JP2016115835A - Oxide layer and method of producing the same, and semiconductor element and method of manufacturing the same, and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin oxide layer excellent in flatness, and capable of being employed in an electronic device or a semiconductor element.SOLUTION: A method of producing one oxide layer of the present invention includes a precursor layer (e.g., precursor layer for channel 42) formation step for forming a precursor of an oxide where a compound of a metal, becoming a metal oxide when oxidized, is dispersed into a solution containing a binder composed of aliphatic polycarbonate (which may contain inevitable impurities) above a substrate 10 in layer, and an irradiation step for irradiating the layer of the precursor with ultraviolet light (UV) while heating under an ozone (O) atmosphere, before the aliphatic polycarbonate is decomposed entirely by heating the layer of the precursor.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an oxide layer and a manufacturing method thereof, a semiconductor element, a manufacturing method thereof, and an electronic device.

  Conventionally, a polycrystalline silicon film or an amorphous silicon film has been mainly used as a channel layer of a thin film transistor which is an example of an electronic device. However, in the case of a polycrystalline silicon film, the electron mobility is limited due to the scattering of electrons occurring at the interface of the polycrystalline particles, resulting in variations in transistor characteristics. In addition, in the case of an amorphous silicon film, there is a problem that the electron mobility is extremely low, the element is deteriorated with time, and the reliability of the element is extremely low. Thus, there is an interest in oxide semiconductors having higher electron mobility than amorphous silicon films and less variation in transistor characteristics than polycrystalline silicon films. In addition to oxide semiconductors, oxide conductors or oxide insulators made of oxides are, for example, indispensable technical elements for realizing electronic devices using only oxides. The interest is very high.

  Recently, an electronic device is formed on a flexible resin substrate using processes such as gravure printing, screen printing, offset printing, and ink jet printing (hereinafter collectively referred to as “low energy manufacturing process”). There are many attempts to make it. By using a printing method or a coating method, the semiconductor layer can be directly patterned on the substrate. As a result, there is an advantage that an etching process step for patterning can be omitted.

  For example, as disclosed in Patent Documents 1 to 3, attempts have been made to produce a coated flexible electronic device using a conductive polymer or an organic semiconductor.

JP 2007-134547 A JP 2007-165900 A JP 2007-201056 A

  While various types of information terminals and information home appliances are demanded by the industry and consumers, semiconductor elements are required to operate at higher speed, to be stable for a long period of time, and to have a low environmental load. However, in the prior art, for example, a process that requires a relatively long time and / or expensive equipment such as a vacuum process or a process using a photolithography method is generally employed. Efficiency is very poor. This is not preferable from the viewpoint of industrial property or mass productivity. On the other hand, at present, it is extremely difficult to form a layer by a low energy manufacturing process on silicon semiconductors or other semiconductors that have been used as the mainstream. Moreover, even if it is a case where the electroconductive polymer and organic semiconductor which were described in patent documents 1-3 are employ | adopted, the electrical property and stability are still inadequate. The “layer” in the present application is a concept including not only a layer but also a film. Conversely, the “film” in the present application is a concept including not only a film but also a layer.

  By the way, the above-mentioned low energy manufacturing process and the semiconductor element and the electronic device manufactured using the functional solution or the functional paste are from the viewpoint of the flexibility of the electronic device and the industrial property or the mass productivity described above. Currently, it is attracting a great deal of attention in the industry.

  However, in general, there is a difference between the thickness of a layer formed by a printing method (particularly a screen printing method), which is a representative example of a low energy manufacturing process, and the layer thickness required for a semiconductor element. Specifically, a relatively thick layer is formed during patterning using a printing method, but the layer thickness required for a semiconductor element is generally very thin. In addition, a paste or solution used in a low energy manufacturing process (for example, a precursor of an oxide semiconductor in which a metal compound that becomes an oxide semiconductor when oxidized is dispersed in a solution containing a binder) is patterned. Since there is a suitable viscosity for carrying out the above, the viscosity is adjusted by adding a binder.

  Here, after the pattern is once formed, the binder is an impurity as viewed from the finally obtained metal oxide, and becomes an object to be decomposed or removed. Therefore, a binder is added when forming a thin layer (typically, an oxide semiconductor layer, an oxide conductor layer, or an oxide insulator layer) constituting a semiconductor element by, for example, a low energy manufacturing process. After the patterning is performed using the paste or solution, the layer is required to be made thin and flat after removing the binder as much as possible. In addition, lowering the processing temperature for forming the layer and / or shortening the processing time is one of the important technical issues for practically adopting a low energy manufacturing process in the industry. Become.

The inventors of the present application conducted research on the formation of various metal oxides from a liquid material. In the process from a liquid to a gel state obtained from the paste or solution described above, “The process leading to the sintered state” was analyzed in detail from many aspects. As a result, mainly in a “process from a liquid to a gel state”, a layer in a gel state (hereinafter also referred to as “gel layer”) is irradiated with ultraviolet rays (UV) in an ozone (O ₃ ) atmosphere. It has been found that by supplying energy, the final fired oxide layer can be made thin and flat. Moreover, the knowledge that the dimensional accuracy of this oxide layer after baking can be improved compared with the past was also obtained. Further, the inventors of the present invention have reduced the processing temperature and / or shortened the processing time for forming the oxide layer pattern by using, for example, a low-energy manufacturing process (for example, fat, which will be described later). (According to the fact that the etching rate of the aromatic polycarbonate can be increased).

  In the present application, the “process from a liquid to a gel state” is a typical example, in which a binder and a solvent are removed by heat treatment, but a metal compound that becomes a metal oxide when oxidized (for example, , A situation where the ligand) is not decomposed. In addition, the “process from a gel state to a solidified state or a sintered state” is a typical example, where the above-mentioned ligand is decomposed and oxidized to form a metal oxide and oxygen. A situation where the bond is almost completed.

The above “mainly” means that irradiation with ultraviolet rays (UV) in an ozone (O ₃ ) atmosphere is not only “a process from a liquid to a gel state” but also “a solidified state or sintered from a gel state. It means that the process leading to the state may also be affected. Although the mechanism is not yet clear, the inventors of the present application have made it possible to heat the gel layer before the decomposition of all of the binder made of aliphatic polycarbonate (which may contain unavoidable impurities; the same applies hereinafter) decomposes. Obtaining knowledge that irradiation of ultraviolet (UV) to the gel layer while heating the gel layer in an (O ₃ ) atmosphere can exert at least some of the effects described above. It was. The present invention has been created based on the above viewpoints and numerous analyses.

  In addition, the inventors of the present application have realized in the past equipment or a method for obtaining an oxide semiconductor layer while accurately decomposing or removing the binder by firing for forming the above-described metal oxide (for example, internationally). (Application number: PCT / JP2014 / 067960) Therefore, in the present application, at least a part of such equipment or method can be utilized. In the present application, it is not always necessary to utilize techniques and technical ideas that have been researched or developed so far. However, utilizing the technology and the technical idea, combined with solving at least a part of the above-described technical problems, further enhances the performance of the above-described semiconductor elements and electronic devices and the manufacturing technology thereof. Can contribute to improvement.

One method for producing an oxide layer according to the present invention is an oxidation in which a metal compound that becomes a metal oxide when oxidized is dispersed in a solution containing a binder (which may contain inevitable impurities) made of an aliphatic polycarbonate. An oxide precursor layer forming step of forming a precursor of the product in a layer on or above the substrate, and heating the precursor layer before decomposing all of the above-described aliphatic polycarbonate, ozone ( An irradiation step of irradiating the precursor layer with ultraviolet rays (UV) while heating the precursor layer in an O ₃ ) atmosphere is included.

