JP2019165040A - Method for manufacturing film containing indium oxide and method for manufacturing field effect transistor - Google Patents

Abstract

To provide a method allowing to form a continuous film without cracks even when forming an oxide film using a coating solution, thereby obtaining an oxide film that exhibits useful conductive properties.SOLUTION: The method for producing a film containing indium oxide on a to-be-coated object includes heating a coating solution after coating the coating solution on the to-be-coated object. The coating solution contains at least indium nitrate and a solvent. An air velocity of an airflow on a surface of the coating solution applied on the to-be-coated object when heating is 0.4 m/s or more.SELECTED DRAWING: None

Description

  The present invention relates to a method for manufacturing a film containing indium oxide and a method for manufacturing a field effect transistor.

Liquid crystal display (LCD), organic EL (electroluminescence) display (OLED), flat and thin displays such as electronic paper (Flat Panel Display: FPD) use amorphous silicon or polycrystalline silicon as the active layer It is driven by a driving circuit including a thin film transistor (TFT). In the development of FPD, there is a technique for manufacturing the TFT using an oxide semiconductor film having a high carrier mobility and a small variation between elements in a channel formation region of the TFT, and applying it to an electronic device, an optical device, or the like. Attention has been paid. For example, the FET using zinc oxide (ZnO), In ₂ O ₃ , In—Ga—Zn—O, or the like as an oxide semiconductor film has been proposed.

  However, TFTs using amorphous silicon (a-Si) or polycrystalline silicon (especially low-temperature poly silicon: LTPS) as active layers have their merits and demerits and satisfy all requirements at the same time. It was difficult.

  For example, a-Si TFTs have the disadvantages that mobility is insufficient to drive a large-screen LCD at high speed and that the threshold voltage shift during continuous driving is large. The LTPS-TFT has high mobility, but there is a problem that the threshold voltage varies greatly due to the process of crystallizing the active layer by excimer laser annealing, and the mother glass size of the mass production line cannot be increased.

In view of this, InGaZnO ₄ (a-IGZO) that exhibits a-Si or higher mobility in an amorphous state has been proposed (see Non-Patent Document 1), and as a trigger, a transistor using an oxide semiconductor with high mobility as an active layer Has been studied energetically.

  A transistor has a structure in which a conductive film such as metal or an insulating film is stacked in addition to a semiconductor serving as an active layer. As a method of forming each film, a method of forming a film by a vacuum process such as CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition), or sputtering has been conventionally used.

  On the other hand, in recent years, due to problems such as an increase in manufacturing cost due to an increase in size of a manufacturing apparatus accompanying an increase in substrate size, technological development for manufacturing a transistor by a coating process has been actively performed. Here, the coating process refers to a process of generating a target film from a coating solution by heat treatment after a coating solution as a raw material is applied to an object to be coated.

  An object of the present invention is to provide a method of obtaining an oxide film that can form a continuous film without cracks even when an oxide film is formed using a coating solution, and thereby exhibits useful conductive properties. And

Means for solving the problems are as follows. That is,
The method for producing a film containing indium oxide according to the present invention includes:
A method for producing a film containing indium oxide, comprising: producing a film containing indium oxide on the object to be coated by heating the coating liquid after applying the coating liquid on the object to be coated;
The coating solution contains at least indium nitrate and a solvent,
The air velocity at the surface of the coating liquid applied on the object to be coated when the heating is performed is 0.4 m / s or more.

  According to the present invention, an oxide film having good conductive properties can be formed in a process using a coating solution. In addition, an oxide semiconductor film having uniform characteristics and useful characteristics when formed into a device can be provided.

