JP5510413B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor device in which a conductive path is formed by fine particles made of a conductor or a semiconductor and organic semiconductor molecules, and a method for manufacturing the same.

  Thin film transistors (hereinafter abbreviated as TFTs) are widely used as switching elements in electronic circuits, particularly active matrix circuits such as displays.

  Currently, most TFTs are Si-based inorganic semiconductor transistors using amorphous silicon (a-Si) or polycrystalline silicon (Poly-Si) as a semiconductor layer (channel layer). Since these manufacture uses a plasma chemical vapor deposition method (hereinafter abbreviated as CVD) for forming a semiconductor layer, the process cost is high. In addition, since heat treatment at a high temperature of about 350 ° C. is necessary, the process cost is increased and the substrate is restricted.

  In recent years, organic semiconductor transistors using organic semiconductor materials have been actively developed because they can be produced by low-cost processes and can be formed on flexible substrates such as plastics that have no heat resistance. Yes.

An organic semiconductor material can produce a TFT at a lower cost and at a lower temperature such as spin coating and immersion, but the mobility, which is a characteristic index of the TFT, is typically 10 ^{−3 to 1} cm ^2. / Vs has only been obtained (CD Dimitrakopoulos et al., Adv. Mater. (2002), 14, 99). This value is lower than α-Si mobility of several cm ² / Vs and Poly-Si mobility of approximately 100 cm ² / Vs, and the mobility required for display TFTs is 1 to 3 cm ² / V. Vs has not been reached. Therefore, improvement of mobility has become a major issue for organic semiconductor materials.

  The mobility of an organic semiconductor material is determined by charge transfer within a molecule and charge transfer between molecules.

  Intramolecular charge transfer is made possible by the delocalization of electrons to form a conjugated system. The movement of charge between molecules is performed by bonding between molecules, conduction due to overlapping of molecular orbitals by van der Waals force, or hopping conduction through trap levels between molecules.

In this case, the mobility in the molecule is μ-intra, the mobility due to the bond between molecules is μ-inter, and the mobility of hopping conduction between molecules is μ-hop.
μ-intra ≫ μ-inter ＞ μ-hop
There is a relationship. In organic semiconductor materials, charge mobility is low because slow intermolecular charge transfer limits mobility as a whole.

  Various studies have been made to improve the mobility of organic semiconductors.

For example, when a pentacene thin film of an organic semiconductor material is formed by a vacuum evaporation method, the deposition rate of evaporation is extremely suppressed, and the substrate temperature is suppressed to room temperature, thereby improving the molecular orientation and the mobility as 0. 0.6 cm ² / Vs is achieved (for example, see Non-Patent Document 1 below).

  This aims to improve mobility by improving the crystallinity of the material and suppressing hopping conduction between molecules. Although there is an improvement in mobility, the movement between molecules limits the mobility as a whole, and a satisfactory mobility is not obtained.

  As an organic semiconductor transistor that positively utilizes charge transfer in a molecule, Lucent Technology has proposed a Self-Assembled Monolayer Field-Effect Transistor (SAMFET). In this method, a semiconductor layer made of a monomolecular film is formed between a source electrode and a drain electrode by self-assembly to realize an FET having a gate length of 1.5 nm.

In this method, since the channel is formed by the monomolecular layer oriented in the direction connecting the source electrode and the drain electrode, the movement of the charge in the channel is only the movement in the molecule. As a result, the Poly− A mobility of 290 cm ² / Vs higher than that of Si is achieved (for example, see Non-Patent Document 2 described later).

  However, in this channel structure, since the gate length is determined by the thickness of the monomolecular film, the gate length is as short as several nanometers, so that the breakdown voltage between the source and the drain is lowered, and the drive voltage can be increased. There is an inconvenience that it cannot be done. Further, in order to prevent the destruction of the monomolecular film, it is necessary to cool the substrate temperature to −172 ° C. to −30 ° C. in order to form the electrode on the monomolecular film, which increases the process cost. Not right.

  Further, a channel material using an organic / inorganic hybrid material has been proposed by International Business Machines (IBM) (for example, see Patent Document 1 described later). In this method, the inorganic component and the organic component form a layered structure, and while utilizing the high carrier mobility characteristics of the inorganic crystalline solid, the organic component utilizes the function of promoting the self-organization of the inorganic material, Allows material to adhere to the substrate under low temperature processing conditions.

Although the mobility is expected to be 1 to 100 cm ² / Vs, the actually achieved mobility is 0.25 cm ² / Vs. This is generally higher in mobility than an organic semiconductor formed by spin coating, but is similar to an organic semiconductor formed by vapor deposition or the like, and a mobility higher than a-Si is not obtained.

JP 2000-260999 A

C. D. Dimitrakopoulos et al., IBM J. Res. & Dev. (2001), 45, 11 J. H. Schoen et al., Nature (2001), 413, 713; Appl. Phys. Lett. (2002), 80, 847

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device that has a novel structure in which a conductive path formed using an organic semiconductor molecule as a material and exhibits high mobility, and It is in providing the manufacturing method.

  That is, the present invention relates to a semiconductor device configured such that a conductive path is formed by fine particles made of a conductor or a semiconductor and organic semiconductor molecules bonded to the fine particles, and the conductivity of the conductive path is controlled by an electric field. This relates to the manufacturing method.

According to the present invention, since the fine particles are connected by the organic semiconductor molecule to form a conductive path, the conductive path in the fine particle and the conductive path along the molecular skeleton in the organic semiconductor molecule are connected. A network-type conductive path can be formed.
As a result, charge transfer in the conductive path is dominant in the molecular axial direction along the main chain of the organic semiconductor molecule. Since the conductive path does not include electron transfer between molecules, the mobility is not limited by the electron transfer between molecules, which is the cause of the low mobility of the conventional organic semiconductor.
Therefore, the charge transfer in the axial direction in the organic semiconductor molecule can be utilized to the maximum extent. For example, when a molecule having a conjugated system formed along the main chain is used as the organic semiconductor molecule, high mobility due to delocalized π electrons can be used.

  Further, since the channel region forming the conductive path can be formed for each layer in a low temperature process of 200 ° C. or lower under normal pressure, a channel layer having a desired thickness can be easily formed, such as a plastic substrate. A semiconductor device can be manufactured on a flexible substrate at low cost.

It is the schematic sectional drawing (a) which shows an example of the structure of the MOS field effect transistor based on Embodiment 1 of this invention, the principal part enlarged view (b), and the image figure (c) of a charge transfer. It is a schematic sectional drawing which shows the structure of the other MOS type field effect transistor. It is a schematic sectional drawing which shows the manufacturing process of the MOS field effect transistor based on Embodiment 2 of this invention. It is a schematic sectional drawing which shows the manufacturing process of a MOS type field effect transistor equally. It is a partially expanded schematic sectional drawing which shows the structure of the MOS type field effect transistor based on Embodiment 4 of this invention. FIG. 6 is a transmission electron micrograph of gold nanoparticles when dodecanethiol is used as a protective film for the gold nanoparticles. 2 is a transmission electron micrograph of gold nanoparticles (manufactured by Harima Chemical Co., Ltd.) when an organic molecule having an amino group at the terminal is used as a protective film for the gold nanoparticles. The same is the particle size distribution of gold nanoparticles measured and analyzed by small-angle X-ray scattering. 3 is a scanning electron micrograph of a SiO ₂ / Si substrate on which a conjugate of the organic semiconductor molecule having an amino group at the end and a gold nanoparticle (manufactured by Harima Chemicals) is formed. FIG. 3 is a transmission electron micrograph when dodecanethiol as an organic semiconductor molecule and gold nanoparticles are adhered on a MoS ₂ substrate cleanly. FIG. 6 is a transmission electron micrograph of a gold nanorod having an aspect ratio of 6: 1 (minor axis = 10.6 nm, major axis = 62.6 nm). FIG. 2 is a conceptual diagram when nanorods are used as the fine particles. FIG. 2 is a conceptual diagram when nanorods are used as the fine particles. It is a partially expanded schematic sectional drawing which compares and shows the MOS field effect transistor based on Embodiment 5 of this invention. Gold fine particles based on the sixth embodiment of the present invention is applied SiO ₂ / Si substrate, which is a transmission electron micrograph of rinsed with toluene. The same is a transmission electron micrograph after gold fine particles are coated on a SiO ₂ / Si substrate, surface-treated with AEAPTMS, and rinsed with toluene. It is a partially expanded schematic sectional drawing which shows an example of the manufacturing process of the MOS field effect transistor based on the Example of this invention. It is a partially expanded schematic sectional drawing which shows an example of the manufacturing process of a MOS type field effect transistor. 4 is a graph of current-voltage characteristics when a source-drain current (I _sd ) with respect to a source-drain voltage (V _sd ) of a field effect transistor is measured. It is a partially expanded schematic sectional drawing which shows the other example of the manufacturing process of a MOS field effect transistor equally.

