JP2005283162A - Reflection type near-field light detection optical system and reflection type near-field optical microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type near-field light detection optical system and a reflection type near-field optical microscope capable of detecting with high sensitivity a fine change of reflected light intensity, polarization, a phase or the like caused by an observation object, while keeping high resolution and heightening the sensitivity. <P>SOLUTION: This microscope is equipped with this reflection type near-field light detection optical system 80 comprising a laser light source 30 for emitting measuring laser light Lin; an optical aperture probe 20 for generating near-field light and allowing the light to enter the surface of an observation object 90, guiding from an optical aperture 22 reflected light LR2 from the observation object 90, and emitting through a rear end side aperture 21 detection light LRout including an interference component of the reflected light LR2 from the observation object 90 guided from the optical aperture 22; a solid vibrator 60 for changing periodically the relative distance between the tip of the optical aperture probe 20 and the observation object 90; and a lock-in amplifier 50 for detecting the interference component of each reflecting film included in the detection light LRout synchronized with a changing period of the relative distance between the tip of the optical aperture probe 20 and the observation object 90 given from the solid vibrator 60. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reflective near-field light detection optical system and a reflective near-field optical microscope that measure surface information, optical information, and the like of a sample using near-field light.

  In recent years, near-field light has attracted attention as a new condensing method that breaks the limit of detection resolution of a condensing system using a normal optical lens. Near-field light is a non-propagating electromagnetic field (evanescent field) formed in the vicinity of a minute optical aperture.

  The minute optical aperture is provided in the light emitting portion of the optical probe, and the periphery of the optical aperture is preferably covered with a reflector. This is to prevent leakage light from a portion other than the opening from entering the subject. When the subject surface is placed close to the evanescent field, propagating scattered light is generated by the near-field interaction. Since the intensity or phase of the scattered light bears optical information on the subject surface, information on the subject surface can be obtained by a normal detection means.

  The resolution when using near-field light is determined by the size of the evanescent field. For example, when the tip of the optical fiber is narrowed down and the tip is covered with a reflector such as metal while leaving the optical aperture of several tens of nm, the resolution can be several tens of nm, which is the same as the optical aperture. For this reason, the resolution is remarkably improved as compared with a condensing system using a conventional objective lens (for example, see Patent Document 1).

JP 2002-340774 A

  However, since the spatial resolution of a near-field optical microscope is determined by the size of the aperture, it is necessary to reduce the aperture in order to increase the resolution. However, if the aperture is reduced, the amount of light that can be detected is drastically reduced. It becomes difficult.

  On the other hand, in order to increase the contrast of the optical microscope, a laser microscope and an optical heterodyne laser microscope, which is a further development of it, were created. Although it has become possible to observe unevenness of the material surface with good contrast, the spatial resolution is comparable to that of an optical microscope because it is limited to the diffraction limit.

  Near-field optical microscopes have high resolution but poor contrast, while laser microscopes have high contrast but poor spatial resolution. Until now, high resolution and high contrast were not compatible. In order to achieve both of these, since the laser microscope cannot limit the resolution further due to the limitation due to the diffraction limit, it is necessary to increase the sensitivity while maintaining the high resolution of the near-field optical microscope.

  Therefore, in view of the conventional problems as described above, the object of the present invention is to increase sensitivity while maintaining high resolution, and to detect minute changes in reflected light intensity, polarization, phase, etc. depending on the observation object with high sensitivity. It is an object of the present invention to provide a reflection type near-field light detection optical system and a reflection type near-field optical microscope.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  In the present invention, for example, an aperture-type near-field optical microscope is used in a local illumination-collection mode, and light returning from the probe tip is converted into an electrical signal by a photodetector, and then a lock-in amplifier. For detection, the relative distance between the probe tip and the observation target is periodically changed to modulate the weak reflected signal light from the observation target that is collected through the opening at the probe tip. Then, a signal component synchronized with this modulation frequency or twice the frequency is detected.

  The light returning from the probe tip is mixed with weak signal light due to the near field near the aperture and strong reflected light (= reference light) from the reflection surface of the aperture formed at the probe tip. The optical interference between the signal light and the reference light occurs. When only the signal light changes slightly with the vibration of the probe, the change is greatly amplified by the optical interference with the reference light, so that the signal light can be detected with high sensitivity.

