JP7149367B2 - Thin film transistor and manufacturing method thereof - Google Patents

Description

The present invention, for example, organic EL (Electro-Luminescence) element (OLED (Organic Light Emitting Diode)) and LCD (Liquid Crystal Display) used for driving a thin film transistor (TFT: Thin Film Transistor), and The present invention relates to a method for manufacturing a thin film transistor, and more particularly to a thin film transistor configured to use a coating-type oxide semiconductor, which has high mobility and is easy to manufacture, for a channel.

Oxide semiconductors are used as driving transistors for high-definition and high-resolution display devices, and it is known that good semiconductor characteristics can be obtained in those manufactured by a vacuum film formation method such as sputtering.
In particular, it is known that an IGZO-based oxide semiconductor TFT using In--Ga--Zn as a metal species usually exhibits a mobility of 5 to 10 cm ² /Vs or more.
However, when the vacuum deposition method is used to manufacture oxide semiconductor TFTs, large-scale vacuum equipment is required, which causes problems such as reduced production efficiency, increased manufacturing costs, and increased environmental impact. Considering the realization of ultra-large displays of 100 inches or more, there is a limit to the size that can be manufactured in a vacuum chamber, and the development of oxide semiconductor TFTs formed by new film-forming technology is urgently needed.
That is, it is required to be an oxide semiconductor that can be easily formed into a film under atmospheric pressure without requiring a vacuum.

As such an oxide semiconductor, a coated oxide semiconductor manufactured by a coating process has attracted attention, and its research and development has been actively carried out.
A coating-type oxide semiconductor is formed by coating and oxidizing a precursor solution of a metal oxide. For example, one formed by thermal oxidation or the like using an organic metal salt is known (see Patent Document 1). Also known is an oxide semiconductor formed by using a metal alkoxide (M-OR) as a precursor and performing an oxidation treatment, for example, at a high temperature of 400° C. or higher.
Various reports have been made on materials for forming oxide semiconductors, including an IGZO system using In-Ga-Zn as a metal species, an IZO system using In-Zn as a metal species, and an IZO system using In-Sn-Ga as a metal species. Many reports have been made on the ITZO system as the seed. Furthermore, research is also underway on rare metal-free oxide semiconductor materials (Zn-O-based and Zn-Sn-O-based) that do not use materials such as indium and gallium that have a large environmental impact (see Non-Patent Document 1).

JP-A-2007-42689

Jpn. J. Appl. Phys. 53, 02BA02 (2014) Review of solution-processed oxide thin-film transistors

However, one of the major problems with the coating-type oxide semiconductor material produced by the coating process is that unlike the oxide semiconductor film formed by sputtering or the like in a clean atmosphere under vacuum, A large amount of residual organic matter (impurities) is included in the oxide semiconductor as it is.
That is, in the coating-type oxide semiconductor, the residual organic matter (impurities) contained in the precursor solution becomes an obstacle, and the mobility of carriers cannot be increased, and good switching characteristics can be obtained. was difficult.
The present invention has been made in view of such circumstances, and manufactures a thin film transistor capable of obtaining a higher carrier mobility than before in a coating-type oxide semiconductor in which a large amount of organic matter or the like remains, and a thin film transistor. The purpose is to provide a method.

In order to achieve the above objects, the thin film transistor of the present invention is
At least a gate electrode, a gate insulating film, a coating-type oxide semiconductor layer, and source/drain electrodes are provided on a substrate, and the coating-type oxide semiconductor layer is positioned above or below the gate insulating film. A coating type semiconductor precursor solution containing two or more metal components selected from indium, zinc, tin and gallium and containing hydrofluoric acid is coated on a predetermined base and oxidized. It is characterized by
Here, the “predetermined base” refers to a layer to which a coating-type semiconductor precursor solution is applied in order to create a coating-type oxide semiconductor layer. In general, the gate insulating film corresponds to the "predetermined base", and in the case of the top-gate structure, the substrate and the source/drain electrodes generally correspond to the "predetermined base".
The same applies to the term "predetermined base" used in the configuration of the method for manufacturing a thin film transistor, which will be described later.
Further, the coating-type oxide semiconductor layer preferably contains at least metal components of indium and zinc, and fluorine.
Moreover, it is preferable that the main component of the solvent constituting the coating-type semiconductor precursor solution is water.
Moreover, it is preferable that the treatment for oxidizing the coating-type semiconductor precursor solution is heat treatment by either microwave irradiation or ultraviolet light irradiation, or baking treatment.