  In the present invention, a functional group at the terminal of the organic semiconductor molecule is chemically bonded to the fine particle, and the organic semiconductor molecule and the fine particle are alternately bonded by the functional group of the organic semiconductor molecule at both ends, A network-type conductive path in which the conductive path in the fine particle and the conductive path in the organic semiconductor molecule are two-dimensionally or three-dimensionally connected is preferably formed.

  As a result, the charge transfer in the conductive path is dominant in the axial direction of the molecule along the main chain of the organic semiconductor molecule, and the mobility in the axial direction of the molecule, for example, due to delocalized π electrons. High mobility can be used to the maximum.

  As a result, an organic semiconductor transistor can be provided that can realize unprecedented high mobility comparable to a monolayer transistor.

  In the present invention, a channel region having the conductive path is formed, source and drain electrodes are provided on both sides of the channel region, a gate electrode is provided between these electrodes, and an insulated gate (for example, MOS: Metal Oxide Semiconductor) type A field effect transistor is preferably constructed. This structure can also operate as an optical sensor or the like by using a dye that absorbs light near the visible region as an organic semiconductor molecule having a conjugated system.

  In this case, the field effect transistor is preferably formed on a flexible substrate made of an organic material, and the gate insulating film on the gate electrode is preferably made of an organic material.

  The source and drain electrodes are preferably made of the same material as the fine particles.

  In the present invention, the conductive path is preferably formed by a single layer or a plurality of layers of a conjugate of the fine particles and the organic semiconductor molecules.

  Specifically, in this case, a single layer of the combined body is formed by performing the step of contacting the organic semiconductor molecules once after forming the layer of fine particles, or by repeating this step twice or more. Multiple layers are formed.

  In this case, the first fine particle layer is preferably formed on a base layer having good adhesion to the fine particles.

  The underlayer is preferably made of a silanol derivative, that is, a silane coupling agent. In this case, the underlayer can also be used as a gate insulating film on the gate electrode.

  According to this, it is not necessary to form the gate insulating film such as an oxide film by an expensive and time consuming process. Therefore, the configuration of the entire transistor becomes simpler, and the number of manufacturing process steps is reduced. In addition, the thickness of the entire transistor can be suppressed, and the gate insulating film formed of the base layer can be manufactured by a manufacturing process using a solution, thereby reducing the cost and time required for manufacturing the device. It becomes possible.

  In order to chemically bond the substrate provided with the gate electrode and the fine particles through the silane coupling agent, the silane coupling agent has an amino group or a thiol group that reacts with the fine particles at one end. It is important to have a functional group and an alkoxyl group that reacts with a hydroxyl group on the substrate at the other end.

  Specific examples of the silane coupling agent include N-2 (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) γ-aminopropyltrimethoxysilane (AEAPTMS, the following structural formula (1)). N-2 (aminoethyl) γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane (APTMS, the following structural formula (2)), 3-aminopropylmethyldiethoxysilane (APMDES, the following structural formula (3) )) 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane (MPTMS, structural formula (4) below), 3-mercaptopropylmethyldimethoxysilane (MPMDMS, Structural formula (5) below, mercaptomethyldi Tyrethoxysilane (MMDMES, structural formula (6) below), Mercaptomethylmethyldiethoxysilane (MMMDES, structural formula (7) below), 3-cyanopropyldimethylmethoxysilane (CPDMMS, structural formula (8) below), 3 -Cyanopropyltriethoxysilane (CPTES, the following structural formula (9)), 2-pyridylethyltrimethoxysilane (PETMS, the following structural formula (10)), 2- (diphenylphosphino) ethyltriethoxysilane (DPPETES, the following) Structural formula (11)) can be given. Here, if the length of the alkyl chain in a molecule | numerator is changed, not only said well-known silane coupling agent but a new material can be synthesize | combined according to the use.

Moreover, not only the above-mentioned general silane coupling agent can be used for the application of the present invention. The silane coupling agent is only required to be chemically bonded to both the substrate provided with the gate electrode and the fine particles, and a dithiol-based material having thiol groups at both ends may be used. For example, decanedithiol _{(HS-C 10 H 20 -SH} ) , and the like.

  The basic structure of the silane coupling agent is a quasi-one-dimensional structure in which many of them can define a main chain, but not limited to this, assuming that a two-dimensional or three-dimensional molecule is used. However, it is sufficient that the element parts to be bonded to each of the substrate and the fine particles are properly bonded. However, the transistor characteristics formed by the network structure composed of the fine particles should not deteriorate or be destroyed at that time.

  Further, when the base layer is also used as the gate insulating film, the silane coupling agent must have poor electrical conductivity. Therefore, there is no problem as long as the main chain of the silane coupling agent is an alkyl chain, but it is difficult to use a conjugated chain that is considered to have good conductivity in the application of the present invention.

  Furthermore, a nucleic acid (DNA) or the like can be used instead of the silane coupling agent.

  In the present invention, the fine particles are preferably fine particles made of gold, silver, platinum, copper, or aluminum as the conductor, or cadmium sulfide, cadmium selenide, or silicon as the semiconductor. The particle diameter is preferably 10 nm or less.

  Here, examples of the shape of the fine particles include a spherical shape, but the present invention is not limited to this. For example, in addition to the spherical shape, a triangular shape, a cubic shape, a rectangular parallelepiped shape, a conical shape, and the like can be given.

  In addition, the microparticles are nanorods (or nanofibers) having a short axis of 10 nm or less having an anisotropic shape in one dimension (Ser-Sing Chang, Chao-Wen Shih, Cheng-Dah Chen, Wei-Cheng Lai, and CR Chris Wang, “The Shape Transition of Gold Nanorods” Langmuir (1999), 15, 701-709) or nanotubes. In this case, it is preferable that the distance between the source and drain electrodes is shorter than the major axis of the nanorod.

  If the nanorods or nanotubes are used as the fine particles, there is a high possibility that they can be arranged more regularly and in parallel than spherical nanoparticles even if the sizes (major axis / minor axis) vary to some extent.

The organic semiconductor molecule is an organic semiconductor molecule having a conjugated bond, and has a thiol group (—SH), an amino group (—NH ₂ ), an isocyano group (—NC), a thioacetoxyl group (—SCOCHH group) at both ends of the molecule. ₃ ) or a molecule having a carboxyl group (—COOH). For example, 4,4′-biphenyldithiol (BPDT) of the following structural formula (12), 4,4′-diisocyanobiphenyl of the following structural formula (13), 4,4′-diisocyano of the following structural formula (14) -P-terphenyl, 2,5-bis (5'-thioacetoxyl-2'-thiophenyl) thiophene of the following structural formula (15), 4,4'-diisocyanophenyl of the following structural formula (16) Or Bovin Serum Albumin, Horse Redish Peroxidase, antibody-antigen, etc. These are all π-conjugated molecules and preferably have functional groups that are chemically bonded to the fine particles in at least two places.

  Further, as the organic semiconductor molecule, a dendrimer represented by the following structural formula (17) can also be used.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1: MOS field effect transistor]
FIG. 1 is a schematic cross-sectional view (a) illustrating an MOS field effect transistor according to the first embodiment, an enlarged view of a main part (b), and an image diagram (c) of charge transfer.

  FIG. 1A shows a device structure of a MOS field effect transistor often used as a TFT. A gate electrode 2, a gate insulating film 3, a source electrode 4, and a drain electrode are formed on a substrate 1 by a known technique. 5 is formed first, and a channel layer 6 composed of a combination of fine particles 8 and organic semiconductor molecules 9 is formed thereon. In addition, illustration and description are abbreviate | omitted here for the molecular solder layer (the said underlayer) mentioned later.

  As the substrate 1, for example, a plastic substrate such as polyimide, polycarbonate, polyethylene terephthalate (PET), glass, quartz, or silicon substrate is used. When a plastic substrate is used, a flexible semiconductor device such as a display having a curved surface can be manufactured.

  The transistor formed on the substrate 1 may be used as a monolithic integrated circuit in which a large number of transistors are integrated together with the substrate 1 as in the case of application as a display device. It may be used as a part.

  Examples of the material of the gate electrode 2 include a conductive polymer, gold (Au), platinum (Pt), aluminum (Al), nickel (Ni), titanium (Ti), and a conductive material such as polysilicon, or these. A combination of these can be used.

