EP1169492B1 - Method of producing thin, poorly soluble coatings - Google Patents

Abstract

For making ceramic or oxidic layers (CL/OL) on substrates (S), the method according to the invention therefore provides that following application (I) and drying (II) of a suitable precursor (P) the formed precursor layer (PLD) is gassed (III) with a moist reactant gas (RG) for conversion into a corresponding hydroxide or complex layer (HL) and then thermally treated (IV) for forming a ceramic or oxidic layer (CL/OL). For the alternative production of other chalcogenidic layers of increased material conversion additional gassing is carried out with a reactant gas containing chalcogen hydrogen. Metallic layers may alternatively be made by use of a reducing reactant gas. The methods in accordance with the invention may be used wherever surfaces, even those of shaded structures, must be protected or modified or provided with functional layers, particularly in solar and materials technology.

Description

The invention relates to a method for producing thin, sparingly soluble Coatings on substrates with any morphology. In doing so prefers ceramic and oxide layers, but also metallic as well further chalcogenidic layers can be produced.

According to the definition (cf. "Technical Ceramics" published by B. Thier, Vulkan Verlag, Essen 1988, pages 2 to 25) of the German Ceramic Society, ceramic materials are inorganic, non-metallic, poorly soluble in water and at least 30% crystalline. However, they can be expanded by the group of glasses, glass ceramics and inorganic binders. The ceramic materials are divided into the two large groups "functional ceramics" and "structural ceramics". Structural ceramics consider materials based on oxides and silicates as well as carbides, nitrides, borides and silicides (MoSi ₂ ) of main group elements.

From a systematic point of view, "oxide ceramics" can be understood to mean all ceramic materials which essentially (> 90%) consist of single-phase and single-component metal oxides. In contrast, all materials based on ceramics made from the boron, carbon, nitrogen, silicon and possibly oxygen system are called "non-oxide ceramics". Oxide-ceramic materials are polycrystalline materials made from pure oxides or oxide compounds; they have a high purity and are usually free of glass phase. In addition to the high-melting metal oxides, such as aluminum, zirconium, magnesium, titanium and beryllium oxide, and calcium oxide, magneto-ceramic materials and materials with a high dielectric constant, piezoceramic, can also be included. However, the limitation to the high-melting oxides is common. However, silicon dioxide (SiO ₂ ) is not classified under oxide ceramics. For this reason and also in consideration of other oxides that are suitable but do not belong to the ceramic materials, the invention also relates to the production of both ceramic and oxide layers. In the case of oxide ceramic materials, a distinction is still made between simple oxides and complex oxides. These include, for example, chromite with a coarse structure and perovskite, ferrites and garnets with a fine structure.

Hardly soluble layers have so far been possible, for example, by sputtering or Evaporation using the sol-gel technique, chemical bath deposition or deposition from the vapor phase (Metal Organic Chemical Vapor Deposition MOCVD) can be applied to surfaces. From the essay "Laser annealing of zinc oxide thin film deposited by spray-CVD" by G.K.Bhaumik et al., Elsevier Materials Science and Engineering B52 (1998) 25-31, it is known to use a polycrystalline ZnO film on quartz and silicon substrates by means of the "spray CVD method". The angry one Film can then improve its crystal structure through laser radiation be heated. The addition of undoped ZnO films through Spray pyrolysis with aqueous zinc nitrate solution is from the article "Optical and electrical properties of undoped ZnO films grown by spray pyrolysis of zinc nitrate solution "by S.A. Studenikin et al., J.of Appl.Phys. Vol.83, No.4, Feb. 15, 1998, 2104-11). The focus of this article is on the determination of the relationships between the pyrolysis temperature and the structural, electrical and optical properties of the ZnO film. Different temperatures were obtained by heating the sample substrates, for example in nitrogen at 400 ° C.

During sputtering (cf. for ZnO: "Use of a helicon wave excited plasma of aluminum-doped ZnO thin-film sputtering "by K.Yamaya et al., Appl. Phys.

