WO2004040034A2

WO2004040034A2 - Method of preparing a solution and application of this solution to prepare functional oxide layers

Info

Publication number: WO2004040034A2
Application number: PCT/IB2003/004434
Authority: WO
Inventors: Wilhelmus C. Keur; Henricus A. M. Van Hal; Danielle Beelen; Mareike K. Klee; Joerg Meyer; Hans-Wolfgang Brand; Gerrit J. W. Huiskamp
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2002-10-31
Filing date: 2003-10-06
Publication date: 2004-05-13
Also published as: WO2004040034A3; AU2003264795A1

Abstract

In the method of preparation of the Pb-Zr-Ti-containing solutions the lead is added to the Zr- and Ti-containing solution in powdery form. This has the advantage that it takes less time, and that nevertheless a stable solution is obtained. Preferably use is made of Zr- and Ti-butoxides and of lead acetate tri-hydrate. A very suitable solvent is 1-methoxy-2-propanol. The solution can be used for the manufacture of layers on a substrate with a high dielectric constant.

Description

Method of preparing a solution and application of this solution to prepare functional oxide layers

The invention relates to a method of preparing a lead- and zirconium- and/or titanium-containing solution, wherein an alkoxy alcohol is used as the solvent.

The invention further relates to the use of the lead- and zirconium- and/or titanium-containing solution.

The invention further relates to a method of manufacturing an electronic appliance, which contains a component equipped with a dielectric layer obtained by the application of a solution to a substrate and subsequent heat treatment.

A solution of this kind and a method of this kind are known from patent application EP-A 676384. Following coating and subsequent heat treatment, the solutions are converted into perovskites. These perovskites are complex oxides, which contain lead and at least titanium or zirconium, but also combinations of titanium and zirconium or combinations of magnesium and niobium and further dopants. Examples are lead titanate, lead zirconate titanate, lead lanthanum zirconate titanate, lead lanthanum titanate, lead zirconate, lead lanthanum zirconate, lead magnesium niobate, lead magnesium niobate-lead titanate.

The known solution is produced by combining a solution of lead acetate in methoxyethanol and a solution of titanium tetra-n-butylate and zirconium tetra-n-butylate in methoxyethanol. If required, the solution obtained may be diluted. One of the disadvantages of the known method is that the solution is difficult to produce in large quantities.

It is therefore the object of the present invention to provide a method that can also be executed in larger quantities.

It is the second object of the present invention to provide a solution with improved properties, and the third object is to use the solution to produce oxidic layers on substrates, and to use these in electronic appliances. The first object is achieved in that, firstly, a solution of zirconium and/or titanium alcoholate is prepared in a solvent, after which, in a second step, a lead salt is dissolved in this solution, wherein the solvent is selected from the group of mono-etherized divalent and polyvalent alcohols. Surprisingly, it is found that the lead is directly soluble in the solution of zirconium and/or titanium alcoholate, and that the solution thereby obtained exhibits a good stability. It is further found that solutions of this kind can easily be produced in larger quantities. As mentioned in the embodiment examples, a kilogram of solution can easily be produced in one batch. This can be compared with the 30 to 50 g solution that can be obtained with the known method. The method in accordance with the invention further comprises a simplification of the preparation method, since the separate step of dissolution of the lead salt in a solvent is dispensed with. This makes the method as a whole simpler and also faster. However, the advantage is not limited solely to the shorter time involved, since it is also simpler to produce different mixtures. As mentioned in example 1 of the patent application EP676384, it is necessary in the case of the normal preparation to wait for 24 hours after the solutions containing the lead and titanium have been homogeneously mixed before passing through a filter. A waiting time of this kind is not necessary in the case of the present invention. In addition, all steps of the method in accordance with the invention can be performed at ambient temperature. A further advantage of the method in accordance with the invention is that it is possible to avoid a toxic solvent such as ethylene glycol monomethylether (= 1 - methoxy ethanol) or ethylene glycol monoethylether, which can only be used in an industrial environment under stringent safety precautions, if at all. Instead, l-methyoxy-2-propanol, for example, can be used. This solvent is non-toxic. One other advantage of the method in accordance with the invention is that a higher concentration of the components of the solution can be achieved. Instead of a concentration of 0.1 - 0.4 mol per liter, a concentration of approximately 0.6 - 0.7 mol per liter has been achieved with the method of the invention.

