KR20100093415A - Near scanning photoacoustic apparatus - Google Patents

Abstract

PURPOSE: A near-field scanning photo-acoustic measure system capable of measuring photo-acoustic signals on a local domain using an optical probe for proximity field is provided to enable minute material property analysis and produce the photo-acoustic images of the high definition on a fine structure. CONSTITUTION: A near-field scanning photo-acoustic measure system(100) comprises a light-generating unit(LS), a near field optical unit(NFO), and a photo-acoustic detecting unit(PAD). The light-generating unit irradiates the light on the material to be inspected. The near field optical unit scans light from the light-generating unit to the material to be inspected or collects light transmitting the material to be inspected. The near field optical unit comprises an optical probe capable of operating in the near-field region of the material to be inspected. The detecting unit detects the photo-acoustic signal from the material to be inspected. The light-generating unit comprises a first light source and a light modulator.

Description

Near scanning photoacoustic apparatus

The present invention relates to a proximity scanning optoacoustic measuring apparatus capable of observing various physical properties and structures of a test substance with high resolution.

In recent years, with the trend of technology advancement, integration, and miniaturization, high sensitivity and high resolution of various measuring devices have become essential requirements. In particular, non-contact and non-destructive measurement technology is becoming more important.

For example, attention has been focused on overcoming the resolution limitation of optical microscopes. Optical microscopes that observe objects with light have limited resolution due to diffraction limits, which means that objects less than half the wavelength of light cannot be optically observed. Near field optical microscopes have emerged that overcome these diffraction limits and allow optical properties to be measured at levels much smaller than the wavelength.

Near-field optical microscopy allows light that passes through an aperture smaller than the wavelength of light to irradiate the test substance at a distance similar to the size of the aperture. A near field within a distance less than the wavelength of light from the surface of the test substance does not cause diffraction Will be used.

1 shows a schematic configuration of a generally known near field optical microscope 10. The near-field optical microscope 10 has an optical fiber near-field optical probe 11 attached to the crystal oscillator 13, and the crystal oscillator 13 is attached to the piezo vibrator 15 and again attached to the piezo transducer 17. Has The lock-in amplifier 18 applies a vibration signal to the piezoelectric vibrator 15, and the signal detected from the crystal oscillator 13 is fed back to the piezoelectric transducer 17 by the integration controller 19. The amount of movement of the piezoelectric translator 17 is corrected using this signal. When the near field optical probe 11 scans the surface of the test substance, the detection signal of the crystal oscillator 13 changes according to the slight change of the surface of the test substance S, and the surface of the test substance is changed by using the change of the detection signal. Precise height information can be obtained.

As a non-destructive measurement technique, research into the measurement method using photoacoustic spectroscopy has been actively conducted. When the light is periodically cut and irradiated to the sample, the electrons in the sample are excited by the incident light and heat up as a non-radiative transition when it returns to the ground state. In this way, the volume of the sample is repeatedly expanded and contracted by the heat generated, and the heat generated from the sample heats the surrounding air layer to generate periodic pressure changes in the air layer, thereby generating sound waves. By detecting this, various physical properties can be analyzed. For example, thermal and optical properties of materials, as well as geometric internal structures can be analyzed. The photoacoustic microscopy has attracted a lot of attention as it has the advantage that non-destructive inspection, which does not require pretreatment, is possible unlike SEM or TEM.

Embodiments of the present invention are to provide a near-scan photoacoustic measurement device that observes a variety of physical properties at a higher resolution using the photoacoustic effect.

An apparatus for measuring proximity scanning optoacoustic according to an embodiment of the present invention includes a light source unit for irradiating light to a test material; A near field optical unit having an optical probe capable of operating in the near field region of the test material by scanning light from the light source unit to the test material or collecting light transmitted through the test material; And an optoacoustic detection unit for detecting an optoacoustic signal from the test substance.

The light source unit may include a first light source and an optical modulator periodically modulating the light generated by the first light source, and the light modulator may be configured as a mechanical chopper.

According to an embodiment of the present invention, the light source unit comprises: a first light source unit irradiating light to the test material through an optical probe; And a second light source unit disposed opposite the optical probe with respect to the test substance.

The first light source unit may include a first modulator and an optical modulator periodically modulating the light generated by the first light source. The optical modulator includes a mechanical chopper and an acoustooptic modulator. Or a digital micromirror device (DMD).