Further, the method for manufacturing a thin film transistor of the present invention includes:
forming at least a gate electrode, a gate insulating film, a coated oxide semiconductor layer, and source/drain electrodes on a substrate;
preparing a coating-type semiconductor precursor solution containing a solution containing two or more metal components selected from indium, zinc, tin, and gallium and containing hydrofluoric acid, which is an additive having fluorine ions;
The coating-type semiconductor precursor solution is coated on a predetermined base such that the coating-type oxide semiconductor layer is positioned above or below the gate insulating film, and then oxidized. .
In this case, the step of applying the coating-type semiconductor precursor solution onto a predetermined base includes first coating the coating-type semiconductor precursor solution containing no additive having fluorine ions onto the predetermined base. forming a thin film, and then coating the thin film with a coating-type semiconductor precursor solution containing a solution containing hydrofluoric acid to form a thin film.

By the way, according to the present invention, as described above, when forming the coating-type oxide semiconductor layer, the precursor solution is configured to contain a predetermined metal component and fluorine. Semiconductor properties can be obtained (see paragraphs 0015-0017 of this specification).
Conventional coating-type oxide semiconductors inevitably contain more residual organic substances and ionic impurities than oxide semiconductor layers fabricated using sputtering or the like, resulting in low mobility and degraded semiconductor characteristics. It was.

This makes it difficult to use a coating-type oxide semiconductor that can simplify manufacturing facilities (see paragraph 0003 of the present specification).
Such a difference between the present invention and the prior art is due to the difference in crystallinity of the oxide semiconductor layer based on the bonding relationship between metal ions and fluorine ions, and the uniform bonding relationship between residual organic matter and ionic impurities and fluorine. However, the degree of penetration of fluorine into the oxide semiconductor layer and subtle differences in the bonding relationship between fluorine and residual organic matter can significantly change the mobility. It is impossible to categorically specify the structure or characteristics of .

On the other hand, the difference in crystallinity or bonding state between the present invention and the prior art can be measured in principle using X-ray diffraction (XRD) or X-ray photoelectric spectroscopy (XPS). In the case of a mold, the influence of impurities and the like can be measured. However, although it may be possible to measure this at one or two points, a statistically significant number of the coated oxide semiconductors of the present invention and the prior art are manufactured or purchased, and the XRD or XPS spectrum After measuring the numerical characteristics of and statistically processing them, it is necessary to find a significant index and its value for distinguishing the present invention from the conventional technology, which requires enormous time and cost. Moreover, since the conventional technology has a huge number of possibilities, it is not possible to uniquely determine a statistically significant number.

It is almost impractical to find the index and its value as described above and thereby directly specify the features of the present invention by the structure or characteristics of the object.
Therefore, the applicant of the present application unavoidably expresses the thin film transistors according to claims 1 to 4 in the style of describing the claims relating to the invention of the method for manufacturing a product.

According to the thin film transistor and the method for manufacturing a thin film transistor according to the present invention, the coating-type semiconductor precursor solution contains two or more metal components selected from indium, zinc, tin, and gallium, and an additive containing fluorine ions. Contains drugs. That is, by introducing fluorine into the precursor solution of the oxide semiconductor, the fluorine binds to the metal element and has the function of suppressing the amount of residual components (impurities). It is conceivable that the free electrons will be increased. In addition, in such a coating-type oxide semiconductor, since fluorine is already mixed in the precursor solution, it is uniformly dispersed in the semiconductor, and compared to the case where fluorine is introduced from the surface by heat treatment or the like later, It is conceivable that the characteristics are made uniform as a whole.

Thus, according to the thin film transistor and the method for manufacturing the thin film transistor according to the present invention, the mobility of carriers can be greatly improved.

In addition, in the technique described in JP-A-2016-72562, as a precursor solution used for a coating-type oxide semiconductor, a metal salt hydrate and an alcohol containing fluorine are disclosed. However, the main purpose of this technique is to improve the wettability problem, and that purpose is different from that of the present invention. In addition, depending on the technique described in this publication, since alcohol is used, the carbon atom functions to bond with fluorine as an impurity, and it is considered that the directionality of the invention is completely different from that of the present invention.

1 shows a cross-sectional structure of a thin film transistor according to an embodiment of the present invention;

A thin film transistor (TFT) according to an embodiment of the present invention and a method for manufacturing the thin film transistor will be described below with reference to the drawings. First, a reference embodiment will be described.

