinity thereof) and scanned. , Second light detection data for detecting light scattered when the scatterer 10 is scanned with the distance Z raised from the height position of the scatterer 10 when the first light detection data is acquired and scanned. , The difference is calculated.

  Here, the distance Z is set to a distance at which near-field light is attenuated but other light is not attenuated. This utilizes the property that near-field light attenuates exponentially as it moves away from the source, while other light (interference light) does not attenuate as rapidly as near-field light. is doing. This is because the interference light changes in the wavelength order of the light source 51 of the near-field light generating element 50.

  For this reason, according to the near-field light evaluation apparatus 100 according to the present embodiment, extraneous optical noise (such as interference light) existing near the near-field light generating element 50 and the near-field light are clearly distinguished. It is possible to accurately measure and evaluate the distribution state of near-field light.

  In the present embodiment, a mechanism in which the near-field light evaluation apparatus 100 distinguishes between noise and near-field light and evaluates the near-field light will be described with a specific example. FIG. 3 shows the distribution of scattered light intensity detected when the scatterer 10 is uniaxially scanned. First, FIG. 3A shows the distribution of scattered light intensity when Z = 0, that is, when the surface of the near-field light generating element 50 is scanned. This figure shows the first photodetection data. In the figure, the largest peak portion indicates near-field light, and the other small peak portion is noise such as interference light.

  FIG. 3B shows the distribution of scattered light intensity when Z = 25 nm, that is, when a height position of 25 nm is scanned from the surface of the near-field light generating element 50. This figure shows the second photodetection data. As shown in FIGS. 3A and 3B, the noise part such as interference light hardly changes even if the scanning position of the scatterer 10 is changed, but only the mountain part showing the near-field light is greatly attenuated. You can see that

  FIG. 3C is a diagram showing the difference between the scattered light intensity distributions shown in FIGS. 3A and 3B. As shown in FIG. 3C, it is understood that only the near-field light is emphasized by calculating the difference between the first light detection data and the second light detection data. In the figure, the width of the peak indicating the near-field light is substantially the same as the opening diameter of the minute opening 54.

  In this way, by measuring the scattered light twice by changing the distance from the source of the near-field light and calculating the difference between the obtained two scattered light distribution states, noise such as interference light can be reduced. In comparison, it is possible to emphasize and evaluate near-field light having a larger change. Therefore, according to the near-field light evaluation apparatus 100 according to the present embodiment, it is possible to clearly distinguish excess optical noise (such as interference light) and near-field light existing in the vicinity of the near-field light generating element 50. It is possible to accurately measure and evaluate the near-field light distribution state.

  The distance Z is preferably smaller than the wavelength of the laser beam 52 emitted from the light source 51, and more preferably less than ½ wavelength of the wavelength of the laser beam 52 emitted from the light source 51. This is because the interference light is present in the vicinity of the minute opening 54 of the near-field light generating element and changes in the order of the light source wavelength. More specifically, bright and dark interference fringes are generated for each half wavelength of the laser light 52 emitted from the light source 51. For this reason, by setting the distance Z to be equal to or less than ½ wavelength of the light source wavelength, which is the light / dark repetition interval of the interference fringes, the vertical direction of the scatterer 10 (high relative to the surface of the near-field light generating element 50). The movement of the vertical direction does not cross the border between the bright and dark interference fringes. For this reason, there is no confusion between the change in the border between the bright and dark interference fringes and the attenuation change in the near-field light. Therefore, the near field light and the interference light can be accurately distinguished by setting the distance Z to be smaller than ½ wavelength of the wavelength of the laser light 52 emitted from the light source 51.

  In addition, when the ½ wavelength Z is actually moved and the difference is taken, the interference fringes are most emphasized. Therefore, the influence of the interference fringes cannot be removed because it does not exceed the bright / dark boundary of the interference fringes, but the influence can be reduced by setting it to ½ wavelength or less (that is, 1 / 2 wavelength or more, the difference is completely 0 at 1 wavelength and the influence can be removed, and the difference is Max again at 3/2 wavelength, but this is a story in an ideal environment. .)

