JP5780920B2 - Electroless copper plating bath - Google Patents

Description

  The present invention relates to an electroless copper plating solution.

  The electroless copper plating solution is a solution used for forming a copper metal film on a non-conductive object to be plated. By immersing the object to be plated in the plating solution, the copper ions in the plating solution are reduced by a reducing agent (or reducing agent system) or an ion redox agent (or ion redox agent system) in the plating solution. It is well known that a copper metal film is formed on the object to be plated.

  In recent years, electroless copper plating has been applied to organic (resin) materials such as epoxy, polyimide, and polyamide, or ceramic materials such as alumina as materials for electronic devices used in semiconductor devices (and related devices). Application to things is increasing. One reason for this is that these materials are lightweight and have excellent flexibility and workability. On the other hand, the use of an electroless copper plating solution under strong alkali or strong acid conditions for these materials may cause a reaction such as hydrolysis. Therefore, it is desirable that the treatment be performed under neutral conditions (for example, a pH range of 4 to 8) as much as possible. Furthermore, due to the recent demand for smaller and lighter electronic devices, the structure of the semiconductor device is increasingly miniaturized to have a smaller and more complicated three-dimensional structure. Therefore, it is desired that the metal copper film formed by electroless copper plating has finer, denser, homogeneous and excellent adhesion.

  Conventionally, formaldehyde, glyoxylic acid, dimethylaminoborane, hydrazine, hypophosphorous acid, and the like are known as the reducing agent of the electroless copper plating solution. Moreover, as an ion redox agent, Co salt bath, Fe salt solution, Sn salt bath, etc. are known (for example, refer patent documents 1, 2; nonpatent literature 1, 2). However, plating solutions using formaldehyde usually require high alkali conditions, and there are problems such as workability and adverse effects on the environment. A plating solution using glyoxylic acid usually uses EDTA as a complexing agent, which causes problems such as adverse effects on the environment in terms of biodegradability. A plating solution using dimethylaminoborane or hydrazine also usually uses EDTA as a chelating agent, which also causes problems such as adverse effects on the environment. Furthermore, they are not sufficient in bath stability. A plating solution using hypophosphorous acid has a problem that the plating can be performed under weak alkaline conditions, but the reactivity rapidly decreases under acidic conditions below neutral conditions. In addition, although ion redox plating solutions can be plated under neutral conditions, EDTA is usually used as a chelating agent, which also causes adverse effects on the environment. Furthermore, it is not sufficient in terms of bath stability and copper deposition rate.

Recently, an electroless copper plating bath using ascorbic acid as a reducing agent has been disclosed. This is because, as a reducing agent, when one or more selected from ascorbic acid, ascorbate, and modified products and derivatives thereof are used, as a complexing agent, carboxylic acid, oxycarboxylic acid, and amino By using one or more selected from carboxylic acids (excluding polyaminocarboxylic acids), ascorbic acid can directly participate in the precipitation of copper metal (Cu ²⁺ → Cu reaction). Yes (see Patent Document 3).

  However, this electroless copper plating bath using ascorbic acid as a reducing agent can be plated under neutral conditions, but its reactivity (for example, the deposition rate) decreases rapidly under mildly acidic conditions. There is a problem that stability is not sufficient. Further, the film thickness, crystallinity (crystal size, denseness, homogeneity), and adhesion of the produced metallic copper film are not sufficient to satisfy the above requirements.

Japanese Patent No. 3243889 Japanese Patent No. 4573445 JP2005-200366

“Surface Technology” Vol. 50, no. 4, 1999 “Surface Technology” Vol. 57, no. 11, 2006

  The present invention has been made in view of the above circumstances. The present invention relates to an electroless copper plating bath exhibiting sufficient bath stability capable of electroless copper plating under neutral conditions (pH 3 to 8). Providing a new electroless copper plating bath with excellent properties that the resulting copper metal deposit has sufficient thickness and good adhesion, and the crystallinity of the deposit is very fine, dense and homogeneous. The task is to do.

  As a result of searching for a new electroless copper plating bath that solves the problems of the above-described conventional techniques, the present inventors have obtained the following knowledge. That is, by adding a specific additive, particularly a nitrogen-containing heterocyclic compound, to an electroless copper plating bath using a normal ascorbic acid-based reducing agent, electroless copper plating with sufficient bath stability and neutral conditions It is a finding that a very fine, dense and homogeneous crystal precipitation film having a possibility and having a sufficient thickness and good adhesion can be provided. The present invention has been made based on such findings.