≪Reference form≫
FIG. 1 shows a cross-sectional structure of a TFT according to a reference embodiment. On a substrate 1, a gate electrode 2, a gate insulating film 3, a semiconductor layer 4 made of a coating type oxide semiconductor, and source/drain electrodes 6 are laminated. configured as The semiconductor layer 4 made of oxide is formed using a coating technique. Although not shown, an etching protection layer may be provided on the semiconductor layer 4 .

The substrate 1 is made of, for example, quartz, glass, or plastic film. By making it out of a flexible plastic film, it can be applied to a flexible display (for example, an organic EL display). Examples of the plastic film include PET, PEN, polyimide, etc. In some cases, a metal plate such as stainless steel can be used. Although not shown, a barrier layer and a flattening layer (inorganic thin film or organic thin film) can be formed on the surface by sputtering or the like.

The gate electrode 2 can be made of, for example, gold, titanium, chromium, aluminum, molybdenum, or alloys or laminated films thereof. The film thickness is, for example, 10 to 100 nm. The gate electrode 2 is patterned into a required size and shape using a photolithography method (a microfabrication technique using ultraviolet light exposure) or the like.

Moreover, the gate insulating film 3 is composed of an inorganic oxide film having a high dielectric constant. Examples of such inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, and titanium. Strontium oxide, barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, trioxide yttrium and the like. Among them, particularly preferred are silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide.
Furthermore, inorganic nitrides such as silicon nitride and aluminum nitride can also be preferably used. The film thickness is, for example, 100 nm to 300 nm.

The semiconductor layer (coating-type oxide semiconductor layer) 4 is formed by applying an oxide precursor solution containing a metal component onto the gate insulating film 3 by a coating method to form a thin film and convert it into a semiconductor.
The oxide precursor solution contains two or more metal components selected from indium, zinc, tin and gallium, and at least one of the selected metal components consists of a metal fluoride salt.
Specific metal fluoride salts include indium fluoride, zinc fluoride, and gallium fluoride.

Other metal components include metal atom-containing compounds, and examples of metal atom-containing compounds include metal salts, metal halide compounds, organometallic compounds, and the like, which contain metal atoms. Other metal elements include Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb , Sr, Y, Zr, Nb, Mo, Cd, In, Ir, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Tl, Pb, Bi, Ce, Pr, Nd, Pm, Eu, Gd , Tb, Dy, Ho, Er, Tm, Yb, Lu and the like.

Indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO), zinc-tin oxide ( ZnSnO), titanium oxide (TiO ₂ ), or other metal oxide particles dispersed therein may be mixed into the precursor solution.

As metal salts other than metal fluoride salts, those formed from inorganic acid salts such as nitrates, chloride salts, sulfates, and acetates can be used. Specific indium compounds include indium chloride, indium acetate, and indium nitrate. Zinc compounds include zinc chloride, zinc acetate, zinc acetate hydrate, and zinc nitrate. Tin compounds include tin chloride and tin acetate.

These metal salts are dissolved in a solvent to prepare a precursor solution. As a solvent for dissolving, water, ethanol, propanol, ethylene glycol, 2-methoxyethanol, acetonitrile, etc. can be used. As a stabilizer, monoethanolamine, acetylacetone, or the like may be mixed.
To improve solubility, the hydrogen ion concentration can be changed to acid or basic to improve solubility.

Further, the solubility may be improved by changing the hydrogen ion concentration to change acidity to basicity or vice versa.
As the solvent, it is preferable to use a solvent having a low molecular weight that does not easily leave residual components, and water is particularly preferable in terms of reducing residual components.
The precursor solution is adjusted by weighing the metal salt concentration so that the concentration of the solution is from 0.1 mol/L to 1 mol/L, and stirring and dissolving in the solution.

A thin film of the precursor solution is formed by applying the precursor solution thus obtained to the upper surface of the gate insulating film 3 (the surface facing upward on the page of FIG. 1).
The thickness of the semiconductor layer 4 can also be adjusted by the solution concentration and the number of times the solution is applied.
It should be noted that the thickness is preferably from 1 nm to 100 nm.
As the coating method, a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, a die coating method, a printing method such as an inkjet method, or the like can be used.

Moreover, the semiconductor layer 4 can be obtained by performing drying and baking, which are techniques for oxidizing the applied thin film. That is, after this coating treatment, a pre-bake treatment is performed at 100 to 150° C. for about 5 to 10 minutes to dry the coating film, and then a baking treatment is performed in the air to promote oxidation of the metal salt. This baking treatment is performed at 150 to 400° C. for 0.5 to 6 hours to form the semiconductor layer 4 .