Examples of the material for the gate insulating film 3 include polymethyl methacrylate (PMMA), spin-on glass (SOG), silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), metal oxide high dielectric insulating film, and the like. A combination of these can be used.

  Examples of the material of the source electrode 4 and the drain electrode 5 include a conductive substance such as gold (Au), palladium (Pd), platinum (Pt), chromium (Cr), nickel (Ni), and a conductive polymer, or A combination of these can be used.

  According to this embodiment mode, since the processing temperature in the manufacturing process can be suppressed to 200 ° C. or lower, all of the above materials can be composed of organic compounds.

  The channel layer 6 is formed of a combined body in which fine particles 8 and organic semiconductor molecules 9 are bonded in a network shape, and carrier movement is controlled by the gate voltage of the gate electrode 2.

  The fine particles 8 are fine particles having a particle diameter of 10 nm or less. Examples of the material thereof include conductors such as gold (Au), silver (Ag), and platinum (Pt), cadmium sulfide (CdS), and cadmium selenide (CdSe). A semiconductor such as silicon (Si) can be used.

The organic semiconductor molecule 9 is an organic semiconductor molecule having a conjugated bond in the molecular skeleton, and a functional group that can be chemically bonded to the fine particle 8 at the end of the molecule, such as a thiol group (—SH), an amino group (—NH ₂ ). ), An isocyano group (—NC), a thioacetoxyl group (—SCOCH ₃ ), a caxboxyl group (—COOH), and the like are used. A thiol group, an amino group, an isocyano group, and a thioacetoxyl group are functional groups that bond to conductive fine particles such as Au, and a caxboxyl group is a functional group that binds to semiconductor fine particles.

  Specifically, as the organic semiconductor molecule 9, for example, 4,4′-biphenyldithiol of the following structural formula (12), 4,4′-diisocyanobiphenyl of the following structural formula (13), the following structural formula (14 ), 4,4′-diisocyano-p-terphenyl, 2,5-bis (5′-thioacetoxyl-2′-thiophenyl) thiophene of the following structural formula (15), 4, of the following structural formula (16) Examples thereof include 4′-diisocyanophenyl, Bovin Serum Albumin, Horse Redish Peroxidase, and antibody-antigen.

  Further, as the organic semiconductor molecule 9, a dendrimer represented by the following structural formula (17) can also be used.

  In the channel layer 6, the fine particles 8 are two-dimensionally or three-dimensionally connected by the organic semiconductor molecules 9, and the conductive path in the fine particles 8 and the conductive paths along the molecular skeleton in the organic semiconductor molecules 9 are connected. A conductive path is formed.

  As shown in the enlarged view of FIG. 1 (b), the above-described conductive path does not include intermolecular electron transfer, which is the cause of the low mobility of the conventional organic semiconductor, and the electron transfer within the molecule is Since it is carried out through a conjugated system formed along the molecular skeleton, high mobility is expected.

  Electron conduction in the channel layer 6 is performed through the network type conductive path 10 as shown in FIG. 1C, and the conductivity of the channel layer 6 is controlled by a voltage applied to the gate electrode 2.

  On the surface of the region where the channel layer 6 is formed on the substrate 1, a molecular solder layer (not shown) is provided as the base layer that serves as an adhesive for fixing the fine particles 8 for one layer. . As a molecule that plays the role of solder, a molecule that is a silane compound and has a functional group that can be chemically bonded to both the substrate provided with the gate electrode and the fine particles is used.

  For example, when the fine particles 8 and the source electrode 4 and the drain electrode 5 are made of gold, (3-aminopropyl) trimethoxysilane (APTMS) having an amino group or a thiol group having an affinity for gold. Or a mercapto silane.

  In the step of forming the channel layer 6, after forming one layer of the fine particles 8, the organic semiconductor molecules 9 are brought into contact with the fine particles 8 to form a combined body of the fine particles 8 and the organic semiconductor molecules 9. One layer is formed. Thus, the channel layer 6 is formed one layer at a time. Therefore, the channel layer 6 having a desired thickness can be formed by repeating this process many times.

  The channel layer 6 may be a single layer, but usually two or more layers and ten layers are preferable. The thickness of one layer is not significantly different from the particle size (several nm) of the fine particles 8. If the fine particles 8 are fine particles made of gold and have a particle size of about 10 nm, and if 10 layers are stacked, the thickness of the channel layer 6 is approximately 100 nm. Therefore, the thickness of the source electrode 4 and the drain electrode 5 is preferably 100 nm or more.

  Since the channel layer 6 is formed independently for each layer, the material constituting the fine particles 8 and the particle diameter of the fine particles 8 or the organic semiconductor molecules 9 are changed for each of the combined layers or for each of the plurality of combined layers. The characteristics of the channel layer may be controlled.

  The MOS field effect transistor may have various structures other than FIG. 1A, and may be any type of structure. The channel layer 6 can be formed first, and the source electrode 4 and the drain electrode 5 can be formed thereon by vapor deposition or the like. In this case, the structure is, for example, the top gate type shown in FIG. 2 (b) bottom gate type. In addition, the dual gate type of FIG. 2C can be used, and in that case, the conductivity of the channel layer 6 can be controlled more effectively.

[Embodiment 2: Fabrication of MOS transistor]
Hereinafter, the manufacturing process of the MOS field effect transistor according to the first embodiment shown in FIG. 1A will be described with reference to FIGS. Here, gold is used as the material of each of the electrodes 2, 4, 5 and the fine particles 8, 4,4′-biphenyldithiol is used as the organic semiconductor molecule 9, and (3-aminopropyl) is used as the solder molecule (silane coupling agent) 7. ) Trimethoxysilane (APTMS) will be used.

  First, the gate electrode 2, the gate insulating film 3, the source electrode 4 and the drain electrode 5 are formed on the substrate 1 using a known method.

Process 1
As the substrate 1, for example, a plastic substrate such as polyimide or polycarbonate, glass, quartz, or a silicon substrate is used.

  Gold (Au) is vapor-deposited on the substrate 1 while masking other portions to form the gate electrode 2. As a material of the gate electrode 2, in addition to gold (Au), for example, a conductive polymer, platinum (Pt), aluminum (Al), nickel (Ni), titanium (Ti) or other conductive substances, or these may be used. Combinations can be used, and they are formed by a lift-off method, a shadow mask method, a screen printing method, an ink jet printing method, or the like.

Process 2
Subsequently, the gate insulating film 3 is formed by a spin coating method, a sputtering method, a dipping method, a casting method, or the like. Examples of the material of the gate insulating film 3 include polymethyl methacrylate (PMMA), spin-on glass (SOG), silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), metal oxide high dielectric insulating film, and the like. A combination of these can be used.

Process 3
On the gate insulating film 3, gold (Au) is vapor-deposited while masking other portions to form the source electrode 4 and the drain electrode 5. As a material of the source electrode 4 and the drain electrode 5, in addition to gold (Au), for example, a conductive substance such as palladium (Pd), platinum (Pt), chromium (Cr), nickel (Ni), conductive polymer, etc. Alternatively, a combination of these can be used, and the film is formed by a lift-off method, a shadow mask method, a screen printing method, an ink jet printing method, or the like.

  Next, a channel layer 6 composed of fine particles 8 and organic semiconductor molecules 9 connected to each other with a three-dimensional network structure is formed.

Process 4
First, the surface of the region for forming the channel layer 6 is immersed in a solution having a volume concentration of several percent in which (3-aminopropyl) trimethoxysilane (APTMS) is dissolved in toluene or hexane, and then washed with toluene or hexane. After replacing the solution, the solvent is evaporated to form the molecular solder layer 7 as the underlayer for fixing the gold fine particles 8 for one layer. For example, mercapto silane may be used instead of APTMS.

Process 5
Next, the substrate 21 on which the molecular solder layer 7 is formed is immersed for several minutes to several hours in a dispersion (concentration of several mM) in which gold fine particles 8 are dispersed in a solvent such as toluene or chloroform, and then the solvent is evaporated. . As a result, the gold fine particles 8 are fixed to the surface of the molecular solder layer 7, and a gold fine particle layer 8 a composed of the gold fine particles 8 is formed on the molecular solder layer 7.

  The molecular solder layer 7 has a functional group such as an amino group that can be chemically bonded to the gold fine particle 8, and only one gold fine particle layer 8 a bonded to the functional group is fixed on the molecular solder layer 7. Is done. Excess gold fine particles 8 not fixed to the molecular solder layer 7 are washed away.

