JP2006215004A - Near-field light microscope, sample measurement method using near-field light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a near-field light microscope capable of preventing damage caused by collision of a probe with a sample and allowing the probe to approach the sample reliably and in a short time.
SOLUTION: Distance detection means 31 for detecting the distance from the tip of the near-field optical probe 2 to the sample, and the near-field optical probe 2 and the sample 20 based on the reference surface position information of the near-field optical probe 2 Alternatively, a near-field light microscope including distance control means 15 for approaching the vicinity thereof.
[Selection] Figure 3

Description

  The present invention relates to a scanning near-field light microscope and a sample measurement method using near-field light. In particular, the measurement time is shortened to increase efficiency, and the probe is prevented from being damaged to avoid high cost. The present invention relates to a technique that can achieve a great effect when measuring a sample having high shape reproducibility, such as a silicon wafer.

When measuring the surface shape of a substance surface, it is known that the resolution is limited to the wavelength of light used or about half of that due to the diffraction limit in an optical microscope. However, with the recent advancement of science and technology, the resolution required for the inspection of products having fine shapes such as semiconductors and the measurement of biological tissues such as DNA is on the order of nanometers.
Examples of devices capable of measuring in nanometer order include an atomic force microscope (AFM), a scanning tunneling microscope (STM), and a scanning near-field light microscope (SNOM) that breaks the diffraction limit described above. . Among these microscopes that can measure in nanometer order, AFM and STM can measure only the surface shape of the object to be measured, whereas SNOM has the merit that it can also analyze the optical properties and composition of the substance.
Non-Patent Document 1 In this document, a probe bonded to a crystal resonator (hereinafter referred to as TF) is brought close to a sample by a coarse copper actuator while being vibrated at a resonance frequency of TF. When the distance between the probe and the sample becomes several tens of nanometers or less, a force called shear force acts on both and changes in the resonance state. Therefore, the fine actuator is switched and driven so that both are at a desired distance.
In this case, unless the approach speed is sufficiently slowed down to the area where shear force works, the probe cannot be stopped in time, and it collides with the sample and is damaged. However, if the initial distance between the probe and the sample is 10 μm, for example, if the probe is approached at 10 nm / sec, it takes about 17 minutes for the shear force to work, and the measurement efficiency becomes very poor. If they accidentally collide with each other, the replacement is more troublesome and takes several tens of minutes or more.
Next, in Patent Document 1, the optical probe probe of the near-field microscope is securely held, and the gap portion for inserting the probe and the probe holding portion are tightened for the purpose of providing a unit that can be easily replaced. A technique constituted by members is shown.
However, the length of the probe is only described as 55 mm, and no reference is made to the length accuracy from the holding portion to the tip. For this reason, although the attachment / detachment may be easy, the efficiency of the subsequent approach work is not considered.
Further, Japanese Patent Application Laid-Open No. H10-228667 discloses a device that generates an electrostatic force by applying a voltage between the probe and the sample, and controls the distance between the probe and the sample by detecting this force. However, there is a limit to the type and range of samples that can be applied to apply voltage.
“Piezoelectric tip-sample distance Control for near field optical microscopes” Khaled Karrai, et al pp.1842, Applied Physics Letters 66 (14), 3 April 1995 JP-A-8-94652 Japanese Patent Laid-Open No. 2001-4519

