Etching solution set, etching method, and method for forming a conductive pattern

Abstract

To provide an etching liquid set capable of selectively etching metals to be treated such as a Ni-Cr alloy and the like.SOLUTION: An etching solution set includes a first liquid containing hydrochloric acid and a thio compound, and a second liquid containing hydrochloric acid and a nitrous acid source. The thio compound contained in the first liquid is a compound having S-H or S=C and having at least one functional group selected from the group consisting of an amino group, an imino group, a carboxy group, a carbonyl group, and a hydroxyl group, and has a carbon number of 7 or less, and a concentration of the thio compound in the first liquid is 0.5 to 30 wt.%. The second liquid has a nitrous acid source concentration of 0.1 to 30 mM, a hydrochloric acid concentration of 8 to 30 wt.%, and a sulfuric acid concentration of 4.5 wt.% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an etching solution set used for etching a metal selected from Ni, Cr, Ni-Cr alloy, and Pd, an etching method using the etching solution set, and a method for forming a conductor pattern.

Background Art

[0002] In a flexible printed wiring board that requires a fine pitch circuit, a two-layer copper-clad laminate in which a copper layer is formed on a polyimide film as an insulating substrate without a resin adhesive layer is used. In particular, a method (semi-additive method) of forming a base layer on a polyimide film and forming a copper layer only on a portion constituting the wiring on the base layer by electrolytic plating is advantageous for forming fine wiring.

[0003] When forming a copper wiring by the semi-additive method, the base layer has a function as a power supply layer (seed layer) for forming a copper layer by electrolytic plating, and is formed by, for example, electroless copper plating using Pd as a catalyst. Further, when the base layer is Ni, Cr, or Ni-Cr alloy, the base layer acts as a power supply layer and also has a function as an adhesive layer for enhancing the adhesion between an insulating substrate such as a polyimide film and the copper wiring.

[0004] After forming a copper layer on the base layer, the base layer in a portion where the copper layer is not formed is etched and removed, thereby forming a wiring composed of the copper layer and the base layer. For etching the base layer, an etching solution mainly composed of ferric chloride is generally used. However, since the etching rate of the metal constituting the base layer is small, there is a problem that the copper layer is dissolved while the base layer is being etched, and the height and width of the wiring are reduced.

[0005] Patent documents 1 and 2 propose using an acidic aqueous solution containing nitric acid or nitrite as an etching method for underlying layers such as Ni-Cr layers. Patent document 1 uses an acidic etching solution containing nitrite and a specific thio compound. Patent document 2 discloses an etching solution set including a first solution and a second solution, and describes that the etching rate of the underlying layer is increased by removing the oxide film on the surface of the underlying layer with the first solution containing hydrochloric acid and a thio compound, and then performing etching with the second solution containing hydrochloric acid, nitric acid, and cupric ions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-229196 [Patent Document 2] Japanese Patent Publication No. 2005-154899 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The etching solutions described in Patent Documents 1 and 2 have a high etching rate for the metal to be treated, such as Ni-Cr alloys that constitute the underlying layer, and can etch and remove the underlying layer in a short time, thus suppressing the etching of the copper layer of the substrate to be treated. However, since it is not possible to completely suppress the dissolution of copper, when etching treatment of multiple substrates to be treated is performed consecutively (when the etching solution is used consecutively), the concentration of copper (copper ions) dissolved in the solution increases.

[0008] Cupric ions act as an oxidizing agent for metallic copper and increase the etching rate of copper; therefore, a higher concentration of copper ions in the etching solution leads to a higher etching rate of copper. In addition, in systems using nitric acid, as described in Patent Document 2, the generation of nitrogen oxides (NOx) in the presence of copper ions also contributes to the increased etching rate of copper.

[0009] When the copper ion concentration or NOx concentration in the solution increases, the etching rate of copper rises, making it impossible to maintain the etching properties. This necessitates replacing the etching solution, leading to decreased process efficiency and increased costs. Therefore, there is a need for an etching solution that exhibits minimal changes in etching properties even with continuous use, thereby reducing the frequency of solution replacement (improving run-through efficiency). [Means for solving the problem]

[0010] One embodiment of the present invention is an etching solution set used for etching metals selected from Ni, Cr, Ni-Cr alloys, and Pd. The etching solution set comprises a first solution containing hydrochloric acid and a thio compound, and a second solution containing hydrochloric acid and a nitrite source.

[0011] The thio compound contained in the first solution is a compound with 7 or fewer carbon atoms that has SH or S=C and one or more functional groups selected from the group consisting of an amino group, imino group, carboxyl group, carbonyl group, and hydroxyl group, and the concentration of the thio compound in the first solution is 0.5 to 30% by weight. The second solution has a nitrite source concentration of 0.1 to 30 mM, a hydrochloric acid concentration of 8 to 30% by weight, and a sulfuric acid concentration of 4.5% by weight or less.

[0012] The metal to be treated (the metal selected from Ni, Cr, Ni-Cr alloy, and Pd) is etched by sequentially contacting it with the first and second solutions described above. For example, the substrate to be treated may be immersed in the first solution to bring the first solution into contact with the surface of the metal to be treated, and then the substrate to be treated may be immersed in the second solution to bring the second solution into contact with the surface of the metal to be treated.

[0013] The substrate to be processed may be an insulating substrate on which the metal to be processed is provided. Alternatively, the substrate to be processed may have both the metal to be processed and a copper layer in the same location.

[0014] An example of a substrate to be processed is a configuration comprising an unpatterned underlayer on an insulating substrate, with a patterned copper layer on top of the underlayer. The underlayer contains the metal to be processed, selected from Ni, Cr, Ni-Cr alloy, and Pd, and this underlayer is etched using an etching solution set. That is, the underlayer is etched by sequentially contacting the underlayer exposed between the copper layers of the substrate with the first and second liquids of the etching solution set. By etching the underlayer exposed between the copper layers, a conductive pattern comprising the patterned underlayer and copper layers in sequence is formed on the insulating substrate.

[0015] When etching multiple substrates in succession using an etching solution set, the composition may be adjusted by adding a replenishment solution to the first and / or second solution in order to maintain etching characteristics. For example, by adding a replenishment solution containing a nitrite source to the second solution, the etching rate of the metal to be treated by the second solution can be maintained above a predetermined value.