Step 6
Subsequently, after immersing the substrate 1 in a solution of 4,4′-biphenyldithiol 9 dissolved in toluene and having a molar concentration of several mM or less, the substrate 1 is washed with toluene to replace the solution, and then the solvent is evaporated. At this time, 4,4′-biphenyldithiol 9 is bonded to the surface of the gold fine particle 8 through the reaction of the thiol group at the end of the molecule. A large number of 4,4′-biphenyldithiol molecules 9 are bonded to the surface of one gold fine particle 8 so as to enclose the gold fine particle 8. Some of them also bind to other gold fine particles 8 through the reaction of the thiol group at the other molecular end, so that the gold fine particles 8 are linked in a two-dimensional network form by the 4,4′-biphenyldithiol molecules 9. Thus, the first combined body layer 6a is formed.

  Since many unreacted thiol groups of 4,4′-biphenyldithiol 9 remain on the surface of this conjugate layer 6 a, the surface of the conjugate layer 6 a has a strong binding force to the gold fine particles 9. doing.

Step 7
Next, in the same manner as in step 5, the substrate 1 is immersed in a dispersion obtained by dispersing gold fine particles 8 in a solvent such as toluene or chloroform for several minutes to several hours, and then the solvent is evaporated. As a result, the gold fine particles 8 are bonded and fixed to the surface of the first combined layer 6a to form the second gold fine particle layer 8b.

  Here, the second-layer gold fine particles 8 are connected to the first-layer gold fine particles 8 by 4,4′-biphenyldithiol 9 and are connected to the same second-layer gold fine particles 8. The eight are indirectly connected through the second layer of gold fine particles 8, and the connection is three-dimensional.

Process 8
Subsequently, the substrate 1 is immersed in a solution having a molar concentration of several mM or less in which 4,4′-biphenyldithiol 9 is dissolved in toluene in the same manner as in Step 6, and then the substrate 1 is washed with toluene to replace the solution. And then the solvent is evaporated. In the same manner as in Step 6, a large number of 4,4′-biphenyldithiol 9 is bonded so as to enclose the gold fine particles 8 and the gold fine particles 8 are connected by the 4,4′-biphenyldithiol molecules 9. Layer 6b is formed.

Step 9
Thereafter, by repeating Step 7 and Step 8, a channel layer in which a three-dimensional network type conductive path is formed can be formed one layer at a time. By appropriately selecting the number of repetitions, a channel layer 6 having a desired thickness can be formed (MD Musick et al., Chem. Mater. (1997), 9, 1499; Chem. Mater. (2000), 12, 2869).

  3 and 4, each combined body layer is formed of the same material. However, for each combined body layer or a plurality of combined body layers, the material constituting the fine particles 8 or the particle diameter of the fine particles 8 or The characteristics of the channel layer may be controlled by changing the organic semiconductor molecule 9. Further, although the channel layer 6 is formed also on the source electrode 4 and the drain electrode 5, the channel layer 6 may be formed only in a recess sandwiched between both electrodes.

  Alternatively, a field effect transistor having a structure shown in FIG. 2A or 2B can be manufactured by forming only a channel layer in advance and attaching it to the substrate 1 or the gate insulating film 3.

[Embodiment 3]
In the first and second embodiments, nanoparticles such as gold are used as the fine particles, and how the fine particles are regularly deposited on the substrate and bridged by the organic semiconductor molecules having a certain length. is important.

  A nanometer-sized particle is a cluster of hundreds to thousands of metal atoms, and is precisely a polyhedron, but is generally considered to be approximately spherical. Nanoparticles can have different diameter distribution widths depending on the raw materials. The narrow distribution width means that the particle diameters are well aligned, and if this is used to construct a two-dimensional network, it can be neatly packed in a close-packed manner. Conversely, if the particle sizes are not uniform, it is difficult to form a regular two-dimensional network.

  In the following, it is shown how the variation in the diameter of the gold nanoparticles affects when the particles are bonded on the substrate.

  As shown in a schematic diagram of an organic semiconductor transistor as a semiconductor device according to the present invention in FIG. 5, in a space where the gate insulating film 3 between the source electrode 4 and the drain electrode 5 having a macro size is exposed, Nanoparticles (for example, gold fine particles) 8 are regularly bonded, and organic semiconductor molecules 9 are bonded to the nanoparticles 8. Here, since the surfaces of the nanoparticles 8 are coated with a protective film made of chain-like insulating organic molecules, the nanoparticles 8 do not aggregate with each other.

  The insulating organic molecule is bonded to a metal cluster (the nanoparticle) that hits the core, but the magnitude of the binding force greatly affects the final diameter distribution when the nanoparticle is synthesized. ing.

One end of the insulating organic molecule is provided with a functional group that chemically reacts (bonds) with the nanoparticles. For example, examples of the functional group can be exemplified thiol group (-SH), mention may be made of dodecanethiol (C ₁₂ H ₂₅ SH) as one molecule with the thiol group at the end. It is said that when the thiol group is bonded to the nanoparticles such as gold, the hydrogen atom is removed to become C ₁₂ H ₂₅ S—Au.

  FIG. 6 is a transmission electron micrograph of gold nanoparticles actually synthesized using dodecanethiol as the protective film. As is apparent from FIG. 6, it can be seen that the diameters of the gold nanoparticles are very well aligned. (For the preparation of gold nanoparticles using the insulating organic molecule having a thiol group as the protective film, the literature Mathias Brust, et al., J. Chem. Soc., Chem. Commun., 801 (1994) See.)

  On the other hand, an amino group can also be mentioned as the functional group that chemically reacts (bonds) with the nanoparticles. FIG. 7 is a transmission electron micrograph of gold nanoparticles actually synthesized using the insulating organic molecule having the amino group as a terminal functional group as the protective film. As is clear from FIG. 7, it can be seen that the size of the gold nanoparticles is larger than that of the thiol group in FIG. (Refer to the document Daniel V. Leff, et al., Langmuir 12, 4723 (1996) for the preparation of gold nanoparticles using the insulating organic molecules having amino groups as the protective film.)

  It is generally known that the bond of “thiol group-gold” is stronger than that of “amino group-gold”. When synthesizing gold nanoparticles using the insulating organic molecule having an amino group as the protective film, the insulating organic molecule is a nanoparticle due to the weak tendency of the “amino group-gold” bond as a general tendency. Before completely enclosing (gold atom), there is a possibility of aggregation with other nanoparticles (gold atom), and as a result, it is considered that particles having a large particle size are likely to be formed. In the case of an amino group, there are not a few that appear to be bonded to each other even after the nanoparticles are encapsulated in the protective film.

  FIG. 8 shows the results obtained by measuring and analyzing the diameter distribution of the gold nanoparticles synthesized using the insulating organic molecules having a thiol group or amino group by small-angle X-ray scattering (transmission type). As is clear from FIG. 8, it can be seen that the gold nanoparticles protected with a thiol group have a smaller particle size than the amino group and a smaller degree of diameter distribution. This result seems to reflect well what was seen in FIG. 6 and FIG.

  Next, it will be shown what kind of difference occurs between nanoparticles having a uniform particle size and nanoparticles not having a uniform particle size when the above-mentioned nanoparticles are attached to the substrate.

  FIG. 9 is a scanning electron micrograph when the gold nanoparticles having the protective film made of the insulating organic molecules having an amino group on the surface are deposited on a substrate. The adhesion process of gold nanoparticles may not be optimized, but focusing on the area where the particles are clogged, rather than being regularly arranged, irregularly sized particles are randomly arranged densely. ing.

  FIG. 10 shows a transmission electron microscope in which a single layer of gold nanoparticles having the protective film made of the insulating organic molecule having a thiol group on the surface and having a very uniform particle size is attached to the substrate. (This transmission electron micrograph is based on the research of Prof. Andres et al., Purdue University, USA. (FIG. RP Andres, et al. J. Vac. Sci. Technol. A 14, 1178 (1996) .1))). According to FIG. 10, it can be seen that the gold nanoparticles are adhered in a very regular and close-packed manner, except for a few defects.

  From the above, it seems that it is not easy to create a regular two-dimensional array using nanoparticles having non-uniform diameters.

  Therefore, in the present embodiment, a nanorod (or nanotube) such as gold having a more one-dimensional shape is used as the fine particle instead of the nanoparticle having a pseudo zero-dimensional shape. As a result, even if there are variations in size (major axis / minor axis) to some extent, there is a high possibility that they can be arranged more regularly and in parallel than spherical nanoparticles. Even when the minor diameter varies, when attention is paid to a single nanorod, even if the minor diameter varies between nanorods, they are easily aligned in parallel.