FIG. 1A is a schematic cross-sectional view for explaining an example of a manufacturing method of a top contact / top gate type field effect transistor (part 1). FIG. 1B is a schematic cross-sectional view for explaining an example of the manufacturing method of the top contact / top gate type field effect transistor (part 2). FIG. 1C is a schematic cross-sectional view for explaining an example of a method for manufacturing a top contact / top gate field effect transistor (part 3). FIG. 1D is a schematic cross-sectional view for explaining an example of the manufacturing method of the top contact / top gate field effect transistor (part 4). FIG. 2 is a schematic configuration diagram illustrating an example of a bottom contact / top gate field effect transistor. FIG. 3 is a schematic configuration diagram illustrating an example of a top contact / bottom gate type field effect transistor. FIG. 4 is a schematic cross-sectional view showing an example of a bottom contact / bottom gate type field effect transistor. FIG. 5A shows the result of measuring the surface of the oxide semiconductor film of Comparative Example 1. FIG. 5B is a cross-sectional profile of FIG. 5A. 6A shows the result of measuring the surface of the oxide semiconductor film of Comparative Example 2. FIG. 6B is a cross-sectional profile of FIG. 6A. 7A shows the result of measuring the surface of the oxide semiconductor film of Comparative Example 3. FIG. FIG. 7B is a cross-sectional profile of FIG. 7A. 8A shows the result of measuring the surface of the oxide semiconductor film of Comparative Example 4. FIG. FIG. 8B is a cross-sectional profile of FIG. 8A. 9A shows the result of measuring the surface of the oxide semiconductor film of Example 1. FIG. FIG. 9B is a cross-sectional profile of FIG. 9A. 10A shows the result of measuring the surface of the oxide semiconductor film of Example 2. FIG. FIG. 10B is a cross-sectional profile of FIG. 10A. FIG. 11A shows the result of measuring the surface of the oxide semiconductor film of Example 3. FIG. 11B is a cross-sectional profile of FIG. 11A. FIG. 12 is a diagram illustrating transfer characteristics (Vg-Ids characteristics) of the field-effect transistor of Example 4. FIG. 13 is a diagram showing transfer characteristics (Vg-Ids characteristics) of the field effect transistor of Comparative Example 5.

Prior to describing embodiments of the present invention, techniques related to the present invention will be described.
Using a coating process for manufacturing a conductive film or a semiconductor film that constitutes a transistor leads to advantages such as simplification of a manufacturing apparatus and reduction in manufacturing cost, but there are also problems peculiar to the coating process. In the process until the coating liquid having fluidity becomes a solid film by heating, a large volume decrease due to evaporation of the solvent, a state change until the metal compound in the coating liquid finally becomes a metal oxide, etc. Since it involves a large change, the shape of the film depends on the heating conditions. For example, when a change in state occurs in which the volume decreases after the fluidity of the coating liquid decreases, the shrunken part does not fill up and becomes an island-like film, or there are cracks in some places even if the film is continuous, The surface unevenness may become a remarkable film. Such a shape problem is a problem because it affects the electrical characteristics of the film. If the film is island-like and discontinuous, current does not flow normally. In addition, partial cracks and severe irregularities on the surface also lead to non-uniformity of the conductive characteristics within the film surface, deteriorating device characteristics. In particular, in the case where an oxide semiconductor film serving as an active layer of a transistor is formed by a coating process, the influence of the shape of the oxide film significantly appears on the electrical characteristics of the transistor. For example, if there is a crack in the active layer, that portion will not conduct and the value of current flowing through the active layer will decrease. When the surface of the active layer is rough, the movement of carriers is hindered, so that the mobility of the transistor is lowered. For these reasons, a transistor having an active layer formed by a coating process cannot achieve good transistor characteristics such as high on-current and high mobility.

  Therefore, there has been a demand for a method for manufacturing an oxide film that has a good shape and can exhibit electrical characteristics suitable for an active layer of a transistor while using a coating process.

The present inventors have intensively studied to solve the above problems. And to achieve the above problem,
In the method for producing a film containing indium oxide, a film containing indium oxide is produced on the object to be coated by heating the coating liquid after applying the coating liquid on the object to be coated.
The coating solution contains at least indium nitrate and a solvent,
It has been found that it is effective to set the air velocity of the airflow on the surface of the coating liquid applied on the object to be coated to 0.4 m / s or more when performing the heating.

  Indium oxide and oxides containing the same are widely used as conductors and semiconductors because of their good conductive properties. When used as a conductor, the carrier density is increased by increasing the amount of oxygen deficiency or doping with tin. In the case of a semiconductor, various elements other than indium may be added in order to control the carrier density. The present invention is a method for manufacturing a film containing indium oxide, and more preferably a method for manufacturing a film containing indium oxide as a main component. Here, the main component means that indium is the most when considering the number of moles of each element other than oxygen in the film.

