TWI557271B - Formaldehyde-free electroless copper plating solution - Google Patents

Description

Formaldehyde-free electroless copper plating solution, use thereof and method of electroless copper plating

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

Electroless plating is controlled autocatalytic deposition of a continuous metal film without the aid of an external electron supply. The non-metallic surface can be pretreated to make it receptive or catalytic to deposition. All or selected portions of the surface should be pretreated. The main components of the electroless copper bath are copper salts, complexing agents, reducing agents and bases as optional components, and additives such as stabilizers. The binder is used to sequester the deposited copper and prevent copper from precipitating from the solution (i.e., in the form of hydroxides and the like). Chelating copper allows copper to be obtained from a reducing agent that converts copper ions to a metallic form.

A common electroless copper bath uses formaldehyde as a reducing agent. Formaldehyde is the most important and recognized reducing agent for common electroless copper plating processes. In 1987, the U.S. Environmental Protection Agency classified formaldehyde as a possible human carcinogen. In June 2004, the International Agency for Research on Cancer (IARC) classified formaldehyde as a human carcinogen. Therefore, formaldehyde-free copper baths have been developed to meet safety and occupational health requirements.

No. 4,617,205 discloses a composition for electroless copper deposition comprising copper ions, glyoxylate as a reducing agent, and a complexing agent, such as EDTA, which is capable of forming a stronger copper complex than copper oxalate complex. Compound.

US 7,220,296 teaches an electroless plating bath comprising a water soluble copper compound , glyoxylic acid and a complexing agent (may be EDTA).

No. 20020064592 discloses an electroless bath comprising a source of copper ions, glyoxylic acid or formaldehyde as a reducing agent, and EDTA, a tartrate or an alkanolamine as a binder.

US 20080223253 discloses an electroless copper plating solution comprising a copper salt, optionally a reducing agent of the following composition: formaldehyde, paraformaldehyde, glyoxylic acid, NaBH ₄ , KBH ₄ , NaH ₂ PO ₂ , hydrazine, formalin (formalin), polysaccharides (such as glucose) and mixtures thereof, and optional combinations of the following components: ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), cyclohexane Aminetetraacetic acid, diethylenetriaminepentaacetic acid, and hydrazine (2-hydroxypropyl)ethylenediamine (hereinafter also referred to as "Quadrol", a trademark of BASF Corporation).

A drawback of EDTA, HEDTA, bismuth (2-hydroxypropyl) ethylenediamine and other related complexing agents is the lack of biodegradability.

The effectiveness of a copper plating solution is generally unpredictable and depends primarily on the molar ratio of its components, especially the binder and reducing agent, and their components.

It is an object of the present invention to provide an electroless copper-free solution that is free of formaldehyde.

Another goal is to provide an electroless copper solution with improved performance, such as improved copper deposition rate.

Another object of the invention is an electroless copper plating solution using a copper biodegradable complexing agent.

Another goal is that the copper-free solution containing formaldehyde must be subjected to the standard of formaldehyde-free copper bath. It should be suitable for horizontal and vertical processes, the most The final products are used, for example, for high-end technologies such as HDI (High Density Interconnect) PCBs and IC substrates (IC = integrated circuits, PCB = printed circuit boards). The solution should also be suitable for the manufacture of displays.

The present invention provides an electroless copper plating solution comprising - a source of copper ions, - a source of glyoxylic acid as a reducing agent, and - at least one polyaminodisuccinic acid or at least one polyamine monosuccinic acid, or at least A mixture of polyaminodisuccinic acid and at least one polyamine monosuccinic acid as a crosslinking agent, wherein the molar ratio of the complexing agent to the copper ion is in the range of 1.1:1 to 5:1.

One or more of the above objects are achieved by an electroless copper solution (hereinafter abbreviated as "solution") as in claim 1 or by an advantageous embodiment as described in the dependent technical solutions and the specification.

The solution of claim 1 contains no formaldehyde and exhibits a modified copper deposition rate. A deposition rate of 0.15-1.0 μm/10 min, 0.15-1.5 μm/10 min or even 0.15-2.0 μm/10 min can be achieved.

The advantages of this novel formaldehyde-free copper bath are good bath performance, bath stability, good coverage, high deposition rate and low foaming tendency. The important bath component formaldehyde is replaced by a non-toxic reducing agent.

The molar ratio of the polyamine succinic acid or polyamine succinic acid to the copper ion produces a favorable property of the plating solution, that is, the precipitation of copper hydroxide is suppressed, the bath stability and the bubble formation in the copper plating process are affected. Inhibition, as further explained below and in the working examples.

In one embodiment of the invention, the molar ratio of glyoxylic acid to the complexing agent is <4.6:1. It has been shown in the present invention that this molar ratio has a beneficial effect on the quality of copper deposition on the substrate, for example in terms of coverage, backlighting and passivation. Further favorable molar ratio of glyoxylic acid and a complexing agent (specifically, EDDS) 4.5:1 4.2:1 4.0:1 3.8:1 3.6:1. A preferred lower limit for the molar ratio of glyoxylic acid to the complexing agent (specifically EDDS) is 0.45:1 or 0.7:1, 1:1 or 2:1. Therefore, the molar ratio of the molar ratio of glyoxylic acid to the complexing agent (specifically, EDDS) is from 0.45:1 to 4.5:1, from 0.45:1 to 4.2:1, from 0.45:1 to 4.0:1, 0.45: 1 to 3.8:1 or 0.45:1 to 3.6:1. Other preferred ranges are from 1:1 to 4.5:1, 1:1 to 4.2:1, 1:1 to 4.0:1, 1:1 to 3.8:1 or 1:1 to 3.6:1. Other preferred ranges for the molar ratio of glyoxylic acid to the complexing agent (specifically EDDS) are from 2:1 to 4.5:1, from 2:1 to 4.2:1, from 2:1 to 4.0:1, from 2:1. To 3.8:1 or 2:1 to 3.6:1. This ratio is related to the amount of molar concentration of the complexing agent. If more than one complexing agent is used, then the total molar concentration of the wronging agent is used herein. The molar concentration of glyoxylic acid is preferably at least as high as the molar concentration of copper in the solution, and more preferably. Therefore, glyoxylic acid is better than Cu 1:1, better 1.5:1 is better 2:1.

