DE102006004826A1 - Etching solution, useful for wet-chemical structuring of metal layers e.g. silver layers, in production of semiconductor components, comprises oxidizing agent and chelating agent - Google Patents

Abstract

Etching solution for the wet-chemical structuring of metal layers, preferably silver layers, in the production of semiconductor components, comprises at least one oxidizing agent and at least a chelating agent (L), where the chelating agent and the metal-cation (M) of the metal layer liberated through the oxidation agent during the etching procedure forms a complex (a), and where the etching procedure is free of metal- and/or cyanide-ions. Etching solution for the wet-chemical structuring of metal layers, preferably silver layers, in the production of semiconductor components, comprises at least one oxidizing agent and at least a chelating agent (L), where the chelating agent and the metal-cation (M) of the metal layer liberated through the oxidation agent during the etching procedure forms a complex (a) of formula (ML x), and where the etching procedure is free of metal- and/or cyanide-ions. x : 1-6, preferably 2. An independent claim is included for an etching technique for the structuring of metal layers, preferably of silver layers in conducting bridging-RAM(random access memory)-cells, using the etching solution.

Description

The The invention relates to an etching solution according to the preamble of claim 1, a use of an etching solution according to Claim 20 and a method according to claim 21.

Resistive storage materials have been known for some time, in particular under the heading "Programmable Metallization Cell (PMC)" as part of the "Nonvolatile Memory Technology". Based on inorganic materials, concepts for changing the conductivity by ion diffusion in glasses, in particular the system GeSe _x / Ag or GeS _x / Ag, are used.

One example for such a system is a Conductive bridging (CB) RAM cell The CB-RAM cell in its simplest version consists of three layers. On a lower electrode of silver, tungsten or similar materials is called active material deposited a germanium chalcogenide, which Contains metals such as silver or copper to form a solid solution. In connection is used as upper electrode and to provide the conductive path deposited a silver layer. When applying a voltage, move the positively charged metal ions from the germanium chalcogenide layer to the cathode and store on the cathode under formation of a Low resistance films. When a reverse voltage is applied a reversal of the deposition process and the deposited metal becomes resolved whereby a high resistance is restored.

in the In the context of a wider application of this technology, it is desirable the metal layers formed in the cell, in particular silver layers, to structure.

The Structuring of silver layers is particularly demanding here Silver as a noble metal has a relatively high reaction potential and thus opposite chemical reactions is relatively inert. The structuring of Silver layers therefore require the use of specific etching solutions.

So far used etching solutions especially cyanide ions as strong complexing agents, since the formed metal-cyano-complexes have a high complex stability exhibit.

When disadvantageous for However, the production turns out to be known to be high toxicity of cyanide solutions and the high cost of the currently preferred tetraalkylammonium cyanides. So are the costs for 200 l of a 0.1-1 Molar cyanide solution in TMA as a developer solution currently at several 10 000 euros.

Of the It is therefore the object of the present invention to provide etching solutions for to provide wet-chemical structuring of metal layers, which are free of metal ions and cyanide ions. In particular, etching solutions should be provided which are the structuring of silver layers in the form of silver electrodes or what after a thermal, electrical or photoinduced Diffusion of it is left in CB-RAM cells. In particular, this method should find application for ADM.

These Task is achieved by an etching solution with the features of claim 1 solved.

The etching solution according to the invention for wet-chemical structuring of metal layers, in particular of silver layers, in the production of semiconductor components is characterized by at least one oxidizing agent and at least one complexing agent L, wherein the complexing agent L and the metal cations M of the metal layer released by the oxidizing agent during the etching process Complex ML _x with x = 1 to 6, preferably 2, where x represents the number of bound ligands. The etching solution according to the invention is free from metal and / or cyanide ions.

Advantageously, the oxidizing agent used has a normal potential of greater than +1 V, in particular +2 V, on. Thus, the strong oxidizing agent peroxodisulfate under the reaction SO ₄ ^2- 2 ⇆ S ₂ O ₈ ^2- + 2e ^- to a normal potential of +2 V.