According to this method for producing an oxide layer, at least in the “process from a liquid to a gel state”, all of the aliphatic polycarbonate that can serve as a binder is decomposed in an ozone (O ₃ ) atmosphere before being decomposed. By heating the precursor layer and irradiating the precursor layer with ultraviolet rays (UV), it is possible to form a thin oxide layer with excellent flatness. More specifically, according to this manufacturing method, the thickness of the oxide layer can be reduced to several tens of nm or less. In addition, in the process of forming the oxide layer, at least the heating temperature from “from the liquid to the gel state” is reduced by several tens of degrees Celsius compared to the case where the aforementioned ultraviolet (UV) is not irradiated, The heating time can be shortened.

In addition, one oxide layer of the present invention is an oxide in which a metal compound that becomes a metal oxide when oxidized is dispersed in a solution containing a binder (which may contain inevitable impurities) made of an aliphatic polycarbonate. The precursor layer is heated to ultraviolet rays (UV) while heating the precursor layer in an ozone (O ₃ ) atmosphere before all of the aforementioned aliphatic polycarbonate is decomposed by heating the precursor layer. ).

According to this oxide layer, at least in the “process from a liquid to a gel state”, all of the aliphatic polycarbonate that can serve as a binder is decomposed before being decomposed in an ozone (O ₃ ) atmosphere. By irradiating the precursor layer with ultraviolet (UV) while heating the layer, a thin oxide layer with excellent flatness can be realized. More specifically, the oxide layer can realize a thickness of several tens of nm or less.

  By the way, “metal oxide” in the present application is a concept including an oxide semiconductor, an oxide conductor, or an oxide insulator. Note that each of the oxide semiconductor, the oxide conductor, and the oxide insulator is a relative concept from the viewpoint of electrical conductivity, and thus is not required to be strictly distinguished. Even if it is the same kind of metal oxide, it may be recognized by those skilled in the art as an oxide semiconductor depending on the requirements of various devices, or may be recognized by those skilled in the art as an oxide conductor or oxide insulator. It is possible that Further, the “substrate” in the present application is not limited to the foundation of the plate-like body, but includes other forms of foundations or base materials.

  Further, the wavelength of ultraviolet (UV) in the present application is a concept including at least a part of far ultraviolet or near ultraviolet. A typical wavelength range is 100 nm to 400 nm, but from the viewpoint of achieving the effect of the present invention, it is about 170 nm or more and about 260 nm or less.

  According to the manufacturing method of one oxide layer of the present invention, it is possible to form an oxide layer that is thin and excellent in flatness. Further, in the process of forming the oxide layer, at least the heating temperature from “from the liquid to the gel state” is reduced by several tens of degrees C. compared to the case where the above-described ultraviolet (UV) is not irradiated. It is possible to shorten the heating time. In addition, one oxide layer of the present invention can realize an oxide layer that is thin and excellent in flatness.

It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a graph which shows an example of the TG-DTA characteristic of the indium-zinc containing solution which comprises the precursor of the oxide semiconductor for forming the channel of the thin-film transistor of the 2nd Embodiment of this invention. It is a graph which shows an example of the TG-DTA characteristic of the polypropylene carbonate solution which is an example of the solution which uses only the binder for forming the component (for example, channel) of the thin-film transistor of the 2nd Embodiment of this invention as a solute. It is a figure which shows the surface roughness of the oxide layer in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the whole structure of the thin-film transistor in the 2nd Embodiment of this invention, and its manufacturing method. It is a graph which shows an example of the result of the Id-Vg characteristic measurement of the thin-film transistor in the 2nd Embodiment of this invention. It is a cross-sectional schematic diagram which shows one process of the manufacturing method of the thin-film transistor in the modification (2) of the 2nd Embodiment of this invention.

  An aliphatic polycarbonate, an oxide precursor, an oxide layer, a semiconductor element, an electronic device, and a manufacturing method thereof according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this description, common parts are denoted by common reference symbols throughout the drawings unless otherwise specified. In the drawings, elements of the present embodiment are not necessarily described with each other kept to scale. Further, some symbols may be omitted to make each drawing easier to see.

<First Embodiment>
1. In the present embodiment, the precursor of the oxide, the structure of the oxide layer, and the manufacturing method thereof. The aliphatic polycarbonate and a metal compound that becomes a metal oxide when oxidized (which may contain unavoidable impurities. , The same applies to each oxide)) is a “oxide precursor”. Therefore, a typical example of this oxide precursor is a compound in which a metal compound that becomes a metal oxide when oxidized is dispersed in a solution containing an aliphatic polycarbonate that is considered to act as a binder. It is. It should be noted that the aliphatic polycarbonate as a binder is an impurity as viewed from the metal oxide finally obtained after a pattern is once formed by, for example, a printing method. It becomes. An example of the metal oxide of this embodiment is an oxide semiconductor, an oxide conductor, or an oxide insulator.

(Binder and solution containing the binder)
Next, paying attention to the binder (which may contain inevitable impurities; hereinafter the same) in this embodiment, the binder and the solution containing the binder will be described in detail.

  In the present embodiment, an endothermic decomposable aliphatic polycarbonate having good thermal decomposability is used as the binder. The fact that the thermal decomposition reaction of the binder is an endothermic reaction can be confirmed by a differential thermal measurement method (DTA). Such an aliphatic polycarbonate has a high oxygen content and can be decomposed into a low molecular weight compound at a relatively low temperature, thereby reducing the residual amount of impurities typified by carbon impurities in the metal oxide. Contribute positively.

  Moreover, in this embodiment, the organic solvent which can be employ | adopted for the solution containing a binder will not be specifically limited if it is an organic solvent which can melt | dissolve an aliphatic polycarbonate. Specific examples of the organic solvent include diethylene glycol monoethyl ether acetate (DEGMEA), α-terpineol, β-terpineol, N-methyl-2-pyrrolidone, 2-nitropropane, isopropyl alcohol, diethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether, toluene , Cyclohexane, methyl ethyl ketone, dimethyl carbonate, diethyl carbonate, propylene carbonate, and the like. Among these organic solvents, diethylene glycol monoethyl ether acetate, α-terpineol, from the viewpoint that the boiling point is moderately high, there is little evaporation at room temperature, and the organic solvent can be removed uniformly when firing the precursor of the oxide. N-methyl-2-pyrrolidone, 2-nitropropane and propylene carbonate are preferably used. In the present embodiment, the binder in the formed pattern is finally subject to decomposition or removal as impurities. Therefore, it is preferable to employ a mixed solvent of DEGMEA and 2-nitropropane from the viewpoint that it is sufficient to maintain the pattern for a relatively short time from the formation of the pattern until it is decomposed or removed.

  The method for producing the oxide precursor of the present embodiment is not particularly limited. For example, a method of uniformly dispersing and dissolving the components of the metal oxide, the binder, and the organic solvent by stirring using a conventionally known stirring method can be employed. Further, a method of obtaining a precursor by stirring an organic solvent containing a metal oxide and a solution obtained by dissolving a binder in an organic solvent using a conventionally known stirring method is also an embodiment.

  The above-mentioned known stirring methods include, for example, a method of mixing using a stirrer, or a method of kneading by rotating and / or vibrating using an apparatus such as a mill filled with ceramic balls.