Therefore, the electroless copper plating bath of the present invention is characterized by being an electroless copper plating bath using a normal ascorbic acid-based reducing agent and containing a nitrogen-containing heterocyclic compound as a specific additive. That is, the electroless copper plating bath of the present invention is an electroless copper plating bath containing a copper water-soluble salt, a complexing agent, a reducing agent, a buffering agent and an additive, wherein the complexing agent is a hydroxycarboxylic acid complexing agent. , and the said reducing agent is ascorbic acid reducing agent, the buffering agent is a pH buffering agent, wherein the additive Ri nitrogen-containing heterocyclic compound der, the nitrogen-containing heterocyclic compound, have a pyrimidine skeleton The pyrimidine skeleton further contains a ketone or thioketone .

  In the present invention, in addition to the electroless copper plating bath according to the present invention, an electroless copper plating method using the electroless copper plating bath and an object to be plated obtained using the electroless copper plating bath. Including.

  The electroless copper plating bath of the present invention is neutral (for example, pH 3 to 8) and can be electroless copper plated. Further, the plating bath exhibits sufficient bath stability, and the resulting metal copper deposit film has a sufficient thickness and very good adhesion. Furthermore, it has an excellent property that the crystallinity of the deposited film is very fine, dense and homogeneous. With these properties, it becomes possible to form a very dense and homogeneous metal copper film on a material to be plated that is weak against strong alkalinity or strong acid (for example, epoxy, polyamide, alumina, etc.).

FIG. 1 a is an electron micrograph (SEM) of the surface of the copper film obtained in Example 7 observed by FE-SEM. FIG. 1 b is an electron micrograph (SEM) of the surface of the copper film obtained in Comparative Example 2. In both cases, the magnification is 10,000 times.

  The mode for carrying out the electroless copper plating bath of the present invention will be specifically described below.

  The electroless copper plating bath of the present invention relates to an electroless copper plating bath containing a copper water-soluble salt, a complexing agent, a reducing agent, a buffering agent and additives. Further, in the present invention, the complexing agent is a hydroxycarboxylic acid complexing agent, the reducing agent is an ascorbic acid reducing agent, the buffering agent is a pH buffering agent, and the additive is a nitrogen-containing heterocyclic ring. It is a compound.

  Hereinafter, an ascorbic acid reducing agent, a copper water-soluble salt, a complexing agent, a reducing agent, a buffering agent and additives will be described. In the present invention, these complexing agent, reducing agent, buffering agent and additive are broadly defined in terms of action and function, and each is a separate chemical substance, compound or composition thereof. It is not necessary to include. For example, the case where a specific chemical substance has a plurality of functions / functions as a complexing agent, a reducing agent, a buffering agent, and an additive as defined in the present invention is included. For those complexing agents, reducing agents, buffering agents, and additives having such a plurality of functions / actions, those skilled in the art will be able to use complexing agents, reducing agents, and buffering agents that can be preferably used in the present invention described below. The additives can be selected as appropriate.

Ascorbic acid reducing agent :
Here, the ascorbic acid-based reducing agent (or the reducing system using the ascorbic acid-based reducing agent) that can be used in the present invention is not particularly limited. What is necessary is just to reduce the copper ions (for example, II or I) in the plating bath and to deposit metallic copper on the object to be plated. Here, the meanings of copper (II) and copper (I) as copper ions mean ordinary copper divalent ions and monovalent ions, but also include all other valence ions.

  Specifically, among known ascorbic acid-based reducing agents, one or two or more compounds selected from ascorbic acid, ascorbic acid salts, modified products and derivatives thereof have the above-described reducing properties. Can be used. Examples include ascorbic acid, sodium ascorbate, isoascorbic acid, sodium ascorbate phosphate, magnesium ascorbate phosphate, ethyl ascorbate, disodium ascorbate sulfate, etc., and these may be used alone or in combination as appropriate. be able to.

  There is no particular limitation on the reducing agent concentration. A person skilled in the art can select appropriately according to the purpose of plating (type of material to be plated, size, thickness of plating film, etc.). In this invention, it is about 0.001-0.3 mol / L especially, Preferably it is about 0.002-0.05 mol / L. If it is lower than 0.001 mol / L, plating may not be deposited. If it is higher than 0.3 mol / L, the bath stability may be deteriorated.