The formed complex ML _x is preferably characterized by a formation constant of greater than or equal to 10 KB ^{2 6} l / mol ^2, in particular greater than or equal to 10 ⁷ l ² / mol ^2,. For example, a [Ag (NH ₃ ) ₂ ] ⁺ complex formed during the etching of silver layers is characterized by a complex formation constant of 10 ⁷ l ² / mol ² .

During the etching process, the metal is transformed by means of a suitable oxidizing agent into the corresponding metal cation according to the equation Ox + ne ^- → Red (1) transferred.

worin E₀ das Normalpotential, R die allgemeine Gas-Konstante, T die Temperatur, n die Anzahl der übertragenden Elektronen, F die Faraday-Konstante, c_0x die Konzentration der freien Metall-Kationen und C_Red die Konzentration des Metalls bedeutenThe redox potential of the reaction is determined according to the Nernst equation

where E _{0 is} the normal potential, R the general gas constant, T the temperature, n the number of transmitted electrons, F the Faraday constant, c _0x the concentration of the free metal cations and C _Red the concentration of the metal

Thus, in the case of oxidation of a silver layer, the metallic silver represents the reduced component and the silver ions the oxidized portion, the normal potential of silver being + 0.7991 V and the metallic silver c _{Red being} equal to 1.

Since silver is difficult to etch, it is desirable to shift the equilibrium of equation (1) to the side of the oxidized step, ie, the side of the soluble silver cations. For the desired shift in the equilibrium, the cations must be removed, for example by the use of strong complexing agents according to the reaction Ag ⁺ + 2L ↔ AgL ₂ ⁺ (3) can be done.

beschreibbar.The constant of the complex formation reaction and thus the stability of the complex formed are by means of the equation

writable.

• a) einem starken Oxidationsmittel zur Überführung des Metalls in das korrespondierende lösliche Kation, sowie
• b) einem starken Komplexbildner, der das gebildete Metallkation dem Redoxgleichgewicht entzieht.

The process of etching, especially of hard-to-etch metal layers, is thus positively influenced by two components:

• a) a strong oxidizing agent for the conversion of the metal into the corresponding soluble cation, and
• b) a strong complexing agent which extracts the metal cation formed the redox equilibrium.

The etching solution according to the invention thus enables the electrode potential of the metal layers to be structured, in particular of silver layers in a region which is favorable for the etching, is preferred in a range of less than 0.4 V, to move.

Strength Oxidizing agent with a normal potential of greater than +1 V, such as. Peroxodisulfate with a normal potential of +2.1 V, should be strong enough per se to oxidize metal layers such as silver with a normal potential of +0.799 V or copper with a normal potential of +0.521 V to etch. The singular use of peroxodisulfate for etching However, by the formation of oxide layers on the mentioned Prevent metals and the associated construction of an overvoltage. By the simultaneous use of complexing agents becomes this overvoltage reduced. It is even possible the potential below the value of the normal potential of, for example Lowering Cu, the known is etched very well by peroxodisulfate without the addition of complexing agents.

The Lowering the potential through the use of oxidizing agents in connection with complexing agents, e.g. for the Nernst equation Estimate the effective silver ion concentration according to Table 1 as follows.

table 1 shows the influence of different complexing agents on the concentration on free silver ions using the example of silver halides and silver sulfide on.

Considering the logarithmic scale and the solubility series of the silver halides, the following sequence of free silver ions is obtained: AgCl> [Ag (NH _{3) 2]} ^+> AgBr> [Ag (S ₂ O _{3) 2]} ^3-> Agl> [Ag (CN) _2] ^-> Ag ₂ S.

In a silver-containing thiosulfate solution thus max. 10 ^-7 mol / l Ag ⁺ ions. Using Nernst's equation (2), the potential of a silver-containing thiosulfate solution is given considering all the constants of equation (2) and the normal potential for silver of +0.799 V according to E = 0.799 V - 0.059 V / n · 7 (with n = 1) to +0.386 V. For a silver-containing thiosulfate solution, the potential is in the range of copper. Since the concentrations of free silver ions of a silver thiosulfate complex generally assume values greater than 2 × 10 ^-7 , the potential is even lower by about 100-150 mV.

at Use of the etching solutions according to the invention for Structuring silver layers is also important that the etching solution advantageously free of sulfide ions is. In the presence of sulfide ions, it would form and deposit of the sparingly soluble Silver sulfide come, which adversely affects the entire etching process.