  The reflective near-field light detection optical system according to the present invention includes a laser light source that emits measurement laser light, an optical opening having a diameter shorter than the wavelength of the measurement laser light at the tip, and a reflective surface around the optical aperture. The measurement laser light input through the rear end side opening is generated to generate near-field light from the optical opening and enter the surface of the observation target, and the observation target Is reflected from the reflection surface of the measurement laser light guided from the rear end side and from the observation object guided from the optical opening. An optical aperture probe for emitting detection light including an interference component of reflected light through the rear end side opening, a vibration applying means for periodically changing the relative distance between the tip of the optical aperture probe and the observation target, and the optical Exit from the rear end opening of the aperture probe Photoelectric conversion means for receiving the detected detection light and converting it into an electrical signal, and the tip of the optical aperture probe provided by the vibration applying means and the observation object by synchronously detecting the electrical signal obtained by the photoelectric conversion means And a synchronous detection means for detecting an interference component of each reflected light included in the detection light synchronized with the change period of the relative distance to the detection distance.

  In the reflection-type near-field light detection optical system according to the present invention, the vibration applying unit includes, for example, a solid vibrator that vibrates the tip of the optical aperture probe in a direction intersecting the axial direction.

  In the reflective near-field light detection optical system according to the present invention, the vibration applying means is, for example, a solid vibrator that vibrates the tip of the optical aperture probe in the axial direction.

  Furthermore, the reflective near-field optical microscope according to the present invention includes a laser light source that emits a measurement laser beam, an optical opening having a diameter shorter than the wavelength of the measurement laser beam at the tip, and a reflective surface around the optical aperture. The measurement laser light input through the rear end side opening is generated to generate near-field light from the optical opening and enter the surface of the observation target, and the observation target Is reflected from the reflection surface of the measurement laser light guided from the rear end side, and from the observation object guided from the optical opening. An optical aperture probe for emitting detection light including an interference component of reflected light through the rear end side opening, a vibration applying means for periodically changing the relative distance between the tip of the optical aperture probe and the observation target, and the optical Is it the rear end opening of the aperture probe? A photoelectric conversion means for receiving the detected detection light and converting it into an electric signal, and an observation of the tip of the optical aperture probe provided by the vibration applying means by synchronous detection of the electric signal obtained by the photoelectric conversion means A reflection type near-field light detection optical system comprising a synchronous detection means for detecting an interference component of each reflected light included in the detection light synchronized with a change period of a relative distance to a target is provided.

  In the present invention, by changing the relative distance between the probe tip and the observation target periodically, the weak reflected signal light from the observation target collected through the opening of the probe tip is modulated, and this weak signal is applied. Using the interference between the reflected signal light and the light reflected by the reflection surface around the optical aperture provided at the probe tip (reference light), the intensity, polarization, or phase of the weak reflected signal light is slight. The shift can be amplified and detected with high sensitivity.

  In the present invention, the signal intensity in the conventional reflective near-field optical microscope can be increased by 2 to 3 digits with a simple optical arrangement, and the nanoscale microstructure on the surface to be observed and the high refractive index distribution are high. Sensitivity detection can be realized, and by applying the present invention to reading of the next generation optical disc, an ultra-high density optical disc can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  The present invention is applied to, for example, a reflective near-field optical microscope 100 configured as shown in FIG.

  The reflection near-field optical microscope 100 includes an observing object 90 mounted thereon, a piezo stage 10 capable of moving in the order of nanometers in three axis directions, and an observing object 90 mounted on the piezo stage 10. An optical aperture probe 20 disposed so that the tip portion is positioned near the surface, and a laser light source 30 that emits the measurement laser light Lin that irradiates the surface of the observation object 90 are emitted from the laser light source 30. The measured laser beam Lin is input to the optical aperture probe 20 from the rear end side opening 21 of the optical aperture probe 20 via the reflecting mirror 31 and the beam splitter 32.

  The piezo stage 10 is connected to a computer 12 via a stage controller 11. The stage controller 11 arbitrarily moves the piezo stage 10 in the X-axis direction, the Y-axis direction, and the Z-axis direction based on the control by the computer 12.