  Further, from the viewpoint of improving the dispersibility of the metal oxide, a dispersant, a plasticizer and the like can be further added to the solution containing the binder as desired.

Specific examples of the above-described dispersant are as follows:
Polyhydric alcohol esters such as glycerin and sorbitan;
Polyether polyols such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol and polypropylene glycol; amines such as polyethyleneimine;
(Meth) acrylic resins such as polyacrylic acid and polymethacrylic acid;
Examples thereof include a copolymer of isobutylene or styrene and maleic anhydride, and an amine salt thereof.

  Specific examples of the plasticizer described above include polyether polyols and phthalate esters.

  The method for forming the oxide precursor layer of the present embodiment is not particularly limited. Formation of the layer by a low energy manufacturing process is a preferred embodiment. More specifically, a printing method such as gravure printing, screen printing, offset printing, or ink jet printing, or a coating method such as spin coating, roll coating, die coating, air knife coating, blade coating, reverse coating, gravure coating, or the like is used. Can do. In particular, it is preferable to form a precursor layer of an oxide by forming a layer on a substrate by a spin coating method which is a simple method and screen printing.

(About aliphatic polycarbonate)
A typical example of the aliphatic polycarbonate is polypropylene carbonate, but the type of the aliphatic polycarbonate used in the present embodiment is not particularly limited. For example, an aliphatic polycarbonate obtained by polymerization reaction of epoxide and carbon dioxide is also a preferable aspect that can be employed in this embodiment. By using an aliphatic polycarbonate obtained by polymerizing such an epoxide and carbon dioxide, an endothermic polycarbonate having a desired molecular weight can be obtained by improving the endothermic degradability by controlling the structure of the aliphatic polycarbonate. The effect is played. In particular, aliphatic polycarbonate is at least one selected from the group consisting of polyethylene carbonate and polypropylene carbonate from the viewpoint of high oxygen content and decomposition into a low molecular weight compound at a relatively low temperature. It is preferable. Any of the above-described aliphatic polycarbonates can achieve the same effects as those of the present embodiment as long as the molecular weight (number average molecular weight) is within a numerical range described later.

  The above epoxide is not particularly limited as long as it is an epoxide that becomes an aliphatic polycarbonate having a structure containing an aliphatic group in the main chain by a polymerization reaction with carbon dioxide. For example, ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, isobutylene oxide, 1-pentene oxide, 2-pentene oxide, 1-hexene oxide, 1-octene oxide, 1-decene oxide, cyclopentene oxide, cyclohexene oxide Styrene oxide, vinylcyclohexene oxide, 3-phenylpropylene oxide, 3,3,3-trifluoropropylene oxide, 3-naphthylpropylene oxide, 3-phenoxypropylene oxide, 3-naphthoxypropylene oxide, butadiene monooxide, 3- Epoxys such as vinyloxypropylene oxide and 3-trimethylsilyloxypropylene oxide are examples that can be employed in this embodiment. Among these epoxides, ethylene oxide and propylene oxide are preferably used from the viewpoint of high polymerization reactivity with carbon dioxide. In addition, each above-mentioned epoxide may be used individually, respectively, and can also be used in combination of 2 or more type.

  The number average molecular weight of the above-mentioned aliphatic polycarbonate is preferably 5,000 to 1,000,000, more preferably 10,000 to 500,000. When the number average molecular weight of the aliphatic polycarbonate is less than 5,000, the effect as a binder may not be sufficiently obtained due to, for example, the influence of a decrease in viscosity. Moreover, when the number average molecular weight of an aliphatic polycarbonate exceeds 1000000, since the solubility to the organic solvent of an aliphatic polycarbonate falls, handling may become difficult. The numerical value of the aforementioned number average molecular weight can be calculated by the following method.

Specifically, a chloroform solution having the above-mentioned aliphatic polycarbonate concentration of 0.5% by mass is prepared and measured using high performance liquid chromatography. After the measurement, the molecular weight is calculated by comparing with polystyrene having a known number average molecular weight measured under the same conditions. The measurement conditions are as follows.
Model: HLC-8020 (manufactured by Tosoh Corporation)
Column: GPC column (trade name of Tosoh Corporation: TSK GEL Multipore HXL-M)
Column temperature: 40 ° C
Eluent: Chloroform Flow rate: 1 mL / min

  In addition, as an example of the method for producing the above-described aliphatic polycarbonate, a method in which the above-described epoxide and carbon dioxide are subjected to a polymerization reaction in the presence of a metal catalyst can be employed.

Here, the example of manufacture of an aliphatic polycarbonate is as follows.
The inside of a 1 L autoclave system equipped with a stirrer, a gas introduction tube, and a thermometer was previously substituted with a nitrogen atmosphere, and then a reaction solution containing an organozinc catalyst, hexane, and propylene oxide were charged. Next, carbon dioxide was added while stirring to replace the inside of the reaction system with a carbon dioxide atmosphere, and carbon dioxide was charged until the inside of the reaction system became about 1.5 MPa. Thereafter, the autoclave was heated to 60 ° C., and a polymerization reaction was carried out for several hours while supplying carbon dioxide consumed by the reaction. After completion of the reaction, the autoclave was cooled, depressurized and filtered. Then, polypropylene carbonate was obtained by drying under reduced pressure.

  Moreover, the specific example of the above-mentioned metal catalyst is an aluminum catalyst or a zinc catalyst. Among these, a zinc catalyst is preferably used because it has high polymerization activity in the polymerization reaction of epoxide and carbon dioxide. Of the zinc catalysts, an organic zinc catalyst is particularly preferably used.

In addition, specific examples of the above-described organozinc catalyst include
Organozinc catalysts such as zinc acetate, diethyl zinc, dibutyl zinc; or
With organic zinc catalysts obtained by reacting compounds such as primary amines, divalent phenols, divalent aromatic carboxylic acids, aromatic hydroxy acids, aliphatic dicarboxylic acids, and aliphatic monocarboxylic acids with zinc compounds is there.
Among these organic zinc catalysts, since it has higher polymerization activity, it is preferable to employ an organic zinc catalyst obtained by reacting a zinc compound, an aliphatic dicarboxylic acid, and an aliphatic monocarboxylic acid. It is an aspect.

Here, the production example of the organozinc catalyst is as follows.
First, zinc oxide, glutaric acid, acetic acid, and toluene were charged into a four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser. Next, after replacing the inside of the reaction system with a nitrogen atmosphere, the temperature of the flask was raised to 55 ° C., and the mixture was stirred at the same temperature for 4 hours to carry out the reaction treatment of each of the aforementioned materials. Thereafter, the temperature was raised to 110 ° C., and the mixture was further stirred for 4 hours at the same temperature for azeotropic dehydration to remove only moisture. Then, the reaction liquid containing an organozinc catalyst was obtained by cooling the flask to room temperature. In addition, IR was measured about the organozinc catalyst obtained by fractionating and filtering this reaction liquid (The product name: AVATAR360 by the Thermo Nicolet Japan Co., Ltd.). As a result, no peak based on the carboxylic acid group was observed.

  Moreover, it is preferable that the usage-amount of the above-mentioned metal catalyst used for a polymerization reaction is 0.001-20 mass parts with respect to 100 mass parts of epoxides, and it is more preferable that it is 0.01-10 mass parts. . When the usage-amount of a metal catalyst is less than 0.001 mass part, there exists a possibility that a polymerization reaction may become difficult to advance. Moreover, when the usage-amount of a metal catalyst exceeds 20 mass parts, there exists a possibility that there may be no effect corresponding to a usage-amount and it may become economical.

