JP2012222019A - Method for aligning nanowire and method for separating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for aligning a nanowire with predetermined length in a predetermined direction and at a predetermined position and a method for separating out a nanowire with predetermined length.SOLUTION: The method for aligning a nanowire at a predetermined position on a circuit board comprises sequential steps of: preparing a substrate having twin fixing sections separated at a predetermined distance from each other for fixing both ends of the nanowire; preparing a nanowire having at both ends a connecting section for forming a specific connection to the fixing section on the substrate; dispersing a liquid containing the nanowire over the substrate to connect the connecting section of the nanowire to the fixing section on the substrate; and flowing a fluid at nearly right angle to the opposite direction of the twin fixing sections.

Description

  The present invention relates to a nanowire arrangement method and a separation method. More specifically, the present invention relates to a method for arranging nanowires having a predetermined length in a predetermined direction and at predetermined positions, and a method for separating and extracting nanowires having a predetermined length.

  With the progress of semiconductor processing technology, it has become difficult to achieve predetermined characteristics with conventional planar scaling. In addition, factors such as the short channel effect are becoming apparent along with the reduction of the design dimension, so that breakthrough other than the simple reduction of the design dimension is required. Among them, semiconductor nanowires are attracting attention because of the possibility of obtaining transistors with good transfer characteristics. In addition, due to the feature of having a very large surface volume ratio, it has attracted attention from the viewpoint of application to sensors. Examples of nanowire manufacturing techniques include a top-down method using lithography and etching, and a bottom-up method typified by a VLS (gas phase-liquid phase-solid phase) method. By using the bottom-up method, for example, a nanowire with a low crystal defect density can be obtained using a single crystal semiconductor having a circular cross section with a diameter of 500 nm or less. These are difficult properties to obtain with nanowires made by top-down. However, the bottom-up method is not yet in practical use as a semiconductor device because of its growth orientation and difficulty in position control. As a method of making a device, the grown nanowire is released from the substrate by stimulation such as ultrasonic waves in the solution, collected, applied on another substrate, placed horizontally, and then electrodes are formed at both ends Has been proposed. In this manufacturing method, since nanowires are randomly laid out on the substrate surface, it is difficult to manufacture a device with good characteristic reproducibility. On the other hand, Patent Document 1 proposes a technique for fixing both ends by modifying functional groups at both ends of the carbon nanotube structure and providing a portion selectively bonded to the functional group on the substrate.

JP 2005-101363 A

Physical Review B 75, 045335, 2007 Lieber. et. al, Science, 2001, 26, p630-633. Y. Cui et. al, Science 293, 1289, 2001 Electrochemical and Solid-State Letters, vol9, no12, c185, 2006

  However, in the conventional arrangement method described in Patent Document 1, it is necessary to fractionate carbon nanotubes having a predetermined length before fixing.

  An object of the present invention is to propose a method for examining, extracting, and arranging wires having a predetermined length in order to improve the production yield and characteristics of elements using nanowires as constituent elements.

The first invention of the present invention is:
A method of arranging nanowires for arranging nanowires at predetermined positions on a substrate, comprising:
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
Is a method for arranging nanowires.

The second invention of the present invention is:
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
Forming an intermediate fixing part for fixing the nanowire and the substrate in the middle of the paired fixing part;
Removing at least a portion of the binding site of the nanowire;
Is a method for separating nanowires, characterized in that the steps are sequentially performed.

  By using the nanowire arrangement method of the present invention, it becomes possible to arrange nanowires having a predetermined length at predetermined positions with good control. Moreover, nanowires other than a predetermined length can be efficiently removed. Therefore, the production yield and characteristics of elements using nanowires as constituent elements are improved.

It is the figure which showed typically the nanowire used by this invention. It is a figure explaining the arrangement | sequence process of the nanowire which concerns on 1st Embodiment. It is a figure explaining the manufacturing process of nanowire FET based on a 1st Example. It is a figure explaining the manufacturing process of nanowire FET based on a 1st Example. It is a figure explaining the nanowire preparation process which has a coupling | bond part in both the ends concerning a 1st Example.

  A preferred embodiment of the present invention will be described in detail.

  First, after describing the arrangement method and the separation method in the present invention, the form of each component will be described in detail. In addition, these figures, Examples, etc. and description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.

<Sequence method>
(First embodiment)
A first embodiment of an arrangement method according to the present invention is an arrangement method for arranging nanowires at predetermined positions on a substrate,
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
Is a method for arranging nanowires.

