JP4332283B2 - Near-field optical microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a near-field optical microscope, and more particularly to improvement of an excitation light irradiation mechanism, a detection light condensing mechanism, and an analysis mechanism for the detection light.
[0002]
[Prior art]
In recent years, in the field of optical analysis, a near-field optical microscope capable of realizing a spatial resolution below the wavelength has started to be applied to various analyzes in place of a general optical microscope or electron microscope.
This near-field optical microscope detects so-called evanescent light. In other words, a minute sample is placed on a flat substrate, and when light is incident at an angle that causes total reflection from the back side of the substrate, all of the propagating light is reflected, but the substrate and the surface of the sample are evanescent. Surface waves called light are generated. This surface wave is localized in a region within a distance within the wavelength of light around the object surface.
[0003]
Therefore, the distance between the probe tip and the sample surface to be measured can be defined by inserting a sharp probe into the evanescent light field, scattering the evanescent light field, and measuring the scattered light intensity. .
Therefore, by scanning the probe while keeping the intensity of the scattered light constant, the tip position of the probe accurately reflects the unevenness of the sample surface to be measured.
[0004]
Moreover, since the probe tip is only present in the field of evanescent light and is not in contact with the sample itself, it can contact the sample non-contact, non-destructively, and can observe objects smaller than the light wavelength value. is there.
Conventionally, such a near-field optical microscope has various measurement modes such as an illumination mode, the collection mode, an illumination-collection mode, and a scattering type.
In the illumination mode, when the excitation light is introduced into the probe and irradiated onto the metal covering the sharpened portion of the tip, evanescent light is generated and oozes out from the minute opening of the tip. The sample is irradiated with evanescent light, and scattered light and light emission from the sample are collected and detected.
[0005]
In the collection mode, the sample is directly irradiated with excitation light, and the probe enters the field of evanescent light generated on the surface of the sample to be measured to scatter the evanescent light and collect and detect the scattered light and luminescence. ing.
In the illumination-collection mode, evanescent light is irradiated onto the surface of the sample to be measured by the probe, and reflected light from the sample is collected by the probe and detected.
[0006]
The scattering type irradiates the surface to be measured with excitation light from an excitation laser from an oblique direction to the surface to be measured, and scatters the field of evanescent light generated on the surface to be measured with a probe made of metal or the like. The scattered light is collected and detected by an objective lens or the like disposed opposite to the excitation laser.
By using such a near-field optical microscope, it is possible to observe an object smaller than the light wavelength value.
[0007]
[Problems to be solved by the invention]
However, even in each of the near-field optical microscopes, although further improvement is desired in terms of measurement accuracy, there has conventionally not been an appropriate technique that can solve this.
The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a near-field optical microscope capable of performing measurement more accurately.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a near-field optical microscope according to the present invention includes excitation light irradiation means, a probe, and spectrum information acquisition means.
Here, the excitation light irradiating means irradiates the surface to be measured of the sample with laser light from an oblique direction to the surface to be measured.
The probe is positioned substantially directly above the surface to be measured, scatters near-field light generated on the surface to be measured by the laser light from the excitation light irradiation means, and collects the scattered light.
[0009]
The spectrum information acquisition means separates the scattered light collected by the probe to obtain spectral spectrum information.
The scattered light here refers to, for example, photoluminescence light or Raman scattered light.
In the present invention, the excitation light irradiation means emits a laser beam to irradiate the surface to be measured, and first to third reflections to irradiate the surface to be measured from different directions. And a mirror.
[0010]
The laser and the first to third reflection mirrors are arranged around the probe.
The first reflection mirror is disposed on the opposite side of the laser with respect to the sample, and receives laser light that reflects the measurement surface and reflects it toward the second reflection mirror.
The second reflecting mirror receives the laser beam and reflects it again toward the surface to be measured.
[0011]
The third reflection mirror is disposed on the opposite side of the sample from the second reflection mirror, and receives the laser beam from the second reflection mirror that reflects the measurement surface again and receives again. Reflects toward the surface to be measured.