  When the nanorods are used as the fine particles, a transistor can be formed by bridging the nanorods with the organic semiconductor molecules in the same manner as described above. Using one organic semiconductor molecule means that a certain length is required between nanorods (or nanoparticles), and it is easy to say that regular arrangement of rods (particles) is very important. I understand.

  The synthesis of the nanorods has been performed so far, and a submicron size such that the major axis direction is from several tens of nanometers to the minor axis, which is a little less than 10 nm, and the long one is more than 500 nm. Even things are synthesized. Furthermore, the aspect ratio is close to 20, and it is possible to synthesize even a very one-dimensional rod (reference Ser-Sing Chang, et al., Langmuir 15, 701 (1999), Hiroshi Yao, et al., (See Chemistry Letters, 458 (2002).)

  In the nanorod, an ammonium bromide-based molecule represented by cetyl bromide, trimethyl ammonium, is used as a protective film. These are made electrochemically in a water-soluble electrolyte. Therefore, what is referred to as a protective film here is a general “surfactant”. Since cetyl, trimethyl, and ammonium bromide are “cationic surfactants”, anionic bromine faces nanorods such as gold. That is, the nanorod such as gold can be formed in a surfactant micelle.

  There is no precedent that the nanorods such as gold are bonded on the substrate, but the simple process of dropping the gold nanorod solution on the observation grid of the transmission electron microscope for diameter observation and evaporating the solvent already Many have been reported to line up regularly. FIG. 11 is a transmission electron micrograph (Ser-Sing Chang, et al., Langmuir 15, 701 (1999)). The aspect ratio of the gold nanorod in FIG. 11 is 6: 1, the minor axis is 10.6 nm, and the major axis is 62.6 nm.

  This suggests that the nanorods can be used as the fine particles instead of the nanoparticles in the production of an organic semiconductor transistor. The path to optimize the process of bonding the nanorods to the substrate is also expected to be less steep than in the case of the nanoparticles.

  In this case, it is preferable that the distance between the source electrode and the drain electrode in the transistor structure is shorter than the major axis of the nanorod.

  In this case, a substrate in which parallel electrodes (source and drain electrodes) are formed in advance so that the distance between the electrodes is shorter than the major axis of the nanorod is immersed in the nanorod solution, and the nanorod is bonded onto the substrate. By making the distance between the electrodes shorter than the major axis of the nanorods, the nanorods can enter the gate insulating film between the parallel electrodes only when the nanorods are positioned parallel to the electrodes.

  FIG. 12A is a conceptual diagram in the case where the distance between the source electrode 4 and the drain electrode 5 in the transistor structure is formed shorter than the major axis of the nanorod 14 and the nanorod 14 forms a large angle with respect to the electrodes 4 and 5. is there. In this case, when some external stimulus (for example, shaking the container of the nanorod solution when the substrate is immersed in the nanorod solution is considered), the nanorod 14 changes its angle, and FIG. It is considered that the nanorods 14 can be accommodated between the electrodes 4 and 5 as shown in FIG. In addition, the nanorods 14 that do not fit between the electrodes 4 and 5 even when the external stimulus is applied can be removed by removing the substrate from the nanorod solution and then rinsing with a solvent or the like.

  At this time, in order to prevent removal of the nanorods 14 accommodated between the electrodes 4 and 5, for example, a silane coupling agent is applied in advance on the substrate between the electrodes 4 and 5, and the nanorods 14 are formed on the silane coupling agent. May be formed.

  FIG. 13C is a conceptual diagram when a plurality of nanorods 14 are arranged in parallel between the electrodes 4 and 5 using the one-dimensionality of the nanorods 14.

  Then, after the nanorods 14 are formed on the substrate, as described above, the organic semiconductor molecules are bonded to the nanorods 14 to form a channel layer to construct a transistor.

  In this case, the channel layer may be a single layer, but usually two or more layers and about ten layers are preferable. The thickness of one layer is not significantly different from the minor axis (10 nm or less) of the nanorod. If the fine particles are nanorods made of gold and have a particle size of about 10 nm and 10 layers are stacked, the thickness of the channel layer is about 100 nm. Therefore, the thickness of the source electrode and the drain electrode is preferably 100 nm or more.

  Here, according to a study by Ser-Sing Chang et al. (Ser-Sing Chang, et al., Langmuir 15, 701 (1999)), it is possible to react thiol groups with gold nanorods surrounded by micelles. It is reported. They used mercaptopropyltrimethoxysilane. Since the thiol group is bonded to gold, in this case, the methoxy group is directed outward. When producing an organic semiconductor transistor, for example, if a dithiol-based conjugated organic semiconductor molecule is used as the organic semiconductor molecule, it will be possible to bridge gold nanorods surrounded by micelles.

[Embodiment 4]
In the other embodiments described above, the channel layer is made of a material composed of the organic semiconductor molecules and the fine particles. The organic semiconductor molecule has a group that can chemically bond to the fine particles at the terminal. Then, a structure is formed in which the organic semiconductor molecules and the fine particles are alternately bonded to form a network. Further, a MIS (Metal Insulator Semiconductor) FET (Field Effect Transistor) can be formed using a material formed by networking the organic semiconductor molecules and the fine particles as a channel material.

In general, the gate insulating film used in a normal silicon-based transistor is silicon oxide (SiO ₂ ). As a manufacturing method thereof, a thermal oxidation method is generally used in which a silicon substrate is processed at a high temperature.

  In an “organic transistor” using a semiconductor organic material that has attracted attention for the channel layer as a channel layer, a manufacturing process using a solution utilizing the characteristics of the organic material is considered promising from an industrial point of view. Conventional silicon transistors require vacuum, high temperature, lithography, etc. in the process, and are very time-consuming, energy-intensive, and costly. In addition, with the progress of miniaturization, it is necessary to invest many times as much to develop a transistor with a smaller structure, and the rate of increase is increasing exponentially. It is said.

  On the other hand, since many organic substances are soluble in a solvent, a technique for manufacturing a transistor using a manufacturing process using a solution has attracted attention. Specific methods include immersing the substrate in a solution, applying the solution onto the substrate with a dropper, etc., forming a thin film using a spin coater, etc., and forming a thin film using a printing technique such as an inkjet printer. Etc. If such a process technology is used, it is possible to form a large area at once, and since no vacuum or high temperature is required, a large-scale apparatus is not required and the cost can be kept low. Since this becomes possible, great expectations are placed on a future transistor manufacturing method.

Therefore, ideally, it would be better if all of the substrate, the electrode, the insulating layer, and the semiconductor channel layer can be formed of an organic material. However, at present, most of the “organic transistors” are those in which only the channel layer of the transistor is replaced with an organic substance (that is, the gate insulating film is made of SiO ₂ and the substrate is made of silicon or the like). In addition, the film formation method often does not take advantage of the characteristics as an organic substance, for example, a conventional vacuum deposition method is often used.

  Therefore, in the present embodiment, a layer of the fine particles is formed on the base layer (the molecular solder layer described above) having good adhesion to the fine particles, and the silanol derivative, specifically, silane coupling is used as the base layer. Use the agent. In this case, the base layer can be used not only for fixing the fine particles constituting the channel layer of the transistor but also as a gate insulating film at the same time.

  Specifically, in the other embodiments described above, as shown in FIG. 14A, the gate insulating film 3 is formed on the substrate 1 such as silicon, and the gate insulating film 3, the channel layer 6, and the like. A molecular solder layer (the base layer) 7 is formed on the gate insulating film 3 to promote the adhesion of the gate insulating film 3.

  In contrast, in the present embodiment, as shown in FIG. 14B, a molecular solder layer (the base layer) 7 made of a silane coupling agent is formed on a substrate 1 such as silicon, and this molecular solder is formed. A channel layer 6 is formed on the layer 7. The molecular solder layer 7 is chemically bonded to the substrate 1 and the channel layer 6 on both sides thereof. That is, the silane coupling agent forming the molecular solder layer 7 has functional groups such as amino groups and thiol groups that react with the fine particles (for example, gold) on the channel layer 6 side, while the substrate 1 On the side, an appropriate functional group corresponding to the material constituting the substrate 1 and the gate electrode (not shown) is provided.

  According to this, it is not necessary to form the gate insulating film such as an oxide film by an expensive and time-consuming process. Therefore, the configuration of the entire transistor becomes simpler, and the number of manufacturing process steps is reduced. Further, the thickness of the entire transistor can be reduced, and the gate insulating film made of the molecular solder layer 7 can be manufactured by a manufacturing process using a solution, thereby reducing the cost and time required for manufacturing the device. It becomes possible.