  The distance Z is preferably smaller than the diameter of the circular opening when the near-field light generating element has a circular shape. This is because the region where the near-field light 60 is distributed in the near-field light generating element 50 is limited to a region about the diameter of the minute opening 54 from the circular minute opening 54 included in the near-field light generating element 50. This is because there is a theory. Therefore, by setting the distance Z to be smaller than the diameter of the minute opening 54 as in the above configuration, the near-field light is attenuated, but other optical noise (interference light or the like) is not attenuated. Can be suitably set.

  The distance Z is preferably smaller than the distance of the narrowest portion of the minute opening 54 when the shape of the minute opening 54 of the near-field light generating element 50 is a shape other than a circle. This is because when the shape of the minute opening 54 is a special shape other than a circle (for example, a polygon such as a triangle or a rectangle, or a combination of a circle and a polygon), the near-field light generating element 50 has a near-field. The region in which the light 60 is distributed is considered to be limited to a region having a diameter of the narrowest (smallest) portion of the minute opening 54 of the special shape from the minute opening 54 of the near-field light generating element 50. Because. For this reason, as in the above configuration, by setting the distance Z, near-field light is attenuated, but other optical noise (interference light or the like) can be suitably set to a distance that is not attenuated.

  More specifically, the distance Z is preferably set to a distance of 1 nm to 100 nm. This is because, by setting the distance, the near-field light is attenuated reliably and easily, but other optical noise (interference light or the like) can be suitably set to a distance that is not attenuated.

  The upper limit of the distance Z is a range in which near-field light can be detected, and is preferably 100 nm. This is because the near-field light generating element 50 is mainly used for the purpose of producing a spot exceeding the diffraction limit, so that a spot having a spot diameter exceeding 100 nm is considered to be meaningless. That is, since the preferable opening diameter of the minute opening 54 is 100 nm or less, the preferable detectable distance of near-field light is also 100 nm or less. Even if the distance Z is more than this distance, the noise due to the interference light only increases and is meaningless. Therefore, it is appropriate to set the upper limit to 100 nm.

  The lower limit of the distance Z is better as it is smaller. This is because the interference light has a slight change even within the range of the distance Z, and the influence of the change of the interference light is reduced. However, the lower limit of the distance Z must be a distance at which the intensity change of the near-field light can be stably measured.

  The distance that can be stably measured is determined by the resolution of the changing mechanism 12, the rigidity of the apparatus body, the apparatus installation environment such as vibration isolation and soundproofing, and the like. The resolution of the change mechanism 12 can be achieved by using a piezo actuator (a general actuator used in AFM). However, in order to stably control the wrinkle order with high reproducibility as a whole device, a high-performance vibration isolation table, a soundproof device, and a highly rigid device skeleton are required. The resolution that can be achieved without using these special devices is 1 nm or more. From the above, it is appropriate that the lower limit of the distance Z is 1 nm.

[Embodiment 2]
Another embodiment of the present invention will be described below with reference to FIGS. In the present embodiment, components having the same functions as the components in the first embodiment are given the same reference numerals, and descriptions thereof are omitted. In the present embodiment, differences from the first embodiment will be described.

  FIG. 4 is a diagram schematically showing a configuration of a near-field light evaluation apparatus according to another embodiment of the present invention. As shown in the figure, the near-field light evaluation apparatus 200 includes a scatterer 10, a scanning mechanism 11, a change mechanism 12, a probe 13, a photodetector 14, a control unit 15, a monitor 16, a vibration mechanism 21, and a lock-in amplifier. 22 and an oscillator (oscillating means) 23 are provided. As in the first embodiment, the near-field light evaluating apparatus 200 evaluates the near-field light 60 generated by the near-field light generating element 50 as an evaluation target. Since it is the same structure as the said Embodiment 1, the description is abbreviate | omitted here.

