JP2007053147A - Organic semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic semiconductor device which can be easily formed without using a special material such as parylene and has a protective film with high passivation effects, and to provide its manufacturing method. <P>SOLUTION: A gate electrode 2 and a gate insulation film 3 are formed on a principal plane of a base substrate 1, a source electrode 4 and a drain electrode 5 are formed on the gate insulation film 3, and an organic semiconductor layer 6 is formed to continuously coat over the electrodes and between the electrodes. Further, a protective film 7 and a protective film 8 coating the organic semiconductor layer 6 are formed by lamination. The protective film 7 is at least a protective film serving to protect the organic semiconductor layer 6 against damage in forming the protective film 8, and is formed by coating or printing. The protective film 8 is at least a protective film serving to prevent oxygen and moisture from entering the semiconductor layer 6. For example, the protective film 7 is formed of PMMA or polyimide, and the protective film 8 made of silicon nitride is formed by a plasma CVD method or a sputtering method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic semiconductor device such as an organic field effect transistor and a manufacturing method thereof, and more particularly to a structure of a protective film (passivation film).

  Conventionally, inorganic semiconductor materials such as silicon have been used for various semiconductor devices (transistors, diodes, photoelectric conversion devices, etc.). For example, most thin film transistors (hereinafter abbreviated as TFTs) that are currently widely used as switching elements in active matrix circuits of liquid crystal display devices are silicon using amorphous silicon or polycrystalline silicon as a semiconductor layer. This is an inorganic semiconductor transistor.

  However, the inorganic semiconductor device has a problem in that the manufacturing cost is high because expensive manufacturing equipment such as a vacuum apparatus or a high-purity material is required for manufacturing the inorganic semiconductor device. In addition, since a heat treatment at a high temperature is necessary, there is a problem that the substrate is restricted.

  On the other hand, an organic semiconductor device having an organic semiconductor layer as a conductive region can be manufactured by a coating method or a dipping method at a relatively low temperature, and can be easily increased in area at low cost. Further, it can be formed on a flexible substrate having no heat resistance such as plastic, and is stable against mechanical impact. For this reason, in recent years, research and development of organic semiconductor devices such as TFTs have been actively conducted assuming application to next-generation display devices.

  However, in the organic semiconductor device, like the organic EL (Electro Luminescence) element, the organic semiconductor layer is deteriorated by oxygen and moisture entering from the outside, and the semiconductor performance is deteriorated. Development of organic semiconductor materials that are not easily affected by oxygen has been carried out, but it is still not sufficient. Therefore, in order to manufacture a highly reliable organic semiconductor device, it is indispensable to form a structure that completely blocks the organic semiconductor layer from the outside by a protective film (passivation film) or the like.

  In such a case, in the case of an inorganic semiconductor device, a dense silicon nitride film or silicon oxide film is generally formed as a protective film by a plasma CVD method (plasma vapor deposition method) or a sputtering method. . It is well known that a protective film made of an inorganic thin film is effective as a block layer for preventing oxygen and water from entering. However, in an organic semiconductor device, plasma damage is likely to occur in the organic semiconductor layer. When a protective film is formed using plasma or CVD or sputtering, plasma damage occurs in the organic semiconductor layer, which will be described later in Examples. As a result, the device characteristics are deteriorated.

  In order to avoid this, conventionally, in an organic semiconductor device, an organic film such as benzocyclobutene (BCB) or polyimide is generally formed as a protective film by a coating method or the like. In this case, the performance of the organic protective film to prevent the entry of oxygen and water is inferior to that of the inorganic protective film. Therefore, the organic semiconductor device penetrates the organic protective film and penetrates into the organic semiconductor layer due to oxygen and moisture. There is concern that device characteristics and reliability will gradually deteriorate.

  Therefore, Patent Document 1 described later proposes an organic semiconductor switching element in which a protective film is formed by laminating a polyparaxylene (parylene) layer and a ceramic film such as silicon oxide.

JP 2004-288774 A (2nd, 4th and 5th pages, FIG. 1)

  In Patent Document 1, a substrate material is provided, and a conductive material as a cathode electrode is patterned on the substrate material, and an electrically connected organic semiconductor material is applied onto the cathode electrode. An anode electrode is formed on the organic semiconductor material by a conductor electrically connected to the organic semiconductor material, and the organic semiconductor material portion where the organic semiconductor material portion is exposed is shielded from outside air. It is described that a switching element made of an organic semiconductor, characterized in that a lens and a ceramic are formed so as to cover the organic semiconductor material portion.

  FIG. 8 is a side sectional view of the switching element according to the first embodiment of the invention of Patent Document 1, and the following explanation is described in this regard.

“A cathode electrode 102 is formed on a substrate material 101 that does not pass a gas such as a glass substrate, an organic semiconductor material 104 is formed on the substrate material 101 and the cathode electrode 102 by vapor deposition, and an anode electrode 103 is formed thereon. Next, the first protective layer 111 made of the material Parylene (trademark) proposed in the present invention is formed on the organic semiconductor material 104 and the anode electrode 103 by coating or film formation, and further, SiO _{2 made of} ceramics. The second protective layer 112 such as is formed by coating or film formation.

A known method by vapor deposition has been proposed for parylene, and SiO ₂ is formed by sputtering or a sol-gel method. By comprising in this way, a transmission cross-sectional area can be reduced by the 1st protective layer 111 which consists of parylene which is a material with especially low gas permeability in an organic material, and also the 2nd protective layer 112 which consists of ceramics. Therefore, a gas harmful to the organic semiconductor material 104 such as oxygen and water vapor can be avoided. In particular, water vapor hardly permeates through the surface of the parylene molecule, as can be seen from its strong hydrophobicity.

