Chemical solution containing sulphamic acid and hydrogen peroxide, suitable for polishing copper and alloys thereof by plasma electropolishing
Patent Information
- Application Number
- EP2024708567
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-07
- Filing Date
- 2024-03-01
- Publication Date
- 2026-01-14
AI Technical Summary
Current plasma electropolishing methods for copper and copper-based alloys do not achieve a mirror-like surface finish due to insufficient roughness reduction, and existing processes are either inefficient or require complex multi-step procedures.
An aqueous solution of sulphamic acid and hydrogen peroxide, optionally including an organic salt and a compound from the alcohol or ether family, is used in a plasma electropolishing process with specific concentration ranges and process parameters, such as voltage and temperature, to effectively smooth metal surfaces.
The solution enables faster and more efficient surface smoothing, achieving a mirror-like finish with less material removal, reduced environmental and health hazards, and eliminates the need for pre-treatments, while being simpler and more efficient than traditional methods.
Smart Images
Figure IB2024051988_12092024_PF_FP
Abstract
Description
[0001] CHEMICAL SOLUTION CONTAINING SULPHAMIC ACID AND HYDROGEN PEROXIDE, SUITABLE FOR POLISHING COPPER AND ALLOYS THEREOF BY PLASMA ELECTROPOLISHING
[0002] Technical field of the invention
[0003] The invention relates to a composition for plasma electrolpolishing of metal surfaces and to the related electropolishing process using said composition. In particular, said composition consists of an aqueous solution of sulphamic acid, hydrogen peroxide, an organic salt, and a compound selected from an alcohol, a diol and an ether; and to the related plasma electropolishing process.
[0004] Prior art
[0005] The present invention relates to a process for plasma electropolishing of metal surfaces. More specifically, the present invention relates to the composition of the polishing solution and optimal process parameters to be applied to the plasma electropolishing process for metal surfaces such as copper (Cu), cupronickel, constantan, brass, copper-zinc-nickel alloys, and copper-based alloys.
[0006] Typically, the polishing of metal surfaces is carried out through chemical or electrochemical processes.
[0007] In chemical polishing, the workpiece is immersed in a concentrated aqueous solution of several acids, the action of which removes a superficial layer of metal, acting preferentially upon the irregularities of the surface and reducing the roughness thereof.
[0008] In the electrochemical process, also referred to as electropolishing or electrolytic polishing, the workpiece is immersed in a concentrated aqueous solution of several acids and connected to the positive pole of an electric circuit, thus acting as the anode of an electrolytic cell. A second metal electrode, immersed in the same solution and facing the workpiece from a suitable distance from the latter (usually about ten centimetres), acts as the cathode. The application of a potential difference across the anode and the cathode triggers an oxidation reaction on the metal of the workpiece to be treated, thereby partially dissolving it into the solution. Such oxidation reaction occurs preferentially on the irregularities of the metal surface, which are thus dissolved to a greater extent and smoothed out. The final effect is a reduction in the workpiece's roughness.
[0009] With reference to copper or copper-alloy surfaces, the solutions used for chemical polishing, in the absence of applied voltage, consist of concentrated solutions of acids (e.g., acetic acid, phosphoric
[0010] 2 acid, nitric acid, hydrochloric acid) or mixtures of sulphamic acid, ammonium citrate, n-butanol and hydrogen peroxide. The solutions most commonly used for electropolishing comprise phosphoric acid (H3PO4) in aqueous solution with the addition of moderators such as butanol, ethylene glycol and glycerol; the operating voltage varies between 0.2V and 2.2V.
[0011] An alternative approach is the so-called plasma electropolishing, or plasma electrolytic polishing (PEP), which differs from traditional electropolishing for the higher voltages employed, between 200 V and 400 V, which allow for faster processing times and permit the use of diluted solutions. In fact, PEP uses diluted aqueous solutions of salts, which allow the creation of a uniform layer of vapor and gas, in which the surface smoothing process can take place. This process is well known in the industry, and is applied to various metals and alloys, such as chrome-cobalt-molybdenum and stainless steel, for which several polishing recipes are available. As concerns copper and its alloys, some compositions are known in the literature for plasma electropolishing [I. A. Kostogrud, E. V. Boyko, P. E. Matochkin, and D. V. Sorokin, 'Comparing the methods of copper substrate polishing for CVD graphene synthesis', J. Phys.: Conf. Ser., vol. 2057, no. 1, p. 012121, Oct. 2021, doi: 10.1088 / 1742-6596 / 2057 / 1 / 012121; United States patent US20100200424A1; Belarussian patent BY 11410; Russian patent RU 2127334; Belarussian patent BY 8424; Russian patent RU2013129493A], which, however, do not provide sufficient roughness reduction to achieve a mirror-like surface. In particular, the above-mentioned patent US20100200424A1 claims a process that requires a significantly lower voltage than described herein, thus not providean efficientpolishing. Patent RU 2127334 describes a process consisting of two distinct steps requiring different compositions and process conditions, thus being more complex and time-consuming than the one disclosed in the present invention, which only requires one step.