The reaction solvent used as needed in the above polymerization reaction is not particularly limited. Various organic solvents can be applied as the reaction solvent. Specific examples of this organic solvent are:
Aliphatic hydrocarbon solvents such as pentane, hexane, octane, decane and cyclohexane;
Aromatic hydrocarbon solvents such as benzene, toluene, xylene;
Chloromethane, methylene dichloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, ethyl chloride, trichloroethane, 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, 1-chloro-2 -Halogenated hydrocarbon solvents such as methylpropane, chlorobenzene, bromobenzene;
Carbonate solvents such as dimethyl carbonate, diethyl carbonate, propylene carbonate, etc.
It is.

  Moreover, it is preferable that the usage-amount of the above-mentioned reaction solvent is 500 to 10000 mass parts with respect to 100 mass parts of epoxides from a viewpoint of making reaction smooth.

  In the above polymerization reaction, the method of reacting epoxide and carbon dioxide in the presence of a metal catalyst is not particularly limited. For example, a method may be employed in which the above epoxide, metal catalyst, and reaction solvent as required are charged into an autoclave and mixed, and then carbon dioxide is injected to react.

  In addition, the operating pressure of carbon dioxide used in the above polymerization reaction is not particularly limited. Typically, the pressure is preferably 0.1 MPa to 20 MPa, more preferably 0.1 MPa to 10 MPa, and further preferably 0.1 MPa to 5 MPa. When the use pressure of carbon dioxide exceeds 20 MPa, there is a possibility that the effect corresponding to the use pressure may not be obtained and it may not be economical.

  Furthermore, the polymerization reaction temperature in the above-mentioned polymerization reaction is not particularly limited. Typically, the temperature is preferably 30 to 100 ° C, and more preferably 40 to 80 ° C. When the polymerization reaction temperature is less than 30 ° C., the polymerization reaction may take a long time. On the other hand, when the polymerization reaction temperature exceeds 100 ° C., side reactions occur and the yield may decrease. Since the polymerization reaction time varies depending on the polymerization reaction temperature, it cannot be generally stated, but typically it is preferably 2 hours to 40 hours.

  After completion of the polymerization reaction, an aliphatic polycarbonate can be obtained by filtering off by filtration or the like, washing with a solvent or the like if necessary, and drying.

<Second Embodiment>
2. 1 to FIG. 4 and FIG. 8 to FIG. 13 are schematic cross-sectional views showing one process of a method of manufacturing a thin film transistor 100 which is an example of a semiconductor element. FIG. 13 is a schematic cross-sectional view showing one process and the entire configuration of the method of manufacturing the thin film transistor 100 in the present embodiment. As shown in FIG. 13, in the thin film transistor 100 according to this embodiment, the gate electrode 24, the gate insulator 34, the channel 44, the source electrode 58, and the drain electrode 56 are stacked in this order on the substrate 10 from the lower layer. . Note that provision or realization of an electronic device (for example, a portable terminal, an information home appliance, or other known electrical appliances) provided with this semiconductor element requires special explanation for those skilled in the art who understand the semiconductor element of this embodiment. Can be fully understood without. In addition, a process for forming various oxide precursor layers, which will be described later, is included in the “precursor layer forming process” in the present application.

  The thin film transistor 100 employs a so-called bottom gate structure, but this embodiment is not limited to this structure. Therefore, a person skilled in the art can form a top gate structure by changing the order of the steps by referring to the description of the present embodiment with ordinary technical common sense. Moreover, the display of the temperature in this application represents the surface temperature of the heating surface of the heater which contacts a board | substrate. Further, in order to simplify the drawing, description of patterning of the extraction electrode from each electrode is omitted.

The substrate 10 of the present embodiment is not particularly limited, and a substrate generally used for a semiconductor element is used. For example, high heat-resistant glass, SiO ₂ / Si substrate (that is, a substrate in which a silicon oxide film is formed on a silicon substrate), alumina (Al ₂ O ₃ ) substrate, STO (SrTiO) substrate, SiO ₂ layer on the surface of Si substrate In addition, various insulating substrates including a semiconductor substrate (for example, a Si substrate, a SiC substrate, a Ge substrate, etc.) such as an insulating substrate in which an STO (SrTiO) layer is formed via a Ti layer can be applied. The insulating substrate is made of materials such as polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide. Film or sheet is included. Further, the thickness of the substrate is not particularly limited, but is, for example, 3 μm or more and 300 μm or less. Further, the substrate may be hard or flexible.

(1) Formation of Gate Electrode In this embodiment, a metal compound that becomes an oxide conductor when oxidized (hereinafter also simply referred to as “oxide conductor”) is employed as the material of the gate electrode 24. be able to. In this case, the gate electrode 24 of the present embodiment is made of an oxide conductor (however, an unavoidable impurity may be included. The same applies to oxides of other materials as well as oxides of this material). It is formed by firing a precursor layer of an oxide conductor (hereinafter, also referred to as “precursor layer of oxide conductor”) dispersed in a solution containing a binder. In this embodiment, as shown in FIG. 1, a low energy manufacturing process (for example, a printing method or a spin coating method) is used on a SiO ₂ / Si substrate (hereinafter also simply referred to as “substrate”) 10 as a base material. Thus, the gate electrode precursor layer 22 can be formed by forming a gate electrode precursor solution layer as a starting material.

Thereafter, the gate electrode precursor layer 22 is heated with respect to the gate electrode precursor layer 22 in an ozone (O ₃ ) atmosphere, for example, while a heater of a stage on which the substrate 10 is placed is heated at 120 to 160 ° C. An irradiation process of irradiating with ultraviolet rays (UV) is performed for about 30 minutes. In addition, about the precursor layer 22 for gate electrodes of this embodiment, even if it is a layer of several micrometers thickness, the irradiation process for about 30 minutes is performed. In the present embodiment, a UV ozone cleaner (model: UV-300h-E) manufactured by SAMCO Co., Ltd. was employed. The irradiated UV spectrum has peaks at 185 nm and 254 nm.

  It is considered that the above-described irradiation process mainly bears a “process from a liquid to a gel state” for the gate electrode precursor solution. By performing this irradiation step before all of the aliphatic polycarbonate as the binder is decomposed, the pre-baking time can be greatly shortened. As a comparative example of the preliminary firing step, a method for forming a desired gate electrode precursor layer 22 only by heat treatment with a heater of a stage on which the substrate 10 is placed without performing the above-described irradiation step. It is possible to adopt. However, in the case where the above-described irradiation step is not performed, processing for a longer time (for example, about 2 hours to about 3 hours in the case of a film having a thickness of several μm) is required under a relatively high temperature condition of 180 ° C. Therefore, in the formation process of the gate electrode precursor layer 22 of the present embodiment, by adopting the above-described irradiation process, lower temperature heating is realized and time for pre-baking is reduced by 50% or more. It shows that it will be possible. From another viewpoint, as described above, the “process from the liquid to the gel state” involves the action of removing the binder and the solvent. Therefore, if this irradiation step is adopted, the binder and the solvent are very fast. Can be realized.

  Thereafter, the gate electrode precursor layer 22 in the gel state is heated at 450 ° C. to 550 ° C. for a predetermined time (for example, 10 minutes to 1 hour), for example, in the atmosphere. Is called. As a result, the gate electrode 24 is formed on the substrate 10 as shown in FIG. In addition, the thickness of the layer of the gate electrode 24 of this embodiment is about 100 nm, for example. In addition, this baking process bears a so-called "process from a gel state to a solidified state or a sintered state".