Parylene is formed as the first protective film 111 at room temperature. Vapor deposition was performed at a vacuum of 1 Pa or less. Then, a first protective film 111 having a parylene film thickness of about 1 μm was formed, and SiO ₂ was further added thereon as a ceramic second protective film 112. The SiO ₂ film is deposited with sufficient consideration for heat dissipation of the sample substrate because the surface temperature of the film inevitably rises to 40 ° C. or more in an apparatus having a distance of 50 cm from the sample when EB deposition is applied to about 0.1 μm. To do. "

However, the invention of Patent Document 1 has some unclear points. In particular, why the first protective layer 111 must be a film made of parylene, and what relationship is there between the second protective layer 112 made of ceramics such as SiO ₂ and the first protective layer 111? It is not clear.

  In order to form a protective layer consisting of parylene, at least the evaporation zone for evaporating parylene dimer, the thermal decomposition region for thermally decomposing gaseous parylene dimer into parylene monomer in the gas phase, and undegraded parylene dimer are removed by adsorption. After that, a special vacuum vapor deposition apparatus having a pyrolysis region and a vapor deposition region in which a gaseous parylene monomer is deposited on a substrate and polymerized to form a parylene polymer on the substrate is required. Further, unlike mature semiconductor manufacturing technology, a technology for producing parylene polymer by optimizing conditions such as temperature and pressure in each of the above-mentioned regions has been established, and it is difficult to say that it is widely used (Special Table 2002). 505803).

  That is, at present, many users who want to apply the invention of Patent Document 1 are not in a state in which parylene can be easily used as a material for forming the first protective layer 111. In addition, since parylene is deposited using a vacuum deposition apparatus, a large-scale vacuum deposition apparatus is required to form a large substrate, which increases costs, so when forming a device on a large-area substrate. Is not suitable. For these reasons, there are cases where it is desired to obtain the same effect as that of the invention of Patent Document 1, using a protective layer forming material other than parylene as the forming material of the first protective layer 111. However, Patent Document 1 describes only Parylene as “an organic material that can be formed by vapor deposition and has a particularly low permeability of gas, particularly water vapor”, and is used as a reference for selecting other protective layer forming materials. What can be done is not described. For example, it is an essential condition that “it can be formed by vapor deposition”, or even if it is a material whose performance for preventing gas permeation is somewhat inferior to parylene, it can be used by increasing the film thickness, That is not shown.

  In addition, regarding the relationship between the second protective layer 112 made of ceramics and the first protective layer 111, “(gas) transmission cross-sectional area can be reduced by the second protective layer 112 made of ceramics in addition to the first protective layer 111. ”And there is no special relationship between the first protective layer 111 and the second protective layer 112, and it can be read that the stacking order of both may be reversed. Therefore, a material suitable for the first protective layer 111 other than parylene cannot be narrowed down due to the relationship with the second protective layer 112, and any clue regarding the laminated structure cannot be obtained.

  Further, although Patent Document 1 states that “the organic semiconductor material is applied” in claim 2, in the first embodiment, “the organic semiconductor material 104 is formed by vapor deposition or the like”. In the first embodiment, “the first protective layer 111 made of parylene (trademark) is formed by coating or film formation” although the parylene film can be formed only through the gas phase. There are discrepancies and misconceptions about matters that are essential in nature.

  As described above, even if the problem of the invention of Patent Document 1 is partially solved by the invention of Patent Document 1, it cannot be said that it has been completely solved.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an organic semiconductor device having a protective film having a high passivation effect that can be easily formed without using a special material such as parylene. It is to provide a manufacturing method.

  As a result of extensive research, the present inventor has found that the first protective layer 111 of Patent Document 1 does not necessarily need to be a layer having a low gas permeability like parylene, and has completed the present invention. .

That is, the present invention provides an organic semiconductor device having an organic semiconductor layer as a conductive region,
The organic semiconductor layer is covered with a first protective film formed by deposition of a solution; and further, the first protective film is covered with a second protective film;
The first protective film has at least an action of protecting the organic semiconductor layer from damage when forming the second protective film;
The second protective film is related to the first organic semiconductor device characterized in that it has an action of preventing at least an external substance from entering the organic semiconductor layer, and the organic semiconductor layer is used as a conductive region. In an organic semiconductor device that
A first protection in which the organic semiconductor layer is made of at least one selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polymethyl methacrylate (PMMA), polyimide, fluorine-containing polymer, and polysilazane. Covered with a film, and further, the first protective film is covered with a second protective film,
The first protective film has at least an action of protecting the organic semiconductor layer from damage when forming the second protective film;
The second protective film relates to the second organic semiconductor device, characterized in that it has at least an action of preventing an external substance from entering the organic semiconductor layer.

Furthermore, in the method for manufacturing the first organic semiconductor device or the second organic semiconductor device, the step of forming the organic semiconductor layer on a substrate;
Depositing the solution containing the material of the first protective film and covering the organic semiconductor layer with the first protective film;
And a step of coating the first protective film with the second protective film.

  The first organic semiconductor device of the present invention is an organic semiconductor device having an organic semiconductor layer as a conductive region, the organic semiconductor layer being covered with a first protective film formed by deposition of a solution, The first protective film is covered with a second protective film. Since the first protective film is formed by depositing the solution, if the appropriate solvent is selected, the first protective film can be formed while minimizing damage to the organic semiconductor layer. it can. Further, the first protective film having a large area can be formed easily and at low cost without requiring a large-scale device such as a vacuum device, and the flatness of the surface is improved as a secondary effect. .

  The term “adhesion” refers to a method for arranging a liquid substance including application and printing. The coating method has an advantage that the first protective film can be easily formed with high productivity, and the printing method has an advantage that the first protective film can be formed and patterned simultaneously, and has a large area. Even if it is formed, there is an advantage that variations in film thickness are hardly deteriorated.

