TWI629376B - Electroless copper plating solution - Google Patents

Abstract

The present invention relates to an electroless copper plating aqueous solution comprising: a source of copper ions, a source of a reducing agent or a reducing agent, and a combination of the following substances as a wronging agent: i) N, N, N ' , N ' - 肆(2-hydroxypropyl)ethylenediamine or a salt thereof, and ii) N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid or a salt thereof, and The solution is a method of electroless copper plating and the use of the solution in plating a substrate.

Description

Electroless copper plating solution

The present invention relates to an electroless copper plating solution, a method of using the solution to electroless copper plating, and the use of the solution in plating a substrate.

Electroless plating is a controlled auto-catalytic deposition of a continuous metal film without externally supplied electrons. The non-metallic substrate can be pretreated to render it acceptable for deposition or catalytic. All or a selected portion of the surface can be suitably pretreated. The main components of the electroless copper plating bath are copper salts, a binder, a reducing agent, and an alkaline agent as an optional component, and an additive such as, for example, a stabilizer. The binder is used to chelate the copper to be deposited and to prevent copper from precipitating from the solution (i.e., as a hydroxide and the like). The chelation of copper allows copper to be used to convert copper ions to a reducing agent in metallic form.

No. 4,617,205 discloses a composition for electroless deposition of copper comprising copper ions, glyoxylate as a reducing agent, and a complexing agent which forms a strong complex with copper as a copper oxalate complex (eg, EDTA) ).

US 7,220,296 teaches an electroless plating bath comprising a water soluble copper compound, glyoxylic acid and a EDTA miscible agent.

US 2002/0064592 discloses an electroless plating bath comprising a source of copper ions, glyoxylic acid or formaldehyde as a reducing agent, and EDTA, a tartrate or an alkanolamine as a complexing agent.

It is difficult to predict the performance of a copper plating solution and its strong dependence on the molar ratio of its components (especially the binder and reducing agent) and its components.

It is an object of the present invention to provide an electroless copper plating solution having improved properties, particularly improved copper deposition rates. Another object of the present invention is to provide an electroless copper solution for obtaining a copper deposit having a low roughness.

The present invention provides an electroless copper plating solution comprising: - a source of copper ions, - a source of a reducing agent or a reducing agent, and - a combination of the following substances as a wronging agent: i) N, N, N ' , N ' - hydrazine (2-hydroxypropyl) ethylenediamine or a salt thereof, and ii) N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid or a salt thereof.

The combination of the combination agents may further comprise iii) ethylenediaminetetraacetic acid or a salt thereof.

In the following, N, N, N ' , N ' - 肆 (2-hydroxypropyl) ethylene diamine is simply written as "Quadrol", which is a trademark of BASF Corporation.

Ethylenediaminetetraacetic acid is also referred to as "EDTA" hereinafter.

N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid is also referred to as "HEDTA" hereinafter.

In one embodiment, the electroless copper plating solution preferably does not comprise cyclohexanediaminetetraacetic acid (CDTA) in an amount ranging from 0.1 mM to 5.5 M. In another embodiment, the electroless copper plating solution is preferably completely free of CDTA.

One or more of the above objects are achieved by an electroless copper plating solution according to the first aspect (hereinafter abbreviated as "solution"), or by an advantageous embodiment as described in the accompanying claims and embodiments. The copper plating solution of the present invention exhibits an improved copper deposition rate. At the same time, a low roughness of the copper surface can be achieved, which is critical to the performance of a particular electronic device. Due to the higher deposition rate, a larger thickness of copper layer can be achieved at the same process time.

The solution according to the invention and the method according to the invention are preferably used for coating printed circuit boards, wafer carriers and semiconductor wafers or any other circuit carrier and interconnection means. The solution Liquids are especially useful for printed circuit boards and wafer carriers, but can also be used in semiconductor wafers to plate copper for surfaces, trenches, micro-blind vias, vias (vias), and the like.

In particular, the solutions of the present invention or the methods of the present invention can be used to deposit copper on surfaces, in trenches, microvias, vias, and printed circuit boards, wafers, carriers, wafers, and various other interconnect devices. Similar in structure. The term "via" or "via" as used in the present invention encompasses all types of vias and so-called "twist holes" included in germanium wafers.