A further method of preparing a lead-, zirconium- and titanium-containing solution is known from JP-A 11-079747. With this method, however, the lead salt is firstly dissolved, after which the solution has to be rendered anhydrous by distillation (at 140°C under reflux). This is a complicated, time-consuming method.

In a first embodiment, titanium and or zirconium as titanium and/or zirconium alcoholates from the group of butylates and isopropylates are used. It was found that butylates and isopropylates contribute to the stability of the solution. In addition, the butylates - i.e. n-butylates, t-butylates and sec-butylates - and the isopropylates have the great advantage that they are scarcely water susceptible, if at all. It is therefore unnecessary to work in a dry atmosphere. In a second embodiment, the solution produced in the first step contains titanium alcoholates and zirconium alcoholates. This gives rise to a lead zirconium titanate, possibly doped, which composite materials have favorable properties for application in ter alia memories and capacitors.

In a preferred embodiment, dopants are dissolved in the zirconium- and/or titanium-containing solution before the lead is added. Examples are doping with lanthanum, niobium, scandium, tantalum, magnesium or iron. These dopants may be added as salts of carbonic acids, e.g. acetates, or as β-diketonates, e.g. acetyl acetonates. It is also possible that these are already mixed with either the titanium- or zirconium-containing solution, so the zirconium or titanium alcoholate is then added, either as a solution or in the pure form. It is preferred if n-butylates are used for the titanium- and zirconium butylates, since they are relatively hydrolysis-resistant as compared with other alcoholates, and therefore contribute to the stability of the solutions.

Especially good results are obtained with lead acetate tri-hydrate as the lead component. This lead salt can be introduced without any pretreatment. The usual pretreatment, with many procedural steps, serves to dehydrate the lead salt. The fact that a pretreatment of this kind is not necessary with the method in accordance with the invention, yet a stable solution is nevertheless obtained is very surprising. If required, different lead salts may also be used, e.g. those of different carbonic acids.

The second object is achieved in that, in accordance with the invention, 1- methoxy-2-propanol is used as the solvent for the lead-, zirconium- and titanium-containing solution. This solution is stable and yields dense layers with outstanding electrical properties. A hydrolysis solution of methoxy propanol/H₂0/HNO₃ can be added to the solution in accordance with the invention for prehydrolysis. In addition, as solvents, lead-zirconium- titanium-containing solutions with l-methoxy-2-propanol have a somewhat higher viscosity as compared with solutions with methoxy ethanol. This brings the advantage that thicker layers can be deposited and that therefore fewer coating stages are needed for a given layer thickness. Since layer thicknesses of 0.1 to 1.0 μm are desired for many applications, and since, in principle, a heat treatment is needed after every coating stage, this gives rise to a clear advantage. It is especially advantageous if there is an excess of lead in the solution. In order to deposit dielectric layers on substrates with this solution, the solution is heated, wherein the solvent is evaporated and the lead-zirconium-titanium-containing substances are converted to an oxide layer through decomposition. A loss of lead thereby occurs, leading to the development of undesired secondary phases. An excess of lead is used in the solution for the crystallization of single-phase layers with high dielectric constants.

The achievement of the third object of the invention is described below. Suitable substrates such as silicon wafers or glass substrates are coated with a thin film of precursor solution by spraying, dip-coating, spin-on or by other suitable methods. The layer is subsequently subjected to heat treatment. This heat treatment preferably takes place at 500 to 800°C. The temperature depends on the composition of the solution. The layer is preferably applied as multiple partial layers, which are subjected to heat treatment successively. One single layer may occasionally suffice for thin layers. The partial layers may have slightly different compositions, such as PbZr_xTi- _-xO₃, with 0.53 < x < 1 and (Pb*. -,_5yLa_y)-Zr_xTi_1-xO₃ with 0.001 < y < 0.20 and 0 < x < 1 which will be also referred to as PZT and PLZT respectively.

