JPH11316242A - Optical fiber probe and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an optical fiber probe with good reproducibility and simply by a method wherein a light-transmitting very small probe which comprises an acute drill-shaped core part is bonded and fixed closely to the tip part of an optical fiber which comprises a core for light propagation and a clad whose refractive index is smaller than that of the core. SOLUTION: A silicon dioxide or silicon nitride protective layer is formed on a silicon substrate 30, its desired place is patterned by a photolithographic operation and an etching operation, silicon is exposed, and a recess is formed by an etching operation. A photocuring resin as a core material is filled into the recess. The central part of an optical fiber 31 which is composed of a core 32 and a clad 33 whose refractive index is smaller than that of the core 32 is aligned with the central part of the recess, and the optical fiber 31 is bonded and fixed closely to the substrate 30. In succession, the substrate 30 is irradiated with ultraviolet rays from the upper part, or it is heated. Then the substrate 30 on which the recess is formed is stripped, and the optical fiber 31 which comprises a light-transmitting very small probe at the tip is created. In this manner, an optical fiber probe can be created with good reproducibility and in a simple process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical fiber probe having a light-transmitting microprobe used in a scanning near-field optical microscope and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller and smaller.
With the increase in density, one basic technique of miniaturizing a device using light in particular is required. However, since light has the property of diffraction, the wavelength of light is the lower limit of the size of the optical element. In addition, since the optical element evaluation system also uses light diffraction, for example, even when observing a sample, a resolution lower than the wavelength of light cannot be obtained in principle.
In recent years, light has been used as a field that mediates electromagnetic interaction in a space below the light wavelength (so-called evanescent field), and material evaluation and fine processing at the nanometer scale, which were difficult with conventional optical systems, have been performed. Attempts have been made to try. In fact, a scanning near-field optical microscope (hereinafter referred to as SNOM) for examining the surface state of a substance using evanescent light exuding from the tip of a light-transmitting microprobe has been developed (for example, see Durig et al., J. Appl. Phys. 5
9 , 3318 (1986)]). Further, light is incident from the surface through a prism under the condition of total reflection, and evanescent light seeping onto the sample surface is detected from the sample surface with an optical probe, and a photon S, which is a kind of SNOM for examining the sample surface, is used.
TM (hereinafter abbreviated as PSTM. For example, Reddick et al.,
Phys. Rev .. B 39 , 767 (1989)]
Was also developed.

In the above-mentioned SNOM, various methods for manufacturing optical probes have been devised so far because the tip diameter of the optical probe determines the resolution. For example, in the initial SNOM, the intersection of the cleavage planes of the transparent crystal is coated with metal, and this is pressed against a hard surface to remove the metal at the intersections, thereby exposing the intersections and producing a minute opening (European Patent No. 112402). ), Mechanical cutting / polishing /
Probes have been manufactured by a mechanical process using ion milling. Also, without providing a small opening at the tip of the optical probe, the tip is sharpened by optimizing the chemical etching conditions of the end face of the optical fiber used as the optical probe,
Resolution has been improved. Further, there are known conventional examples such as a method of forming a minute opening by using a lithography technique and a method of forming an optical probe by integrally forming a minute opening and an optical waveguide (US Pat. No. 5,354,985).

[0004]

However, among the conventional methods for forming the light-transmitting microprobe described above, for example, a method using a crystal cleavage plane or a mechanical processing method causes variations in the size of the microscopic aperture. And the yield was not good. Also, it has been difficult to integrate and reduce the size. In addition, in the method of forming a fine opening using photolithography, 100 μm
An aperture with a diameter of about [nm] is a limit, and it is difficult to produce a small aperture with a diameter of about 10 [nm], which limits the resolution of the SNOM device. In addition, there is a problem that the process is complicated, time is required, and the cost is high. If an EB processing apparatus or FIB processing apparatus is used, it is possible in principle to form an opening of 100 nm or less, but the alignment control is complicated, variation easily occurs, and a processing method for one point at a time. Therefore, the yield was not good. Further, in the conventional example in which the minute aperture and the optical waveguide are integrally formed, there is a problem in terms of cost, such as the use of a larger amount of "probe" material as a result.