Another application in which the solution can be used to obtain a beneficial effect is metallization of a smooth substrate preferably having a large surface area made of glass, ceramic or plastic. Examples are any type of display such as, for example, any type of TFT-display and liquid crystal display (LCD). As described above, the low roughness of the copper surface can be achieved by the solution of the present invention. This effect is particularly advantageous for display applications because the copper layer can be made to have good electrical conductivity.

The electroless copper plating solution of the present invention can be advantageously used to deposit copper on a glass substrate (especially those having a large surface area such as a glass panel). As noted above, glass substrates are used (without limitation) for display applications. Wet electroless copper deposition on a glass substrate by solution as described above is advantageous compared to the metal sputtering processes used to date. The advantages of sputtering technology can be achieved by wet electroless deposition, especially for reduced internal stress and reduced bending of glass substrates, reduced equipment maintenance, efficient use of metals, reduced material waste, and reduced processes. temperature.

Furthermore, the electroless copper plating solution of the present invention can be advantageously used for electroplating glass substrates, particularly glass panels for displays.

In summary, commonly used wet electroless deposition typically produces a rougher metal surface than the sputtering process. In the case of display manufacture, this leads to poor switching properties, in particular unfavorable extended switching times. Therefore, in terms of display manufacturing, it is necessary to form a metal layer having a roughness within a range achieved by the sputtering process. Surprisingly, the electroless copper plating solution of the present invention can not only form a metal layer at a higher deposition rate, but also has a sputtering process. Achieve low roughness within the range.

In addition, the substrate for display fabrication is activated by a metal seed layer for subsequent deposition of a metal layer to create the desired circuitry and switching elements. Thus, the metal seed layer has exhibited a pattern of future circuits and switching elements including small and/or isolated active regions and combinations of small and large active regions. The high copper deposition rate on a glass substrate, especially on a glass substrate having such small and/or isolated activation regions, is achieved by the solution of the invention. In addition, the solution of the present invention can simultaneously deposit a metal layer having a uniform thickness at a high deposition rate on small and large activation regions.

The solution of the invention is an aqueous solution. The term "aqueous solution" means that the main liquid medium, which is the solvent in the solution, is water. Other liquids that are miscible with water, such as, for example, alcohols and other polar organic liquids, may be added.

The solution of the present invention can be prepared by dissolving all components in an aqueous liquid medium, preferably dissolved in water.

The solution contains a source of copper ions, which can be, for example, any water soluble copper salt. Copper may, for example, (without limitation) be added with copper sulfate, copper chloride, copper nitrate, copper acetate, copper methanesulfonate ((CH ₃ O ₃ S) ₂ Cu), copper hydroxide; or a hydrate thereof.

A reducing agent is used to reduce copper ions to obtain metallic copper for electroplating. Reducing agents which can be used, for example (without limitation) are formaldehyde, glyoxylic acid, hypophosphite, hydrazine, and borohydride. Preferred reducing agents are formaldehyde and glyoxylic acid.

The term "source of reducing agent" means a substance that is converted into a reducing agent in a solution. The source is, for example, a reductant precursor that is converted to a reducing agent. An example is given below for glyoxylic acid.

Glyoxylic acid is a preferred reducing agent based on safety, health and environmental requirements. Although formaldehyde is an extremely important and established reducing agent for commonly used electroless copper processes, it is classified as a possible human carcinogen. Thus, in one embodiment, the electroless copper plating solution comprises a source of glyoxylic acid or glyoxylic acid. In this embodiment, the solution of the present invention contains no formaldehyde or is exchanged. In other words, according to this embodiment, the solution contains no formaldehyde.

The term "source of glyoxylic acid" encompasses all compounds, such as precursors, which can be converted to glyoxylic acid in aqueous solution. A preferred precursor is dichloroacetic acid. Glyoxylic acid is a reducing agent for reducing copper ions to elemental copper. In this solution, glyoxylic acid and glyoxylate ions may be present. As used herein, the term "glyoxylic acid" includes salts thereof. The exact nature of the substance (acid or salt) present will depend on the pH of the solution. This same consideration applies to other weak acids and weak bases.