[0016] When adding a replenishment solution to the second solution, for example, the replenishment solution should be added so that the etching rate of the metal to be treated by the second solution remains above a predetermined value. Alternatively, the replenishment solution may be added so that the nitrite source concentration in the second solution remains within a predetermined range. [Effects of the Invention]

[0017] By using the etching solution set of the present invention, it is possible to rapidly etch metals to be treated, such as Ni-Cr alloys, thereby suppressing excessive etching of copper and other metals on the substrate to be treated. Furthermore, even when the etching solution is used continuously, the etching characteristics do not change significantly, and the etching rate of copper does not easily increase. As a result, the frequency of etching solution replacement is reduced, which is advantageous for improving process efficiency and reducing costs. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view showing an example of the configuration of a substrate to be processed. [Figure 2]It is a cross-sectional view of a printed wiring board having a conductor pattern on an insulating substrate. [Figure 3] It is a schematic diagram showing an example of a process for forming a substrate to be processed.

Embodiments for Carrying out the Invention

[0019] The present invention relates to an etching liquid set used for etching at least one metal selected from Ni, Cr, Ni-Cr alloys, and Pd (hereinafter sometimes referred to as "metal to be processed"). The etching liquid set includes a first liquid and a second liquid. In one embodiment, the etching liquid set is used for selective etching of the metal to be processed in a substrate to be processed in which the metal to be processed and a copper layer coexist.

[0020] FIG. 1 is a cross-sectional view showing an example of a substrate to be processed. The substrate to be processed shown in FIG. 1 includes a Ni-Cr alloy layer as an underlayer 20 on a polyimide film as an insulating substrate 10, and a copper conductor pattern 31 is formed on the underlayer 20. By sequentially contacting the first liquid and the second liquid of the etching liquid set with the underlayer 20 exposed in the region 5 between the conductor patterns 31 of this substrate to be processed (the region where the conductor pattern is not formed), the underlayer is etched and removed, and as shown in FIG. 2, a printed wiring board is obtained in which a conductor pattern 3 composed of a patterned copper layer 31 and an underlayer 21 is formed on the insulating substrate 10.

[0021] [Composition of Etching Liquid] The etching liquid set includes a first liquid and a second liquid. The first liquid is an aqueous solution containing hydrochloric acid and a thio compound, and the second liquid is an aqueous solution containing hydrochloric acid and a nitrite source (nitrous acid or nitrite ion).

[0022] A metal to be processed such as a Ni-Cr alloy is mainly etched by the action of hydrochloric acid and nitrous acid in the second liquid, and the thio compound brought from the first liquid to the second liquid has the effect of promoting the etching of the metal to be processed and suppressing the etching of copper.

[0023] <First Liquid> (hydrochloric acid) The hydrochloric acid in the first solution removes oxide films and other materials formed on the surface of the metal to be treated, thereby enhancing the etching ability of the metal to be treated by the second solution. Furthermore, the hydrochloric acid enhances the solubility of the complex formed by the thio compound and copper (described later) when the copper of the substrate is etched and dissolved in the solution. The hydrochloric acid concentration in the first solution is preferably 0.5 to 30% by weight. If the hydrochloric acid concentration is excessively low, the removal of oxide films will be insufficient, reducing the etching rate of the metal to be treated by the second solution. Also, if etching of multiple substrates is performed consecutively without changing the etching solution, turbidity or precipitation of the solution may occur due to insoluble copper-thio compound complexes. If the hydrochloric acid concentration is excessively high, it becomes difficult to maintain a constant concentration. In terms of oxide film removal (cleaning ability) and copper-thio compound solubility, there is no particular difference if the hydrochloric acid concentration of the first solution is within the above range.

[0024] When a substrate treated with the first solution is immersed in the second solution, the first solution adhering to the surface of the substrate is carried into the second solution. When etching multiple substrates continuously without changing the etching solution, it is preferable that the difference between the hydrochloric acid concentration of the first solution and the hydrochloric acid concentration of the second solution is small, from the viewpoint of suppressing fluctuations in the composition of the second solution and maintaining constant etching characteristics. The hydrochloric acid concentration of the first solution is preferably 0.3 to 2 times, and more preferably 0.5 to 1.5 times, the hydrochloric acid concentration of the second solution. The hydrochloric acid concentration of the first solution may also be 3 to 30% by weight, 5 to 25% by weight, 7 to 23% by weight, or 10 to 20% by weight.

[0025] (Other acids) The first solution may contain an acid other than hydrochloric acid. Examples of acids other than hydrochloric acid include inorganic acids such as sulfuric acid, nitric acid, nitrous acid, and phosphoric acid, as well as various organic acids.

[0026] If the first solution contains nitric acid, nitrogen oxides (NOx) are generated when the copper of the substrate to be treated is etched and dissolved in the solution. The generated NOx has the effect of increasing the etching rate of copper. As the copper ion concentration in the solution increases with copper etching, the etching rate of copper increases even further. Also, if the first solution contains nitric acid, the thio compounds described later are easily decomposed, and their concentration decreases over time. From the viewpoint of suppressing copper etching and the decrease in the concentration of thio compounds, it is preferable that the first solution is substantially free of nitric acid. The nitric acid concentration in the first solution is preferably 1% by weight or less, more preferably 0.5% by weight or less, even more preferably 0.1% by weight or less, and may be 0.05% by weight or less or 0.01% by weight or less. It is particularly preferable that the first solution does not contain nitric acid.

[0027] If the first solution contains nitrite, the thio compounds described later are easily decomposed, and their concentration decreases over time. From the viewpoint of suppressing the decrease in the concentration of thio compounds, it is preferable that the first solution is substantially free of a nitrite source (nitrite or nitrite salt). The nitrite concentration in the first solution is preferably 0.001% by weight or less, more preferably 0.0005% by weight or less, and even more preferably 0.0001% by weight or less. It is particularly preferable that the first solution does not contain a nitrite source.

[0028] If the first solution contains sulfuric acid, the sulfuric acid concentration in the second solution increases as the sulfuric acid from the first solution adhering to the surface of the substrate to be treated is carried into the second solution. As described later, if the sulfuric acid concentration of the second solution is high, the nitrite source concentration in the second solution tends to decrease over time, which can lead to poor solution stability. From the viewpoint of suppressing the transfer of sulfuric acid into the second solution, it is preferable that the first solution has a low sulfuric acid concentration. The sulfuric acid concentration of the first solution is preferably 4.5% by weight or less, but may also be 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0.1% by weight or less. It is particularly preferable that the first solution does not contain sulfuric acid.