  The optical aperture probe 20 has a structure in which an optical aperture 22 having a diameter shorter than the wavelength of the laser beam for measurement Lin is provided at the tip of a tapered portion having a tapered reflecting surface 23 that is sharpened. The measurement laser light Lin is input through the fiber coupler 21A provided in the rear end side opening 21, and the detection light LRout is output. Here, in this embodiment, the tapered reflecting surface 23 that is sharpened is formed by the metal reflecting film 23A, but the measurement laser light Lin input from the rear end side opening 21 is sharpened at the tip. The metal reflection film 23A may be an air layer or the like as long as it is reflected by a portion around the optical opening 23 at the tip.

  As schematically shown in FIG. 2, the optical aperture probe 20 guides the measurement laser light Lin inputted through the fiber coupler 21A to generate near-field light from the optical aperture 22. The reflection surface of the measurement laser light Lin incident on the surface of the observation object 90 and guided from the optical aperture 22 through the reflected light LR2 from the observation object 90 and guided from the rear end side. The detection light LRout including the interference component of the reflected light LR1 by the light 23 and the reflected light LR2 from the observation object 90 guided from the optical aperture 22 is emitted through the fiber coupler 21A.

  As the laser light source 30, for example, a He—Ne laser is used.

  The reflection near-field optical microscope 100 further includes a photodetector 40 to which the detection light LRout emitted through the fiber coupler 21A is input through the beam splitter 32. The light detector 40 receives the detection light LRout and outputs a detection signal SD having a signal level corresponding to the light intensity of the detection light LRout to the lock-in amplifier 50.

  Further, the reflection near-field optical microscope 100 includes a solid vibrator 60 that periodically changes the relative distance between the tip of the optical aperture probe 20 and the surface of the observation object 90. The solid vibrator 60 is made of, for example, a tuning fork crystal and is driven by a tuning fork driver 61 configured by an oscillation circuit so as to vibrate the tip of the optical aperture probe 20 at a frequency f in a direction intersecting the axial direction. It has become.

  The tuning fork driver 61 moves the piezo stage 10 in the Z-axis direction by the stage controller 11, and the atomic force generated when the tip of the optical aperture probe 20 approaches the surface of the observation object 90 The oscillation output level changes. The change in the oscillation output level is taken out by a filter (not shown) and fed back to the stage controller 11 as a shear force control signal SHC, so that the distance between the tip of the optical aperture probe 20 and the surface of the observation object 90 is constant. It is controlled to become.

  The tuning fork driver 61 supplies an oscillation output, that is, an oscillation signal that vibrates at the oscillation frequency of the solid vibrator 60, to the lock-in amplifier 50 as a reference signal Fref.

  In the reflective near-field optical microscope 100 having such a configuration, the tip of the optical aperture probe 20 and the observation object 90 are vibrated by vibrating the tip of the optical aperture probe 20 in a direction intersecting the axial direction at a frequency f. Therefore, the reflected light LR2 from the observation object 90 guided from the optical aperture 22 is modulated at the frequency f. Become.

  The optical aperture probe 20 includes the reflected light LR1 reflected by the reflection surface 23 of the measurement laser light Lin guided from the rear end side, and the observation object 90 guided from the optical aperture 22. The detection light LRout including the interference component of the reflected light LR2 modulated at the frequency f is emitted through the fiber coupler 21A.

  Then, the lock-in amplifier 50 has a vibration level f of the solid vibrator 60 provided by the tuning fork driver 61 with a detection signal SD having a signal level corresponding to the light intensity of the detection light LRout obtained by the photodetector 40. By performing synchronous detection with the reference signal Fref, only the signal component synchronized with the vibration frequency f, that is, the signal component amplified by the phase shift between the reflected light LR1 and the reflected light LR2, is extracted as the measurement signal MS. The signal MS is supplied to the computer 12 via the stage controller 11.

  The computer 12 moves the piezo stage 10 in the x-axis direction and the Y-axis direction, and scans the surface of the observation object 90 on the piezo stage 10 with the tip of the optical aperture probe 20, thereby observing the observation. As the surface information of the object 90, the measurement signal MS obtained by the lock-in amplifier 50 is stored, and for example, an image based on the measurement signal MS is displayed on the monitor screen.