In addition to one of the above reducing agents, one or more other reducing agents such as, for example, diphosphoric acid, glycolic acid or formic acid, or a salt of the foregoing may be added. The other reducing agent is preferably used as a reducing agent but not as the sole reducing agent (see, for example, US 7,220,296, at column 4, lines 20 to 43 and lines 54 to 62). Therefore, the other reducing agent is also referred to as a "promoter" in this sense.

The electroless copper bath using the above reducing agent preferably uses a relatively high pH, usually between 11 and 14, preferably between 12.5 and 13.5, and is typically made up of potassium hydroxide (KOH), It is adjusted with sodium hydroxide (NaOH), lithium hydroxide (LiOH), ammonium hydroxide or quaternary ammonium hydroxide such as tetramethylammonium hydroxide (TMAH). Thus, the solution may comprise a source of hydroxide ions such as, for example, but not limited to, one or more of the compounds listed above. The source of the hydroxide is, for example, added if the desired solution is at an alkaline pH and the pH is not already in the alkaline range due to other components.

Potassium hydroxide is preferably used. If glyoxylic acid is used as the reducing agent, potassium hydroxide is advantageous because of the high solubility of potassium oxalate. An oxalate anion is formed in the solution due to oxidation of glyoxylic acid. Therefore, potassium hydroxide is particularly preferred in terms of the stability of the solution of the present invention.

The solution of the present invention further comprises a mixture of the complexing agent i) Quadrol or a salt thereof and a complexing agent ii) HEDTA or a salt thereof. The complexing agent i) Quadrol or a salt thereof and a mixture of the ii) HEDTA or a salt thereof may further comprise a complexing agent iii) EDTA or a salt thereof. will The addition of Quadrol or its salt to the complexing agent ii) or to the mixture of the complexing agent ii) and the complexing agent iii) results in an effective increase in copper deposition. Prior to carrying out the invention, it has been observed that an increase in the rate of metal deposition results in an increased roughness of the metal surface. In the present invention, surprisingly, a high copper deposition rate and a copper surface having a low roughness are obtained.

The salt of Quadrol, HEDTA or EDTA can be any suitable water soluble salt. The counter ion of the salt of Quadrol, HEDTA or EDTA is preferably selected from the group consisting of alkali metal ions, alkaline earth metal ions and ammonium ions. The counter ion of the salt of Quadrol, HEDTA or EDTA is more preferably selected from the group consisting of lithium ion, sodium ion, potassium ion, magnesium ion, calcium ion and ammonium ion.

The solution of the invention is free of toxic co-metals. The solution of the invention is especially free of nickel. Nickel forms a more stable complex with copper than the complexing agents used herein. It thus reduces copper mismatch and negative effects or hinders copper deposition. Furthermore, the presence of nickel in the bath will result in unnecessary nickel deposition, which must be avoided especially in display manufacturing.

In one embodiment of the solution of the present invention, the molar ratio of the cross-linking agent to copper ion in terms of the total molar amount of all of the complexing agents is from 1:1 to 10:1, preferably from 1:1 to 8:1. More preferably 2:1 to 8:1, even more preferably 2:1 to 5:1, even better: 1.5:1 to 4:1, and most preferably in the range of 2:1 to 4:1. The molar ratio of the complexing agent to the copper ion in terms of the total molar amount of all the wronging agents is defined as the ratio of the total molar amount of all the wronging agents to the molar amount of the copper ions. The total molar amount of all the wrong agents is the sum of the individual moles of all the wrong agents. The "all miscible agents" may be a mixture of the complexing agent i) and the complexing agent ii) or may be a mixture of the complexing agent i), the complexing agent ii) and the complexing agent iii). In the examples, the amount of the cross-linking agent is also given in equivalents. One equivalent is the amount of the complexing agent that is completely mismatched with the specified amount of copper ion. In the case of Quadrol, EDTA and HEDTA or a salt thereof, one equivalent of the complexing agent corresponds to a molar ratio of 1:1 to the copper ion. In the case of Quadrol, EDTA and HEDTA, the molar ratio of 1:1 to 10:1 to copper ion means 1 to 10 equivalents of the copper-associated complexing agent.