[0029] (Thio compounds) The thio compound contained in the first solution is a compound with 7 or fewer carbon atoms that has -SH or S=C and one or more functional groups selected from the group consisting of an amino group, imino group, carboxyl group, carbonyl group, and hydroxyl group. The number of carbon atoms in the thio compound is preferably 1 to 5. The molecular weight of the thio compound is preferably 60 to 300, and may be 70 to 200.

[0030] Specific examples of thio compounds containing an amino group include thiourea, thiourea dioxide, N-methylthiourea, 1,3-dimethylthiourea, and 1,3-diethylthiourea. Specific examples of thio compounds containing an imino group include ethylenethiourea. Specific examples of thio compounds containing a carboxyl group include sulfur atom-containing carboxylic acids such as thiosalicylic acid, thioglycolic acid, β-mercaptopropionic acid, 2-mercaptopropionic acid, 2,2'-thiodiglycolic acid, thiomalic acid, mercaptosuccinic acid, cysteine, and cystine, and their salts (sodium salts, potassium salts, calcium salts, ammonium salts, etc.). Specific examples of thio compounds containing a carbonyl group include 2-thiobarbituric acid. Specific examples of thio compounds containing a sulfo group include 2-mercaptoethanesulfonic acid, 3-mercapto-1-propanesulfonic acid, 2-mercaptobenzenesulfonic acid, and their salts. Specific examples of thio compounds containing a hydroxyl group include sulfur atom-containing alcohols such as thioglycerol.

[0031] When the copper on the substrate being treated is etched and dissolved into the solution by the action of the acid, the copper ions act as an oxidizing agent, thus accelerating the etching of the copper on the substrate. The thio compound contained in the first solution has the effect of suppressing the etching of the copper on the substrate by chelating and capturing copper ions.

[0032] When a substrate treated with the first solution is immersed in the second solution, the first solution adhering to the surface of the substrate is carried into the second solution. Therefore, the thio compounds contained in the first solution also contribute to suppressing copper etching in the second solution. Furthermore, the thio compounds carried from the first solution to the second solution also contribute to improving the etching properties of the metal being treated in the second solution.

[0033] The content of the above-mentioned thio compound in the first solution is 0.5% by weight or more. If the content of the thio compound is low, when etching multiple substrates is performed consecutively (when the etching solution is used continuously), the thio compound is easily consumed by the copper dissolved in the first solution. As the concentration of the thio compound in the first solution decreases with continuous use of the etching solution, the etching rate of copper in the first solution increases. Furthermore, as the concentration of the thio compound in the first solution decreases, the amount of thio compound carried over to the second solution decreases, so the etching rate of copper in the second solution tends to increase.

[0034] If the concentration of the thio compound in the first solution is 0.5% by weight or higher, the concentration of the thio compound is sufficiently high compared to the copper ions dissolved in the first solution, so the copper ions are easily chelated by the thio compound, and etching of copper in the first solution is suppressed. Because etching of copper by the first solution is suppressed, the consumption of the thio compound is small (the thio compound concentration does not decrease easily), and the composition fluctuates little. In addition, the action of the thio compound carried from the first solution to the second solution promotes etching of the metal to be treated in the second solution, while etching of copper by the second solution is suppressed.

[0035] The concentration of the thio compound in the first solution is more preferably 0.7% by weight or more, even more preferably 1.0% by weight or more, and may also be 1.3% by weight or more, 1.5% by weight or more, or 1.7% by weight or more. The higher the concentration of the thio compound in the first solution, the greater the effect of suppressing copper etching. Furthermore, the higher the concentration of the thio compound in the first solution, the smaller the change in the concentration of the thio compound (decrease in concentration) with continuous use of the etching solution, so the frequency of replenishing the thio compound in the first solution or replacing the first solution is reduced, which is advantageous for process efficiency and cost reduction.

[0036] The concentration of the thio compound in the first solution is preferably 30% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and may also be 7% by weight or less or 5% by weight or less. If the concentration of the thio compound in the first solution is excessively high, the amount of thio compound carried into the second solution will be excessive, which may inhibit the etching of the metal to be treated in the second solution.

[0037] <Second liquid> (hydrochloric acid) The hydrochloric acid in the second solution, along with the nitrite source described later, has the effect of dissolving and etching the metal to be treated. The hydrochloric acid concentration in the second solution is preferably 8 to 30% by weight, more preferably 10 to 25% by weight, and even more preferably 12 to 20% by weight. If the hydrochloric acid concentration is too low, the etching rate of the metal to be treated tends to decrease, and if the hydrochloric acid concentration is too high, the etching rate of copper tends to increase.

[0038] (nitrite source) The nitrite source in the second solution has the effect of dissolving and etching the metal to be treated. The nitrite source is nitrite and nitrite ions, and by incorporating nitrite or nitrite salts, it exists in the second solution in the form of nitrite or nitrite ions. Examples of nitrite salts include sodium nitrite, lithium nitrite, potassium nitrite, calcium nitrite, and barium nitrite.

[0039] The nitrite source concentration of the second solution (total concentration of nitrite and nitrite ions) is 0.1 to 30 mM, preferably 0.15 to 25 mM, more preferably 0.2 to 20 mM, even more preferably 0.3 to 17 mM, and may also be 0.4 to 15 mM, 0.5 to 12 mM, or 0.6 to 10 mM. If the nitrite source concentration is excessively low, the etching rate of the metal to be treated tends to decrease, and if the nitrite source concentration is excessively high, the etching rate of copper tends to increase.

[0040] While nitrite sources mostly exist in the form of nitrite in acidic aqueous solutions, free nitrite has low stability, and the concentration of nitrite sources in the second solution may decrease over time. Therefore, it is preferable to prepare the second solution by adding nitrites, etc., immediately before using the etching solution so that the concentration of nitrite sources is within the above range. Furthermore, if the concentration of nitrite sources decreases during use of the etching solution, it is preferable to replenish with nitrites, etc., to maintain the concentration of nitrite sources in the second solution within the above range.