Polyaminodisuccinic acid and polyamine monosuccinic acid show excellent or even high biodegradability. The electroplating solution of the present invention does not contain ethylenediaminetetraacetic acid (EDTA), N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid (HEDTA) and hydrazine (2-hydroxypropane). Ethylenediamine.

The solutions of the present invention and the process of the present invention are preferably used to coat printed circuit boards, wafer carriers and semiconductor wafers or also to coat any other circuit carrier and interconnect device. The solution is specifically used for printed circuit boards and wafer carriers, as well as semiconductor wafers to surface, trench, blind microchannels, vias Channel (through hole) and similar structures are plated with copper.

In particular, the solution of the present invention or the process of the present invention can be used on the surface of printed circuit boards, wafers, carriers, wafers, and various other interconnected devices, trenches, blind microchannels, via vias, and equivalent structures. Deposit copper. As used in this invention, the term "via" or "via" encompasses all types of via vias and includes so-called "through silicon vias" in germanium wafers.

Another application envisioned for solutions is the metallization of display applications. In this regard, copper is specifically deposited on a glass substrate, in particular on the surface of a flat glass. Wet electroless copper deposition on a glass substrate is advantageous compared to the metal sputtering processes used to date. The benefits that can be achieved with wet electroless deposition compared to sputtering techniques are, inter alia, reduced internal stress and reduced bending of the glass substrate, reduced equipment maintenance, efficient use of metals, and reduced material waste. Furthermore, the high copper deposition rate on the glass substrate is achieved with the solution of the invention, especially on glass substrates pretreated with relatively few metal seed crystals.

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

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

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

The electroless copper bath using the above reducing agent preferably employs a relatively high pH, typically between 11 and 14 or between 12.5 and 14, preferably between 12.5 and 13.5 or between 12.8 and 13.3. The pH is generally adjusted by potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), ammonium hydroxide or tetramethylammonium hydroxide (TMAH). Thus, the solution may contain a source of hydroxide ions such as, but not limited to, one or more of the compounds listed above. If the alkaline pH of the solution is desired and if the pH is not in the alkaline range by other components, for example, a source of hydroxide is added.

Since potassium oxalate has a high solubility, potassium hydroxide is particularly preferably used. An oxalate anion is formed in the solution by oxidizing glyoxylic acid used as a reducing agent.

Glyoxylic acid is a reducing agent for reducing copper ions to elemental copper. As used herein, the term "glyoxylic acid" includes undissociated glyoxylic acid and glyoxylate ions. In solution, undissociated glyoxylic acid and glyoxylate ions may be present. The exact nature of the substance (acid or salt) present will depend on the pH of the solution. The same considerations apply to other weak acids and weak bases.

The term "glyoxylic acid source" encompasses glyoxylic acid and all compounds which can be converted to glyoxylic acid in aqueous solution. In aqueous solution, the aldehyde-containing acid is in equilibrium with its hydrate. A suitable source of glyoxylic acid is dihaloacetic acid, such as dichloroacetic acid, which will hydrolyze to glyoxylate hydrate in an aqueous medium. An alternative source of glyoxylic acid is a bisulfite adduct such as a hydrolyzable ester or other acid derivative. The bisulfite adduct can be added to the composition or formed on the spot. The bisulfite adduct can be prepared from glyoxylate and bisulfite, sulfite or metabisulfite.

One or more other reducing agents may be added as necessary, such as low phosphoric acid, glycolic acid or formic acid, or salts of the above acids. However, the solution of the invention does not contain formaldehyde. Therefore, the solution does not contain formaldehyde. Other reducing agents are preferably used as reducing agents, but not as the sole reducing agent (see US 7,220,296, column 4, lines 20-43 and lines 54-62). In this sense, another reducing agent is also referred to as a "enhancer."

Polyaminodisuccinic acid is a compound having two or more nitrogen atoms, wherein two nitrogens are bonded to a succinic acid (or salt) group, preferably only two nitrogen atoms are each bonded to a dibutyl group. Acid (or salt) group. The term succinic acid, as used herein, includes salts thereof. The compound has at least 2 nitrogen atoms and preferably has no more than about 10 nitrogen atoms, more preferably no more than about 6, most preferably 2 nitrogen atoms due to the commercial availability of the amine. The nitrogen atom to which the succinic acid moiety is not attached is preferably substituted with a hydrogen atom. More preferably, the succinic acid group is attached to the terminal nitrogen atom. Most preferably, each of the nitrogens also has a hydrogen substituent. The end means the first or last nitrogen atom present in the compound, regardless of the other substituents. Another definition of terminal nitrogen is the primary amine nitrogen prior to attachment of the succinic acid moiety. After the attachment of the succinic acid moiety, the terminal nitrogen is transferred to the secondary amine nitrogen. Because of the steric hindrance of the two succinic acid groups on a nitrogen, each nitrogen having a succinic acid group preferably has only one such group. The remaining bonds on the nitrogen having a succinic acid group are preferably hydrogen or an alkyl group or an alkyl group (linear, branched or cyclic, including a ring in which one or more nitrogen atoms or one or more bonds of a single nitrogen atom are bonded). a structure, preferably a straight chain) or such a group having an ether or a thioether linkage (all preferably having from 1 to 10 carbon atoms, more preferably from 1 to 6, most preferably from 1 to 3 carbon atoms, but The best for hydrogen) is filled. Preferred alkyl groups are methyl or ethyl And propyl. More preferably, the nitrogen atom is bonded to an alkyl group, and each of the alkyl groups preferably has 2 to 12 carbon atoms, more preferably 2 to 10 carbon atoms, even more preferably 2 to 8, most preferably 2 to 6 carbons. Atom, that is, an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group. The polyaminodisuccinic acid compound preferably has at least about 10 carbon atoms and preferably has up to about 50, more preferably up to about 40, and most preferably up to about 30 carbon atoms. The term "succinic acid" is used herein for acids and their salts; salts include metal cations (eg, potassium, sodium) and ammonium or amine salts.

