KR20070101196A - Eching agent for ti-based film and method of eching by use of same - Google Patents

Abstract

An etching agent for Ti-based films and an etching method using the same are provided to prevent the generation of damage on a resist surface or an under layer by removing etching residual and to improve process margin by applying a wet etching method. An etching method of Ti-based films on a semiconductor substrate is executed by using a solution having hydrogen peroxide and a chelate agent selected from polyphosphonic acids. The chelate agent is selected from a group constituted with alkane polyphosphonic acids capable of having hydroxyl and polyphosphonic acids including nitrogen with 1 to 3 of nitrogen atom and 2 to 5 of phosphon of molecules. The chelate agent is alkane polyphosphonic acids capable of having hydroxyl.

Description

Etching agent and method for etching Ti-based film {ECHING AGENT FOR Ti-BASED FILM AND METHOD OF ECHING BY USE OF SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to processing of semiconductor substrates, and mainly relates to etching methods and etching agents for Ti-based films such as Ti films and TiW alloy films.

Conventionally, the RIE (reactive ion etching) method which can perform anisotropic etching was mainly used for etching Ti type films, such as Ti and TiW. In the RIE method, in particular, the parallel plate type RIE method, a halogen compound such as Cl ₂ , BCl ₃ , HBr or the like is usually used as a gas for etching, and a general positive type resist is used as a mask to protect the pattern, and a pressure of 50 mTorr (6.7 Pa), RF-POWER 250 W, dry etching is performed under conditions of a substrate temperature of 60 ° C.

However, as a problem in this case, the etching selectivity of the resist to be used (the ratio of the etching rate between the etching target material and the underlying material of the photoresist and etching target material) becomes small and there is no margin in the process margin, and the pattern is protected. The photoresist mask to be lost is not obtained to obtain a desired etching pattern, the TiW film is an alloy used by a high-temperature sputtering method, and residues are liable to occur in dry etching.

In addition, Ti-based films generally have the disadvantage of having a slower etching rate and poor throughput than Al-based films, and the RIE method also has economic disadvantages such as the use of expensive RIE devices.

In view of the above circumstances, the problem to be solved by the present invention is a method for etching a Ti-based film and an etching method for a Ti-based film, in which an etching selectivity is improved so that etching residues are not generated and damage to a resist surface or an underlying film is not caused. Providing an etchant to be used, and furthermore, by applying an inexpensive wet etching method, overcomes the economic disadvantages of requiring an expensive dry etching apparatus.

The present invention relates to an etching method comprising etching a Ti-based film on a semiconductor substrate using a solution containing hydrogen peroxide and a chelating agent.

Moreover, this invention relates to the etching agent for Ti type films on a semiconductor substrate comprised from the solution containing hydrogen peroxide and a chelating agent.

Furthermore, the present invention consists of a solution comprising hydrogen peroxide, alkane polyphosphonic acids which may have a hydroxy group, and ammonium borate, and a solution comprising ammonia, and when used, these solutions are mixed to form hydrogen peroxide. Ti-based film etchant used as an etchant comprising 15 to 25 wt%, 0.01 to 6 wt% of alkane polyphosphonic acids which may have a hydroxy group, 0.01 to 20 wt% of ammonia and 0.01 to 10 wt% of ammonium borate The invention relates to.

The inventors of the present invention have intensively studied to solve the above problems, and as a result, when etching a Ti-based film using a solution containing hydrogen peroxide and a chelating agent, the etching selectivity can be improved, so that a desired pattern can be obtained. Since the chemical dissolution reaction is used for etching, even if the alloy film produced by the hot sputtering method does not produce etching residues, the problem in the conventional method can be solved as described above. Furthermore, when the solution of the present invention is used, batch processing in the wet etching method using the solution is possible, and the throughput is improved compared to the dry etching method of sheet processing, and the equipment cost is inexpensive. It has been found that the present invention can be obtained, and the productivity and economic efficiency can be greatly improved, and thus the present invention has been completed. .

In the present invention, the Ti-based film refers to a film formed on a substrate by a Ti alloy such as Ti or TiW.

In the present invention, hydrogen peroxide is used for the purpose of oxidizing a Ti film, a TiW alloy film, or the like and facilitating a dissolution reaction with an alkali compound.

The concentration of hydrogen peroxide used is usually 15 to 25% by weight, preferably 18 to 23% by weight as the concentration in the solution of the present invention.

