Etching solution assembly, etching method, and method for forming conductor patterns

Abstract

The etching solution system of the present invention comprises: a first solution containing hydrochloric acid and a thiocyanate compound, and a second solution containing hydrochloric acid and a nitrous acid source. The thiocyanate compound contained in the first solution is a compound with 7 or fewer carbon atoms, having an S-H or S=C group, and possessing one or more functional groups selected from the group consisting of amino, imine, carboxyl, carbonyl, and hydroxyl groups; the concentration of the thiocyanate compound in the first solution is 0.5% to 30% by weight. The concentration of the nitrous acid source in the second solution is 0.1 mM to 30 mM; the concentration of hydrochloric acid is 8% to 30% by weight; and the concentration of sulfuric acid is 4.5% by weight or less. The etching solution system of the present invention is applicable to the selective etching of metals such as Ni-Cr alloys.

Description

Technical Field

[0001] The present invention relates to an etching solution set 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. Prior Art

[0002] Flexible printed circuit boards (FPCs) requiring fine-pitch circuits utilize a two-layer copper-clad laminate (CCL) with a copper layer formed on a polyimide film serving as an insulating substrate, without intervening a resin adhesive layer. The semi-additive method, in which a base layer is formed on the polyimide film and the copper layer is formed by electrolytic plating only on the portion of the base layer that will form the circuits, is particularly advantageous for forming fine circuits.

[0003] When forming copper circuits using a semi-additive process, the base layer functions as a feed layer (seed layer) for forming the copper layer by electrolytic plating, for example, by electroless copper plating using a Pd catalyst. Furthermore, when the base layer is made of Ni, Cr, or a Ni-Cr alloy, in addition to serving as a feed layer, it also functions as an adhesive layer to improve the adhesion between an insulating substrate such as a polyimide film and the copper circuits.

[0004] After forming a copper layer on a base layer, etching away the unfinished portion of the base layer creates a circuit composed of the copper layer and the base layer. Typically, etching the base layer uses an etchant primarily composed of iron (III) chloride. However, due to the low etching rate of the metal that makes up the base layer, this process presents the following problems: During etching of the base layer, the copper layer dissolves, reducing the height and width of the circuit.

[0005] Patent Documents 1 and 2 propose methods for etching underlayers such as Ni-Cr layers using aqueous solutions containing nitric acid or nitrous acid. Patent Document 1 uses an acidic etching solution containing nitrous acid and a specific thio compound. Patent Document 2 discloses an etching solution set comprising a first solution and a second solution. It states that after removing the oxide film on the surface of the underlayer using the first solution containing hydrochloric acid and a thio compound, etching with a second solution containing hydrochloric acid, nitric acid, and divalent copper ions increases the etching rate of the underlayer. [Prior Art Literature] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-229196. [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-154899. Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] The etching solutions described in Patent Documents 1 and 2 have a high etching rate for the target metal, such as Ni-Cr alloy, which constitutes the base layer, and can quickly remove the base layer. Therefore, they can suppress the etching of the copper layer of the substrate being processed. However, since they cannot completely suppress the dissolution of copper, the concentration of dissolved copper (copper ions) increases when etching multiple substrates is performed continuously (when the etching solution is used continuously).

[0009] Since divalent copper ions act as an oxidant for metallic copper, they increase the copper etching rate. Therefore, as the copper ion concentration in the etching solution increases, the copper etching rate also increases. Furthermore, in systems using nitric acid, as described in Patent Document 2, the presence of copper ions produces nitrogen oxides (NOx), which also increases the copper etching rate.

[0010] If the copper ion concentration or NOx concentration in the solution increases, and the copper etching rate increases, the etching characteristics cannot be maintained, and the etching solution needs to be replaced, which reduces process efficiency and increases costs. Therefore, it is necessary to minimize the change in etching characteristics even when the etching solution is used continuously, and to reduce the frequency of solution replacement (to improve operability). [Methods used to solve the problem]

[0011] One embodiment of the present invention is an etching solution set for etching a metal selected from Ni, Cr, Ni-Cr alloy, 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 nitrous acid source.

