EP2467514B1 - Process for preparing indium oxide containing layers - Google Patents

Description

The invention relates to a process for the preparation of indium oxide-containing layers, to the process producible layers and their use.

Indium oxide (indium (III) oxide, In ₂ O ₃ ) is due to the large band gap between 3.6 and 3.75 eV (measured for evaporated layers) [ HS Kim, PD Byrne, A. Facchetti, TJ Marks; J. Am. Chem. Soc. 2008, 130, 12580-12581 ] a promising semiconductor. In addition, thin films of a few hundred nanometers in thickness can have a high transparency in the visible spectral range of greater than 90% at 550 nm. In extremely highly ordered indium oxide single crystals, it is also possible to measure charge carrier mobilities of up to 160 cm ² / Vs.

Indium oxide is often used together with tin (IV) oxide (SnO ₂ ) as semiconducting mixed oxide ITO. Due to the relatively high conductivity of ITO layers with simultaneous transparency in the visible spectral range, it is used, inter alia, in the field of liquid crystal display (LCD), in particular as a "transparent electrode". These mostly doped metal oxide layers are industrially produced mainly by cost-intensive vapor deposition in a high vacuum.

Indium oxide-containing layers and their production, in particular ITO layers and pure indium oxide layers, and their production are therefore of great importance for the semiconductor and display industries.

A variety of classes of compounds are discussed as possible starting materials or precursors for the synthesis of indium oxide-containing layers. These include, for example, indium salts. Thus, Marks et al. Components in whose preparation a precursor solution of InCl ₃ and the base monoethanolamine (MEA) dissolved in methoxyethanol is used. After spinning (spin-coating) the solution, the corresponding indium oxide layer by a thermal Treatment produced at 400 ° C. [ HS Kim, PD Byrne, A. Facchetti, TJ Marks; J. Am. Chem. Soc. 2008, 130, 12580-12581 and supplemental information]

Elsewhere, indium alkoxides are discussed as possible starting materials or precursors for indium oxide synthesis. Under an indium alkoxide is a compound consisting of at least one indium atom, at least one alkoxide radical of the formula -OR (R = organic radical) and optionally one or more organic radicals -R, one or more halogen radicals and / or one or more radicals -OH or -OROH.

Independent of a possible use for indium oxide formation, various indium alkoxides and indium oxoalkoxides are described in the prior art. In contrast to the indium alkoxides already mentioned, indium oxoalkoxides also have at least one further oxygen radical (oxo radical) bonded directly to an indium atom or bridging at least two indium atoms.

Mehrotra et al. describe the preparation of indium tris alkoxide In (OR) ₃ from indium (III) chloride (InCl ₃ ) with Na-OR, wherein R is methyl, ethyl, iso-propyl, n-, s-, t- Butyl and pentyl radicals is. [ S. Chatterjee, SR Bindal, RC Mehrotra; J. Indian Chem. Soc. 1976, 53, 867 ].

A review article by Carmalt et al. (Coordination Chemistry Reviews 250 (2006), 682-709 ) describes various gallium (III) - and indium (III) alkoxides and -aryloxides, which may be partially bridged via alkoxide groups. Furthermore, an oxo-centered cluster of the formula In ₅ (μ-O) (O ⁱ Pr) ₁₃ , more precisely [In ₅ (μ ₅ -O) (μ ₃ -O ⁱ Pr) ₄ (μ ₂ -O ⁱ Pr) ₄ (O ⁱ Pr) ₅ ], which is an oxo-alkoxide and which can not be prepared from [In (O ⁱ Pr) ₃ ].

A review article by N. Turova et al., Russian Chemical Reviews 73 (11), 1041-1064 (2004 ) summarizes the synthesis, properties and structures of metal oxo alkoxides, which are considered as precursors for the preparation of oxidic materials via sol-gel technology. In addition to a variety of others Compounds become the synthesis and structure of [Sn ₃ O (O ⁱ Bu) ₁₀ ( ⁱ BuOH) ₂ ], of the already mentioned compound [In ₅ O (O ⁱ Pr) ₁₃ ] and of [Sn ₆ O ₄ (OR) ₄ ] (R = Me, Pr ⁱ ).