Next their ability The reduction of the potential of a metal layer constitutes the etching solution according to the invention inexpensive and harmless alternative to the previously known cyanide-containing etching solutions.

The etching solution points advantageously from 0.1 to 10% by weight of oxidizing agent and from 0.1 to 10% by weight Complexing agent on.

The etching solution points with advantage as complexing agent L compounds with nitrogen and / or Sulfur donor atoms on. Preference is given to linear, cyclic, chelating Amines, oximes and / or nitrates and thiols, and / or thiosulphates used.

The Number of ligands containing transition metals To be able to form complexes is exceptionally big. The introduction The ligands are usually based on the number of complexing Atoms with which they can attach themselves to a center. These Property is described by the term "denticity". They are monodentate ligands and mehrzähinige Chelated ligands known.

The Complex formation takes place by means of an attachment of free electrons or electron pairs provided molecules in the coordination sphere of the transition metal. Ligands with nitrogen and sulfur donor atoms have joined as very beneficial for the solution the task set, as this one very stable Complex and cost-effective and non-toxic. chelating Amines form particularly stable complexes and thereby reduce very much effectively the metal cation concentration during the etching process.

With advantage as linear amines primary, secondary and / or tertiary amines according to the formula NR ₁ R ₂ R ₃ used, where the radicals R ₁ , R ₂ and R _{3 can} independently be alkyl and / or aryl radicals. Preferred alkyl or aryl radicals are methyl, ethyl, propyl, benzyl and / or phenyl.

When cyclic amines are preferably non-substituted pyridine, alkyl-substituted Pyridines and / or pyridinecarboxylic acids, and as chelating amines bipyridine, phenanthroline, ethylenediamine and / or oligomeric analogs of ethylenediamine used. The used Oxime is advantageously diacetyldioxime (dimethylglyoxime).

With Advantage than thiols are propanethiol, ethanethiols, butanethiol and / or Used thiophenol.

The used complexing agents L are preferably in the form of compounds from thiosulfates, thiocyanates and / or nitrates as anions and Tetraalkylammonium before as cations. The alkyl radicals are methyl, Ethyl, propyl, benzyl or their permutation. It can too Lithium, sodium, potassium, calcium or magnesium ions as cations be used when using metal ion-containing etching solutions.

Especially advantageous is the use of ammonia and / or ammonium thiosulfate as complexing agent L. Both compounds have very good complexing properties Properties on and are very cost effective.

As the oxidizing agent, peroxo compounds are preferably used. To be particularly advantageous, the use of hydrogen peroxide H ₂ O ₂ and / or peroxodisulfates, especially ammonium peroxodisulfate (NH _{4) 2} S ₂ O _8, proved.

Further advantageous oxidizing agents are hypochlorites, hypobromides, peroxophosphates, Peroxodiphosphates, permanganates, peroxochromates, perrhenates, ozonides and / or organic peroxides, in particular di-tert-butyl peroxide or dibenzoyl peroxide.

The salt-like Oxidizing agents are advantageously in the form of lithium, sodium, Potassium, calcium, magnesium in metal ion-containing etching solutions and / or Tetraalkylammonium salts for metal ion-free etching solutions, where as alkyl radicals methyl, ethyl, propyl, benzyl, and their permutations be used.

The etching solution points also solvents and other additives on.

When solvent are preferably water, alcohols, especially methanol, ethanol, iso- or n-propanol, cyclic ethers, in particular dioxane or Tetrahydrofuran, dimethyl sulfoxide and / or dimethylformamide used, which are pure or in mixtures. The mixtures are included adjusted so that oxidizing agent and Komplexbildenr and solve the formed metal-ion complexes well in it.

When additions are in an advantageous concentration 0.01 to 10% by volume Surfactants, alcohols, solvents, inert salts and / or bases or acids used to adjust the pH.