[0012] The thio compound contained in the first liquid is a compound with 7 or fewer carbon atoms, possessing SH or S=C, and having one or more functional groups selected from the group consisting of an amine group, an imine group, a carboxyl group, a carbonyl group, and a hydroxyl group. The concentration of the thio compound in the first liquid is 0.5% to 30% by weight. The concentration of the nitrite source in the second liquid is 0.1mM to 30mM, the concentration of hydrochloric acid is 8% to 30% by weight, and the concentration of sulfuric acid is 4.5% or less by weight.

[0013] The first and second liquids are sequentially brought into contact with a metal (the metal to be treated) selected from Ni, Cr, a Ni-Cr alloy, and Pd, thereby etching the metal to be treated. For example, the substrate to be treated may be immersed in the first liquid, contacting the first liquid with the surface of the metal to be treated, and then immersed in the second liquid, contacting the surface of the metal to be treated.

[0014] The processed substrate may also be provided with a processed metal on an insulating substrate. In addition, the processed substrate may also be a substrate in which the processed metal and a copper layer coexist.

[0015] An example of a substrate to be processed includes the following configuration: an unpatterned base layer is provided on an insulating substrate, and a patterned copper layer is provided on the base layer. The base layer comprises a metal to be processed selected from the group consisting of Ni, Cr, a Ni-Cr alloy, and Pd, and the base layer is etched using an etching solution set. Specifically, the base layer is etched by sequentially contacting the first and second liquids of the etching solution set with the base layer exposed between the copper layers of the substrate to be processed. By etching the base layer exposed between the copper layers, a conductive pattern is formed on the insulating substrate. The conductive pattern comprises, in sequence, the patterned base layer and the copper layer.

[0016] When using an etching solution set to continuously etch multiple substrates, replenishing liquids may be added to the first and / or second liquids to adjust the composition, for example, to maintain etching characteristics. For example, by adding replenishing liquid containing a nitrous acid source to the second liquid, the etching rate of the metal being processed by the second liquid can be maintained above a predetermined value.

[0017] When adding replenishing liquid to the second liquid, for example, replenishing liquid can be added in a manner that maintains the etching rate of the metal being processed by the second liquid above a predetermined value. Alternatively, replenishing liquid can be added in a manner that maintains the concentration of the nitrous acid source in the second liquid within a predetermined range. [Effects of the invention]

[0018] Because the etching solution set of the present invention rapidly etches the Ni-Cr alloy and other metals being processed, it is possible to suppress excessive etching of copper and other metals in the substrate being processed. Furthermore, since the etching characteristics rarely change during continuous use and the copper etching rate rarely increases, the frequency of changing the etching solution is low, contributing to process efficiency and cost reduction. Simple diagram description

[0019] [Figure 1] is a cross-sectional view showing an example of the structure of a substrate to be processed. [Figure 2] is a cross-sectional view of a printed wiring board having a conductor pattern on an insulating substrate. FIG3 is a schematic diagram showing an example of a process for forming a substrate to be processed. Implementation Method

[0020] The present invention relates to an etching solution set for etching at least one metal selected from the group consisting of Ni, Cr, a Ni-Cr alloy, and Pd (hereinafter sometimes referred to as the "target metal"). The etching solution set comprises a first solution and a second solution. In one embodiment, the etching solution set is used for selectively etching the target metal in a target substrate in which the target metal and a copper layer coexist.

[0021] Figure 1 is a cross-sectional view of an example substrate to be processed. The substrate shown in Figure 1 comprises a Ni-Cr alloy layer as a base layer 20 on a polyimide film as an insulating substrate 10, with a copper layer 31 formed on the base layer 20. By sequentially contacting the first and second etchant solutions of an etching solution set with the base layer 20 exposed between the copper layers 31 of the substrate (in areas 5 where no conductive pattern is formed), the base layer is etched away. As shown in Figure 2, a printed wiring board is obtained, comprising the patterned copper layer 31 and the conductive pattern 3 formed by the base layer 21 on the insulating substrate 10.