Therefore, the present invention solves the above-mentioned problems of the conventional device, and can be easily manufactured with good reproducibility, and can improve the productivity and reduce the cost. An object is to provide an optical fiber probe used for a microscope and a method for manufacturing the same.

[0006]

According to the present invention, an optical fiber probe used in a scanning near-field optical microscope and a method of manufacturing the same are configured as follows to achieve the above object. Things. That is, the optical fiber probe of the present invention is an optical fiber probe having a light-transmitting microprobe used in a scanning near-field optical microscope, and a light-transmitting microprobe having a conical core portion having an acute angle. An optical fiber having a core for light propagation and a cladding covering the core and having a refractive index smaller than the refractive index of the core is formed independently, and the light transmitting fine It is characterized in that the probe is closely fixed. Further, the optical fiber probe of the present invention is characterized in that at least the conical core portion is made of a photocurable resin. In addition, the method of manufacturing an optical fiber probe having a light-transmitting microprobe used in the scanning near-field optical microscope of the present invention includes a light-transmitting microprobe having a conical core portion having an acute angle, And an optical fiber having a cladding covering the core and having a refractive index smaller than the refractive index of the core are independently formed, and the light-transmitting microprobe is closely fixed to the tip of the optical fiber. And forming an optical fiber probe. Also, the method for manufacturing an optical fiber probe of the present invention includes: (a) forming a concave portion on the surface of a silicon substrate; and (b) filling the concave portion with a core material composed of a photocurable resin precursor.
(C) positioning an optical fiber having a core for light propagation and a cladding covering the core and having a refractive index smaller than the refractive index of the core such that the center of the optical fiber overlaps the center of the recess. And irradiating the core material with ultraviolet rays while being in close contact with the substrate to cure the material.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 shows a process of manufacturing a light-transmitting microprobe according to the present invention, and FIGS. 1A to 1C show a process of forming a concave portion on the surface of a substrate 10. The substrate 10 uses a silicon substrate. A protective layer 11 is formed on the substrate 10 (a), and a desired portion of the protective layer 11 is patterned by photolithography and etching to expose a part of the silicon (b), and then etched. The concave portion 12 is formed by etching the silicon using (c). As the protective layer 11, silicon dioxide or silicon nitride can be used. Further, it is preferable to use crystal axis anisotropic etching capable of sharply forming the deepest portion of the concave portion for the etching. By using an aqueous solution of potassium hydroxide or the like as an etching solution, an inverted pyramid-shaped concave portion 20 surrounded by four surfaces equivalent to the (111) plane can be formed. The recess 1
2, a peeling protection layer 13 made of silicon dioxide or the like may be formed as needed (d).

In the step shown in FIG. 2, the concave portion 21 formed as described above is filled with a photo-curable resin material 22 as a core material. As the material 22, a light or heat polymerizable material can be used. Preferably, a monofunctional or polyfunctional methacrylic acid derivative / acrylic acid derivative monomer or prepolymer, or a mixture or copolymer thereof can be used. When photopolymerization is carried out, the photopolymerization initiator is used in a total weight ratio of 1% to 10
% Can be mixed.

Next, in the step shown in FIG. 3, an optical fiber 31 composed of a core 32 having a refractive index equal to that of the core material and a clad 33 having a lower refractive index than the core is placed at the center of the concave portion. The substrate is tightly fixed to the substrate 30 while being positioned so as to overlap. Subsequently, the substrate is irradiated with ultraviolet light from above or heated. In addition, ultraviolet irradiation may be performed while heating.

Next, in the step shown in FIG. 4, the substrate on which the concave portion is formed as shown in FIG. 4A is peeled off, and the light-transmitting microprobe 51 shown in FIG. The optical fiber 50 having a tip is manufactured. In some cases, the microprobe 51 may be provided with a light-shielding coating 52 at least in the vicinity of the distal end thereof, and the coating at the tip of the probe may be opened. In addition, the substrate 40 having the concave portions used above can be used again by performing cleaning using a cleaning method that does not change the shape of the concave portions after the core portion is peeled off.