The item by Turova, N., et al., Journal of Sol-Gel Science and Technology, 2, 17-23 (1994 ) presents results of studies on alkoxides, which are considered as a scientific basis for the development of sol-gel processes of alkoxides and alkoxide-based powders. In this context, among other things, on a supposed "indium isopropoxide" is addressed, which is as the Carmalt et al. described Oxoalkoxid with a central oxygen atom and five surrounding metal atoms of the formula M ₅ (μ-O) (O ⁱ Pr) ₁₃ proved.

A synthesis of this compound and its crystal structure will be by Bradley et al., J.Chem.Soc., Chem. Commun., 1988, 1258-1259 described. Further studies of the authors led to the conclusion that the formation of this compound is not due to a hydrolysis of interim In (O ⁱ Pr) ₃ ( Bradley et al., Polyhedron Vol. 9, no. 5, pp. 719-726, 1990 ). Suh et al., J. Am. Chem. Soc. 2000, 122, 9396-9404 also noted that this compound can not be prepared thermally from In (O ⁱ Pr) ₃ . In addition, Bradley ( Bradley et al., Polyhedron Vol. 9, no. 5, pp. 719-726, 1990 ) found that this compound can not be sublimated.

Metal oxide layers can be prepared in principle by various methods.

One way to make metal oxide layers is based on sputtering techniques. However, these techniques have the disadvantage that they must be performed under high vacuum. Another disadvantage is that the films made with them have many oxygen defects that make it impossible to set a targeted and reproducible stoichiometry of the layers and thus lead to poor properties of the layers produced. Another principal possibility for the production of metal oxide layers is based on chemical vapor deposition. For example, indium oxide-containing Layers of indium oxide precursors such as indium alkoxides or Indiumoxoalkoxiden be prepared by vapor deposition. For example, teaches US 6,958,300 B2 , at least one metal-organo-oxide precursor (alkoxide or oxoalkoxide) of the generic formula M ¹ _q (O) _x (OR ¹ ) _y (q = 1 - 2, x = 0 - 4, y = 1 - 8, M ¹ = metal, eg Ga, In or Zn, R ¹ = organic radical, alkoxide for x = 0, oxo-alkoxide for ≥ 1) in the production of semiconductors or metal oxide layers by gas phase deposition, such as CVD or ALD. However, all gas phase deposition processes either have the disadvantage that they require i) in the case of a thermal reaction, the use of very high temperatures or ii) in the case of introducing the required energy for the decomposition of the precursor in the form of electromagnetic radiation high energy densities. In both cases, it is only possible with the highest expenditure on equipment to introduce the energy required for the decomposition of the precursor in a targeted and uniform manner.

Thus, metal oxide layers are advantageously produced by liquid-phase techniques, i. by processes comprising at least one process step before conversion to the metal oxide, in which the substrate to be coated is coated with a liquid solution of at least one precursor of the metal oxide and optionally subsequently dried. A metal oxide precursor in this case is a compound which can be decomposed thermally or with electromagnetic radiation and with which metal oxide-containing layers can be formed in the presence or absence of oxygen or other oxidizing substances. Prominent examples of metal oxide precursors are e.g. Metal alkoxides. In principle, the layer production can be carried out i) by sol-gel processes, in which the metal alkoxides used are first converted into gels in the presence of water by hydrolysis and subsequent condensation and then converted into metal oxides, or ii) from non-aqueous solution.

In this case, the production of indium oxide-containing layers of indium alkoxides from liquid phase belongs to the prior art.

The production of indium oxide-containing layers from indium alkoxides via sol-gel processes in the presence of significant amounts of water belongs to the prior art. WO 2008/083310 A1 describes methods for producing inorganic layers or organic / inorganic hybrid layers on a substrate, in which a metal alkoxide (for example one of the generic formula R ¹ M- (OR ² ) _{y x} ) or a prepolymer thereof is applied to a substrate and then the resulting metal alkoxide Layer is cured in the presence of and reaction with water. The usable metal alkoxides may be, inter alia, those of indium, gallium, tin or zinc. A disadvantage of the use of sol-gel method, however, is that the hydrolysis-condensation reaction is started automatically by addition of water and is difficult to control after their start. If the hydrolysis-condensation process is already started prior to application to the substrate, the gels produced in the meantime, because of their increased viscosity, are often unsuitable for processes for producing fine oxide layers. On the other hand, if the hydrolysis-condensation process is started only after application to the substrate by supplying water in liquid form or as a vapor, the resulting poorly mixed and inhomogeneous gels often lead to correspondingly inhomogeneous layers having disadvantageous properties.