Lett. 72 (2), January 12, 1998, 235-37) atoms are released from a metal cathode by impacting ions of a gas discharge ("cathode sputtering"). The atomized metal is then deposited on a surface as a uniform layer. With molecular beam epitaxy using oxygen-containing plasma in the presence of a microwave field, single-crystalline ZnO thin layers can be produced on c-planar sapphire (cf. "Plasma assisted molecular beam epitaxy of ZnO on c-plane sapphire: Growth and characterization" by Y.Chen et al ., J.of Appl.Phys., Vol. 84, No.7, October 1, 1998, 3912-18). ZnO films with good quality can also be produced by direct electrode deposition from aqueous solutions at a low process temperature (see: "reparation Of ZnO Films By Electrodepositon From Aqueous Solution" by S.Peulon at al., 13th European Photovoltaic Solar Energy Conference , 23-27 October 1995, Nice, France, 1750-52). In the sol-gel technique (cf. "Micostructure of TiO ₂ and ZnO Films Fabricated by the Sol-Gel-Method" by Y.Ohya et al., J.Am.Ceram.Soc. 79 [4] 825-30 (1996)) solidify colloid solutions present as sol under reaction with water and removal of solvent with the firmly adsorbed solvent residues to form a gel that can be attached to surfaces and dried.

In the process of chemical bath deposition (Chemical Bath Deposition CBD, cf. for ZnO / CdS / CIS / Mo structures: "Effects of Cd-Free Buffer Layer For CuInSe ₂ Thin Solar Cells" by T.Nii et al., First WCPEC; Dec.5-9, 1994; Hawaii, 254-57) a distinction is made between the two different variants "SILAR process" (Successive lonic Layer Adsorption and Reaction) and "Chalcogeno-urea process" in the production of poorly soluble metal chalcogenide layers.

Subject of the publication "CuInS ₂ as an extremely thin absorber in an eta solar cell" by J. Möller et al. (Conference Proceedings of the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, July 6-10, 1998, pages 209-211, XP 002110735 Vienna) is a method based on the above-mentioned methods for the improved production of thin metal chalcogenide layers Specification of different material compositions With this method, a solution of a metal compound is first applied to a substrate so that ions accumulate there. The solvent is then removed from the substrate in a drying process. A chalcogen-containing gas is then brought into contact with the attached ion layer to cause a reaction with the metal ions. With this process, homogeneous metal chalcogenide layers of consistent quality can be easily produced. Such layers are used, for example, as absorber or buffer layers in solar cells. The invention is based on the method described in this article, which can be referred to as the ILGAR method (lonic layer gas reaction), as the closest prior art.

Compared to this known method, the object of the present invention is also to enable the production of further surface layers in other material compositions. The process should still be simple in its sequence, also in ecological and economic terms. Furthermore, an expanded range of applications should be achieved through the materials that can then be used. A qualitatively improved coating with improved utilization of the materials used compared to the known coatings with chalcogenide structure should also be aimed at as a sub-item in this problem area.

I. Aufbringen zumindest einer geeigneten Ausgangssubstanz zum Schichtaufbau auf die Substratoberfläche,

II. Trocknen der gebildeten Ausgangssubstanz-Schicht in einem inerten Gasstrom oder durch Verdunstung,

III. Begasung der getrockneten Ausgangssubstanz-Schicht mit einem feuchten Reaktantgas zur Umwandlung in eine entsprechende Hydroxid- oder Komplex-Schicht,

IV. thermische Behandlung der gebildeten Hydroxid- oder Komplex-Schicht zur Bildung der jeweiligen Endschicht und anschließend
in Abhängigkeit vom Auftreten nicht umgesetzter Ausgangskomponenten oder unerwünschter Nebenprodukte:

V. Spülen zu deren Entfernung und anschließendes Trocknen.

A solution for the production of thin, sparingly soluble coatings on substrates with any morphology is therefore provided as a solution to the stated main problem, with the following process steps to be carried out cyclically depending on the desired layer thickness for the production of ceramic or oxide layers:

I. applying at least one suitable starting substance for the layer structure to the substrate surface,

II. Drying the starting substance layer formed in an inert gas stream or by evaporation,

III. Fumigation of the dried starting substance layer with a moist reactant gas for conversion into a corresponding hydroxide or complex layer,

IV. Thermal treatment of the hydroxide or complex layer formed to form the respective final layer and then
depending on the occurrence of unreacted starting components or undesired by-products:

V. Rinse to remove and then dry.

I. Aufbringen zumindest einer geeigneten Ausgangssubstanz zum Schichtaufbau auf die Substratoberfläche,

II. Trocknen der gebildeten Ausgangssubstanz-Schicht in einem inerten Gasstrom oder durch Verdunstung,

III. Begasung der getrockneten Ausgangssubstanz-Schicht mit einem feuchten, reduzierend wirkend Reaktantgas zur Bildung einer metallischen Schicht und

IV. thermische Behandlung der gebildeten Metall-Schicht zur Entfernung nicht umgesetzter Ausgangskomponenten oder unerwünschter Nebenprodukte.

Another solution to the problem of alternative production of metallic layers is provided by an analogous process with the following process steps:

I. applying at least one suitable starting substance for the layer structure to the substrate surface,

II. Drying the starting substance layer formed in an inert gas stream or by evaporation,

III. Fumigation of the dried starting substance layer with a moist, reducing reactant gas to form a metallic layer and

IV. Thermal treatment of the metal layer formed to remove unreacted starting components or unwanted by-products.

I. Aufbringen zumindest einer geeigneten Ausgangssubstanz zum Schichtaufbau auf die Substratoberfläche,

II. Trocknen der gebildeten Ausgangssubstanz-Schicht in einem inerten Gasstrom oder durch Verdunstung,

III. Begasung der getrockneten Ausgangssubstanz-Schicht mit einem feuchten Reaktantgas zur Umwandlung in eine entsprechende Hydroxid- oder Komplex-Schicht,

IIIa. Begasung der Hydroxid- oder Komplex-Schicht mit einem zusätzlichen, Chalkogenwasserstoffverbindungen enthaltenden Reaktantgaszur Bildung der chalkogenidischen Endschicht und

IV. thermische Behandlung der gebildeten Hydroxid- oder Komplex-Schicht und/oder der chalkogenidischen Endschicht.

A further solution to the problem for the alternative production of other chalcogenide coatings is also provided by an analogous process with the following process steps:

I. applying at least one suitable starting substance for the layer structure to the substrate surface,

II. Drying the starting substance layer formed in an inert gas stream or by evaporation,

III. Fumigation of the dried starting substance layer with a moist reactant gas for conversion into a corresponding hydroxide or complex layer,

IIIa. Fumigation of the hydroxide or complex layer with an additional reactant gas containing chalcogen hydrogen compounds to form the final chalcogenide layer and

IV. Thermal treatment of the hydroxide or complex layer formed and / or the chalcogenide final layer.

Advantageous developments of the inventive method for alternative production of ceramic and oxide, metallic or other chalcogenidic layers are the individual subclaims refer to. Their content is described below in connection with the general explanations of the invention implicitly explained.

With the method according to the invention, films of sparingly soluble can Oxides and generally of such compounds that can be converted a dry solid starting compound with a gaseous reactant form, simply be made. This is crucial the first hydrolysis to achieve a homogeneous Dried starting substance layer by a moist surface Reactant gas to form hydroxides or complexes, for example Amine complexes when using moist ammonia gas as the reactant gas. The reactant gas can also be another, preferentially reacting steam or possibly for water vapor alone act. With the designation "steam" always moist gases, i.e. on Mixture of gaseous water, basic gas and in most cases an inert carrier gas. Moist ammonia gas is generated by simply "bubbling" nitrogen through a wash bottle aqueous ammonia solution. The generation of metallic layers by Fumigation accordingly requires treatment with reducing effects Gases.