Less complexing agent can result in instability of the bath or no initial deposition. More complexing agents relative to copper result in a higher density of the bath, which also leads to a shortened life of the bath and no stability. The use of these ranges results in a beneficial combination of high copper deposition rates and low roughness.

In another embodiment, the molar ratio of the cross-linking agent to the copper ion in terms of the total molar amount of all of the complexing agents is from 3:1 to 8:1, more preferably from 3:1 to 5:1, even better. Within the range of 3:1 to 4:1. The use of these ranges results in a combination of particularly beneficial high copper deposition rates and low roughness. Reproducible performance, highly reproducible copper deposits, and a copper layer with extremely uniform thickness.

In one embodiment, the molar ratio of the molar amount of the complexing agent i) to the molar amount of the complexing agent ii) is from 1:0.05 to 1:20, preferably from 1:0.1 to 1:10, more preferably from 1:1 to 1:5, even better from 1:1 to 1:4, best from 1:2 to 1:4. The molar ratio of the molar amount of the wrong agent i) to the molar amount of the mixture of the wrong agent ii) and the complexing agent iii) (coupling agent i): [complexing agent ii) + the complexing agent iii)]) ranges from 1: 0.05 to 1:20, preferably from 1:0.1 to 1:10, more preferably from 1:1 to 1:5, even more preferably from 1:1 to 1:4, optimal from 1:2 to 1:4 .

The molar amount of the mixture of the wronging agent ii) and the complexing agent iii) ([clipping agent ii) + the complexing agent iii)]) is the sum of the individual molar amounts of the complexing agent ii) and the complexing agent iii).

In another embodiment, the molar ratio of the molar amount of the complexing agent i) to the molar amount of the complexing agent ii) is from 1:0.05 to 1:5, preferably from 1:0.05 to 1:3, more preferably 1: 0.1 to 1:2. The molar ratio of the molar amount of the wrong agent i) to the molar amount of the mixture of the wrong agent ii) and the complexing agent iii) (coupling agent i): [complexing agent ii) + the complexing agent iii)]) ranges from 1: 0.05 to 1:5, preferably from 1:0.05 to 1:3, more preferably from 1:0.1 to 1:2.

In another embodiment, the molar ratio of the molar amount of the complexing agent i) to the molar amount of the complexing agent ii) is from 1:5 to 1:20, preferably from 1:7 to 1:15, more preferably. From 1:7 to 1:10. The molar ratio of the molar amount of the wrong agent i) to the molar amount of the mixture of the wrong agent ii) and the complexing agent iii) (coupling agent i): [complexing agent ii) + the complexing agent iii)]) ranges from 1: 5 to 1:20, preferably from 1:7 to 1:15, more preferably from 1:7 to 1:10.

The use of the above range results in a beneficial combination of high copper deposition rate and low roughness.

In one embodiment, the electroless copper plating aqueous solution comprises a combination of the following materials as a complexing agent: i) N, N, N ' , N ' - 肆 (2-hydroxypropyl) ethylene diamine (Quadrol) or a salt thereof, and Ii) N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid (HEDTA) or a salt thereof.

In still another embodiment, the electroless copper plating solution comprises a combination of the following materials as a blocking agent: i) N, N, N ' , N ' - 肆 (2-hydroxypropyl) ethylene diamine (Quadrol) or a salt thereof, Ii) N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid (HEDTA) or a salt thereof, and iii) ethylenediaminetetraacetic acid (EDTA) or a salt thereof.

In one embodiment, the solution of the invention comprises the following class of ingredients at the following concentrations:

Copper ion: 1-5 g / l, equivalent to 0.016 to 0.079 mol / l, preferably 2.0 to 3.0 g / l

Reducing agent: 0.027 to 0.270 mol/l, preferably, glyoxylic acid: 2 to 20 g/l, or formaldehyde: 0.8 to 8.5 g/l.

The complexing agent (the total amount of all the complexing agents): 5 to 50 g/l, preferably 20 to 40 g/l, more preferably 20 to 30 g/l.