  (A)-(f) of FIG. 2 is the figure which best represents 1st Embodiment of the arrangement | sequence method in this invention.

  FIG. 2A is a diagram showing a process in which an immobilization site pair 103 in which an immobilization site 102 is paired is arranged at a predetermined position on the substrate 101. The immobilization site is composed of a material that selectively binds to a binding site provided at the end of the nanowire. As the binding reaction, biotin-avidin bond, gold-thiol bond and the like can be applied. The immobilization site can be easily patterned by lithography or the like.

  The interval between the immobilization sites 102 constituting the immobilization site pair 103 in the present invention can be arranged according to a predetermined length of the nanowire. As an arrangement method, for example, as described later, an electrode can be arranged in a predetermined shape at a predetermined position by using electron beam lithography.

In order to avoid interference with adjacent immobilization site pairs, the distance between a specific immobilization site pair 103 and another adjacent immobilization site pair 103 is:
Condition A: It is preferable that the design is made larger than the interval between the immobilization sites 102 constituting the immobilization site pair 103.

Furthermore,
Condition B: It is preferably designed to be larger than the maximum value in the assumed nanowire variation range.

  By designing the layout so as to satisfy the conditions A and B at the same time, it is possible to prevent the nanowire from being fixed so as to straddle the adjacent fixed site pair 103.

  Note that the intervals between the immobilization sites 102 constituting the immobilization site pair 103 are not necessarily the same on the substrate, and a plurality of intervals can be provided as long as the above-described conditions A and B are satisfied. Thereby, it is also possible to lay out nanowires having a predetermined length at predetermined positions.

  On the other hand, the nanowire used in the present invention needs to have binding sites at both ends as shown in FIG. For example, nanowires are grown on a substrate by a VLS (vapor-liquid-solid) method via a gold catalyst. Next, this substrate is immersed in an electroless gold plating solution and irradiated with ultrasonic waves, the nanowire is removed from the substrate, Si is exposed at the end opposite to the catalyst Au, and gold is deposited. As a result, a nanowire having Au at both ends can be obtained.

  Next, a solution in which the prepared nanowires are dispersed is prepared. By preparing a solution in which nanowires are dispersed, the nanowires can be prevented from agglomerating at the time of arrangement, and the nanowires can be arranged at predetermined positions. For the preparation, it can be efficiently dispersed using ultrasonic waves or the like. Moreover, aggregation of nanowires can be prevented by adding a salt to the solution or adjusting the pH of the solution using a buffer solution.

  In the case where the arranged nanowires are used as a channel of a field effect transistor or the like, it is preferable to use a solvent containing pure water, alcohols such as ethanol and isopropyl alcohol, and a solvent containing an organic salt as a dispersion solvent. This is to prevent degradation of device performance due to alkali metal contamination in the nanowire. The dispersion solution thus prepared is dropped onto the substrate 101 as shown in FIG. Thereafter, the end binding sites of the nanowires 104 to 106 are bonded to any of the immobilized site pairs 102, and the wires are dispersed until the state shown in FIG. In order to efficiently combine the two, it is more preferable to use a technique such as stirring the dispersion using an agitator or a stirrer.

  In this process, only one end of each nanowire 104 longer than a predetermined length and nanowire 106 shorter than a predetermined length is fixed on the fixing site 102, and both ends of the nanowire 105 fixed at a predetermined length are fixed. Is done.

  As shown in Non-Patent Document 1, the nanowire growth rate depends on the catalyst diameter.

として表される。よって、曲げストレスは根元が最も強くなる。このことから、ナノワイヤも根元から破断する確率が高いと推測される。
よって、分散液中のナノワイヤの長さは成長直後のナノワイヤの長さと略等しく、成長速度に相関関係があると考えられる。 Further, when the nanowire is approximated to a cantilever beam having a uniform length L, and assuming that a uniform pressure p is applied from the lateral direction by ultrasonic waves, the bending stress M (x) with respect to the distance x from the root is

Represented as: Therefore, the root of bending stress is the strongest. From this, it is presumed that the nanowire also has a high probability of breaking from the root.
Therefore, the length of the nanowire in the dispersion is approximately equal to the length of the nanowire immediately after the growth, and it is considered that the growth rate has a correlation.