By carrying out a thermal after fumigation Treatment is then by elimination of water - and also with complexes by ligand elimination - the desired ceramic or oxidic Surface layers or other end layers created. The thermal Treatment of the hydroxide or complex layers can be done in a separate Process step after gassing with the reactant gas, for example by heating the layers in an oven. But it can also during the process of gassing by increasing the process temperature be effected. By applying a higher temperature the optional cleaning step may omitted, because this already undesirable Substances can be removed from the film. In particular Cases can even be brought about without using a targeted one Temperature increase immediately form an oxide. In the manufacture of chalcogenide layers, the thermal treatment can affect both extend necessary fumigations. The thermal treatment for education The respective final layer can also be removed in individual cases be understood by disruptive components. In the preparation of metallic layers, this is used to create unwanted by-products to remove.

As a rule, the starting substance is a metal compound, for example metal halides such as ZnCl ₂ or AlCl ₃ , of the metal whose oxide, ceramic (for example ZnO, Al ₂ O ₃ ) or metal is desired as the end product for the coating. The correspondingly dissolved metal salt is then applied to the substrate, dried (if necessary up to a defined residual moisture) and reacted with gaseous reactants.

Layers produced with the method according to the invention can Solar technology used in the manufacture of many components of solar cells Find. In materials technology, a coating can be used by everyone possible smooth, rough and porous substrates. Still allowed the process through the use of starting material mixtures or different starting substances and their alternating use, also the production of homogeneously doped layers and mixed layers and the generation of multilayers. The thin, heavy ones can be used soluble coatings especially wherever there is an extended Surface protection is required. This can be purely mechanical and chemical protection of the surface, but also about influencing their physical and chemical surface properties, such as for example conductivity, reflection and absorption behavior or Catalysis or chemisorption.

• niedrige Kosten, da moderate, unkritische Prozessparameter, kein Vakuum
• Unempfindlichkeit gegen Variation der Prozessparameter
• einfache Schichtdickeneinstellung durch Anzahl der zu durchlaufenden Zyklen
• hohe Reproduzierbarkeit hergestellter Schichten
• homogene Beschichtung von Substraten mit beliebiger Oberfläche
• Beschichtung auch von abgeschatteten inneren Oberflächen
• vollständige Ausnutzung des Ausgangsmaterials und
• einfache Automatisierbarkeit.

Further advantages over known methods are also to be mentioned:

• low costs because of moderate, uncritical process parameters, no vacuum
• Insensitivity to variation of the process parameters
• Simple layer thickness setting through the number of cycles to be run
• high reproducibility of manufactured layers
• homogeneous coating of substrates with any surface
• Coating also of shaded inner surfaces
• full utilization of the raw material and
• easy automation.

Starting from the crystal structure of a starting compound, the Chalcogenization step for the formation of sulfides, selenides or tellurides in that described in the older German application DE 198 31 214 ILGAR processes also changed the crystal structure in certain cases.

However, this requires a conversion energy which is necessary for the implementation of the ILGAR process at room temperature only available to a limited extent is. There, this leads to a reduced turnover of the starting material End product or at a slower reaction rate, so that Residues of the starting compound in the metal chalcogenide thin film produced remain stored and only removed by additional rinsing steps can be. With a decrease in film quality and an increased Deposition time can therefore be expected with the ILGAR process.

In contrast, an improvement can be achieved in the methods according to the invention. For this purpose, for the alternative production of other chalcogenide coatings, it is provided that after conversion of the dried starting substance layer into a corresponding hydroxide or complex layer, it is gassed with an additional reactant gas containing chalcogen hydrogen compounds. This reaction path via the formation of a metal hydroxide and integration of the heating process enables significantly higher sales to be achieved, as a result of which fewer residues of the starting material occur in the end product. For the chalcogenides based on sulfur, selenium or tellurium, moist ammonia gas (NH ₃ ) can also be used as an additional reactant gas. The lower activation energy through this intermediate step can be seen as a possible explanation for this effect. In addition, many metal hydroxides do not have a crystal structure, but are amorphous. This makes them less compact and allows the reactant gas to penetrate better into the chalcogenizing layer.