  Furthermore, the protective film has at least the first protective film having an action of protecting the organic semiconductor layer from damage when forming the second protective film, and at least the external substance to the organic semiconductor layer Is formed in a laminated structure with the second protective film having an action of preventing the intrusion. When the second protective film is formed, the first protective film having the function of protecting the organic semiconductor layer from damage at that time has already been formed. Without worrying about the above, it is possible to select, as the second protective film, a film that is most excellent in the action of preventing the entry of the external substance into the organic semiconductor layer. Further, since the intrusion of the external substance into the organic semiconductor layer is blocked by the second protective film, the first protective film does not have to have the performance of blocking the intrusion of the external substance. The protective film 1 only needs to have an action of protecting the organic semiconductor layer from damage when forming the second protective film.

  As described above, the protective film of the organic semiconductor layer is composed of the first protective film and the second protective film, and the protective function is divided in stages by the two protective films, thereby providing each protective film. Therefore, the optimum material and manufacturing method can be selected from a wider range of options for each protective film. For example, if the second protective film is a dense silicon nitride film formed by a plasma CVD method (chemical vapor deposition method), it is possible to prevent oxygen and moisture from entering the organic semiconductor layer. At this time, if the first protective film is a polymethyl methacrylate (PMMA) film or a polyimide film, the organic semiconductor layer can be protected from plasma damage when the silicon nitride film is formed. As a result, an organic semiconductor device having a protective film having a high passivation effect can be easily formed without using a special material such as parylene.

  In the second organic semiconductor device of the present invention, like the first organic semiconductor device, the protective film of the organic semiconductor layer protects the organic semiconductor layer from damage when forming the second protective film. The first protective film having at least an action and the second protective film having at least an action to prevent the external substance from entering the organic semiconductor layer are formed in a laminated structure. In addition, the first protective film is a film made of at least one selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polymethyl methacrylate (PMMA), polyimide, fluorine-containing polymer, and polysilazane. It is. Since the films made of these materials are films that can be formed by deposition of a solution, the second organic semiconductor device has the same effect as the first organic semiconductor device due to such material limitation. It is a device that can be obtained reliably.

  In the first and second organic semiconductor devices of the present invention, the first protective film and the second protective film may be a single layer or a plurality of stacked layers. May be. If it consists of a single layer, there is a merit that it is easy to form. If it consists of multiple layers, it takes time to form, but the combination of multiple layers can realize performance that cannot be achieved with a single layer. There is.

  The method for manufacturing an organic semiconductor device of the present invention is a method for manufacturing a semiconductor device that makes it possible to manufacture the first or second organic semiconductor device efficiently.

  In the manufacturing method of the first organic semiconductor device or the second organic semiconductor device of the present invention, the first protective film material is dissolved using a solvent having poor properties for dissolving the organic semiconductor layer, When deposited on the organic semiconductor layer, the first protective film can be formed without damaging the organic semiconductor layer. At this time, when the material of the first protective film is dissolved using a solvent having a surface energy lower than that of the outermost surface and the solution is formed, the wettability is improved and a protective film with few pinholes can be formed. Yes (see Journal of Applied Physics, vol. 96, p. 2286). Specifically, the solvent is selected from the group consisting of 2-propanol (isopropyl alcohol), butanol, cyclopentanone, 1,4-dioxane, γ-butyllactone, anisole, and polyethylene glycol monomethyl ether acetate (PEGMEA). It is good to consist of at least one.

  Further, the first protective film has at least an action of protecting the organic semiconductor layer from damage caused by plasma, and the second protective film uses a method using plasma, for example, a plasma CVD method or a sputtering method. It is good to be formed. For example, a dense silicon nitride film formed by a plasma CVD method or an aluminum oxide (alumina) film formed by a sputtering method is used to prevent oxygen and moisture from entering the organic semiconductor layer. As a suitable film.

  The second protective film may be formed by vacuum deposition or solution deposition. In this case, each of the first protective films protects the organic semiconductor layer from a solvent that protects the organic semiconductor layer from heat during vacuum deposition or a solution that contains a material for the second protective film. It should be a thing.

  As described above, since the organic semiconductor layer is deteriorated by oxygen and moisture entering from the outside, it is important that the second protective film can prevent entry of oxygen and moisture as the external material. .

  In the first organic semiconductor device of the present invention, the organic semiconductor layer is formed on a base, and a third protective film for preventing the external substance from entering the organic semiconductor layer is formed on the base. It is good. By adopting such a structure, it is possible to prevent the external substance from entering the organic semiconductor layer from the base side even if the base body is made of a material that allows permeation of the external substance. . For example, even when the base is a plastic substrate, it is possible to prevent oxygen and moisture from entering and form a highly reliable organic semiconductor device.

  Further, the first protective film is made of at least one selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polymethyl methacrylate (PMMA), polyimide, fluorine-containing polymer and polysilazane. Is good.

The second protective film is made of aluminum oxide (alumina) Al ₂ O ₃ , silicon nitride SiN _x , silicon oxide SiO ₂ , silicon oxynitride SiO _x N _y , titanium oxide TiO ₂ , thallium oxide Ta ₂ O _5, It is preferable to consist of at least one selected from the group consisting of hafnium oxide HfO _x and parylene.

  The third protective film is made of at least one selected from the group consisting of aluminum oxide (alumina), silicon nitride, silicon oxide, silicon oxynitride, titanium oxide, thallium oxide, hafnium oxide, and parylene. Good.

  The organic semiconductor layer may be made of a polythiophene compound or a pentacene compound. These organic semiconductor materials are known to exhibit excellent semiconductor properties such as high mobility. In addition, "... type | system | group compound" means the compound itself and the compound induced | guided | derived and derived from the compound, for example, a polythiophene type compound shall mean a polythiophene and a polythiophene derivative.