Copper water-soluble salt :
Moreover, there is no restriction | limiting in particular also about the copper water-soluble salt which can be used by this invention, All the water-soluble copper salts known normally can be used preferably. In the present invention, examples of the water-soluble copper salt include copper sulfate, copper chloride, copper sulfate, copper nitrate, and copper acetate. The copper of these salts may be divalent ions, monovalent ions, other ions or mixtures thereof in the plating bath or in the plating reaction.

  There is no restriction | limiting in particular also about the density | concentration of copper water-soluble salt, If it is an expert, it can select suitably according to the objective (the kind of to-be-plated material, size, the thickness of a plating film), etc. In this invention, it is 0.001-0.2 mol / L especially, Preferably it is about 0.01-0.05 mol / L.

Complexing agent :
There is no particular limitation on the complexing agent in the plating bath of the present invention. Included are all known complexing agents commonly used in ascorbic acid based reduction systems. Here, the complexing agent in the present invention broadly means a substance that acts on copper ions (in the above-mentioned meaning) in a plating bath and improves the plating reactivity of copper ions. Therefore, the above-described action may be anything as long as it has some interaction (for example, ionic bond / action) in addition to the chelate bond / action in the usual sense. In addition, the complexing agent in the plating bath of the present invention not only acts on copper ions in the plating bath, but also on copper (not only ions but all forms) involved in the plating reaction on the object to be plated. It means what improves plating reactivity by acting.

  Since the ascorbic acid-based reducing agent is used in the present invention, the following complexing agent is preferably used in combination with the ascorbic acid-based reducing agent. That is, boric acid, carboxylic acid, hydroxycarboxylic acid, oxycarboxylic acid, and aminocarboxylic acid (however, excluding polyaminocarboxylic acid) can be mentioned. In the present invention, use of hydroxycarboxylic acid is particularly preferred. Specifically, formic acid, acetic acid, propionic acid, benzoic acid, lactic acid, oxalic acid, malonic acid, succinic acid, malic acid, tartaric acid, glycolic acid, diglycolic acid, citric acid, nitrilotriacetic acid, glycine, dimethylglycine Glycylglycine, glutamic acid, adipic acid, thiodiglycolic acid and salts thereof, and the like.

  Further, in the present invention, it is preferable to use the above acid and salt in combination. The reason is that the pH of the plating bath of the present invention is preferably neutral (for example, pH 3 to 8) that is neither strongly acidic nor strongly alkaline. Therefore, a buffering action can be obtained by appropriately selecting the acid and the salt thereof.

  Furthermore, in the present invention, in addition to the above complexing agents, all complexing agents known as so-called copper ion chelating agents (or ligands, ligands, etc.) can be included. For example, known complexing agents with affinity for copper (II) or copper (I) or copper (II and I). Specific examples include bipyridine, phenanthroline, and hydroquinone.

  Furthermore, in the present invention, it is preferable to include not only a complexing agent for copper (II) but also a complexing agent for copper (I) in the plating bath or during the plating reaction. For this reason, in this invention, it is possible to contain 2 or more types of complexing agents, such as these copper (II) complexing agents and copper (I) complexing agents. It is also possible to contain at least one complexing agent having affinity for both copper (II) and copper (I).

  For example, sodium citrate and 2,2'-bipyridyl, or sodium tartrate and 1,10-phenanthroline. By using these at least two different complexing agents in combination, bath stability is imparted to the plating bath of the present invention as a result of a synergistic action with the additives described below. Therefore, the obtained metal copper deposit film has a sufficient thickness and very good adhesion, and further exhibits excellent properties that the crystallinity of the deposit film is very fine, dense and homogeneous. .

  The concentration of the complexing agent is about 0.005 to 2 mol / L, preferably about 0.03 to 0.3 mol / L. If it is lower than 0.005 mol / L, the bath stability may be deteriorated, and if it is higher than 2 mol / L, there is a possibility that a coarse crystal deposited film lacking in denseness, which is insufficient in plating, may be deposited.

Buffer :
The plating bath of the present invention further contains a buffer. Here, the buffering agent means a component for enhancing the stability of each component of the plating bath of the present invention (copper water-soluble salt, complexing agent, reducing agent and additive) in the plating bath. For example, the pH, ionic strength, viscosity, etc. of the plating bath can be mentioned. In the present invention, since the plating reaction is preferably carried out at a neutral pH, examples of the buffer include a pH buffer.