  Here, an example of the above-described oxide conductor is a material having a structure in which a ligand is coordinated to a metal that becomes an oxide conductor when oxidized (typically, a complex structure). For example, a metal organic acid salt, a metal inorganic acid salt, a metal halide, or various metal alkoxides can be included in the oxide conductor of this embodiment. An example of a metal that becomes an oxide conductor when oxidized is ruthenium (Ru). In this embodiment, a precursor solution for a gate electrode starting from a solution obtained by dissolving ruthenium (III) nitrosyl acetate in a mixed solvent of propionic acid and 2-aminoethanol containing a binder made of an aliphatic polycarbonate, For example, the ruthenium oxide which is an oxide conductor is performed by performing a baking step of heating at about 450 ° C. to about 550 ° C. for a predetermined time (for example, 10 minutes to 1 hour) in the air after the irradiation step. Since an object is formed, the gate electrode 24 can be formed.

  In the present embodiment, in particular, when the gate electrode precursor solution employing the aliphatic polycarbonate of the first embodiment is used, the pattern of the gate electrode precursor layer 22 is formed using a low energy manufacturing process. A good pattern can be formed. More specifically, the gate electrode precursor layer 22 can be planarized, and a thin oxide layer with excellent planarity after the main firing can be achieved. In addition, an oxide layer pattern with high dimensional accuracy can be formed.

In this embodiment, instead of the gate electrode 24 described above, for example, a refractory metal such as platinum, gold, silver, copper, aluminum, molybdenum, palladium, ruthenium, iridium, tungsten, or an alloy thereof is used. A metal material, or a p ⁺ -silicon layer or an n ⁺ -silicon layer can be used. In that case, the gate electrode 24 can be formed on the substrate 10 by a known sputtering method or CVD method.

(2) Formation of Gate Insulator In the present embodiment, the material of the gate insulator 34 is a metal compound that becomes an oxide insulator when oxidized (hereinafter also simply referred to as “oxide insulator”). ) Is dispersed in a solution containing an aliphatic polycarbonate binder, and the oxide insulator precursor layer (hereinafter also referred to as “oxide insulator precursor layer”) is fired to obtain a gate insulator. It is formed.

  Specifically, as shown in FIG. 3, a layer of the above-described oxide insulator precursor solution is formed on the gate electrode 24 by using a low energy manufacturing process (for example, a printing method or a spin coating method). Thus, the gate insulator precursor layer 32 is formed.

Thereafter, the gate insulator precursor layer 32 is formed on the gate insulator precursor layer 32 in an ozone (O ₃ ) atmosphere while heating, for example, a stage heater on which the substrate 10 is placed at 120 to 160 ° C. On the other hand, an irradiation process of irradiating ultraviolet rays (UV) is performed for about 30 minutes.

  It is considered that the above-described irradiation process is mainly responsible for the “process from a liquid to a gel state” for the precursor solution for a gate insulator. By performing this irradiation step before all of the aliphatic polycarbonate as the binder is decomposed, the pre-baking time can be greatly shortened. As a comparative example of the preliminary firing step, a method for forming a desired gate electrode precursor layer 22 only by heat treatment with a heater of a stage on which the substrate 10 is placed without performing the above-described irradiation step. It is possible to adopt. However, in the case where the above-described irradiation step is not performed, processing for a longer time (for example, about 2 hours to about 3 hours in the case of a film having a thickness of several μm) is required under a relatively high temperature condition of 180 ° C. Accordingly, in the process of forming the gate insulator precursor layer 32 of the present embodiment, by employing the above-described irradiation process, lower temperature heating is realized and the time for pre-baking is reduced by 50% or more. It shows that it will be possible. From another viewpoint, as described above, the “process from the liquid to the gel state” involves the action of removing the binder and the solvent. Therefore, if this irradiation step is adopted, the binder and the solvent are very fast. Can be realized.

  The gate insulator precursor layer 32 in a gel state is then fired at, for example, about 450 ° C. to about 550 ° C. for a predetermined time (for example, 10 minutes to 1 hour) in the atmosphere (main firing). By performing the process, for example, an oxide made of lanthanum (La) and zirconium (Zr) which are oxide insulators is formed. As a result, the gate insulator 34 can be formed as shown in FIG. In addition, the thickness of the layer of the gate insulator 34 of this embodiment is about 100 nm to about 250 nm, for example.

  Here, an example of the above oxide insulator is a material having a structure in which a ligand is coordinated to a metal that becomes an oxide insulator when oxidized (typically a complex structure). For example, metal organic acid salts, metal inorganic acid salts, metal halides, or various metal alkoxides, or other organic acid salts, inorganic acid salts, halides, or various alkoxides are also used in the oxide insulation of the present embodiment. Can be included in the body.

  Note that a typical example of the oxide insulator is an oxide composed of lanthanum (La) and zirconium (Zr). This oxide can be employed as the gate insulator 34. In the present embodiment, the first solution in which lanthanum acetate (III) is dissolved in propionic acid (solvent) containing a binder made of an aliphatic polycarbonate, and propionic acid (solvent) containing zirconium butoxide in the form of a binder made of an aliphatic polycarbonate. A second solution dissolved in (1) is prepared. The gate insulator precursor solution mixed with the first solution and the second solution, for example, in the atmosphere after the above-described irradiation step, for a predetermined time (for example, 10 minutes to 1 hour), An oxide insulator can be formed by performing a baking step of heating at about 450 ° C. to about 550 ° C.

  In the present embodiment, the pattern of the gate insulator precursor layer 32 is formed using a low-energy manufacturing process, particularly when the oxide insulator precursor employing the aliphatic polycarbonate of the first embodiment is used. In this case, a good pattern can be formed. More specifically, the gate insulator precursor layer 32 can be flattened, and a thin oxide layer having excellent flatness after firing can be realized. In addition, an oxide layer pattern with high dimensional accuracy can be formed.

  In this embodiment, for example, silicon oxide or silicon oxynitride can be applied instead of the gate insulator 34 described above. In that case, the gate insulator 34 can be formed on the gate electrode 24 by a known CVD method or the like.

(3) Formation of Channel In the present embodiment, as a material of the channel 44, a metal compound that becomes an oxide semiconductor when oxidized (hereinafter also simply referred to as “oxide semiconductor”) is formed from an aliphatic polycarbonate. A channel is formed by firing an oxide semiconductor precursor layer (hereinafter also referred to as an “oxide semiconductor precursor layer”) dispersed in a solution containing a binder. In this embodiment, as shown in FIG. 8, a layer of a channel precursor solution as a starting material is formed on the gate insulator 34 by using a low energy manufacturing process (for example, a printing method or a spin coating method). Thus, the channel precursor layer 42 can be formed.

  Thereafter, the channel precursor layer 42 is subjected to an ultraviolet ray (UV) irradiation process (preliminary baking process) and a baking process (main baking process) described later, whereby a channel 44 is formed as shown in FIG.

  Here, an example of the above metal compound is a material having a structure (typically a complex structure) in which a ligand is coordinated to a metal that becomes an oxide semiconductor when oxidized. For example, a metal organic acid salt, a metal inorganic acid salt, a metal halide, or various metal alkoxides can be included in the metal compound of this embodiment. Note that a typical example of the metal compound is indium-zinc oxide (hereinafter also referred to as “InZnO”). For example, an indium-zinc oxide which is an oxide semiconductor (hereinafter also referred to as “InZnO”) is obtained by baking a solution in which indium acetylacetonate and zinc chloride are dissolved in propionic acid containing a binder made of an aliphatic polycarbonate. Can be formed.