The laser beam from the third reflection mirror that reflects the measurement surface reflects each reflection mirror in the order of the second reflection mirror and the first reflection mirror, and irradiates the measurement surface again.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a schematic configuration of a near-field optical microscope 10 according to an embodiment of the present invention.
The microscope 10 shown in the figure includes excitation light irradiation means 12, a probe 14, and spectrum information acquisition means 16.
[0013]
The excitation light irradiation means 12 is disposed obliquely above the outside of the sample chamber 18. Then, laser light (non-diffusible excitation light) 24 is applied to the surface to be measured 20 of the sample through the entrance window 22 of the sample chamber 18 from above and obliquely above the surface to be measured.
The probe 14 is composed of a probe having a minute opening formed in the tip portion 14a, the tip portion 14a is located immediately above the measured surface 20, and is generated by irradiating the measured surface 20 with laser light 24. The near-field light is scattered and the Raman scattered light 26 is collected.
[0014]
The spectrum information acquisition unit 16 includes a spectrometer 28, a detector 30, and a computer main body 32. The Raman scattered light 26 collected by the probe 14 is separated by the spectroscope 28. The Raman scattered light 26 separated by the spectroscope 28 is detected by the detector 30 and stored in the computer main body 32 together with the wavelength information of the spectroscope 28.
[0015]
In the present embodiment, the control optical system 34 scatters the near-field light generated by irradiating the measurement target surface 20 of the sample with the laser light 24, detects the Rayleigh scattered light 42, and based on the output. The stage controller 36 scans the surface to be measured 20 in the XY direction (direction substantially orthogonal to the optical axis) while controlling the position of the probe 14 in the Z-axis direction so that the intensity of the Rayleigh scattered light 42 is constant.
Thereby, the computer main body 32 receives the X and Y coordinates of each measurement point, the height information of the measurement surface at each measurement point, and the spectrum information or component information of the measurement surface at each measurement point from the stage controller 36, respectively. Obtained and displayed on the display 40.
[0016]
By the way, according to the near-field optical microscope 10 according to the present embodiment, compared to a general optical microscope or an electron microscope, it is possible to observe an object smaller than the light wavelength value, but the accuracy of measurement is still improved. There is room for it.
Therefore, in the present invention, the first characteristic is that the surface to be measured is irradiated with excitation light from an oblique direction with respect to the surface to be measured, and is measured on the surface to be measured by a probe substantially directly above the surface to be measured. The generated near-field light is scattered, the scattered light is collected, and the scattered light collected by the probe is dispersed to obtain spectral information.
[0017]
Therefore, in the present embodiment, as shown in an enlarged view in FIG. 2, the laser 12 as the excitation light irradiation means is disposed obliquely above the measurement surface 20 of the sample, and the tip of the probe 14 is covered. It is arranged immediately above the measurement surface 20. A spectrum information acquisition means 16 is provided after the probe 14.
Then, the laser beam 24 from the laser 12 is irradiated obliquely from the outside of the probe 14, the near-field light generated thereby is scattered at the tip of the probe 14, and the Raman scattered light is sampled from the scattered light, and the spectrum The information acquisition means 16 separates the Raman scattered light to obtain spectral spectrum information.
[0018]
As a result, the measurement can be performed more accurately.
Although there are still unclear points about the details of the measurement accuracy improvement mechanism, when the optical arrangement of the laser 12 and the probe 14 as shown in FIG. 2 is adopted, the excitation surface 24 is irradiated with the excitation light 24, The near-field light generated on the measurement target surface 20 is scattered, and the Rayleigh scattered light 42 is reflected to the outside of the probe 14, so that the tip of the probe 14 is located almost directly above the measurement target surface 20. If the position is set, only the Raman scattered light 26 can be collected well. Furthermore, it is considered that the spectral information acquisition means 16 in the subsequent stage separates the Raman scattered light and obtains spectral spectrum information, so that the measurement can be performed accurately.
[0019]
More specifically, to obtain high sensitivity, it is generally considered to use strong excitation light.