  In the present embodiment, the scanning mechanism 11 functions as scanning means capable of biaxial scanning. The probe 13 is a member for connecting the scatterer 10 to the excitation mechanism 21, the scanning mechanism 11, and the change mechanism 12. It is for transmission.

  The lock-in amplifier 22 is connected to the photodetector 14, the control unit 15, and the oscillator 23. The lock-in amplifier 22 functions as a minute signal detection means for detecting a minute repetitive signal (alternating current) buried in noise, and is normally used in combination with an oscillator 23 that functions as an oscillating means. Only the signal synchronized with is detected. That is, the lock-in amplifier 22 selectively detects only the signal synchronized with the oscillator 23 among the signals detected by the photodetector 14, and selectively selects the control unit 15 functioning as calculation means. The detected signal is output. For this reason, by using the lock-in amplifier 22, for example, the influence of stationary noise such as light from a fluorescent lamp can be eliminated.

  The vibration mechanism 21 is connected to an oscillator 23 and functions as a vibration unit that vibrates the scatterer 10 via the probe 13 in synchronization with a signal from the oscillator 23. The vibration mechanism 21 is for scanning the surface of the near-field light generating element 50 where the near-field light 60 is generated while vibrating the scatterer 10. That is, the vibration mechanism 21 can be said to be a means for causing the scatterer 10 to scan the surface of the near-field light generating element 50 in a so-called tapping mode. Here, the tapping mode will be briefly described.

  The tapping mode is one type of scanning mode performed in a scanning probe microscope (for example, an atomic force microscope (AFM)). In the contact mode (contact mode), resolution up to the atomic size may be obtained. However, since the probe is scanned while contacting the sample surface, the sample surface or the probe may be damaged. On the other hand, in the non-contact mode (NC-mode, non-contact mode), there is no problem of damage to the sample and the probe in principle, but resolution is generally excluded except for observation of a specific sample by the frequency modulation type NC-mode. Is inferior. As a compromise, a scanning mode developed as a method for obtaining an AFM image of a sample by bringing a vibrating probe closer from above the sample and touching the sample lightly is a tapping mode (for example, (1) “Nanotechnology's Scanning Probe Microscope "(2002), edited by Japan Surface Science Society, Maruzen, (2) Characterization and optimization of scan speed for tapping-mode atomic force microscopy; Rev. Sci. Instrum., Vol.73, No. 8, pp. 2928-2936 (2002); T. Sulchek, GG Yaralioglu, CF Quate and SC Minne; American Institute of Physics etc.).

  By performing scanning in this tapping mode, in addition to the effect of preventing damage to the sample and the scatterer 10 described above, an excellent effect can be obtained by combining with the lock-in amplifier 22. Hereinafter, a combination of the tapping mode by the vibration mechanism 21 and the lock-in amplifier 22 will be described.

  When the vibration mechanism 21, the oscillator 23, and the lock-in amplifier 22 are connected and the period of the tapping mode by the vibration mechanism 21 and the period of the signal detected by the lock-in amplifier 22 are synchronized, steady noise (fluorescent lamp) ) And the transmitted light from the light source 51 can be reduced. Specifically, the transmitted light from the light source 51 hits the scatterer 10 and is detected by the light detector 14. However, at a moving distance that causes the scatterer 10 to amplitude by the tapping mode, the intensity of steady noise and transmitted light is almost the same. Does not change (intensity is uniform in the z-axis direction). That is, steady noise and transmitted light are not modulated by the vibration mechanism 21. For this reason, by passing through the lock-in amplifier 22, most of the effects of this steady noise and transmitted light can be removed.

  However, as described above, the transmitted light is diffracted and scattered at various locations around the microscopic aperture 54, and as a result, a large amount of interference light is present around the microscopic aperture 54. Since the interference light changes in the wavelength order of the light source 51, these cannot be completely removed by the lock-in amplifier 22 and become noise sources.