The increased energy requirement during the crystal transformation can in the sense of well-known tempering of course also directly through an increased Process temperature provided during the chalcogenization step become. In this case, the substrate can already be illuminated with a Halogen lamp is sufficient. An implementation of the chalcogenization step inside a furnace is also possible. The measures mentioned lead to purer and higher quality thin films with a simultaneous reduction in quantity of the chalcogen-containing reactant gas to be used and reduce the deposition time, as on rinsing steps, the time costs and reduce the quality of the end product can be. When the hydroxide reaction is introduced there are no starting material residues more to expect, the by-products that occur here are relatively volatile and with a suitable temperature selection in the last Process step removable. If the crystallite size of the final product is below Maintaining high sales, however, remain small, the temperature must only be increased as little as necessary so that in such a case the Combination of the hydroxide step with a slightly increased one Process temperature makes sense. Nano-crystallites are getting increasingly Importance in research and technology because they lead to quantum-size effects in Lead thin film, which affect the optical and electrical properties of the material.

Figur 1

den erfindungsgemäßen Prozessablauf bei der Herstellung einer keramischen Beschichtung in einer geeigneten Anordnung und

Figur 2

den erfindungsgemäßen Prozessablauf bei der Herstellung einer chalkogenidischen Beschichtung.

Forms of embodiment of the invention are explained in more detail below with reference to the schematic figures. It shows:

Figure 1

the process flow according to the invention in the production of a ceramic coating in a suitable arrangement and

Figure 2

the process flow according to the invention in the production of a chalcogenide coating.

FIG. 1 shows the production of a zinc oxide layer on an amorphous substrate S , which is clamped in a substrate holder SH that can be moved in three-dimensional space. The substrate holder SH has a cover C to cover the individual baths. In a first method step I , the substrate S is immersed in a suitable starting substance P (precursor). In the selected exemplary embodiment, this is a solution bath LB with the dissolved metal compound zinc chloride ZnCl ₂ . After pulling out, there is a starting substance layer PL, here ZnCl ₂ , on the substrate surface.

The ZnCl ₂ layer is first dried in a vessel V in a second process step II , for example by introducing a gas stream GS. This can be inert nitrogen. In a third process step III , the dried starting substance layer PLD is again gassed in the vessel V with a moist reactant gas RG, here moist ammonia gas. The moist ammonia gas is produced by simply introducing nitrogen N ₂ into a wash bottle B in which there are concentrated ammonia solution NH ₄ OH and water H ₂ O. After gassing, a hydroxide layer HL has formed on the substrate S , in the exemplary embodiment zinc hydroxide Zn (OH) ₂ . Different vessels V can also be used for drying and gassing.

In a fourth method step IV , the substrate S provided with the zinc hydroxide Zn (OH) _{2 is} introduced into an oven H. In this process step IV, the Zn (OH) ₂ is thermally converted into zinc oxide ZnO by elimination of water by supplying energy. This oxide or ceramic layer OL / CL covers the entire accessible surface of the substrate, including the inner surface, safely and exerts its functionality there. A subsequent rinsing and drying process step is optional and not shown here. Depending on the desired layer thickness, the process steps mentioned can be cycled through several times.

FIG. 2 schematically shows the process sequence according to the invention for producing other chalcogenide coatings using the example of cadmium sulfide CdS. Process steps and reference numerals which are not further explained here can be found in the description of FIG. 1. After carrying out process steps I to III with adsorption P (CdCl ₂ ), drying PLD (CdCl ₂ ), gassing (N ₂ + NH ₃ ) and hydroxide formation HL (Cd (OH) ₂ ), a further process step IIIa follows which the hydroxide layer HL (Cd (OH) ₂ ) formed is brought into contact with an additional reactant gas CRG (here hydrogen sulfide H ₂ S) containing chalcogen hydrogen compounds. This process step IIIa, the chalcogenization step, produces a chalcogenide coating CHL in the form of cadmium sulfide (CdS) on the substrate S. During the execution of process steps II-IIIa , the process temperature TP is increased, for example by carrying out the process steps in a muffle furnace H, in order to improve the material conversion. The thermal treatment in process step IV therefore extends to both fumigations III, IIIa.