The solution of the present invention may contain, but does not necessarily contain, other components such as, for example, stabilizers, surfactants, additives (such as rate controlling additives, grain refining additives), pH buffers, pH adjusters, and Promoter. Such other components are described, for example, in the subsequent documents incorporated by reference in its entirety: US 4,617,205 (especially the disclosure of column 6, line 17 to column 7, line 25), US 7,220,296 (especially section 4) Columns 63 to 6 (line 26), US 2008/0223253 (see paragraphs 0033 and 0038 of the specific words).

Stabilizing agents (also known as stabilizers) are compounds that stabilize the electroless plating solution in the overall solution to prevent unnecessary external plating. The term "external plating" means that copper is unnecessarily and/or uncontrolledly deposited on, for example, the bottom or other surface of a reaction vessel. The stabilizing function can be achieved, for example, by a substance that acts as a catalytic poison (for example, a compound containing sulfur or other chalcogen elements) or by a compound that forms a copper (I)-de complex, thereby inhibiting the formation of copper (I) oxide. .

The solution of the invention may comprise one or more stabilizers. Suitable stabilizers are (without limitation) bipyridyl (2,2'-bipyridyl, 4,4'-bipyridyl), morpholine, mercaptobenzothiazole, thiourea or derivatives thereof, cyanide (eg NaCN) , KCN, K ₄ [Fe(CN) ₆ ]); Na ₂ S ₂ O ₃ , K ₂ S ₂ O ₃ , thiocyanate, iodide, ethanolamine, polymer (eg polyacrylamide, polyacrylate) , polyethylene glycol, or polypropylene glycol) and copolymers thereof.

In another aspect, the invention is directed to a method for electroless copper plating, the method comprising contacting a substrate with an electroless copper plating solution as described above.

For example, the substrate can be impregnated or soaked in the solution of the invention. In this method, the entire surface of the substrate or only selected portions may be plated with copper.

The solution is preferably stirred while in use. In particular, handling and/or solution-stirring can be used.

The method will be carried out for a period of time sufficient to form a deposit of the desired thickness, which will thus depend on the particular application.

One contemplated application of this method is the fabrication of printed circuit boards. Electroless deposition of copper in accordance with the method of the present invention is particularly useful for through plating of holes, surfaces, trenches, and micro-blind holes in printed circuit boards. Double or multi-layer sheets (rigid or flexible) can be plated by the present invention.

The method of the present invention can be used to provide an electroless copper deposit having a thickness in the range of from 0.05 μm to 10 μm, preferably from 0.1 μm to 10 μm, from 0.1 μm to 5 μm, from 0.5 μm to 3 μm. As described in the examples, the thickness of the copper layer was measured by a white light interferometer.

The method of the present invention forms a copper layer having a roughness expressed by a root mean square roughness parameter of 5 nm to 60 nm, preferably 5 nm to 55 nm, and more preferably 10 nm to 45 nm on the substrate. The obtained roughness is reduced by 30% to 60%, preferably by 40% to 50, compared to the method using only the wrong agent ii) or only the wrong agent iii) or only the mixture of the wrong agents ii) and iii). %. In this case, the term "only" means: no Quadrol is added. As described in the examples, the roughness of the copper layer was measured by a white light interferometer.

Most commonly, substrates commonly used in printed circuit board manufacturing are epoxy or epoxy. Glass composite. However, other substances can be used, in particular, phenolic resins, polytetrafluoroethylene (PTFE), polyimine, polyphenylene ether, BT (bismaleimide triazine)-resin, cyanate ester and polyfluorene.

In addition to the application of this method in the manufacture of printed circuit boards, it has been found to be suitable for electroplating from glass, ceramics or plastics such as, for example, ABS, polycarbonate, polyimide or polyethylene terephthalate. The substrate is made.

In another embodiment of the method, the substrate is a substrate having a large surface area, preferably made of glass, ceramic or plastic. A large surface area means an area of preferably at least 1 m ² , preferably at least 3 m ² , more preferably at least 5 m ² . In another embodiment, the large surface area means an area of preferably from 1 m ² to 9 m ² , more preferably from 3 m ² to 9 m ² , even more preferably from 3 m ² to 6 m ² , still more preferably from 5 m ² to 6 m ² . The substrate preferably has a smooth surface. The term smooth means a roughness (Sq or RMS) of preferably several nanometers. Preferably, the roughness is 5 to 30 nm as measured by RMS. Descriptions of the methods for roughness measurement and the terms "Sq" and "RMS" are provided in the examples.