  Examples of metals that become oxide semiconductors when oxidized include indium, tin, zinc, cadmium, titanium, silver, copper, tungsten, nickel, indium-zinc, indium-tin, indium-gallium-zinc, and antimony. -One or more selected from the group consisting of tin, gallium-zinc, indium-gallium-zinc oxide, and zirconium-indium-zinc. However, in terms of device performance and stability, indium-zinc oxide, indium-gallium-zinc oxide, and zirconium-indium-zinc are used as metals that become oxide semiconductors when oxidized. It is preferable.

  In the present embodiment, the channel precursor solution employing the aliphatic polycarbonate of the first embodiment is particularly suitable when the pattern of the channel precursor layer 42 is formed using a low energy manufacturing process. Various patterns can be formed. More specifically, since the spinnability of the aliphatic polycarbonate that can serve as a binder in the channel precursor solution can be appropriately controlled, a good pattern of the channel precursor layer 42 is formed. can do.

  Further, in the present embodiment, in particular, when forming the channel 44 that is an oxide semiconductor layer, the present inventors have created so far, for example, disclosed in International Application No. PCT / JP2014 / 067960. A part of the invention relating to the method for producing a metal oxide can be adopted as a preferred example.

<TG-DTA (thermogravimetry and differential heat) characteristics>
More specifically, FIG. 5 shows a TG of an indium-zinc-containing solution (hereinafter also referred to as “InZn solution”) that constitutes a precursor of an oxide semiconductor for forming a channel of the thin film transistor of this embodiment. -It is a graph which shows an example of a DTA characteristic. FIG. 6 is a graph showing an example of TG-DTA characteristics of a polypropylene carbonate solution, which is an example of a solution containing only the binder for forming the constituent elements (for example, channels) of the thin film transistor in the present embodiment as a solute. . As shown in FIGS. 5 and 6, the solid line in each figure is a thermogravimetric (TG) measurement result, and the dotted line in the figure is a differential heat (DTA) measurement result. The results shown in FIGS. 5 and 6 are obtained by performing only the heat treatment with the heater on which the substrate 10 is placed, and ozone (O ₃ ) employed in the method for manufacturing the thin film transistor 100 of the present embodiment. Irradiation with ultraviolet rays (UV) in an atmosphere is not performed.

  From the results of thermogravimetry in FIG. 5, a significant decrease in weight, considered to be the evaporation of the solvent, was observed near 120 ° C. Moreover, as shown in (X) of FIG. 5, the exothermic peak in the graph of the differential thermal measurement result of the InZn solution was confirmed at around 330 ° C. Therefore, it is confirmed that indium and zinc are bonded to oxygen at around 330 ° C.

  On the other hand, from the results of thermogravimetry in FIG. 6, from about 140 ° C. to about 190 ° C., the disappearance of the solvent of the polypropylene carbonate solution is accompanied by a significant decrease in weight due to the decomposition or disappearance of part of the polypropylene carbonate itself. It was seen. In addition, it is thought that polypropylene carbonate has changed into carbon dioxide and water by this decomposition. Further, from the results shown in FIG. 6, it was confirmed that the binder was decomposed and removed by 90 wt% or more at around 190 ° C. In more detail, it can be seen that the binder is decomposed by 95 wt% or more around 250 ° C., and the binder is almost entirely decomposed (99 wt% or more) around 260 ° C.

Here, the formation method of the channel 44 as one of the typical processes that the present inventors have adopted so far mainly includes the following processes (a) and (b).
(A) A precursor in which a precursor of an oxide semiconductor in which a metal compound that becomes an oxide semiconductor when oxidized is dispersed in a solution containing a binder made of an aliphatic polycarbonate is layered on or above the substrate. A body layer forming step and a pre-baking step of heating the precursor layer at a first temperature (which corresponds to 190 ° C. in FIG. 6) that decomposes the binder by 90 wt% or more.
(B) After heating at the first temperature, the temperature is higher than the first temperature and at which the metal and oxygen are combined, and is the exothermic peak value in the differential thermal analysis (DTA) of the precursor described above. A firing (main firing) step of firing the precursor layer at a temperature equal to or higher than a certain second temperature (which corresponds to 330 ° C. in FIG. 5).

On the other hand, as described above, in the present embodiment, each layer (gate electrode, gate insulator, channel, etc.) constituting the thin film transistor 100 is heated by the heater of the stage on which the substrate 10 is placed, and ozone (O ₃ ) Irradiation with ultraviolet rays (UV) in an atmosphere. Therefore, the application of the ultraviolet ray (UV) has the effect of lowering the first temperature substantially as compared with the case where only the heat treatment by the heater is performed. The inventors are thinking. In other words, ultraviolet (UV) irradiation in an ozone (O ₃ ) atmosphere is active to decompose and remove 90 wt% or more (or 95 wt% or more or 99 wt% or more) of the binder. Since it plays a role, it is considered that the binder can be decomposed by 90 wt% or more even at a lower temperature (for example, 120 ° C.). In addition, it is very interesting that such irradiation with ultraviolet rays (UV) not only lowers the processing temperature by the heater, but also realizes flattening of each precursor layer and It is worthy of special mention that it can contribute to the realization of a thin oxide layer with excellent flatness. It is also very interesting to contribute to the realization of an oxide layer with good dimensional accuracy.

  In addition, the inventors of the present application have described the first temperature and the second temperature for various metal-containing pastes, which are finally represented by various binders (aliphatic polycarbonates) and InZn solutions, and finally become metal oxides. The difference is more preferably 50 ° C. or higher, and further preferably 100 ° C. or higher, whereby the remaining of impurities represented by carbon impurities in the oxide semiconductor layer can be suppressed. From the viewpoint of controlling the final thickness of the oxide semiconductor layer and / or realizing a thin layer and reducing the remaining impurities, the second temperature is most preferably higher than the first temperature by 100 ° C. or more. This is a preferred example. On the other hand, the maximum difference between the second temperature and the first temperature is not particularly limited.

  In this embodiment, by performing the above-described ultraviolet (UV) irradiation step, 90 wt% or more (or 95 wt% or more or 99 wt% or more) of the binder is decomposed by pre-baking at a relatively low first temperature. Can be realized. Therefore, it is suggested that by performing the firing step (main firing) at a temperature equal to or higher than the second temperature, the remaining of impurities represented by carbon impurities in the oxide layer can be suppressed with higher accuracy than before. Yes.

  By the way, the phase state of the oxide semiconductor is not particularly limited. For example, it may be crystalline, polycrystalline, or amorphous. Further, as a result of crystal growth, a dendritic or scaly crystal is also one phase state that can be employed in the present embodiment. In addition, it cannot be overemphasized that it is not specified also in the shape (for example, spherical shape, elliptical shape, rectangular shape) patterned.

<Investigation of surface flatness of oxide layer by AFM>
FIG. 7 is a diagram showing the surface roughness of the oxide layer which is the channel 44 in the present embodiment. The flatness of the surface of the channel 44 obtained by performing the ultraviolet ray (UV) irradiation step (preliminary firing step) and the firing step (main firing step), which will be described later, is measured by AFM (Atomic Force Microscope: manufactured by Keyence Corporation). Measurement was performed using a nanoscale hybrid microscope, model VN-8000).