In the present invention, a chelating agent is used which has a function of preventing decomposition of hydrogen peroxide, coordinating with Ti to maintain oxidizing power or hydrogen peroxide to form a water-soluble complex, and dissolving Ti.

As this chelating agent, what is normally used in this field may be used, for example, the alkylimino polycarboxylic acid [hydroxyethylimino diacetic acid (HIDA), imino diacetic acid (IDA) etc. which may have a hydroxy group], Mono or polyalkylene polyamine polycarboxylic acid which may have nitrilopolycarboxylic acid [nitrilo triacetic acid (NTA), nitrilo tripropionic acid (NTP), etc.], hydroxyalkyl group, hydroxyaryl group, or hydroxy aralkyl group. Acids [ethylenediamine tetraacetic acid (EDTA), ethylenediamine diacetic acid (EDDA), ethylenediamine propionic acid dihydrochloride (EDDP), hydroxyethylethylenediamine triacetic acid (EDTA-OH), 1,6-hexamethylenediamine-N , N, N ', N'-4 acetic acid (HDTA), triethylenetetramine hexaacetic acid (TTHA), diethylenetriamine-N, N, N', N '', N ''-5 acetic acid (DTPA) , N, N-bis (2-hydroxybenzyl) ethylenediamine-N, N-2 acetic acid (HBED), etc.], polyaminoal Canpolycarboxylic acid [diaminopropane tetraacetic acid (methyl-EDTA,), trans-1,2-diaminocyclohexane-N, N, N ', N'-4 acetic acid (CyDTA), etc.], polyaminoalkane 1-4 nitrogen atoms in the molecule | numerators, such as an all polycarboxylic acid [diaminopropanol tetraacetic acid (DPTA-OH) etc.], a hydroxyalkyl ether polyamine polycarboxylic acid [glycol ether diamine tetraacetic acid (GEDTA), etc.]; Nitrogen-containing polycarboxylic acids having 2 to 6 carboxyl groups such as aminopoly (alkylphosphonic acid) [aminotris (methylenephosphonic acid) and the like], nitrilopoly (alkylphosphonic acid) [nitrilotris (methylenephosphonic acid) (NTPO) and the like], mono or polyalkylene polyamine poly (alkylphosphonic acid) [ethylenediaminetetrakis (methylenephosphonic acid) (EDTPO), ethylenediamine-N, N'-bis (methylenephosphonic acid) (EDDPO), Isopropylenediaminetetrakis (methylenephosphonic acid), diethylenetriamine-N, N, N ', N'',N''-penta (meth Renphosphonic acid), ethylenediaminebis (methylenephosphonic acid), hexenediaminetetrakis (methylenephosphonic acid) and the like], alkylaminopoly (alkylphosphonic acid) [ethylaminobis (methylenephosphonic acid), dodecylaminobis (methylene Phosphonic acid) and the like, and nitrogen-containing polyphosphonic acids having 1 to 3 nitrogen atoms and 2 to 5 phosphonic acid groups, such as methyldiphosphonic acid, ethylidenediphosphonic acid, and 1-hydroxy. Hydroxy groups such as thilidene-1,1'-diphosphonic acid (HEDPO), 1-hydroxypropylidene-1,1'-diphosphonic acid and 1-hydroxybutylidene-1,1'-diphosphonic acid Alkan polyphosphonic acids which may have, for example, N-substituted amino acids such as dihydroxyethylglycine (DHEG) and N-acetylglycine, for example amides such as benzylamide, for example ethylenediamine, propylenediamine, isopropylenediamine Alkylenediamines such as butylenediamine, such as triethanol Polyalkanolamines such as min, for example aromatic diamines such as diaminobenzene, diaminonaphthalene, for example, polyalkylene polyamines such as diethylenetriamine, dipropylenetriamine, triethylenetetraamine, for example tripolyphosphoric acid, hexa condensation of acids such as metaphosphoric acid, such as acetyl acetone, such as Hexafluoroacetylacetone alkanoyl ketones, such as halide ion ^{(F -, Cl -, Br} -, I -), cyanide ion, thiocyanate ion, And inorganic ions having complex-forming ability such as thiosulfate ions and ammonium ions.

