Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents

Definitions

• the present application relates to an electroless copper plating solution, particularly to a reducing electroless copper plating solution used in a neutral range.
• an electroless copper plating solution that uses formaldehyde as a reducing agent for copper ions.
• formaldehyde has an irritating odor that deteriorates the working environment and causes adverse effects on the human body.
• the electroless copper plating solution using formaldehyde is strongly alkaline, and thus the use of the electroless copper plating solution is difficult especially when the object to be plated is aluminum, aluminum alloy, or the like.
• Patent Literature 1 discloses “an electroless copper plating bath having a pH of 4 to 9, containing a water-soluble copper salt, amino borane or a substituted derivative thereof as a reducing agent, and no formaldehyde, the electroless copper plating bath containing polyaminopolyphosphonic acid as a complexing agent, an anionic surfactant, an antimony compound, and a nitrogen-containing aromatic compound”.
• the first problem is that if the electroless copper plating bath disclosed in Patent Literature 1 is left in a plating bath for a long time after use, copper tends to deposit on the bottom of the bath, stirring jigs, and the like, resulting in a high tendency to have a lack of solution stability as a plating solution;
• the second problem is that an electroless copper plating layer formed using the electroless copper plating bath disclosed in Patent Literature 1 tends to have a non-uniform appearance;
• the third problem is that when plating is performed on an aluminum material using the electroless copper plating bath disclosed in Patent Literature 1, the copper plating layer tends to swell even if the aluminum itself is not damaged, resulting in a tendency for pits to occur.
• an object of the present application is to provide an electroless copper plating solution with excellent solution stability and easy composition control, which does not cause the above-mentioned problems.
• the electroless copper plating solution according to the present application is a reducing electroless copper plating solution used in a neutral range that contains a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and contains a tellurium compound serving as a deposition stabilizer, and that has a solution pH of 6 to 9.
• the tellurium compound serving as a deposition stabilizer is preferably used in a concentration range of 0.1 mg/L to 100 mg/L in terms of tellurium.
• the complexing agent for chelating copper ions is preferably a phosphonic acid-based chelating agent is used in a concentration range of 0.1 to 10 times the number of moles of copper.
• the reducing agent is preferably amine borane or a derivative thereof.
• the surfactant is preferably an anionic surfactant used in a concentration range of 0.01 mg/L to 1500 mg/L.
• the aromatic compound containing nitrogen is preferably used in a concentration range of 0.01 mg/L to 1000 mg/L.
• the electroless copper plating solution according to the present application contains a tellurium compound serving as a deposition stabilizer for the electroless copper plating solution, thereby dramatically improving the solution stability as a plating solution even though it is used in a neutral range without containing formaldehyde.
• a change in the composition of the plating solution during plating operation is small, a stable copper plating layer can be formed even if the composition is slightly changed, and it becomes possible to obtain layer thickness uniformity and uniform appearance quality of the copper plating layer.
• unnecessary copper deposition does not occur while a plating solution is less deteriorated, making it possible to prolong the life of the solution.
• aluminum itself is not damaged when the solution is plated on an aluminum material, and plating defects such as blisters and pits in the plating layer can be efficiently eliminated.
• Embodiments of the electroless copper plating solution according to the present application and electroless copper plating methods using the same will be described below.
• the electroless copper plating solution according to the present application is an electroless copper plating solution used in a neutral range, and this electroless copper plating solution contains a tellurium compound serving as a deposition stabilizer in terms of a component and has a solution pH of 6 to 9.
• the solution pH of the electroless copper plating solution will be described below, and then each component will be described.
• the solution pH is preferably 6.0 to 9.0.
• the electroless copper plating solution is in an acidic range, which is not preferable because the effect of components such as the reducing agents described below is likely to decrease, making it difficult to prolong the life of the electroless copper plating solution.
• the solution pH is more than 9.0, the electroless copper plating solution is in an alkaline range, which is not preferable because the surface of the object to be plated, such as an aluminum material or a ceramic material, is more likely to be damaged.
• the solution pH is more preferably 6.5 to 8.5, which is even closer to neutral, and in this case, the damage to the object to be plated can be prevented more reliably.
• hydrochloric acid, sulfuric acid, or the like may be used to adjust the solution pH to the acid side while sodium hydroxide, potassium hydroxide, or the like may be used to adjust the solution pH to the alkali side.
• the tellurium compound serving as a deposition stabilizer is used.
• the tellurium compound include any one or more of telluric acid and a salt thereof, tellurous acid and a salt thereof, tellurium dioxide, tellurium trioxide, tellurium chloride, and dimethyl telluride.