The second light source unit may include a second light source and an objective lens for focusing light from the second light source to a test material.

The method may further include a first photodetector for detecting light reflected from the test material and / or a second photodetector for detecting light transmitted through the optical probe after passing through the test material.

The photoacoustic detection unit comprises: a sensor for detecting sound waves from the test substance as an electrical signal; And an amplifier for amplifying a signal detected from the sensor.

The sensor may be a microphone or a piezoelectric transducer.

The proximity scanning optoacoustic measuring apparatus according to the embodiment of the present invention employs an optoacoustic detection technique, and thus, an optoacoustic signal can be detected with respect to a local region of a test substance using a near field optical probe. Therefore, more accurate physical property analysis is possible, and it is possible to realize high-resolution photoacoustic images of microstructures.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals refer to the same components, and the size of each component in the drawings may be exaggerated for convenience of explanation.

2 is a conceptual block diagram of an apparatus for measuring proximity scanning optoacoustic of the present invention. Referring to the drawings, the proximity scanning optoacoustic measuring apparatus 100 includes a light source unit LS, a near field optical unit NFO, and an optoacoustic detection unit PAD.

The light source unit LS generates light to be irradiated to the test substance S. The light source unit LS may include, for example, one or more laser light sources, and may further include other optical elements for irradiating light suitable for physical properties and structures to be observed.

The near field optical unit NFO includes an optical probe configured to operate in the near field region of the test substance S. When the optical probe enters the near field region of the test substance S, the interaction between the probe and the surface of the test substance S causes a change in amplitude of the probe, thereby determining the gap between the probe and the surface of the test substance. Can be. In addition, the optical probe scans the light to the test material (S) or collects light from the test material (S), that is, the optical probe is reflected from the light or the test material (S) passing through the test material (S) Light is collected and transmitted or reflected. Such light can be analyzed to find out the optical properties of the test material (S).

The photoacoustic detection unit PAD includes a sensor that detects sound waves generated from the test material S, and analyzes the detected signal to find various physical properties of the test material S.

The proximity scanning optoacoustic measuring apparatus 100 may further include a first photodetector D1 or a second photodetector D2 to detect light from the test substance S.

In addition, the processor may further include a processor P for performing an operation required for analysis of the detected signals. The processor P uses signals detected by the near field optical unit NFO, signals detected by the optoacoustic detection unit PAD, signals detected by the first photodetector D1, and the second photodetector D2. Perform the calculations necessary for the analysis of the characteristics to be observed. In addition, the operation of the light source unit LS is controlled to irradiate light in a form suitable for the characteristic analysis to be observed with respect to the test substance S.

3 shows a schematic structure of a proximity scan optoacoustic measuring apparatus 200 according to an embodiment of the present invention. The proximity scanning optoacoustic measuring device 200 includes a light source unit, a near field optical unit, and an optoacoustic detection unit.

The light source unit includes a first light source 211 for generating light to be irradiated to the test object S and a light modulator 213 for periodically modulating the light generated by the first light source 211. Various light sources may be used to generate continuous wave or pulse laser light as the first light source 211. For example, a He-Ne laser, an Ar laser, or a He-Cd laser may be used. Can be employed. The light modulator 213 is for periodically modulating the light generated by the first light source 211. It is necessary to periodically modulate the light in the first light source 211 to form an optoacoustic signal on the test material S. For this purpose, a mechanical chopper as shown may be employed. In addition, modulators such as an acoustooptic modulator and a digital micromirror device may be employed. The modulation of the input light directly affects the optoacoustic signal, and the rotational speed of the chopper is appropriately adjusted in consideration of this. The optical modulator 213 may not be required when the pulsed laser light is generated by the first light source 211. In the optical path between the optical modulator 213 and the optical fiber 233, a collimating lens 215 may be further provided to shape the light into the optical fiber 233.