In a particular embodiment, the substrate is a glass substrate, preferably a glass panel. These glass substrates (especially glass panels) can be used in applications such as liquid crystal display TFT displays. Therefore, the glass substrate is specifically intended to conform to the glass substrate such as, for example, thickness and smoothness used in the manufacture of the display. A preferred glass-based alkali-free, such as an alkali-free borosilicate glass.

As explained further below, the glass substrate can be pretreated, for example by metal seeding, prior to performing the method of the invention.

In one embodiment of the process of the invention, the process is carried out at a temperature in the range of from 20 to 60 ° C, preferably from 30 to 55 ° C. It has been confirmed in the present invention that when Quadrol is used as a binder in combination with another compounding agent, copper deposition can be carried out at a temperature which is low in the presence of the component. Although the temperature is lower, the deposition rate is higher than in the case of using a bath containing no Quadrol.

The substrate (ie, the surface of the substrate to be copper plated, especially the non-metallic surface) can be genus The method of the art, such as, for example, described in column 8 of US Pat. No. 4,617,205, is pre-treated to make it more acceptable for copper deposition acceptability or autocatalytic. All or selected portions of the surface can be pretreated. However, pretreatment is not required in each case, depending on the type of substrate and surface. In the pretreatment, the substrate may be sensitized prior to electroless deposition of copper thereon. This can be achieved by adsorbing a catalytic metal such as a noble metal such as palladium onto the surface of the substrate.

The pretreatment process is highly dependent on parameters such as the substrate, the desired application, and the desired properties of the copper surface.

An exemplary and non-limiting pretreatment process, particularly for printed circuit board laminates and other suitable substrates, can include one or more of the following steps: a) cleaning and processing the substrate as needed to enhance adsorption. The organic matter and other residues are removed by a cleaning agent. The cleaning agent may also comprise other materials (conditioners) which are prepared for subsequent activation steps (i.e., to enhance adsorption of the catalyst and to produce a more uniform activated surface), b) etched from the surface of the copper, especially The oxide is removed from the inner layer of the hole. This can be accomplished by a persulfate or peroxide based etching system, c) contact with a prepreg such as a hydrochloric acid solution or a sulfuric acid solution, optionally with an alkali metal salt (such as sodium chloride) also present in the prepreg. Contact, d) contact with an activator solution comprising a colloidal or ionically catalyzed metal such as a noble metal, preferably palladium, such that the surface becomes catalytic.

The pre-dip in step c) can be used to protect the activator from being carried in and contaminated, and optionally, in the case where the activator comprises an ion-catalyzed metal, e) is contacted with a reducing agent, wherein the metal ion of the ion activator is Revert to elemental metal.

Or, if the activator comprises a colloidal catalytic metal, f) is contacted with an accelerator, wherein the autocatalytic metal removes the colloid (eg, a protective colloid) Component.

In another type of pretreatment process, a permanganate etching step is employed. The so-called desmear process is a multi-stage process, and the steps are an expansion step, a permanganate etching step, and a reduction step. The expansion agent used in the expansion step is composed of a mixture of organic solvents. In this step, the drilled slag and other impurities are removed from the surface of the substrate. A high temperature of 60 to 80 ° C promotes the wetting of the expanding agent to obtain an expanded surface. Therefore, in the permanganate etching step, the subsequently applied permanganate solution can be more strongly eroded. Subsequently, the reducing solution of the reduction step removes manganese dioxide produced in the permanganate step from the surface. The reducing solution contains a reducing agent and, if desired, a conditioning agent.

The desmear process can be combined with the above steps. The desmear process may be performed prior to step a) of the above pretreatment process or the desmear process may be performed in place of steps a) and b) of the above pretreatment process.

In a pretreatment process that is particularly suitable for metallization of display applications and metallization of glass substrates, the surface is only in contact with the prepreg and activator solutions and then with the solution of the invention. The contact with the cleaning solution and the adhesion promoter prior to the pre-dip step can be carried out in advance as needed.