  Specific examples of the silane coupling agent include N-2 (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) γ-aminopropyltrimethoxysilane (AEAPTMS, the following structural formula (1)). N-2 (aminoethyl) γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane (APTMS, the following structural formula (2)), 3-aminopropylmethyldiethoxysilane (APMDES, the following structural formula (3) )) 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane (MPTMS, structural formula (4) below), 3-mercaptopropylmethyldimethoxysilane (MPMDMS, Structural formula (5) below, mercaptomethyldi Tyrethoxysilane (MMDMES, structural formula (6) below), Mercaptomethylmethyldiethoxysilane (MMMDES, structural formula (7) below), 3-cyanopropyldimethylmethoxysilane (CPDMMS, structural formula (8) below), 3 -Cyanopropyltriethoxysilane (CPTES, the following structural formula (9)), 2-pyridylethyltrimethoxysilane (PETMS, the following structural formula (10)), 2- (diphenylphosphino) ethyltriethoxysilane (DPPETES, the following) Structural formula (11)) can be given. Here, if the length of the alkyl chain in a molecule | numerator is changed, not only said well-known silane coupling agent but a new material can be synthesize | combined according to the use.

Moreover, not only the above-mentioned general silane coupling agent can be used for the application of the present invention. The molecular solder layer only needs to be chemically bonded to both the substrate provided with the gate electrode and the fine particles, and a dithiol-based material having thiol groups at both ends may be used. For example, decanedithiol _{(HS-C 10 H 20 -SH} ) , and the like.

  The basic structure of the silane coupling agent is a quasi-one-dimensional structure in which many of them can define a main chain, but not limited to this, assuming that a two-dimensional or three-dimensional molecule is used. However, it is sufficient that the element portions to be bonded to each of the gate electrode (or the substrate) and the fine particles are properly bonded. However, the transistor characteristics formed by the network structure composed of the fine particles should not deteriorate or be destroyed at that time.

  Further, when the base layer is also used as the gate insulating film, the silane coupling agent must have poor electrical conductivity. Therefore, there is no problem as long as the main chain of the silane coupling agent is an alkyl chain, but it is difficult to use a conjugated chain that is considered to have good conductivity in the application of the present invention.

  Furthermore, a nucleic acid (DNA) or the like can be used instead of the silane coupling agent.

  The structure itself of “substrate—molecular solder layer (underlayer) made of silane coupling agent—channel layer” in the present embodiment is not entirely new, and research close to that has been made in recent years. According to a French group report in 2000 (J. Collet, et al., Applied Physics Letters, vol. 76, pages 1339-1341 (2000)), tetradecyl-1 is a silane coupling agent on a substrate. -A layer composed of enyltrichlorosilane is formed as a single layer, and the vinyl group at the upper end thereof is oxidized to -COOH. On this single layer film, another organic single layer film (π-conjugated system) that reacts with —COOH is formed. Since the silane coupling agent is a non-conjugated system (σ system), a substrate-σ system silane coupling agent monolayer film-π system monolayer film can be formed here. However, they did not manufacture a transistor as in the present embodiment, but only examined the anisotropic conduction of the thin film configured as described above.

  Further, in contrast to the above-mentioned documents, the present invention is a conjugated molecule (the organic semiconductor molecule) in which the carrier actually flows in the channel layer of the transistor and the part that causes the transistor operation bridges the fine particles. It is. The present embodiment has a configuration of “substrate-molecular solder layer (underlayer) -channel layer”, but the silane coupling agent constituting the molecular solder layer is bonded to (gold) particles in the channel layer. Yes, it does not bind to a semiconductor conjugated molecule (the organic semiconductor molecule) that bridges the fine particles.

  Hereinafter, it will be specifically shown how the silane coupling agent can bind the fine particles (here, gold) strongly.

FIG. 15 is a transmission electron micrograph when gold fine particles are applied on a SiO ₂ / Si substrate (a substrate having a natural oxide film SiO ₂ formed on the surface of the Si substrate) and then the substrate surface is washed with toluene. is there. In FIG. 15, white dots are gold fine particles, and the background is a SiO ₂ / Si substrate. In this case, since the fine particles are only physically weakly adsorbed on the substrate, it can be seen that most of the fine particles can be removed after washing with toluene.

FIG. 16 shows AEAPTMS (N-2 (aminoethyl) γ-aminopropyltrimethyl) as a silane coupling agent on a SiO ₂ / Si substrate (substrate having a natural oxide film SiO ₂ formed on the surface of a Si substrate). It is a transmission electron micrograph when a thin film of (methoxysilane) is formed, gold fine particles are further coated on this thin film, and then the substrate surface is washed with toluene. In FIG. 16, the white dots are the gold fine particles, and the background is the SiO ₂ / Si substrate.

  As is apparent from FIG. 16, when gold fine particles are applied after forming an AEAPTMS (N-2 (aminoethyl) γ-aminopropyltrimethoxysilane) thin film as the underlayer, the fine particles are missing even when rinsed with toluene. Never do. That is, the fine particles are fixed to the substrate by AEAPTMS.

  To explain chemically, AEAPTMS firstly has an alkoxyl group (Si-OR, OR = methoxy group, ethoxy group) formed by hydrolysis on a substrate (however, the surface is previously cleaned and the hydroxyl group fills the surface). It becomes a silanol group, which is chemically bonded to the substrate by a condensation reaction with a hydroxyl group on the substrate. In addition, the end of the AEAPTMS having a chain shape that is not on the substrate side has an amino group, which is bonded to the fine particles such as gold. Thereby, the said board | substrate and the said microparticles | fine-particles can be chemically couple | bonded via AEAPTMS, and the coupling | bonding will not be broken to the extent wash | cleaned with toluene.

  Here, in this embodiment, the layer made of the silane coupling agent is used as it is as a gate insulating layer, so that a conventional gate insulating film such as silicon oxide is not required. Therefore, as a whole, the transistor can be made thinner. In addition, the organic transistor satisfies the desire to replace more constituent elements with organic substances.

  If all the components of the organic transistor are composed of organic materials, the cost and time required for manufacturing the organic transistor will be very small. For example, according to a report by Philips Institute in the Netherlands, they have succeeded in making all of the transistors from organic materials (polymers), not only the channel layer, but also the electrodes and gate insulating film (document M. Matters, et al., Optical Materials, vol. 12, pages 189-197 (1997), GH Gelinck, et al., Applied Physics Letters, vol. 77, pages 14871489 (2000)). Examples of reported materials include polyimide and polyethylene terephthalate (PET) for the substrate, polyaniline for the electrode, and photoresist and polyvinylphenol (PVP) for the gate insulating film.

  In order to arrange the fine particles regularly (that is, close-packed) and form a two-dimensional network, the terminal functional groups themselves of the silane coupling agent that chemically bond with the fine particles serving as the foundation thereof are regularly arranged. Must-have. For this purpose, it is necessary to form the silane coupling agent as a monomolecular layer. Since it usually forms a multilayer when applied, it is preferable to rinse away in a solvent (for example, hexane) to remove molecules other than the chemically bonded bottom layer.

  Here, it seems that it is a point to worry whether a very thin film of nano-order called a monomolecular layer actually functions as the gate insulating film (for example, a leakage current is sufficiently small) This has been dispelled by the study of Vullaume et al. (See literature D. Vullaume, et al., Applied Physics Letters, vol. 69, pages 1646-1648 (1996)). They report that a monolayer with a silane coupling agent has a leakage current that is 4 to 5 orders of magnitude lower than that of silicon oxide of the same thickness. The thickness of the organic thin film tested here is 1.9 nm to 2.6 nm, and these have different alkyl chain lengths. Thus, it is considered that the physical thickness of the transistor and the characteristics as the gate insulating layer can be changed by changing the length of the alkyl chain portion of the molecule.

  From the above, the use of a layer made of a silane coupling agent as the gate insulating film can not only chemically fix the fine particles forming the channel layer but also exhibit sufficient characteristics as a gate insulating film. I think that the.

[Substrate (Gate electrode) (1)]
When a thin film layer made of a silane coupling agent is also used as a gate insulating film, the insulating film must be adjacent to the gate electrode, so it is convenient that the gate electrode is a substrate at the same time. The most typical example in practice is a doped silicon substrate (note that the surface of the silicon substrate usually has a very thin native oxide film without the need for time and money in a separate process). ing). Since it is doped, it is in a low resistance state and can be used as a (gate) electrode.