The polyaminodisuccinic acid suitable for use in the practice of the invention is unsubstituted (preferably) or inertly substituted, i.e., a group which does not adversely interfere with the activity of the polyaminodisuccinic acid in the selected application. Replaced by the regiment. Such inert substituents include alkyl groups (preferably having from 1 to 6 carbon atoms); aryl groups, including arylalkyl groups and alkylaryl groups (preferably having from 6 to 12 carbon atoms), wherein the alkyl group is Preferably, the methyl group and the ethyl group in the alkyl group are preferred.

The inert substituent is preferably on any part of the molecule, preferably on a carbon atom, more preferably on an alkyl group (for example, an alkyl group between nitrogen atoms or between carboxylic acid groups), most preferably nitrogen. The alkyl group is between the groups.

Preferred polyaminodisuccinic acids include ethylenediamine-N,N'-disuccinic acid (EDDS), di-ethyltriamine-N,N"-disuccinic acid, tri-ethylidene tetramine -N,N"'-disuccinic acid, 1,6-hexanediamine N,N'-disuccinic acid, tetra-extension ethylpentamine-N,N""-disuccinic acid, 2-hydroxyl extension Propyl-1,3-diamine-N,N'-disuccinic acid, 1,2 propanediamine-N,N'-disuccinic acid, 1,3-propanediamine-N,N"- Succinic acid, cis-cyclohexanediamine-N,N'-disuccinic acid, trans-cyclohexanediamine-N,N'-disuccinic acid and ethyl bis(oxyethyl) Nitro)-N,N'-dibutyl acid. A preferred polyaminodisuccinic acid is ethylenediamine-N,N'-disuccinic acid.

Such polyamine succinic acid can be prepared, for example, by the process disclosed in U.S. Patent No. 3,158,635, the entire disclosure of which is incorporated herein by reference. Kezerian et al. disclose the reaction of maleic anhydride (or ester or salt) with a polyamine corresponding to the desired polyaminodisuccinic acid under basic conditions. The reaction yields a plurality of optical isomers, for example, because of the presence of two asymmetric carbon atoms in ethylenediamine disuccinic acid, the reaction of ethylenediamine with maleic anhydride yields three optical isomers [R, R] , a mixture of [S, S] and [S, R] ethylenediamine disuccinic acid (EDDS). These mixtures are used in the form of a mixture or separated by means within the current state of the art to obtain the desired isomer. Alternatively, the [S,S] isomerized system is prepared by reacting an acid such as L-aspartic acid with a compound such as 1,2-dibromoethane, such as Neal and Rose, "Stereospecific Ligands and Their Complexes of Ethylenediaminedisuccinic Acid, Inorganic Chemistry, Vol. 7, (1968), pp. 2405-2412.

Polyaminomonosuccinic acid is a compound having at least two nitrogen atoms and a succinic acid (or salt) moiety attached to a nitrogen atom. Preferably, the compound has at least 2 nitrogen atoms and preferably has no more than about 10 nitrogen atoms, more preferably no more than about 6, and most preferably 2 nitrogen atoms due to the commercial availability of the amine. The remaining nitrogen atom (i.e., the nitrogen atom to which the succinic acid moiety is not attached) is preferably substituted with a hydrogen atom. Although the succinic acid moiety can be attached to any amine, the succinic acid group is preferably attached to the terminal nitrogen atom. The terminus means the first or last amine present in the compound, regardless of the other substituents. Another definition of terminal nitrogen is the primary amine nitrogen followed by the attachment of the succinic acid moiety. In the connection of the succinic acid moiety After that, the terminal nitrogen is transferred to the secondary amine nitrogen. The remaining bonds on the nitrogen having a succinic acid group are preferably hydrogen or an alkyl group or an alkyl group (linear, branched or cyclic, including a ring in which one or more nitrogen atoms or one or more bonds of a single nitrogen atom are bonded). a structure, preferably a straight chain) or such a group having an ether or a thioether linkage (all preferably having from 1 to 10 carbon atoms, more preferably from 1 to 6, most preferably from 1 to 3 carbon atoms, but Best for hydrogen) filling. Preferred alkyl groups are methyl, ethyl and propyl. The nitrogen atom is generally bonded by an alkylene group each having 2 to 12 carbon atoms, preferably 2 to 10 carbon atoms, more preferably 2 to 8 and most preferably 2 to 6 carbon atoms, that is, It is an ethyl group, a propyl group, a butyl group, a pentyl group or a hexyl group. The polyamine monosuccinic acid compound preferably has at least about 6 carbon atoms and preferably has up to about 50, more preferably up to about 40 and most preferably up to about 30 carbon atoms. The polyamine-based monosuccinic acid suitable for use in the practice of the invention is unsubstituted (preferably) or inertly substituted as described above for the polyaminobisduccinic acid compound.