A further process typically used for glass substrates can be performed prior to copper plating using the following steps: the surface of the glass to be plated exhibits a metal seed layer. The metal seed layers can be brought to the surface by sputtering techniques. An exemplary seed crystal is a layer composed of copper, molybdenum, titanium, or a mixture thereof. The pretreated glass surface is contacted with an activator solution comprising an ion catalyzed metal such as a noble metal, preferably palladium, to render the surface catalytic. The ion-catalyzed metal is reduced by the seed metal and deposited on the surface. In this process, the addition of another reducing agent may be omitted. This process is especially useful for copper plating of glass substrates used in display applications.

If desired, the exemplary pre-treatment process, or individual steps thereof, can be combined into an alternative pre-treatment process.

In another aspect, the present invention relates to an electroless copper solution as described above. Plating printed circuit boards, wafers, integrated circuit substrates, molded interconnect devices (MID) components, displays (such as liquid crystal or plasma displays, especially for electronic devices or TV displays), display components, or plastic components Uses such as plastic parts for functional or decorative purposes.

The invention will now be discussed in more detail by subsequent examples. The examples are described to illustrate the invention, but should not be construed as limiting the invention.

Roughness measurement method:

The thickness of the electroless copper plating layer (the height difference between the substrate plane and the plating pattern) and the surface roughness were measured using an optical surface profiler/white light interferometer (model MIC-520, ATOS GmbH (Germany)). A white light interferometer is an optical microscopy method known to those skilled in the art to project a target region of a sample onto a CCD camera. A high-precision reference mirror is also projected onto the CCD camera using an interference objective equipped with an internal partial light. Based on the overlap of the two images, a spatially resolved interferogram reflecting the height difference between the extremely flat reference mirror and the associated sample is established. A vertical scanning scheme is used to image a sample with a large height distribution, i.e., to image the interferogram of the relevant region as a series within a range of different sample-objective distances. From these data, a full three-dimensional image is assembled. With this method, a configuration image in the range of 60 μm × 60 μm to 1.2 mm × 1.2 mm can be recorded with a vertical resolution in the range of several nm.

The configuration data is used to calculate the surface roughness expressed by the root mean square roughness parameter, which is abbreviated as Rq or RMS (contour roughness parameter) on the surface profile and Sq (area roughness parameter) on the surface configuration. The meaning of Rq has the same meaning as RMS. Rq has the meaning and Sq as defined in DIN EN ISO 4287 (German and English, 1998, Chapter 4.2.2) Has the meaning as defined in ISO 25178-2 (April 2012) (Chapter 4.1.1).

Further, the configuration data is used to calculate the thickness of the copper plating layer from the difference in height between the substrate surface (base plane) and the surface of the plated metal pattern. To calculate the configuration image, layer thickness and surface roughness, the optical surface profilometer/white light interferometer (model MIC-520, ATOS GmbH (Germany)) was equipped with the computer software Micromap 123 (version 4.0, Micromap Corporation).

The measurement mode is Focus 560M. The conformal image is measured by an objective lens having a magnification of 10 times and an eyepiece having a magnification of 2 times. The configuration image was recorded in the range of 312 μm × 312 μm and consisted of 480 × 480 dots.

Example 1: Combination of Quadrol and another wrong agent

Substrate: alkali-free borosilicate glass, 0.7 mm thick, copper sputtered seed layer.

Pretreatment:

1. Alkaline cleaner 40 ° C / 1 min

2. Flush with H ₂ O

3. Sulfuric acid pre-dip solution, room temperature (RT) / 20 seconds

4. Ionic Pd-activator (exchange reaction between Cu and Pd) RT/2min

5. Flush with H ₂ O

An electroless copper plating solution was prepared. Regarding the complexing agent, a combination of Quadrol/EDTA (control) and Quadrol/HEDTA (example of the present invention) was used. The Quadrol was added in an amount of 0 g/l, 2.7 g/l, and 5.4 g/l, respectively. The Cu ²⁺ ion is added as CuSO ₄ *6H ₂ O. The pH of the bath was 13.2 at 21 °C.

Each time the substrate was contacted with the respective plating solution as described above at 45 ° C for 12 min. The sample of the deposited Cu layer was analyzed according to the method described in the measurement mode "Focus 560M". The results are shown in Tables 1 and 2 below. Figures 1 and 2 show graphs of the results obtained.