[0041] The nitrite source can be added to the second solution as a solid or liquid (solution). Since the nitrite source exists stably as nitrite ions in neutral or weakly alkaline solutions, it is preferable to replenish the nitrite source by adding nitrite as a neutral or weakly alkaline aqueous solution to the second solution. When adding an aqueous solution of nitrite as a replenishment solution to the second solution, the concentration of nitrite in the replenishment solution is, for example, about 0.1 to 75% by weight, and may be 1 to 70% by weight, 5 to 60% by weight, or 10 to 50% by weight.

[0042] Although nitrite has low stability in acidic aqueous solutions, its concentration decreases slowly at concentrations below 30 mM, and it can be replenished by adding nitrites, etc. Furthermore, as described later, if sulfuric acid is not used as the acid in the second solution, or if sulfuric acid is used, the decrease in nitrite can be suppressed if its concentration is low. Moreover, since the source of nitrite can be quantified by spectroscopy, concentration control is easy.

[0043] When nitric acid is used as the etching component in the second solution, nitrogen oxides (NOx) are generated when the copper of the substrate being treated is etched and dissolved in the solution. The generated NOx has the effect of increasing the etching rate of copper. As the copper is etched, the concentration of copper ions in the solution increases, which further increases the etching rate of copper, making it impossible to maintain etching performance, and thus requiring frequent replacement of the etching solution.

[0044] On the other hand, when nitrite is used as the etching component of the second solution, NOx is less likely to be generated even in the presence of copper ions. Therefore, in the present invention, which uses a nitrite source in the second solution, etching performance can be stably maintained, and the frequency of solution changes is reduced, which is advantageous in terms of process efficiency and cost.

[0045] Furthermore, the continuous introduction of thio compounds from the first to the second etching solution during use also contributes to the stabilization of etching characteristics (suppression of the increase in copper etching rate). As mentioned above, thio compounds have the effect of improving the etching properties of the metal to be treated and suppressing copper etching.

[0046] In the presence of a nitrite source, thio compounds are easily decomposed, and their concentration decreases over time. Therefore, in one-component etching solutions where both a nitrite source and thio compounds are present, the concentrations of both tend to decrease over time. It is necessary to individually manage the concentrations of each and replenish them to maintain them within the specified range.

[0047] On the other hand, when using the etching solution set of the present invention, in which the first solution contains a thio compound and the second solution contains a nitrite source, the thio compound is supplied to the second solution by the first solution adhering to the surface of the substrate to be treated being carried into the second solution, so the concentration of the thio compound in the second solution is kept approximately constant. Therefore, for the second solution, it is sufficient to manage the concentration of the nitrite source to be within a predetermined range as described above, making the management of the solution simpler compared to a one-component etching solution.

[0048] (Other acids) The second solution may contain acids other than hydrochloric acid and nitrite. Examples of acids other than hydrochloric acid and nitrite include inorganic acids such as sulfuric acid, nitric acid, and phosphoric acid, as well as various organic acids.

[0049] If the second solution contains nitric acid, when the copper of the substrate to be treated is etched and dissolved in the solution, nitrogen oxides (NOx) are generated from the nitric acid, and the generated NOx has the effect of increasing the etching rate of copper. From the viewpoint of suppressing copper etching, it is preferable that the second solution is substantially free of nitric acid. The nitric acid concentration in the second solution is preferably 1% by weight or less, more preferably 0.5% by weight or less, even more preferably 0.1% by weight or less, and may be 0.05% by weight or less or 0.01% by weight or less. It is particularly preferable that the second solution does not contain nitric acid.

[0050] The second solution may contain sulfuric acid as the acid, but if the sulfuric acid concentration is high, the nitrite source concentration in the second solution tends to decrease over time, which may result in poor solution stability. Therefore, the sulfuric acid concentration of the second solution is preferably 4.5% by weight or less, and may also be 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0.1% by weight or less. The second solution does not need to contain sulfuric acid.

[0051] When nitric acid is used as an etching agent for a metal to be treated, sulfuric acid is used to convert the nitric acid to nitrous acid to increase the etching efficiency. On the other hand, if the etching agent is nitrous acid, the etching rate of the metal to be treated can be sufficiently increased without using sulfuric acid.

[0052] <Preparation of the first and second solutions> The first and second solutions described above can be prepared by dissolving each of the above components in water. Water from which ionic substances and impurities have been removed is preferred. Specifically, it is preferable to use ion-exchanged water, pure water, ultrapure water, etc.

[0053] The first and second liquids may further contain various additives as needed. For example, surfactants may be used as additives to improve wettability or prevent copper corrosion.

[0054] Examples of surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. If the first and / or second liquids contain a surfactant, its concentration may be 0.001 to 5% by weight, 0.01 to 4% by weight, or 0.1 to 3% by weight.

[0055] The first liquid and / or the second liquid may contain additives such as defoaming agents and rust inhibitors.

[0056] When etching using an etching apparatus, the first and second solutions may be prepared by first adjusting all components to a predetermined composition before supplying them to the etching apparatus, or each component may be supplied to the etching apparatus individually and mixed within the apparatus to achieve the predetermined composition. Alternatively, a solution containing some of the components of the first and second solutions may be supplied to the etching apparatus, and then the remaining components may be added and mixed within the etching apparatus to achieve the predetermined composition.

[0057] As mentioned above, the concentration of nitrite tends to decrease over time in acidic solutions. Therefore, it is preferable to supply the components other than the nitrite source to the etching apparatus in advance for the second solution, and then add the nitrite source just before use to adjust the composition.

[0058] [Etching of the metal to be treated using an etching solution set] Etching of the metal to be treated is performed by bringing the first solution into contact with the surface of the metal to be treated, followed by contact with the second solution. Methods for bringing the first and second solutions into contact with the metal to be treated include immersion, spraying, and bar coating.

[0059] From the viewpoint of suppressing copper etching by introducing the first liquid adhering to the surface of the substrate to be treated into the second liquid, thereby incorporating a thio compound into the second liquid, immersion is preferred as a method for bringing the first and second liquids into contact with the metal to be treated. That is, it is preferable to immerse the substrate to be treated in the first liquid, treat it in the first liquid, and then immerse the substrate, which has been removed from the first liquid, in the second liquid. It is preferable to immerse the substrate, which has been removed from the first liquid, directly into the second liquid without washing its surface.