  The pH buffer of the present invention is not particularly limited as long as it exhibits the buffering effect as described. In addition to the addition of a compound other than the copper water-soluble salt, complexing agent, reducing agent and additive as a buffering agent, each component of the copper water-soluble salt, complexing agent, reducing agent and additive comprises The thing which shows the effect | action as a buffering agent is also included. For example, what exhibits pH buffering action by the combination of a plurality of complexing agents described above is a pH buffering agent as used herein.

  As the pH buffering agent, monocarboxylic acid, dicarboxylic acid, oxycarboxylic acid, inorganic acid or a salt thereof can be used alone or in appropriate mixture. Examples of the monocarboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, acrylic acid, trimethylacetic acid, benzoic acid, chloroacetic acid, and salts thereof. Examples of the dicarboxylic acid include oxalic acid, succinic acid, maleic acid, itaconic acid, paraphthalic acid or salts thereof. Examples of the oxycarboxylic acid include glycolic acid, lactic acid, salicylic acid, tartaric acid, citric acid, and salts thereof. Examples of the inorganic acid include boric acid, carbonic acid, sulfurous acid, phosphoric acid, and salts thereof.

  In the present invention, in order to maintain a constant pH during the plating bath or during the plating reaction, it is preferable to add a pH adjusting agent as appropriate in addition to the buffer. For example, sodium hydroxide, potassium hydroxide, ammonia water, tetramethylammonium hydroxide, sulfuric acid, hydrochloric acid, boric acid, phosphoric acid, monocarboxylic acid, dicarboxylic acid and the like can be used alone or in combination as appropriate.

  By suitably selecting these buffers and pH adjusters, the pH of the plating bath of the present invention can be adjusted in the range of about 3 to 8 according to the purpose.

Additives :
The electroless copper plating bath according to the present invention is characterized by further containing a specific additive in the copper water-soluble salt, complexing agent, reducing agent, and buffering agent described above. The additive is a group of compounds collectively referred to as nitrogen-containing heterocyclic compounds, and is a compound having a heterocyclic structure containing at least one nitrogen. Further, the nitrogen-containing heterocyclic compound includes those having various substituents on the heterocyclic structure (derivatives). Further, salts of those nitrogen-containing heterocyclic compounds are also included.

  In the present invention, the number of members of the ring structure is not particularly limited, but is preferably at least a 4- to 10-membered ring, and more preferably a 4- to 6-membered ring.

  Further, the number and position of nitrogen contained in the ring structure are not particularly limited, but in the present invention, it is preferable that at least two nitrogens are contained as a bond represented by the formula, —N—C—N—. Specifically, the heterocyclic structure is not limited, and examples thereof include an imidazole ring structure in the case of a 5-membered ring and a pyrimidine ring structure in the case of a 6-membered ring. Further, in the present invention, for example, in the case of these imidazole ring structures, and in the case of a 6-membered ring, a pyrimidine ring structure further includes a heterocyclic structure in which nitrogen or other hetero atoms (O, S, etc.) are contained.

  Furthermore, in the heterocyclic structure of the present invention, it is particularly preferable that the carbon atom of the bond of —N—C—N— further has a specific substituent. Specifically, it is a bond represented by -NC (Y) -N-, and Y includes H, O, S, N and the like. Here, when Y is O, it becomes a so-called ketone group, that is, a urea bond, and when Y is S, it becomes a thioketone group, that is, a thiourea bond.

  In the present invention, X is preferably H in the case of a 5-membered heterocyclic structure, and Y is preferably O or S in the case of a 6-membered heterocyclic structure.

The nitrogen-containing heterocyclic compound of the present invention can further contain various substituents in the nitrogen-containing heterocyclic skeleton so as to have an appropriate solubility in a water-soluble plating bath. Such a substituent can be appropriately selected by those skilled in the art based on the desired solubility. For example, hydrophobic substituents include alkyl groups and aryl groups (which may be substituted with alkyl groups), and hydrophilic substituents include OH, COOH, CHO, CH ₂ —CH (H) (NH ₂ ) COOH and the like.

  The nitrogen-containing heterocyclic compound that can be preferably used in the present invention is a compound represented by the following formula (I), (II), (III) or (IV) exemplified below.