• the tellurium compound serving as a deposition stabilizer is preferably contained in the electroless copper plating solution in a concentration range of 0.1 mg/L to 100 mg/L in terms of tellurium.
• the content of the tellurium compound is less than 0.1 mg/L in terms of concentration of tellurium, the solution stability of the electroless copper plating solution cannot be improved, the lifetime extension of the plating solution cannot be achieved, and the characteristics of the plating solution vary due to the change in the composition, making it difficult to use the electroless copper plating solution for a long time, which is not preferable.
• the content of the tellurium compound is more than 100 mg/L in concentration as tellurium, the phenomenon that copper deposition is markedly reduced is observed, which is not preferable because rapid copper plating layer formation becomes difficult.
• the content of the tellurium compound is more preferably in the concentration range of 0.3 mg/L to 70 mg/L in terms of concentration of tellurium.
• the tellurium compound is most preferably contained in the concentration range of 0.5 mg/L to 50 mg/L in terms of tellurium.
• Copper ion supply source The copper salt serving as a copper ion supply source is used in the electroless copper plating solution according to the present application.
• the copper salt include any one or more of water-soluble copper salts such as copper sulfate, copper nitrate, copper chloride, copper acetate, copper citrate, copper tartrate, copper gluconate, and hydrates thereof.
• two or more copper salts of the present application can be simultaneously used in combination, and there is no particular limitation on the mixing ratio of two or more copper salts as long as the amount of copper ions is in the following range.
• the most widely available is copper sulfate (copper sulfate pentahydrate) or a combination of copper sulfate and copper hydrochloride.
• the content of the copper salt is preferably in the concentration range of 0.01 mol/L to 1 mol/L in terms of concentration of copper.
• the content of the copper salt in the electroless copper plating solution according to the present application is less than 0.01 mol/L in terms of concentration of copper because the copper deposition rate is remarkably decreased, the time required for operation becomes long, and the productivity required for industrial purposes cannot be obtained, which is not preferable.
• the content of copper salt is more than 1 mol/L in terms of concentration of copper, the copper deposition rate is not improved, but rather the appearance defects of the formed copper plating layer tend to increase, which is not preferable.
• the content of the copper salt is preferably in the concentration range of 0.02 mol/L to 0.5 mol/L in terms of concentration of copper.
• the electroless copper plating solution according to the present application is used in the neutral range, and it is preferable to use a phosphonic acid-based chelating agent as the complexing agent. This is because the phosphonic acid-based chelating agent easily forms a complex of copper ions in the neutral range.
• the phosphonic acid-based chelating agent includes 1-hydroxyethane-1,1-diphosphonic acid, N,N,N′,N′-ethylenediaminetetrakis(methylenephosphonic acid), nitrilotris(methylenephosphonic acid), diethylenediaminepenta(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), bis(hexamethylenetriaminepenta(methylenephosphonic acid)), glycine-N,N-bis(methylenephosphonic acid), and salts thereof, and one or more of them can be used simultaneously.
• the amount of the complexing agent added is determined by the copper content in the electroless copper plating solution.
• the phosphonic acid-based chelating agent as a complexing agent is preferably used in a concentration range of 0.1 to 10 times the number of moles of copper in the electroless copper plating solution.
• concentration of the phosphonic acid-based chelating agent is less than 0.1 times the number of moles of copper, copper ions cannot be sufficiently complexed, and solution stability as an electroless copper plating solution cannot be ensured, which is not preferable.
• the concentration of the phosphonic acid-based chelating agent is more than 10 times the number of moles of copper
• the amount of the chelating agent is more than the amount required for the complexation of copper ions, which is not preferable because it wastes resources and also causes the appearance quality of the copper plating layer to deteriorate.
• Reducing agent Various reducing agents can be used for copper ions. In the case of the electroless copper plating solution according to the present application, however, since it is used in the neutral range, it is preferable to use amine borane or a derivative thereof as a reducing agent usable in the neutral range in order to ensure the solution stability. More specifically, any one or more of dimethylamine borane, diethylamine borane, tert-butylamine borane, triethylamine borane, trimethylamine borane, and the like can be used. The concentration of this reducing agent is not particularly limited, but it is reasonable to set the concentration in the range of 0.01 mol/L to 0.5 mol/L.
• the concentration of the reducing agent is less than 0.01 mol/L, the copper deposition rate is slow, which is not preferable.
• the concentration of the reducing agent is more than 0.5 mol/L, it is not preferable because the copper deposition rate does not increase and is simply a waste of resources.