Preferred polyamine-based mono-succinic acid includes ethylenediamine monosuccinic acid, di-extension ethyltriamine monosuccinic acid, tri-extension ethyltetraamine monosuccinic acid, 1,6-hexanediamine monobutane Acid, tetra-extension ethyl pentamine mono-succinic acid, 2-hydroxy-propyl-1,3-diamine monosuccinic acid, 1,2-propylenediamine monosuccinic acid, 1,3-propanediamine Succinic acid, cis-cyclohexanediamine monosuccinic acid, trans-cyclohexanediamine monosuccinic acid, and ethyl bis(oxyethylidene)-succinic acid. A preferred polyamine monosuccinic acid is ethylenediamine monobutyric acid.

Such polyamine-based succinic acid can be prepared, for example, by the process disclosed in Bersworth et al., U.S. Patent No. 2,761,874, the disclosure of which is incorporated herein by reference in Ready. In general, Bersworth et al. disclose the reaction of alkylenediamines and dialkyltriamines under mild conditions with maleic acid esters under mild conditions (in alcohols) to give N-alkyl groups. Substituted amino derivative of aspartic acid. This reaction gives a mixture of the R isomer and the S isomer.

In one embodiment, when the solution contains a mixture of polyaminodisuccinic acid and polyamine monosuccinic acid, the polyamino substituent of polyaminodisuccinic acid and polyamine monosuccinic acid is more The same is true. Thus, for example, if the polyaminodisuccinic acid is ethylenediamine-N,N'-disuccinic acid, the polyamine monosuccinic acid is ethylenediamine monobutyric acid.

In a preferred embodiment, ethylenediamine-N,N'-disuccinic acid (EDDS) is used as a blocking agent. EDDS is a preferred binder because of its high biodegradability. Other electroless copper baths containing biodegradable complexing agents such as tartrate typically use toxic co-metal nickel. It has been found that toxic co-metals can be avoided in the present invention. Thus, the solution of the invention is free of toxic co-metals. The solution of the invention is preferably nickel free.

The inventors of the present invention have found that a significantly improved copper deposition rate is obtained in the inventive solution comprising glyoxylic acid and EDDS. This is an unexpected result because in the comparative example using formaldehyde, the copper deposition was not improved or only slightly improved when the formaldehyde-EDDS combination was compared with formaldehyde-EDTA.

The term "EDDS" includes racemic EDDS or all optically active isomers thereof, such as (S,S)-EDDS, and salts and derivatives thereof. The term preferably means (S,S)-EDDS or a salt thereof. EDDS can be prepared by the process of PCT/GB94/02397. In solution, depending on the pH of the solution, ethylenediamine disuccinic acid and ethylenediamine disuccinate ions may be present.

In one embodiment, the solution of the invention contains copper ions, a complexing agent (preferably EDDS) and glyoxylic acid in the following concentrations:

Cu ion: 1-5 g/l corresponds to 0.016-0.079 mol/l

Mixing agent: 5-50 g/l corresponds to 0.034-0.171 mol/l

Glyoxylic acid: 2-20 g/l corresponds to 0.027-0.270 mol/l

The solution of the present invention more preferably contains copper ions, a complexing agent (preferably EDDS) and glyoxylic acid in the following concentrations:

Cu ion: 2-3 g/l corresponds to 0.031-0.047 mol/l

Mismatch agent: 20-40 g/l corresponds to 0.068-0.137 mol/l

Glyoxylic acid: 2-20 g/l corresponds to 0.027-0.270 mol/l

In the present invention, the amount of the wrong agent (in this case, the total amount of the wrong agent, that is, the sum of the molar numbers of all the wrong agents if one or more of the complexing agents are used) and the molar ratio of the copper ions are at 1.1:1. Up to 5:1, better in the range of 1.5:1 to 5:1. It has been shown that the solution of the present invention has a better performance when this molar ratio is used, i.e., when a miscible agent (specifically, EDDS) is used in excess of the molar concentration of copper. In the present invention, when glyoxylic acid is used as the reducing agent, it is necessary to exhibit a mismatching agent (specifically, EDDS) and a molar ratio of at least 1.1:1 of copper to the copper ion. A molar ratio of <1:1 causes copper hydroxide to precipitate and copper plating may not occur. On the other hand, a molar ratio of >5:1 causes bath instability and high bubble formation on the substrate surface during the copper plating process.

In another embodiment, the molar ratio of the cross-linking agent (in this case, the total amount of the cross-linking agent) to the copper ion is from 2:1 to 5:1, more preferably from 3:1 to 5:1. If the copper bath is agitated during deposition, it is preferably agitated with air, and when another reducing agent (also referred to as "enhancer") is used in addition to glyoxylic acid, the other reducing agent is more This embodiment is particularly advantageous since it is preferably selected from the group consisting of glycolic acid, low phosphoric acid or formic acid, most preferably glycolic acid.

The solution of the present invention may and need not include other components such as stabilizers, surfactants, additives (as rate controlling additives), grain micronization additives, pH buffers, pH adjusters, and enhancers. Such other components are described, for example, in the following documents (incorporated by reference in their entirety): US 4, 617, 205 (specifically, the disclosure of column 6, line 17 to column 7, line 25), US 7,220,296 (specific It is referred to as column 4, line 63 to column 6, line 26), US 2008/0223253 (see paragraphs 0033 and 0038 for specific words).