In a microscope using near-field light, near-field light exists in a region substantially the same as the minute aperture diameter provided at the probe tip. Therefore, the probe and the sample are brought close to each other on the order of nm, and measurement is performed while relatively scanning while maintaining the state.
That is, prior to the measurement, the probe and the sample must be approached in advance, but if they collide with each other at this time, the probe is damaged and the desired resolution cannot be achieved. The distance between the probe and the sample is generally detected using shear stress called shear force. That is, the probe is vibrated in the lateral direction, and this vibration state is detected by a monitoring method.
However, since the vibration state does not change unless approaching to about 10 nm, it is necessary to approach at a very slow speed. Therefore, there is a problem that it takes a lot of time to set the probe to a position where near-field light measurement is possible.
There is also a method of observing the distance between the probe and the sample with a CCD camera and approaching to a certain distance and then approaching with a fine movement actuator such as PZT. However, when a high-magnification objective lens is used, the depth of focus becomes shallow. Therefore, much adjustment time for observing the CCD is also consumed.
As described above, the process of bringing the near-field light probe and the measurement sample closer to the near-field light region is very troublesome, but requires carefulness. This is one of the major factors that increase the time required for measurement. Even when a probe unit with a clear distance from the reference surface to the probe tip is used, the probe may collide with the sample and be damaged depending on an attachment error or the like.
In view of this drawback, the object of the present invention is to provide a near-field light microscope capable of preventing damage due to collision of the probe with the sample and allowing the probe to approach the sample reliably and in a short time, and sample measurement using near-field light. Is to provide a method.

In order to achieve the above object, the invention described in claim 1 includes a distance detecting means for detecting reference surface position information of the near-field optical probe based on a distance from the tip of the near-field optical probe to the sample surface, and the reference surface. And distance control means for bringing the near field light probe and the sample closer to the near field light region or the vicinity thereof based on the position information.
A second aspect of the present invention is the method according to the first aspect, further comprising sample surface position detecting means for detecting the position of the sample surface, wherein the distance control means is configured to detect the distance between the near-field optical probe and the sample based on the sample position information. The positional relationship is made close to the near-field light region or the vicinity thereof.
A third aspect of the present invention is the method according to the first or second aspect, further comprising tilt detecting means for detecting the tilt of the near-field optical probe with respect to the sample, wherein the distance control means is configured to detect the near-field optical probe based on tilt information. And the sample are brought close to the near-field light region or the vicinity thereof.
According to a fourth aspect of the present invention, there is provided a first step of generating near-field light at the tip of the near-field light probe having a known or constant length from the reference surface of the near-field light probe unit to the probe tip, and the proximity to the sample A second step of approaching the field light probe unit to the vicinity of the near-field light region; a third step of detecting near-field light scattered by the sample; and scanning the probe relative to the sample plane. However, it has the 4th process which repeats this 3rd process, and the 5th process which detects the position of the above-mentioned reference plane, and the 2nd process is a position detected by the 5th process. It is a step of approaching the near-field optical probe unit to the sample based on the information.
The invention of claim 5 has a sixth step of detecting the position of the sample surface in claim 4, wherein the second step is based on the position information obtained by the fifth and sixth steps. Based on this, it is a step of approaching the near-field optical probe unit to the sample.
The invention of claim 6 has the seventh step of detecting tilts of the near-field optical probe unit and the sample in claims 4 and 5, wherein the second step is the fifth to seventh steps. This is a step of approaching the sample with the near-field optical probe unit based on the position and tilt information obtained by the above.