[0012] Notwithstanding the advantages offered by plasma electropolishing over the polishing methods described above, the identification of parameters for the composition of the electrolyte and the ideal time and current conditions to be applied when treating other metals is still unresolved.
[0013] It is the object of the present invention to provide a polishing solution composition and optimal process parameters to be applied to a plasma electropolishing process for processing metal surfaces of copper (Cu) or copper-based alloys such as, for example, cupronickel, constantan, brass, copper- zinc-nickel alloys, such as to give better results than traditional electrolytic polishing techniques. Summary of the invention
[0014] 3 The present invention relates, in general, to a composition of a solution to be used in a plasma electropolishing process for metal surfaces. More specifically, the invention relates to an aqueous solution of sulphamic acid (H2NSO3H) and hydrogen peroxide (H2O2). In some preferred embodiments of the invention, the solution further comprises an organic salt and / or a compound selected from an alcohol and an ether.
[0015] Furthermore, the present invention defines a process for plasma electropolishing of metal surfaces using said solution. In particular, said plasma electropolishing relates metal surfaces made of one of the following metals: copper (Cu), zinc (Zn), nickel (Ni), low-carbon steels, or alloys containing one or more of such metals.
[0016] Brief description of the drawings
[0017] Figure 1: Schematic description of the plasma electropolishing process
[0018] Key
[0019] 1 - surface to be treated, 2 - composition for plasma electropolishing, 3 - second metal element, 4 - positive pole, 5 - negative pole, 6 - voltage generator.
[0020] Detailed description of the invention
[0021] In the description of the present invention, the expression "surface to be polished" refers to any object having an exposed metal surface, the roughness of which has to be reduced; the "anode" means the electrode of an electrochemical cell undergoing an oxidation reaction, and the "cathode" means the electrode where a reduction reaction occurs.
[0022] According to the present invention, an aqueous solution is provided for use in a plasma electropolishing process for metal surfaces as set out in claim 1.
[0023] For a better understanding of the present invention, a preferred embodiment thereof will be described below merely by way of non-limiting example.
[0024] The present invention concerns an aqueous solution of sulphamic acid and hydrogen peroxide for use in a plasma electropolishing process for metal surfaces. According to the preferred embodiment of the invention, the concentration of sulphamic acid (H2NSO3H) is comprised between 5 g / l and 30 g / l, while the concentration of hydrogen peroxide (H2O2) is comprised between 45 ml / l and 55 ml / l.
[0025] 4 In order to achieve more control over the plasma electropolishing process, it is possible to add to the above-described solution further components, which for clarity will be classified into two categories: a component A belonging to a first group, and a component B belonging to a second group.
[0026] The additional component A, which is optional for the purposes of defining the protection scope of the present patent, is typically a salt such as, for example, ammonium citrate in its monobasic, dibasic or tribasic form, or tartrate of sodium and potassium.
[0027] Said salt also plays a crucial role in stabilizing the pH of the solution of sulphamic acid and hydrogen peroxide, i.e. the so-called buffer effect.
[0028] An additional component B is represented by a so-called moderator. Forthe purposes of the present invention, the term moderator refers to a compound that reduces the speed of a process, e.g. phosphoric acid in copper chemical polishing [1] or in niobium polishing [2], The function performed by the component B, or moderator, is to modify the conductivity of the final solution, increase viscosity, and modify the ratio among the other solution components, thus affecting the speed of the polishing process, which will consequently be reduced.
[0029] In one embodiment of the invention, the component B may also be a compound which increases the viscosity and the wettability, or surface tension, of the solution. In such a case, these are often organic components of different composition belonging to the alcohols and ethers family. They are often defined in these cases as corrosion inhibitors [4], The main function performed by such compounds is to reduce electric conductivity, copper dissolution, and the amount of oxygen adjacent to the metal surface during the process.
[0030] Merely by way of non- exhaustive example, the following are some examples of components B: 1,2,4-butanetriol; 1,2,6-hexanetriol; 2-butoxyethanol; ethyl acetate; n-butyl acetate; cetyl alcohol; isobutyl alcohol; n-propyl alcohol; t-butyl alcohol; allyl alcohol; butyl carbitol; carbitol; propanone; ethanol; ethyl ether; propylene glycol ethers and acetates thereof; glycerol; ethylene glycol; isopropanol; methanetriol; pentaerythritol; sodium lauryl sulphate.