[0060] The temperatures of the first and second solutions, as well as the processing times for each solution, are not particularly limited and should be set appropriately according to the type of metal to be etched, the amount of etching (thickness), etc. For example, the temperatures of the first and second solutions are approximately 20 to 65°C, and the processing time is approximately 5 to 60 seconds.

[0061] When etching solutions are used continuously, the composition of the solution may change over time, which can alter the etching properties (etching rate). To maintain a constant etching property, a replenishment solution may be added to the first and / or second solutions. In particular, since the concentration of the nitrite source in the second solution decreases over time, it is preferable to replenish the second solution with a nitrite source. As mentioned above, an aqueous nitrite solution is preferred as the replenishment solution for supplying the nitrite source to the second solution, and the nitrite concentration of the replenishment solution is, for example, about 0.1 to 75% by weight, and may be 1 to 70% by weight, 5 to 60% by weight, or 10 to 50% by weight.

[0062] When adding a replenishment solution to the second solution to replenish the nitrite source, the replenishment solution should be added in such a way that the nitrite source concentration remains within the aforementioned range. Alternatively, the etching rate of the metal being treated may be monitored, and the replenishment solution may be added in such a way that the etching rate remains above a predetermined value.

[0063] As described above, since the second solution does not contain sulfuric acid or has a low sulfuric acid concentration, the decrease in the concentration of the nitrite source in the second solution is suppressed. When using the etching solution set of the present invention, the change in the concentration of the nitrite source is small, so the change in etching rate is suppressed. In addition, the amount and frequency of supplying the nitrite source to the second solution can be reduced, simplifying process control when etching metals to be treated continuously.

[0064] In the first solution, the concentration of the thio compound may decrease due to the consumption (oxidation) of copper ions dissolved in the solution. To maintain a constant concentration of the thio compound in the first solution, an aqueous solution of the thio compound may be added to the first solution as a replenishment solution. As described above, if the concentration of the thio compound in the first solution is set high beforehand, the copper dissolved in the first solution will be properly chelated, suppressing the dissolution of copper in the substrate to be treated. This reduces the consumption of the thio compound by copper and suppresses the decrease in the concentration of the thio compound. Therefore, when using the etching solution set of the present invention, the frequency of replenishing the thio compound in the first solution can be reduced, simplifying the process control when continuously etching the metal to be treated.

[0065] [Formation of conductor patterns] By using the etching solution set described above, it is possible to efficiently etch the metal to be treated while suppressing the dissolution of copper. By applying the etching solution set to a substrate in which the metal to be treated and a copper layer coexist, the metal to be treated on the substrate can be selectively etched to form a conductive pattern. Examples of conductive patterns include wiring patterns, land patterns, or combinations thereof.

[0066] As an example of a substrate to be treated in which the metal to be treated and a copper layer coexist, as shown in Figure 1, a configuration is provided in which an underlayer 20 of the metal to be treated is placed on an insulating substrate 10, and a conductor pattern 31 is placed on top of that.

[0067] Figures 3A to 3E are schematic diagrams illustrating an example of the process for forming the substrate to be processed shown in Figure 1. First, a base layer 20 of the metal to be processed is formed on the insulating substrate 10 (Figure 3A).

[0068] Examples of insulating materials for the insulating substrate 10 include thermoplastic resins such as AS resin, ABS resin, fluororesin, polyamide, polyethylene, polyethylene terephthalate, polyvinylidene chloride, polyvinyl chloride, polycarbonate, polystyrene, polysulfone, polypropylene, and liquid crystal polymer; and thermosetting resins such as epoxy resin, phenolic resin, polyimide, polyurethane, bismaleimide-triazine resin, and modified polyphenylene ether. These resins may be reinforced with glass fibers, aramid fibers, etc. The insulating substrate 10 may also be made of ceramic material or glass. In flexible printed circuit boards, polyimide film is preferably used as the insulating substrate 10.

[0069] The material of the base layer 20 is Ni,Cr or a Ni-Cr alloy. When the base layer is a Ni-Cr layer, the atomic ratio of Ni to Cr is not particularly limited. Examples of Ni-Cr alloys include those with a Ni / Cr mass ratio of 6 / 1, 7 / 1, or 3 / 1. The thickness of the base layer 20 is approximately 5 to 500 nm. The base layer 20 is formed by sputtering, vapor deposition, electroless plating, or the like.

[0070] A plating resist layer 40 is formed on the underlayer 20 (Figure 3B), and a resist pattern 41 is formed by patterning the plating resist layer 40 using photolithography or the like (Figure 3C).

[0071] By using this substrate and performing electrolytic copper plating while supplying power to the underlayer 20, the copper layer 31 is deposited only in the areas that constitute the conductor pattern (Figure 3D). The thickness of the copper layer 31 is, for example, about 1 to 30 μm.

[0072] After forming the copper layer 31, the plating resist is removed to obtain a substrate in which the underlayer 20 is exposed between the patterned copper layers 31 (region 5 where the copper layer 31 is not formed) (Figure 3E, Figure 1). By sequentially treating this substrate with the first and second solutions of the etching solution set, the underlayer 20 in region 5 is etched away, and a printed circuit board is obtained on the insulating substrate 10 with a conductor pattern 3 consisting of the patterned copper layer 31 and the underlayer 21, as shown in Figure 2.

[0073] The process described above is a method for forming a conductor pattern using the so-called semi-additive method, but the conductor pattern may also be formed using the subtractive method. In the subtractive method, after forming a base layer 20 on the insulating substrate 10, an electrolytic copper plating layer is formed on the base layer, and the copper layer in the portion constituting the conductor pattern is covered with an etching resist. After etching the copper layer in the area not covered with the etching resist using a copper etching solution, the resist is peeled off to obtain a substrate to be processed in which the base layer 20 is exposed between the patterned copper layers 31. By sequentially treating this substrate to the first and second solutions of the etching solution set, the base layer 20 in region 5 is etched away, and a printed circuit board is obtained on the insulating substrate 10 with a conductor pattern 3 consisting of patterned copper layers 31 and a base layer 21, as shown in Figure 2.

[0074] In both the semi-additive and subtractive methods, by sequentially contacting the substrate with the first and second solutions, the underlying layer in areas where a copper layer has not formed can be selectively etched and removed while suppressing copper etching. Therefore, insulation between conductor patterns can be ensured without significantly altering the shape of the copper layers constituting the conductor patterns.

