JP2010016280A - Organic tft manufacturing method, and organic tft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing the organic TFT capable of obtaining excellent characteristics and high reliability, without incurring complication and a high cost in manufacturing process, and provide the organic TFT. <P>SOLUTION: The method includes the steps of: dropping liquid material having liquid repellent nature onto a base layer; drying the dropped liquid material to form a bank film of a coffee stain shape having a bank in periphery; and coating organic semiconductor material at the inside of the bank film to form an organic semiconductor film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic TFT manufacturing method and an organic TFT.

  In recent years, a technique for forming a thin film transistor (hereinafter also referred to as TFT) on a substrate has greatly advanced, and in particular, application development to a drive element of an active matrix type large screen display device has been advanced. TFTs that are currently in practical use are manufactured with Si-based inorganic materials such as a-Si and poly-Si, but the manufacture of TFTs using such inorganic materials requires a vacuum process or a high-temperature process. And greatly affects the manufacturing cost.

  Therefore, in order to deal with such problems, various TFTs using organic materials (hereinafter also referred to as organic TFTs) have been studied in recent years. Organic materials have a wider choice of materials than inorganic materials, and the manufacturing process of organic TFTs uses processes with excellent productivity such as printing and coating instead of the vacuum process and high temperature process described above. Cost can be reduced. Furthermore, it may be formed on, for example, a plastic film substrate having poor heat resistance, and is expected to be applied to various fields.

  As a method for applying the organic semiconductor material, there are known droplet application techniques such as an inkjet method and a dispenser method in which a solution in which the organic semiconductor material is dissolved is directly applied. These techniques are: 1. No vacuum process is required. 2. There is no waste of materials. Since direct patterning is possible, there is an advantage that an etching process is not required as compared with the photolithography method. As a result, manufacturing costs can be reduced, and extensive research has been conducted.

  By the way, in such an organic TFT, in order to obtain excellent electrical characteristics and high reliability, it is necessary to accurately form an organic semiconductor film at a predetermined position with an appropriate film thickness. However, when the organic semiconductor film of the organic TFT is formed using the above-described inkjet method, dispenser method, or the like, the discharged droplet spreads before drying and reaches the adjacent pixels. There are problems such as poor patterning that leads to an increase in crosstalk, leakage current, and the like, and that satisfactory characteristics of the transistor cannot be obtained due to an insufficient film thickness.

Therefore, various techniques have been studied to deal with such problems. For example, by using a photolithography method, a wall called a bank is formed at the periphery of the application region to prevent the discharged droplets from flowing out of the application region. Furthermore, a technique is known that prevents the liquid droplet from flowing out of the coating area by making the coated area more lyophilic than the bank (Patent Document). 1).
Japanese Patent No. 3692524

  However, in the method disclosed in Patent Document 1, in order to form a bank, for example, at least the following steps 1 to 6 are required. Therefore, there are problems that the manufacturing process is complicated and the manufacturing cost is increased.

  1. Film forming process: Photosensitive resin, which is a bank material, is formed on the entire surface by spin coating.

  2. Pre-bake: solvent is dried.

  3. Exposure process: A photomask is placed and exposed to ultraviolet rays.

  4). PEB (post-exposure bake): Promotes the progress of chemical reaction by exposure, such as curing the resin at about 100 ° C.

  5. Development process: Immerse in the developer and remove only the resin irradiated with ultraviolet rays.

  6). PB (post bake): The remaining resin is cured.

  The present invention has been made in view of the above problems, and an organic TFT manufacturing method and an organic TFT capable of obtaining excellent characteristics and high reliability without complicating the manufacturing process and increasing the cost. The purpose is to provide.

  The above object is achieved by the invention described in any one of 1 to 8 below.

1. Dropping a liquid material having liquid repellency on the underlayer;
Forming a coffee stain-shaped bank film having a bank on the periphery by drying the dropped liquid material; and
And a step of applying an organic semiconductor material to the inside of the bank film to form an organic semiconductor film.

  2. The film thickness of a region excluding the bank of the bank film is extremely smaller than the film thickness of the bank, or the region excluding the bank of the bank film has the underlying layer exposed. The manufacturing method of organic TFT of description.

  3. 3. The method of manufacturing an organic TFT as described in 2 above, wherein the underlayer is a source electrode / drain electrode and a gate insulating film.