[0031] Another moderator example is found in the solution called "SUBU", developed by CERN, which is composed of four components: sulphamic acid, hydrogen peroxide, butanol and ammonium citrate [4], According to the authors, n-butanol limits the violent and exergonic reaction between hydrogen peroxide, sulphamic acid and ammonium citrate. In particular, said moderator limits the reactivity of oxygen with the compounds in the solution. In such heating situation, in the presence of an
[0032] 5 oxidizing product, butanol oxidizes to butyric acid (resembling acetic acid) and is a derivative of the corresponding ester. Over time, this acid increases the bath acidity and reacts with copper or copper oxide.
[0033] In a preferred embodiment of the invention, the component A is tribasic ammonium citrate (NH4)3- C6H5O7 with a concentration between 0.5 g / l and 3.0 g / l; the component B is 1-butanol (CH3(CH2)3OH) with a concentration of 50 ml / l.
[0034] In a preferred embodiment of the invention, the concentration of sulphamic acid (H2NSO3H) is 5 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is tribasic ammonium citrate (NHzih-CeHsOy with a concentration of 1.0 g / l; the component B is 1-butanol (CHsfCI-hhOH) with a concentration of 50 ml / l.
[0035] In a second preferred embodiment of the invention, the concentration of sulphamic acid (H2NSO3H) is 20 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI-khH-CeHsO? with a concentration of 1.0 g / l; the component B is ethanol (C2H5OH) with a concentration of 50 ml / l.
[0036] In a third preferred embodiment of the invention, the concentration of sulphamic acid (H2NSO3H) is 10 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI-khH-CeHsO? with a concentration of 1.0 g / l; the component B is n-butyl acetate (C6H12O2) with a concentration of 50 ml / l.
[0037] In a fourth preferred embodiment of the invention, the concentration of sulphamic acid (H2NSO3H) is 25 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI-khH-CeHsO? with a concentration of 0.5 g / l; the component B is glycerol (C3H8O3) with a concentration of 45 ml / l.
[0038] Advantageously, according to the invention, the solution composition described herein is used in a plasma electropolishing process for metal surfaces comprising one of the following metals: copper (Cu), zinc (Zn), nickel (Ni), low-carbon steels, or alloys containing such metals.
[0039] With reference to Figure 1, according to another aspect of the invention, the plasma electropolishing process defined by the present invention comprises the following steps: a) Placing the metal surface to be polished 1 in contact with the composition 2;
[0040] 6 b) Placing at least one further metal element 3 in contact with said composition 2, so that electrical contact between the metal surfaces 1 and 3 is ensured through said composition 2; c) Connecting the metal surface to be polished 1 to the positive pole 4 of a voltage generator 6 and the further metal element 3 to the negative pole 5 of said voltage generator 6, so that the metal surface to be polished 1 acts as an anode of an electrochemical cell; d) Increasing the temperature of the composition so that it is comprised between 70°C and 97°C; e) Applying a continuous potential difference comprised between 200 V and 400 V across the two electrodes.
[0041] Advantageously, according to the invention, the potential difference applied across the two electrodes is 300 V, while the temperature of the solution is maintained at 85°C.
[0042] The purpose of the present invention is to provide a composition for plasma electropolishing of metal surfaces, as well as an electropolishing process using said composition to overcome the limitations of the prior art.
[0043] An advantage of the present invention over the prior art is the speed at which the desired treatment is accomplished; in fact, the process according to the invention is 10-100 times faster than conventional electropolishing, and approximately 10 times faster than chemical polishing.
[0044] A further advantage of the present invention over the prior art lies in its higher efficiency; as a matter of fact, the polished effect of the treated surface is achieved by removing less material in comparison with processes known in the art.
[0045] Another advantage concerns the compositions covered by the present invention which, being comprising solutions at lower concentrations, they are less harmful for the environment and the health of operators than those used in the prior art.
[0046] A further advantage of the invention is the capability of removing contaminants from the processed surface due to the higher power used per area unit, thus avoiding the need for pre-treatments as commonly required by conventional electropolishing and chemical polishing processes (degreasing, ultrasonic cleaning, activation, polishing).
[0047] 7 Bibliography
[0048] [11 G. Petzow, Metallographic Etching, 2nd Edition: Techniques for Metallography, Ceramography, Plastography. ASM International, 1999.
[0049] [2] M. L. Kinter, I. Weissman, and W. W. Stein, 'Chemical polish for niobium microwave structures'. Journal of Applied Physics, vol. 41, no. 2, pp. 828-829, 1970.