The near field optical unit has an optical probe 231 for scanning light to or from the material S. For example, the optical probe 231 may be thinned by applying heat to the optical fiber 233 or may be etched with chemicals so that one end has a size of several tens to hundreds of nanometers, and the metal film is deposited and the opening is formed. Can be made. The optical probe 231 is configured to be operated in the near field region of the test substance S. The optical probe 231 is attached to the crystal oscillator 235 attached to the piezoelectric vibrator 237 and the piezoelectric vibrator 237 is attached to the piezoelectric transducer 239. A lock-in amplifier 241 for detecting a vibration signal of the crystal oscillator 235 and an integral controller 243 for providing a feedback signal to the piezoelectric transducer 239 are provided. When the crystal vibrator 235 is vibrated at a constant frequency using the piezo vibrator 237, a signal detected from the crystal vibrator 235 changes according to a change in distance between the optical probe 231 and the test material S. The signal is detected to adjust the distance between the probe 231 and the test substance S. The detected signal is provided to the piezoelectric translator 239 as a feedback signal through the lock-in amplifier 241 and the integration controller 243, and the amount of movement of the piezoelectric translator 239 is corrected using this signal.

The optoacoustic detection unit includes a sensor for detecting the optoacoustic signal and an amplifier for amplifying the signal detected from the sensor. As a sensor for detecting the photoacoustic signal, a microphone 251 for detecting sound waves from the test substance as an electrical signal may be employed. When the light periodically modulated by the light modulator is irradiated to the test material S, the electrons in the test material S are heated by non-radiative transition when they are excited by the incident light and return to the ground state. The volume of the test material (S) is periodically expanded and contracted by the heat generated in this way, and the heat generated therein generates a periodic pressure change by heating the air layer in contact with the test material (S) on the microphone 251 side. Thus, sound waves are generated. As a structure for sensing the generated sound waves, a portion of the test material S may be provided to contact the air layer of the measurement cell 259, and the microphone 251 may detect sound waves formed in the measurement cell 259. Prepared. The arrangement form of the microphone 251, the measuring cell 259, and the test substance S is not limited to the illustrated structure, and may be changed into various forms suitable for detecting the photoacoustic signal. As the sensor for detecting the photoacoustic signal, a piezoelectric transducer or the like may be used in addition to the microphone 251. The signal detected by the microphone 251 is amplified through the preamplifier 253, and the noise is removed through the lock-in amplifier 257.

The signal from the near field optical unit or optoacoustic detection unit may be transmitted to, for example, a computer (PC) 270 so that the computation necessary for the analysis of the signal is performed and the result displayed.

By using the near-scanning photoacoustic measuring apparatus 200 having such a structure, various physical properties and structures of the test object S can be observed.

For example, it operates as a general near field optical microscope, and it is possible to observe the surface state of the test substance S in high resolution. That is, when the optical probe 231 scans the surface of the test substance S, the detection signal of the crystal oscillator 235 changes according to the slight change of the surface of the test substance S, and the change of the detection signal is used. The precise height information of the surface of the test substance S can be obtained. The optical probe 231 is moved to a range of several tens of nanometers from the test material S, and then the light is scanned on the surface of the test material S to measure the reflected light signals at each scanning point and measure the light signals. Synthesize to get a full video.

In addition, by detecting the photoacoustic signal it is possible to obtain geometric information about the internal structure of the test material (S). Depending on the internal structure of the test material (S), the absorption and reflection characteristics at the point where the light is irradiated are different, thereby changing the photoacoustic signal. It is possible to analyze the internal structure from the wavelength or modulation frequency characteristics of the incident light to generate the detected optoacoustic signal and the optoacoustic signal. For example, the presence or absence of a defect of a semiconductor material or the presence of impurities can be found. At this time, since the test material (S) is scanned through the optical probe 231 operating in the near field region, the photoacoustic signal for the local region can be detected, and the microstructure can be observed in a high resolution image.

4 shows a schematic structure of a proximity scanning optoacoustic measuring apparatus 300 according to another embodiment of the present invention. In this embodiment, the light passing through the test material S on the opposite side of the optical probe 231 to collect and analyze the light passing through the test material S through the optical probe 231 to determine the optical characteristics. There is a major difference from the embodiment of FIG. 3 in that a second light source unit for irradiating is added. The description will be made based on differences, and for the components not described, the same reference numerals will be used as described with reference to FIG. 3.

The proximity scanning optoacoustic measuring device 300 includes a light source unit, a near field optical unit, and an optoacoustic detection unit.

The light source unit includes a first light source unit for irradiating light to the test material S through the optical probe 231 and a second light source unit disposed opposite the optical probe 231 to the test material S. . The first light source unit includes a first light source 211 and a light modulator 213, which are the same as described in the embodiment of FIG. The second light source unit includes an objective lens 315 that focuses the light from the second light source 311 and the second light source 311 to the test material S. As various light sources that generate laser light to the second light source 311, a He-Ne laser, an Ar laser, or a He-Cd laser may be employed.