The stabilizer is a compound that stabilizes the electroless plating solution against undesired outplating in the bulk solution. The term "external plating" means non-specific and/or uncontrolled copper deposition. Copper (II) reduction should occur only on the surface of the desired substrate and not in the entire bath. The stabilizing function can be achieved, for example, by a substance that acts as a catalyst poison (for example, a compound containing sulfur or other chalcogenide) or by forming a copper (I) complex, thereby inhibiting the formation of a compound of copper (I) oxide.

Suitable stabilizers are (not limited to) bipyridyl (2,2'-bipyridyl, 4,4'bipyridyl), phenanthroline, decyl-benzothiazole, thiourea or derivatives thereof (eg diethyl Thiourea), cyanide (such as NaCN, KCN, K ₄ [Fe(CN) ₆ ]), thiocyanate, iodide, ethanolamine, mercapto-benzotriazole, Na ₂ S ₂ O ₃ , polymer ( Such as polyacrylamide, polyacrylate, polyethylene glycol or polypropylene glycol and copolymers thereof, of which 2,2'-bipyridyl (abbreviated as "DP"), diethyl-thiourea, K ₄ [ Fe(CN) ₆ ], NaCN and mercapto-benzothiazole are particularly suitable.

In one embodiment, the stabilizer is selected from the group consisting of cyanide-free stabilizers, primarily for environmental and occupational health reasons. Therefore, the solution of the present invention is preferably free of cyanide. In this connection, 2,2'-bipyridyl is a preferred stabilizer. The bipyridyl group is preferably added in an amount of from 1 to 10 mg/l.

European application EP 1816262 discloses an electroless copper bath containing one or more thiocarboxylic acids as an essential component. The thio compounds mentioned in EP 1 876 262 include compounds having the formula HS-(CX1)r-(CHX2)s-COOH, wherein X1 is -H or -COOH; X2 is -H or -SH; r and s are positive integers Where r is 0 to 2, or 0 or 1; and s is 1 or 2. Specific examples of thio compounds mentioned in EP1876262 are thioglycolic acid, thiopropionic acid, thiomalic acid and dithiodisuccinic acid. According to EP1876262, these thiocarboxylic acids are compatible with glyoxylic acid and its salts and stabilize the electroless copper composition by preventing the formation of copper oxide. According to EP1876262, the minimum necessary amount of thio compounds is 0.01 ppm. In the present invention, it is shown that the efficacy of the electroless copper bath is better when the thiocarboxylic acid component generally and specifically mentioned in EP1876262 is exempt from use or at least below the limits mentioned in EP1876262. Trace amounts of thiocarboxylic acids, as generally and specifically mentioned in EP1876262, may be present, provided that the amount is less than 0.01 ppm. Preferably, however, no thiocarboxylic acid is added to the solution of the invention, i.e., the bath does not contain any of the thiocarboxylic acids generally and specifically mentioned in EP1876262.

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

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

Preferably, the solution is agitated during use. In particular, working agitation and/or solution agitation can be used. The preferred agitation type is air agitation of the solution. Air agitation can be achieved by bubbling air through the solution in use.

The process will be carried out for a sufficient period of time to obtain a deposit of the desired thickness, which in turn will depend on the particular application.

One application of the invention envisaged will be particularly suitable for the preparation of printed circuit boards. Electroless copper deposition in accordance with the process of the present invention is particularly useful for through-plating holes, surfaces, trenches, blind microchannels in printed circuit boards. Double or multi-layer sheets (rigid or flexible) can be electroplated by means of the invention.

The process of the present invention can be adapted to provide electroless copper deposits having a thickness in the range of from 0.1 μm to 25 μm, preferably between 0.25 μm and 3 μm.

Substrates commonly used in the manufacture of printed circuit boards are most often epoxy or epoxy glass composites. However, other substances can be used, in particular phenolic resin, polytetrafluoroethylene (PTFE), polyimide, polyphenylene ether, bis-maleic acid triazine-resin (BT resin), cyanate ester and polyfluorene.

In addition to the application of this process in the manufacture of printed circuit boards, the process is generally found to be suitable for electroplating non-conductive substrates, including plastics such as acrylonitrile butadiene styrene (ABS) and polycarbonate; ceramics and glass.

In one embodiment of the process of the present invention, the process is in the range of 20-60 ° C, preferably 20-55 ° C, more preferably 20-50 ° C, even more preferably 20-45 ° C and most preferably 20-40 ° C. Perform at temperature. This embodiment is extremely advantageous because of the use of formaldehyde-based solutions of the current state of the art, which are necessary for good plating performance, especially for sufficient copper deposition rates.

The substrate to be plated, i.e., the surface of the substrate, especially the non-metallic surface, may be pretreated by means within the skill of the art (e.g., as described in column 8 of US 4,617,205) for copper deposition. Higher acceptability or autocatalytic. All or selected portions of the surface may be pretreated. However, it is not necessary to pretreat in each case and depending on the type of substrate and surface. In the pretreatment, the substrate may be sensitized, followed by deposition of electroless copper thereon. This can be achieved by adsorbing a catalytic metal such as a noble metal such as palladium on the surface of the substrate.

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

Exemplary and non-limiting pretreatment processes, particularly for printed circuit board laminates and other suitable substrates, can include the steps of: a) contacting the substrate with an activator solution containing a colloidal or ion catalyzed metal, such as a precious metal. Preferably, the palladium is such that the surface of the substrate becomes catalytic, and optionally, if the activator contains an ion-catalyzed metal, b) contacting the substrate with a reducing agent, wherein the metal ion of the ion activator is reduced to an elemental metal Or if the activator contains a colloidal catalytic metal, c) contacting the substrate with an accelerator wherein the components of the colloid (eg, protective colloid) are removed from the catalytic metal.