  When forming a film containing indium oxide by a coating process, the present inventors use a coating solution containing at least indium nitrate and a solvent, and in the heating step after coating the substrate on the substrate, near the surface of the coating solution. The inventors have found that a continuous film without cracks can be formed by setting the air velocity of the air flow to 0.4 m / s or more, and have reached the present invention. Here, the crack refers to a deep groove-like hole, and at the bottom, the film thickness may be reduced to half or less, or the substrate surface (base) may be exposed. The presence or absence of cracks can be examined by, for example, a scanning probe microscope (SPM) such as an atomic force microscope (AFM) or a scanning tunneling microscope (STM).

(Method for producing a film containing indium oxide)
The manufacturing method of the film | membrane containing indium oxide of this invention includes the process of apply | coating a coating liquid on a to-be-coated object, and the process of heating a coating liquid. The object to be coated is, for example, a substrate, a laminated body including the substrate, or the like. Here, the substrate is a support such as a glass substrate. When an electronic device is manufactured by laminating a functional thin film on a support, an electrode layer or an insulating layer may already be formed on the substrate, and the coating solution is applied onto the substrate containing these layers. The When applying the coating solution, methods such as spin coating, dip coating, nozzle printing, die coating, ink jet, nanoimprint, and gravure can be used. Note that so-called printing is an example of application. The heating process may be performed as long as at least the coating solution is heated to a desired temperature, or a local heating method such as laser annealing may be used, or the entire object to be coated with the coating solution may be heated in an oven or the like. good.

  The coating liquid in the method for producing a film containing indium oxide of the present invention contains at least indium nitrate and a solvent, and further contains other components as necessary.

  There is no restriction | limiting in particular as content of indium nitrate in a coating liquid, According to the objective, it can select suitably.

  When it is desired to form a film containing the metal element A in addition to indium, a coating solution is formed by adding a compound containing the metal element A. The metal element is not limited to one type and may be a plurality of types.

  Examples of the compound containing the metal element A include an inorganic compound of the metal element A, an organic compound of the metal element A, and the like.

Examples of the inorganic compound of metal element A include nitrate of metal element A, sulfate of metal element A, chloride of metal element A, fluoride of metal element A, bromide of metal element A, and metal element A. And the like.
The organic compound of the metal element A is not particularly limited as long as it is a compound having the metal element A and an organic group, and can be appropriately selected according to the purpose. The metal element A and the organic group are bonded by, for example, an ionic bond, a covalent bond, or a coordinate bond.
The organic group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include an alkyl group which may have a substituent, an alkoxy group which may have a substituent, and a substituent. An acyloxy group which may have a substituent, a phenyl group which may have a substituent, an acetylacetonate group which may have a substituent, a sulfonic acid group which may have a substituent, etc. Can be mentioned. As said alkyl group, a C1-C6 alkyl group etc. are mentioned, for example. As said alkoxy group, a C1-C6 alkoxy group etc. are mentioned, for example. Examples of the acyloxy group include an acyloxy group having 1 to 10 carbon atoms, an acyloxy group partially substituted with a benzene ring such as benzoic acid, an acyloxy group partially substituted with a hydroxy group such as lactic acid, Examples include oxalic acid and acyloxy groups having two or more carbonyl groups such as citric acid.

  The solvent is not particularly limited as long as it is a solvent that stably dissolves or disperses indium nitrate and the various compounds, and can be appropriately selected according to the purpose. Examples thereof include an organic solvent and water. Examples of the organic solvent include toluene, xylene, mesitylene, cymene, pentylbenzene, dodecylbenzene, bicyclohexyl, cyclohexylbenzene, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, tetralin, decalin, ethyl benzoate, N, Examples thereof include N-dimethylformamide, propylene carbonate, 2-ethylhexanoic acid, mineral spirits, dimethylpropylene urea, 4-butyrolactone, 2-methoxyethanol, ethylene glycol, propylene glycol, isopropyl alcohol, and methanol.