  In the first organic semiconductor device of the present invention, a source electrode and a drain electrode are provided in contact with the conductive region, and a gate electrode is provided between the two electrodes via a gate insulating film. It is preferable to be configured as an effect transistor (insulated gate FET). The organic FET is preferably used as a pixel transistor of a liquid crystal display device. In addition, the above 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.

  For example, when an organic FET is applied to an RF-ID tag (Radio Frequency Identification: automatic recognition technology using electromagnetic waves) or a backplane of a display, reliability such as long-term stability is required. If this organic semiconductor device is used, initial deterioration of the FET can be prevented and deterioration with time can be minimized.

  Next, a preferred embodiment of the present invention will be described specifically and in detail with reference to the drawings.

  In the present embodiment, an insulated gate field effect transistor and a manufacturing method thereof will be described mainly as an example of the manufacturing method of the organic semiconductor device described in claim 1 or 2 and the organic semiconductor device described in claim 15.

  FIG. 1 is a cross-sectional view showing the structure of an organic field effect transistor (organic FET) 10 configured as an insulated gate field effect transistor according to the present embodiment.

  As shown in FIG. 1, in the organic FET 10, the gate electrode 2 and the gate insulating film 3 are formed on one main surface of the support substrate 1. A source electrode 4 and a drain electrode 5 are formed on the gate insulating film 3, and are in contact with at least the source electrode 4 and the drain electrode 5 so as to continuously cover the electrodes and the electrodes. An organic semiconductor layer 6 made of a material is provided.

  In the organic FET 10, carrier movement in the organic semiconductor layer 6 is controlled by a gate voltage applied to the gate electrode 2. Although FIG. 1 shows an example in which the organic FET 10 is a bottom gate type FET capable of obtaining excellent transistor characteristics, the organic FET 10 is not limited to this and may be a top gate type or a double gate type FET.

  On the organic semiconductor layer 6, a protective film 7 that is the first protective film and a protective film 8 that is the second protective film are used as protective films for the organic semiconductor layer 6. It is formed to cover.

  Hereinafter, each part will be described in more detail.

  The material of the support substrate 1 may be anything as long as it is generally used as a substrate material, and examples thereof include plastics, metals, semiconductors such as silicon, glass, and ceramics. In particular, a plastic substrate made of an organic polymer such as polyethylene naphthalate (PEN) is preferable because a flexible screen can be formed and it is inexpensive and lightweight.

  The material of the gate electrode 2 is preferably aluminum Al, gold Au, silver Ag, chromium Cr, nickel Ni, or the like.

The gate insulating film 3 is made of an inorganic material such as silicon oxide SiO ₂ , silicon nitride SiN _x , aluminum oxide (alumina) Al ₂ O ₃ , thallium oxide Ta ₂ O ₅ , titanium oxide TiO ₂ , and hafnium oxide HfO _x , polyvinyl It may be made of an organic polymer material such as phenol (PVP), polymethyl methacrylate (PMMA), polyimide, and parylene.

  The source electrode 4 and the drain electrode 5 are deposited from a mixed aqueous solution of gold, silver, chromium, PEDOT / PSS (poly (3,4-ethylenedioxythiophene which is a hydrophilic organic semiconductor molecule) and polystyrene sulfonic acid. And a mixture of both) and polyaniline are preferred.

  The organic semiconductor layer 6 is provided in contact with at least the source electrode 4 and the drain electrode 5 so as to continuously cover the electrodes and between the electrodes. The material of the organic semiconductor layer 6 is preferably a high molecular compound such as a polythiophene compound, a polyfluorene compound, or a polyallylamine compound, but may be a low molecular compound such as a pentacene compound or an oligothiophene compound. These are known to exhibit excellent semiconductor properties such as high carrier mobility.

  The source electrode 4 and the drain electrode 5 may be patterned in the shape of a comb electrode. In that case, the organic semiconductor layer 6 is formed so as to enclose the entire comb-shaped electrode. By making the source electrode 4 and the drain electrode 5 comb-shaped electrodes, the substantial cross-sectional area of the channel portion formed by the organic semiconductor layer 6 is increased, and even the organic semiconductor layer 6 having a low mobility is sufficient. An amount of current can be obtained.

  The protective film 7 is preferably made of an organic polymer material such as polyvinyl alcohol (PVA), PVP, PMMA, polyimide, and a fluorine polymer, or an inorganic polymer material such as polysilazane. The protective film 7 is formed by depositing these solutions on the organic semiconductor layer 6 and then evaporating the solvent.

  The protective film 8 is preferably made of an inorganic material such as aluminum oxide (alumina), silicon nitride, silicon oxide, silicon oxynitride, titanium oxide, thallium oxide, and hafnium oxide, or an organic polymer material such as parylene.

  Here, the protective film 8 is a protective film having a function of preventing at least the external substance such as oxygen and moisture from entering the organic semiconductor layer 6. The film thickness of the protective film 8 is appropriately selected according to the performance of preventing the permeation of oxygen and moisture, and is about 100 nm for aluminum oxide (alumina) or silicon nitride. The protective film 7 is a protective film having an action of protecting the organic semiconductor layer 6 from damage at the time of forming the protective film 8. The material and film thickness of the protective film 7 are appropriately selected according to the method for forming the protective film 8 and the like. For example, when PMMA or polyimide is formed to protect the organic semiconductor layer 6 from plasma damage, the film thickness is about 100 nm.

