JPH06201353A - Optical near field microscope - Google Patents

Abstract

PURPOSE:To provide an optical near field microscope capable of dividing a detected evanescent wave into surface shape information and information of physical properties and simultaneously observing a surface shape and a surface optical characteristic. CONSTITUTION:A laser beam (wavelength not absorbed in test) to acquire surface shape information of a sample 25 radiated from a light source 21 and white light to acquire surface material information of the sample 25 are composed on the same optical axis by a half mirror 23, and it is made incident so as to be totally reflected by the sample 25 connected to the surface of a prism 24. By detecting an evanescent wave leaking from the surface of the sample 25 by an optical fiber probe 26, dividing it into a monochromatic component (surface shape information) and a white light component (material information), detecting them by PM 32, 35 respectively and making them picture images, it is possible to simultaneously acquire a surface shape and a surface optical characteristic of the sample 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical near field microscope for detecting the intensity of an evanescent wave generated by irradiation of light and obtaining the surface shape and the optical characteristics of the surface.

[0002]

2. Description of the Related Art Generally, it is known that the resolution of an optical microscope is limited by the diffraction limit and has a value comparable to the wavelength. However, even in the light wave region, it is possible to exceed the diffraction limit by using an evanescent wave (tunnel effect of photons) and a probe having a minute aperture.
A system constructed based on this concept is an optical near field microscope. FIG. 3 shows the basic principle of the conventional optical near-field microscope, and FIG. 4 shows the relationship between the light intensity and the probe-sample distance for explanation.

In this optical near-field microscope, the laser light emitted from the semiconductor laser 1 is incident on the prism 2. A sample 3 is placed on the prism 2, and the laser light is reflected by the bottom surface of the sample, and at that time, evanescent light is generated on the upper part of the sample. This evanescent wave is captured by the optical fiber probe 4 having a minute aperture.

That is, assuming that the surface direction of the sample 3 is the xy axes and the direction perpendicular to the boundary surface is the z axis, the normal direction z <on the surface of the sample 1 under the condition that the laser light is totally reflected. Considering in the near field of <λ (wavelength of light λ), the amplitude decreases exponentially in the z-axis direction, and evanescent light is generated.

When this light is regarded as a photon and the mechanism of generation is interpreted, the photon is out of the sample due to the tunnel effect depending on the height of the potential barrier of the photon confinement determined by the value of the refractive index of the two media. It is presumed that this is a phenomenon that seeps out.

The observation probability of such tunneling photons decays exponentially as z increases.
High vertical resolution can be obtained. The photon field is destructively measured by a probe having an aperture diameter (a) smaller than the light wavelength, and the measurement error of the photon momentum is Δp = hk / 2π · Δλ / λ = h / a. The minimum uncertainty of the position measurement of the photon detected at the aperture due to this error is Δx = a / 2π

Therefore, a high lateral resolution determined by the aperture diameter a can be obtained. That is, while the conventional optical microscope has a resolution according to the uncertainty principle based on the diffraction effect, the lateral resolution is determined here by scanning the photon position using a probe having a minute aperture. Next, a basic device of a conventional transmission type near-field microscope is shown in FIG. 5 and explained.

In this near-field microscope, the monochromatic laser light emitted from the semiconductor laser 1 is made incident on the prism 2 at an angle for total reflection. At this time, the prism 2
It is assumed that the sample 3 placed on the prism is bonded to the surface of the prism.

By the incidence of the laser light, an evanescent wave depending on the surface shape is generated from the surface of the sample 3. This evanescent wave is detected by the optical fiber probe 4 having a minute aperture. The optical fiber probe 4 is held by a piezoelectric actuator 5 for three-dimensional (XYZ) fine movement. By applying an XY scanning signal, which will be described later, to the piezoelectric actuator 5 for fine movement of the XY axes, the optical fiber probe 4 is moved to the XY plane. Scan inside. The piezoelectric actuator 5 is attached to a coarse movement stage 6 for optical probe approach.

The evanescent wave detected by the optical fiber probe 4 is an interference filter 7a, a photomultiplier (PM) 7b and a current-voltage conversion amplifier 8.
Photoelectric conversion is performed by the photodetector unit constituted by and output to the probe position control feedback circuit 9.

The probe position control feedback circuit 9 comprises a fine movement mechanism controller (PZT controller) 10 and an optical probe / auto approach controller 11.