A beam splitter 313 for splitting light from the second light source 311 may be further provided between the second light source 311 and the objective lens 315. The light from the second light source 311 is focused on the test object S by the objective lens 315. A part of the light passes through the test material S and a part of the light is reflected from the test material S. A first photodetector 317 is provided to detect light reflected from the test material S. The optical characteristics of the test material S may be determined from the signal detected by the first photodetector 317. For example, the amount of interference light of the light reflected from the test material S and the light reflected by the optical probe 231 may be determined. By detecting the refractive index of the test material (S) can be found.

The beam splitter 217 may be further provided in the optical path through which the light from the first light source 211 travels. The beam splitter 217 branches the light passing through the test material S and transmitted through the optical probe 231 to be detected by the second photodetector 219. From the signal detected by the second photodetector 219, an optical characteristic such as an absorption rate of the test substance S may be determined.

The photoacoustic sensor (PA sensor) 252 is provided at a position where the light from the second light source 311 does not overlap with the optical path focused on the test substance S, and is, for example, the side of the measuring cell 259. Can be provided. The PA sensor 252 may be a microphone or a piezoelectric transducer, and the arrangement of the PA sensor 252, the measuring cell 259, and the test material S may be applied in various forms suitable for detecting the optoacoustic signal. Can

 The near-scanning photoacoustic measuring device 300 having such a structure is controlled to operate the first light source 211 or the second light source 311 according to a control signal input from a user to a computer, and the surface structure of the test material S It may be used as a general near-field optical microscope for observing optical properties, or may be used to observe the internal structure of the test material (S) in a high resolution image by analyzing the photoacoustic effect by the near-field scanning light.

The present inventors have been described with reference to the embodiment shown in the drawings for the purpose of understanding the near-optical photoacoustic measurement device, but this is merely illustrative, and those skilled in the art from various modifications and equivalents therefrom It will be appreciated that embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

1 shows a schematic structure of a general near field scanning optical microscope.

2 is a conceptual block diagram of an apparatus for measuring proximity scanning optoacoustic of the present invention.

3 shows a schematic structure of an apparatus for measuring proximity scanning optoacoustic according to an embodiment of the present invention.

4 shows a schematic structure of an apparatus for measuring proximity scanning optoacoustic according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

211,311 ... First and second light sources 213 ... Light modulator

215 ... collimating lens 217,313 ... beam splitter

219 ... second photodetector 231 ... optical probe

233 ... optical fiber 235 ... crystal oscillator

237 Piezo Oscillator 239 Piezo Translator

251 ... microphone 252 ... PA sensor

315 ... Objective lens 317 ... First photodetector

Claims (11)

A light source unit for irradiating light to the test substance; A near field optical unit having an optical probe capable of operating in the near field region of the test material by scanning light from the light source unit to the test material or collecting light transmitted through the test material; And a photoacoustic detection unit for detecting a photoacoustic signal from the test substance. The method of claim 1, The light source unit, A first light source; And a light modulator periodically modulating the light generated by the first light source. The method of claim 2, The optical modulator comprises one of a mechanical chopper, an optical acoustic modulator or a digital micromirror device (DMD). The method of claim 1, wherein the light source unit, A first light source unit irradiating light to the test material through the optical probe; And a second light source unit disposed opposite the optical probe with respect to the test substance. The method of claim 4, wherein The first light source unit, A first light source; And a light modulator periodically modulating the light generated by the first light source. The method of claim 5, The optical modulator comprises one of a mechanical chopper, an optical acoustic modulator or a digital micromirror device (DMD). The method of claim 4, wherein The second light source unit A second light source; And an objective lens for focusing light from the second light source onto a test material. The method of claim 4, wherein And a first photodetector for detecting an amount of light reflected from the test object by the light from the second light source. The method of claim 4, wherein And a second photodetector for detecting the amount of light transmitted through the optical probe after the light from the second light source has passed through the test substance. The method according to any one of claims 1 to 9, The photoacoustic detection unit, A sensor for detecting sound waves from the test substance as an electrical signal; And an amplifier for amplifying the signal detected from the sensor. The method of claim 10, The sensor is a proximity scanning optoacoustic measuring device consisting of a microphone (piezoelectric transducer).

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