The layers are suitable for a plurality of applications, e.g. for capacitors, integrated capacitors, capacitors for dynamic write-read memories with random access, ferroelectric non-volatile memories, actuators, integrated actuators, ultrasonic transducers, sensors or integrated sensors. One very favorable application is known from WO-A 02/075780. In this application, the layer is used as a dielectric of a capacitor on a substrate, that further comprises at least one semiconductor component, and a diode in particular. The combination of a diode and a capacitor, and in addition generally a resistor, is very suitable for use as an ESD protection with filtering, h order to be suitable therefor, there is not only needed a capacitor with a sufficiently high capacitive density, for instance of 20nF/mm² or more.

Moreover, a good breakdown voltage is required, particulary of at least 50V, and preferably the temperature dependence of the capacity fulfills the X7R-standard. These requirements are met by the capacitor obtainable with the method of the present invention.

In a preferred embodiment, the overgrown oxidic layer is etched in a wet- chemical etching process by applying firstly a first aqueous etching solution with HF and HC1 and then a second aqueous etching solution with HNO₃, in which first etching solution the weight ratio between HF and HC1 is between 0.15:1 and 1.5:1, and the concentration of HC1 is between 1 and 10 percent by weight. The etching of the sintered perovskite layers is known er se from US 4,759,823. The preferred first etching solution from this patent is prepared by diluting a 70% solution of HC1 and an aqueous solution of 7.8% HF and 33.6% NFL-F in a ratio of 2:1 with 50 - 70 percent by volume of water. The etching time for a layer of 0.45 μm is approximately 8 to 12 seconds. The etching process with this solution is, however, difficult to control. The different constituents of the layer are etched at different rates, and the solubility of the metal ions is not optimal. Lead-containing precipitates, which are subsequently virtually insoluble, are deposited. With longer etching times, parts of the layer below the etching mask are also etched (underetching), which also happens with higher HC1 concentrations. Unexpectedly, it has been found that a first etching solution with a lower concentration and proportionately more HF yields good results, at least with the solutions in accordance with the invention in particular. With etching times of approximately 60 seconds, a hole occurs down to the substrate, always without underetching or sediments. The ratio between HF and HC1 preferably lies between 0.5:1 and 1.5:1. The acids are diluted with 60 - 90 % by volume, preferably 75 - 90 %, water. If strongly diluted, it is useful if the etching solution is provided with further acids, e.g. HNO or acetic acid.

It is suspected that the layer structure plays a role here. The PLZT layer from US 4,759,823 is produced with a solution prepared by mixing two solutions - one solution with butanol as the solvent and the other lead(TV)acetate in acetic acid. During mixing, hydrolysis of the metal alcoholates takes place with gel formation. A dry or inert atmosphere is necessary here in order that the oxides are not formed, as mentioned, in 9:52 - 55. In the solution of the invention, however, the hydrolysis is less problematic. The hydrolysis and condensation processes therefore take place mainly during the coating and thermal treatment of the layers, and provide dense layers with a columnar layer structure. This influences the etching process.