• Surfactant In the electroless copper plating solution according to the present application, it is preferable to use a surfactant for the purpose of improving the solution stability and improving the layer thickness uniformity and appearance quality of the plating layer to be formed. Especially in the case of an electroless copper plating solution used in the neutral range, it is preferable to use an anionic surfactant.
• anionic surfactants all the surfactants which are called “anionic surfactants” or “anionic surface-active agents” in the market can be used.
• examples include any one or more of alkylcarboxylic acid-based surfactants, naphthalene sulfonate formaldehyde condensates such as sodium salts of ⁇ -naphthalene sulfonate formalin condensate, polyoxyalkylene ether sulfates such as sodium polyoxyethylene lauryl ether sulfate and triethanolamine polyoxyethylene alkyl ether sulfate, and sodium dodecyl sulfate, but not special limitations are required.
• the concentration of the surfactant is not particularly limited, but it is reasonable to set the concentration in the range of 0.01 mg/L to 1500 mg/L.
• concentration of the surfactant is less than 0.01 mg/L, it is not preferable since the solution stability of the electroless copper plating solution does not improve, making it difficult to prolong the life of the plating solution, and the appearance quality of the copper plating layer tends to deteriorate.
• concentration of the surfactant is more than 1500 mg/L, there is no particular problem, but the solution stability is not further improved nor the appearance quality is improved. Besides, the bath control during the plating operation becomes complicated, which is not preferable.
• Aromatic compound containing nitrogen In the electroless copper plating solution according to the present application, an aromatic compound containing nitrogen (so-called a heterocyclic aromatic compound containing nitrogen) is used to stabilize copper deposition in electroless copper plating.
• the nitrogen-containing aromatic compounds include any one or more of: imidazole or substituted derivatives thereof; pyrazole or substituted derivatives thereof; oxazole or substituted derivatives thereof; thiazole or substituted derivatives thereof; pyrazine or substituted derivatives thereof; pyridazine or substituted derivatives thereof; triazine or substituted derivatives thereof; benzothiazole or substituted derivatives thereof; pyridines such as pyridine, 2,2′-dipyridyl, 4,4′-dipyridyl, nicotinic acid, nicotinamide, picolines, and lutidines, or substituted derivatives thereof; quinolines such as quinoline and hydroxyquinoline, or substituted derivatives thereof; acridines such
• the concentration of the aromatic compound containing nitrogen that is contained in the electroless copper plating solution according to the present application is preferably 0.01 mg/L to 1000 mg/L.
• concentration of the aromatic compound containing nitrogen is less than 0.01 mg/L, the effect as a deposition stabilizer for copper cannot be exhibited, which is not preferable because the appearance of the formed copper plating layer is also impaired.
• concentration of the aromatic compound containing nitrogen is more than 1000 mg/L, the solution stability of the electroless copper plating solution becomes excessive, which is not preferable because it causes a decrease in the copper deposition rate and an undeposited portion of the plating layer is generated.
• electroless copper plating method conventionally known electroless plating methods and conditions may be applied using the above-mentioned electroless copper plating solution. Therefore, it is considered unnecessary to describe the electroless copper plating method in detail here, and the electroless plating methods and conditions are described in Example.
• Example 1 the solution stability as a plating solution was confirmed after electroless copper plating was performed using an electroless copper plating solution containing a copper salt serving as a copper ion supply source, a complexing agent for chelating copper ions, a reducing agent, a surfactant, an aromatic compound containing nitrogen, and containing a tellurium compound serving as a deposition stabilizer, and having a solution pH of 7.7 and a solution temperature of 60° C.
• the evaluation of the solution stability as a plating solution is indicated by “ ⁇ ” when no deposition was observed on a part other than the object to be treated, by “ ⁇ ” when the deposition was slightly observed, and by “X” when the deposition was remarkably or decomposition of the plating solution occurred during plating, after the electroless copper plating solution is heated and plated while keeping the solution temperature constant, and then the electroless copper plating solution is left for 12 hours.
• Table 3 The results of this confirmation are shown in Table 3 below.
• Example 1 a substrate with an aluminum circuit (hereinafter simply referred to as a substrate), an object to be plated, was subjected to pretreatment under the conditions listed in Table 1 below (in the order from the top in the table), and then immersed in an electroless copper plating solution for 120 minutes to perform electroless copper plating, thereby forming a copper plating layer on the surface of the aluminum circuit pattern.