  As a result, from the result calculated from FIG. 7 and the result, the surface roughness (RMS) of the channel 44 of the present embodiment was about 6.9 nm. On the other hand, as a comparative example, this embodiment is performed except that the heater temperature of the stage on which the substrate 10 is placed is pre-baked at 180 ° C. for 2 hours without performing the above-described ultraviolet (UV) irradiation process (pre-baking process). The surface roughness (RMS) of the sample subjected to the same treatment as the morphology channel 44 was about 31.6 nm. Therefore, it was confirmed that the surface roughness (RMS) of the channel 44 of the present embodiment can form a layer with extremely excellent flatness. Further, according to the visual confirmation of the inventors of the present application, the dimensional accuracy when the channel precursor layer 42 of the present embodiment is formed using the screen printing method and the dimensional accuracy of the channel 44 after the subsequent main firing are confirmed. It was found that the dimensional accuracy corresponding to the comparative example described above was clearly improved.

(Baking process of channel precursor layer)
Next, a specific method for forming the channel 44 will be described. Note that at least a part of the formation method of the channel 44 can be applied to the manufacture of the above-described oxide conductor or oxide insulator.

  As already described, in this embodiment, as shown in FIG. 8, a layer of the channel precursor solution is formed on the gate insulator 34 by using a low energy manufacturing process (for example, a printing method or a spin coating method). Thus, the channel precursor layer 42 is formed. Note that the thickness (wet) of the channel precursor layer 42 which is an oxide semiconductor precursor layer is not particularly limited.

  Thereafter, as a pre-baking (also referred to as “first pre-baking”) step, the channel precursor layer 42 having a thickness of about 600 nm is formed by heating at a predetermined time (for example, 3 minutes), for example, 150 ° C. The first pre-baking step is mainly intended for fixing the channel precursor layer 42 on the gate insulator 34. Therefore, when the second pre-baking step described later is performed, the first pre-baking step is performed. Can be omitted.

In this embodiment, in order to decompose the binder in the channel precursor layer 42 thereafter, a predetermined temperature (90 wt% or more (or 95 wt% or more or 99 wt% or more) of the binder is decomposed and removed). ) To perform the second pre-baking step. Specifically, the channel precursor layer 42 is heated with respect to the channel precursor layer 42 in an ozone (O ₃ ) atmosphere, for example, while heating a heater of a stage on which the substrate 10 is placed at 120 to 160 ° C. The irradiation process of irradiating ultraviolet rays (UV) is performed for about 30 minutes. In addition, about the channel precursor layer 42 of this embodiment, even if it is a layer of several micrometers thickness, the irradiation process for about 30 minutes is performed.

  It is considered that the above-described irradiation process is mainly responsible for the “process from a liquid to a gel state” for the channel precursor solution. By performing this irradiation step before all of the aliphatic polycarbonate as the binder is decomposed, the pre-baking time can be greatly shortened. As a comparative example of the preliminary firing step, a method of forming the desired channel precursor layer 42 only by the heat treatment with the heater of the stage on which the substrate 10 is placed without performing the above-described irradiation step. It is possible to adopt. However, in the case where the above-described irradiation step is not performed, processing for a longer time (for example, about 2 hours to about 3 hours in the case of a film having a thickness of several μm) is required under a relatively high temperature condition of 180 ° C. Therefore, in the formation process of the channel precursor layer 42 of the present embodiment, by adopting the above-described irradiation process, lower temperature heating is realized and the time for pre-baking is reduced by 50% or more. Indicates that it will be possible. From another viewpoint, as described above, the “process from the liquid to the gel state” involves the action of removing the binder and the solvent. Therefore, if this irradiation step is adopted, the binder and the solvent are very fast. Can be realized.

  Here, the second pre-baking step is not limited to normal pressure conditions. For example, a reduced pressure condition or a high pressure condition may be employed as long as it does not adversely affect the substrate, the gate insulator, and the like. Note that the second pre-baking step is a step that can affect the increase or decrease in the surface roughness of the oxide semiconductor layer, but the behavior during drying differs depending on the solvent. Therefore, the second pre-baking step is appropriately performed depending on the type of the solvent. Process temperature conditions are selected.

  In addition, the above pre-baking is performed, for example, in an oxygen atmosphere or in the air (hereinafter collectively referred to as “oxygen-containing atmosphere”). Note that the second pre-baking step is performed in a nitrogen atmosphere.

  Thereafter, as a main firing, that is, a “firing step”, the channel precursor layer 42 is further subjected to, for example, a predetermined time in an oxygen-containing atmosphere at 200 ° C. or higher, more preferably 300 ° C. or higher, and further in electrical characteristics. Preferably, heating is performed in a range of 500 ° C. or higher. Typically, heating is performed at 450 ° C. to 550 ° C. for 10 minutes to 1 hour. As a result, as illustrated in FIG. 9, a channel 44 that is an oxide semiconductor layer is formed over the gate insulator 34. Note that the final thickness of the oxide semiconductor layer after the main baking is typically 0.01 μm or more and 10 μm or less. In particular, even when a very thin layer of about 0.01 μm (that is, about 10 nm) is formed, it is worthy of special mention that cracks hardly occur.

  Here, the set temperature in the firing step is a temperature at which the metal and oxygen are bonded after the ligand of the oxide semiconductor is decomposed in the formation process of the oxide semiconductor, and differential calorimetry (DTA). A temperature (second temperature) equal to or higher than the temperature of the exothermic peak value at is selected. By this firing step, the binder, the dispersant, and the organic solvent in the channel precursor layer 42 are decomposed and / or removed with high accuracy.

  Note that, in any of the first pre-baking step, the second pre-baking step, and the main baking (baking step) described above, a heating method for each precursor at the time of ultraviolet (UV) irradiation employed in the present embodiment. Is not particularly limited. For example, a thermostatic bath or an electric furnace can be used as long as ultraviolet (UV) irradiation is not hindered.

  In the formation process of the channel 44, the aliphatic polycarbonate not only can reduce or eliminate the decomposition products remaining in the oxide semiconductor layer after the calcination decomposition, but also contributes to the formation of a dense oxide semiconductor layer. be able to. Therefore, employing an aliphatic polycarbonate is a preferred aspect of this embodiment.

  In this embodiment, the final channel can be obtained by changing the weight ratio of the metal compound and the binder, which becomes an oxide semiconductor when oxidized, or by changing the concentration of the binder or metal compound. It was also confirmed by the present inventors' study that the thickness of 44 can be controlled. For example, it has been found that a channel 44 having a thickness of 10 nm to 50 nm, which is a very thin layer, can be formed without generating cracks. It should be noted that not only the aforementioned thin layer but also a layer having a thickness of 50 nm or more can be formed relatively easily by appropriately adjusting the thickness of the channel precursor layer 42, the aforementioned weight ratio, and the like. . In general, the thickness of the layer used for the channel is 0.01 μm (that is, 10 nm) or more and 1 μm or less, so that the final thickness of the channel 44 can be controlled. It can be said that the semiconductor precursor and the oxide semiconductor layer are suitable as materials for forming the thin film transistor.