  Considering the above as a whole, it is considered that nanowires having similar diameters are selected by selecting nanowires having similar lengths from the nanowires in the dispersion broken by ultrasonic waves.

  Subsequently, as shown by the arrow in FIG. 2D, the fluid is allowed to flow substantially perpendicularly to the direction in which the immobilized site pair faces.

  The fluid in the present invention means a solution or solvent that flows substantially perpendicular to the direction in which the immobilized sites of the immobilized site pair 102 face each other. The step of flowing a fluid in the present invention includes a method of flowing a solvent using a liquid feed pump by providing a flow path on the substrate, a method of flowing a solvent in an arbitrary direction by taking the substrate from the liquid phase to the gas phase, and the like Can be used. The flow path used in the present invention can also be produced by producing a flow path mold using lithography, pouring a polymer material into the mold, and curing it. The material constituting the flow path is preferably a material that has high adhesion to the substrate and can be easily molded, and examples thereof include PDMS (polydimethylsiloxane). By providing holes in the inlet portion and outlet portion on the flow path, attaching a silicon tube to these holes, and connecting to a liquid feed pump, it becomes possible to flow the fluid in the flow path. The channel width is desirably a sufficiently wide width so that the nanowire is not clogged in the channel. For example, a channel having a width of 0.1 to 5.0 mm can be used. For example, by using the method described in Non-Patent Document 2, it is possible to align the direction of the nanowire with the direction in which the fluid flows.

  In this step, the nanowires 104 longer than the predetermined length and the short nanowires 106 are aligned in the direction in which the fluid flows. On the other hand, the direction of the nanowire 105 of a predetermined length does not change because both ends are fixed.

  In the present invention, when a fluid is flowed using a flow path, it is desirable to use a degassed solvent having low volatility as the fluid. Thereby, generation | occurrence | production of the bubble in a flow path is prevented and a fluid can be made to contact a nanowire efficiently. As a result, the orientations of the nanowires are well reproduced. The degassed solvent is prepared by bubbling the solvent with nitrogen for a predetermined time.

  The flow rate for aligning the nanowires can be referred to the value described in Non-Patent Document 2 above. When nanowires having a diameter of 1 μm or less and a length of 1 μm or more are aligned by a fluid, the direction of the nanowires is aligned with the direction of fluid flow by flowing the fluid at a flow rate of 0.01 m / sec or more.

  By controlling the arrangement and interval of the immobilization sites and the flow direction of the fluid by the above steps, only the nanowires having a predetermined length can be fixed in a predetermined position and direction.

  Furthermore, it is more preferable that nanowires other than a predetermined length are removed for device formation. For this purpose, as shown in FIG. 2 (e), an intermediate binding site 107 for binding the nanowire to the substrate is formed in the middle of the pair of opposing fixed sites 102. This bonding may be due to physical bonding force or may be due to chemical bonding force.

  As a forming method, for example, a method of physically depositing a film that covers a nanowire at a site corresponding to an intermediate binding site and is connected to a substrate can be applied. A polymer coating such as PMMA is also applicable. As described above, since nanowires other than the predetermined nanowire remain on the substrate in a state where one end is fixed, it is preferable that the formation of the intermediate fixing site is a process that does not use a technique such as spin coating. Specifically, partial polymer coating by a dispenser, insulating film using a hard mask, sputtering of metal or the like, vapor deposition, and the like can be applied. Further, a method of forming a site for photocrosslinking the nanowire surface and the substrate surface and irradiating light that causes a crosslinking reaction only at the intermediate fixing site can be applied. In this step, the nanowires 104 longer than the predetermined length and the nanowires 106 shorter than the predetermined length are aligned in a direction different from the opposing direction of the pair of immobilization sites 102, so It is not fixed to the substrate by formation.

  Thereafter, as shown in FIG. 2F, at least a part of the binding site at the end of the nanowire is removed. For example, when Au is formed on the end surface of the nanowire, only Au can be selectively dissolved and removed by immersion in a potassium iodide solution. In this step, the nanowire 105 having a predetermined length is fixed to the substrate at the intermediate fixing portion, but the nanowire 104 longer than the predetermined length or the nanowire 106 shorter than the predetermined length loses the connection portion with the substrate. Subsequently, the nanowire 104 longer than the predetermined length and the nanowire 106 shorter than the predetermined length are removed by flowing and replacing the solution and the solvent on the substrate, and only the nanowire 105 having the predetermined length is arranged in a predetermined position and direction. Immobilized on a substrate.