JP 2007-042689 A describes metal alkoxide solutions which may contain indium alkoxides, as well as methods of making semiconductor devices using these metal alkoxide solutions. The metal alkoxide films are thermally treated and converted to the oxide layer, but these systems do not provide sufficiently homogeneous films. However, pure indium oxide layers can not be produced by the process described therein.

The not yet revealed DE 10 2009 009 338.9-43 describes the use of indium alkoxides in the production of indium oxide-containing layers from anhydrous solutions. Although the resulting layers are more homogeneous than those produced by sol-gel processes, the use of indium alkoxides in anhydrous systems still has the disadvantage that indium oxide-containing formulations are converted by the conversion of indium oxide-containing formulations Layers no sufficiently good electrical performance of the resulting layer is given.

It is thus the object of the present invention to provide a process for producing indium oxide-containing layers, which avoids the disadvantages of the prior art. In particular, a method is to be provided which avoids the use of high vacuum, in which the energy required for the decomposition or conversion of precursors or educts can be easily introduced in a targeted and uniform manner, which avoids the mentioned disadvantages of sol-gel techniques and this leads to indium oxide layers with targeted, uniform and reproducible stoichiometry, high homogeneity and good electrical performance.

These objects are achieved by a liquid-phase process for producing indium oxide-containing layers from nonaqueous solution in which an anhydrous composition containing i) at least one Indiumoxoalkoxid the generic formula M _x O _y (OR) _z [O (R'O) _c H ] _a X _b [R "OH] _d where M = In, x = 3 - 25, y = 1-10, z = 3 - 50, a = 0 - 25, b = 0 - 20, c = 0 - 1 , d = 0-25, R, R ', R "= organic radical, X = F, Cl, Br, I and ii) at least one solvent applied to a substrate, optionally dried, and converted into an indium oxide-containing layer becomes.

The liquid phase process according to the invention for producing indium oxide-containing layers from nonaqueous solution is a process comprising at least one process step in which the substrate to be coated is coated with a liquid nonaqueous solution containing at least one metal oxide precursor and optionally subsequently dried , In particular, this is not a sputtering, CVD or sol-gel process. In this case, a metal oxide precursor is a compound that can be decomposed thermally or with electromagnetic radiation, with which metal oxide-containing layers can be formed in the presence or absence of oxygen or other oxidizing substances. For the purposes of the present invention, liquid compositions are to be understood as meaning those which are stable under SATP conditions ("Standard Ambient Temperature and Pressure ", T = 25 ° C. and p = 1013 hPa) and when applied to the substrate to be coated are in liquid form. A non-aqueous solution or an anhydrous composition is to be understood here and below as meaning a solution or formulation. which has not more than 200 ppm H ₂ O.

The process product of the process according to the invention, the layer containing indium oxide, is to be understood as meaning a metal- or semimetallin-containing layer which has indium atoms or ions which are substantially oxidic. Optionally, the indium oxide-containing layer may also have carbene, halogen or alkoxide fractions from incomplete conversion or incomplete removal of by-products formed. The indium oxide-containing layer may be a pure indium oxide layer, i. when ignoring any carbene, alkoxide or halogen fractions essentially consist of oxidically present indium atoms or ions, or proportionally even more metals, which may be present even in elemental or oxidic form, have. To produce pure indium oxide layers, only indium-containing precursors, preferably only indium oxo alkoxides and indium alkoxides, should be used in the process according to the invention. In contrast, other metals containing layers in addition to the indium-containing precursors are also precursors of metals in the oxidation state 0 (for the production of layers containing other metals in neutral form) or metal oxide precursors (such as other metal alkoxides or oxoalkoxide ).

The indium oxoalkoxide is preferably one of the generic formula M _x O _y (OR) _z where x = 3 to 20, y = 1 to 8, z = 3 to 25, OR = C 1 -C 15 -alkoxy, - Oxyalkylalkoxy, -aryloxy or -oxyarylalkoxy group and particularly preferably one of the generic formula M _x O _y (OR) _z where x = 3 to 15, y = 1 to 5, z = 10 to 20, OR = - OCH ₃ , -OCH ₂ CH ₃ , -OCH ₂ CH ₂ OCH ₃ , -OCH (CH ₃ ) ₂ or -OC (CH ₃ ) ₃ .