Among these chelating agents, considering the stability in the presence of hydrogen peroxide and the like, nitrogen-containing polyphosphonic acids having 1 to 3 nitrogen atoms and 2 to 5 phosphonic acid groups in the molecule, and an alkane polyphosphone which may have a hydroxy group Polyphosphonic acids, such as acids, are preferable, and polyphosphonic acids, such as alkane polyphosphonic acids which may have a hydroxyl group, are especially preferable. More specifically, nitrilotris (methylenephosphonic acid), 1-hydroxyethylidene-1,1'-diphosphonic acid, 1-hydroxypropylidene-1,1'-diphosphonic acid, 1-hydride Preferred are hydroxybutylidene-1,1'-diphosphonic acid, and among these, 1-hydroxyethylidene-1,1'-diphosphonic acid and 1-hydroxypropylidene-1,1'-diphosphonic acid , 1-hydroxybutylidene-1,1'-diphosphonic acid is particularly preferred.

The concentration of the chelating agent is usually 0.01 to 6% by weight, preferably 0.1 to 5% by weight, more preferably 1 to 3% by weight in the solution of the present invention.

The solution (etching agent of the present invention) used in the present invention contains at least hydrogen peroxide and a chelating agent, and the solution is usually adjusted and maintained so that the pH is in the range of 7.2 to 10, preferably 8 to 10. It is usually desirable to use a buffer to keep the pH of the solution in this range.

The buffer used in the present invention is not particularly limited and can be used as long as it is commonly used in this field. Among them, ammonium salts such as ammonia, such as ammonium chloride, ammonium nitrate, ammonium fluoride, and ammonium borate, are preferred. You may use as this and may use 2 or more types together.

In addition, when using this ammonium salt, the salt itself may be added directly to the solution of this invention, or the acid and ammonia which can form the salt in the solution may be added to this solution separately, respectively. More specifically, ammonia and inorganic acids such as hydrochloric acid, nitric acid, hydrofluoric acid and boric acid or salts thereof (e.g., alkali metal salts such as sodium, potassium and lithium (specifically, sodium tetraborate and the like)) are respectively separately reacted. It exists in the middle. In this case, when ammonia is excessively used with respect to the acid or its alkali metal salt, both the ammonia salt and the ammonia salt of the inorganic acid coexist in the reaction system as a result.

Among these, ammonia and inorganic acids, especially ammonia and boric acid, are preferably added to the solution of the present invention, or ammonium salts of ammonia and inorganic acids, particularly ammonium salts of ammonia and boric acid, are added to the solution.

Although the concentration of these buffers varies depending on the type of buffer to be used and the like, they cannot be uniformly described. However, in the case of using an ammonium salt, for example, the concentration in the solution of the present invention is usually 0.01 to 10% by weight, preferably 0.05. It is -6 weight%, More preferably, it is 0.1-5 weight%.

In the case where ammonia and ammonium salt are used in combination, the amount of ammonium salt is as described above, and the amount of ammonia is usually 0.01 to 20% by weight, preferably 0.05 to 12% by weight, more preferably as the concentration in the solution of the present invention. Is 0.1 to 10% by weight.

In the method of the present invention, in etching a TiW-based film on a semiconductor substrate using the solution of the present invention (etchant of the present invention), it is preferable to perform this under alkaline conditions.

That is, as shown in the following Chemical Formulas 1 and 2, tungsten (W) is oxidized with hydrogen peroxide to produce tungsten oxide (WO ₃ ). The WO ₃ is because it is soluble in alkali, and acts as the alkali tungstate ions are soluble in water (WO ₄ ^{2 -)} is a. Ti likewise acts with hydrogen peroxide and a chelating agent in the alkaline region to form [TiO (H ₂ O ₂ ) EDTA] ² -complex as shown in Formula 3. Also in a TiW alloy film, it is thought that etching is progressing by reaction as represented by this Formula (1)-(3). The change of pH and etching time at this time is shown in FIG.

As is clear from the results of FIG. 1, it can be seen that the etching tends to proceed in a short time as the pH becomes a high alkali region. That is, it is preferable to etch in an alkali region, and as a specific pH range, it turns out that it is 7.2-10 normally, Preferably it is 7.8-9.8, More preferably, it is pH 8.2-9.2. At a pH lower than the above range, the pattern formation is not affected, but it takes some time for the progress of etching, and at a pH higher than the pH range, it does not take time for the progress of etching, but the protection of the pattern The resist which is a mask is melt | dissolved and peeled.