It may be performed in any combination as appropriate, preferably other steps before step a) above are:

i. Clean and adjust the substrate to increase adsorption. Remove organic matter with detergent And other residues. The cleaning agent may also contain other materials (regulators) that prepare the surface for the activation step, i.e., enhance the adsorption of the catalyst and produce a more uniformly activated surface.

Ii. Etching the substrate to remove oxide from the copper surface, especially from the inner layer of the hole. This can be done by a persulfate or peroxide based etching system.

Iii. contacting the substrate with a pre-dip solution such as a hydrochloric acid solution or a sulfuric acid solution, which optionally contains an alkali metal salt such as sodium chloride. The pre-dip solution serves to protect the activator from carry-in and contamination.

In another type of pretreatment process, a permanganate etching step is employed. The so-called Desmear process using the permanganate etching step is described in the accompanying examples. The decontamination process can be combined with the above steps. In particular, the decontamination process can be performed prior to step a) above, or in the case of performing one or more of steps i) - iii), prior to steps i) - iii) above. A decontamination process can also be performed instead of steps i) and ii).

In a pretreatment process that is particularly suitable for metallization of display applications and metallization of glass substrates, only the surface is contacted with the prepreg solution and the activator solution, followed by contact with the solution of the present invention. The step of contacting the cleaning liquid and the adhesion enhancer prior to the pre-impregnation step is optionally carried out, which may be carried out in advance.

Another process that is often used for glass substrates can be carried out in the following steps before copper plating: the surface of the glass to be electroplated exhibits metal particles as seed crystals. Metal particles can be brought to the surface by sputtering techniques. An exemplary seed crystal is a particle composed of copper, titanium, molybdenum, zirconium, aluminum, chromium, tungsten, rhenium, ruthenium or the like. Compound or alloy. Another seed crystal may be a metal oxide, or a mixed metal oxide such as indium tin oxide. The process can also be applied to plastic substrates such as those made from polyethylene terephthalate.

Contacting the pretreated glass surface with an activator solution containing an ion catalyzed metal such as a noble metal, preferably palladium, renders the surface catalytic. The ion-catalyzed metal is reduced to the surface by the seed metal. In this process, the addition of another reducing agent may be omitted. This process is especially useful for copper plating of glass substrates for display applications.

An exemplary pretreatment process or a single step thereof can be combined into an alternative pretreatment process as necessary.

In another aspect, the invention relates to the use of an electroless copper solution as described above for electroplating the following: printed circuit boards, wafers, integrated circuit substrates, MID (Molded Interconnect) components, Display (such as liquid crystal display, TFT display, plasma display, electroluminescent display (ELD) and electrochromic display (ECD), specifically for display of: electronic device or TV, display component, flat panel sensing Devices, such as X-ray imaging devices, or plastic parts, such as plastic parts for functional or decorative purposes.

The invention will now be described in more detail by the following examples. These examples are set forth to illustrate the invention, but are not to be construed as limiting the invention.

Instance method Backlight method:

The coverage of electroless copper plated in the vias can be evaluated using an industry standard Backlight Test in which the electrolessly plated test pieces are cut so that areas that are not completely covered when viewed by a strong light source are detected as bright spots. [US 2008/0038450 A1].

The quality of the copper deposit is determined by the amount of light observed under a conventional optical microscope.

The results of the backlight measurements are given on the D1 to D10 scale, where D1 means the worst result and D10 means the best result. Figure 3 shows a reference sample showing the results of D1 to D10.

1. Example Bath composition

Operating temperature: 38-50 ° C

Deposition rate: about 0.6 μm/10 min.

Job Description

In this example, the test sample is processed in a common decontamination process to clean the pore wall surface and the inner copper surface. In addition, the surface of the resin is roughened to achieve good copper adhesion.

The decontamination process is a multi-stage process, the steps of which are shown in Figure 1.

The expansion agent is made of a mixture of organic solvents. During this step, drill smear and other impurities are removed. The high temperature of 60-80 ° C promotes the expansion of the expansion agent, thereby producing an expanded surface. Therefore, the subsequently coated permanganate solution may cause strong erosion. Thereafter, the reducing solution (reaction modifier) removes manganese dioxide produced during the permanganate step from the surface.

In the PTH (Plated Through Hole) process, a non-conductive material is prepared for copper deposition. Figure 2 shows the activation steps of the PTH process.

A cleaning agent is used to remove the organics and adjust the surface for subsequent activation steps.

The etch cleaner removes oxide from the surface of the copper inner layer in the hole. The substance used as the etching cleaning agent is selected from a mixture of sulfuric acid and hydrogen peroxide, or is selected from peroxodisulfate or selected from peroxymonosulfate. The etching cleaning solution may contain additives and/or stabilizers in addition to the etching component.

The palladium-activated panel and the pore surface are carried out in an activator containing a colloidal or ionic catalytic metal such as a noble metal, preferably palladium, to render the surface catalytic. In one possible configuration, the activator contains palladium ions that are mismatched by the organic ligand. Predip (Predip) should protect the activator from being carried in and contaminated.

The final step in the activation process is the reducing agent. At one point, palladium ions are reduced to elemental palladium with high catalytic activity. After the reducing agent step, electroless copper deposition is carried out using the solution of the present invention. A reducing agent is used as an activator in combination with an ionic metal compound. It employs a reducing agent such as hypophosphite, borohydride, or amine borohydride.

For electroless copper deposition, the bath components were added in the order outlined in Table 1. Add to the right amount of water to create a bath composition. Use air to agitate. The operating temperature varies between 38-50 °C. Again, the deposition time is set to 10-60 minutes to achieve the desired copper thickness.