  That is, the reflective near-field optical microscope 100 includes a laser light source 30 that emits the measurement laser beam Lin, an optical opening 22 having a diameter shorter than the wavelength of the measurement laser beam Lin, and a reflection that covers the periphery thereof. A surface 23 is provided, and the measurement laser light Lin input through the rear end side opening 21 is guided to generate near-field light from the optical opening 22 so that the observation object 90 Reflected light LR1 incident on the surface and reflected by the reflecting surface 23 of the measurement laser light Lin guided from the optical opening 22 and reflected from the observation object 90 from the optical aperture 22 An optical aperture probe 20 that emits the detection light LRout including the interference component of the reflected light LR2 from the observation object 90 guided from the optical aperture 22 through the rear end side aperture 21, and the optical aperture The solid vibrator 60 that periodically changes the relative distance between the tip of the probe 20 and the observation object 90 and the detection light LRout emitted from the rear end side opening 21 of the optical aperture probe 20 are received as electrical signals. The optical detector 40 to be converted, and the tip of the optical aperture probe 20 provided by the solid vibrator 60 and the observation object 90 are detected by synchronous detection of the electrical signal obtained as the detection signal SD by the photodetector 40. A reflective near-field light detection optical system 80 including a lock-in amplifier 50 that detects interference components of the reflected lights LR1 and LR2 included in the detection light LRout in synchronization with a change period of the relative distance of the first and second light beams.

  Here, by using the optical aperture probe 20 having an aperture diameter of 40 nm, the tip of the optical aperture probe 20 is vibrated at a frequency f in a direction intersecting the axial direction, and the detection output is synchronously detected at the frequency f. 3A and 3B show the results of observing a diffraction grating (3600 lines / mm) as the observation object 90 by the method and the conventional method of measuring the detection output as it is.

  In the conventional method, as shown in FIG. 3B, the diffraction grating is not confirmed because it is buried in noise, but the tip of the optical aperture probe 20 is vibrated at a frequency f in a direction intersecting the axial direction. According to the method of the invention, as shown in FIG. 3A, the diffraction grating could be clearly observed without being buried in noise.

  Here, in the reflective near-field optical microscope 100 described above, in order to obtain a shear force control signal SHC for controlling the distance between the tip of the optical aperture probe 20 and the surface of the observation object 90 to be constant. Tuning that also serves as vibration applying means for applying minute vibration to the tip of the optical aperture probe 20 and vibration applying means for modulating the reflected light LR2 from the observation object 90 guided from the optical opening 22 The tip of the optical aperture probe 20 is vibrated in a direction crossing its axial direction using a solid vibrator 60 made of a fork crystal. The vibration applying means for obtaining the shear force control signal SHC, and the observation In order to modulate the reflected light LR2 from the object 90, the vibration applying means can be individual.

  Further, the vibration applying means for modulating the reflected light LR2 from the observation object 90 has the tip of the optical aperture probe 20 in the axial direction as in, for example, the reflective near-field optical microscope 200 shown in FIG. You may make it vibrate.

  The reflection-type near-field optical microscope 200 shown in FIG. 4 obtains a shear force control signal SHC for controlling the distance between the tip of the optical aperture probe 20 and the surface of the observation object 90 to be constant. A piezo element 260 for applying a minute vibration to the tip of the optical aperture probe 20, a piezo driver 261 for driving the piezo element 260, and a minute vibration applied to the tip of the optical aperture probe 20 by the piezo element 260 are detected. Further, a semiconductor laser 262 that irradiates a laser beam on the metal reflecting film 23A covering the tip of the optical aperture probe 20 from the outer peripheral side, a photodetector 263 that receives and detects the reflected light from the metal reflecting film 23A, and this light A lock-in amplifier 264 to which a detection signal from the detector 263 is supplied, and the observation guided from the optical aperture 22 Comprising a solid vibrator 160 consisting of the tuning fork crystal to modulate the reflected light LR2 from elephant 90.

  The lock-in amplifier 264 is supplied with a drive signal of the piezo element 260 from a piezo driver 261 that drives the piezo element 260 as a reference signal, and the detection signal SD of the photodetector 263 is synchronously detected by the reference signal. The shear force control signal SHC obtained by doing so is fed back to the stage controller 11.

  In the reflective near-field optical microscope 200, the vibration direction of the solid vibrator 160 coincides with the axial direction (z direction) of the optical aperture probe 20, and the tip of the optical aperture probe 20 is in the axial direction. Then, the reflected light LR2 from the observation object 90 is modulated at the frequency f.

  The other components in the reflective near-field optical microscope 200 are the same as those in the reflective near-field optical microscope 100 described above, and thus the same reference numerals are given in FIG.