  In addition, if the oxide semiconductor precursor of the present embodiment is employed, even if an oxide semiconductor precursor layer having a considerably thick film (for example, 10 μm or more) is initially formed, a binder or the like may be formed by a subsequent baking step. Will be decomposed with high accuracy, the thickness of the layer after firing can be very thin (eg, 10-100 nm). Furthermore, it is worthy of special mention that even such a thin layer will not cause cracks or be suppressed with high accuracy. Therefore, the oxide semiconductor precursor and the oxide semiconductor layer of this embodiment, which can sufficiently secure the initial thickness and can finally form an extremely thin layer, are described in a low-energy manufacturing process or described later. It was found that it is very suitable for the process by stamping. In addition, the use of an oxide semiconductor layer in which even such an extremely thin layer does not generate cracks or is suppressed with high accuracy greatly enhances the stability of the thin film transistor 100 of this embodiment.

  Furthermore, in this embodiment, the electrical characteristics and stability of the oxide semiconductor layer forming the channel are improved by appropriately adjusting the types and combinations of the above-described oxide semiconductors and the ratio of mixing with the binder. Can do.

(4) Formation of Source Electrode and Drain Electrode Further, as shown in FIG. 10, after a resist film 90 patterned by a known photolithography method is formed on the channel 44, the channel 44 and the resist film 90 are formed. Then, the ITO layer 50 is formed by a known sputtering method. The target material of the present embodiment is, for example, ITO containing 5 wt% tin oxide (SnO ₂ ), and is formed under conditions of room temperature to 100 ° C. Thereafter, when the resist film 90 is removed, the drain electrode 56 and the source electrode 58 made of the ITO layer 50 are formed on the channel 44 as shown in FIG.

  Thereafter, as shown in FIG. 12, a resist film 90 patterned by a known photolithography method is formed on the drain electrode 56, the source electrode 58, and the channel 44, and then one of the resist film 90 and the drain electrode 56 is formed. The exposed channel 44 is removed by using a known dry etching method with argon (Ar) plasma using a part of the source electrode 58 and a part of the source electrode 58 as a mask. As a result, as shown in FIG. 13, the patterned channel 44 is formed, whereby the thin film transistor 100 is manufactured.

  FIG. 14 is a graph illustrating an example of a result of Id-Vg characteristic measurement of the thin film transistor 100 according to the present embodiment. This example is a result when the heater of the stage on which the substrate 10 is placed is heated at 120 ° C. in the irradiation step in the present embodiment. As shown in FIG. 14, although there is still a lot of room for improvement, the basic operation of the thin film transistor 100 that realizes low-temperature and short-time processing could be confirmed.

  In this embodiment, instead of the drain electrode 56 and the source electrode 58 described above, the drain electrode and the paste electrode (indium tin oxide) are used by using paste silver (Ag) or paste ITO (indium tin oxide), for example, by a printing method. The method of forming the pattern of the source electrode is one aspect that can be adopted. Instead of the drain electrode 56 and the source electrode 58, a pattern of a drain electrode and a source electrode of gold (Au) or aluminum (Al) formed by a known vapor deposition method may be employed.

<Modification (2) of the second embodiment>
The thin film transistor of this embodiment is a manufacturing process of the thin film transistor 100 of the second embodiment, except that an irradiation process of irradiating ultraviolet rays is further performed after the channel baking process (main baking) in the second embodiment. And the configuration is the same. Therefore, the description which overlaps with 2nd Embodiment is abbreviate | omitted.

  In the present embodiment, after the channel firing step (main firing) in the second embodiment, using a known low-pressure mercury lamp (SAMCO UV UV cleaner, model: UV-300h-E), the wavelength is 185 nm. Ultraviolet rays having a spectrum peak at 254 nm were irradiated. Thereafter, the same steps as the manufacturing method of the thin film transistor 100 of the second embodiment were performed. In the present embodiment, the wavelength of ultraviolet rays is not particularly limited. Similar effects can be achieved even with ultraviolet rays other than 185 nm or 254 nm.

<Modification (2) of Second Embodiment>
In the second embodiment, as shown in FIG. 12, a channel 44 patterned by a known photolithography method and dry etching is formed. However, for example, when a printing method typified by a screen printing method is employed, a desired pattern of the channel precursor layer 42 can be obtained without using a known photolithography method and dry etching, as shown in FIG. Can be formed. Therefore, the adoption of the printing method is a preferred embodiment because the pattern forming step shown in FIG. 12 is not necessary. 15 and the subsequent steps are performed according to the steps of the second embodiment except for the steps based on the known photolithography method and dry etching shown in FIG. Similarly, in each layer (gate electrode 24, gate insulator 34, etc.) other than the channel in the thin film transistor 100, for example, when a printing method typified by a screen printing method is adopted, a known photolithography method and dry etching are performed. A pattern can be formed without using it.

<Other embodiments>
By the way, in each of the above-described embodiments, a thin film transistor having a so-called inverted staggered structure is described, but each of the above-described embodiments is not limited to the structure. For example, not only a thin film transistor having a staggered structure but also a thin film transistor having a so-called planar structure in which a source electrode, a drain electrode, and a channel are arranged on the same plane can achieve the effects of the above-described embodiments. The same effect can be achieved. Furthermore, it is another aspect in which the channel (that is, the oxide semiconductor layer) of each of the above embodiments is formed over a substrate.

  As described above, the disclosure of each of the above-described embodiments and experimental examples is described for explaining the embodiments and experimental examples, and is not described for limiting the present invention. In addition, modifications that exist within the scope of the present invention including other combinations of the embodiments are also included in the scope of the claims.

The present invention relates to portable terminals including various semiconductor elements, information appliances, sensors, other known electrical appliances, MEMS (Micro Electro Mechanical Systems) or NEMS (Nano
Electro Mechanical Systems) and electronic device fields including medical equipment and the like can be widely applied.

DESCRIPTION OF SYMBOLS 10 Substrate 24 Gate electrode 32 Gate insulator precursor layer 34 Gate insulator 42 Channel precursor layer 44 Channel 50 ITO layer 56 Drain electrode 58 Source electrode 90 Resist film 100 Thin film transistor

Claims (7)

An oxide precursor in which a metal compound that becomes a metal oxide when oxidized is dispersed in a solution containing a binder made of an aliphatic polycarbonate (which may contain inevitable impurities) is formed on or above the substrate. A precursor layer forming step to form a layer;
Before the aliphatic polycarbonate is completely decomposed by heating the precursor layer, ultraviolet rays (UV) are applied to the precursor layer while heating the precursor layer in an ozone (O ₃ ) atmosphere. And an irradiation step of irradiating
A method for producing an oxide layer. The metal oxide is an oxide semiconductor, and the metal is indium, tin, zinc, cadmium, titanium, silver, copper, tungsten, nickel, indium-zinc, indium-tin, indium-gallium-zinc, antimony. -One or more selected from the group of tin, gallium-zinc, indium-gallium-zinc oxide, and zirconium-indium-zinc,
The manufacturing method of the oxide layer of Claim 1. The aliphatic polycarbonate is at least one selected from the group consisting of polyethylene carbonate and polypropylene carbonate.
The manufacturing method of the oxide layer of Claim 1 or Claim 2. The precursor layer forming step according to claim 1,
The irradiation step according to claim 1,
A method for manufacturing a semiconductor device. By heating a precursor layer of an oxide in which a metal compound that becomes a metal oxide when dispersed is heated in a solution containing a binder made of an aliphatic polycarbonate (which may contain unavoidable impurities) Formed by irradiating the precursor layer with ultraviolet rays (UV) while heating the precursor layer in an ozone (O ₃ ) atmosphere before all of the group polycarbonate is decomposed.
Oxide layer. Comprising the oxide layer of claim 5;
Semiconductor element. The oxide layer according to claim 5 or the semiconductor element according to claim 6.
Electronic devices.