LIST OF REFERENCE NUMBERS

B

bubbler

C

cover

CHL

chalcogenide layer

CL

ceramic layer

CRG

Reactant gas containing chalcogen hydrogen compounds

H

oven

HL

hydroxide

LB

solution bath

OIL

oxide layer

P

starting substance

PL

Starting material layer

PLD

dried starting substance layer

RG

moist reactant gas

S

substratum

SH

substrate holder

TP

process temperature

V

vessel

Claims (9)

1. Process for the preparation of thin, sparingly soluble coatings on substrates (S) having any desired morphology, which process comprises the following process steps for the preparation of ceramic or oxidic layers (CL/OL), which steps are to be carried out cyclically in dependence on the desired layer thickness:

   I. application of at least one suitable precursor (P) for layer formation to the substrate surface (S),

   II. drying of the resulting precursor layer (PL) in an inert gas stream (GS) or by evaporation,

   III. gassing of the dried precursor layer (PLD) with a moist reactant gas (RG) in order to convert it into a corresponding hydroxide or complex layer (HL),

   IV. thermal treatment of the resulting hydroxide or complex layer (HL) in order to form the respective final layer (CL/OL), and then
   in dependence on the occurrence of unreacted precursor components or undesired by-products:

   V. rinsing for the removal thereof, and subsequent drying.
2. Process for the preparation of thin, sparingly soluble coatings on substrates (S) having any desired morphology, which process comprises the following process steps for the preparation of metallic layers, which steps are to be carried out cyclically in dependence on the desired layer thickness:

   I. application of at least one suitable precursor (P) for layer formation to the substrate surface (S),

   II. drying of the resulting precursor layer (PL) in an inert gas stream (GS) or by evaporation,

   III. gassing of the dried precursor layer (PLD) with a moist reactant gas (RG) having a reducing action, in order to form a metallic layer, and

   IV. thermal treatment of the resulting metal layer in order to remove unreacted precursor components or undesired by-products.
3. Process for the preparation of thin, sparingly soluble coatings on substrates (S) having any desired morphology, which process comprises the following process steps for the preparation of other chalcogenidic coatings (CHL), which steps are to be carried out cyclically in dependence on the desired layer thickness:

   I. application of at least one suitable precursor (P) for layer formation to the substrate surface (S),

   II. drying of the resulting precursor layer (PL) in an inert gas stream (GS) or by evaporation,

   III. gassing of the dried precursor layer (PLD) with a moist reactant gas (RG) in order to convert it into a corresponding hydroxide or complex layer (HL),

   IIIa. gassing of the hydroxide or complex layer (HL) with an additional reactant gas containing hydrogen chalcogenide compounds (CRG) in order to form the chalcogenidic final layer (CHL), and

   IV. thermal treatment of the resulting hydroxide or complex layer (HL) and/or of the chalcogenidic final layer (CHL).
4. Process according to any one of claims 1 to 3,
   characterised in that
   the thermal treatment (IV) is carried out either by separately heating the layer in question after its formation or by increasing the process temperature (TP) during its formation.
5. Process according to any one of claims 1 to 4,
   characterised in that
   the precursor (P), of which there is at least one, is in the form of a solution with a preferably readily volatile solvent, and the solution is applied to the substrate (S) by immersion (LB) or spraying.
6. Process according to any one of claims 1 to 5,
   characterised in that
   the precursor (P) is a salt.
7. Process according to any one of claims 1 to 6,
   characterised in that
   the moist reactant gas (RG) is a gas that preferably reacts basic, or is gaseous water.
8. Process according to any one of claims 1 to 7,
   characterised in that
   the precursor (P) is a mixture of various compounds.
9. Process according to any one of claims 1 to 8,
   characterised in that
   different precursors (P) are used in the individual process cycles, especially in recurring sequence.

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