  According to the present invention, it is possible to quickly bring both of them closer to the near-field light region without damaging the probe due to contact with the sample or the like regardless of the mounting state of the probe unit. It becomes possible to achieve efficiency improvement.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a general near-field light microscope.
The laser emitted from the light source (LD) 1 is collected by a lens (not shown) and guided to a near-field probe (optical fiber) 2. Since the tip of the probe 2 is sharpened by etching or the like, and the minute opening 3 is formed at the tip by means such as FIB or pressing method, the near-field light 4 is generated.
As is generally known, the near-field light 4 is non-propagating light existing within a distance that is approximately the same as the aperture diameter, and is not usually observed. However, when the sample 20 placed on the tube scanner 15 is brought close to the near-field light region, the near-field light 4 is scattered and converted into propagating light. This scattered light again passes through the probe 2, is deflected by the beam splitter 8, and is detected by the photodetector (PMT) 9.
Depending on the detected light intensity and frequency spectrum, for example, the surface shape, the structure and composition of the sample can be measured. Regarding the detection of the near-field scattered light, in this example, the light returning to the probe 2 is detected. However, since there is also light that does not return to the probe 2 but scatters to the surroundings, this light depends on the sample and the measurement environment. May be detected.
The distance between the probe and the sample can be controlled using a force called shear force. For example, a crystal resonator (TF) 5 is attached to an appropriate position of the probe 2 and resonated in the horizontal direction by an arbitrary waveform generator (FG) 11. When the probe 2 is brought close to the sample in this state, the amplitude is reduced by the shear force, and the resonance frequency is changed.
The vibration state is monitored using the lock-in amplifier 12, and the distance between the probe and the sample is kept constant by controlling the position of the tube scanner (distance control means) 15 in the vertical direction so as to be in a constant state. It becomes possible. Further, the sample is scanned and measured in a plane perpendicular to the probe 2, and the correspondence and analysis of the probe position information and the near-field scattered light information at each point are comprehensively performed using the PC 10 (distance control means). By controlling, the data of the sample surface can be obtained, and for example, it can be displayed three-dimensionally on the screen of the PC 10. In FIG. 1, reference numeral 6 denotes a probe fixing jig, 7 denotes a probe unit mounting surface (reference surface), 13 denotes a stage controller (SC, distance control means), and 14 denotes a coarse movement Z stage.

In such a near-field light microscope, an approach between the tip of the probe 2 and the sample is a bottleneck. The distance (shear force region) between the probe tip and the sample that can be detected by shear force is generally about 10 nm. The probe 2 must be brought close to this small area, but if it is approached at high speed, even if a stop command is sent to the stage after detecting the shear force, the probe 2 is moved to the sample by overshooting of the control system. It crashes and breaks.
When approaching at a low speed to prevent this damage, it takes a long time to reach the shear force region. For example, when approaching at 10 nm / sec from a place 100 μm away, it takes about 3 hours to reach the shear force region.
Even if the initial position is made closer by using a CCD camera,
It is only possible to approach an area of several μm at most. If a high-magnification objective lens is used for accurately grasping the interval, there is a disadvantage that the adjustment time increases.
As shown in FIG. 2, by realizing a near-field optical probe unit having a clear distance (A) from the reference surface 6a of the near-field optical probe fixing jig 6 to the probe tip, the distance to which the probe 2 should be approached is clarified. There are also devices and methods that overcome the above disadvantages. However, since the distance may change due to an attachment error or the like that occurs when the probe unit is installed, an apparatus and a method for dealing with such a situation will be described with reference to the flowcharts of FIGS.

As shown in FIG. 3, it is assumed that a laser displacement meter (distance detection means) 31 is added to the near-field light microscope apparatus of FIG.
That is, the present invention includes a distance detection unit 31 that detects the distance from the tip of the near-field optical probe 2 to the sample 20 or the reference surface 6a of the probe unit mounting surface 7, and a near-field optical probe detected by the distance detection unit 31. The configuration includes a near-field optical probe and a distance control means 10 for bringing the sample close to or near the near-field light region based on the reference plane position information.
First, the sample 20 and the near-field optical probe unit are attached (S1), and in this state, the distance to the reference surface 6a is measured using the laser displacement meter (first laser displacement meter 31) (S2). Since the first laser displacement meter 31 is attached to the stage 14, if the height of the sample 20 is constant, the measured distance, the probe length known in advance, and the first laser displacement meter 31 and the sample 20 are measured. The distance from the relative position of the probe tip to the sample 20 is calculated using the PC 10 or the like.
In the next step 3, the probe 2 or the sample 20 is approached (preset) to a predetermined distance based on the obtained distance information. The distance at this time may be determined based on the accuracy of the first laser displacement meter 31, the height variation of the sample 20, and the like. If the accuracy is low, the probe 2 may be brought close to a position where it does not collide with the sample 20 accordingly.
After the presetting is completed, the probe 2 is resonated using, for example, a tuning fork (TF) 5 in order to follow the sample surface for scanning (S4). The probe 2 and the sample 20 are brought close to each other until this resonance is in a desired state (amplitude or phase) (S5 to 8). While maintaining this state, a desired position or area on the sample surface is irradiated with the near-field light 4, and the scattered light is detected (S9).
By using the configuration and method as described above, it is possible to accurately detect the distance between the sample 20 and the near-field optical probe unit when the near-field optical probe unit is attached, and based on this distance information, the distance between the two is a predetermined value, for example, proximity It can be approached at a high speed up to about 1 μm in anticipation of the aperture diameter, which is the field light generation region, or the unevenness of the sample surface, and the measurement time can be greatly reduced compared to conventional devices and methods. It becomes possible. In addition, the possibility of probe breakage can be reduced.
For example, even when the probe unit is manufactured by controlling the distance from the surface 6b to the tip in FIG. 2, the thickness of the fixing jig 6 is separately measured by using a displacement meter or a thickness meter. By subtracting the length from the probe length, the distance from the reference surface 6a to the tip can be accurately grasped.