Table 1: Combination of Quadrol/EDTA

The residence time means the time during which the substrate is in contact with the electroless copper plating solution.

When the same process time is selected, the combination of Quadrol/EDTA (Table 1, Figure 1) or Quadrol/HEDTA (Table 2, Figure 2) results in an increase in copper thickness compared to EDTA alone or HEDTA alone. . These results show that the addition of Quadrol increases the deposition rate while significantly reducing the roughness of the deposited copper layer. Adding Quadrol to already included In the case of a solution with HEDTA, the roughness versus deposition rate is lower than in the case where Quadrol is added to a solution that already contains EDTA alone.

Example 2: Comparative Example

The substrate used in Example 1 was pretreated as described in Example 1.

An electroless copper plating solution was prepared as described in Example 1. The copper plating solutions comprise a combination of the wrong agents Quadrol and HEDTA at a molar ratio of 1:20. As shown in Table 3, the amount of moles of the wrong agent was changed relative to the amount of moles of copper ions. A mixture of cyanide and sulfur compounds is added as a stabilizer.

Each of the two pretreated substrates (samples A and B) was contacted with each of the respective plating solutions as described above at 45 ° C for 10 min each time. A sample of the deposited Cu layer was analyzed as described in Example 1. The results are shown in Table 3.

Both of the electroless copper plating solutions deposit copper at a high deposition rate, however, the roughness of the resulting copper layer is too high. In addition, when Quadrol and HEDTA were used at a molar ratio of 0.5:1 relative copper ion, the electroless copper plating solution became unstable. When Quadrol and HEDTA were used at a molar ratio of 11:1 relative copper ion, the deposited copper layer showed wild-type growth and foaming.

Figure 1. Effect of the combination of Quadrol and other EDTA in the electroplating process on copper thickness and roughness.

Figure 2 Effect of the combination of Quadrol and other miscinders HEDTA on copper thickness and roughness in the electroplating process.

Claims (15)

An electroless copper plating aqueous solution comprising: a source of copper ions, a source of a reducing agent or a reducing agent, and a combination of the following substances as a wronging agent: i) N, N, N ' , N ' - 肆 (2-hydroxyl Propyl)ethylenediamine or a salt thereof, and ii) N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid or a salt thereof. The electroless copper plating solution of claim 1, wherein the combination of the wrong agents further comprises iii) ethylenediaminetetraacetic acid or a salt thereof. An electroless copper plating solution according to claim 1 or 2, wherein the ratio of the total molar amount of all the wronging agents to the copper ions is in the range of 1:1 to 8:1. The electroless copper plating solution of claim 1 or 2 wherein the ratio of the molar amount of the complexing agent i) to the molar amount of the complexing agent ii) ranges from 1:0.05 to 1:20. An electroless copper plating solution according to claim 1 or 2, wherein the molar ratio of the molar amount of the complexing agent i) to the molar amount of the mixture of the wronging agent ii) and the complexing agent iii) is from 1:0.05 to 1:20. An electroless copper plating solution according to claim 1 or 2, wherein the reducing agent is selected from the group consisting of glyoxylic acid and formaldehyde. A method for electroless copper plating, the method comprising contacting a substrate with an electroless copper plating solution according to any one of claims 1 to 6. The method of claim 7, wherein the substrate is a substrate made of glass, ceramic or plastic. The method of claim 7 or 8, wherein the substrate is a glass substrate, preferably a glass panel. The method of claim 7 or 8, wherein the substrate has a large surface area. The method of claim 10, wherein the large surface area is a surface area of at least 5 m ² . The method of claim 7 or 8, wherein a copper layer having a thickness of from 0.5 μm to 3 μm is formed on the substrate. The method of claim 7 or 8, wherein a copper layer having a roughness represented by a root mean square roughness parameter of 5 to 60 nm is formed on the substrate. Use of an electroless copper plating solution according to any one of claims 1 to 6 for plating a printed circuit board, integrated circuit substrate, wafer, molded interconnection device, display, display assembly or plastic part. A use of an electroless copper plating solution according to any one of claims 1 to 6 for electroplating a glass substrate, in particular for a glass panel for a display.