  In general, in the tapping mode, the probe 13 is vibrated at a moving distance of 50 nm or more in order to reduce the influence of an adsorption layer (such as a moisture layer) on the sample surface. If the moving distance is small, the surface shape cannot be measured accurately. Also in the present embodiment, the probe 13 and the scatterer 10 are vibrated at a moving distance of 50 nm or more. However, when the height changes by 50 nm, the transmitted light hardly changes, but the interference light changes slightly. Therefore, even if the tapping mode is used, the influence of the interference light remains (near-field light is Change a lot).

  Therefore, in order to clearly distinguish between interference light and near-field light, scanning is performed twice while changing the height in the tapping mode. This means that scanning is performed by a so-called “two-pass method” in a scanning probe microscope (see Beeco / Digital Instruments, SPM catalog, etc.). That is, in the present embodiment, the scanning in the tapping mode method and the lock-in amplifier are combined (that is, the signal period selectively detected by the lock-in amplifier 22 is synchronized with the tapping mode period), and A two-pass method is also combined to separate near-field light and other optical noise (such as interference light).

  In the following, a detailed description of the operation when the near-field light 60 generated in the near-field light generating element 50 is evaluated by the near-field light evaluation apparatus 200 will be described.

  First, the scatterer 10 performs the first scanning on the surface of the near-field light generating element 50 where the near-field light 60 is generated (first pass). In the first scanning, the scatterer 10 is scanned by the scanning mechanism 11, the vibration mechanism 21, and the oscillator 23 so as to be in contact with the surface of the near-field light generating element 50 in the above-described tapping mode.

  Then, the light scattered by the first pass scanning is detected by the photodetector 14. The photodetector 14 is connected to the lock-in amplifier 22. For this reason, in the first pass, as described above, among the detection data in which the light detector 14 detects the light scattered when the scatterer 10 is placed on the surface of the near-field light 60 and scanned. Only the signal synchronized with the oscillator 23 is detected and output as first photodetection data to the control unit 15 functioning as calculation means.

  Next, the scatterer 10 is arranged by raising the distance Z from the height position of the scatterer 10 when the first photodetection data is acquired by the changing mechanism 12. That is, when the surface of the near-field light generating element 50 where the near-field light 60 is generated is scanned in the first pass, the distance Z height is changed from the surface of the near-field light generating element 50, and the scatterer 10 Will be placed. Subsequently, the scatterer 10 is scanned in the tapping mode in the same manner as in the first pass (second pass) while maintaining this height position.

  Then, the light scattered by the second pass scanning is detected by the photodetector 14. In the second pass, as described above, only the signal synchronized with the oscillator 23 is detected from the detection data in which the light detector 14 detects the light scattered when the scatterer 10 is scanned. 2 is output to the control unit 15 functioning as calculation means.

  Finally, a difference between these two pieces of photodetection data is obtained by the control unit 15 functioning as calculation means. That is, the control unit 15 detects the light that is scattered when the scatterer 10 is scanned on the surface of the near-field light 60 in the so-called tapping mode, and the scatterer in the tapping mode. 10 is the difference between the second photodetection data and the second photodetection data detected when the light is scattered when scanning is performed by raising the distance Z from the height position of the scatterer 10 when acquiring the first photodetection data. Is calculated. Here, the distance Z is set to a distance at which near-field light is attenuated but other light is not attenuated.

  Therefore, according to the near-field light evaluation apparatus 200 according to the present embodiment, extraneous light noise (such as interference light) and near-field light existing in the vicinity of the near-field light generating element 50 can be easily and clearly distinguished. It is possible to accurately measure and evaluate the distribution state of near-field light.