As a general rule serve as additives Substances that stop the wetting behavior of the formulation. These are the commercially available additives of various Manufacturers and surfactants (cationic, anionic and neutral). Of the Addition of alcohols such as methanol, ethanol, i, n-propanol, i, n, t-butanol and other higher quality Alcohols, and phenols such as phenol or o, m, p-cresol, causes a Improvement of wetting behavior. Other water-miscible or conditionally mixable additives are: acetonitrile, acetone, tetrahydrofuran, dioxane, γ-butyrolactone, Cyclohexanone, N-methylpyrrolidinone, triethylamine, pyridine, dimethyl sulfoxide, Dimethylformamide etc.

Under the term additions are also mixtures of inert salts, such as halides, Sulfates, tosylates, acetates, propionates, phosphates of ammonium or tetraalkylammonium ions in metal ion-free solutions as well as lithium, Sodium, potassium, calcium, magnesium ions in metal ion-containing Solutions.

Additions from Ammonia, tetraalkylammonium hydroxide, wherein the alkyl radical is a methyl, Ethyl, propyl, benzyl radical and their permutations can be, Sodium or potassium hydroxide or formic acid, acetic acid, hydrochloric acid, phosphoric acid or nitric acid are used to adjust the pH.

The Another object is the use of an etching solution according to the invention Claim 21 and an etching method solved according to claim 22.

So is the etching solution according to the invention for Structuring of metal layers, in particular of silver layers in Conducting Bridging (CB) RAM cells, can be used.

The inventive etching solution is but also suitable for structuring GeS and / or GeSe. Especially for the CB-RAM application, this feature is beneficial.

The etching process according to the invention allows using the etching solution according to the invention, the structuring of Metal layers, in particular silver layers, in conducting bridging (CB) RAM cells.

The etching solution is also usable for Silver conductive tracks in electronic components, in particular in HF components or antenna structures. Since the solution according to the invention, in particular the amine-containing Solution, also etches copper, it can also be used to structure copper-silver-containing Alloys or multilayer systems are used.

The Invention will be described below with reference to the figures of Drawings on several embodiments explained in more detail. It demonstrate:

1 Schematic representation of a CB-RAM cell

2 Top view of an etched with an etching solution of H ₂ O ₂ and NH ₃ silver layer

3 Top view of an etched with an etching solution of (NH ₄ ) ₂ S ₂ O ₈ and NH ₃ silver layer

4 Top view of a silver layer structured with an etching solution of H ₂ O ₂ and (NH ₄ ) ₂ S ₂ O ₃

5 Top view of a silver layer structured with an etching solution of (NH ₄ ) ₂ S ₂ O ₈ and (NH ₄ ) ₂ S ₂ O ₃

1 schematically illustrates the structure of a CB-RAM cell, wherein the upper electrode consists of a thin layer of silver to be structured.

Embodiment 1

2 shows the result of patterning a silver layer with a freshly prepared aqueous H ₂ O ₂ / NH ₃ solution at a magnification of 20,000. The solution used with a pH of 10 contains 1% H ₂ O ₂ as the oxidizing agent and 0.27 ml of a 28% aqueous NH ₃ solution in 20 ml of water as a complexing agent.

For structuring, all embodiments are prepared as follows. First, an approximately 35 nm thick silver layer was evaporated on a silicon wafer in a vacuum. Subsequently, a photoresist was spin-coated at 2500 rpm and dried at 110 ° C. for 1 min on a hotplate. The photoresist was exposed to i-line (365 nm) through a chromium-on-quartz mask for 7 sec at an intensity of 7 mW / cm ² . The development is carried out in a standard Tetramethylammonioumhydroxid developer (2.38%) for 45 seconds, whereby the exposed areas are peeled off. The unexposed areas stop and serve as an etching mask. However, the unexposed areas are only stable for a certain time over strong bases. Therefore, it is advantageous if the pH of the etching solution is not too basic, ie is more in the neutral range.

The Silver layer comes with an etching rate of 5.0 nm / s structured. After the etching, the resist will pass through rinse removed with acetone again.

The etching rate plays in the structuring process an important role. Very high etching rates to lead to that the etching process difficult to control. Undercutting / overetching is the consequence of e.g. small Structures are no longer resolved. Large areas etch i.a. a little slower i.e. solve the small structures get off before big ones Surfaces at all etched are.