[0022] [Composition of etching solution] The etching solution system includes a first liquid and a second liquid. The first liquid system includes an aqueous solution of hydrochloric acid and a thio compound, and the second liquid system includes an aqueous solution of hydrochloric acid and a nitrous acid source (nitrous acid or nitrite ions).

[0023] The Ni-Cr alloy and other processed metals are mainly etched by the hydrochloric acid and nitrous acid in the second liquid. The sulfide compounds carried into the second liquid from the first liquid not only promote the etching of the processed metal, but also have the effect of inhibiting the etching of copper.

[0024] <First Liquid> (hydrochloric acid) The hydrochloric acid in the first solution removes oxide films and other substances formed on the surface of the metal being treated, while also enhancing the etching efficiency of the metal being treated by the second solution. Furthermore, the hydrochloric acid enhances the solubility of the complex formed between the sulfide compound and copper (described later) when the copper on the substrate being treated is etched and dissolved in the solution. The hydrochloric acid concentration in the first solution is preferably between 0.5% and 30% by weight. Excessively low hydrochloric acid concentrations can lead to insufficient oxide film removal, a decrease in the etching rate of the metal being treated by the second solution, and turbidity or precipitation due to insoluble copper-sulfide complexes can occur when etching multiple substrates continuously without changing the etching solution. Excessively high hydrochloric acid concentrations can make it difficult to maintain a constant concentration. From the perspectives of oxide film removal (cleaning efficiency) and copper-sulfide compound solubility, the hydrochloric acid concentration of the first solution within the above ranges makes no significant difference.

[0025] When a substrate treated with the first liquid is immersed in the second liquid, any first liquid adhering to the surface of the substrate is carried into the second liquid. To minimize variations in the second liquid's composition and maintain consistent etching characteristics when etching multiple substrates continuously without changing the etching liquid, the difference between the hydrochloric acid concentrations of the first and second liquids is preferably small. The hydrochloric acid concentration of the first liquid is preferably 0.3 to 2 times that of the second liquid, more preferably 0.5 to 1.5 times. The hydrochloric acid concentration of the first liquid can also be 3% to 30% by weight, 5% to 25% by weight, 7% to 23% by weight, or 10% to 20% by weight.

[0026] (Other acids) The first liquid 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, and various organic acids.

[0027] If the first liquid contains nitric acid, nitrogen oxides (NOx) are generated when the copper on the substrate being processed is etched and dissolved in the liquid. The generated NOx has the effect of increasing the copper etching rate. As the copper ion concentration in the liquid increases with copper etching, the copper etching rate further increases. Furthermore, if the first liquid contains nitric acid, the sulfide compounds described below are easily decomposed, and their concentration decreases over time. To suppress copper etching and reduce the concentration of sulfide compounds, the first liquid preferably contains substantially no nitric acid. The nitric acid concentration in the first liquid 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. The first liquid particularly preferably contains no nitric acid.

[0028] If the first liquid contains nitrous acid, the thio compounds described below are easily decomposed, and their concentration decreases over time. To prevent the concentration of thio compounds from decreasing, the first liquid preferably contains substantially no nitrous acid source (nitrous acid or nitrite salt). The concentration of nitrous acid in the first liquid 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. The first liquid particularly preferably contains no nitrous acid source.

[0029] If the first liquid contains sulfuric acid, the first liquid adhering to the surface of the substrate being processed is carried into the second liquid, increasing the sulfuric acid concentration in the second liquid. As described later, when the sulfuric acid concentration in the second liquid is high, the concentration of the nitrous acid source in the second liquid may tend to decrease over time, resulting in poor liquid stability. To prevent sulfuric acid from being carried over into the second liquid, a low sulfuric acid concentration in the first liquid is preferred. The sulfuric acid concentration in the first liquid 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 first liquid particularly preferably contains no sulfuric acid.