The probe position control feedback circuit 9 applies a drive signal to the Z-axis piezoelectric actuator 5 so as to make the intensity of the evanescent light detected by the optical fiber probe 4 constant, and controls the probe-sample. Keep the distance between them constant. As a result obtained in this way, by imaging the Z-axis control voltage of the piezoelectric actuator 5 (information on the unevenness of the sample surface),
The shape of the sample surface is observed.

[0013]

In the above-mentioned conventional optical near-field microscope, monochromatic light (wavelength region where the sample does not absorb) is incident on the sample, and the evanescent wave emitted from the sample surface is detected to detect the surface. We are observing the shape. But with this optical near-field microscope,
Since the monochromatic light is incident, it is not possible to evaluate the optical properties of the sample such as the spectral characteristics of the sample.

Furthermore, in the light in the wavelength region where the optical properties of the sample are observed, the intensity of the evanescent wave emitted from the sample surface includes information on the shape of the sample surface and physical property information, and the obtained evanescent wave is obtained. It was difficult to control the position between the probe and the sample only from the wave intensity.

Therefore, an object of the present invention is to provide an optical near-field microscope that separates the detected evanescent wave into surface shape information and physical property information, and at the same time, can observe the surface shape and the optical characteristics of the surface.

[0016]

In order to achieve the above object, the present invention provides a prism for holding a sample, a first light source for irradiating laser light in a predetermined wavelength region, and a second light source for irradiating white light. A light source, a means for synthesizing the respective optical axes of the laser light and the white light into the same optical axis, and causing the prism to enter the prism under a condition satisfying a total reflection angle, and a tip of a minute aperture for taking in an evanescent wave emitted from the sample. An optical fiber probe, an optical component separating means for separating an evanescent wave from the optical fiber probe into a laser light component and a white light component, and a first photodetector for photoelectrically converting the intensity of the evanescent wave of the laser light component to detect it. Means, a second light detecting means for photoelectrically detecting the intensity of the evanescent wave of the white light component, and a signal from the first light detecting means, and the optical fiber The probe movement means for scanning the probe in the XY directions and for controlling the position in the Z direction so as to keep the distance between the fiber probe and the sample constant, and the signal from the second photodetection means forms an image as sample surface information. An optical near-field microscope including a display means is provided.

[0017]

With the optical near-field microscope configured as described above, a monochromatic laser beam (a wavelength that does not absorb light over the entire sample) for observing the shape of the sample surface and a white color for detecting physical property information on the sample surface are used. The evanescent waves leaking from the sample surface are combined into a monochromatic light component (surface shape) by synthesizing so that the optical axes of the light and the light are the same optical axis, and are incident on the sample bonded to the prism surface at an incident angle that satisfies the total reflection angle. information)
And the white light component (physical property information) are separated, the unevenness information of the sample surface is imaged, and the surface shape and the optical characteristics of the surface are observed.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows the configuration of an optical near-field microscope as a first embodiment according to the present invention, which will be described.

In this optical near-field microscope, a light source 21 for irradiating a laser beam (semiconductor laser beam) in a wavelength region where the sample does not absorb, that is, a near infrared region, and a sample having characteristic absorption of the sample, such as optical absorption, are peculiar to the sample. And a light source 22 that emits white light for observing the optical properties of The laser light emitted from each of the light sources 21 and 22 and the white light are combined by the half mirror 23 so as to be on the same axis,
The combined light is incident on the sample 25 mounted on the prism 24 at an angle at which the combined light is totally reflected. Above the sample 25, in order to detect the evanescent wave emitted from the sample 25, an optical fiber probe 26 having a tip of a minute aperture is provided.

The optical fiber probe 26 has X, Y
It is supported by a piezoelectric actuator (PZT) 27 that performs scanning and fine movement in the Z direction. The piezoelectric actuator 27 is mounted on the XYZ coarse movement stage 28.

Then, a fine movement mechanism controller (PZT controller) 2 for servo-controlling the applied voltage that finely moves in the Z-axis direction so that the intensity of the evanescent wave detected through the optical fiber probe 26 becomes constant.
9 is provided to keep the distance between the optical fiber probe 26 and the sample 25 constant.

Evanescent wave (combined light of laser light and white light) emitted from the optical fiber probe 26.
Is separated into a laser light component and a white light component by the optical filter 30 that transmits only the white light component.