[0075] In the method of the present invention, which uses a first solution containing hydrochloric acid and a thio compound, and a second solution containing hydrochloric acid and a nitrite source, the variation in the solution composition is small even when multiple substrates are processed consecutively. Furthermore, even if the copper ion concentration in the solution increases due to continuous use, the etching rate of copper does not increase easily, so the frequency of solution replacement is reduced, resulting in excellent running performance.

[0076] The etching solution set described above also exhibits excellent etching properties for PD (palmate). While PD is used as a catalyst in electroless copper plating during the manufacturing of printed circuit boards, if PD catalyst remains on the surface of the insulating substrate after the electroless copper plating layer has been etched away, the electrical insulation between patterns will decrease. Furthermore, the remaining PD catalyst can cause unwanted gold deposition during subsequent gold plating processes. By using the etching solution set described above, it is possible to selectively etch away PD remaining on the surface of the insulating substrate while suppressing the etching of the copper layer constituting the conductor pattern. [Examples]

[0077] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0078] [Preparation of etching solution] <First liquid> The first solution was prepared by mixing hydrochloric acid and a thio compound to the concentrations (by weight) shown in Table 1. The remainder in Table 1 is water (the same applies to the second solution). The abbreviations for the thio compounds are as follows. Note that propionic acid (PA) used in Comparative Example 3 is not a thio compound. ATG: Ammonium thioglycolate (Molecular weight: 109.15) TGA: Thioglycolic acid (Molecular weight: 92.11) TG: Thioglycerol (Molecular weight: 108.16) TU: Thiourea (Molecular weight: 76.12) RCoM: 2-mercaptoethanesulfonic acid (molecular weight: 142.19) MPA: β-Mercaptopropionic acid (Molecular weight: 106.14) DETU: Diethylthiourea (Molecular weight: 132.23) ETU: Ethylenethiourea (Molecular weight: 102.16) PA: Propionic acid

[0079] <Second solution Hydrochloric acid and nitrite (sodium nitrite or calcium nitrite) were blended to obtain the concentration (weight %) shown in Table 1, and the second solution was prepared. In Comparative Examples 4 and 6, nitrite was not blended, and nitric acid and sulfuric acid were blended. Also, sulfuric acid was blended in Examples 2 to 4 and Comparative Example 2. In Comparative Example 2, 0.5 wt% of β-mercaptopropionic acid was blended as the thio compound. Nitrite and nitric acid were blended to the concentrations shown in Table 1 immediately before using the etching solution. The nitrite concentration (mM) in Table 1 is the molar concentration of the nitrite source. For the example using calcium nitrite as the nitrite, the value shown is twice the molar concentration of calcium nitrite.

[0080] [Evaluation] <Etching property of Ni-Cr alloy On one surface of a polyimide film with a thickness of 50 μm, a Ni-Cr alloy film (atomic ratio of Ni:Cr = 88:12) with a thickness of 20 nm was formed by sputtering. This sample was cut into a 40 mm × 40 mm square, immersed in the first solution (50°C) for 30 seconds, and then immersed in the second solution (50°C) for 30 seconds to dissolve the Ni-Cr alloy film. After the sample was washed with water and dried, it was observed at 50 times magnification using a digital microscope (Keyence's "VHX-5000") to confirm the presence or absence of etching residue of the Ni-Cr alloy film. Those with no residue were rated as good etching property (〇), and those with residue were rated as poor etching property (×).

[0081] <Etching rate of copper A double-sided copper-clad laminate manufactured by Rishou Kogyo (40 x 40 mm, plate thickness 0.2 mm, copper thickness 35 μm) was immersed in the first solution (50°C) for 30 seconds, and then in the second solution (50°C) for 30 seconds. After that, the double-sided copper-clad laminate was washed with water and dried, and the etching rate of copper was calculated from the change in weight (amount of copper etching).

[0082] <Etching properties in the presence of copper ions> Double-sided copper-clad laminates were immersed in the second solution (50°C) and copper was dissolved until the copper concentration in the solution reached 0.05, 0.2, 0.35, 1.0, or 2.0 g / L. Then, the nitrite source in the solution was quantified using the Griess method (described later). If the nitrite source concentration decreased, nitrite was added to bring the nitrite source concentration to the same level as the formulation composition (immediately after preparation) shown in Table 1. In Comparative Examples 4 and 6, since nitrite was not used, the quantification of the nitrite source and the addition of nitrite were not performed.

[0083] As the second solution, a solution prepared to the specified copper concentration using the method described above (a model solution that reproduces the state in which copper from the substrate to be treated is dissolved in the second solution due to the use of the etching solution, and a nitrite source is replenished) was used to evaluate the etching properties of the Ni-Cr alloy and the etching rate of copper in the same manner as described above.

[0084] Table 1 shows the formulations of the first and second solutions in the examples and comparative examples, as well as the evaluation results of the etching properties of the Ni-Cr alloy and the etching rate of copper. In Table 1, when the copper concentration of the second solution is 0, the evaluation results are for when the first and second solutions were used immediately after preparation.

[0085] [Table 1]

[0086] The etching solution set in the example exhibited excellent Ni-Cr removal properties and a low copper etching rate, resulting in superior etching selectivity, in its initial formulation (copper concentration of 0). Furthermore, even when the copper concentration in the solution was increased to 2.0 g / L, the Ni-Cr removal properties were maintained, and the copper etching rate remained below 0.35 μm / min, demonstrating excellent etching selectivity.

[0087] The etching solution set in the example demonstrates excellent run-through performance, as it maintains a low copper etching rate while not compromising the Ni-Cr removal capabilities even when the copper concentration in the solution increases due to continuous processing of the substrate to be treated.

[0088] In Comparative Example 1, where only treatment with the second solution containing hydrochloric acid and nitrite was performed without treatment with the first solution, Ni-Cr residue was observed after 30 seconds of immersion, indicating poor etching of the metal to be treated. Similarly, in Comparative Example 3, where treatment with the second solution was performed after treatment with the first solution which did not contain a thio compound, the etching of Ni-Cr was also poor, as in Comparative Example 1.

[0089] These results suggest that in the etching solution set of the example, the thio compound from the first solution is carried into the second solution, improving the etching properties of Ni-Cr in the second solution and suppressing copper etching. In contrast, in Comparative Examples 1 and 3, the etching properties of Ni-Cr were low because the thio compound was not supplied to the second solution. It should be noted that Comparative Example 3 showed a higher copper etching rate than Comparative Example 1. In Comparative Example 3, the absence of a thio compound, coupled with the high concentration of the nitrite source in the second solution, is considered to be the reason for the increased copper etching rate.