Very particular preference is given to a process in which the indium oxoalkoxide used [In ₅ (μ ₅ -O) (μ ₃ -O ⁱ Pr) ₄ (μ ₂ -O ⁱ Pr) ₄ (O ⁱ Pr) ₅ ].

The present inventive method is particularly well suited for the production of indium oxide layers, when the Indiumoxoalkoxid is used as the sole metal oxide precursor. Very good layers result when the only metal oxide precursor is [In ₅ (μ ₅ -O) (μ ₃ -O ⁱ Pr) ₄ (μ ₂ -O ⁱ Pr) ₄ (O ⁱ Pr) ₅ ].

The at least one indium oxoalkoxide is preferably present in proportions of from 0.1 to 15% by weight, more preferably from 1 to 10% by weight, very preferably from 2 to 5% by weight, based on the total mass of the anhydrous composition.

The anhydrous composition further contains at least one solvent, i. the composition may contain both a solvent or a mixture of different solvents. Preferably used in the formulation for the process according to the invention are aprotic and weakly protic solvents, i. those selected from the group of aprotic nonpolar solvents, i. alkanes, substituted alkanes, alkenes, alkynes, aromatics with or without aliphatic or aromatic substituents, halogenated hydrocarbons, tetramethylsilane, the group of aprotic polar solvents, i. the ethers, aromatic ethers, substituted ethers, esters or acid anhydrides, ketones, tertiary amines, nitromethane, DMF (dimethylformamide), DMSO (dimethylsulfoxide) or propylene carbonate, and the weakly protic solvent, i. alcohols, primary and secondary amines and formamide. Particularly preferably usable solvents are alcohols and toluene, xylene, anisole, mesitylene, n-hexane, n-heptane, tris- (3,6-dioxaheptyl) -amine (TDA), 2-aminomethyltetrahydrofuran, phenetole, 4-methylanisole, 3 Methylanisole, methyl benzoate, N-methyl-2-pyrrolidone (NMP), tetralin, ethyl benzoate and diethyl ether. Very particularly preferred solvents are methanol, ethanol, isopropanol, tetrahydrofurfuryl alcohol, tert-butanol and toluene, and mixtures thereof.

The composition used in the process according to the invention preferably has a viscosity of from 1 mPa.s to 10 Pa.s, in particular from 1 mPa.s to 100 mPa.s, determined in accordance with DIN 53019 in order to achieve particularly good printability Part 1 to 2 and measured at 20 ° C on. Corresponding viscosities can be set by addition of polymers, cellulose derivatives, or, for example, SiO ₂ obtainable under the trade name Aerosil, and in particular by PMMA, polyvinyl alcohol, urethane thickener or polyacrylate thickener.

The substrate used in the method according to the invention is preferably a substrate consisting of glass, silicon, silicon dioxide, a metal or transition metal oxide, a metal or a polymeric material, in particular PI or PET.

The process according to the invention is particularly advantageously a coating process selected from printing processes (in particular flexographic / gravure printing, inkjet printing, offset printing, digital offset printing and screen printing), spraying processes, spin-coating processes, dip processes (dip -coating ") and methods selected from Meniscus Coating, Slit Coating, Slot Die Coating, and Curtain Coating. Most preferably, the printing process of the invention is a printing process.

After coating and before conversion, the coated substrate can continue to be dried. Corresponding measures and conditions for this are known to the person skilled in the art.

The conversion to an indium oxide-containing layer can be effected by thermal means and / or by irradiation with electromagnetic, in particular actinic radiation. Preferably, the conversion takes place on the thermal paths through temperatures of greater than 150 ° C. Particularly good results can be achieved, however, if temperatures of 250 ° C to 360 ° C are used for the conversion.

It typically uses conversion times from a few seconds to several hours.

The thermal conversion can furthermore be assisted by irradiating UV, IR or VIS radiation before or during the thermal treatment or by treating the coated substrate with air or oxygen.

The quality of the layer produced by the process according to the invention can furthermore be determined by a combined temperature and gas treatment (with H ₂ or O ₂ ) following the conversion step, plasma treatment (Ar, N ₂ , O ₂ or H ₂ plasma), laser Treatment (with wavelengths in the UV, VIS or IR range) or an ozone treatment can be further improved.

The invention furthermore relates to indium oxide-containing layers which can be prepared by the process according to the invention. Particularly good properties have indium oxide-containing layers, which are pure indium oxide layers, which can be prepared by the process according to the invention.