• Treatment Treatment step Name of bath condition Degreasing Melcleaner SC-7001 70° C., 30 secs Etching Melplate E-7121 70° C., 30 secs Conditioning Melplate Conditioner 7230 22° C., 20 secs Single zincate treatment Melplate FZ-7350 22° C., 20 secs Zinc stripping 20 wt % nitric acid 22° C., 10 secs Double zincate treatmen Melplate FBZ 22° C., 30 secs
• Example 1 an electroless copper plating solution having the composition shown below was prepared.
• Example 1 the deposition rate of the electroless copper plating layer, the plating appearance, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the copper plating layer after the plating layer was formed on the surface of the aluminum circuit pattern (hereinafter, also simply referred to as a pattern) on the substrate were confirmed.
• the above-mentioned “presence or absence of undeposition in pattern” indicates whether or not an undeposited portion of the copper plating layer is generated on the surface of the aluminum circuit pattern.
• the deposition rate of the electroless copper plating layer was determined by measurement with a fluorescent X-ray film thickness gauge.
• the plating appearance was visually evaluated (“ ⁇ ” for the uniform plating appearance and “X” for the uneven plating appearance). The results of these confirmations are shown in Table 3 as well.
• Example 2 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 2, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “2 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 2 is omitted.
• Example 3 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 3, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “10 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 3 is omitted.
• Example 4 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 4, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “20 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 4 is omitted.
• Example 5 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 5, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “50 mg/L” in terms of concentration of tellurium. Accordingly, the description of the conditions for the electroless copper plating in Example 5 is omitted.
• Example 6 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 6, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 6.5. Accordingly, the description of the conditions for the electroless copper plating in Example 6 is omitted.
• Example 7 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 7, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 7.0. Accordingly, the description of the conditions for the electroless copper plating in Example 7 is omitted.
• Example 8 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Example 8, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 8.0. Accordingly, the description of the conditions for the electroless copper plating in Example 8 is omitted.
• Example 9 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1.
• the results of this confirmation are shown in Table 3.
• the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “5 mg/L” in terms of concentration of tellurium and the solution pH was changed to 8.5. Accordingly, the description of the conditions for the electroless copper plating in Example 9 is omitted.
• Comparative Example 1 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 1, the electroless copper plating was performed under the same conditions as in Example 1, except that “antimony oxide” was used in place of sodium tellurate as a deposition stabilizer in the electroless copper plating solution composition in order to compare with Examples 1 to 9, the content thereof was set at 4 mg/L in terms of concentration of antimony, and the concentration of the reducing agent was set at 0.14 mol/L. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 1 is omitted.
• Comparative Example 2 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 2, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition, was changed to “0 mg/L (i.e., no sodium tellurate)” in terms of concentration of tellurium in order to compare with Examples 1 to 9. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 2 is omitted.
• Comparative Example 3 the solution stability of the plating solution, the deposition rate of the electroless copper plating layer, and the presence or absence of out-of-pattern deposition and undeposition in pattern of the plating layer were confirmed as in Example 1. The results of this confirmation are shown in Table 3. Note that in Comparative Example 3, the electroless copper plating was performed under the same conditions as in Example 1, except that the content of sodium tellurate, a deposition stabilizer, in the electroless copper plating solution composition was changed to “200 mg/L” in terms of concentration of tellurium in order to compare with Examples 1 to 9. Accordingly, the description of the conditions for the electroless copper plating in Comparative Example 3 is omitted.
• compositions of the electroless copper plating solutions used in Examples and Comparative Examples are listed in Table 2.
• Examples 1 to 9 gave good results in all of “plating appearance”, “out-of-pattern deposition”, “undeposition of pattern”, and “solution stability”.
• Comparative Example 1 when antimony was contained instead of tellurium as a deposition stabilizer in the electroless copper plating solution, a decrease in solution stability was observed. Furthermore, in Comparative Example 1, the plating layer was not formed sufficiently on the surface of the aluminum circuit pattern on the substrate, nor was the plating appearance uniform.
• the concentration of tellurium in the deposition stabilizer was less than 0.5 mg/L, as in Comparative Example 2, deteriorated plating appearance and solution stability was also observed as. In Comparative Example 2, a protrusion from the pattern was further observed.
• the concentration of tellurium in the deposition stabilizer was more than 100 mg/L, as in Comparative Example 3, almost no plating was deposited, and thus the plating layer was not formed on the surface of the aluminum circuit pattern on the substrate.
• the electroless copper plating solution according to the present application is used in a neutral range and does not cause damage to an object to be plated. Therefore, the electroless copper plating solution is usable in the object to be plated such as an aluminum material or a ceramic material, which is easily damaged. In addition, since the electroless copper plating solution has a long life and excellent solution stability, the running cost of electroless copper plating can be reduced.

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