  When the protective film 8 is formed, since the protective film 7 having the function of protecting the organic semiconductor layer 6 from damage at that time has already been formed, there is no need to worry about damage to the organic semiconductor layer 6. A film that is most excellent in the function of preventing the external substance from entering the organic semiconductor layer 6 can be selected as the protective film 8. Further, since the intrusion of the external substance into the organic semiconductor layer 6 is blocked by the protective film 8, it is not necessary for the protective film 7 to have the performance of blocking the intrusion of the external substance. It is only necessary to protect the organic semiconductor layer 6 from damage when forming.

  As described above, the protective film of the organic semiconductor layer 6 is constituted by a laminated structure of the protective film 7 and the protective film 8, and the protective function is divided in stages by the two protective films 7 and 8, thereby providing each protective film. The performance required is limited. Therefore, it is possible to select an optimum material and manufacturing method for each protective film from a wider range of options. For example, if the protective film 8 is a dense silicon nitride film formed by plasma CVD (chemical vapor deposition), it is possible to prevent oxygen and moisture from entering the organic semiconductor layer 6. If the protective film 7 is a PMMA film or a polyimide film, the organic semiconductor layer 6 can be protected from damage caused by plasma when the silicon nitride protective film 8 is formed. As a result, an organic semiconductor device having a protective film having a high passivation effect can be easily formed without using a special material such as parylene.

  When the protective film 8 is made of an inorganic material and the protective film 7 is made of an organic material, the protective film 7 relieves mechanical stress that occurs when the organic semiconductor layer 6 and the inorganic protective layer 8 are in direct contact with each other. It also has an effect as a buffer layer.

  2 and 3 are cross-sectional views showing the flow of the manufacturing process of the organic FET 10 based on the present embodiment.

  First, a support substrate 1 made of, for example, polyethylene naphthalate (PEN) is prepared. As shown in FIGS. 2A to 2C, Al, Au, Ag, Cr, or The gate electrode 2 made of a metal thin film such as Ni is formed by patterning.

  That is, first, as shown in FIG. 2A, a photoresist layer is formed on the entire surface of the support substrate 1 by a coating method or the like, and then patterned by photolithography to cover a region other than the region where the gate electrode 2 is formed. A mask 51 is formed.

  Next, as shown in FIG. 2B, an electrode material layer 52 is formed on the entire surface by vapor deposition or the like. Next, by dissolving and removing the mask layer 51, the electrode material layer 52 deposited thereon is removed, leaving only the electrode material layer 52 to be the gate electrode 2 as shown in FIG.

  The electrode forming method by the lift-off method has been described above. As another method, after forming a metal thin film on the entire surface by vapor deposition or the like, the metal thin film is patterned by lithography and etching to form the gate electrode 2. Also good. In addition, metal fine particles such as Au and Ag are patterned and deposited on the support substrate 1 by a printing method such as an ink jet printing method, a micro contact printing method, and a screen printing method, and the gate electrode 2 made of the metal fine particles is formed. It can also be formed.

Next, as shown in FIG. 2D, a gate insulating film 3 made of an inorganic material or an organic polymer material is formed on the entire surface of the support substrate 1 including the gate electrode 2. Specifically, the gate insulating film 3 made of an inorganic material such as SiO ₂ , SiN _x , Al ₂ O ₃ , Ta ₂ O ₅ , TiO ₂ , and HfO _x is formed by CVD, RF (radio frequency) sputtering, and vacuum. A film is formed by vapor deposition. Further, the gate insulating film 3 made of an organic polymer material such as PVP, PMMA, or polyimide is applied by a coating method such as a spin coating method, a die coating method, a capillary coating method, or a dip coating method, an ink jet printing method, or a micro contact printing method. These solutions are deposited on the support substrate 1 by a printing method such as a screen printing method, and then the solvent is evaporated to form a film. Parylene is deposited by vacuum deposition.

  Next, as illustrated in FIG. 2E, the source electrode 4 and the drain electrode 5 are formed on the gate insulating layer 3 by the same method as that for the gate electrode 2. That is, the source electrode 4 and the drain electrode 5 made of a metal thin film such as gold, silver, or chromium are formed by a lift-off method, vapor deposition, and subsequent lithography and etching. The source electrode 4 and the drain electrode 5 made of metal fine particles such as Au and Ag, and organic semiconductor materials such as PEDOT / PSS and polyaniline are formed by a printing method.

  Next, as shown in FIG. 3 (f), an organic semiconductor layer 6 made of an organic semiconductor material so as to be in contact with at least the source electrode 4 and the drain electrode 5 and to continuously cover the electrodes and between the electrodes. Form. Specifically, when the organic semiconductor material is a high molecular weight compound such as poly (3-hexylthiophene) (P3HT), for example, first, it is dissolved in a suitable solvent, and a 0.1 to 1% by mass solution is prepared. Prepare. Next, the solution is applied to the gate insulating layer 3 in a nitrogen atmosphere or in the air by a coating method such as a spin coating method, a dip coating method, a capillary coating method, a dispenser method, a die coating method, or a printing method such as an ink jet printing method. The entire surface or a desired region is applied. Thereafter, the remaining solvent is evaporated by heat treatment for about 30 minutes at a temperature of 100 to 160 ° C. in a nitrogen atmosphere or in vacuum. In this way, the organic semiconductor layer 6 having a thickness of 50 to 100 nm is formed. The solvent used here is not particularly limited, but chloroform, toluene, xylene, tetrahydrofuran (THF) and the like are preferable.

  If the organic semiconductor material is a low molecular weight compound such as pentacene or oligothiophene, the organic semiconductor layer 6 is formed by a vapor deposition method using a resistance heating type vapor deposition source.