W + 3H ₂ O ₂ → WO ₃ + 3H ₂ O

_{WO 3 + 2NH 4 OH → 2NH} 4 + + WO 4 2 - + H 2 O

Ti + H ₂ O ₂ + Y + 2NH ₄ OH → 2NH ₄ ⁺ + [TiO (H ₂ O ₂ ) Y] ^2- + H ₂ O

In Schemes 2 to 3, Y represents ethylenediamine tetraacetic acid.

As is clear from the above, in the method of the present invention, the conditions (pH range) when etching the TiW-based film on the semiconductor substrate are preferably an alkaline region, and as a specific pH range, for example, usually 7.2 to 10, preferably Is 7.8 to 9.8, more preferably pH 8.2 to 9.2.

In addition, the pH of the solution of the present invention used in the method of the present invention is also preferably in the pH range as described above.

The solution of the present invention can be prepared by mixing and dissolving hydrogen peroxide and a chelating agent as described above, preferably a buffer, in water to the concentration as described above. In addition, each component may be added and mixed sequentially with water in an appropriate order, and may be dissolved in water after adding all the components.

The solution of the present invention thus prepared is preferably subjected to filtration treatment or the like before use. In addition, the water used here may be purified by distillation, ion exchange treatment or the like.

In the present invention, reagents usually used by etching methods known per se can be used, except for using hydrogen peroxide and a chelating agent as described above, preferably a buffer.

Examples of such reagents include surfactants such as nonionic surfactants, anionic surfactants, cationic surfactants and amphoteric surfactants used for the purpose of reducing the surface tension of the solution to improve the wettability to the semiconductor surface. Especially, nonionic surfactants, such as NCW1002 (polyoxyethylene polyoxypropylene alkyl ether and Wako Pure Chemical Industries, Ltd. make), are especially preferable.

These surfactants may be generally used in the concentration range used in this field, and are usually 0.001 to 1.0% by weight, preferably 0.01 to 0.5% by weight as the concentration in the solution of the present invention.

As described above, the etchant of the present invention is prepared by using hydrogen peroxide, a chelating agent, preferably a buffer, or the like as its main component, and is supplied in various forms such as a multi-liquid system such as a one-liquid system or a two-liquid system.

In the case of using the etchant, in the case of a one-liquid system, it may be used as it is, and in the case of a multi-liquid system such as a two-liquid system, all the solutions are properly mixed before use to contain all of the above components. A solution may be prepared and used.

Among them, from the problems of safety or solution stability during transportation, storage, and the like, a two-liquid or more multi-liquid system is preferable, and specifically, for example, (1) a solution containing hydrogen peroxide and a chelating agent, preferably a buffer; 2) It is preferable that it is a two-liquid system comprised of the solution containing a buffer.

As mentioned above, although the preferable form of each component in a two-liquid system is as above-mentioned, More specifically, (1) the solution comprised containing hydrogen peroxide, the alkane polyphosphonic acid which may have a hydroxyl group, and ammonium borate; And (2) particularly preferably composed of a solution containing ammonia.

In addition, as mentioned above, the use concentration of each component in a multi-liquid system is appropriate so that the concentration in the solution containing all the components, ie, the final concentration, prepared by properly mixing all the solutions may be in the concentration range as described above. It may be selected in the solution.

That is, in the case of the two-liquid system described above, for example, hydrogen peroxide is usually 15 to 25% by weight, preferably 18 to 23% by weight, and the chelating agent is usually 0.01 to 6 as the final concentration when the two liquids are mixed. % By weight, preferably 0.1 to 5% by weight, more preferably 1 to 3% by weight, and when an ammonium salt of an inorganic acid is used as a buffer, for example, the ammonium salt is usually 0.01 to 10% by weight, preferably 0.05 to 6% by weight, more preferably 0.1 to 5% by weight, and when ammonia is used as the buffer, for example, ammonia is usually 0.01 to 20% by weight, preferably 0.05 to 12% by weight, more preferably 0.1 to What is necessary is just to prepare two solutions respectively so that it may become 10 weight%.

More specifically, as a final concentration when two liquids are mixed, hydrogen peroxide is usually 15 to 25% by weight, preferably 18 to 23% by weight, and the chelating agent is usually 0.01 to 6% by weight, preferably 0.1 to 5% by weight. %, More preferably 1 to 3% by weight, ammonium salt of inorganic acid is usually 0.01 to 10% by weight, preferably 0.05 to 6% by weight, more preferably 0.1 to 5% by weight of hydrogen peroxide and chelating agent, preferably The buffer is contained in water and the final concentration when the two liquids are mixed is usually 0.01 to 20% by weight, preferably 0.05 to 12% by weight, more preferably 0.1 to 10% by weight. It is good to prepare each solution by making it contain in water.