Next, observation of an evanescent wave using the optical fiber probe according to the present invention will be described. FIG. 5 is a schematic diagram showing a configuration example of the entire evaluation device. The sample to be measured 60 is provided on a substrate 61. Sample 60 to be measured
Is a printing method on the transparent substrate 61 as a solution or a mixed solution,
A spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, an LB method and the like can be used. The LB method has a high uniformity of the obtained cumulative film and can control the film thickness in the order of one molecule. The material density per unit area is high and uniform. The conditions for forming the cumulative film are mild. Features include the ability to use the method or device and no special modification required. Next, the minute probe 6 is placed on the surface of the sample 60 to be measured.
3 is brought close. The proximity method uses an atomic force microscope (AFM, [G. Binnig et al, Ph.D.) that detects the atomic force acting between the sample and the probe and observes the shape of the sample surface.
ys. Rev .. Lett. , 56, 930 (198
6)]) is used. That is, the proximity state of the micro probe 63 to the sample 60 is monitored by the displacement detecting means 69, and the height in the z direction is controlled by the actuator 67 through the servo control circuit 68.

The micro probe 63 manufactured according to the present invention is carried on the tip of an optical fiber 64. Irradiation light generating means 65
Light is radiated vertically from the upper surface of the sample 60 through the micro probe 63. At this time, light called evanescent light oozes very close to a distance of 0.1 [μm] or less from the surface of the sample 60. In order to detect the evanescent light, a highly sensitive light detecting means 66 such as an avalanche photodiode or a photomultiplier is provided near the surface of the sample 60. The evanescent light detected by the light detecting means 66 is used as a current signal as an I / V
The signal is converted into a voltage signal by a conversion circuit, and is used as an SNOM signal. The signal is converted into a three-dimensional image via the computer 610, and the image is displayed on the display device 611. The substrate 61 is fixed to an actuator 67 via a stage 62. The actuator 67 is connected to the sample 60.
Performs two-dimensional relative scanning in the in-plane direction and control in the height direction. By plotting the magnitude of the SNOM signal at each position in the xy plane, an SNOM observation image of the surface of the sample 60 can be obtained.

FIG. 6 is a schematic diagram showing another example of the configuration of the entire evaluation apparatus. The sample 70 to be measured is a conductive substrate 71
It is provided above. Micro probe 7 prepared according to the present invention
3 is provided with a conductive coating 712 near the tip, and the conductive coating is open at the tip of the probe. It is carried at the tip of the optical fiber 74. Light is emitted vertically from the upper surface of the sample 70 by the irradiation light generating means 75 through the micro probe 73. At this time, light called evanescent light oozes very close to a distance of 0.1 [μm] or less from the surface of the sample 70. In order to detect the evanescent light, a highly sensitive light detecting means 76 such as an avalanche photodiode or a photomultiplier is provided near the surface of the sample 70. The evanescent light detected by the light detection means 76 is converted into a voltage signal by an I / V conversion circuit as a current signal, and is used as a SNOM signal. The signal is converted into a three-dimensional image via the co-computer 710 and the image is displayed on the display device 711.

The method of approaching the microprobe 73 to the sample 70 in this configuration example is to monitor the tunnel current flowing between the conductive coating 712 applied to the microprobe 73 and the sample 70. Scanning tunneling microscope (STM,
[G. Binnig et al, Phys. Rev ..
Lett. , 49 , 57 (1982)]) and their composite devices (AFM / STM, (JP-A-3-27790)).
Apply the principle of 3). That is, the proximity state of the micro probe 73 to the sample 70 is monitored by the displacement detecting means 79, and the height control in the z direction is performed by the actuator 77 through the servo control circuit 78. At the same time, voltage applying means 71
By applying a voltage to the sample 70 to be measured through the conductive coating 712 from 1, conductivity information on the surface of the sample 70 can be obtained. This conductivity information is converted into a three-dimensional image via the computer 79 and displayed on the display device 710 simultaneously with the SNOM signal.