[0030] (Thio compounds) The thio compound contained in the first liquid is a compound having 7 or fewer carbon atoms, having -SH or S=C, and having one or more functional groups selected from the group consisting of an amine group, an imine group, a carboxyl group, a carbonyl group, and a hydroxyl group. The thio compound preferably has 1 to 5 carbon atoms. The molecular weight of the thio compound is preferably 60 to 300, and may also be 70 to 200.

[0031] Specific examples of thio compounds having an amino group include thiourea, thiourea dioxide, N-methylthiourea, 1,3-dimethylthiourea, and 1,3-diethylthiourea. Specific examples of thio compounds having an imino group include ethylenethiourea. Specific examples of thio compounds having a carboxyl group include sulfur-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, as well as their salts (sodium, potassium, calcium, and ammonium salts). Specific examples of thio compounds having a carbonyl group include 2-thiobarbituric acid. Specific examples of thio compounds having a sulfonic group include 2-mercaptoethanesulfonic acid, 3-mercapto-1-propanesulfonic acid, 2-mercaptobenzenesulfonic acid, and their salts. Specific examples of the thio compound having a hydroxyl group include sulfur-atom-containing alcohols such as thioglycerol.

[0032] When the copper on the substrate is etched by the acid and dissolved in the solution, the copper ions act as oxidants, accelerating the etching of the copper on the substrate. The thio compound contained in the first solution acts by chelating and capturing the copper ions, thereby inhibiting the etching of the copper on the substrate.

[0033] When a substrate treated with the first liquid is immersed in the second liquid, the first liquid adhering to the surface of the substrate is carried into the second liquid. Therefore, the thio compound contained in the first liquid also helps inhibit the etching of copper in the second liquid. Furthermore, the thio compound carried from the first liquid into the second liquid also helps enhance the etching properties of the metal being treated in the second liquid.

[0034] The content of the aforementioned thio compound in the first solution is 0.5% by weight or greater. If the content of the thio compound is low, copper dissolved in the first solution may be easily consumed by the thio compound when etching multiple substrates continuously (when the etching solution is used continuously). As the concentration of the thio compound in the first solution decreases with continued use of the etching solution, the copper etching rate 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 into the second solution decreases, and the copper etching rate in the second solution tends to increase.

[0035] If the sulfide compound concentration in the first liquid is 0.5% by weight or greater, the concentration of the sulfide compound is sufficiently high compared to the copper ions dissolved in the first liquid that the copper ions are easily chelated by the sulfide compound, thereby suppressing copper etching in the first liquid. Since copper etching by the first liquid is suppressed, sulfide compound consumption is low (sulfide compound concentration is less likely to decrease) and composition fluctuations are minimal. Furthermore, the sulfide compound carried over from the first liquid into the second liquid not only promotes etching of the metal being treated in the second liquid but also suppresses copper etching by the second liquid.

[0036] The thio compound concentration in the first solution is more preferably 0.7% by weight or greater, even more preferably 1.0% by weight or greater, and can also be 1.3% by weight or greater, 1.5% by weight or greater, or 1.7% by weight or greater. The higher the thio compound concentration in the first solution, the greater the copper etching inhibition effect. Furthermore, the higher the thio compound concentration in the first solution, the smaller the change (concentration decrease) in the thio compound concentration with continued use of the etching solution. This reduces the frequency of replenishing the thio compound to the first solution or replacing the first solution, contributing to process efficiency and cost reduction.

[0037] The sulfide compound concentration in the first solution is preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 10% by weight or less. It may also be 7% by weight or less, or 5% by weight or less. If the sulfide compound concentration in the first solution is excessively high, the amount of sulfide compound carried over into the second solution may become excessive, and etching of the metal being treated in the second solution may be hindered.

[0038] <Second Liquid> (hydrochloric acid) The hydrochloric acid in the second solution and the nitrous acid source described below both dissolve the metal being treated, thereby etching it. 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. Excessively low hydrochloric acid concentrations tend to reduce the etching rate of the metal being treated, while excessively high concentrations tend to increase the etching rate of copper.