The laser light component separated by the optical filter 30 enters the photomultiplier (PM) 32 through the interference filter 31, and the photomultiplier (PM) 32 intensifies the laser light component. In response to this, an output that is position information of the optical fiber probe 26 is output to the PZT controller 29. Next, the white light component is incident on the detector and photoelectrically converted into an electric signal.

That is, the white light component is incident on the monochromator (spectrometer) 34 for photoelectric conversion and signal amplification via the optical filter (cut filter, bandpass filter, etc.) 33. The light whose wavelength is selected by the monochromator 34 is supplied to a photomultiplier (PM) 35.
And is photoelectrically converted by a built-in photomultiplier tube.
Then, the photoelectrically converted output is the photon counting unit (Phot
It is amplified by an ocurrent detector 37, A / D converted, and taken into a host computer 38. The monochromator 34 is drive-controlled by an MC scan controller 36 driven by a control signal from the host computer 38. Then, the optical spectrum is observed by measuring the intensity of the evanescent wave while performing the wavelength scan of the monochromator 34 at a desired measurement point on the sample 25.

The host computer 38 has
For example, a CRT for imaging the applied voltage for finely moving the piezoelectric actuator (PZT) 27 in the Z-axis direction when the optical fiber probe 26 is scanned in the XY plane or the evanescent wave intensity as information on the surface of the sample 25. A display system 39 for the like is provided. The measurement operation will be described with the optical near-field microscope configured as described above.

First, the sample 25 is irradiated with near-infrared laser light which is not absorbed by the sample 25 from the light source (semiconductor laser) 21, passes through the half mirror 23, and is incident on the prism 24 at an incident angle that satisfies the condition of total reflection. The sample 25, which is in close contact with the upper surface of the prism 24, is irradiated. Here, the laser light selects a wavelength whose optical characteristics are constant over the entire region of the sample, that is, the evanescent wave intensity leaking from the sample depends on the difference in the optical properties of the minute region of the sample. Instead, a wavelength that depends only on the uneven shape of the sample surface is selected.

The white light for observing the optical characteristics (optical spectrum, etc.) of the surface of the sample 25 is reflected by the half mirror 23 and made incident on the prism 24 with the same optical axis as the laser light.

When light is incident on the prism 24 so as to satisfy the condition of total reflection, the evanescent wave (laser light component + white light component) leaking from the surface of the sample 25 due to an optical tunneling phenomenon is It is detected by the optical fiber probe 26 having a minute aperture.

The evanescent light that has entered the optical fiber probe 26 is emitted from the outlet of the optical fiber probe 26, and separated into a laser light component and a white light component by the optical filter 30.

The laser light component is photoelectrically converted by the photomultiplier 32 through the optical interference filter 31 that selectively transmits only the wavelength of the laser light, and only the evanescent wave component depending on the shape of the sample surface is obtained. Is detected as an electrical signal.

The position of the optical fiber probe 26 is controlled by the electric signal so as to keep the intensity of the laser light component of the evanescent wave constant while scanning the optical fiber probe in the XY plane, and the shape of the sample surface is controlled. And scanned to obtain surface shape information.

The white light component is photoelectrically converted by the photomultiplier 35 through the optical filter 33 which transmits the white light component (visible portion) and does not transmit the laser light component (near infrared). It

That is, at a given measurement point in the XY plane of the sample 25, a state in which the distance between the optical fiber probe 26 and the surface of the sample 25 is kept constant by the laser light (the intensity of the evanescent wave by the laser light). Is kept constant), and the photomultiplier 35 is wavelength-driven to measure the optical spectrum at each point, whereby optical physical property information of the sample can be obtained.

By measuring the optical spectrum of the sample 25 at any measurement point, the distribution of the optical characteristics on the surface of the sample 25 can be observed. That is, since the probe position is controlled so that the distance between the probe and the sample is kept constant, the original optical characteristics of the sample can be observed without depending on the sample-probe distance.

Therefore, by simultaneously observing the laser light component of the evanescent wave (information about the surface shape) and the white light component (information about the optical properties), the surface shape of the sample and the spectrum data at each point are displayed as image data. can do. For example, by mapping the intensity of the white light component of the evanescent wave at a specific wavelength as image data and displaying it by superimposing it on the unevenness shape data (laser light component), information regarding the correlation between the unevenness shape and optical physical properties is displayed. Is obtained.