  4). Between the step of forming the bank film and the step of forming the organic semiconductor film, at least the bank film in a region excluding the bank of the bank film formed on the source electrode / drain electrode is removed. 4. The method for producing an organic TFT as described in 3 above, comprising the step of:

  5. 3. The method for producing an organic TFT according to 1 or 2, wherein the underlayer is a gate insulating film.

  6). 6. The method for producing an organic TFT according to any one of 1 to 5, wherein the liquid material having liquid repellency is dropped using an ink jet method or a dispenser method.

  7). 7. The method of manufacturing an organic TFT according to any one of 1 to 6, wherein the organic semiconductor material is applied using an inkjet method or a dispenser method.

  8). 8. An organic TFT manufactured using the method for manufacturing an organic TFT according to any one of 1 to 7 above.

  According to the present invention, the bank is formed by using the coffee stain phenomenon generated by drying the liquid material having liquid repellency dropped onto the underlayer, and forming the coffee stain shape. Thus, a bank can be easily formed at a desired position without using a photolithography method as in the prior art, and an organic semiconductor film having a predetermined thickness can be formed by using the formed bank. It can be accurately formed at the position. As a result, it is possible to manufacture an organic TFT capable of obtaining excellent characteristics and high reliability without causing the manufacturing process to be complicated and expensive.

  Embodiments of an organic TFT according to the present invention will be described below with reference to the drawings. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not limited to this embodiment.

  First, the configuration of a bottom gate bottom contact type organic TFT which is one of the typical embodiments of the organic TFT according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a schematic configuration of a bottom gate bottom contact type organic TFT 1.

  As shown in FIG. 1, the organic TFT 1 includes a substrate P, a gate electrode G, a gate insulating film IF, a source electrode S / drain electrode D, a bank B, an organic semiconductor film SF, a passivation film (not shown), and the like.

  In the organic TFT 1, a gate electrode G, a gate insulating film IF, a source electrode S / drain electrode D, and a bank B are sequentially formed on a substrate P, and an organic semiconductor film SF is further formed thereon.

  In the organic TFT 1 having such a configuration, the bank B is used to accurately form the organic semiconductor film SF at a predetermined position with an appropriate film thickness, and is not shown which is dropped on the gate insulating film IF. It is formed on the source electrode S and the drain electrode D by utilizing a coffee stain phenomenon generated by drying a liquid material LM having liquid repellency described later. The cross-sectional shape of the coffee stain has a thick film at the peripheral part and an extremely thin film at the central part, or the film at the central part is broken by a drying process, and the underlying layer (gate insulating film IF, source electrode S / drain electrode D) ) Is exposed.

  In addition, although the structure of the bottom gate bottom contact type organic TFT 1 was shown here, the element structure of the organic TFT according to the present invention is not particularly limited, and may be a bottom gate top contact type. In this case, the bank B may be formed on the gate insulating film IF as shown in FIG. Furthermore, a top gate type may be used.

  Here, the coffee stain phenomenon will be described with reference to FIG. 4A and 4B are schematic cross-sectional views illustrating the coffee stain phenomenon. In addition, the coffee stain phenomenon which produces a coffee stain shape is also called a saddle phenomenon, and is a well-known phenomenon.

  In the coffee stain phenomenon, the liquid material LM dropped on the substrate P (FIG. 4A) is dried to form a donut-shaped coffee stain CP (FIG. 4B) due to the Marangoni effect. The bank B is formed on the periphery thereof.

  As a method of forming a coffee stain shape, the temperature of the substrate P is raised and the dropped liquid material LM is dried. A liquid material LM having a high evaporation heat or a high drying rate is selected or partially mixed with the solvent of the liquid material LM. In order to bring out the Marangoni effect, such as mixing a solute or dispersoid having a high pinning effect into the liquid material LM (combining with a solvent having a low dissolution rate so that the solute pinned at the periphery is re-dissolved by Marangoni convection and does not depin). The method is mentioned.

  Usually, in the process using the ink jet method, when the viscosity of the ink is low or the contact angle between the substrate to be applied and the ink is small, there is a problem that the ink is excessively spread. In particular, in the process of forming an organic semiconductor film using an organic semiconductor material or the like, since the surface of the substrate is required to be clean, the surface energy of the substrate tends to increase. There is a problem that the contact angle becomes small.