[0015]

EXAMPLES Examples of the present invention will be described below, but they do not limit the present invention in any way. Example 1 First, a substrate used in this example was manufactured by the steps shown in FIG. A single crystal silicon wafer having a plane orientation (100) was prepared as the substrate 10 in FIG. 1A. Next, a silicon thermal oxide film having a thickness of 100 nm was formed as the protective layer 11. Next, a desired portion of the protective layer 11 is patterned by photolithography and etching to a thickness of 50 μm.
Square silicon was exposed (FIG. 2b). Next, the silicon in the patterning portion was etched by crystal axis anisotropic etching using an aqueous potassium hydroxide solution. The etching conditions were a 30% concentration aqueous potassium hydroxide solution, a liquid temperature of 90 ° C., and an etching time of 20 minutes. At this time, a depth of about 5 surrounded by four planes equivalent to the (111) plane
An inverted pyramid-shaped concave portion 12 of 0 μm was formed (FIG. 3C). Next, the silicon thermal oxide film as the protective layer 11 is coated with a mixed aqueous solution of hydrofluoric acid and ammonium fluoride (HF: NH ₄ F).
= 1: 5). Next, the substrate 11 was washed using a mixed solution of sulfuric acid and hydrogen peroxide solution heated to 120 ° C. and a 2% aqueous hydrofluoric acid solution. Next, the substrate 10 was heated to 1000 ° C. in an oxygen and hydrogen atmosphere using an oxidation furnace, and silicon dioxide as the peeling layer 13 was deposited to a thickness of 500 nm (FIG. 3c). Next, 60 parts of 2-hydroxymethyl methacrylate, 30 parts of hydroxyethyl acrylate, 8 parts of hexanediol diacrylate, 2 parts of trimethylolpropane triacrylate, 2 parts of Irgacure 184/0.
Three parts of the mixed solution were applied and filled (FIG. 2). Next, the end face of the plastic optical fiber 31 having polymethyl methacrylate as a core is positioned at the center of the core of the fiber.
2 and adhere at 10 ° C.
Irradiation was performed at an intensity of W / cm ² for 10 minutes. Further at 60 ° C 3
Heating was continued for 0 minutes (FIG. 3).

Thereafter, as shown in FIGS. 4A and 4B, the substrate 40 and the fiber 50 having the microprobe 51 formed at the tip were separated. When the tip of the microprobe 51 was observed with a scanning electron microscope, the tip diameter was at least 30 nm or less. Subsequently, Al was vapor-deposited on the microprobe 51 at 500 ° to perform light-shielding coating. Next, the microprobe 51 is brought into contact with a platinum plate electrode (not shown) and a voltage is applied thereto, whereby
1. An opening having a diameter of about 20 nm was formed at the forefront. Next, a sample to be measured was prepared in the following steps. First, a undoped silicon wafer having a thickness of 0.5 mm was immersed in 10% hydrofluoric acid for 1 minute, and mounted on a substrate driving mechanism of an LB film forming apparatus such that the electrode surface was perpendicular to the water surface. Subsequently, 98 parts of behenic acid / (N- (7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino) stearic acid (NBD-stearic acid, excitation wavelength 488 nm, emission wavelength 540 n)
m) 2 parts (final concentration 0.3 mg / ml) were dissolved in chloroform. Subsequently, the mixed solution was spread on the water surface of the LB film forming apparatus, compressed to a surface pressure of 26 mN / m, and allowed to stand for 5 minutes while maintaining the surface pressure. Next, the substrate driving mechanism 33 was operated, and the substrate mounted on the mechanism was moved up and down at a speed of 10 mm / min. Next, the sample to be measured prepared as described above was mounted on the apparatus shown in FIG. 5, and the micro probe 63 was brought close to the sample 60. And a wavelength of 488n
Then, the sample to be measured 60 was scanned in a two-dimensional plane by the actuator 67 by irradiating the laser beam of m. The probe 6
Evanescent light was detected from the three tips by the photodiode 66 and superimposed on the positional information of the microprobe 63 by the computer 610. As a result, evanescent light emission in the form of a domain presumably derived from NBD-stearic acid was observed.