  There is no restriction | limiting in particular as content of the solvent in a coating liquid, According to the objective, it can select suitably.

In the step of heating the coating solution (hereinafter referred to as “heating step”), the solvent in the coating solution evaporates, and the metal element in the coating solution is combined with oxygen to generate an oxide.
The temperature and time of the heating step can be appropriately selected according to the purpose. In general, the heating step includes a step of raising the temperature of the coating solution from room temperature, a step of holding at a constant temperature, and a step of lowering the temperature. These steps may be performed step by step, and a step of holding at a plurality of temperatures may be provided.
There is no restriction | limiting in particular as a temperature increase rate in the process to raise temperature, According to the objective, it can select suitably.
There is no restriction | limiting in particular as temperature in the process hold | maintained at fixed temperature, Although it can select suitably according to the objective, 100 degreeC or more and less than 550 degreeC are preferable, and 200 to 500 degreeC is more preferable.
In addition, the said temperature increase rate and the said temperature are the temperature increase rate and temperature measured in the surface vicinity of the said coating liquid in the to-be-coated object to which the coating liquid was apply | coated, for example.
As a holding time in the step of holding at a constant temperature, a time sufficient for the evaporation of the solvent and the generation of the oxide may be set, and examples thereof include 1 minute to 5 hours.

When indium nitrate in the coating solution is heated, nitrogen is first released and In (NO ₃ ) ₃ changes to In (OH) ₃ . It is known that when the temperature further rises, H ₂ O is released to become InOOH, and In ₂ O ₃ is generated at a higher temperature. Here, the change from In (OH) ₃ to InOOH and from InOOH to In ₂ O ₃ proceeds relatively slowly, but the first change from In (NO ₃ ) ₃ to In (OH) ₃ is around 120 ° C. It progresses rapidly and is accompanied by significant fever. As a result of the study by the present inventors, when the coating solution reaches a temperature at which a rapid change from In (NO ₃ ) ₃ to In (OH) ₃ occurs in the step of heating the coating solution, a large amount is present in the coating solution. It was found that when the solvent remained, the finally formed film would have cracks. In order to suppress the occurrence of cracks, it is effective to promote the evaporation of the solvent before the coating solution reaches the temperature at which the change from In (NO ₃ ) ₃ to In (OH) ₃ occurs. is there. Accordingly, the present inventors have studied a method for promoting evaporation by blowing off the vapor of the solvent with an air flow near the surface of the coating solution, and found that no cracks occur if the air velocity of the air flow is 0.4 m / s or more. It was.

  In order to generate such an air flow, it is preferable to use a blower such as a fan. When the coating liquid on the substrate is heated in the oven, it is preferable to include a mechanism for sending gas into the oven and an exhaust mechanism for discharging the atmosphere in the oven to the outside. By exhausting, it is possible to prevent the vapor concentration of the solvent from increasing in the oven and further promote the evaporation of the solvent.

There is no restriction | limiting in particular as an upper limit of the said wind speed, According to the objective, it can select suitably, For example, the said wind speed may be 6 m / s or less, and may be 3 m / s or less. .
Note that the wind velocity of the airflow at or near the surface of the coating solution may be measured, for example, in an oven at a position where the object to be coated with the coating solution is disposed, and at that time, the coating solution is applied. It is not necessary that the coated material is actually arranged.

  There is no restriction | limiting in particular as the direction of the airflow in the surface vicinity of the said coating liquid, According to the objective, it can select suitably. That is, the airflow may be parallel to the surface, may be perpendicular to the surface, or may be oriented in other directions.

  Since the film containing indium oxide formed in this manner is a continuous film without cracks, the film has good conductive properties. When this is used as the conductive film, a film having lower resistance can be obtained. In the case of using this as a semiconductor film, since the transport of carriers is not hindered by a crack, for example, a transistor using this for an active layer can achieve high mobility.

(Method for producing field-effect transistor)
A method for manufacturing a field effect transistor according to the present invention is a method for manufacturing a field effect transistor including an active layer including an oxide semiconductor film that is a film including indium oxide. The manufacturing method includes a step of forming the film containing the indium oxide, and further includes other steps as necessary.