  Next, as shown in FIG. 3G, a protective layer 7 covering the organic semiconductor layer 6 is formed. Specifically, a solution of an organic polymer material such as polyvinyl alcohol (PVA), PVP, PMMA, polyimide, and a fluorine polymer, which is a material of the protective layer 7, or a solution of an inorganic polymer material such as polysilazane, After depositing the organic semiconductor layer 6 by a coating method such as a dip coating method, a capillary coating method, a dispenser method, a die coating method, or a printing method such as an ink jet printing method, the solvent is evaporated to form the protective layer 7. To do. Thereafter, the remaining solvent is evaporated by heat treatment for about 1 hour at a temperature of 100 to 160 ° C. in a nitrogen atmosphere or in vacuum. The material, film thickness, and the like are appropriately selected according to the method for forming the protective film 8 to be described below. However, when PMMA or polyimide is formed to protect the organic semiconductor layer 6 from plasma damage, The film thickness is about 500 nm.

  At this time, as a solvent, the property of dissolving the organic semiconductor material constituting the organic semiconductor layer 6 is poor, and a solvent having a surface energy lower than that of the outermost surface is used to dissolve the material of the protective film 7 to form a solution. It is good. Specifically, the solvent is selected from the group consisting of 2-propanol (isopropyl alcohol), butanol, cyclopentanone, 1,4-dioxane, γ-butyllactone, anisole, and polyethylene glycol monomethyl ether acetate (PEGMEA). It is good to consist of at least one of them.

  Thus, in the present embodiment, an appropriate solvent is selected and the protective film 7 is formed by depositing the solution, so that damage to the organic semiconductor layer 6 is minimized and there are few pinholes. A protective film 7 can be formed. Further, since a large-scale device such as a vacuum device is not required, the large-area protective film 7 can be formed easily and at low cost. In addition, as a secondary effect, the flatness of the surface is improved, so that subsequent processes such as a wiring forming process are facilitated, and accuracy is improved.

  Next, as shown in FIG. 3H, aluminum oxide (alumina), silicon nitride, silicon oxide, silicon oxynitride, titanium oxide, and thallium oxide are laminated on the protective film 7 so as to cover the protective film 7. And a protective film 8 made of an inorganic material such as hafnium oxide or an organic polymer material such as parylene. The film thickness is appropriately selected according to the ability to prevent the permeation of oxygen and moisture, but about 100 nm is preferable for aluminum oxide (alumina) and silicon nitride.

  When the protective film 8 is formed, since the protective film 7 having the function of protecting the organic semiconductor layer 6 from damage at that time has already been formed, there is no need to worry about damage to the organic semiconductor layer 6. A film having the best action for preventing the external substance from entering the organic semiconductor layer 6 can be selected as the protective film 8 from a wide range of options.

  For example, a dense silicon nitride film formed by a plasma CVD method or an aluminum oxide (alumina) film formed by a sputtering method is suitable as the protective film 8 that prevents intrusion of oxygen and moisture into the organic semiconductor layer 6. It is a membrane. When the protective film 8 is formed using a method using plasma, for example, a plasma CVD method or a sputtering method, the protective film 7 has at least an action of protecting the organic semiconductor layer 6 from damage caused by plasma. A protective film is formed. However, since intrusion of oxygen and moisture into the organic semiconductor layer 6 is blocked by the protective film 8, the protective film 7 does not need to have the performance of blocking these penetrations, and the material of the protective film 7 is a wide choice. The optimum material can be selected from among them.

  Further, the protective film 8 may be formed by vacuum deposition or solution deposition. In this case, as the protective film 7, a film that protects the organic semiconductor layer 6 from heat during vacuum deposition or a film that protects the organic semiconductor layer 6 from a solvent of a solution containing the material of the protective film 8 is formed. deep.

  The formation of the organic semiconductor layer 6, the formation of the protective film 7, and the formation of the protective film 8 are performed so that a series of treatments can be performed without being exposed to the outside air in order to avoid the influence of oxygen and moisture. It is preferably performed under a processing system configured as a cluster tool coupled to a box.

  As described above, the organic semiconductor device manufacturing method according to the present embodiment uses only the techniques and facilities that have already been established and spread in each process, and thus the organic FET 10 is manufactured efficiently and reliably. be able to.

  FIG. 4 is a cross-sectional view showing the structure of an organic FET 20 according to a modification of the present embodiment, corresponding to claim 7. As shown in FIG. 4, the organic FET 20 is different from the organic FET 10 only in that a protective film 11 as the third protective film is formed on the support substrate 1 side when viewed from the organic semiconductor layer 6. Yes. The material of the protective film 11 may be the same as the material of the protective film 8, and may be an inorganic material such as aluminum oxide (alumina), silicon nitride, silicon oxide, silicon oxynitride, titanium oxide, thallium oxide, and hafnium oxide, or parylene. Organic polymer materials.

  For example, when the support substrate 1 cannot sufficiently block the permeation of the external substance as in the case where the support substrate 1 is a thin plastic substrate, the protective film 8 is formed on the external substance that has permeated the support substrate 1. An attempt is made to enter the organic semiconductor layer 6 from the side not present. The protective film 11 corresponds to this, and by providing the protective film 11, it is possible to block the external substances such as oxygen and moisture that try to enter the organic semiconductor layer 6 from the support substrate 1 side.

  In addition, when a plastic substrate or the like is used as the support substrate 1, gas may be released from the support substrate 1 during the processing process, which may cause deterioration in the quality of the organic semiconductor device. However, a protective film 11 is provided. As a result, an effect of suppressing gas release from the support substrate 1 can also be obtained.

  By providing the protective film 11 as described above, the reliability and manufacturing yield of the organic FET 20 are improved, and the degree of freedom of the material and thickness of the support substrate 1 is also increased.