As the drying and baking treatment, natural drying, hot/cold/room temperature air drying, infrared light drying, reduced pressure drying, and the like can be used. Further, semiconductor processing can be carried out by using a reaction using a heating device using microwaves or using an oxidation treatment using ultraviolet rays such as a mercury lamp. Each firing process may be performed not only in the atmosphere but also in a gas atmosphere such as oxygen, nitrogen, or argon.

The source/drain electrodes 6 described above can be formed using transparent materials such as ITO and IZO, metal materials such as Al, Ag, Cr, Mo and Ti, and alloys thereof. By stacking two or more layers, contact resistance can be reduced and adhesion can be improved, which is preferable.

As the etching solution, various etching solutions such as a mixed acid of phosphoric acid, acetic acid and nitric acid (PAN etchant) and oxalic acid can be used.
When patterning the source/drain electrodes 6 by wet etching, it is possible to introduce an etching stop layer to suppress deterioration of the semiconductor characteristics in order to further alleviate damage to the semiconductor layer 4 .

By the way, the residual components in the coating-type oxide semiconductor are mainly components contained in the precursor solution, and it is extremely important to reduce the residual components in order to improve the semiconductor characteristics of the coating-type oxide semiconductor. is important. Chloride ions, nitrate ions, and residual organic components that are expected to remain when chloride salts, nitrates, acetates, or the like are used are components that inhibit carrier conductivity in oxide semiconductors. However, fluorine, which is a residual component in the metal fluoride in this reference embodiment, behaves as a dopant that improves conductivity in the coated semiconductor layer. Therefore, it is possible to reduce residual components that act as defects contained in the coating-type semiconductor layer, and to provide a more excellent coating-type semiconductor.
As a result, it is possible to fabricate a coating type semiconductor device exhibiting good switching characteristics.

Next, a method for manufacturing a thin film transistor according to the reference embodiment will be described.
First, it is assumed that a coated oxide semiconductor is used as a channel layer of a TFT element. That is, in this case, the gate electrode 2 and the gate insulating film 3 are laminated on the substrate 1 as shown in FIG. 1 before manufacturing the coated oxide semiconductor.

That is, a substrate 1 made of glass, resin, or the like is washed, a barrier layer or a planarizing layer (inorganic thin film or organic thin film) is formed on the surface of the substrate 1 (not shown), and then a gate electrode 2 is laminated, Pattern to the required shape. Note that photolithography (microfabrication technology by ultraviolet exposure) is used for patterning the fine shape. Next, a gate insulating film 3 is formed on the gate electrode 2 and the substrate 1 (region where the gate electrode 2 is not formed). As the gate insulating film 3, a silicon oxide film (SiO ₂ ) having a thickness of 400 nm is used. A chemical vapor deposition method or a sputtering method is used for film formation. Of course, it is also possible to form the film using an organic material.

After that, a semiconductor layer (coating-type oxide semiconductor) 4 is formed on the gate insulating film 3 . That is, the semiconductor layer 4 is formed by coating a predetermined oxide precursor solution on the gate insulating film 3 by a coating method to form a thin film, followed by drying.
First, a coating-type semiconductor solution adjusting step for adjusting a semiconductor precursor solution is performed.
At this time, the precursor solution contains two or more metal components selected from indium, zinc, tin and gallium, and at least one of the selected metal components is a metal fluoride salt.

That is, a metal salt of this metal oxide is produced. Since the details of the metal salt have been described above, the description is omitted here.
Next, these metal salts are dissolved in a solvent to prepare a precursor solution. As a solvent for dissolving, water, ethanol, propanol, ethylene glycol, or the like described above can be used.
After that, the concentration of the metal salt is weighed so that the concentration of the solution is from 0.1 mol/L to 1 mol/L, and the metal salt is dissolved in the solution by stirring.

Next, the obtained precursor solution is applied onto the gate insulating film 3 .
The coating thickness of the semiconductor layer 4 is adjusted to a predetermined thickness of, for example, 1 nm to 100 nm, depending on the concentration of the solution and the number of times of coating.
As the coating method, as described above, a spray coating method, a spin coating method, a printing method, or the like can be used.

Moreover, the semiconductor layer 4 is obtained by performing drying and baking which are methods for oxidizing the applied thin film.