<Separation method>
(Second Embodiment)
A second embodiment according to the invention
A method for separating nanowires having a predetermined length, comprising:
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
Forming an intermediate fixing part for fixing the nanowire and the substrate in the middle of the paired fixing part;
Removing at least a portion of the binding site of the nanowire;
Is a nanowire separation method characterized by sequentially performing the steps.

  In the second embodiment, by the same method as the method described in the first embodiment, only the nanowires 105 having a predetermined length are arranged in a predetermined position and direction, and then the intermediate fixing site is continuously removed. Thereby, it is separated from the predetermined nanowire 105 substrate. For example, when the intermediate fixing part is a polymer such as PMMA, the intermediate fixing part can be removed with an organic solvent such as acetone without damaging the nanowire or the substrate. In this way, nanowires having a predetermined length can be separated and extracted.

<Board>
The substrate used in the present invention is not particularly limited in shape and configuration as long as it is a material on which an electrode can be placed. However, when a substrate having arranged nanowires is used as a device such as a field effect transistor, a substrate insulator It is desirable to use a material consisting of For example, as the insulator, glass, oxide, carbide, nitride, plastic made of a polymer material, or the like can be used. Further, even if the substrate is a conductor or a semiconductor, it can be applied by forming an insulator as described above on the surface thereof.

<Nanowire>
The nanowire used in the present invention is made of, for example, a semiconductor, a metal, a dielectric, or a composite thereof. As a semiconductor material, a group IV semiconductor such as silicon or germanium, a group III-V compound semiconductor such as GaAs, a group II-VI compound semiconductor such as InP, SiC, or the like can be used. Au, Pt, Pd, Ti, or the like can be used as the metal material. As the dielectric, SiO ₂ , SiN, HfO ₂ , Al ₂ O ₃ or the like can be used.

The nanowire can be formed using, for example, a VLS method.
The VLS method includes at least one material selected from Au, Al, Si, Sn, Pb, Ni, Fe, Ag, and the like, and a eutectic with a semiconductor to be a nanowire, such as Si, Ge, and C, described later. The material to be formed is applicable.

  The catalyst can be formed by a lift-off method or patterning by ordinary lithography. Further, it can be formed by dropping a solution containing metal fine particles (for example, an Au colloid-containing solution) onto the substrate. The particle size when the catalyst melts into droplets is preferably 200 nm or less. This is because supersaturation in the VLS growth of the nanowire described later can occur more suitably. In the case of using a thin film catalyst, the particle size can be controlled by the initial film thickness and the annealing conditions before supplying the semiconductor raw material to be nanowires. On the other hand, when a colloid is used, a nanowire having a diameter substantially equal to the initial colloid particle diameter is obtained.

Next, a nanowire raw material capable of forming a eutectic with the catalyst is supplied, and the substrate is heated to a temperature at which the catalyst and the semiconductor serving as the nanowire can take a eutectic state. For example, in the growth of silicon nanowires using catalyst Au, the temperature is higher than the eutectic temperature of 363 ° C. As the semiconductor material, a gas containing atoms constituting nanowires such as SiH ₄ , SiF ₄ , SiCl ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , GeH ₄ , CH ₄ , and C ₂ H ₆ can be used. Further, it is also possible to apply a gas phase supply from a solid semiconductor raw material which is a vapor deposition source or a target using a technique such as PLD or sputtering. By supplying the semiconductor raw material, the semiconductor species are dissolved in the catalyst to form eutectic molten droplets. By continuing to supply the semiconductor raw material, the composition ratio of the semiconductor species in the molten droplet reaches supersaturation, and the semiconductor crystal grows. This is a so-called VLS growth method, and nanowires can be obtained by this method.

  The nanowire used in the present invention preferably has a diameter in the range of 1 nm to 200 nm, more preferably 5 nm to 100 nm. The length is preferably 1 μm or more and 50 μm or less.

<Fluid>
As the fluid used in the present invention, it is desirable to use a solvent that has low volatility and is deaerated. By using such a solvent, generation of oxygen and bubbles in the flow path are prevented, and the fluid can be efficiently contacted with the nanowire. For example, the fluid used in the present invention includes pure water, metal salt buffer aqueous solution, organic salt buffer aqueous solution containing a salt of carboxylic acid derivative such as triethylammonium acetate and ammonium derivative, imidazolium ion, pyridinium ion, etc. An ionic liquid composed of an anion such as a cation and tetrafluoroborate ion or hexafluorophosphate ion, or a low-volatile organic solvent such as dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, dioxane or N-methylpyrrolidone can be used. The degassed solvent is prepared by bubbling the solvent with nitrogen for a predetermined time.