(Here, n represents an integer of 1 to 6, and R represents an alkyl group having 1 to 6 carbon atoms.)
Nitrogen-containing heterocyclic compounds that can be preferably used in the present invention include 2-thiouracil, 4-thiouracil, 2-thiobarbituric acid, 1,3-diethylthiobarbituric acid, orotic acid, methylorotic acid, 1,3- Examples include dimethyluracil, histidine, and imidazole.

  These nitrogen-containing heterocyclic compounds (substituted derivatives) that can be used in the present invention can be used as they are on the market, and can be obtained by manufacturing them using a generally known chemical synthesis method. it can.

  Although there is no restriction | limiting in particular in the addition density | concentration of a nitrogen-containing heterocyclic compound, It is 0.005-0.1 g / L, Preferably it is the range of about 0.01-0.08 g / L. If it is lower than 0.005 g / L, the bath stability may be deteriorated, and if it is higher than 0.08 g / L, plating is not sufficiently precipitated, and a coarse crystal precipitate film lacking in denseness may be precipitated.

Other additives :
(Redox agent)
In the present invention, in addition to an ascorbic acid-based reducing agent, other reducing systems, for example, ions of transition metals such as Co (cobalt), Ti (titanium), and Fe (iron), which are known as redox-based reducing agents, are included. You can also In the present invention, the concentration is 100 mg / L or less. By further including this redox-based reducing agent, denser and finer copper crystal precipitation becomes possible.

(Surfactant)
In addition, the plating bath of the present invention includes various additives for improving the physical properties of the deposited film and various additives for improving the permeability of the plating bath that penetrates into fine parts of the object to be plated. As described above, various surfactants can be included. As the surfactant that can be used in the present invention, all known surfactants that can be used in an electroless copper plating bath can be used, and anionic surfactants, cationic surfactants, and zwitterionic surfactants can be used. And nonionic surfactants.

  As the anionic surfactant, a sulfonate, sulfate, carboxylate, or phosphate ester salt can be used. Moreover, as a cationic surfactant, an ammonium salt type, an alkylamine salt type, and a pyridinium salt type can be used. As the zwitterionic surfactant, betaines, aminocarboxylic acids, amine oxides, and nonionic surfactants can be used ethers, esters, and silicones.

  More specifically, as the anionic surfactant, alkylbenzene sulfonate, sulfosuccinate, polyoxyethylene sulfate alkyl salt, alkyl phosphate, long chain fatty acid soap and the like can be used. Further, as the cationic surfactant, alkyltrimethylammonium chloride salt, dialkyldimethylammonium chloride salt, alkylpyridinium chloride salt and the like can be used. As the zwitterionic surfactant, betaine sulfonates and betaine aminocarboxylic acid amine salts can be used. As the nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyalkylene-modified polysiloxane and the like can be used.

  The concentration of the surfactant in the solution containing the surfactant is appropriately selected, but is preferably 0.001 to 10% by weight, particularly 0.01 to 1% by weight.

Method of using the electroless copper plating bath of the present invention :
There is no particular limitation on the object to be plated that can be plated using the electroless copper plating bath of the present invention. When the electroless copper plating bath of the present invention is used, as will be apparent from the following examples, very fine copper crystals (including all copper films) become a very dense and uniform film. Therefore, it is possible to form a very dense and uniform film with very fine copper crystals on the surface of the fine structure (three-dimensional structure) of the object to be plated. As an object to be plated (or a part to be plated), for example, it can be applied to an electronic device that is miniaturized and has a smaller and more complicated three-dimensional structure.

  Moreover, there is no limitation in particular as pre-processing of a to-be-plated object, It is preferable to perform normal or well-known pre-processing, for example, pre-processing which provides a suitable catalyst (catalysts, such as Pd).

  Moreover, there is no restriction | limiting in particular about the method and apparatus etc. which implement copper plating to this to-be-plated object. Plating conditions and apparatuses using various ordinary reducing systems, particularly plating conditions and apparatuses using ascorbic acid-based reducing agents can be used as they are. For example, the electroless plating bath according to the present invention is prepared and stored in advance. The method of immersing is mentioned. The plating bath capacity and the apparatus to be used can be appropriately selected according to the size of the object to be plated and the intended plating. The plating reaction normally proceeds smoothly at room temperature, but preferably the plating reaction temperature is controlled to be constant, for example, in the range of 10 ° C to 90 ° C. If the pH varies during the plating reaction, it is preferable to monitor the pH of the plating bath. In some cases, it is preferable to control the pH regulator as described above, either automatically or manually, as appropriate.