In addition, as mentioned above, the pH of each solution in the multi-liquid system is not particularly limited, and the pH of the solution containing all of the above-mentioned components prepared by mixing all the solutions as appropriate, that is, the final pH is described above. What is necessary is just to adjust the pH of each solution so that it may become a pH range as shown.

That is, for example, in the case of the two-liquid system as described above, the final pH when the two liquids are mixed is in the alkali region, specifically pH 7.2-10, preferably pH 7.8-9.8, more preferably pH 8.2-. The pH of each solution can be adjusted to 9.2.

The method of the present invention is an immersion method which is a well-known etching method other than etching a Ti-based film on a semiconductor substrate using a solution of the present invention containing hydrogen peroxide and a chelating agent as described above, preferably a buffer, as an etchant. What is necessary is just to perform this according to the spray etching method.

More specifically, for example, (1) a method in which a semiconductor substrate on which a Ti-based film is formed is immersed in an etchant, (2) a solution of the semiconductor substrate on which a Ti-based film is formed is immersed in an etchant, and the solution is stirred by mechanical means. (3) a method of vibrating and stirring the solution by ultrasonic waves or the like while the semiconductor substrate having the Ti-based film formed thereon is immersed in an etchant, (4) a method of spraying the etchant into the semiconductor substrate having the Ti-based film, or the like. Can be mentioned.

In the method of the present invention, when performing the etching as described above, the Ti-based film may be shaken as necessary.

In addition, in the method of this invention, an etching method is not specifically limited, For example, batch type, sheet type, etc. can be used.

When the etching is warmed, the etching is completed in a shorter time than at normal temperature, but it becomes difficult to control the etching due to the decrease in pH. Therefore, it is preferable to set the temperature at the time of etching to 35 degreeC-45 degreeC.

As described above, the present invention provides a method for etching a Ti-based film without generating an etching residue and an etchant used for etching the Ti-based film. By using the present invention, the etching effect is superior to that of the conventional method, and there is no need to use an expensive apparatus, and the etching of the Ti-based film can be performed at low cost with a large process margin.

Although an Example and a comparative example are given to the following and this invention is demonstrated in detail, this invention is not limited at all by these.

Example 1

(1) Preparation of etchant

The etchant comprised with the following composition was prepared.

20% by weight of hydrogen peroxide

Ammonium borate 0.6 wt%

Ammonia 2 wt%

2 wt% chelating agent (NTPO: nitrilotrismethylphosphonic acid)

Water 75.4% by weight

pH 9.0

(2) etching

* The etchant obtained in said (1) was put into the general purpose wet booth, and it set to the liquid temperature of 40 degreeC, and circulating flow rate of 28 L / min by the liquid circulation type temperature regulator.

The etching of the etching target substrate on which the TiW film was formed was performed by the immersion method using the etching agent. In addition, a positive resist having a film thickness of 1.8 m was used for the etching target substrate and the mask on which the TiW film having a film thickness of 500 nm was formed for the etching.

(3) results

The results are shown in FIG.

2, each number represents the following, respectively.

21: positive resist

22: Al

23: TiW film

24: not oxide film

25: TiW etching residue

Comparative Example 1

(1) etching

The etching target substrate on which the TiW film was formed was performed by the RIE method. As in Example 1, a positive resist having a film thickness of 1.8 m was used for the etching target substrate and the mask on which the TiW film having a film thickness of 500 nm was formed.

(2) results

The result is shown in FIG. 2 with Example 1. FIG.

As can be seen from the results of Fig. 2, etching residues are generated in the conventional RIE method (Comparative Example 1), whereas etching residues are not generated in the method (Example 1) of the present invention and can be etched satisfactorily. I can see that there is. Moreover, since excessive side etching does not generate | occur | produce and furthermore, the etching selectivity with a resist or an underlying film improved, it turns out that process margin became large.