  The position where the protective film 11 is provided is not limited to the upper surface side of the support substrate 1 shown in FIG. 4, and may be provided on the lower surface side or on both surfaces. Further, since the gate insulating film 3 exists between the support substrate 1 and the organic semiconductor layer 6, it can be considered that the protective film 11 provided on the upper surface side also serves as the gate insulating film 3. However, since the gate insulating film 3 has an optimum film thickness as a gate insulating film, if this does not coincide with the optimum film thickness as a protective film, it is better to provide an independent protective film 11.

Examples 1 and 2 are examples in which the organic FET 10 shown in FIG. In these examples, a plastic substrate made of polyethylene naphthalate (PEN) is used as the support substrate 1, a gate electrode 2 made of aluminum, a source electrode 4 and a drain electrode 5 made of gold, and a gate insulating film made of silicon oxide SiO _2. 3 was formed. Further, an organic semiconductor layer 6 made of poly (3-hexylthiophene) (P3HT) was formed using chloroform as a solvent. Note that the source electrode 4 and the drain electrode 5 were patterned in the shape of a comb-shaped electrode.

  In Example 1, a protective film 7 was formed by depositing PMMA to a thickness of about 100 nm by spin coating using anisole as a solvent, and then nitrided by RF magnetron sputtering at an output of 100 W and 25 ° C. In this example, the protective film 8 made of silicon is formed to a thickness of about 100 nm. The gate length Lg is 5 μm, and the gate width Wg is 47.2 mm.

  In the comparative example, the protective film 8 made of silicon nitride was formed to a thickness of about 100 nm directly on the organic semiconductor layer 6 without forming the protective film 7 by the RF sputtering method in the same manner as in Example 1. It is. As in the first embodiment, the gate length Lg is 5 μm and the gate width Wg is 47.2 mm.

  FIG. 7 is a graph showing the relationship between the drain current Id and the gate voltage Vg in the organic FET of the comparative example with the drain voltage Vd kept at −80V. The dotted line is a graph of the organic FET before the protective film 8 is formed, and the solid line is a graph after the silicon nitride protective film 8 is formed by the RF sputtering method.

From the graph of FIG. 7, in the FET of the comparative example, when a negative gate voltage Vg is applied, a large drain current Id flows, the transistor is in an on state, and the applied gate voltage Vg is a positive or near zero voltage. It can be seen that the drain current Id is minimized and the transistor is turned off. In the organic FET before the protective film 8 is formed by the RF sputtering method, the ratio of the on current to the off current, that is, the on / off ratio is about 2 × 10 ^{5 at the} maximum, whereas the protective film is formed by the RF sputtering process. In the organic FET after forming 8, the on-current is decreased, the off-current is increased, and the on / off ratio is degraded to about 2 × 10 ^{3 at the} maximum.

  Since the plasma output in the RF sputtering process when the silicon nitride protective film 8 is formed is 100 W and the plasma has a relatively small energy, the organic semiconductor layer 6 made of P3HT is extremely susceptible to plasma damage, When the silicon nitride protective film 8 is directly formed on the semiconductor layer 6, it can be seen that the FET characteristics are remarkably deteriorated by the RF sputtering process.

On the other hand, FIG. 5 is a graph showing the relationship between the drain current Id and the gate voltage Vg in the organic FET of Example 1 while keeping the drain voltage Vd at −80V. From the graph of FIG. 5, even in the FET of Example 1, when the negative gate voltage Vg is applied, the transistor is in an on state, and when the applied gate voltage Vg is a positive voltage, the transistor is in an off state. I understand that The ratio between on-current and off-electricity, that is, the on / off ratio is about 2 × 10 ^{5 at the} maximum, which is the same as the FET of the comparative example before the RF sputtering process. Therefore, in the FET of Example 1, since the protective film 7 made of PMMA was formed prior to the RF sputtering process, the plasma when the organic semiconductor layer 6 made of P3HT formed the silicon nitride protective film 8 was formed. It can be seen that it was completely protected from damage caused by.

  In Example 2, γ-butyllactone was used as a solvent, and a protective film 7 was formed by forming a polyimide film with a thickness of about 100 nm by a spin coating method, and then an output of 100 W at 25 ° C. by an RF magnetron sputtering method. In this example, a protective film 8 made of silicon nitride is formed to a thickness of about 100 nm. The gate length Lg is 10 μm and the gate width Wg is 0.56 mm.

  FIG. 6 is a graph showing the relationship between the drain current Id and the gate voltage Vg in the organic FET of Example 2 while keeping the drain voltage Vd at −80V. From the graph of FIG. 6, even in the FET of Example 2, when the negative gate voltage Vg is applied, the transistor is in the on state, and when the applied gate voltage Vg is almost zero, the transistor is in the off state. I understand that. In this FET, the turn-on voltage is in the vicinity of 0V, and when the gate voltage Vg is set to 0V, the FET is turned off, which is convenient in terms of control.

Since this FET has a gate length Lg and a gate width Wg different from those of the first and comparative examples, the magnitude of the drain current cannot be directly compared with these. The / off ratio is 1 × 10 ⁶ or more at the maximum. From this, it can be estimated that there was no deterioration due to the RF sputtering treatment. That is, in the FET of Example 2, since the protective film 7 made of polyimide was formed prior to the RF sputtering process, the organic semiconductor layer 6 made of P3HT was damaged by plasma when the silicon nitride protective film 8 was formed. It can be seen that it was completely protected.

  As described above, in Example 1 and Example 2, the organic FET 10 is manufactured based on the embodiment of the present invention, and the relationship between the drain current Id and the gate voltage Vg is measured, and the first of the present invention. Alternatively, based on the second organic semiconductor device, it was confirmed that an organic FET having the protective film 8 that prevents intrusion of oxygen and moisture can be obtained without deteriorating the transistor characteristics of the organic semiconductor layer 6.

  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. .