[0039] (nitrite source) The nitrite source in the second solution dissolves the metal being treated, thus etching it. Nitrite sources are nitrous acid and nitrite ions. Nitrous acid or nitrite salts are mixed and present in the second solution as nitrous acid or nitrite ions. Examples of nitrite salts include sodium nitrite, lithium nitrite, potassium nitrite, calcium nitrite, and barium nitrite.

[0040] The concentration of the nitrite source in the second solution (the combined concentration of nitrous acid and nitrite ions) is 0.1mM to 30mM, preferably 0.15mM to 25mM, more preferably 0.2mM to 20mM, and even more preferably 0.3mM to 17mM. It can also be 0.4mM to 15mM, 0.5mM to 12mM, or 0.6mM to 10mM. If the nitrite source concentration is too low, the etching rate of the metal being treated tends to decrease. If the nitrite source concentration is too high, the etching rate of copper tends to increase.

[0041] Nitrous acid sources often exist in the form of nitrous acid in acidic aqueous solutions. However, nitrous acid as a free acid is less stable, and the concentration of the nitrous acid source in the second solution may decrease over time. Therefore, it is preferable to prepare the second solution by mixing nitrite salts or the like immediately before using the etching solution so that the nitrous acid source concentration falls within the aforementioned range. Furthermore, if the nitrous acid source concentration decreases during use of the etching solution, it is preferable to replenish nitrite salts or the like to maintain the nitrous acid source concentration in the second solution within the aforementioned range.

[0042] The nitrite source can be added to the second liquid 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 add nitrite salts to the second liquid as neutral or weakly alkaline aqueous solutions to replenish the nitrite source. When a nitrite salt aqueous solution is added to the second liquid as the replenishing liquid, the nitrite concentration of the replenishing liquid is, for example, approximately 0.1% to 75% by weight, and may also be 1% to 70% by weight, 5% to 60% by weight, or 10% to 50% by weight.

[0043] Although nitrous acid has low stability in acidic aqueous solutions, its concentration decreases slowly as long as it remains below 30 mM, allowing it to be replenished by adding nitrites, etc. Furthermore, although sulfuric acid is not used as the acid in the second liquid as described below, even using sulfuric acid can suppress the decrease in nitrous acid as long as the concentration is low. Furthermore, since the nitrous acid source can be quantified by spectrometry, concentration management is easy.

[0044] When using nitric acid as the etching component of the second solution, if copper on the substrate is etched and dissolved in the solution, nitrogen oxides (NOx) are generated. These NOx increase the copper etching rate. As copper etching progresses, the copper ion concentration in the solution increases, further increasing the copper etching rate and making it difficult to maintain etching performance, necessitating frequent replacement of the etching solution.

[0045] On the other hand, when nitrous acid is used as the etching component of the second liquid, NOx is less likely to be generated even in the presence of copper ions. Therefore, in the present invention, where a nitrous acid source is used as the second liquid, etching performance can be maintained stably, and the frequency of liquid replacement is reduced, which is advantageous in terms of process efficiency and cost.

[0046] Furthermore, the continuous introduction of the thio compound from the first solution to the second solution during the use of the etching solution also helps stabilize the etching characteristics (suppressing increases in the copper etching rate). As previously mentioned, thio compounds enhance the etching properties of the metal being treated and inhibit copper etching.

[0047] In the presence of a nitrous acid source, sulfo compounds are easily decomposed, and their concentration decreases over time. Therefore, in a one-liquid etching solution containing both a nitrous acid source and a sulfo compound, the concentrations of both the nitrous acid source and the sulfo compound tend to decrease over time, requiring individual management of their concentrations to ensure they remain within a predetermined range.

[0048] On the other hand, when using the etching solution set of the present invention, in which the first liquid contains a thio compound and the second liquid contains a nitrous acid source, the first liquid adhering to the surface of the substrate being processed is carried into the second liquid, and the thio compound is supplied to the second liquid, thereby maintaining a substantially constant concentration of the thio compound in the second liquid. Therefore, the second liquid can simply be managed to keep the concentration of the nitrous acid source within a predetermined range, as described above. This makes liquid management simpler than with a one-liquid etching solution.