  The plating reaction time using the plating bath of the present invention can be appropriately selected so as to suit the size of the object to be plated and the thickness and quality of the film. The formation of the plating film on the object to be plated can be monitored by a normal method.

  After the plating reaction is completed, the plating bath according to the present invention does not contain any component that imposes a burden on the environment (for example, EDTA, etc.), so that its disposal is relatively easy.

Analysis of electroless copper plating bath :
Components contained in the electroless copper plating bath of the present invention, copper water-soluble salts, complexing agents, reducing agents, buffering agents and additives, and other additives are the usual or known chemical analysis methods. Alternatively, it can be analyzed qualitatively and quantitatively by a physical analysis method. These analysis methods include metal ion analysis, anion analysis, organic compound analysis, pH measurement, and the like, and various conventionally known (or known) analysis methods can be applied thereto. For example, known AA, ICPMS analysis methods for analysis of metal analysis ions, ion chromatography methods for anion analysis, ion chromatography, gas chromatograph, IR, NMR, MS analysis methods, etc. are appropriately selected for organic compounds Can be applied.

Copper plating film obtained by the electroless copper plating method of the present invention :
Further, the plating surface of the object plated using the electroless copper plating bath of the present invention is characterized in that the deposited copper crystals have a very fine size and are a dense uniform film. Therefore, by observing the surface of these features using, for example, a scanning electron microscope, the size, denseness, and uniformity of the deposited copper crystals can be determined.

  EXAMPLES Hereinafter, although the Example and comparative example of this invention are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

Plating bath preparation :
For Examples 1 to 6, 8, 9 , Reference Example 7, and Comparative Examples 1 to 3, an electroless copper plating bath was prepared according to the composition and content shown in Table 1.

In Table 1, copper sulfate means pentahydrate and copper chloride means dihydrate. Surfactant S-141 (made by Sey Chemical Co., Ltd.), which is a fluorine-containing surfactant, was used as the surfactant.

Material to be plated :
The materials to be plated used in Examples , Reference Examples, and Comparative Examples were prepared by applying a Pd catalyst to a plate of epoxy resin (dimension 3 cm × 5 cm).

Plating reaction:
Said to-be-plated material was immersed in each plating bath of Table 1. The plating bath temperature was controlled at 40 ° C. and reacted for 60 minutes. During the reaction, in order to maintain the pH of the plating bath at the pH shown in Table 1, it was adjusted using 25% sodium hydroxide, 25% aqueous ammonia or 10% sulfuric acid.

Deposited film :
After completion of the plating reaction, the material to be plated was taken out, washed with deionized water, and dried.

  Thereafter, the film thickness and crystallinity (crystal size, denseness, homogeneity) of the deposited film were evaluated with an electron microscope “scanning electron microscope (SEM)”.

  The adhesion of the deposited film was determined by taking out the obtained plated material and bending it to determine whether the film peeled off. In the case of non-peeling, it was evaluated as “good”, and in the case of peeling (including the case of peeling during plating or after plating), x was given.

Furthermore, the bath stability was determined visually after the preparation in Table 1 above. Judgment evaluated whether it stabilized or decomposed | disassembled after progress for 2 hours after preparation. The results are summarized in Table 2 as “stable” and “decomposed”. Furthermore, the electron micrograph (SEM) of the surface of the precipitation technical film | membrane obtained by the reference example 7 and the comparative example 2 is shown in FIG.

Discussion of results :
From Tables 1 and 2 and FIG.

(I) All the plating baths of Examples 1 to 6, 8, 9 and Reference Example 7 exhibit sufficient bath stability at a temperature of 40 ° C. under conditions of pH 4 to 7, and therefore the plating bath of the present invention is excellent. It has a good bath stability.

(Ii) All the plating baths of Examples 1 to 6, 8, 9 and Reference Example 7 form a deposited film with very good adhesion, and the deposited film thickness is in the range of 0.5 μm to 1.1 μm. Gives a very fine, dense and homogeneous microcrystalline film. Therefore, it can be seen that by using the plating bath of the present invention, a very fine, dense and homogeneous copper film can be formed on the object to be plated with a desired thickness. Furthermore, it shows that a good plating film can be provided even if the object to be plated has a very fine and complicated three-dimensional structure.