<Sequence method>
Example 1
In this example, a nanowire having binding sites at both ends of the nanowire is produced using (a)-(j) in FIG. 3, and the immobilization site placed on the substrate has a predetermined length. The production of a field effect transistor sensor using a technique for arranging nanowires will be described.

(1-1) Fabrication of a substrate on which an immobilization site is installed As shown in FIG. 3 (a), on a silicon substrate 201 on which an oxide film is formed, at a predetermined position on the substrate using a known lithography process. A pair of immobilization sites 202 separated by a predetermined distance is formed. Specifically, patterning is performed with a photoresist (manufactured by Sumitomo Chemical Co., Ltd.), and openings are formed in predetermined shapes and positions. Then, after immobilizing APTES (Aminopropyltrioxysilane) in a solution diluted with ethanol by 10%, the resist is removed with acetone to form the immobilization site 203. When patterning to a width of submicron or less, patterning is performed using an electron beam (electron beam lithography). In this embodiment, the interval between the immobilization site pairs is 40 μm, and a circular APTES pattern pair of 500 nm is formed. At the same time, in order to prevent connection between adjacent immobilization sites, the interval between adjacent immobilization sites is set to 80 μm or more.

(1-2) Immobilization and arrangement of nanowires As shown in FIG. 3 (b), formed in (1-1) in a dispersion containing silicon nanowires 204, 205, and 206 terminated at both ends with Au. Immerse the finished substrate. Here, the length of the nanowire is different depending on the variation in the catalyst diameter described above. It is assumed that a nanowire shorter than a predetermined length is 206, a nanowire having a predetermined length is 205, and a nanowire longer than a predetermined length is 204. A method for forming silicon nanowires terminated at both ends with Au will be described in (1-a). Thereafter, as shown in FIG. 3C, stirring is performed so that the end bonding site of the nanowire is bonded to the fixing site on the substrate.
Thereafter, the substrate is pulled out of the solution in a direction perpendicular to the fixing portion where the nanowires are arranged, so that the liquid flows on the substrate as shown by the arrow in FIG. 3D, and the nanowire longer than a predetermined length is obtained. 204 and nanowires 206 shorter than a predetermined length are aligned in the direction of flow. On the other hand, since both ends of the nanowire 205 having a predetermined length are fixed, the direction does not change. Then, only predetermined nanowires are arranged by natural drying.

(1-3) Formation of intermediate fixing portion As shown in FIG. 3 (e), in the substrate manufactured in (1-2), intermediate fixing is performed at a location that covers substantially the middle of the pair of fixing portions. Site 207 is formed. In this step, since a wire longer or shorter than a predetermined length is fixed on one end of the substrate, a process capable of selectively forming a film without using a fluid flow method such as spinner coating is preferable. In this example, a dispenser (NanoMaster SMP-III, manufactured by Musashi Engineering Co., Ltd.) is used, and positive photoresist ma-P1275 (manufactured by OSTECH) is coated in the middle of the immobilization site with a diameter of 20 μm. Subsequently, PMMA is solidified by baking at 100 ° C. for 5 minutes. In order to reduce the adhesion of the resist and the spread after dispensing, the substrate is preferably subjected to UVO3 treatment in advance. For example, UV-300H (manufactured by SUMCO) may be used for about 1 minute. Since both ends of the nanowire 205 having a predetermined length are bonded so as to straddle the opposite immobilization sites, the nanowire 205 is fixed on the substrate with a photoresist. The directions of the nanowires other than the predetermined length are aligned substantially perpendicular to the opposing direction of the pair of immobilization sites, and thus are not affected by the formation of the intermediate immobilization site.

(1-4) Removal of Binding Site Subsequently, the substrate is immersed in a gold etching solution AURUM-302 (Kanto Chemical) for 1 minute. As a result, Au at both ends of the nanowire is etched. As shown in FIG. 3 (f), the nanowire 205 having a predetermined length in the fixing of (1-3) is not released from the substrate because it is fixed to the substrate at the intermediate fixing portion 207, but is longer than the predetermined length. The long nanowire 204 and the nanowire 206 shorter than a predetermined length are released from the substrate because the binding site with the substrate disappears. By rinsing with ethanol after the etching, the nanowire 204 longer than the predetermined length and the short nanowire 206 are removed from the substrate.