Bath characteristics

Deposition rate (measured for FR4 material (eg, Matsushita MC 100 EX)): about 0.6 μm/10 min.

Foaming tendency (test material: ABF GX-92 from Ajinomoto): low or no

Coverage (FR4 and GX-92): Good

Color (FR4 and GX-92): orange red

FR4 test backlight with through holes covering copper.

Plating example

The test panel is subjected to the entire decontamination process (below).

Decontamination process

Activation process based on ion activator system:

Activation process

An example of the composition of the copper bath is described in the following table.

Bath composition example

Operating temperature: 38 ° C

Deposition rate: 0.6 μm/10 min.

Foaming trend: none

Coverage: good

Backlight D8

Color: orange red

2. Comparative example: glyoxylic acid with HEDTA or glyoxylic acid and several biodegradable complexing agents Comparative Example 2.1: HEDTA (N'-(2-hydroxyethyl)-ethylenediamine-N,N,N'-triacetic acid) Bath composition

Operating temperature: 45 ° C

Deposition rate: 0.5μm/10min

Backlight: D7

Bath stability: good

Coverage: good

Color: orange red

Disadvantages: non-biodegradable complex

Comparative Example 2.2: Biodegradable sorbitol Bath composition

Operating temperature: 60 ° C

Deposition rate: 0.3μm/10min

Backlight: D8

Bath stability: low

Coverage: good

Color: orange red

Disadvantages: low deposition rate

Comparative Example 2.3: Biodegradable sodium potassium tartrate Bath composition

Operating temperature: 38 ° C

Deposition rate: 0.3μm/10min

Backlight: D8-D9

Bath stability: low

Foaming trend: low

Coverage: good

Color: orange red

Disadvantages: high concentration of mixed agent is required and deposition rate is low

Comparative Example 2.4: Biodegradable Gluconic Acid Bath composition

Operating temperature: 50 ° C

Deposition rate: 0.4μm/10min

Backlight: D4-D5

Bath stability: very low

Coverage: bad

Color: micro deep orange red

Disadvantages: poor copper deposition and very low bath activity

Overview: When glyoxylic acid is used as a reducing agent, common biodegradable complexing agents (such as tartrate) can no longer meet bath requirements. Glyoxylic acid containing the above test Comparative biodegradable complexes exhibit low deposition rates and/or require high levels of complexing agents. Other biodegradable complexes tested did not show copper deposition at all or showed poor results with respect to coverage, deposition rate and foaming tendency. In contrast, (S,S)-ethylenediamine-N,N'-disuccinic acid ((S,S)-EDDS) is biodegradable and meets the requirements of the electroplating industry. The solution of the invention containing EDDS is characterized by good bath performance, good coverage, high deposition rate and low foaming tendency. Due to the strong mismatch nature of EDDS, the copper bath of the present invention is much more stable than other biodegradable complexes.

3. Example: Comparing EDDS to EDTA with different reducing agents 3.1 Examples of glyoxylic acid as a reducing agent 3.1.1 Bath Composition 1: Solution of the invention containing glyoxylic acid/EDDS

Operating temperature: 38 ° C

Deposition rate: 0.8μm/10min

Backlight: D6

Bath stability: good

Coverage: good

Color: orange red

Foaming: no bubbles

3.1.2 Bath Composition 2: Comparative Example with Glyoxylic Acid/EDTA

Operating temperature: 38 ° C

Deposition rate: 0.4μm/10min

Backlight: D4

Bath stability: good

Coverage: poor, observable passivation

Color: micro deep orange red

Foaming: none

result:

When comparing Examples 3.1.1 and 3.1.2, the copper plating bath containing EDDS was twice as fast as the bath containing EDTA for the copper deposition rate under the same plating conditions. In addition, better coverage is achieved with EDDS.

3.2 Comparative example of using formaldehyde as a reducing agent 3.2.1 Bath Composition 3: Comparative Example of Formaldehyde/EDDS

Operating temperature: 38 ° C

Deposition rate: 1.1μm/10min

Backlight: D7

Bath stability: good

Coverage: good

Color: orange red

Foaming: no bubbles

3.2.2 Bath Composition 4: Comparative Example with Formaldehyde/EDTA

Operating temperature: 38 ° C

Deposition rate: 0.9μm/10min

Backlight: D6

Bath stability: low

Coverage: poor, slightly passivated

Color: micro deep orange red

Foaming: yes

Results: The bath containing EDDS/formaldehyde showed a slightly higher deposition rate than the bath containing EDTA/formaldehyde. However, when EDTA is replaced by EDDS (see Examples 3.1.1 and 3.1.2), the deposition rate increases much less than with glyoxylic acid. Thus, in a bath containing formaldehyde, the EDDS can be equivalent or slightly better than EDTA. However, with glyoxylic acid as the reducing agent, EDDS showed much better results than EDTA (deposition rate increased by about 100%), which could not be foreseen in view of the prior art.

4. Example: Experiment with different concentrations of the wrong agent EDDS and copper

Moerby EDDS: Change of Cu

Bath composition

Operating temperature: 36 ° C

Test Results

Deposition rate: 0.6μm/10min

At least a molar ratio of 1.1:1 to EDDS:Cu is required to misalign the copper ions in the alkaline solution. Mohr ratio <1.1:1 causes precipitation of copper hydroxide. Therefore, there may be no plating copper.

Mobi ratio >5:1 causes bath instability and high foaming tendency on PCB material. The deposited color is dark orange red and the backlight is at the desired value of D7.