Next, source/drain electrodes 6 are formed. If an etching stop layer is introduced on the semiconductor layer 4, it is possible to suppress deterioration of semiconductor characteristics, which is preferable. As materials for the electrodes, transparent electrodes such as ITO and IZO, metal electrodes such as Al, Ag, Cr, Mo and Ti, and alloys thereof can be used.
<Reference Examples 1 and 2>

Hereinafter , coating-type oxide semiconductors (TFTs) according to Reference Examples 1 and 2 corresponding to Reference Modes will be described by making a comparison with Comparative Examples 1 and 2. FIG.
(Overview)
TFTs of Reference Examples 1 and 2 and TFTs of Comparative Examples 1 and 2 were fabricated using a low-resistance silicon wafer with a thermal oxide film having a thickness of 200 nm.

That is, in Reference Example 1, a coating-type semiconductor layer was applied on a silicon wafer by a spin coating method, and was formed by firing in a firing furnace. After that, the coated semiconductor layer was patterned into islands by photolithography.
The source/drain electrodes were patterned by sputtering as they were using a metal mask, and a sample of a reference TFT device was produced. Low resistance silicon was used as the gate electrode, a thermal oxide film was used as the gate insulating film, and molybdenum was used as the source/drain electrodes.

その後、室温にて、6時間撹拌することで完全に溶解した状態の前駆体溶液を作製した。
続いて、得られた前駆体溶液をスピンコート法によりシリコンウエハ上に塗布し、150℃のホットプレート上にて10分間乾燥させた。その後、300度の大気雰囲気オーブンにて1時間焼成処理を行うことにより半導体層を形成した。
このときの膜厚は15 nmであった。
この後半導体層をフォトリソグラフィー法によりアイランド状にパターニング化し、塗布型半導体層を形成した。続いてメタルマスクを用い、モリブデンでDCスパッタリング法によりソース・ドレイン電極を形成し、参考例１の評価用TFTサンプルを作製した。 <Specific description of Reference Example 1>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich), gallium fluoride (GaF ₃ Aldrich), and zinc fluoride tetrahydrate (ZnF ₂ 4H ₂ O Aldrich) were weighed. , respectively, in pure water to prepare a coating-type semiconductor precursor solution shown in Table 1 below. At this time, the sample concentration was 0.15 mol/L.

Then, the mixture was stirred at room temperature for 6 hours to prepare a completely dissolved precursor solution.
Subsequently, the resulting precursor solution was applied onto a silicon wafer by spin coating and dried on a hot plate at 150° C. for 10 minutes. After that, a semiconductor layer was formed by performing a baking treatment in an air atmosphere oven at 300° C. for 1 hour.
The film thickness at this time was 15 nm.
After that, the semiconductor layer was patterned into islands by photolithography to form a coated semiconductor layer. Subsequently, using a metal mask, source and drain electrodes were formed from molybdenum by a DC sputtering method, and a TFT sample for evaluation of Reference Example 1 was produced.

その後は、上記参考例１と同様にして、参考例２の評価用TFTサンプルを作製した。 <Specific description of Reference Example 2>
Indium nitrate hydrate (In(NO ₃ ) ₃ ·xH ₂ O manufactured by Aldrich) and zinc fluoride tetrahydrate (ZnF ₂ ·4H ₂ O manufactured by Aldrich) were weighed and dissolved in pure water. A coating type semiconductor precursor solution shown in Table 2 was prepared. At this time, the sample concentration was 0.15 mol/L.

Thereafter, in the same manner as in Reference Example 1, a TFT sample for evaluation of Reference Example 2 was produced.

その後は、上記参考例１と同様にして、評価用比較例１のTFTサンプルを作製した。 <Specific description of Comparative Example 1>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich), Gallium nitrate hydrate (Ga(NO ₃ ) ₃ xH ₂ O Aldrich), Zinc nitrate hydrate (Zn(NO ₃ ) ₂ ·xH ₂ O (manufactured by Aldrich) were weighed and dissolved in pure water to prepare coating-type semiconductor precursor solutions shown in Table 3 below. At this time, the sample concentration was 0.15 mol/L.

After that, in the same manner as in Reference Example 1, a TFT sample of Comparative Example 1 for evaluation was produced.

その後は、上記参考例１と同様にして、比較例２の評価用TFTサンプルを作製した。 <Specific description of Comparative Example 2>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich) and zinc nitrate hydrate (Zn(NO ₃ ) ₂ xH ₂ O Aldrich) were weighed and dissolved in pure water. , to prepare a coating type semiconductor precursor solution shown in Table 4 below. At this time, the sample concentration was 0.15 mol/L.

Thereafter, in the same manner as in Reference Example 1, a TFT sample for evaluation of Comparative Example 2 was produced.