(1-5) Wiring and Electrode Formation Subsequently, as shown in FIG. 3G, the electrode 208 is formed so as to cover both ends of the nanowire. Both ends are exposed by a known lithography technique and immersed in 5% diluted hydrofluoric acid for 1 minute to remove the natural oxide film on the nanowire surface. Then, Ti5nm and Au100nm are vapor-deposited in this order, and an electrode can be formed in the silicon | silicone exposed part of both ends of nanowire by immersing in acetone for 10 minutes. In order to supply a potential so as not to interfere with a later-described solution cell, the electrode is preferably formed by extending to the end of the chip.
By the above-mentioned acetone immersion, the photoresist that has formed the intermediate fixing portion 207 as shown in FIG. Since both ends of the nanowire 205 having a predetermined length are fixed by the electrodes 208, they are not released from the substrate.

(1-6) Formation of Insulating Film Subsequently, in order to electrically separate the electrode and the solution containing the measurement object to be filled in the solution cell described later, only the region of the nanowire 205 serving as a sensor is exposed, and the solution cell As shown in FIG. 3I, the insulating film 209 is covered so as to cover the electrode 208 in the formation region. This can be easily achieved by silicon oxide film formation by normal lithography and sputtering, and lift-off.

(1-7) Flow path formation Subsequently, the solution cell 210 for storing the solution containing the detection object is produced in the following procedure using PDMS (polydimethylsiloxane). On a glass substrate, a mixture of PDMS (manufactured by Aldrich) and a curing agent (manufactured by Aldrich) at a ratio of 10: 1 is poured, baked and cured. Thereafter, the exposed portion of the nanowire 205 shown in FIG. 3I and the portion of the electrode 208 that is not covered with the insulating film 209 are removed. The removal can be easily processed with a tool capable of cutting the PDMS.
Alternatively, a mold that can form PDMS having the above-described shape is formed, and a mixture of PDMS (manufactured by Aldrich) and a curing agent (manufactured by Aldrich) in a ratio of 10: 1 is poured into the mold and baked. Then, the solution cell 210 can also be formed by curing.
Thereafter, the cured PDMS is peeled off and attached to the insulating film 209 on the substrate 201 manufactured as described above. Cured PDMS has self-adhesiveness to a flat surface and can be easily attached. FIG. 3J shows a device conceptual diagram after pasting.

  Through the above steps, a nanowire FET sensor as reported in Non-Patent Document 3 can be produced by selectively using nanowires having a predetermined length and diameter at predetermined positions.

(1-a) Method for Producing Dispersion Containing Silicon Nanowire Ended with Au at Both Ends Hereinafter, a method for producing a nanowire and a method for forming binding sites at both ends will be described with reference to FIG.
A silicon substrate having a plane orientation (111) is used as the substrate 301 shown in FIG. Organic substances are removed from the substrate 301 by RCA cleaning, a natural oxide film is removed with a diluted HF solution, and then Au is deposited. Thereafter, the substrate is transferred to a CVD growth apparatus, annealed with an inert gas in a vacuum chamber, and then silane is introduced. As a result, silicon nanowires 302 are grown on the silicon substrate by the above-described VLS process. The nanowire diameter and length can be adjusted by the Au thickness, annealing temperature, annealing time, growth temperature, growth time, and reaction gas pressure. In this embodiment, the maximum value of the assumed length variation is minimum at 40 μm or more. The parameter is controlled so that the value is 40 μm or less. Furthermore, control is performed so that the maximum value of variation becomes smaller than the adjacent fixed pair interval of 80 μm. This prevents a wire longer than a predetermined length from interfering with an adjacent immobilization site. For example, annealing is performed in He gas at 2 Torr at an Au thickness of 3 nm and a temperature of 550 ° C. for 30 minutes. Subsequently, silane gas diluted by 10% with He is introduced under the same temperature condition, and grown for 60 minutes. A nanowire centered on 40 nm and 40 μm in length will be obtained. Since the VLS method is used as shown in FIG. 4A, catalyst Au303 remains on the tip of the nanowire after growth.