The indium oxide-containing layers which can be produced by the process according to the invention are advantageously suitable for the production of electronic components, in particular the production of transistors (in particular thin-film transistors), diodes, sensors or solar cells.

The following example is intended to explain the subject matter of the present invention in more detail.

Embodiment:

A doped silicon substrate having an edge length of about 15 mm and having an approximately 200 nm thick silicon oxide coating and ITO / gold finger structures was coated with 100 μl of a 5% by weight solution of [In ₅ (μ ₅ -O) (μ ₃ -O ⁱ Pr) ₄ (μ ₂ -O ⁱ Pr) ₄ (O ⁱ Pr) ₅ ] in alcohol (methanol, ethanol or isopropanol) or toluene by spin coating (2000 rpm). To exclude water, dry solvents (less than 200 ppm water) were used and the coating was still carried out in a glove box (less than 10 ppm H ₂ O). After the coating operation, the coated substrate was annealed in the air at a temperature of 260 ° C or 350 ° C for one hour.

The inventive coating exhibits a charge carrier mobility of up to 6 cm ² / Vs (at 30 V gate-source voltage, 30 V source-drain voltage, 1 cm channel width and 20 μm channel length). Table 1. Carrier mobilities Carrier mobility solvent 260 ° C 350 ° C methanol 0.2 1.0 ethanol 0.6 6.0 (Sample 1) isopropanol 0.4 1.3 toluene 0.2 0.6

Claims (12)

1. Liquid phase process for producing indium oxide-containing layers from nonaqueous solution,
   characterized in that
   an anhydrous composition containing

   i) at least one indium oxo alkoxide of the generic formula M_xO_y(OR)_z[O(R'O)_cH]_aX_b[R"OH]_d where

   x = 3-25,

   y = 1-10,

   z = 3-50,

   a = 0-25,

   b = 0-20,

   c = 0-1,

   d = 0-25,

   M = In,

   R, R', R" = organic radical,

   X = F, Cl, Br, I and

   ii) at least one solvent

   are applied to a substrate, optionally dried, and converted to an indium oxide-containing layer.
2. Process according to Claim 1,
   characterized in that
   the at least one indium oxo alkoxide used is an oxo alkoxide of the formula M_xO_y(OR)_z where x = 3-20, y = 1-8, z = 3-25, OR = C1-C15-alkoxy, -oxyalkylalkoxy, -aryloxy- or - oxyarylalkoxy group;
   more preferably one of the generic formula M_xO_y(OR)_z where x = 3-15, y = 1-5, z = 10-20, OR = -OCH₃, - OCH₂CH₃, -OCH₂CH₂OCH₃, -OCH(CH₃)₂ or -OC(CH₃)₃.
3. Process according to Claim 2,
   characterized in that
   the at least one indium oxo alkoxide is [In5(µ5-O)(µ3-OⁱPr)₄(µ₂-OⁱPr)₄(OⁱPr)₅].
4. Process according to any one of the preceding claims,
   characterized in that
   the at least one indium oxo alkoxide is the sole metal oxide precursor used in the process.
5. Process according to any one of the preceding claims,
   characterized in that
   the at least one indium oxo alkoxide is present in proportions of 0.1 to 15% by weight, based on the total mass of the anhydrous composition.
6. Process according to any one of the preceding claims,
   characterized in that
   the at least one solvent is an aprotic or weakly protic solvent.
7. Process according to Claim 6,
   characterized in that
   the at least one solvent was selected from the group consisting of methanol, ethanol, isopropanol, tetrahydrofurfuryl alcohol, tert-butanol and toluene.
8. Process according to any one of the preceding claims,
   characterized in that
   the composition has a viscosity of 1 mPa·s to 10 Pa·s.
9. Process according to any one of the preceding claims,
   characterized in that
   the substrate consists of glass, silicon, silicon dioxide, a metal oxide or transition metal oxide, a metal or a polymeric material.
10. Process according to any one of the preceding claims,
    characterized in that
    the aqueous composition is applied to the substrate by means of a printing process, a spraying process, a rotary coating process, a dipping process, or a process selected from the group consisting of meniscus coating, slit coating, slot-die coating and curtain coating.
11. Process according to any one of the preceding claims,
    characterized in that
    the conversion is effected thermally by means of temperatures greater than 150°C.
12. Process according to Claim 11,
    characterized in that
    UV, IR or VIS radiation is injected before, during or after the thermal treatment.

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