このように、In、Zn、SnおよびGaから選ばれる2種類以上の金属成分が含まれ、そのうちの少なくとも1つが金属フッ化塩である参考例１、２においては、そのような条件を満たしていない比較例１、２に比べて、より優れた半導体特性が得られた。 <Evaluation of Reference Examples 1 and 2>
The TFTs of Reference Examples 1 and 2 are evaluated by comparing the samples of Reference Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described above.
The field effect mobility (mobility) was measured for each of the above samples, and the measurement results are shown in Table 5 below.

Thus, Reference Examples 1 and 2, in which two or more metal components selected from In, Zn, Sn and Ga are contained, and at least one of which is a metal fluoride salt, do not satisfy such conditions. Better semiconductor properties were obtained than in Comparative Examples 1 and 2, which did not contain any.

≪Embodiment≫
The coating-type oxide semiconductor (and thin film transistor (hereinafter simply referred to as TFT)) according to the embodiment has the same layer structure as the TFT according to the reference embodiment shown in FIG. In order to avoid complication due to redundant description, the description in the reference form will be substituted, and the points different from the reference form will be mainly described below.
Further, it is assumed that the coating-type oxide semiconductor according to the embodiment is also used as the coating-type oxide semiconductor in the TFT according to the embodiment, as in the reference mode described above. However, the above reference form contains two or more metal components selected from indium, zinc, tin, and gallium as a precursor solution for the coating-type oxide semiconductor, and at least one of the selected metal components 1 consists of a metal fluoride salt, whereas in this embodiment, two or more metal components selected from indium, zinc, tin and gallium are used as the precursor solution of the coating-type oxide semiconductor. It is different in that it contains an additive having fluorine ions.

Further, the TFT according to the embodiment is configured by laminating a gate electrode 2 , a gate insulating film 3 , a semiconductor layer 4 made of a coating-type oxide semiconductor, and source/drain electrodes 6 on a substrate 1 . However, in the semiconductor layer 4 according to this embodiment, the precursor solution of the semiconductor layer 4 contains two or more kinds of metal components selected from indium, zinc, tin and gallium as described above, and fluorine ions contains additives with

Here, since the specific configurations of the substrate 1, the gate electrode 2, the gate insulating film 3, and the source/drain electrodes 6 are the same as those of the reference embodiment, detailed description thereof will be omitted.
The precursor solution of the semiconductor layer 4 contains the above-described metal component and an additive containing fluorine ions.
Specific fluorine ion-containing additives include the following fluorine compounds.
For example, hydrogen fluoride, hydrofluoric acid, sodium fluoride, potassium fluoride, ammonium fluoride, ammonium silicofluoride, ammonium hydrofluoride, fluoroboric acid, fluorobromine, ammonium fluoride ( _NH4F ) , ammonium monohydrogen difluoride ( _NH4FHF ), methylamine fluoride _{( CH3NH3F} ), ethylamine fluoride _{( C2H5NH3F} ) _{, butylamine} fluoride _{( C4H9NH3F} ) , dimethylamine fluoride ((CH ₃ ) ₂ NH ₂ F), diethylamine fluoride ((C ₂ H ₅ ) ₂ NH ₂ F), triethylamine fluoride ((C ₂ H ₅ ) ₃ NHF) and the like.

The configuration of other metal components is the same as in the reference embodiment.
The metal element-containing compound is the same as that of the reference embodiment.
Also, as the metal salt, as in the reference form, those formed from inorganic acid salts such as nitrates, chlorides, sulfates, and acetates can be used. Specific indium compounds include indium chloride, indium acetate, and indium nitrate. Zinc compounds include zinc chloride, zinc acetate, zinc acetate hydrate, and zinc nitrate. Further, tin compounds include tin chloride, tin acetate, and the like.

As the solvent, it is the same as in the reference form, and a solvent having a small molecular weight that does not easily leave residual components is preferable. Water is particularly preferable in terms of reducing residual components.
Similarly to the reference form, the precursor solution is prepared by weighing the metal salt concentration so that the concentration of the solution is from 0.1 mol/L to 1 mol/L, and stirring and dissolving in the solution. be done.
By coating the precursor solution thus obtained on the substrate 1, a thin film of the precursor solution is formed.
The thickness of the semiconductor layer 4 is preferably 1 nm to 100 nm as in the reference embodiment.

The method of applying the precursor solution includes a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, a die coating method, a printing method such as an inkjet method, and the like. It is the same. Note that the surface of the substrate may be modified by UV, ozone, ashing, or the like at the time of coating at an appropriate intensity.
The semiconductor layer 4 is obtained by drying and baking the applied thin film for oxidation, and the actual procedure is the same as in the case of the reference embodiment.