Example 2 In this example, a substrate as shown in FIG. 1 was manufactured in the same manner as in Example 1. Next, Aronix M-
A mixed solution of 80 parts of 5600 (monofunctional acrylate oligomer), 20 parts of Aronix M-6100 (bifunctional acrylate oligomer), and 184 / 0.3 parts of Irgacure was applied and filled (FIG. 2). Next, a microprobe shown in FIG. 4B was formed in the same manner as in Example 1. Next, a sample to be measured was prepared by the method described in Example 1, mounted on the apparatus shown in FIG. 5, and evaluated and observed in the same manner as in Example 1. As a result, a domain believed to be derived from NBD-stearic acid was obtained. Evanescent light emission was observed.

Embodiment 3 In this embodiment, a substrate as shown in FIG. 1 was manufactured in the same manner as in Embodiment 1. Next, 80 parts of 2-hydroxymethyl methacrylate / Aronix M-560 is applied to the concave portion 22 formed above by spin coating.
0 (monofunctional acrylate oligomer) 18 parts / Aronix M-6100 (bifunctional acrylate oligomer) 2
Part / Irgacure 184 / 0.3 part mixed solution,
Filled (FIG. 2). Next, a microprobe shown in FIG. 4B was formed in the same manner as in Example 1. Next, a sample to be measured was prepared by the method described in Example 1, mounted on the apparatus shown in FIG. 5, and evaluated and observed in the same manner as in Example 1. As a result, a domain believed to be derived from NBD-stearic acid was obtained. Evanescent light emission was observed.

[Embodiment 4] In this embodiment, a substrate as shown in FIG. Next, a microprobe shown in FIG. 4B was formed in the same manner as in Example 1. Subsequently, Al was vapor-deposited on the microprobe at a thickness of 200 [deg.] To provide a conductive coating. Next, a sample to be measured used in the present example was prepared with the following recipe. Au was vapor-deposited on a non-doped silicon wafer substrate 10 having a thickness of 0.5 mm to a thickness of 300 °. Next, the substrate is subjected to UV-O ₃ cleaning (60 ° C., 30
After washing in (1), the substrate was mounted on a substrate drive mechanism of an LB film forming apparatus such that the electrode surface was perpendicular to the water surface, and immediately immersed in a pure water phase. Subsequently, octadecylamine (0.3 mg /
ml) was dissolved in chloroform, spread on the water surface, compressed to a surface pressure of 20 mN / m, and allowed to stand for 5 minutes while maintaining the surface pressure. Next, the substrate driving mechanism 33
Is operated, and the substrate 30 mounted on the mechanism is moved at a speed of 10 mm.
/ Min. As a result, octadecylamine was transferred to the substrate with one layer of hydrophobic group on the outside, and the outermost surface of the substrate could be made hydrophobic. Next, poly (p-phenylenevinylene)
The solvent-soluble precursor of [M. Era et alChe
m. Lett. , 1097 (1988)], and 10 layers were accumulated on the substrate 30. Subsequently, the substrate 30 was heated at 200 ° C. for 2 hours under reduced pressure to obtain a poly (p-phenylenevinylene) thin film as a final product. Next, the microprobe 73 provided with the conductive coating 712 prepared in this embodiment was attached to the apparatus according to the present invention (FIG. 6) shown in FIG. 6, and was brought into contact with the platinum substrate. Further, a voltage is applied from a voltage generator 712, and a diameter of about 2
An opening of 0 nm was formed. Next, the substrate 71 with the sample to be measured 70 was mounted. Next, the micro probe 73 provided with the conductive coating 712 was brought close to the measured sample 70, and a DC voltage was applied so that the measured sample 70 side became +. As a result, evanescent light was detected by the photodiode 76 from the tip of the conductive micro probe 73.