[0049] (Other acids) The second liquid may also contain an acid other than hydrochloric acid and nitrous acid. Examples of acids other than hydrochloric acid and nitrous acid include inorganic acids such as sulfuric acid, nitric acid, and phosphoric acid, and various organic acids.

[0050] If the second liquid contains nitric acid, when the copper on the substrate being processed is etched and dissolved in the liquid, nitrogen oxides (NOx) are generated from the nitric acid. The generated NOx has the effect of increasing the copper etching rate. From the perspective of suppressing copper etching, the second liquid preferably contains substantially no nitric acid. The concentration of nitric acid in the second liquid 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 can also be 0.05% by weight or less, or 0.01% by weight or less. The second liquid particularly preferably contains no nitric acid.

[0051] The second liquid may also contain sulfuric acid as an acid. However, if the sulfuric acid concentration is high, the concentration of the nitrous acid source in the second liquid may tend to decrease over time, resulting in poor liquid stability. Therefore, the sulfuric acid concentration in the second liquid 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 liquid may also contain no sulfuric acid.

[0052] When nitric acid is used as the etching component for the metal being processed, sulfuric acid is used to convert the nitric acid into nitrous acid, thereby improving the etching efficiency. On the other hand, when the etching component is nitrous acid, the etching rate of the metal being processed can be sufficiently improved even without the use of sulfuric acid.

[0053] <Preparation of the First and Second Liquids> The first and second liquids can be prepared by dissolving the aforementioned components in water. Water from which ionic substances and impurities have been removed is preferred. Specifically, ion-exchanged water, pure water, ultrapure water, etc. are preferably used.

[0054] The first liquid and the second liquid may further contain various additives as needed. As additives, for example, surfactants may be used for purposes such as improving wettability or preventing copper corrosion.

[0055] Examples of surfactants include cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. When the first and / or second liquids contain a surfactant, the concentration may be 0.001% to 5% by weight, 0.01% to 4% by weight, or 0.1% to 3% by weight.

[0056] The first liquid and / or the second liquid may also contain a defoaming agent, a rust inhibitor, etc. as additives.

[0057] When etching is performed using an etching apparatus, the first and second liquids may be prepared separately so that all components have a predetermined composition and then supplied to the etching apparatus. Alternatively, each component may be supplied to the etching apparatus separately and then mixed within the etching apparatus to achieve the predetermined composition. Alternatively, a solution prepared by premixing a portion of the first and second liquids may be supplied to the etching apparatus, and then other components may be added and mixed within the etching apparatus to achieve the predetermined composition.

[0058] As previously mentioned, the concentration of nitrous acid in an acidic solution tends to decrease over time. Therefore, it is preferable that the second solution contain components other than the nitrous acid source and be supplied to the etching apparatus in advance, with the nitrous acid source added immediately before use to adjust the composition.

[0059] [Etching of the metal to be treated using an etching solution set] The metal being treated is etched by contacting the first liquid with the surface of the metal being treated and then contacting the second liquid. Examples of methods for contacting the metal being treated with the first and second liquids include dipping, spraying, and bar coating.

[0060] From the perspective of suppressing copper etching by allowing the first liquid adhering to the surface of the substrate to be processed to be carried into the second liquid, resulting in the second liquid containing a thio compound, an immersion method is preferred for contacting the first and second liquids with the metal to be processed. Specifically, a method is preferred in which the substrate to be processed is immersed in the first liquid, treated in the first liquid, and then immersed in the second liquid after being removed from the first liquid. The substrate removed from the first liquid is preferably immersed directly in the second liquid without cleaning its surface.

[0061] The temperatures of the first and second liquids, as well as the treatment times for the first and second liquids, are not particularly limited and can be appropriately set based on the type of metal being etched, the amount (thickness) to be etched, etc. For example, the temperatures of the first and second liquids are approximately 20°C to 65°C, and the treatment time is approximately 5 to 60 seconds.