The invention will be further described with reference to examples of embodiments shown in the drawing, to which, however, the invention is not restricted. Fig. 1 shows a schematic cross-section through a semiconductive substrate with a diode, a capacitor and a resistor. An electronic appliance may be, for instance, an appliance for electronic data processing, such as a computer, laptop or a PDA (Personal Digital Assistant). It may also be a mobile data transmission appliance, such as a mobile radio device. Appliances of this kind contain many components constructed from active elements, such as diodes and transistors, and passive elements, such as capacitors, resistors and coils. The solution in accordance with the invention can be advantageously used to produce components with active and/or passive elements of this kind. One especially favorable embodiment is a module with active and passive components. This could concern, for example, modules with capacitors as storage elements and transistors as control elements. In order to produce an electronic module as shown in Fig. 1, a semiconductive substrate 1 was provided with first semiconductor areas 2 and second semiconductor areas 3. The semiconductive substrate 1 made of Si is equipped with a dopant B of a first doping type with a first doping density nl. Semiconductive substrate 1 is equipped with first semiconductor areas 2, which are equipped with Si with B as the dopant of the first doping type with a second doping density n2. Doping density nl is greater than doping density n2. In each first semiconductor area 2 is located a second, smaller semiconductor area 3, which is equipped with Si with P as the dopant of a second doping type with a third doping density n3. Applied to semiconductive substrate 1 is an insulating layer 4 of SiO or Si₃N₃ or a combination of SiO₂ and Si₃N₄. On insulating layer 4 is located a barrier layer 5, which may be, for example, TiO₂₎ Al₂O₃, MgO, Si₃N₄ or a combination of Si₃N₄ and TiO₂, or a combination of SiO₂, Si N₄ and TiO or a combination of Si₃N₄ and Al₂O . Applied to barrier layer 5 is a structured, first electrically conductive layer 6, which may be, for example, Pt with a layer thickness of 50 nm to 1 μm, and is structured in such a way that it forms first electrodes of the capacitors to be formed. The first dielectric layer 7, made of PbZr_xTi_1-x0₃ with a lanthanum doping, is applied over this entire structure by means of the solution of the invention, the production of which is described in the embodiment examples. Openings in the first dielectric layer 7 to the first electric layer 6 were etched by a wet-chemical etching process. In addition, an opening to each second semiconductor area 3 was etched. Furthermore, openings to a resistor layer 18 of poly Si and to the semiconductive substrate were etched. The openings were filled with an electrically conductive material, e.g. Al, Al doped with Cu and/or Si or a combination of layers comprising e.g. TiN or TiW or TiW(N), in this case with Al. Onto the first dielectric layer was applied a second electrically conductive layer 10, which comprises a combination of layers comprising e.g. TiN or TiW or TiW(N) and e.g. Al or Al doped with Cu or Al doped with Si or Cu. hi this example, the second layer 10 comprises Al, but may also comprise a different material, e.g. Al doped with Cu and/or Si or Cu, or be composed of multiple layers. This electrically conductive layer design has been structured in such a way that, on the one hand, as the second electrically conductive layer 10, it forms the second electrodes of the capacitors, and, on the other, in the area of the openings it acts as first power supply 8, as second power supply 9, as third power supply 19 and as the connecting line between the individual components of the circuit configuration. On the entire structure is located a protective layer 11 of Si₃N . Located in protective layer 11 are openings that define the input 12 and the output 13 and the ground contact 15 of the circuit configuration. Bump contacts are grown into the openings for the electrical contacting of input 12, output 13 and ground contact 15. Embodiment example 1

0.123 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.202 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. Subsequently, 0.346 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/zirconium/titanium solution is 1.15/0.55/0.45. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500

- 750°C. The layer exhibits the desired electrical properties, that means a relative dielectric constant in the range between 500 and 750 and a breakdown voltage of at least 50 V.

Embodiment example 2

0.129 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.195 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. Subsequently, 0.332 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/zirconium/titanium solution is 1.10/0.53/0.47. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500

- 750°C. The layer exhibits the desired electrical properties. Embodiment example 3

0.129 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.195 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. Subsequently, 0.346 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead zirconium/titanium solution is 1.15/0.53/0.47. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties. Embodiment example 4

0.129 kg titanium-tetra-n-butylate is dissolved in 1.1 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.193 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 7.0 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.338 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter and then diluted with l-methoxy-2- propanol, wherein a molarity of 0.43 M is obtained. The molar ratio of the lead/lanthanum/zirconium/titanium solution is 1.12/0.02/0.53/0.47. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties. Embodiment example 5

0.129 kg titanium-tetra-n-butylate is dissolved in 1.1 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.193 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 17.5 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.32 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter and then diluted with l-methoxy-2- propanol, wherein a molarity of 0.43 M is obtained. The molar ratio of the lead lanthanum zirconium/titanium solution is 1.06/0.05/0.53/0.47. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties. Embodiment example 6 0.129 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.195 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 17.5 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.322 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/lanthanum/zirconium/titanium solution is 1.06/0.05/0.53/0.47. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties.

Embodiment example 7

0.178 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.128 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. Subsequently, 0.332 kg lead acetate tri-hydrate is dissolved in the Ti-Zr-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/zirconium/titanium solution is 1.10/0.35/0.65. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties.

Embodiment example 8

0.123 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.20 kg zirconium tetra-n-butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 3.511 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.342 kg lead acetate tri- hydrate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/lanthanum/zirconium titanium solution is 1.13/0.01/0.55/0.45. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties.