Although the above scanning is performed in one dimension (for example, in the x-axis direction), it can be performed in two dimensions. In this case, the first pass and the second pass are scanned on one axis (for example, the x-axis), and then another axis (for example, the y-axis) is moved. Do. By repeating these operations, a two-dimensional image can be obtained. A method of performing the second pass scan after performing the first pass scan in two dimensions is also possible, but in order to reduce the influence of the scan position shift due to thermal drift or the like, the first pass and the second pass are possible. It is preferable to perform the above scanning continuously as much as possible.
In the present embodiment, a mechanism in which the near-field light evaluation apparatus 100 distinguishes between noise and near-field light and evaluates the near-field light will be described with a specific example. FIG. 5 is a diagram showing a distribution of scattered light intensity detected when the scatterer 10 is scanned in two axes. FIG. 5A is a diagram visualizing the distribution of scattered light intensity when the scatterer 10 scans the surface (Z = 0) of the near-field light generating element 50 in the tapping mode. FIG. 5B is a diagram visualizing the distribution of scattered light intensity when the scatterer 10 scans a position (Z = 25) at a height of 25 nm from the surface of the near-field light generating element 50 in the tapping mode. is there. In FIG. 5B, the tip of the scatterer 10 is not in contact with the surface of the near-field light generating element 50 (in the tapping mode). FIG. 5C is a diagram in which the difference between FIG. 5A and FIG. 5B is calculated and visualized.

  FIG. 6 is a diagram that makes the visualized data of FIG. 5 schematic to make it easier to understand. 6A is a schematic diagram of FIG. 5A, FIG. 6B is a schematic diagram of FIG. 5B, and FIG. 6C is a schematic diagram of FIG. 5C.

  Here, FIGS. 5A and 6A show the first photodetection data, and FIGS. 5B and 6B show the second photodetection data. As shown in FIG. 5 and FIG. 6, the near-field light evaluation apparatus 200 calculates the difference between the first light detection data and the second light detection data, thereby obtaining the results shown in FIGS. As shown in c), it is possible to obtain a result that the near-field light component looks conspicuous. Therefore, according to the near-field light evaluation apparatus 200, near-field light can be clearly and easily evaluated.

  In the present embodiment, the tapping mode and the lock-in amplifier are combined and scanned by a two-pass method to acquire two pieces of light detection data. For this reason, compared with the above-mentioned Embodiment 1, since the influence of the stationary noise and the transmitted light from a light source can be removed or reduced, it can be said that it is a more practical embodiment.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Needless to say, these are also included in the technical scope of the present invention.

  Finally, each block of the control unit 15, in particular, a block that functions as a calculation unit or a block that controls a change mechanism may be configured by hardware logic, or realized by software using a CPU as follows. Also good.

  That is, the control unit 15 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, a RAM (random access memory) that expands the program, A storage device (recording medium) such as a memory for storing the program and various data is provided. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the control unit 15 which is software that realizes the functions described above is recorded so as to be readable by a computer. This can also be achieved by supplying the control unit 15 and reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU).

  Examples of the recording medium include tapes such as magnetic tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks / hard disks, and disks including optical disks such as CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The control unit 15 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Also, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  According to the present invention, near-field light can be more accurately evaluated, so a more precise near-field optical microscope can be manufactured, and not only surface shape observation but also through spectral information such as light emission, Raman scattering, and polarization, Nano-physical property evaluation that is very useful in industry can be performed. Furthermore, the principle of near-field optics can be applied to fields such as optical processing and optical information recording / reproduction. For example, near-field light is very sensitive to distance, so the intensity of near-field light can be measured. Thus, it can be used for a flying height sensor (gap sensor) of a slider head used in a hard disk drive or the like.

It is a figure which shows typically the structure of the near-field light evaluation apparatus of one Embodiment which concerns on this invention. It is a figure which shows typically the structure of a near-field light generating element. It is a figure which shows distribution of the scattered light intensity detected when the scatterer 10 is scanned by 1 axis | shaft, (a) is a case where the scatterer scans the surface (Z = 0) of a near-field light generating element. The distribution of scattered light intensity is shown. This figure shows the first light detection data, and (b) shows the scattered light when the scatterer scans a position (Z = 25) at a height of 25 nm from the surface of the near-field light generating element. It is a figure which shows distribution of intensity | strength, (c) is the figure which took the difference of distribution of scattered light intensity shown to (a) and (b). It is a figure which shows typically the structure of the near-field light evaluation apparatus of other one Embodiment which concerns on this invention. It is a figure which shows distribution of the scattered light intensity detected when a scatterer is scanned by 2 axis | shafts, (a) scans the surface (Z = 0) of a near-field light generating element in a tapping mode. FIG. 8B is a diagram visualizing the distribution of scattered light intensity in the case where the scatterer scans the position (Z = 25) at a height of 25 nm from the surface of the near-field light generating element in the tapping mode. (C) is the figure which computed and calculated the difference of (a) and (b). FIG. 6 is a diagram that makes the visualized data of FIG. 5 schematic and easier to understand. FIG. 5A shows FIG. 5A, FIG. 5B shows FIG. 5B, and FIG. 5C shows FIG. FIG.