However, according to the present inventors, in a near-field optical microscope operating in a general illumination mode or illumination-collection mode, the surface to be measured is irradiated from the probe with evanescent light. For this reason, when strong excitation light passes through the probe, light emitted from the probe itself is irradiated onto the surface to be measured and overlaps the spectrum, which may hinder measurement.
[0020]
Therefore, in this embodiment, in order to solve the problem in the case of using strong excitation light, the excitation light is irradiated to the measurement surface of the sample from the diagonally upper outside of the probe, and the measurement surface is irradiated from diagonally upward, In addition, the probe 14 is positioned immediately above the surface to be measured, and the spectrum information acquisition means 16 is provided at the subsequent stage.
As a result, in the present embodiment, the probe itself can be prevented from emitting light even when strong excitation light is used only by the combination of the laser 12, the probe 14, and the spectrum information acquisition unit 16 as described above. Only weak Raman scattered light can be collected well to obtain spectral information.
[0021]
Here, even in a general scattering type, the measurement surface is irradiated with excitation light from an excitation laser obliquely from above. In this case, for the condensing mechanism, an objective lens or the like disposed opposite to the excitation laser is generally used.
However, when strong excitation light is used, the measurement cannot be performed accurately.
Although the cause of this is still unclear, according to the present inventors, an irradiation mechanism and a condensing mechanism are arranged as in the scattering type, and the light selectivity as in the objective lens is used as the condensing mechanism. If a light source having a low value is used, scattered light other than the scattered light in the field of evanescent light is collected by an objective lens or the like and rides as a background.
[0022]
It is considered that when strong excitation light is used, the influence of such stray light appears more conspicuously and extremely weak Raman scattered light is buried.
In the present embodiment, this problem is also solved by the combination of the laser 12 capable of emitting strong excitation light as described above, the probe 14 having excellent light selectivity, and the spectrum information acquisition means 16.
As described above, in this embodiment, the accuracy of measurement is improved by the combination of the laser 12, the probe 14, and the spectrum information acquisition unit 16 as described above. However, the present inventors have further shown the excitation shown in FIG. Techniques for achieving higher accuracy when measurement was performed using a light irradiation mechanism and a light collection mechanism were studied.
[0023]
That is, according to the present inventors, in the optical system arrangement of the laser 12 and the probe 14 shown in FIG. 2, when illumination is performed from one direction, a shadow is formed on the illumination.
Even if the shadow is a size that does not cause a problem in a general microscope, a near-field optical microscope that observes a light having a wavelength smaller than the wavelength value can shadow the illumination by the shadow of the probe and the structure of the surface to be measured.
For this reason, artifacts are added to the measurement result, which may cause a reduction in measurement accuracy. Therefore, reducing such a shadow leads to an improvement in measurement accuracy.
[0024]
Therefore, in the present invention, the second characteristic is that a plurality of excitation light irradiating means are provided so that the optical axes of the excitation light irradiated on the surface to be measured are different, and the surface to be measured is nondiffusible. It is that the irradiation part which irradiates excitation light is included. Therefore, in the present embodiment, a plurality of lasers 12a to 12d (irradiation units) are employed as shown in an enlarged view in FIG.
That is, the lasers 12a to 12d are provided at substantially equal intervals around the surface to be measured 20 of the sample.
[0025]
Then, the laser beams 24 a to 24 d from the lasers 12 a to 12 d are incident on the measurement surface 20 substantially simultaneously from obliquely above the probe 14. The field of the evanescent light generated by the excitation light 24a to 24d is scattered at the tip of the probe 14, and the Raman scattered light is condensed at the tip of the probe 14 substantially above the surface 20 to be measured. Yes.
As a result, in the present embodiment, the laser light 24a to 24d from the plurality of lasers 12a to 12d irradiates the surface 20 to be measured substantially uniformly from multiple directions, so that compared to the case where illumination is performed from one direction, It is possible to greatly reduce the shadows on the lighting.