Next, a binding site is formed at the other end of the nanowire.
As shown in FIG. 4B, a natural oxide film 304 is formed on the surface of the nanowire by sufficiently exposing to the atmosphere or oxygen atmosphere after the growth. Thereafter, as shown in FIG. 4 (c), the nanowire growth substrate was immersed in a solution 305 obtained by diluting sodium tetrachloroaurate (III) acid (dihydrate) (Mitsuwa Chemical Co., Ltd.) to 1 mM with ethanol. Then, as shown in FIG. 4D, ultrasonic waves are applied so that the nanowire starts to peel from the substrate. Thereafter, the ultrasonic wave is stopped and kept in the solution for 30 minutes, so that the deposited Au 306 is formed only on the end face of the nanowire where silicon is exposed as shown in FIG. 4E (Non-patent Document 4).
In this way, silicon nanowires terminated at both ends with Au, and a dispersion containing the nanowires are obtained.

(Example 2)
In this example, fabrication of a MOSFET using a technique in which a nanowire having a binding site at both ends of a nanowire is fabricated and a nanowire having a predetermined length is disposed on an immobilization site disposed on a substrate will be described. .

  The same procedure is performed from (1-1) preparation of the substrate provided with the immobilization site described in Example 1 to (1-2) immobilization and arrangement of nanowires. Thereafter, the intermediate immobilization site is formed of an electrically conductive material. A material other than Au is deposited in consideration of the binding site removal step described later. In this embodiment, Ag paste (Nanopaste for fine wiring manufactured by ULVAC MATERIAL) is applied to a width of 20 μm between a pair of immobilization sites and baked at 250 ° C. Thereafter, (1-4) bonding site removal and (1-5) electrode formation are performed in the same manner as in Example 1 to form a MOSFET structure.

(Example 3)
In this example, fabrication of a MOSFET using a technique in which a nanowire having a binding site at both ends of a nanowire is fabricated and a nanowire having a predetermined length is disposed on an immobilization site disposed on a substrate will be described. .

  (1-1) Preparation of the substrate provided with the immobilization site described in Example 1 (1-5) Electrode formation is performed in the same manner as in Example 1. Thereafter, the intermediate binding site is removed by immersing the substrate in an acetone solution. Thereafter, using a known lithography technique, a MOSFET structure is formed by forming a gate electrode with a predetermined gate so as to cover the nanowire between the pair of fixed sites.

<Separation method>
Example 4
In this embodiment, a technique for separating and collecting only nanowires having a predetermined length will be described.
The same procedure is performed from (1-1) preparation of the substrate provided with the immobilization site described in Example 1 to (1-4) removal of the binding site. Thereafter, the substrate is immersed in an acetone solution, whereby PMMA is dissolved, and only nanowires having a predetermined length are collected in the solution.
The collected nanowire can then be used for sensor fabrication using the technique of Example 1, and can also be used for MOSFET fabrication using the techniques of Examples 2 and 3.

11 Nanowire 12 Binding site 101 Substrate 102 Immobilization site 103 Immobilization site pair 104 Nanowire 105 long for a predetermined length 105 Nanowire 106 of a predetermined length Nanowire 107 short for a predetermined length 107 Intermediate binding site 201 Substrate 202 Immobilization site pair 203 Immobilization site 204 Nanowire 205 long for a predetermined length Nanowire 206 for a predetermined length Short nanowire 207 for a predetermined length Intermediate immobilization site 208 Electrode 209 Insulating film 210 Solution cell 301 Substrate 302 Silicon nanowire 303 Catalyst Au
304 Natural oxide film 305 Solution 306 Precipitated Au

Claims (2)

A method of arranging nanowires for arranging nanowires at predetermined positions on a substrate, comprising:
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
A method of arranging nanowires, characterized in that the steps are sequentially performed. A method for separating nanowires having a predetermined length, comprising:
Producing a substrate provided with a pair of immobilization sites separated by a predetermined distance for fixing both ends of the nanowire;
Producing nanowires having binding sites for forming specific bonds with the immobilized sites on the substrate at both ends;
Dispersing the liquid containing the nanowire on the substrate, and binding the nanowire binding site to the immobilization site on the substrate;
Flowing a fluid substantially perpendicular to the opposing direction of the paired immobilization sites;
Forming an intermediate fixing part for fixing the nanowire and the substrate in the middle of the paired fixing part;
Removing at least a portion of the binding site of the nanowire;
A method for separating nanowires, characterized in that the steps are sequentially performed.

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