Note that in this embodiment, the semiconductor film can be applied in a plurality of times, and precursor solutions of oxide semiconductors having different material compositions can be used. If the fluorine ion concentration is high (20% or more), for example, the reactivity of hydrofluoric acid may etch the surface of the insulating film. In this case, a precursor solution containing no fluorine ions is applied to form a thin film, and then a precursor solution containing fluorine ions is formed as a thin film, so that the surface of the insulating film retains good fluorine ions. A coating-type oxide semiconductor film can be formed.
The subsequent method of forming the source/drain electrodes 6 is the same as that of the reference embodiment.

The residual components in the coating-type semiconductor are mainly components contained in the precursor solution, and it is extremely important to reduce the residual components in order to improve the semiconductor properties of the coating-type semiconductor. Chloride ions, nitrate ions, and organic residues that are expected to remain when chloride salts, nitrates, acetates, and the like are used are components that inhibit carrier conductivity in oxide semiconductors. However, by mixing a small amount of an additive containing fluorine ions in the present embodiment, selective bonding to metal atoms is promoted due to the high electronegativity of fluorine, and as a result, it behaves as a defect contained in the coating type semiconductor layer. Residual components can be reduced, and a more excellent coating-type semiconductor can be provided. Fluorine also acts as a conductivity-improving dopant in the coated semiconductor layer. As a result, it is possible to fabricate a coating type semiconductor device exhibiting good switching characteristics.
<Examples 1 and 2>

Hereinafter, the TFTs according to Examples 1 and 2 corresponding to the embodiments of the present invention will be described by comparing with the coated oxide semiconductor (TFT) according to Comparative Example 3. FIG.
(Overview)
TFTs of Examples 1 and 2 and a TFT of Comparative Example 3 were fabricated using low-resistance silicon wafers with a thermal oxide film having a thickness of 200 nm.

That is, in Examples 1 and 2, a coating-type semiconductor layer was applied onto a silicon wafer by spin coating, and was formed by firing in a firing furnace. After that, the coated semiconductor layer was patterned into islands by photolithography.
The source/drain electrodes were patterned by direct sputtering using a metal mask, and a sample of the TFT element of the embodiment was produced. Molybdenum was used as the source/drain electrodes. Low resistance silicon was used as the gate electrode, a thermal oxide film was used as the gate insulating film, and molybdenum was used as the source/drain electrodes.

その後、室温にて、6時間撹拌することで完全に溶解した状態の前駆体溶液を作製した。 <Specific description of Example 1>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich), Gallium nitrate hydrate (Ga(NO ₃ ) ₃ xH ₂ O Aldrich), Zinc nitrate hydrate (Zn(NO ₃ ) ₂ ·xH ₂ O (manufactured by Aldrich) was weighed, hydrofluoric acid (0.6%) was added as an additive, and each solution was dissolved in pure water to prepare a coating type semiconductor precursor solution shown in Table 6 below. At this time, the sample concentration was 0.3 mol/L.

Then, the mixture was stirred at room temperature for 6 hours to prepare a completely dissolved precursor solution.

Subsequently, the resulting precursor solution was applied onto a silicon wafer by spin coating and dried on a hot plate at 150° C. for 10 minutes. After that, a semiconductor layer was formed by performing a baking treatment in an air atmosphere oven at 300° C. for 1 hour.
The film thickness at this time was 15 nm.
After that, the semiconductor layer was patterned into islands by photolithography to form a coated semiconductor layer. Subsequently, using a metal mask, source and drain electrodes were formed with molybdenum by a DC sputtering method, and a TFT sample for evaluation of Example 1 was produced.

その後は、上記実施例１と同様にして、実施例２の評価用TFTサンプルを作製した。 <Specific description of Example 2>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich), Gallium nitrate hydrate (Ga(NO ₃ ) ₃ xH ₂ O Aldrich), Zinc nitrate hydrate (Zn(NO ₃ ) ₂ ·xH ₂ O (manufactured by Aldrich) was weighed, hydrofluoric acid (0.3%) was added as an additive, and each solution was dissolved in pure water to prepare a coating type semiconductor precursor solution shown in Table 7 below. At this time, the sample concentration was 0.3 mol/L.

After that, a TFT sample for evaluation of Example 2 was produced in the same manner as in Example 1 above.