  The field effect transistor includes, for example, a gate electrode, a source electrode and a drain electrode, the active layer, and a gate insulating layer.

<Gate electrode>
The gate electrode is not particularly limited as long as it is an electrode for applying a gate voltage, and can be appropriately selected according to the purpose.
The material of the gate electrode is not particularly limited and may be appropriately selected depending on the purpose. For example, platinum, palladium, gold, silver, copper, zinc, aluminum, nickel, chromium, tantalum, molybdenum, titanium, etc. Metals, alloys thereof, mixtures of these metals, and the like. Also, In ₂ O ₃ (ITO) to which indium oxide, zinc oxide, tin oxide, gallium oxide, niobium oxide, tin (Sn) is added, ZnO to which gallium (Ga) is added, and aluminum (Al) are added. ZnO, conductive oxides such as SnO ₂ to which antimony (Sb) is added, composite compounds thereof, mixtures thereof, and the like.

  There is no restriction | limiting in particular as average thickness of the said gate electrode, Although it can select suitably according to the objective, 10 nm-500 nm are preferable, and 50 nm-300 nm are more preferable.

  There is no restriction | limiting in particular as a formation method of the said gate electrode, According to the objective, it can select suitably, For example, (i) After film-forming by sputtering method, coating methods (for example, spin coating, slit coating, etc.), etc. A step of patterning by photolithography, and (ii) a step of directly forming a desired shape by a printing process such as inkjet, nanoimprint, or gravure.

<Source electrode and drain electrode>
There is no restriction | limiting in particular as said source electrode and a drain electrode, According to the objective, it can select suitably.

The material of the source electrode and drain electrode is not particularly limited and can be appropriately selected according to the purpose. For example, platinum, palladium, gold, silver, copper, zinc, aluminum, nickel, chromium, tantalum, molybdenum And metals such as titanium, alloys thereof, and mixtures of these metals. Also, In ₂ O ₃ (ITO) to which indium oxide, zinc oxide, tin oxide, gallium oxide, niobium oxide, tin (Sn) is added, ZnO to which gallium (Ga) is added, and aluminum (Al) are added. ZnO, conductive oxides such as SnO ₂ to which antimony (Sb) is added, composite compounds thereof, mixtures thereof, and the like.

  There is no restriction | limiting in particular as average thickness of the said source electrode and the said drain electrode, Although it can select suitably according to the objective, 10 nm-500 nm are preferable and 50 nm-300 nm are more preferable.

  There is no restriction | limiting in particular as a formation method of the said source electrode and the said drain electrode, According to the objective, it can select suitably, For example, (i) Sputtering method, coating method (for example, spin coating, slit coating etc.), etc. (Ii) A step of directly forming a desired shape by a printing process such as ink jet, nanoimprint, or gravure.

<Gate insulation layer>
The gate insulating layer is not particularly limited as long as it is an insulating layer provided between the gate electrode and the active layer, and can be appropriately selected according to the purpose.

There is no restriction | limiting in particular as a material of the said gate insulating layer, According to the objective, it can select suitably, For example, an inorganic insulating material, an organic insulating material, etc. are mentioned.
Examples of the inorganic insulating material include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, zirconium oxide, silicon nitride, aluminum nitride, and mixtures thereof.
Examples of the organic insulating material include polyimide, polyamide, polyacrylate, polyvinyl alcohol, and novolac resin.

  There is no restriction | limiting in particular as average thickness of the said gate insulating layer, Although it can select suitably according to the objective, 50 nm-1,000 nm are preferable and 100 nm-500 nm are more preferable.

  There is no restriction | limiting in particular as a formation method of the said gate insulating layer, According to the objective, it can select suitably, For example, (i) Film formation by a sputtering method, a coating method (for example, spin coating, slit coating, etc.) etc. Thereafter, a step of patterning by photolithography, (ii) a step of directly forming a desired shape by a printing process such as ink jet, nanoimprint, gravure, and the like are included.

<Active layer>
The active layer includes an oxide semiconductor film.
The oxide semiconductor film is a film containing indium oxide.
The active layer is provided adjacent to the source electrode and the drain electrode.
The film containing indium oxide is produced by the method for producing a film containing indium oxide according to the present invention.