Next, the sample measurement method realized by the apparatus configuration of the present invention includes the following steps.
That is, in the first step, near-field light is generated at the tip of the near-field light probe whose length from the reference surface 6a of the near-field light probe unit to the tip of the probe 2 is known or constant.
Next, in the second step, the near-field optical probe unit is approached to the vicinity of the near-field light region with respect to the surface of the sample 20.
Next, in the third step, the near-field light scattered by the sample 20 is detected.
In the fourth step, the third step is repeated while scanning the probe 2 relative to the sample plane.
In the fifth step, the position of the probe unit reference surface is detected.
In the second step, the near-field optical probe unit may be approached to the sample based on the position information detected in the fifth step.
According to each sample measurement method described above, regardless of the probe unit mounting state, it is possible to quickly bring them closer to the near-field light region without damaging the probe due to contact with the sample, etc., and shorten the measurement time. And the efficiency of measurement work can be achieved.

According to the first embodiment, the probe 2 can be approached at high speed without colliding with the sample 20. In this embodiment, a more preferable example will be described with reference to FIG.
In the configuration of this embodiment, in addition to the first embodiment, a second laser displacement meter (second laser displacement meter 32, sample surface position detection means) is attached to the probe unit attachment surface 7. The distance to the sample 20 is measured using the second laser displacement meter 32. Since the second laser displacement meter 32 is fixed, the information of the position of the sample 20 obtained here, the position of the probe unit mounting surface 7 measured by the second laser displacement meter 32, and the probe length is included. Based on this, the distance from the tip of the probe 2 to the sample 20 is calculated using the PC 10.
In the sample measurement method of the present invention, in addition to the first to fifth steps, a sixth step of detecting the position of the sample surface 20 is added, and the second step is the fifth and sixth steps. The near-field optical probe unit is approached with respect to the sample based on the positional information obtained by the process.
By using the above configuration and method, even when the sample height varies from sample to sample, the probe 20 can be approached at high speed, and measurement time can be shortened and probe breakage can be prevented.
In the present embodiment (FIG. 4), the position approached by the probe tip and the position measured by the laser displacement meter are shown differently. An accurate approach is possible.