  Here, in the reflective near-field optical microscope 100 and the reflective near-field optical microscope 200 described above, the tip of the optical aperture probe 20 is vibrated at the frequency f by the solid vibrators 60 and 160 made of tuning fork crystals. However, a piezo element may be used instead of the tuning fork crystal. In addition, the relative distance between the tip of the optical aperture probe 20 and the observation object 90 may be periodically changed. Instead of vibrating the tip of the optical aperture probe 20, the piezo stage 10 is vibrated. Also good.

It is a block diagram which shows the structure of the reflection type near field optical microscope to which this invention is applied. It is sectional drawing which shows typically the structure of the front-end | tip part of the optical aperture probe in the said reflection type near field optical microscope. Using the optical aperture probe 20 with an aperture diameter of 40 nm, the tip of the optical aperture probe is vibrated at a frequency f in the direction intersecting the axial direction, and the conventional method that does not vibrate is used as an observation object. It is a figure which shows the result of having observed the diffraction grating (3600 piece / mm). It is a block diagram which shows the other structural example of the reflection type near field optical microscope to which this invention is applied.

Explanation of symbols

  10 piezo stage, 11 stage controller, 12 computer, 20 optical aperture probe, 21 rear end side aperture, 21A fiber coupler, 22 optical aperture, 23 reflective surface, 23A metal reflective film, 30 laser light source, 31 reflective mirror, 32 beam splitter , 40 photodetector, 50 lock-in amplifier, 60,160 solid state oscillator, 61 tuning fork driver, 80 reflective near-field light detection optical system, 90 observation object, 100, 200 reflective near-field optical microscope, 260 piezo Element, 261 piezo driver, 262 semiconductor laser, 263 photodetector, 264 lock-in amplifier, Lin measurement laser light, LRout detection light, LR1, LR2 reflected light, SD detection signal, Fref reference signal, SHC shear force control signal, MS measurement signal

Claims (4)

A laser light source for emitting measurement laser light;
It has a structure in which an optical opening having a diameter shorter than the wavelength of the laser beam for measurement at the front end and a reflective surface around it are provided, and guides the laser beam for measurement input through the rear end side opening. The near-field light is generated from the optical aperture and incident on the surface of the observation target, and the reflected light from the observation target is guided from the optical aperture and guided from the rear end side. An optical aperture probe that emits detection light including reflected light from the reflection surface of laser light and an interference component of reflected light from the observation object guided from the optical aperture through the rear end side aperture;
Vibration applying means for periodically changing the relative distance between the tip of the optical aperture probe and the observation target;
Photoelectric conversion means for receiving detection light emitted from the rear end side opening of the optical aperture probe and converting it into an electrical signal;
By synchronously detecting the electrical signal obtained by the photoelectric conversion means, each reflection included in the detection light synchronized with the change period of the relative distance between the tip of the optical aperture probe and the observation target given by the vibration applying means. A reflective near-field light detection optical system, comprising: a synchronous detection unit that detects an interference component of light.   2. The reflection type near-field light detection optical system according to claim 1, wherein the vibration applying means comprises a solid vibrator that vibrates the tip of the optical aperture probe in a direction crossing the axial direction.   2. The reflection type near-field light detection optical system according to claim 1, wherein the vibration applying means comprises a solid vibrator that vibrates the tip of the optical aperture probe in the axial direction. A laser light source for emitting measurement laser light;
It has a structure in which an optical opening having a diameter shorter than the wavelength of the laser beam for measurement at the front end and a reflective surface around it are provided, and guides the laser beam for measurement input through the rear end side opening. The near-field light is generated from the optical aperture and incident on the surface of the observation target, and the reflected light from the observation target is guided from the optical aperture and guided from the rear end side. An optical aperture probe that emits detection light including reflected light from the reflection surface of laser light and an interference component of reflected light from the observation object guided from the optical aperture through the rear end side aperture;
Vibration applying means for periodically changing the relative distance between the tip of the optical aperture probe and the observation target;
Photoelectric conversion means for receiving detection light emitted from the rear end side opening of the optical aperture probe and converting it into an electrical signal;
By synchronously detecting the electrical signal obtained by the photoelectric conversion means, each reflection included in the detection light synchronized with the change period of the relative distance between the tip of the optical aperture probe and the observation target given by the vibration applying means. A reflective near-field optical microscope comprising a reflective near-field light detection optical system comprising synchronous detection means for detecting an interference component of light.

Images