  There is no restriction | limiting in particular as average thickness of the said active layer, Although it can select suitably according to the objective, 1 nm-200 nm are preferable and 2 nm-100 nm are more preferable.

Here, an example of a manufacturing method of the field effect transistor (top contact / top gate type) of the present invention will be described with reference to the drawings.
1A to 1D are schematic cross-sectional views for explaining an example of a method for manufacturing a top contact / top gate type field effect transistor.
First, an active layer 22 is formed on a base material 21 made of a glass substrate or the like (FIG. 1A). The active layer 22 is an n-type oxide semiconductor containing indium oxide. The n-type oxide semiconductor is obtained by applying a coating solution (a coating solution for forming an n-type oxide semiconductor film) on the substrate 21 and heating the coating solution. At the time of heating, the wind speed of the air current near the surface of the coating solution is set to 0.4 m / s or more.
Next, a conductive film made of ITO, metal, or the like is formed on the active layer 22 by sputtering or the like, and the formed conductive film is patterned by etching to form the source electrode 23 and the drain electrode 24 (FIG. 1B). ).
Next, a gate insulating layer 25 made of SiON or the like is formed by CVD or the like so as to cover the region formed on the active layer 22 and between the source electrode 23 and the drain electrode 24 (FIG. 1C). ).
Next, a conductor film made of metal or the like is formed on the gate insulating layer 25 by sputtering or the like, and the gate electrode 26 is formed (FIG. 1D).
Thus, a field effect transistor is manufactured.

  The structure of the field effect transistor is not particularly limited and may be appropriately selected depending on the purpose. For example, the top contact / top gate type (FIG. 1D), the bottom contact / top gate type (FIG. 2), Examples include a top contact / bottom gate type (FIG. 3) and a bottom contact / bottom gate type (FIG. 4).

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Comparative Examples 1-4, Examples 1-3)
<Formation of n-type oxide semiconductor>
35.488 g (0.1 mol) of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) and 2.330 g (0.01 mol) of zirconium chloride (ZrCl ₄ ) were weighed and dissolved in 100 mL of propylene glycol. A solution was obtained. Subsequently, 80 mL of methanol and 80 mL of 2-methoxyethanol were mixed and stirred at room temperature to prepare an n-type oxide semiconductor forming coating solution.

  Next, the n-type oxide semiconductor forming coating solution was applied onto a glass substrate (substrate) by a spin coating method. Subsequently, this substrate was put in an oven, and the inside of the oven was heated under the conditions shown in Table 1. The atmosphere in the oven was air. Different ovens were used for each of Comparative Examples 1-4 and Examples 1-3. All of the seven types of ovens used here are designed to circulate airflow in the cabinet. The numerical value of the wind speed of Table 1 is the result of measuring the wind speed in advance for each oven. When measuring the wind speed, the sensor head of the wind speed sensor was installed at the position where the substrate was placed, and the same air flow as that during heating was generated in the chamber for measurement. The oven temperature settings are as follows. First, the substrate coated with the coating solution is placed at a predetermined position in the oven, and heating is started. The temperature increase rate is 5 ° C./min, and after the temperature reaches 300 ° C., this temperature is maintained for 1 hour. Thereafter, the temperature is lowered to room temperature.

  The solvents contained in the coating solution for forming an n-type oxide semiconductor used here are methanol, 2-methoxyethanol, and propylene glycol, and the boiling points of these solvents are 65 degrees, 124 degrees, and 187 degrees. is there. After evaporating these solvents and changing the state of the indium compound and the zirconium compound in the temperature rising process from room temperature to 300 ° C., and passing through the baking step of holding at 300 ° C. for 1 hour, it consists of indium oxide and zirconium oxide. An n-type oxide film is obtained.

  The thickness of the oxide film to be formed can be adjusted by the concentrations of indium nitrate and zirconium chloride in the coating solution, spin coating conditions, and the like. This time, the conditions were set so that the film thickness after the firing step was about 30 nm.