Uncontrolled copper deposition on the beaker can be found after electroless copper plating in bath 6 (6:1 molar ratio EDDS:Cu). Bath stability is not enough.

5. Example: plating solution with different glyoxylic acid: EDDS molar ratio

The different molar ratios of EDDS to glyoxylic acid in the electroless copper bath were tested as shown in the following tables.

Bath composition:

Mo concentration and quality of Cu, misc and reducing agent

The test panels were subjected to the entire decontamination process (Table 2) and an activation process based on the ion activator system (Table 3) as described in Example 1.

The following parameters apply to electroless plating in an electroless copper bath:

- T=38°C

- Dummy plating: 10-15 minutes

- Exposure time: 10 minutes

- Test material: In addition to the GX-92 (short decontamination: 2', 4', 4') and FR4 which have been described in Example 1, test panels made of the following materials were also used.

ABS (short decontamination: 2', 4', 2') was used to test coverage and passivation; R1755C (decontamination: 5', 10', 5') was used for backlight testing.

In the table below, the results of the deposition test are shown.

In all baths, bath stability decreased after one day. The next day, copper hydroxide precipitation occurred. To improve bath stability, an EDDS:copper ratio of at least 1.1:1 is recommended. However, the experiments of the present invention show the effect of glyoxylic acid: EDDS molar ratio on the copper deposition quality on the substrate.

Tests have shown that copper deposition quality decreases as the concentration of glyoxylic acid increases. When the concentration of glyoxylic acid in the electroless copper bath is high, the copper-glyoxylate complex may compete with the Cu-EDDS complex and the glyoxylic acid also acts as a binder rather than a reducing agent.

Although the glyoxylic acid concentration is sufficiently high to serve two purposes (a complexing agent and a reducing agent), the reduction process with a copper-glyoxylate complex seems to be limited. The formation of a copper-glyoxylate complex can cause bath instability and passivation on the copper-coated material. Here, passivation means that the copper surface becomes inactive to the electroless copper process; the electroless copper process terminates on the passivated surface. When the molar ratio of glyoxylic acid:EDDS is 4.6:1 or more, the copper deposition quality is lowered. Initial reactivity, copper coverage and passivated glyoxylic acid: erDS molar ratio And set.

The wrong agent plays an important role in the electroless copper plating process. Not every compounding agent can be used in the reduction process. The wrong agent EDDS forms a complex with copper that can be easily reduced. At a glyoxylic acid:EDDS ratio of less than 4.6:1, specifically at 3.6:1 or below 3.6:1, the deposition quality (coverage, backlight) is excellent.

6. Example: Experiment with thiocarboxylic acid

Comparison of EDTA with EDDS with or without thiocarboxylic acid

Thioglycolic acid was used as the thiocarboxylic acid in the experiment.

Test schedule using different baths

Operating temperature: 55 ° C

Test Results

The thioglycolic acid causes a dark color of electroless copper deposition. Deposition rate due to no electricity The copper bath is reduced by the use of thioglycolic acid.

7. Example: Copper deposition on a glass substrate using a copper bath containing different binders

Sample: Glass sputtered with Ti/Cu seeds

Figure 4 shows the results of copper thickness obtained for different complexing agents.

Figure 1 is a step of cleaning the surface of the multi-stage cleaning process, Figure 2 is used for the step of activating the plated through hole process, and Figure 3 is for the reference sample of the backlight measurement, showing the results of D1 to D10, and Figure 4 is used differently. The thickness of the copper on the glass substrate during the bath of the wrong agent.

Claims (13)

An electroless copper plating solution comprising a source of copper ions, a first reducing agent comprising glyoxylic acid, and a second reducing agent selected from the group consisting of low phosphoric acid, glycolic acid, formic acid, and salts of such acids, and a complexing agent Is selected from the group consisting of polyaminosuccinic acid, polyamine monosuccinic acid or a mixture thereof, wherein the molar ratio of the binder to copper ions is in the range of from 1.1:1 to 5:1, and The pH of the solution is in the range of 11 to 14. The electroless copper plating solution of claim 1, wherein the molar ratio of glyoxylic acid to the complexing agent is <4.6:1. An electroless copper plating solution according to claim 1 or 2, wherein the molar ratio of the binder to the copper ion is in the range of from 1.5:1 to 5:1. An electroless copper plating solution according to claim 1 or 2 which contains less than 0.01 ppm of thiocarboxylic acid. An electroless copper plating solution according to claim 1 or 2, wherein the crosslinking agent is polyaminodisuccinic acid. An electroless copper plating solution according to claim 1 or 2, wherein the crosslinking agent is ethylenediamine-N,N'-disuccinic acid (EDDS). An electroless copper plating solution according to claim 1 or 2, wherein the solution further comprises a stabilizer. An electroless copper plating solution according to claim 7, wherein the stabilizer is selected from the group consisting of bipyridine, phenanthroline, mercapto-benzothiazole, thiourea or a derivative thereof, cyanide, thiocyanate, iodide, ethanolamine, sulfhydryl - benzotriazole, Na ₂ S ₂ O ₃ , polymers such as polyacrylamide, polyacrylate, polyethylene glycol or polypropylene glycol or copolymers thereof. An electroless copper plating solution according to claim 1 or 2, wherein the solution further comprises a source of hydroxide ions. 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 9. The method of claim 10, which is carried out at a temperature in the range of from 20 to 60 °C. Use of an electroless copper plating solution according to any one of claims 1 to 9 for electroplating printed circuit boards, integrated circuit substrates, wafers, molded interconnect devices, displays or plastic parts. Use of an electroless copper plating solution according to any one of claims 1 to 9 for electroplating a glass substrate, in particular a glass substrate for a display.