  This substrate is immersed in a piranha solution (a mixture of sulfuric acid and aqueous hydrogen peroxide (30%) in a volume ratio of 3: 1) heated to a high temperature (for example, 60 to 110 ° C.) (soaked for 20 minutes or more). In general, the substrate surface can be hydroxylated at the same time as the organic impurities adhering to the surface are removed. In addition to the treatment with the Piranha solution, the treatment with the oxygen plasma asher device can effectively obtain the same effect. For example, a normal silane coupling agent having a terminal alkoxyl group is suitable for this substrate.

[Substrate (Gate electrode) (2)]
It is also possible to use a metal plate (regardless of thickness) as the gate electrode substrate. In this case, since the thiol group is chemically strongly bonded to gold, dithiol or the like is preferably used as the silane coupling agent that also functions as a gate insulating film.

[About gold fine particles]
In the present embodiment, the fine particles may have a particle size of 10 nm or less as described above. It is known that such nano-sized fine particles can be chemically synthesized relatively easily. Nanoparticles are agglomerated alone, and are not thermally stable. For this reason, each nanoparticle must be protected by a chain organic molecule having a thiol group or an amino group at one end. However, the chain organic molecule is different from the above silane coupling agent, and the other end is terminated with, for example, a methyl group. When the other end facing the outside with respect to the fine particles such as gold is also a thiol group, the nanoparticles are considered to easily aggregate.

[Embodiment 5]
An electric field that is a semiconductor device configured such that the conductive path is formed by the fine particles made of a conductor or a semiconductor and the organic semiconductor molecules chemically bonded to the fine particles, and the conductivity of the conductive path is controlled by an electric field. Another example of the effect transistor manufacturing method will be described below.

1. Modification of the substrate surface The substrate surface is modified so that the silane coupling agent can be easily bonded. For example, it is effective to hydrate the substrate surface by a method such as immersing the substrate in a Piranha solution made of sulfuric acid and hydrogen peroxide solution, or irradiating the substrate surface with oxygen plasma or ozone.

  However, when a plastic substrate is used instead of a silicon substrate provided with an insulating film as the substrate, the substrate surface is easily dissolved with acid if the Piranha solution is used. Therefore, the substrate surface is modified by oxygen plasma or ozone irradiation. Good to do.

2. Bonding of Silane Coupling Agent to Substrate Surface A silane coupling agent is adhered to the surface of the substrate having the surface hydroxylated as described above to form a thin film made of the silane coupling agent.

A silane coupling agent is a substance composed of silicon (Si) and an organic substance, and generally has two types of functional groups with different reactivity, and one of the functional groups is an alkoxy group (-OR (R is an alkyl chain)). have hydrolyzable and easily reacts with an inorganic substance, the other functional group is a thiol group (-SH), liable to react with organic substances such as amino (-NH _2), binding of an inorganic substance and organic substance To play a role. The reactive group (-SiOR) chemically bonded to the fine particles in the silane coupling agent is silanolated (-SiOH) by hydrolysis with moisture and partially dehydrated to form an oligomer. At this time, the moisture may be in the air or may be intentionally dissolved in water. This silanol group and the hydroxyl group on the surface of the substrate are easily adsorbed by hydrogen bonding, whereby a silane coupling agent can be attached to the substrate.

  Specifically, the silane coupling agent can be attached to the substrate surface by immersing the substrate in a solution obtained by diluting the silane coupling agent with an appropriate solvent. There is a method using steam as a completely different method from the immersion. For example, a dilute solution of silane coupling agent or a stock solution of silane coupling agent is placed in a sealed container, a substrate is placed in the container, and the diluted solution of silane coupling agent or the vapor of the silane coupling agent stock solution is used. Thus, a silane coupling agent can be attached to the substrate surface.

  Next, dehydration condensation for strengthening the bond between the substrate surface and the thin film surface made of the silane coupling agent, dehydration condensation for strengthening the bonds between molecules in the thin film, and the like are performed. The dehydration condensation can accelerate the dehydration condensation reaction by heating the substrate to a high temperature (see Shin-Etsu Chemical Co., Ltd., “Silane Coupling Agent, 2 (2002)”). Further, this dehydration condensation reaction may be performed after the step of removing the silane coupling agent adhering to the substrate surface, which will be described later, and the order is not limited.

  The dehydration condensation can be performed, for example, by heating the substrate from the back side to 100 ° C. or higher with a hot plate or the like.

  After the dehydration condensation reaction, a process for making the thickness of the thin film made of the silane coupling agent on the substrate uniform with an external force is performed. The more uniform the thickness of the thin film, the more uniform the thickness of the channel layer produced through the subsequent steps, and it is considered that the scattering of electrons passing through the channel layer is reduced. Accordingly, the current value that can be passed as the semiconductor device can also be increased, leading to improvement in characteristics.

  Thereafter, the silane coupling agent that has adhered to the substrate surface is removed. Here, the extra silane coupling agent adhering to the above refers to a silane coupling material that is van der Waals bonded or mounted on the substrate surface, not a covalent bond or a hydrogen bond on the substrate surface. As a removing method, for example, a substrate weakly bonded to the substrate, that is, a silane coupling agent not dehydrated and condensed, can be removed by immersing the substrate in hexane and performing ultrasonic cleaning. Ultrasonic cleaning allows weakly bound molecules to dissolve in hexane and be removed.

3. Next, the fine particles made of a conductor or a semiconductor are chemically bonded onto a thin film made of a silane coupling agent. The fine particles that are not chemically bonded to the thin film made of the silane coupling agent may be removed. The fine particles are usually used in a state of being dispersed (colloid) in a suitable solvent. After drying the solvent, the fine particles not chemically bonded to the silane coupling agent are rinsed with a separately prepared solvent. remove.

4). Bonding of Organic Molecules and Fine Particles Subsequently, the fine particles already bonded to a thin film made of a silane coupling agent and the organic semiconductor molecules having conductivity were bonded, and the fine particles were crosslinked with the organic semiconductor molecules. Put it in a state. After the organic semiconductor molecules are bonded, the organic semiconductor molecules that are not chemically bonded to the fine particles are removed. When the organic semiconductor molecules are dissolved and bonded in a liquid, excess organic semiconductor molecules can be removed by drying the solvent used.

  As described above, the conductive path is formed by the fine particles made of a conductor or a semiconductor and the organic semiconductor molecules chemically bonded to the fine particles, and the conductivity of the conductive path is controlled by an electric field. A field effect transistor which is a semiconductor device can be manufactured.

  Next, the present embodiment will be described in more detail with specific examples.

<Example 1>
First, as shown in FIGS. 3A to 3C, silicon dioxide as a gate insulating film is formed by thermal oxidation on a silicon substrate on which a gate electrode is formed and doped, and then the gate insulating film Titanium was disposed thereon, and electrodes corresponding to a source electrode and a drain electrode were formed thereon using gold. A substrate having an electrode and a gate insulating film formed on the substrate is hereinafter referred to as a substrate.

  Hereinafter, FIG. 17 and FIG. 18 will be referred to, and these figures are views after performing the step of forming the electrode and the gate oxide film on the substrate as shown in FIGS. It is a partially expanded sectional view for demonstrating the surface state between source-drain electrodes.

  Next, as shown in FIG. 17A, the surface of the substrate 15 on which the electrode and the gate oxide film are formed on the substrate as described above is easily bonded to the silane coupling agent in a later step. In order to do so, it was hydroxylated. Specifically, a piranha solution, which is a mixed solution of sulfuric acid and 30% hydrogen peroxide solution in a volume ratio of 3: 1, is prepared, and the piranha solution is heated to several tens of degrees (for example, about 60 ° C.). The substrate 15 was immersed for several tens of minutes (for example, about 10 minutes). After the substrate 15 was taken out from the solution, the piranha solution remaining on the surface of the substrate 15 was washed away with high-purity running water for several tens of minutes (for example, about 20 minutes).

  Here, instead of using the above-mentioned piranha solution, the surface of the base 15 may be hydroxylated by irradiating the surface of the base 15 with oxygen plasma. When irradiating oxygen plasma, for example, it is performed for 3 minutes at an output of 200 W and a pressure of 133 MPa.

  Next, the operation of immersing the substrate 15 in ethanol (purity 99.5% or more; for high performance liquid chromatography; the same applies hereinafter) was performed once or several times (for example, twice). Next, the operation of immersing the substrate 15 in an equal volume mixture of ethanol and hexane (purity 96.0% or more; for high performance liquid chromatography; the same applies hereinafter) was performed once or several times (for example, twice). Next, the operation of immersing the substrate 15 in hexane was performed once or several times (for example, twice). These steps are for facilitating the formation of the layer comprising the silane coupling agent in the next step on the surface of the substrate 15. However, when the surface of the substrate 15 is hydroxylated, if the surface of the substrate 15 is irradiated with oxygen plasma or ozone, a series of steps in which the substrate 15 is immersed in hexane in an equal volume mixture of ethanol and ethanol and hexane. It is not necessary to perform this work.