With the configuration and method shown in the second embodiment, the near-field optical probe can be approached at high speed without colliding with the sample. In this embodiment, a further improved example will be described with reference to FIG.
The present invention has an inclination detecting means 33 for detecting the inclination of the near-field optical probe 2 with respect to the sample 20, and the distance control means 10 determines the near-field optical probe and the sample based on the inclination information obtained from the inclination detecting means 33. It is made to approach to the near field light area | region or its vicinity.
Specifically, in addition to the second embodiment, another laser displacement meter (third laser displacement meter 33 = tilt detection means) is newly installed to detect the tilt. When the ratio of the distance to the probe unit mounting reference surface 6a detected by the two laser displacement meters 31 and 33 is deviated from a predetermined value, it becomes an inclination error α. Since the position error and the tilt direction of the probe tip can be grasped based on the already known probe length A and the detection result, the distance between the tip of the probe 2 and the sample 20 may be used for calculation by the PC 10.
In the sample measurement method according to this embodiment, in addition to the steps 1 to 6 described above, the sample measurement method includes a seventh step of detecting the near-field optical probe unit and the tilt of the sample, and the second step includes the first step. It is a step of approaching the near-field optical probe unit to the sample based on the position and tilt information obtained by the steps 5 to 7.

  The probe produced according to the present invention can be applied to all samples measured with a near-field optical microscope, such as semiconductor structure analysis and biomolecule measurement.

The main figure of a general scanning near-field optical microscope. The schematic diagram of a near-field optical probe unit. 1 is a schematic diagram of a near-field light microscope according to Embodiment 1. FIG. FIG. 6 is a schematic diagram of a near-field light microscope according to Example 2. FIG. 6 is a schematic diagram of a near-field light microscope according to Example 3. The flowchart which shows the process step of the sample measuring method by near field light.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light source (LD), 2 ... Near field probe, 3 ... Small aperture, 4 ... Near field light, 5 ... Quartz crystal | crystallization vibrator (TF), 6 ... Probe fixation treatment Tool, 6a Reference surface, 7 ... Probe unit mounting surface, 8 ... Beam splitter, 9 ... Photodetector (PMT), 10 ... PC, 11 ... Arbitrary waveform generator (FG) , 12 ... Lock-in amplifier (LIA), 13 ... Stage controller (SC), 14 ... Coarse movement Z stage, 15 ... Tube scanner (distance control means), 20 ... Sample, 31 ... 1st laser displacement meter (distance detection means), 32 ... 2nd laser displacement meter, 33 ... 3rd laser displacement meter

Claims (6)

  Distance detecting means for detecting the reference surface position information of the near-field optical probe based on the distance from the tip of the near-field optical probe to the sample surface, and the positional relationship between the near-field optical probe and the sample based on the reference surface position information A near-field light microscope comprising: a distance control means for approaching the near-field light region or the vicinity thereof.   2. The method according to claim 1, further comprising sample surface position detecting means for detecting the position of the sample surface, wherein the distance control means determines the positional relationship between the near-field light probe and the sample based on the sample position information. Alternatively, a near-field light microscope characterized in that it is brought close to the vicinity.   3. The apparatus according to claim 1, further comprising an inclination detection unit that detects an inclination of the near-field optical probe with respect to the sample, wherein the distance control unit determines a positional relationship between the near-field optical probe and the sample based on the inclination information. A near-field light microscope characterized by approaching a near-field light region or the vicinity thereof. A first step of generating near-field light at a near-field light probe tip having a known or constant length from the near-field probe unit reference surface to the probe tip;
A second step of approaching the near-field light probe unit to the vicinity of the near-field light region with respect to the sample;
A third step of detecting near-field light scattered by the sample;
A fourth step of repeating the third step while scanning the probe relative to the sample plane;
A fifth step of detecting the position of the reference plane;
Have
The method of measuring a sample using near-field light, wherein the second step is a step of approaching the near-field optical probe unit to the sample based on the position information detected in the fifth step. In claim 4,
A sixth step of detecting the position of the sample surface;
Sample measurement by near-field light, wherein the second step is a step of approaching the near-field optical probe unit to the sample based on the positional information obtained by the fifth and sixth steps. Method. In claims 4 and 5,
A seventh step of detecting an inclination of the near-field optical probe unit and the sample;
The sample by near-field light, wherein the second step is a step of approaching the near-field optical probe unit to the sample based on the position and tilt information obtained by the fifth to seventh steps. Measuring method.

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