[0090] Comparative Example 5, in which the concentration of the thio compound in the first solution was low, exhibited excellent Ni-Cr removal and low copper etching rate, as well as excellent etching selectivity, in its initial formulation (when the copper concentration was 0). Even at high copper concentrations, the increase in copper etching rate was suppressed. However, when the copper concentration was 2.0 g / L, the etching performance of Ni-Cr decreased. In Comparative Example 5, the concentration of the thio compound in the first solution decreased with continuous use of the etching solution. When etching was performed continuously until the copper concentration in the second solution reached 2.0 g / L, it is thought that the etching performance of Ni-Cr decreased because the thio compound concentration necessary for etching Ni-Cr could not be maintained (see Examples 12-14 and Comparative Examples 10 and 11 below for the residual rate of the thio compound and etching characteristics).

[0091] Comparative Example 2, in which treatment was performed with a second solution containing hydrochloric acid, nitrite, and a thio compound without treatment with the first solution, showed excellent Ni-Cr removal and low copper etching rate, and excellent etching selectivity in the initial formulation (copper concentration 0). However, when the copper concentration was 1.0 g / L or higher, the Ni-Cr removal performance decreased, and the copper etching rate increased significantly. In Comparative Example 2, the thio compound in the second solution was consumed as copper dissolved, and no thio compound was supplied from the first solution. It is thought that the decrease in the thio compound led to a decrease in Ni-Cr removal performance, a loss of the copper etching inhibitory effect, and an increase in the copper etching rate. It should be noted that although the second solution in Comparative Example 2 has a sufficiently high thio compound concentration in its initial formulation, the coexistence of the thio compound and the nitrite source in the second solution easily accelerates the decomposition of the thio compound. It is thought that the decrease in the thio compound concentration due to the decomposition of the thio compound, in addition to the consumption of the thio compound due to copper dissolution, contributes to the decrease in Ni-Cr removal performance and the increase in the copper etching rate.

[0092] Comparative Example 7, which had a low concentration of nitrite source in the second solution, exhibited poor Ni-Cr removal. Comparative Example 8, which had a high concentration of nitrite source in the second solution, showed a high copper etching rate even in the initial formulation with a copper concentration of 0, resulting in poor etching selectivity of the metal being treated.

[0093] In Comparative Examples 4 and 6, where the second solution did not contain a nitrite source but instead contained nitric acid, the etching properties of Ni-Cr were poor in the initial formulation. However, when the copper concentration was 0.05 g / L, the etching properties of Ni-Cr improved. At even higher copper concentrations, the etching properties of Ni-Cr decreased again. At a copper concentration of 2.0 g / L, the etching properties of Ni-Cr improved again, but the etching rate of copper also increased.

[0094] In Comparative Examples 4 and 6, the initial formulations likely resulted in poor etching of Ni-Cr because the second solution did not contain a nitrite source and copper ions were absent, making it difficult to generate nitrite from nitric acid. When the copper concentration of the second solution was 0.05 g / L, it is thought that the copper ions in the second solution acted catalytically, converting nitric acid to nitrite, thereby improving the etching of Ni-Cr. As the copper concentration increased further, the etching rate of copper increased, and most of the nitrite generated from nitric acid was consumed in the etching of copper, thus reducing the etching of Ni-Cr. At even higher copper concentrations, it is thought that the amount of nitrite generated from nitric acid exceeded the amount consumed by etching, and the etching power of copper ions increased, leading to a further increase in the etching of Ni-Cr.

[0095] As shown in Comparative Examples 4 and 6, when nitric acid is used as the second solution, the amount of nitrite produced and consumed changes significantly due to changes in the composition associated with continuous use of the solution. Consequently, the etching characteristics change, resulting in a lack of stability and posing challenges to the running performance.

[0096] [Investigation of the effect of thio compound concentration in the first solution] <Percentage of thio compounds remaining> The first and second solutions were prepared in the same manner as in Example 1, except that the type and amount of thio compounds were changed as shown in Table 2. Cupric oxide was added to the first solution to a concentration of 0.025% by weight (copper concentration of 0.2 g / L), and cupric oxide was added to the second solution to a concentration of 0.25% by weight (copper concentration of 2 g / L). After adding the cupric oxide, the first and second solutions were stirred at room temperature for 5 hours. The concentration of the thio compound in the first solution after stirring for 5 hours with the addition of cupric oxide was quantified by iodine titration, and the remaining percentage relative to the initial concentration was calculated.

[0097] <Etching rate of copper> Using the first and second solutions (model solutions that reproduce the state in which copper from the substrate to be treated dissolves in the second solution as a result of using the etching solution) which were mixed with cupric oxide and stirred, the etching rate of copper was measured in the same manner as described above.

[0098] Table 2 shows the formulations of the first and second solutions for Examples 1, 12-14 and Comparative Examples 10 and 11, as well as the etching rates of copper using the first and second solutions after stirring for 5 hours with copper oxide, and the remaining percentage of the thio compound in the first solution.

[0099] [Table 2]

[0100] As shown in Table 2, the higher the initial concentration of the thio compound in the first solution, the higher the residual rate of the thio compound after 5 hours, and the lower the etching rate of copper when treated with the second solution containing copper after treatment with the first solution. The decrease in the residual rate of the thio compound and the increase in the etching rate of copper were particularly pronounced when the thio compound concentration was less than 0.5% by weight.

[0101] When the concentration of the thio compound in the first solution is low, the thio compound is easily consumed in the presence of copper ions, and because less thio compound is carried from the first solution to the second solution, the etching rate of copper by the second solution is thought to be higher. From these results, it can be seen that the higher the concentration of the thio compound in the first solution, the less the concentration of the thio compound decreases and the less likely the etching rate of copper is to increase, resulting in superior etching stability and running performance.