[Embodiment 5] In this embodiment, the substrate 10 (FIG. 1d) on which the concave portion 12 and the release layer 13 used in the embodiment 1 are formed is made to have a 5% concentration of RBS35 (Fluka).
Company), perform ultrasonic cleaning, rinse thoroughly with ultrapure water,
A microprobe was manufactured again in the same process as in Example 1.
Next, a microprobe shown in FIG. 4B was formed in the same manner as in Example 1. Next, a sample to be measured was prepared by the method described in Example 1, mounted on the apparatus shown in FIG. 5, and evaluated and observed in the same manner as in Example 1. As a result, a domain believed to be derived from NBD-stearic acid was obtained. Evanescent light emission was observed.

[0021]

According to the present invention, a light-transmissive microprobe used for evanescent light detection can be manufactured with a tip diameter of the order of 10 nm with good reproducibility and a simpler process than the conventional example. By attaching this to a scanning near-field light microscope, evanescent light can be detected without any problem. In addition, by reusing the substrate used during the process of the present invention to produce a light-transmissive microprobe again, it is possible to produce a completely light-transmissive probe that is exactly the same as the initially produced light-transmissive probe. It is possible to improve the productivity and reduce the cost of the light-transmitting microprobe.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a process for producing a light-transmitting microprobe according to the present invention.

FIG. 2 is a schematic view showing a process of manufacturing a light-transmitting microprobe according to the present invention.

FIG. 3 is a schematic view showing a process for producing a light-transmitting microprobe according to the present invention.

4A and 4B are diagrams illustrating a state in which a fiber having a micro probe formed at the tip is separated from a substrate, FIG. 4A is a diagram illustrating a substrate in which a micro probe is separated, and FIG. The figure which shows the optical fiber probe in which the micro probe which was formed was formed in the tip.

FIG. 5 is a block diagram of an apparatus for detecting evanescent light by attaching the microprobe.

FIG. 6 is a block diagram of an apparatus for detecting evanescent light by attaching the microprobe.

[Explanation of symbols]

 10, 20, 30, 40: substrate 11: protective layer 12, 21: concave portion 13: release layer 22: core material 31: optical fiber 32: core portion 33: clad portion 50: optical fiber 52: light shielding coating 60, 70: Samples to be measured 61, 71: Substrate 62, 72: Stage 63, 73: Light-transmitting microprobe 64, 74: Optical fiber 65, 75: Light irradiating means 66, 76: Light detecting means 67, 77: Actuator 68, 78 : Servo control means 69, 79: Micro probe position detecting means 610, 710: Computer 611, 711: Display device 612: Light shielding coating 712: Conductive coating

Claims (4)

[Claims] 1. An optical fiber probe having a light-transmitting microprobe used in a scanning near-field optical microscope, comprising: a light-transmitting microprobe having a conical core portion having an acute angle; An optical fiber having a core and a cladding covering the core and having a refractive index smaller than the refractive index of the core is independently formed, and the light-transmitting microprobe is closely fixed to the tip of the optical fiber. An optical fiber probe, comprising: 2. The optical fiber probe according to claim 1, wherein at least the conical core portion is made of a photocurable resin. 3. A method for manufacturing an optical fiber probe having a light-transmitting microprobe used in a scanning near-field light microscope, comprising: a light-transmitting microprobe having an acute angled conical core portion; An optical fiber having a propagation core and a cladding covering the core and having a refractive index smaller than that of the core is independently formed, and the light-transmitting microprobe is provided at the tip of the optical fiber. A method for manufacturing an optical fiber probe, wherein the optical fiber probe is formed by closely contacting and fixing. 4. A method of manufacturing an optical fiber probe, comprising: (a) forming a concave portion on a surface of a silicon substrate; and (b) filling the concave portion with a core material made of a photocurable resin precursor. And (c) an optical fiber having a light-propagating core and a clad covering the core and having a refractive index smaller than the refractive index of the core such that the center of the optical fiber overlaps the center of the recess. 4. The method according to claim 3, further comprising: irradiating the core material with ultraviolet rays while being in close contact with the substrate after being aligned with the substrate, and curing the material.