  For this reason, when the inkjet method is used to form a fine pattern, it is necessary to take measures such as forming a bank or increasing the contact angle by using a liquid repellent material for the underlayer in order to suppress the spread of ink. is there.

  However, in order to form a bank, a photolithography method that leads to an increase in manufacturing cost is necessary. In addition, if the liquid repellent material layer is provided on the underlayer and the contact angle is increased, the adhesion of the ink to the substrate decreases, and the ink moves due to the movement of the substrate in the drying process or the external force resulting from drying of the solvent of the ink itself This causes a problem that the film cannot be applied at a predetermined position because it rolls and moves.

  The present inventor has intensively studied to cope with these problems, and as a result, has found a method of forming a bank using the coffee stain phenomenon.

  In other words, a liquid material having liquid repellency as a bank material is applied onto an underlayer by an ink jet method, and a coffee stain shape is formed by using a coffee stain phenomenon generated by drying, and a photolithography method This makes it possible to form a bank at a desired position without using. Details of the bank forming method will be described later.

  Next, an example of a manufacturing process of the organic TFT 1 having such a configuration will be described with reference to FIG. FIG. 3A to FIG. 3H are schematic cross-sectional views illustrating an example of the manufacturing process of the organic TFT 1.

  First, a substrate P is prepared (FIG. 3A). The material of the board | substrate P is not specifically limited, For example, resin sheets, such as glass, such as soda glass and an alkali free glass, and a flexible plastic film, can be used. Specific examples of the plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate. Examples thereof include a film made of (CAP) or the like. By using such a plastic film, the weight can be reduced as compared with the case of using a glass substrate, the portability can be improved, and the resistance to impact can be improved. A metal plate such as stainless steel or brass can also be used.

  Next, the gate electrode G is formed (FIG. 3B). As the electrode material of the gate electrode G, when a thin film is formed by sputtering or vapor deposition, Au, Ag, Pb, Al, Cr, Pt, Cu, Mo, ITO, or a material obtained by adding a dopant to these may be used. it can. In the case of the droplet coating method, metal nanoparticle ink in which metal nanoparticles such as Ag nanoparticles, Au nanoparticles, and AgPb nanoparticles are dispersed in a solvent, and metal oxide in which metal oxides such as ITO nanoparticles are dispersed in a solvent An organic material-dispersed ink in which an organic material such as nanoparticle ink or PEDOT / PSS is dispersed in a solvent can be used. As a forming method, a method of patterning a substrate P on which a thin film of an electrode material is formed by a sputtering method, a vapor deposition method, or the like using a photolithography method, or a desired method using various printing methods or a droplet coating method. A thin film can be formed only on this part.

  Next, the gate insulating film IF is formed (FIG. 3C). As a material of the gate insulating film IF, inorganic oxides such as silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide, and inorganic nitrides such as silicon nitride and aluminum nitride can be used. Or, polyimide, polyamide, polyester, polyacrylate, photo-curing polymer of photo radical polymerization, photo cation polymerization, copolymer containing acrylonitrile component, organic compound such as polyvinyl phenol, polyvinyl alcohol, novolac resin, cyanoethyl pullulan Etc. can also be used. As a forming method, for example, in addition to a vacuum deposition method, a CVD method, a sputtering method, an atmospheric pressure plasma method, etc., an insulating film formed by a coating method such as spin coating is patterned using a patterning method such as a photolithography method. It is possible to form a thin film only on a desired portion by using a printing method, various printing methods, or droplet coating methods such as inkjet.

  Next, the source electrode S and the drain electrode D are formed (FIG. 3D). As the electrode material of the source electrode S / drain electrode D, the same electrode material as that of the gate electrode G can be used. After cleaning the substrate P on which the gate insulating layer IF is formed, it can be formed by using a photolithography method, various printing methods, a droplet coating method, or the like in the same manner as the method for forming the gate electrode G described above.

  Next, the liquid material LM is dropped (FIG. 3E). As the liquid material LM, materials having liquid repellency, such as Cytop (manufactured by Asahi Glass Co., Ltd.), NPAR-502, 503 (Nissan Chemical Co., Ltd .: surface liquid repellent positive photosensitive resin), and other silicon-based resins are used. Etc. can also be used. As the dropping method, an inkjet method or a dispenser method can be used.