その後は、上記実施例１と同様にして、比較例３の評価用TFTサンプルを作製した。 <Specific description of Comparative Example 3>
Indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O Aldrich), Gallium nitrate hydrate (Ga(NO ₃ ) ₃ xH ₂ O Aldrich), Zinc nitrate hydrate (Zn(NO ₃ ) ₂ ·xH ₂ O (manufactured by Aldrich) were weighed and dissolved in pure water to prepare coating-type semiconductor precursor solutions shown in Table 8 below. At this time, the sample concentration was 0.3 mol/L.

Thereafter, in the same manner as in Example 1, a TFT sample for evaluation of Comparative Example 3 was produced.

このように、In、ZnおよびGaから選ばれる2種類以上の金属成分が含まれるとともに、フッ素イオンを有する添加剤を含む実施例１、２においては、そのような条件を満たしていない比較例３に比べて、より優れた半導体特性が得られた。 <Evaluation of Examples 1 and 2>
The TFTs of Examples 1 and 2 are evaluated by comparing the samples of Examples 1 and 2 and Comparative Example 3 obtained as described above.
The field effect mobility (mobility) was measured for each of the above samples, and the measurement results are shown in Table 9 below.

Thus, in Examples 1 and 2 containing two or more kinds of metal components selected from In, Zn and Ga and containing an additive having fluorine ions, Comparative Example 3 which does not satisfy such conditions Better semiconducting properties were obtained compared to

The thin film transistor and the method for manufacturing the thin film transistor of the present invention are not limited to those described in the above embodiments, and various other modifications are possible.
For example, the metal components contained in the coating-type semiconductor precursor solution may be two, three, or all of indium, zinc, tin, and gallium.

Further, the thin film transistor of the present invention is not limited to the above embodiments, and it is possible to adopt a configuration in which another layer is interposed between each layer shown in the embodiments.
In addition, in the above-described embodiments, the coating type oxide semiconductor has a bottom gate configuration, but the coating type oxide semiconductor of the thin film transistor according to the present invention has a top gate configuration. can be similarly adapted. However, in the case of the top-gate type coating-type oxide semiconductor, the coating-type semiconductor precursor solution is usually applied onto the source/drain electrodes and the substrate to form the oxide semiconductor layer.
In addition, the coating type oxide semiconductor is not limited to being used as a channel layer of a thin film transistor, and can be suitably used for display elements such as liquid crystal, plasma, and EL, solar cells, touch panels, various electrodes, and the like.

In the embodiment of the present invention, the semiconductor layer is of the coating type, and the other layers are not necessarily of the coating type. However, all the layers may be of the coating type. In some cases, the entire system for processing in vacuum can be dispensed with.
Further, by forming a display driver using the thin film transistor described above, various display devices such as an organic EL display (OLED) and an LCD can be formed.

REFERENCE SIGNS LIST 1 substrate 2 gate electrode 3 gate insulating film 4 semiconductor layer (coated oxide semiconductor layer)
6 source/drain electrodes

Claims (6)

At least a gate electrode, a gate insulating film, a coating-type oxide semiconductor layer, and source/drain electrodes are provided on a substrate, and the coating-type oxide semiconductor layer is positioned above or below the gate insulating film. A coating type semiconductor precursor solution containing two or more metal components selected from indium, zinc, tin and gallium and containing hydrofluoric acid is coated on a predetermined base and oxidized. A thin film transistor characterized by: 2. The thin film transistor according to claim 1 , wherein the coating type oxide semiconductor layer contains at least metal components of indium and zinc, and fluorine. 3. The thin film transistor according to claim 1, wherein water is the main component of the solvent constituting the coating type semiconductor precursor solution. 4. The process according to any one of claims 1 to 3 , wherein the treatment for oxidizing the coating-type semiconductor precursor solution is heat treatment by either microwave irradiation or ultraviolet light irradiation, or baking treatment. thin film transistor. forming at least a gate electrode, a gate insulating film, a coated oxide semiconductor layer, and source/drain electrodes on a substrate;
preparing a coating-type semiconductor precursor solution containing a solution containing two or more metal components selected from indium, zinc, tin, and gallium and containing hydrofluoric acid, which is an additive having fluorine ions;
The coating type semiconductor precursor solution is coated on a predetermined base such that the coating type oxide semiconductor layer is positioned above or below the gate insulating film, and then oxidized. Method. The step of applying the coating type semiconductor precursor solution onto a predetermined base includes first coating the coating type semiconductor precursor solution containing no additive having fluorine ions on the predetermined base to form a thin film. and then coating a coating-type semiconductor precursor solution containing a solution containing hydrofluoric acid on the thin film to form the thin film. Method.

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