Embodiment example 9

0.123 kg titanium-tetra-n-butylate is dissolved in 1.3 liters l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.20 kg zirconium tetra-n-butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 3.5 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.327 kg lead acetate tri- hydrate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/lanthanum zirconium/titanium solution is 1.08/0.01/0.55/0.45. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties. Embodiment example 10

0.129 kg titanium-tetra-n-butylate is dissolved in 0.94 kg l-methoxy-2- propanol at ambient temperature. Added to the solution is 0.194 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. Subsequently, 0.297 kg anhydrous lead acetate is dissolved in the Ti-Zr-containing solution at ambient temperature. A solution comprising 0.390 kg l-methoxy-2-propanol, 11.2 ml 65% HNO3 and 21.8 g H2O is then added for partial hydrolysis. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/zirconium/titanium solution is 1.15/0.53/0.47. The solution thus obtained is only partially hydrolyzed. If desired, additional water may be added to the solution. This may be required for adjusting the viscosity of the solution. It is also possible for the lead acetate to be added partly as anhydrous lead acetate and partly as lead acetate tri- hydrate.

The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties. Embodiment example 11

0.11 kg titanium-tetra-n-butylate is dissolved in 0.33 kg ethylene glycol monomethylether at ambient temperature. Added to the solution is 0.17 kg zirconium tetra-n- butylate, which is homogeneously dissolved in the solution. An La dopant is then added as lanthanum acetyl acetonate in a quantity of approximately 17 g to the Ti/Zr-containing solution and dissolved in the solution at ambient temperature. Subsequently, 0.23 kg anhydrous lead acetate is dissolved in the Ti-Zr-La-containing solution at ambient temperature. A solution comprising 0.14 kg ethylene glycol monomethylether, 14 g 65% HNO3 and 18 g H2O is then added. The clear solution is filtered through a 0.2 μm filter. The molar ratio of the lead/lanthanum/zirconium/titanium solution is 1.05/0.05/0.53/0.47. The solution thus obtained is only partially hydrolyzed. If desired, water may be added to the solution. This may be required for adjusting the viscosity of the solution. It is also possible for the lead acetate to be added partly as anhydrous lead acetate and partly as lead acetate tri- hydrate. The solution is applied as a layer, as described with reference to Fig. 1. It is then subjected to heat treatment at approximately 500 - 750°C. The layer exhibits the desired electrical properties.

Embodiment example 12 A PLZT layer, which was obtained in accordance with example 4 in a thickness of approximately 0.3 μm and provided with a conventional photolithographic, ready structured mask, was etched, firstly with a first etching solution and then with a second etching solution. The first etching solution was prepared from 10% by weight HF, 37% by weight HC1 and water in a ratio of 5:2:30. The second etching solution was a 3% HNO₃ solution. The Si substrate with the PLZT layer was immersed for 60 seconds in a bath of the first etching solution. It was then cleaned and immersed for 120 seconds in a bath of the second etching solution, and again cleaned with water. During the etching, the Si substrate with the PLZT layer was moved. The cleaning stages lasted approximately 2 seconds. The etching process was not repeated but nevertheless yielded a hole that extended as far as the substrate. Neither underetching nor sediments were perceived on the substrate. The requirements were therewith met.

Embodiment example 13

A PLZT layer, which was obtained in accordance with example 4 in a thickness of approximately 0.3 μm and provided with a conventional photolithographic, ready structured mask, was etched, firstly with a first etching solution and then with a second etching solution. The first etching solution was prepared from buffered oxide etch (HF/NH₄F 1 :7, 5.5% by weight HF), 37% by weight HC1, 65% HNO₃ and water in a ratio of 3:3:3:75. The second etching solution was a 3% by weight HNO₃ solution. The Si substrate with the PLZT layer was immersed for 60 seconds in a bath of the first etching solution. It was then cleaned and immersed for 120 seconds in a bath of the second etching solution, and again cleaned with cleaning fluid, in this case water. The cleaning stages lasted approximately 1 - 10 seconds. The results fulfilled the requirements. Embodiment example 14