  Next, the dropped liquid material LM is dried. The liquid material LM dropped by the coffee stain phenomenon generated in the drying process is formed as a bank film BF having a coffee stain shape (FIG. 3F).

  Next, the bank film BFc and the bank film BFa slightly remaining on the gate insulating film IF and the source electrode S / drain electrode D are removed by light etching, and formed on the periphery of the bank film BF. Only the bank B is left (FIG. 3 (f), FIG. 3 (g)). Note that dry etching that does not significantly change the surface state of the bank film BF is suitable for the slite etching, but wet etching may be used as long as the functional aspect related to the shape of the bank B is not hindered. For dry etching, atmospheric pressure plasma is suitable in addition to a normal vacuum process.

  While leaving the bank B formed on the source electrode S / drain electrode D, the bank film BFa is removed by light etching, thereby forming the organic semiconductor film formed in the next step with the source electrode S / drain electrode D Electrical contact with SF can be enhanced, and more stable characteristics can be obtained.

  Next, the organic semiconductor film SF is formed (FIG. 3H). As a material of the organic semiconductor film SF, a polycyclic aromatic compound, a conjugated polymer, or the like can be used, but is not particularly limited. A polymer material, an oligomer, or a low-molecular material may be used, and a material in which molecules are regularly arranged by intermolecular interaction to form a crystal after film formation is particularly preferable. Pentacene, porphyrin, phthalocyanine, oligothiophene, oligophenylene, polythiophene, polyphenylene, and derivatives thereof can be used. Specifically, pentacene, 6,13-bis (triisopropylsilylethynyl) pentacene, tetrabenzoporphyrin, poly (3-hexylthiophene), or the like can be used. Further, these precursors can be converted into an organic semiconductor material or the like by heat treatment after the film formation.

  The method of forming the organic semiconductor film SF is not particularly limited as long as it can increase the accuracy of the application position by the effect of the bank B. Screen printing, inkjet method, microcontact printing, SIJ, dispenser method When printing methods such as letterpress and transfer are used, patterning can be performed simultaneously with coating, which is preferable because the manufacturing cost can be reduced. In particular, it is particularly preferable to use a droplet coating method such as an inkjet method, SIJ, or a dispenser method.

  In the case of using the droplet coating method, the organic semiconductor film SF is preferably dissolved or dispersed in a solvent among the materials described above, and is soluble on the organic low molecular weight material in order to increase the solubility. The present invention can also be applied to a solution provided with a chain or a solution of a semiconductor precursor.

  The solvent is not particularly limited, and is suitable for semiconductor materials from aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, esters, halogenated hydrocarbons, phenols, etc. Solvents can be selected.

  The passivation film is appropriately formed in order to shield and protect the organic semiconductor film SF from the external atmosphere.

  Next, examples of the bottom gate bottom contact type organic TFT 1 according to the embodiment of the present invention will be described.

(Example)
First, a photosensitive resist is applied to a soda lime glass substrate (FIG. 3A: substrate P) for STN liquid crystal having a Cr film sputtered on the surface, and then passed through a photomask having a pattern of the gate electrode G. Then, exposure and development were performed to form a resist layer in the shape of the gate electrode G. After the etching of Cr, the resist layer was removed to form the gate electrode G (FIG. 3B).

Next, a sputtering method was used to form SiO ₂ to form a gate insulating film IF having a thickness of 500 nm (FIG. 3C). In order to protect the terminal portion of the gate electrode G, a lift-off resist (manufactured by ZEON Co., Ltd.) was applied in advance by a spin coating method, and then patterned using a photolithography method to form a protective film. After forming the gate insulating film IF, ultrasonic cleaning was performed with dimethylformamide at room temperature to remove the unnecessary portion of the gate insulating film IF and lead out the terminals.

  Next, after applying a lift-off resist on the gate insulating film IF and patterning using a photolithography method, a Cr film was formed in this order with a thickness of 5 nm and Au with a thickness of 50 nm. Thereafter, ultrasonic cleaning was performed with dimethylformamide at room temperature to remove the unnecessary lift-off resist, and the source electrode S and drain electrode D were formed (FIG. 3D). The distance between the source electrode S and the drain electrode D, which is the channel length, was 25 μm, and the channel width was 250 μm.