[0050] [3] A. A. Attia, E. M. Elmelegy, M. El-Batouti, and A.-M. M. Ahmed, 'Studying Copper Electropolishing Inhibition in Presence of Some Organic Alcohols':, Port. Electrochim. Acta, vol. 34, no. 2, pp. 105- 118, 2016, doi: 10.4152 / pea.201602105.
[0051] [4] J. D. Adams, J. P. Birabeau, J. Guerin, and S. Pousse, 'Copper surface preparation processes compatible with Niobium sputter deposition: Presentation of a chemical polishing bath of a chemical polishing bath meeting this criterion', CERN-Technical-Note-85, 1985. [Online],
[0052] Available: https: / / cds.cern.ch / record / 2646136 / files / 85-SB-AC-B-3199-gp.pd
[0053] 8
Claims
Claims1. Composition for use in a plasma electropolishing process for metal surfaces, comprising an aqueous solution of sulphamic acid and hydrogen peroxide.
2. Composition according to the preceding claim, wherein the concentration of sulphamic acid (H2NSO3H) is comprised between 5 g / l and 30 g / l, and the concentration of hydrogen peroxide (H2O2) is comprised between 45 ml / l and 55 ml / l.
3. Composition according to the preceding claim, further comprising a component A selected from ammonium citrate in its monobasic, dibasic or tribasic form or tartrate of sodium and potassium.
4. Composition according to one of claims 1 and 2, further comprising a component B selected from: 1,2,4-butanetriol; 1,2,6-hexanetriol; 2-butoxyethanol; ethyl acetate; n-butyl acetate; cetyl alcohol; isobutyl alcohol; n-propyl alcohol; t-butyl alcohol; allyl alcohol; butyl carbitol; carbitol; propanone; ethanol; ethyl ether; propylene glycol ethers and acetates thereof; glycerol; ethylene glycol; isopropanol; methanetriol; pentaerythritol; sodium lauryl sulphate.
5. Composition according to one of the preceding claims, comprising a component A and a component B.
6. Composition according to the preceding claim, wherein the component A is tribasic ammonium citrate (NI- h-CeHsO? with a concentration between 0.5 g / l and 3.0 g / l, and the component B is 1-butanol (CHsfCI-hhOH) with a concentration of 50 ml / l.
7. Composition according to claim 5, wherein the concentration of sulphamic acid (H2NSO3H) is 5 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is tribasic ammonium citrate (NI- h-CeHsChwith a concentration of 1.0 g / l; the component B is 1-butanol (CHsfCI-hhOH) with a concentration of 50 ml / l.
8. Composition according to claim 5, wherein the concentration of sulphamic acid (H2NSO3H) is 20 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI- hH-CeHsOy with a concentration of 1.0 g / l; the component B is ethanol (C2H5OH) with a concentration of 50 ml / l.
9. Composition according to claim 5, wherein the concentration of sulphamic acid (H2NSO3H) is 10 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI- hH-CeHsO? with a concentration of 1.0 g / l; the component B is n-butyl acetate (C6H12O2) with a concentration of 50 ml / l.
10. Composition according to claim 5, wherein the concentration of sulphamic acid (H2NSO3H) is 25 g / l; the concentration of hydrogen peroxide (H2O2) is 50 ml / l; the component A is dibasic ammonium citrate (NI-khH-CeHsOy with a concentration of 0.5 g / l; the component B is glycerol (C3H8O3) with a concentration of 45 ml / l.
11. Plasma electropolishing process for metal surfaces using the composition according to one of the preceding claims, comprising the steps of: a) Placing the metal surface to be polished (1) in contact with the composition (2); b) Placing at least one further metal element (3) in contact with the same composition (2), so that electrical contact between the metal surfaces (1) and (3) is ensured through said composition (2); c) Connecting the metal surface to be polished (1) to the positive pole (4) and the further metal element (3) to the negative pole (5) of a voltage generator (6), so that the metal surface to be polished (1) acts as an anode of an electrochemical cell; d) Increasing the temperature of the composition so that it is comprised between 70°C and 97°C; e) Applying a continuous potential difference comprised between 200 V and 400 V across the two electrodes.
12. Process according to the preceding claim, wherein the metal surface to be polished (1) comprises at least one of: copper (Cu), zinc (Zn), nickel (Ni), low-carbon steels, or an alloy of said metals.
13. Process according to the preceding claim, wherein the potential difference applied across the two electrodes is 300 V.
14. Process according to the preceding claim, wherein the temperature of the solution is maintained at 85°C.