By displaying the optical spectrum of each point on one line at the same time as the concavo-convex shape, it is possible to analyze the structure of a substance from both the geometrical structure, the electronic state, and the vibrational state (optical spectrum). it can.

Next, FIG. 2 shows the structure of an optical near-field microscope as a second embodiment according to the present invention, which will be described. Here, the members of the second embodiment which are the same as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the second embodiment, the detection unit consisting of the monochromator 34 and the photomultiplier (photomultiplier tube) 35 in the first embodiment is a spectroscope using a polychromator 40 and a one-dimensional line. The combination of the sensor (one-dimensional photodiode array) 41 enables immediate measurement of the spectrum of the white light component of the evanescent wave at each point on the sample.

The evanescent wave incident on the polychromator 40 through the optical filter 33 disperses the light dispersed by the built-in diffraction grating without passing through the slit.
By detecting with the one-dimensional line sensor 41, the optical spectrum of the evanescent wave can be observed without wavelength driving.

Since it is possible to immediately observe the spectrum at each point on the sample, it becomes possible to map the optical characteristics on the sample surface in a short time. It is particularly suitable when the spectrum of the optically unstable sample surface must be measured in a short time. However, the system in which the polychrometer 40 and the line sensor 41 are combined in this way is different from the system in which the monochromator 34 and the photomultiplier 35 of the first embodiment are combined.
Wavelength resolution and light detection sensitivity are slightly inferior.

Therefore, in the case of detecting a very weak evanescent wave or in the case of observing the fine structure of the optical spectrum (requiring wavelength resolution), the configuration of the first embodiment is suitable. Further, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and applications can be made without departing from the scope of the invention.

[0042]

As described in detail above, according to the present invention, an optical near-field microscope capable of separating a detected evanescent wave into surface shape information and physical property information and at the same time observing the surface shape and the optical characteristics of the surface. Can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical near-field microscope as a first embodiment according to the present invention.

FIG. 2 is a diagram showing a configuration of an optical near-field microscope as a second embodiment according to the present invention.

FIG. 3 is a diagram for explaining the basic principle of a conventional optical near-field microscope.

FIG. 4 is a diagram showing a relationship between a light intensity and a probe-sample distance.

FIG. 5 is a diagram showing a basic device of a conventional transmission type near-field microscope.

[Explanation of symbols]

1 ... Semiconductor laser, 2, 24 ... Prism, 3, 25 ... Sample, 4, 26 ... Optical fiber probe, 5, 27 ... Piezoelectric actuator (PZT), 6, 28 ... Optical probe approach coarse movement stage (XYZ coarse movement) Stage), 7
a, 31 ... Interference filter, 7b, 32, 35 ... Photomultiplier (PM), 8 ... Current-voltage conversion amplifier, 9 ...
Feedback circuit for probe position control 10, 29 ...
Fine movement mechanism controller (PZT controller), 11
… Optical probe / auto approach controller, 1
2, 38 ... Host computer 21, 22 ... Light source, 2
8 ... XYZ coarse movement stage, 30, 33 ... Optical filter,
34 ... Monochromator (spectrometer), 36 ... MC scan controller, 37 ... Photon counting unit (Photocurrent
detector), 39 ... Display system, 40 ... Polychrometer, 4
1 ... (one-dimensional) line sensor.

Claims (1)

[Claims] 1. A prism for holding a sample, a first light source for irradiating laser light in a predetermined wavelength region, a second light source for irradiating white light, and the same optical axis for each of the laser light and white light. Synthesize on the optical axis,
Means for allowing the prism to enter under a condition that satisfies a total reflection angle, an optical fiber probe having a tip of a minute aperture for capturing an evanescent wave emitted from the sample, a laser light component and a white light component for the evanescent wave from the optical fiber probe A first light detecting means for photoelectrically converting and detecting the intensity of the evanescent wave of the laser light component; and a second light detecting means for photoelectrically converting the strength of the evanescent wave of the white light component. A light detecting means, and a probe moving means for performing scanning in the XY directions of the optical fiber probe and position control in the Z direction so as to keep a distance between the fiber probe and the sample constant by a signal from the first light detecting means, Display means for forming an image as sample surface information by a signal from the second light detecting means. Optical near-field microscope, wherein the door.