A PLZT layer, which was obtained in accordance with example 4 in a thickness of approximately 0.3 μm and provided with a conventional photolithographic, ready structured mask, was etched, firstly with a first etching solution and then with a second etching solution. The first etching solution was prepared from buffered oxide etch (HF/NH₄F 1 :7, 5.5% by weight HF), 37% by weight HC1 and water in a ratio of 3:3:80. The second etching solution was a 3% by weight HN0₃ solution. The Si substrate with the PLZT layer was immersed for 60 seconds in a bath of the first etching solution. It was then cleaned and immersed for 120 seconds in a bath of the second etching solution, and again cleaned with cleaning fluid, in this case water. The cleaning stages lasted approximately 1 - 10 seconds. The etching process did not yield a complete etching result. Embodiment example 15

A PLZT layer, which was obtained in accordance with example 4 in a thickness of approximately 0.3 μm and provided with a conventional photolithographic, ready structured mask, was etched, firstly with a first etching solution and then with a second etching solution. The first etching solution was prepared from buffered oxide etch (HF/NH₄F 1:7, 5.5% by weight HF), 37% by weight HCl and water in a ratio of 1 :2:6. The second etching solution was a 3% by weight HN0₃ solution. The Si substrate with the PLZT layer was immersed for 60 seconds in a bath of the first etching solution. It was then cleaned and immersed for 120 seconds in a bath of the second etching solution, and again cleaned with cleaning fluid, in this case water. The cleaning stages lasted approximately 1 - 10 seconds. The results fulfilled the requirements.

Claims

CLAIMS:

1. A method of preparing a lead- and zirconium- and/or titanium-containing solution, wherein the zirconium and or titanium are used as zirconium- and titanium alcoholates, and wherein an alkoxy alcohol is used as the solvent, characterized in that, in a first step, a solution of zirconium- and/or titanium alcoholate is prepared in the appropriate solvent, after which, in a second step, a lead salt is dissolved in this solution, wherein the solvent is selected from the group of mono-etherized divalent and polyvalent alcohols.

2. A method as claimed in claim 1, characterized in that the titanium and/or zirconium alcoholates have been selected from the group of butylates and isopropylates.

3. A method as claimed in claim 1, characterized in that the solution produced in the first step contains titanium alcoholates and zirconium alcoholates from the group of butylates and isopropylates.

4. A method as claimed in claim 1 or claim 3, characterized in that dopants are dissolved in the zirconium- and or titanium-containing solution before the lead is added.

5. A method as claimed in claim 1, characterized in that lead acetate tri-hydrate is used as the lead salt.

6. A method as claimed in claim 1, characterized in that l-methoxy-2-propanol is used as the solvent.

7. A method as claimed in claim 4, characterized in that a dopant or a combination of dopants from the group of lanthanum, niobium, scandium, tantalum, magnesium and iron in the form of salts of carbonic acids, β-diketonates or alcoholates is used.

8. A lead-, zirconium- and/or titanium-containing solution with l-methoxy-2- propanol as the solvent.

9. A solution as claimed in claim 8, characterized in that butylates are used as the raw materials.

10. A solution as claimed in claim 8, characterized in that the solution contains a dopant or combination of dopants from the group of lanthanum, niobium, scandium, tantalum, magnesium and iron.

11. A solution as claimed in claim 8, characterized in that an excess of lead is used.

12. A use of the solution as claimed in any one of claims 7 to 11 to produce a layer on a substrate.

13. A method of manufacturing an electronic appliance with an electronic component equipped with at least one oxidic layer obtained by the application of a solution to a substrate and subsequent heat treatment, characterized in that the solution as claimed in any one of claims 7 to 11 or the solution obtained by the method as claimed in any one of claims 1 to 7 is used.

14. A method as claimed in claim 13, characterized in that the overgrown oxidic layer is etched in a wet-chemical etching process by applying firstly a first aqueous etching solution with HF and HCl and then a second aqueous etching solution with HNO₃, in which first etching solution the weight ratio between HF and HCl is between 0.15:1 and 1.5:1, and the concentration of HCl is between 1 and 10 percent by weight.

15. An etching solution for layers from the PLZT group containing HCl and HF, in which etching solution the weight ratio between HF and HCl is between 0.15:1 and 1.5:1, and the concentration of HCl is between 1 and 10 percent by weight.