<Evaluation of surface roughness of oxide semiconductor>
The surface roughness of the oxide semiconductor after the firing step was measured using a scanning probe microscope (Nano-Im manufactured by Pacific Nanotechnology). The measurement range was a square area of 5 microns.

  5A, FIG. 5B to FIG. 8A, FIG. 8B are the results of measuring the surface of the oxide semiconductors of Examples 1 to 3, and FIG. 9A, FIG. 9B to FIG. In each figure, A indicates the height information in the measurement area of 5 micron square in color, and B in each figure indicates a cross-sectional profile of the white line portion of A. First, in Comparative Examples 1-4, it turns out that the crack has generate | occur | produced in the film | membrane. The groove-like crack has a depth of 20 nm or more, and conversely, the periphery of the groove is raised at a height of 10 nm or more. A column for presence or absence of cracks was provided in Table 1, and the conditions under which cracks of this shape occurred were described as having cracks.

  Table 1 shows the value of arithmetic average roughness Sa, which is an index generally used when evaluating the surface roughness. Sa is a value obtained by averaging the absolute values of the height in the measurement area, and the influence of sudden irregularities caused by dust, scratches, etc. is reduced, and the overall roughness of the surface is compared. Suitable for

  As shown in Table 1, in Examples 1 to 3 in which the coating liquid was heated in an airflow with a wind speed of 0.4 m / s or higher, a crack-free film was obtained, and a good surface with Sa of 0.5 nm or less An oxide semiconductor was obtained. In Comparative Examples 1 to 4 where the wind speed was less than 0.4 m / s, cracks occurred in the film.

Example 4
<Fabrication of field effect transistor>
-Formation of active layer-
An oxide semiconductor was formed on a glass substrate in the same procedure as in Example 1. Subsequently, patterning was performed to a desired shape by photolithography. When the surface roughness of this oxide semiconductor was measured in the same manner as in Example 1, it had smooth surface properties without cracks, and Sa was 0.370 nm. Further, when the step of the pattern corresponding to the thickness of the oxide semiconductor was measured, it was found that the thickness was 28 nm.

-Formation of source and drain electrodes-
A source electrode and a drain electrode having a thickness of about 100 nm were formed in a region including the active layer on the glass substrate by using a DC magnetron sputtering method. Mo was used for the target. Argon gas was introduced as the sputtering gas, and the total pressure was 1.1 Pa. Patterning was performed by forming a film through a metal mask, and the source electrode and the drain electrode were formed in two parallel line shapes. The channel length of the field effect transistor is defined as the interval between these lines, this time 50 μm.

-Formation of gate insulation layer-
Next, a SiON film having a thickness of 200 nm was formed at a temperature of 200 ° C. using SiH 4 gas and N 2 O gas as raw materials by plasma CVD. This is a gate insulating layer.

-Formation of gate electrode-
Next, a gate electrode having a thickness of about 100 nm was formed using a DC magnetron sputtering method. Mo was used for the target. Argon gas was introduced as the sputtering gas, and the total pressure was 1.1 Pa. Patterning was performed by forming a film through a metal mask to form a line shape perpendicular to the source electrode and the drain electrode. The channel width of the field effect transistor is defined as the line width of the gate electrode, and this time is 400 μm.

  Through the above process, a top contact / top gate type field effect transistor similar to FIG. 1D was obtained.

<Transistor performance evaluation>
About the obtained field effect transistor, transistor performance evaluation was implemented using the semiconductor parameter analyzer apparatus (Agilent Technology company make, semiconductor parameter analyzer 4156C). The source-drain voltage Vds was set to 10 V, the gate voltage Vg was changed from -15 V to +15 V, the source-drain current Ids was measured, and the transfer characteristics (Vg-Ids characteristics) were evaluated. The obtained results are shown in FIG.
In the saturation region, the field effect mobility μ and the threshold voltage Vth were calculated. Also, the Ids on / off ratio was calculated. Here, the Ids in the on state was calculated as a value at Vg = 15V, and the Ids in the off state was calculated as a value at Vg = −15V. The results are shown in Table 2.
12 to 13, “e” represents a power of 10. That is, “1e-3” represents “1 × 10 ⁻³ ”, and “1e-10” represents “1 × 10 ⁻¹⁰ ”.