  (Iii) It can be seen from Example 6 that a good electroless plating electroplated film can be obtained even with a composition that does not contain a general copper chelate, as in Examples 1-5. From this, it can be seen that the plating bath of the present invention has a very low environmental load.

(Iv) Reference Example 7 and Example 8 are electroless plating solutions containing a so-called redox-based reducing agent containing a metal having a polyvalent valence other than copper, but good as in Examples 1-6. It can be seen that a copper film is obtained. From this, it can be seen that the electroless copper plating of the present invention exhibits a synergistic effect in combination with the conventional redox reduction system and enables a very excellent electroless copper plating.

  (V) From Example 9, it can be seen that the plating bath of the present invention exhibits a sufficiently excellent effect even if it does not contain a surfactant. From this, it can be seen that the plating bath of the present invention has a very low environmental load.

(Vi) Further, as shown in FIG. 1, according to surface observation (SEM) using an electron microscope, it can be seen that the film obtained in Reference Example 7 has a copper fine crystal size of at least smaller than 0.1 μm. This indicates that even if the object to be plated has a very fine and complicated three-dimensional structure, it is possible to provide a good plating film, and it can be seen that this is a plating bath that satisfies the demand for electronic devices in recent years.

  (Vii) On the other hand, the plating baths of Comparative Examples 1 to 3 have sparse, fine (or coarse) crystals with insufficient bath stability, thin film thickness (or no precipitation), and poor adhesion. It turns out that it is what gives. Particularly, in the electroless copper plating solution of Comparative Example 1, the plating solution started to decompose immediately after immersion, and no deposited film was obtained. Moreover, in the electroless copper plating liquid of the comparative example 2, it started to decompose | disassemble gradually, and it turned out that copper powder precipitates on the plating bath bottom after one hour. Further, it can be seen that the amount of the deposited film is small. As shown in FIG. 1, according to surface observation (SEM) using an electron microscope, it can be seen that the crystals are coarse and heterogeneous as compared with the film obtained in Example 7.

Claims (10)

In an electroless copper plating bath containing a copper water-soluble salt, a complexing agent, a reducing agent, a buffering agent and additives, the complexing agent is a hydroxycarboxylic acid complexing agent, and the reducing agent is an ascorbic acid reducing agent. , and the said buffering agent is a pH buffering agent, wherein the additive Ri nitrogen-containing heterocyclic compound der,
The electroless copper plating bath, wherein the nitrogen-containing heterocyclic compound has a pyrimidine skeleton, and the pyrimidine skeleton further contains a ketone or a thioketone . Billing an electroless copper plating bath according to claim 1, wherein the complexing agent is 2,2'-bipyridine, 1,10-phenanthroline, 8-hydro alkoxy containing at least one quinoline, electroless copper plating bath. The electroless copper plating bath according to claim 1 or 2 , wherein the nitrogen-containing heterocyclic compound is a compound represented by the following formula (I), (II), or (III ) .
(Here, n represents an integer of 1 to 6, and R represents an alkyl group having 1 to 6 carbon atoms.) The nitrogen-containing heterocyclic compound is 2-thiouracil, 4-thiouracil, 2-thiobarbituric acid, 1,3-diethyl thiobarbituric acid, orotic acid, Mechiruorochin acid, 1,3 Jimechiruurashi Le, wherein Item 4. The electroless copper plating bath according to Item 3 . The electroless copper plating bath according to any one of claims 1 to 4 , wherein a concentration of the nitrogen-containing heterocyclic compound is in a range of 0.005 to 0.1 g / L. The electroless copper plating bath according to any one of claims 1 to 5 , wherein the copper water-soluble salt contains copper sulfate or copper chloride, and the pH in the bath is 3 to 8. bath. The electroless copper plating bath according to any one of claims 1 to 6 , wherein the pH buffering agent contains the hydroxycarboxylic acid complexing agent and an alkali salt thereof. The electroless copper plating bath according to any one of claims 1 to 7 , further comprising metal ions that can exchange electrons in a plating solution. The electroless copper plating bath according to claim 8 , wherein the metal is at least one of Ti, Co, and Fe. The electroless copper plating bath according to any one of claims 1 to 9 , further comprising a surfactant.