Example 2

(1) Preparation of etchant

The etchant comprised with the following composition was prepared.

a) first liquid

22% by weight of hydrogen peroxide

4.8 wt% ammonium borate

2.2 wt% chelating agent

 (HEDPO: 1-hydroxyethylidene-1,1'-diphosphonic acid)

71% by weight of water

pH 3.5

b) second liquid

Ammonia Water 14 wt%

86% by weight of water

pH 12

(2) etching

The etching of the etched substrate on which the TiW film was formed was performed in the same manner as in Example 1, except that 900 ml of the first liquid obtained in the above (1) and 100 ml of the second liquid were mixed (final pH 8.2) as an etchant. It was.

(3) results

As in Example 1, in the method of Example 2, no etching residue was generated, and further, the etching selectivity between the resist and the underlying film was improved, thereby increasing the process margin.

1 shows the relationship between etching time and pH.

Fig. 2 is a schematic diagram showing the results of etching by the method of the present invention obtained in Example 1 and the results of etching by the conventional method obtained in Comparative Example 1, respectively.

<Explanation of symbols for main parts of drawing>

21: positive resist

22: Al

23: TiW film

24: bottom oxide film

25: TiW etching residue

Claims (21)

An etching method of etching a Ti-based film on a semiconductor substrate using a solution containing a chelating agent selected from hydrogen peroxide and polyphosphonic acids. The chelating agent is selected from the group consisting of nitrogen-containing polyphosphonic acids having 1 to 3 nitrogen atoms and 2 to 5 phosphonic acid groups in the molecule, and alkanpolyphosphonic acids which may have a hydroxy group. Etching method. The etching method according to claim 2, wherein the chelating agent is an alkane polyphosphonic acid which may have a hydroxy group. The alkane polyphosphonic acids according to claim 3, wherein the alkane polyphosphonic acids which may have a hydroxy group are 1-hydroxyethylidene-1,1'-diphosphonic acid, 1-hydroxypropylidene-1,1'-diphosphonic acid, 1-hydroxybutylidene-1,1'-diphosphonic acid. The etching method according to any one of claims 1 to 4, wherein the solution further contains a buffer. 6. The buffer according to claim 5, wherein the buffer is (1) ammonia, (2) ammonium salt of inorganic acid, (3) ammonium salt of ammonia and inorganic acid, (4) ammonia and inorganic acid, or (5) alkali metal salt of ammonia and inorganic acid. Etching method. The etching method according to claim 6, wherein the buffer is ammonia and an inorganic acid or an ammonium salt of ammonia and an inorganic acid. The etching method according to claim 6, wherein the inorganic acid is boric acid. The etching method according to claim 1, wherein the solution is an alkaline solution. The etching method according to claim 1, wherein the pH of the solution is 7.2 to 10. An etching agent for Ti films on a semiconductor substrate composed of a solution containing a chelating agent selected from hydrogen peroxide and polyphosphonic acids. The chelating agent is selected from the group consisting of nitrogen-containing polyphosphonic acids having 1 to 3 nitrogen atoms and 2 to 5 phosphonic acid groups in the molecule, and alkanpolyphosphonic acids which may have a hydroxy group. Etching agent, characterized in that. The etchant according to claim 12, wherein the chelating agent is an alkane polyphosphonic acid which may have a hydroxy group. The alkane polyphosphonic acid which may have a hydroxy group is 1-hydroxyethylidene-1,1'- diphosphonic acid, 1-hydroxypropylidene-1,1'-diphosphonic acid, 1-hydroxybutylidene-1,1'-diphosphonic acid. The etchant according to any one of claims 11 to 14, wherein the solution further contains a buffer. The buffer according to claim 15, wherein the buffer is (1) ammonia, (2) ammonium salt of inorganic acid, (3) ammonium salt of ammonia and inorganic acid, (4) ammonia and inorganic acid, or (5) alkali metal salt of ammonia and inorganic acid. Etchant. The etchant according to claim 16, wherein the buffer is ammonia and inorganic acids or ammonium salts of ammonia and inorganic acids. 18. The etchant according to claim 17, wherein the solution comprises hydrogen peroxide, nitrogen-containing polyphosphonic acids, ammonium salts of ammonia and inorganic acids. The etchant according to claim 16, wherein the inorganic acid is boric acid. The etchant according to claim 19, comprising 15 to 25 wt% hydrogen peroxide, 0.01 to 6 wt% nitrogen-containing polyphosphonic acids, 0.01 to 20 wt% ammonia and 0.01 to 10 wt% ammonium borate. The etchant according to claim 11, wherein the pH of the solution is 7.2 to 10.

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