Explanation of symbols

10 Scattering body 11 Scanning mechanism (scanning means)
12 Change mechanism (position change means)
14 Photodetector (light detection means)
15 Control unit (calculation means)
21 Excitation mechanism (excitation means)
22 Lock-in amplifier (micro signal detection means)
23 Oscillator (oscillation means)
DESCRIPTION OF SYMBOLS 50 Near field light generation element 51 Light source 54 Micro opening 60 Near field light 100,200 Near field light evaluation apparatus

Claims (10)

In the near-field light evaluation apparatus for evaluating the near-field light generated by the near-field light generating element,
A scattering means for scattering light;
A light detection means for detecting light scattered by the scattering means;
Position changing means for moving the position of the scattering means by a distance Z in the vertical direction with respect to the near-field light;
The position changing means measures the scattered light before and after moving the position of the scattering means by the distance Z, and includes a calculating means for calculating the difference between the two light detection data before and after the movement,
The near-field light evaluation apparatus, wherein the distance Z is a distance at which near-field light is attenuated but other light is not attenuated. The calculation means is
First light detection data for detecting light scattered when the scattering means is arranged on the surface of the near-field light generating element where the near-field light is generated or in the vicinity thereof;
The difference between the scattering means and the second light detection data for detecting the scattered light when the first light detection data is acquired and moved by a distance Z from the position of the scattering means is calculated. The near-field light evaluation apparatus according to claim 1, wherein: And a scanning means for scanning the scattering means in a horizontal direction with respect to the surface where the near-field light in the near-field light element is generated,
The calculating means detects the light scattered when the scattering means is scanned before and after the position changing means moves the position of the scattering means by the distance Z, and calculates the difference between the two light detection data. The near-field light evaluation apparatus according to claim 1 or 2, wherein   The scanning means is the same scanning line as the scanning line for acquiring the first photodetection data as the scanning line for acquiring the second photodetection data, and 4. The near-field light evaluation apparatus according to claim 3, wherein scanning is performed at a position moved by a distance Z in the vertical direction. Furthermore, a near-field light evaluation apparatus comprising a vibration means for vibrating the scattering means, an oscillation means, and a minute signal measurement means,
The excitation means vibrates the scattering means with a signal synchronized with the oscillation means,
The minute signal measuring means selectively detects only the signal synchronized with the oscillating means among the signals detected by the light detecting means, and outputs only the selectively detected signal to the calculating means. The near-field light evaluation apparatus according to any one of claims 1 to 4, wherein   6. The near-field light evaluation apparatus according to claim 1, wherein the distance Z is smaller than a wavelength of incident light emitted from a light source included in the near-field light generating element.   6. The near-field light evaluation apparatus according to claim 1, wherein the distance Z is smaller than ½ of the wavelength of incident light emitted from a light source included in the near-field light generating element.   The near field according to any one of claims 1 to 5, wherein the distance Z is smaller than a diameter of the circular opening when the near-field light generating element has a circular shape. Light evaluation device.   The distance Z is smaller than the distance of the narrowest portion of the opening when the shape of the minute opening of the near-field light generating element is a shape other than a circle. The near-field light evaluation apparatus according to claim 1. The near field light evaluation apparatus according to claim 1, wherein the distance Z is not less than 1 nm and not more than 100 nm.

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