[0026]
Therefore, the shadow of the probe 14 and the shadow due to the structure of the surface to be measured can be greatly reduced, and the artifacts on the measurement result can be greatly reduced, so that the measurement can be performed more accurately.
Further, in the present invention, instead of the excitation light irradiation mechanism shown in FIG. 3, first, excitation light is irradiated on the measured surface of the sample from one direction, and the light reflected by the measured surface is turned back and forth. It is also preferable to provide a reflection mirror that irradiates the surface to be measured again as light. Therefore, in the present embodiment, it is also preferable to provide a first reflection mirror 44, a second reflection mirror 46, and a final reflection mirror 48 as a plurality of reflection mirrors as shown in an enlarged manner in FIG.
[0027]
That is, the first reflecting mirror 44 and the second reflecting mirror 46 irradiate the surface to be measured 20 of the sample with one laser beam 24 from the laser 12, and turn back the light reflected by the surface to be measured 20. The surface 20 to be measured is irradiated again, but the mirror surface is adjusted so that the reflected light is irradiated to the surface 20 to be measured from the direction deviated from the first optical path.
In addition, a final reflection mirror 48 is installed so that the light reflected from the surface to be measured 20 by the first reflection mirror 44 and the second reflection mirror 46 follows the optical path up to the previous stage upside down.
[0028]
That is, the laser beam 24 from the laser 12 is
(1) Irradiate the surface to be measured 20 (optical path + x1),
(2) From the measured surface 20 to the first reflecting mirror 44 (optical path-x2),
(3) From the first reflecting mirror 44 to the second reflecting mirror 46 (optical path + x3),
(4) Re-irradiate the surface to be measured 20 from the second reflecting mirror 46 (optical path + x4)
(5) The light is incident from the surface to be measured 20 onto the final reflecting mirror 48 (optical path-x5).
[0029]
Then, the light incident on the final reflecting mirror 44 follows (1) to (5) in the reverse order. That is,
(5) Re-irradiate the surface to be measured 20 from the final reflecting mirror 48 (optical path + x5)
{Circle over (4)} From the surface to be measured 20 to the second reflecting mirror 46 (optical path-x4)
(3) From the second reflecting mirror 46 to the first reflecting mirror 44 (optical path + x3)
{Circle around (2)} Re-irradiate the surface to be measured 20 from the first reflecting mirror 44 (optical path + x2)
(1) 'Guided from the measurement surface 20 to the outside (optical path-x1).
[0030]
As a result, as shown in FIG. 5 as a view of the optical path shown in FIG. 4 as viewed from above, a plurality of reflecting mirrors 44, 46, and 48 are used to change the measurement target surface 20 of the sample in different directions. In the embodiment, since light is irradiated substantially uniformly from multiple directions of the optical path + x1, the optical path + x2, the optical path + x4, and the optical path + x5, the shadow caused by illumination is greatly reduced as in the excitation light irradiation mechanism shown in FIG.
[0031]
In addition, by installing the final reflecting mirror 48, it is possible to reliably illuminate the opposite side of the measurement surface 20 once illuminated, so that the substantially entire circumference of the measurement surface 20 is illuminated more uniformly, The shadows on the lighting are greatly reduced.
Therefore, since the shadow of the probe and the shadow due to the structure of the surface to be measured are greatly reduced, it is possible to significantly reduce the presence of artifacts on the measurement result and perform measurement more appropriately.
[0032]
Further, the normal measurement is often performed in a sample chamber where the measurement environment such as temperature, humidity, and pressure is kept constant. In the excitation light irradiation mechanism shown in FIG. 3, the incident window for each excitation light is used. Must be provided in the sample chamber. On the other hand, in the configuration shown in FIG. 4, the illumination effect similar to that of the irradiation mechanism shown in FIG. 3 can be obtained by providing only one incident window. Therefore, the measurement environment varies due to an increase in the number of incident windows installed. Etc. can be largely prevented.
[0033]
Furthermore, in the present embodiment, by arranging the excitation light irradiation means on the measured surface side, the degree of freedom in designing the optical system is improved as compared with the case where it is provided on the back surface side.