[0102] [Investigation of sulfuric acid concentration in the second solution] <Percentage of nitrite source remaining> In the preparation of the second solution in Examples 1 to 4, sodium nitrite was added after heating to 50°C to a concentration of 0.006% by weight (nitrite source concentration of 0.87 mM). The nitrite source concentration in the solution was measured immediately after the addition of sodium nitrite and after standing in an open system at 50°C for 1 hour, and the remaining percentage of the nitrite source was calculated. For Comparative Examples 12 to 14 shown in Table 3, the remaining percentage of the nitrite source after standing at 50°C for 1 hour was determined in the same manner as in Examples 1 to 4.

[0103] The residual amount of nitrite source was quantified by the Griess method. Griess reagent (containing sulfanilamide and ortho-(1-naphthyl)ethylenediamine) was added to the sampled material, and after standing at room temperature for 30 minutes, the absorbance of the sample at 520–550 nm was measured using a spectrophotometer. The nitrite source concentration was calculated from the absorbance of the sample based on a calibration curve created using standard samples with known nitrite ion concentrations.

[0104] When Griess reagent is added to a sample containing a nitrite source, it turns reddish-purple, the color intensifies over time, and the absorbance at 520-550 nm increases. After adding Griess reagent, the absorbance remains constant for 30 minutes to several hours, after which the color fades and the absorbance decreases.

[0105] <Etching properties> As the second solution, a model solution prepared and left at 50°C for 1 hour (reproducing the condition in which the nitrite source concentration decreases with the use of the etching solution) was used to evaluate the Ni-Cr removal capacity and measure the copper etching rate using the same method as described above.

[0106] Table 3 shows the formulations of the first and second solutions for Examples 1-4 and Comparative Examples 12-14, the residual rate of the nitrite source in the second solution 1 hour after the addition of nitrite to the second solution, and the etching properties (Ni-Cr removal ability and copper etching rate) when using this second solution.

[0107] [Table 3]

[0108] A tendency was observed where the higher the sulfuric acid concentration of the second solution, the lower the residual rate of the nitrite source after 1 hour. In comparative examples 12-14, where the sulfuric acid content was 5% by weight or more, the residual rate of the nitrite source after 1 hour was less than 40%, and when this was used as the second solution, the Ni-Cr removal performance was poor.

[0109] If the sulfuric acid concentration of the second solution is high, using the second solution immediately after preparation may result in good etching properties. However, because the rate of decrease of the nitrite source is high, the Ni-Cr removal efficiency (etching rate) tends to decrease, and frequent addition of the nitrite source is necessary to maintain etching properties.

[0110] These results suggest that a low sulfuric acid concentration in the second solution is preferable in order to suppress the decrease in the concentration of the nitrite source in the second solution and to reduce the frequency of adding the nitrite source with the replenishment solution or changing the solution. Furthermore, the results from the above examples and comparative examples show that etching solution sets in which the second solution contains a nitrite source exhibit excellent etching characteristics and running performance even when sulfuric acid is not included. [Explanation of Symbols]

[0111] 10 Insulating substrate 20,21 Base layer 31 Copper layer 3 Conductor Patterns 40,41 Plating Resist

Claims

1. An etching solution set comprising: a first solution containing hydrochloric acid and a thio compound; and a second solution containing hydrochloric acid and a nitrite source, The thio compound is a compound having 7 or fewer carbon atoms and having S-H or S=C, and one or more functional groups selected from the group consisting of an amino group, an imino group, a carboxyl group, a carbonyl group, and a hydroxyl group. The concentration of the thio compound in the first solution is 0.5 to 30% by weight. The nitrite source concentration in the second solution is 0.1 to 30 mM. The hydrochloric acid concentration in the first solution is 5 to 30% by weight, and the sulfuric acid concentration is 4.5% by weight or less. The hydrochloric acid concentration in the second solution is 8 to 30% by weight, and the sulfuric acid concentration is 4.5% by weight or less. The hydrochloric acid concentration in the first solution is 0.3 to 2 times the hydrochloric acid concentration in the second solution. Etching solution set.

2. A method for etching a metal to be treated, selected from Ni, Cr, Ni-Cr alloy, and Pd, using the etching solution set described in claim 1, An etching method comprising bringing the first liquid into contact with the surface of the metal to be treated, and then bringing the second liquid into contact with the surface of the metal to be treated.

3. By immersing the substrate to be treated, which has the metal to be treated on an insulating substrate, in the first liquid, the surface of the metal to be treated is brought into contact with the first liquid. The etching method according to claim 2, wherein the substrate to be treated is immersed in the second liquid to bring the second liquid into contact with the surface of the metal to be treated.

4. The etching method according to claim 3, wherein the substrate to be processed has the metal to be processed and a copper layer coexisting.

5. An etching method which repeatedly uses the first liquid and the second liquid, The etching method according to any one of claims 2 to 4, wherein a supplemental solution containing a nitrite source is added to the second solution to maintain the etching rate of the metal to be treated by the second solution at or above a predetermined value.

6. An etching method which repeatedly uses the first liquid and the second liquid, The etching method according to any one of claims 2 to 4, wherein a supplement solution containing a nitrite source is added to the second liquid so that the concentration of the nitrite source in the second liquid is maintained in the range of 0.1 to 30 mM.

7. A method for forming a conductor pattern on an insulating substrate, comprising a patterned underlayer and a copper layer in sequence, A substrate to be treated is prepared, comprising an unpatterned underlayer and a patterned copper layer in sequence on an insulating substrate, wherein the underlayer contains a metal to be treated selected from Ni, Cr, Ni-Cr alloy and Pd. The first liquid and the second liquid of the etching solution set described in claim 1 are brought into sequential contact with the underlying layer exposed between the copper layers of the substrate to be processed, thereby etching the underlying layer. A method for forming a conductor pattern.

8. By immersing the substrate to be treated in the first liquid, the first liquid is brought into contact with the surface of the metal to be treated. The method for forming a conductive pattern according to claim 7, wherein the substrate to be treated is immersed in the second liquid to bring the second liquid into contact with the surface of the metal to be treated.

9. A method for forming a conductive pattern according to claim 7 or 8, wherein a supplement solution containing a nitrite source is added to the second solution, and a plurality of substrates to be processed are processed in succession while maintaining the etching rate of the metal to be processed by the second solution to a predetermined value or higher.

10. A method for forming a conductive pattern according to claim 7 or 8, wherein a plurality of substrates to be processed are processed in succession while adding a supplement solution containing a nitrite source to the second liquid so that the concentration of the nitrite source in the second liquid is maintained in the range of 0.1 to 30 mM.

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