(Comparative Example 5)
A field effect transistor was manufactured in the same procedure as in Example 4 except that the formation conditions of the oxide semiconductor to be the active layer were the same as those in Comparative Example 4. The film thickness of the oxide semiconductor was 29 nm, innumerable cracks existed, and the surface roughness Sa was 1.93 nm. The transistor performance was evaluated. The transfer characteristics are shown in FIG. 13 and the characteristic values are shown in Table 2.

In Table 2, “E” represents a power of 10. That is, “1E + 05” represents “1 × 10 ⁵ ” and “1E + 08” represents “1 × 10 ⁸ ”.

The field-effect transistor of Example 4 using an oxide semiconductor with no cracks and a smooth surface as the active layer showed good switching characteristics in which Ids sharply rises in the vicinity of Vg = 0 V in the transfer characteristics. Even in the characteristic values shown in Table 2, a field effect mobility of 2 cm ² / Vs or more and an on / off ratio of 10 ⁸ or more are achieved, and a practical level is achieved. Since this transistor is a top gate type, the upper surface (surface opposite to the substrate) of the active layer is in contact with the gate insulating film, which contributes to transport of carriers. By using an oxide semiconductor with a smooth surface as the active layer, the interface between the active layer and the gate insulating film in the channel portion is also smooth, carriers can move quickly, and good transistor characteristics are realized.

On the other hand, in the field-effect transistor of Comparative Example 5 in which the active layer is an oxide semiconductor having many cracks, the field-effect mobility value is extremely small as 0.04 cm ² / Vs, and the on-current value is also small. It is considered that the crack portion did not function effectively as an active layer, leading to extreme deterioration of transistor characteristics.

Aspects of the present invention are as follows, for example.
<1> A method for producing a film containing indium oxide, comprising: producing a film containing indium oxide on the object to be coated by heating the coating liquid after applying the coating liquid on the object to be coated;
The coating solution contains at least indium nitrate and a solvent,
In the method for producing a film containing indium oxide, the air velocity of the air current on the surface of the coating solution applied on the object to be coated is 0.4 m / s or more when performing the heating. is there.
<2> A method of manufacturing a field effect transistor including an active layer including an oxide semiconductor film that is a film including indium oxide,
A method for producing a field effect transistor, comprising a step of producing a film containing indium oxide by the method for producing a film containing indium oxide according to <1>.
<3> The field effect transistor is
A gate electrode for applying a gate voltage;
A source electrode and a drain electrode;
The active layer provided adjacent to the source and drain electrodes;
A gate insulating layer provided between the gate electrode and the active layer;
It is a manufacturing method of the field effect transistor as described in said <2> provided with.

  The method for producing a film containing indium oxide according to <1> and the method for producing a field effect transistor according to <2> to <3> can achieve the object of the present invention.

21 Substrate 22 Active layer 23 Source electrode 24 Drain electrode 25 Gate insulating layer 26 Gate electrode

K. Nomura, et al., “Room-temperament fabrication of transparent flexible thin-film transformers using amorphous semiconductors”, NATURE, VOL4. 25, NOVEMBER, 2004, p. 488-492

Claims (3)

A method for producing a film containing indium oxide, comprising: producing a film containing indium oxide on the object to be coated by heating the coating liquid after applying the coating liquid on the object to be coated;
The coating solution contains at least indium nitrate and a solvent,
A method for producing a film containing indium oxide, wherein a wind velocity of an air flow on a surface of the coating solution applied on the object to be coated is 0.4 m / s or more when the heating is performed. A method of manufacturing a field effect transistor including an active layer including an oxide semiconductor film that is a film including indium oxide,
A method for producing a field effect transistor, comprising the step of producing a film containing indium oxide by the method for producing a film containing indium oxide according to claim 1. The field effect transistor comprises:
A gate electrode for applying a gate voltage;
A source electrode and a drain electrode;
The active layer provided adjacent to the source and drain electrodes;
A gate insulating layer provided between the gate electrode and the active layer;
The manufacturing method of the field effect transistor of Claim 2 provided with these.