  The organic semiconductor device and the manufacturing method thereof of the present invention are used as a semiconductor device such as a thin film transistor (TFT) widely used as a switching element for various electronic circuits, in particular, an active matrix circuit of a display, and a manufacturing method thereof. It can contribute to the development of new uses such as cost reduction and application to flexible substrates without heat resistance such as plastic.

It is sectional drawing which shows the structure of organic FET based on embodiment of this invention. It is sectional drawing which shows the flow of the manufacturing process of organic FET same as the above. It is sectional drawing which shows the flow of the manufacturing process of organic FET same as the above. It is sectional drawing which shows the structure of organic FET based on a modification similarly. In the organic FET of Example 1 according to the present invention, it is a graph showing the relationship between the drain current I _d the gate voltage V _g. In the organic FET of the second embodiment according to the present invention, it is a graph showing the relationship between the drain current I _d the gate voltage V _g. In the organic FET of the comparative example, it is a graph showing the relationship between the drain current I _d the gate voltage V _g. 1 is a side sectional view of a switching element according to a first embodiment of the invention disclosed in Patent Document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Support substrate, 2 ... Gate electrode, 3 ... Gate insulating layer, 4 ... Drain electrode,
5 ... Source electrode, 6 ... Organic semiconductor layer, 7 ... Protective film, 8 ... Protective film, 10 ... Organic FET,
DESCRIPTION OF SYMBOLS 11 ... Protective film, 51 ... Mask layer, 52 ... Electrode material layer, 101 ... Substrate,
102 ... Cathode electrode, 103 ... Anode electrode, 104 ... Organic semiconductor material,
111 ... 1st protective layer, 112 ... 2nd protective layer

Claims (18)

In an organic semiconductor device having an organic semiconductor layer as a conductive region,
The organic semiconductor layer is covered with a first protective film formed by deposition of a solution; and further, the first protective film is covered with a second protective film;
The first protective film has at least an action of protecting the organic semiconductor layer from damage when forming the second protective film;
The organic semiconductor device, wherein the second protective film has an action of preventing at least an external substance from entering the organic semiconductor layer. In an organic semiconductor device having an organic semiconductor layer as a conductive region,
A first protection in which the organic semiconductor layer is made of at least one selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polymethyl methacrylate (PMMA), polyimide, fluorine-containing polymer, and polysilazane. Covered with a film, and further, the first protective film is covered with a second protective film,
The first protective film has at least an action of protecting the organic semiconductor layer from damage when forming the second protective film;
The organic semiconductor device, wherein the second protective film has an action of preventing at least an external substance from entering the organic semiconductor layer.   The organic semiconductor device according to claim 1, wherein the first protective film has at least an action of protecting the organic semiconductor layer from damage due to plasma, and the second protective film is formed using plasma. .   The organic semiconductor device according to claim 3, wherein the second protective film is formed using a plasma CVD method (chemical vapor deposition method) or a sputtering method.   The organic semiconductor device according to claim 1, wherein the second protective film is formed by vacuum deposition or solution deposition.   The organic semiconductor device according to claim 2, wherein the first protective film is formed by depositing a solution.   2. The organic semiconductor device according to claim 1, wherein the organic semiconductor layer is formed on a base, and a third protective film that prevents an external substance from entering the organic semiconductor layer is formed on the base.   The first protective film is made of at least one selected from the group consisting of polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polymethyl methacrylate (PMMA), polyimide, fluorine-containing polymer, and polysilazane. 1. The organic semiconductor device described in 1. The second protective film is made of aluminum oxide (alumina) Al ₂ O ₃ , silicon nitride SiN _x , silicon oxide SiO ₂ , silicon oxynitride SiO _x N _y , titanium oxide TiO ₂ , thallium oxide Ta ₂ O _5, hafnium oxide comprises at least one selected from the group consisting of HfO _x and parylene, organic semiconductor device according to claim 1. The third protective film includes aluminum oxide (alumina) Al ₂ O ₃ , silicon nitride SiN _x , silicon oxide SiO ₂ , silicon oxynitride SiO _x N _y , titanium oxide TiO ₂ , thallium oxide Ta ₂ O ₅ , hafnium oxide The organic semiconductor device according to claim 7, comprising at least one selected from the group consisting of HfO _x and parylene.   The organic semiconductor device according to claim 1, wherein the organic semiconductor layer is made of a polythiophene compound.   The source electrode and the drain electrode are provided in contact with the conductive region, and a gate electrode is provided between the two electrodes via a gate insulating film, and the device is configured as an insulated gate field effect transistor. Organic semiconductor device. A method for producing an organic semiconductor device according to claim 1 or 2, wherein the organic semiconductor layer is formed on a substrate.
Depositing the solution containing the material of the first protective film and covering the organic semiconductor layer with the first protective film;
And a step of covering the first protective film with the second protective film.   14. The organic semiconductor device according to claim 13, wherein the solution containing the material of the first protective film is formed using a solvent having poor property of dissolving the organic semiconductor layer and having a surface energy lower than that of the outermost surface. Production method.   The solvent is at least one selected from the group consisting of 2-propanol (isopropyl alcohol), butanol, cyclopentanone, 1,4-dioxane, γ-butyllactone, anisole, and polyethylene glycol monomethyl ether acetate (PEGMEA). The method for manufacturing an organic semiconductor device according to claim 14.   The first protective film is formed using at least a material having an action of protecting the organic semiconductor layer from damage caused by plasma, and the second protective film is formed using plasma. Method for manufacturing an organic semiconductor device.   The method of manufacturing an organic semiconductor device according to claim 16, wherein the second protective film is formed using a plasma CVD method or a sputtering method.   The method of manufacturing an organic semiconductor device according to claim 13, wherein the second protective film is formed by vacuum deposition or deposition of a solution.

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