Etch rate and etch rate are also strongly influenced by the ambient temperature. That's how it works an increase the temperature is an increase the etching rate.

The top view of 2 shows a relatively good resolution of the structured silver surface. The structures, however, have a strong regression of the metal. In addition, a strong evolution of oxygen is observed.

Embodiment 2

To structure the in 3 The silver layer (2000 × magnification) shown was an aqueous solution with a total volume of 20 ml of 1% (NH ₄ ) ₂ S ₂ O ₈ as an oxidizing agent and 5 drops of 0.27 ml of an aqueous 28% NH ₃ solution in 20 ml Water used. The pH of the etching solution is 10. The silver layer was patterned at an etch rate of 5.0 nm / s.

The resolution However, the structures are not very good here. In addition, the shelf life is the prepared solution only a few hours, what a the application in an industrial process is disadvantageous.

Embodiment 3

In 4 For example, the plan view is shown on a silver surface (5000x magnification) treated with an aqueous etch solution containing 1% H ₂ O ₂ and 5% (NH ₄ ) ₂ S ₂ O ₃ . The silver layer was patterned at an etch rate of 1.5 nm / s.

The structure resolution is very good, but it also comes here due to the reduction of H ₂ O ₂ for the development of oxygen.

Embodiment 4

5 shows the result of structuring a silver layer (10000 times magnification) with an aqueous etching solution with 1% (NH ₄ ) ₂ S ₂ O ₈ as oxidizing agent and 5% (NH ₄ ) ₂ S ₂ O ₃ as complexing agent. The pH of the solution is 5, which avoids attack on the resist.

The structuring took place with an etching rate of 0.58 nm / s. The etching rate can also be controlled by increasing the pH by adding NH ₃ . Thus, the etching rate at a pH of 7 is 0.88 nm / s.

(NH ₄ ) ₂ S ₂ O ₈ / (NH ₄ ) ₂ S ₂ O ₃ form metastable solutions which after about one day have low sulfur precipitates. It is therefore important that the components of the solution are mixed just before use. The stability of the solution is also controllable by the pH.

The top view of 5 shows a very good resolution and clear structures.

The in comparison to the embodiments 1 and 2 improved resolution the embodiments 3 and 4 can with the high complexing constant of the thiosulfate complex related, the order of several major orders is larger as that of the ammonium complex. The high complex formation constant thiosulfate is converted by its action as a chelating ligand Sulfur and an oxygen atom conditionally. Furthermore are also Peroxodisulfate complexes of silver are known.

table 1 summarizes the results of the experiments performed.

The results clearly show that an etching solution of an oxidizing agent and a complexing agent is well suited for structuring silver layers. The best result was achieved with a (NH ₄ ) ₂ S ₂ O ₈ / (NH ₄ ) ₂ S ₂ O ₃ solution, wherein the etching rate can be controlled by the pH. The solution is also non-toxic and the substances used are inexpensive.

The Restricted invention in their execution not to the preferred embodiments given above. Rather, a number of variants are conceivable that of the etching solution according to the invention also at basically different types Make use.

1

upper electrode

2

active material

3

lower electrode

Claims (30)