Next, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane ((CH ₃ O) ₃ SiC ₃ H ₆ NHC ₂ H ₄ NH ₂ as a silane coupling agent, manufactured by Shin-Etsu Chemical Co., Ltd., hereinafter. The substrate 15 was immersed for several minutes to several tens of minutes (for example, about 10 minutes) in a dilute solution of 0.01 to 10% by volume (for example, 0.5% by volume) in which AEAPTMS was dissolved in hexane. As a result, as shown in FIG. 17B, the silane coupling agent could be bonded to the surface of the substrate 15 (in FIG. 17B, the alkyl chain was simply represented by a refracted line. The same applies hereinafter.) Here, instead of the above, the substrate 15 may be placed in a saturated vapor made of a dilute hexane solution or stock solution of AEAPTMS and allowed to stand for several tens of minutes to several hours (for example, 30 minutes).

  Next, the substrate 15 is taken out from the above-mentioned AEAPTMS dilute hexane solution (or a saturated vapor composed of AEAPTMS dilute hexane solution or stock solution), and the substrate 15 is immersed in hexane or high-purity water, and ultrasonic waves are applied for several minutes to several tens of minutes. After cleaning, the substrate 15 was heated at a temperature of 100 to 120 ° C. The ultrasonic treatment was performed, for example, at an output of 110 W to 120 W and an oscillation frequency of 38 kHz for 10 minutes.

  It is possible to remove AEAPTMS that is excessively attached to the surface of the substrate 15 by the cleaning by the ultrasonic treatment, that is, that is not chemically bonded to the hydroxyl group on the surface of the substrate 15. Further, by drying the substrate 15 by heating the substrate 15 at a temperature of 100 ° C. or higher, the dehydration condensation reaction in the AEAPTMS thin film and between the AEAPTMS and the hydroxyl group on the substrate surface can be promoted and the chemical bond can be strengthened. . More specifically, the hydrogen bond is changed to a covalent bond in the dehydration condensation reaction, and the bond strength is increased.

  Next, the operation of immersing the substrate 15 in the hexane solution was performed once or several times (for example, twice). Next, the operation of immersing the substrate 15 in an equal amount mixed solution of hexane and toluene (purity 99.7% or more; for high performance liquid chromatography; the same applies hereinafter) was performed once or several times (for example, twice). Next, the operation of immersing the substrate 15 in the toluene solution was performed once or several times (for example, twice). These steps are intended to facilitate the subsequent bonding of the gold fine particles to the silane coupling agent.

  Next, a 100 to 1000 ppm (for example, 1000 ppm) solution in which gold fine particles having a diameter of several nanometers were dissolved in toluene was prepared, and the substrate 15 was immersed in the gold fine particle-toluene solution for several hours (for example, about 1 hour). Thereby, as shown in FIG.17 (c), a chemical bond arises between the gold fine particle 8 and the AEAPTMS thin film.

  Next, the substrate 15 was taken out from the gold fine particle-toluene solution, and the operation of lightly washing the gold fine particles 8 not chemically bonded to the AEAPTMS thin film with toluene was performed once or several times (for example, twice).

Next, 4,4′-biphenyldithiol (HSC ₆ H ₄ C ₆₎ as the organic semiconductor molecule.
The substrate 15 was immersed in an approximately 1 mM solution in which H ₄ SH) was dissolved in toluene for several hours to one day (for example, about one day). Thereby, as shown in FIG. 18D, the gold fine particles 8 and 4,4′-biphenyldithiol are chemically bonded.

  Next, the substrate 15 is removed from the toluene solution of 4,4′-biphenyldithiol, and the operation of lightly washing 4,4′-biphenyldithiol not chemically bonded to the gold fine particles 8 with toluene once or several times (for example, 2 Times). Thereafter, the substrate 15 was dried.

  As described above, a channel region having the conductive path composed of the gold fine particles 8 and 4,4′-biphenyldithiol as the organic semiconductor molecule is formed, and source and drain electrodes are provided on both sides of the channel region. Thus, a MOS field effect transistor as shown in FIG. 1 in which a gate electrode was provided between these two electrodes could be produced.

  In this MOS field effect transistor, the current flowing between the source electrode and the drain electrode was measured while changing the voltage applied to the gate electrode with respect to the voltage applied between the source electrode and the drain electrode. Thus, the semiconductor operation could be confirmed. In the current-voltage characteristic graph of FIG. 19, the numerical value on the right end means the voltage value applied to the gate electrode of each measurement.

<Example 2>
The same as in Example 1 except that 3-mercaptopropyltrimethoxysilane ((CH ₃ O) ₃ SiC ₃ H ₆ SH, manufactured by Shin-Etsu Chemical Co., Ltd.) was used instead of AEAPTMS as the silane coupling agent. A MOS field effect transistor was fabricated by this method (FIG. 20). When the current-voltage characteristics of the transistor were measured in the same manner as described above, the semiconductor operation could be confirmed.

  As mentioned above, although this invention was demonstrated based on embodiment and an Example, this invention is not limited to these examples at all, and it cannot be overemphasized that it can change suitably in the range which does not deviate from the main point of invention. .

  For example, although the example which uses the gold | metal | money as the said conductor as the said microparticles | fine-particles was mentioned above, the microparticles | fine-particles which consist of silver or platinum or cadmium sulfide, cadmium selenide, or a silicon | silicone as said semiconductor can be used. The particle diameter is preferably 10 nm or less.

  Further, the shape of the fine particles has been described by taking a spherical shape, a rectangular shape, or a nanorod as an example. However, the present invention is not limited to this, and examples thereof include a triangle, a cube, a rectangular parallelepiped, a cone, and a nanotube.

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Gate electrode, 3 ... Gate insulating film, 4 ... Source electrode, 5 ... Drain electrode,
6 ... channel layer, 6a ... first combination layer, 6b ... second combination layer,
7 ... molecular solder layer, 8 ... fine particles such as Au, 8a, 8b ... gold fine particle layer,
9 ... Organic semiconductor molecules such as 4,4′-biphenyldithiol,
10 ... Network-type conductive path, 11 ... Gold paste film, 11a ... Gold paste (counter electrode),
DESCRIPTION OF SYMBOLS 12 ... Conjugate, 13 ... Bonding site, 14 ... Gold nanorod, 15 ... Base

Claims (10)

Organic semiconductor molecules and fine particles made of a conductor or a semiconductor are alternately bonded by functional groups of the organic semiconductor molecules at both ends to form a network-type conductive path, and charge transfer in the conductive path is caused by the organic semiconductor molecule It occurs in dominant by charge transfer in the molecule definitive axially semiconductor device the conductivity of the conductive path is controlled by an electric field. The semiconductor device according to claim 1 , wherein charge transfer in the conductive path occurs predominantly in an axial direction along a main chain of the organic semiconductor molecule. The semiconductor device according to claim 1 , wherein charge transfer in the conductive path occurs predominantly in an axial direction along a molecular skeleton of the organic semiconductor molecule. 4. The semiconductor device according to claim 1 , wherein the organic semiconductor molecule and the fine particles are connected two-dimensionally or three-dimensionally by the functional group to form the conductive path. 5. A channel region having the conductive path is formed, source and drain electrodes are provided on both sides of the channel region, and an insulated gate field effect transistor is provided in which a gate electrode is provided between the two electrodes. The semiconductor device according to claim 1 . The semiconductor device according to claim 1 , wherein a combination of the organic semiconductor molecules and the fine particles forms a single layer or a plurality of layers to form the conductive path. The semiconductor device according to claim 1 , wherein the fine particles are made of gold, silver, platinum, copper, or aluminum as the conductor, or cadmium sulfide, cadmium selenide, or silicon as the semiconductor. . The semiconductor device according to claim 1, wherein the fine particles are fine particles having a particle diameter of 10 nm or less. The organic semiconductor molecule is an organic semiconductor molecule having a conjugated bond, and a thiol group —SH, an amino group —NH ₂ , an isocyano group —NC, a thioacetoxyl group —SCOCH ₃ or a carboxyl group —COOH is attached to both ends of the molecule. The semiconductor device according to claim 1, comprising: a semiconductor device according to claim 1 ; The semiconductor device according to claim 5 , wherein the field effect transistor is formed on a flexible substrate made of an organic material.

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