  Next, a liquid material LM having liquid repellency was discharged onto the gate insulating film IF between the channels (channel portion) by using an ink jet method (FIG. 3E). As the liquid material LM having liquid repellency, Cytop manufactured by Asahi Glass Co., Ltd. was sufficiently diluted with a diluent. At this time, the substrate P was previously heated to 60 ° C. with a hot plate.

  Next, the dropped liquid material LM was dried by the heated heat of the substrate P and adjusted so as to have a coffee stain shape (FIG. 3F). When the shape of the dried bank film BF was observed with an optical microscope and AFM (manufactured by Keyence Corporation), a coffee stain shape having a diameter of about 300 μm and a peripheral edge height of about 0.2 μm was confirmed. Also, almost no internal thickness was observed.

Next, the surface of the substrate P on which the bank film BF is formed is subjected to surface treatment (slight etching) with Ar—O ₂ atmospheric pressure plasma (atmospheric pressure plasma apparatus manufactured by Konica Minolta Co., Ltd.), the gate insulating film IF, and the source electrode The bank film BFc and the bank film BFa slightly remaining on the S / drain electrode D were removed (FIG. 3 (f), FIG. 3 (g)).

  Next, a solution obtained by dissolving 3% by mass of 6,13-bistriethylsilylethynylpentacene in tetrahydronaphthalene as a semiconductor solution is discharged onto the source electrode S / drain electrode D using a piezo-type ink jet method, and has a diameter of 270 μm. Then, an organic semiconductor film SF having an average film thickness of 50 nm was formed (FIG. 3F), and a bottom gate / bottom contact type organic TFT 1 was completed.

  In this way, 20 elements of the organic TFT 1 were manufactured, and the shape of the organic semiconductor film SF was observed with an optical microscope and AFM (manufactured by Keyence Corporation). It has been confirmed that.

  As described above, in the method for manufacturing the organic TFT 1 according to the embodiment of the present invention, the liquid material LM having liquid repellency dropped on the base layer (gate insulating film IF, source electrode S / drain electrode D) is dried. The bank B is formed by forming the coffee stain shape by utilizing the coffee stain phenomenon generated by the above. As a result, the bank B can be easily formed at a desired position without using a photolithography method as in the prior art, and the organic semiconductor film SF can be formed into an appropriate film thickness by using the formed bank B. Thus, it can be accurately formed at a predetermined position. As a result, it is possible to manufacture the organic TFT 1 that can obtain excellent characteristics and high reliability without complicating the manufacturing process and increasing the price.

It is a cross-sectional schematic diagram which shows the structure of the organic TFT of the bottom gate bottom contact type | mold which concerns on embodiment of this invention. It is a cross-sectional schematic diagram which shows the structure of the organic TFT of the bottom gate top contact type | mold which concerns on embodiment of this invention. It is a cross-sectional schematic diagram which shows an example of the manufacturing process of the bottom gate bottom contact type organic TFT which concerns on embodiment of this invention. It is a cross-sectional schematic diagram explaining a coffee stain phenomenon.

Explanation of symbols

1 Organic TFT (Organic Thin Film Transistor)
B bank BF bank film D drain electrode G gate electrode IF gate insulating film LM liquid material S source electrode SF organic semiconductor film P substrate

Claims (8)

Dropping a liquid material having liquid repellency on the underlayer;
Forming a coffee stain-shaped bank film having a bank on the periphery by drying the dropped liquid material; and
And a step of applying an organic semiconductor material to the inside of the bank film to form an organic semiconductor film. 2. The film thickness of a region excluding the bank of the bank film is extremely smaller than the film thickness of the bank, or the base layer is exposed in a region of the bank film excluding the bank. A method for producing an organic TFT as described in 1. The method of manufacturing an organic TFT according to claim 2, wherein the base layer is a source electrode / drain electrode and a gate insulating film. Between the step of forming the bank film and the step of forming the organic semiconductor film, at least the bank film in a region excluding the bank of the bank film formed on the source electrode / drain electrode is removed. The method for producing an organic TFT according to claim 3, further comprising the step of: The organic TFT manufacturing method according to claim 1, wherein the underlayer is a gate insulating film. The method for producing an organic TFT according to claim 1, wherein the liquid material having liquid repellency is dropped using an ink jet method or a dispenser method. The method of manufacturing an organic TFT according to claim 1, wherein the organic semiconductor material is applied using an inkjet method or a dispenser method. An organic TFT manufactured using the method for manufacturing an organic TFT according to claim 1.

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