Etching solution for wet-chemical structuring of metal layers, in particular layers of silver, in the production of semiconductor devices, characterized by at least one oxidizing agent and at least one complexing agent L, wherein the complexing agent L and the released by the oxidizing agent during the etching metal cations M of the metal layer a complex ML _x with x is 1 to 6; form and wherein the etching solution is free of metal and / or cyanide ions. Etching solution according to claim 1 characterized by the formation of a metal complex ML _x with x equal to 2. Etching solution after Claim 1 or 2 characterized by at least one oxidizing agent with an oxidation potential greater than + 1 V. The etching solution of at least one of the preceding claims, characterized in that the complex ML formed during the etching process _x is a complex formation constant of greater than or equal to 10 ⁶ l ² / mol ^2, in particular greater than or equal to 10 ⁷ l ² / mol ^2, comprising KB. Etching solution after characterized in at least one of the preceding claims, characterized that the etching solution is free of sulfide ions. Etching solution after at least one of the preceding claims, characterized by 0.1 to 10% by weight of at least one oxidizing agent Etching solution after at least one of the preceding claims, characterized by 0.1 up to 10% by weight of at least one complexing agent L. Etching solution after at least one of the preceding claims, characterized by compounds with nitrogen and / or sulfur donor atoms as complexing agent L. Etching solution after at least one of the preceding claims, characterized by linear, cyclic, chelating amines, oximes and / or nitrates as complexing agents L. Etching solution according to at least one of the preceding claims, characterized by primary, secondary and / or tertiary amines according to the formula NR ₁ R ₂ R ₃ as a complexing agent, wherein the radicals R ₁ , R ₂ and R _{3 are} independently alkyl and / or aryl radicals , Etching solution after Claim 10, characterized by methyl, ethyl, propyl, benzyl and / or phenyl as alkyl or aryl radicals. Etching solution after at least one of the preceding claims, characterized by cyclic amines in the form of non-substituted pyridine, alkyl-substituted pyridines and / or pyridinecarboxylic acids as complexing agent (L). Etching solution according to at least one of the preceding claims, characterized by chelating amines bipyridine, phenanthroline, ethylenediamine and / or oligomeric analogs of ethylenediamine as Complexing agent L. Etching solution after at least one of the preceding claims, characterized by oximes in the form of diacetyldioxime (dimethylglyoxime) as complexing agent L. Etching solution after at least one of the preceding claims, characterized by thiols, and / or Thiosulfates as complexing agent L. Etching solution after Claim 15, characterized by thiols in the form of propanethiol, Ethanthiole, butanethiol and / or thiophenol. Etching solution after at least one of the preceding claims, characterized by complexing agents L from compounds of thiosulfates, thiocyanates and / or nitrates as anions and Li, Na, K, Ca, Mg and / or tetraalkylammonium as Cations, wherein the alkyl radicals methyl, ethyl, propyl, benzyl radicals or their permutation. Etching solution after at least one of the preceding claims, characterized by L Ammonia and / or ammonium thiosulfate as complexing agent. Etching solution after at least one of the preceding claims, characterized by peroxo compounds as an oxidizing agent. Etching solution according to at least one of the preceding claims, characterized by hydrogen peroxide H ₂ O ₂ and / or peroxodisulfates, in particular ammonium peroxodisulfate (NH ₄ ) ₂ S ₂ O ₈ , as oxidizing agent. Etching solution after at least one of the preceding claims, characterized by hypochlorites, Hypobromides, peroxophosphates, peroxodiphosphates, permanganates, peroxochromates, Perrhenates, ozonides and / or organic peroxides as oxidizing agents. Etching solution after Claim 21, characterized by di-tert-butyl peroxide or dibenzoyl peroxide as organic peroxides. Etching solution after Claim 20 or 21, characterized in that the salt-form oxidizing agent in Form of tetraalkylammonium salts are present. Etching solution after at least one of the preceding claims, characterized by the Use of water, alcohols, especially methanol, ethanol, iso- or n-propanol, cyclic ethers, in particular dioxane or tetrahydrofuran, dimethyl sulfoxide and / or dimethylformamide as a solvent. Etching solution after at least one of the preceding claims, characterized by 0, 01 to 10% by volume of other additives in the form of surfactants, alcohols, solvents, inert salts and / or bases or acids for adjusting the pH value. Use of an etching solution after at least one of the preceding claims for structuring metal layers, in particular silver layers in Conducting Bridging (CB) RAM cells. Use of an etching solution after at least one the claims 1 to 25 for the structuring of silver conductive paths in electronic Components. Use of an etching solution after at least one the claims 1 to 25 for the structuring of copper- and silver-containing alloys and / or multilayer systems. Use of an etching solution after at least one the claims 1 to 25 for structuring layers of germanium chalcogenides, in particular germanium sulphide and / or germanium selenide. etching for structuring metal layers, in particular silver layers in Conducting Bridging (CB) - RAM cells, characterized by the use of an etching solution according to any one of claims 1 to 25th