That is, a stage, a controller for the stage, etc. are generally arranged on the back side of the surface to be measured of the sample. With a relatively small number of optical axes such as a collection mode, excitation light is emitted from the back side of the surface to be measured. Irradiation is also possible.
[0034]
However, when it is necessary to arrange a large number of optical axes of excitation light as in this embodiment, excitation light irradiation means is provided on the measured surface side particularly in terms of securing space and design freedom. It is preferable to illuminate the excitation light from the surface to be measured.
However, in the irradiation mechanism shown in FIG. 3, it is possible to provide excitation light irradiation means on the back side of the surface to be measured and to illuminate from the back side.
[0035]
Further, in the configuration shown in FIG. 3, an example in which a plurality of lasers corresponding to the required number of laser beams are used and the sample is irradiated with the laser beams from these lasers has been described. Two or more lasers may be used, and the laser beams from the lasers may be divided to align a desired number of laser beams.
Furthermore, in the above-described configuration, an example has been described in which Raman scattered light obtained by scattering near-field light on the surface to be measured is assumed as detection light. However, the present invention can also be applied to photoluminescence light or the like.
[0036]
【The invention's effect】
As described above, according to the near-field optical microscope of the present invention, excitation light irradiating means for irradiating the surface to be measured of the sample with excitation light obliquely with respect to the surface to be measured, and the surface to be measured by the probe The near-field light generated on the surface to be measured by the excitation light is scattered and the probe that collects the scattered light and the collected scattered light are dispersed to obtain spectral spectrum information. Since the spectrum information acquisition means is provided, measurement can be performed accurately.
Further, in the present invention, a plurality of the excitation light irradiating means are provided so that the optical axes of the excitation light irradiated to the measurement surface are different, and irradiation for irradiating the measurement surface with non-diffusible excitation light By including the part, the measurement can be performed more accurately.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a near-field optical microscope according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of the arrangement of characteristic excitation light irradiation means, probes, and spectrum information acquisition means in the near-field optical microscope according to one embodiment of the present invention.
FIG. 3 is an explanatory diagram of a more preferable specific example of the excitation light irradiation means shown in FIG.
4 is an explanatory diagram of a modification of the excitation light irradiation means shown in FIG.
FIG. 5 is an explanatory view of the excitation light irradiation means shown in FIG. 4 as viewed from above.
[Explanation of symbols]
10 Near-field optical microscope 12 Laser (excitation light irradiation means, irradiation section)
14 Probe 16 Spectral information acquisition means 20 Surface to be measured 24 Laser light (excitation light)
26 Raman scattered light (scattered light)
44, 46, 48 Reflection mirror (irradiation part)

Claims (1)

Excitation light irradiation means for irradiating the measured surface of the sample with laser light from an oblique direction to the measured surface;
A probe that is positioned substantially directly above the surface to be measured, scatters near-field light generated on the surface to be measured by the laser light from the excitation light irradiation means, and collects the scattered light;
Spectral scattered light collected by the probe, spectral information acquisition means to obtain spectral spectral information ,
The excitation light irradiation means includes a laser that emits laser light to irradiate the surface to be measured, and first to third reflecting mirrors that irradiate the surface to be measured from different directions.
The laser and first to third reflecting mirrors are disposed around the probe;
The first reflection mirror is disposed on the opposite side of the laser with respect to the sample, and receives the laser beam reflected from the surface to be measured and reflects it toward the second reflection mirror,
The second reflection mirror receives the laser beam and reflects it again toward the surface to be measured.
The third reflection mirror is disposed on the opposite side of the sample from the second reflection mirror, and receives the laser beam from the second reflection mirror that reflects the measurement surface again and receives again. Reflected toward the surface to be measured,
The laser light from the third reflecting mirror that reflects the measured surface reflects each reflecting mirror in the order of the second reflecting mirror and the first reflecting mirror and irradiates the measured surface again. A near-field optical microscope.

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