[0062] If an etching solution is used continuously, the composition of the solution may change over time, causing changes in etching properties (etching rate). To maintain constant etching properties, a replenishing liquid may be added to the first and / or second liquids. In particular, since the concentration of the nitrite source in the second liquid decreases over time, it is preferable to replenish the nitrite source in the second liquid. As mentioned above, the replenishing liquid used to replenish the nitrite source in the second liquid is preferably an aqueous nitrite solution. The nitrite concentration of the replenishing liquid is, for example, approximately 0.1% to 75% by weight, and may also be 1% to 70% by weight, 5% to 60% by weight, or 10% to 50% by weight.

[0063] When replenishing the nitrous acid source by adding replenishing liquid to the second liquid, the replenishing liquid can be added in such a manner as to maintain the nitrous acid source concentration within the aforementioned range. Alternatively, the replenishing liquid can be added in such a manner as to monitor the etching rate of the metal being processed and maintain the etching rate above a predetermined value.

[0064] As described above, since the second liquid system contains no sulfuric acid or has a low sulfuric acid concentration, the concentration of the nitrous acid source in the second liquid is suppressed from decreasing. When the etching solution set of the present invention is used, the concentration of the nitrous acid source changes little, thereby suppressing changes in the etching rate. Furthermore, the amount of nitrous acid source supplied to the second liquid and the frequency of replenishment can be reduced, simplifying the management of the steps during the continuous etching of the metal being processed.

[0065] The first liquid may experience a decrease in concentration due to the consumption (oxidation) of sulfide compounds by copper ions dissolved in the liquid. To maintain a constant sulfide compound concentration in the first liquid, an aqueous solution of the sulfide compound may be added to the first liquid as a replenishing solution. As described above, by pre-raising the sulfide compound concentration in the first liquid, the copper dissolved in the first liquid is properly chelated, suppressing the dissolution of copper from the substrate being processed. This reduces the consumption of sulfide compounds by copper and suppresses the decrease in sulfide compound concentration. Therefore, when using the etching solution set of the present invention, the frequency of replenishing the sulfide compound in the first liquid can be reduced, simplifying the management of the steps during the continuous etching of the metal being processed.

[0066] [Formation of Conductor Pattern] By using the aforementioned etching solution set, the dissolution of copper can be suppressed while efficiently etching the target metal. By applying the aforementioned etching solution set to a target substrate containing both the target metal and a copper layer, the target metal on the target substrate can be selectively etched to form a conductor pattern. Examples of the conductor pattern include a circuit pattern, a land pattern, or a combination of these patterns.

[0067] As an example of a substrate to be processed in which a metal to be processed and a copper layer coexist, a structure including a base layer 20 of a metal to be processed on an insulating substrate 10 and a copper layer 31 on the base layer 20 can be cited as shown in FIG. 1 .

[0068] Figures 3A to 3E are schematic diagrams showing an example of a process for forming the substrate to be processed as shown in Figure 1. First, a base layer 20 of a metal to be processed is formed on an insulating substrate 10 (Figure 3A).

[0069] Examples of insulating materials for insulating substrate 10 include thermoplastic resins such as AS resin (acrylonitrile-styrene resin), ABS resin (acrylonitrile-butadiene-styrene resin), fluororesins, polyamides, polyethylene, polyethylene terephthalate, polyvinylidene chloride, polyvinyl chloride, polycarbonate, polystyrene, polysulfone, polypropylene, and liquid crystal polymers; and thermosetting resins such as epoxy resins, phenolic resins, polyimides, polyurethanes, bismaleimide-triazine resins, and modified polyphenylene ethers. These resins may also be reinforced with glass fiber, aromatic polyamide fiber, or the like. Insulating substrate 10 may also be made of ceramic or glass. In flexible printed circuit boards, polyimide films are suitable for use as insulating substrate 10.

[0070] 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 nm to 500 nm. The base layer 20 is formed by sputtering, vapor deposition, electroless plating, or other methods.

[0071] A plating resist layer 40 is formed on the base layer 20 ( FIG. 3B ) and patterned by photolithography or the like to form a resist pattern 41 ( FIG. 3C ).

[0072] By using this substrate and performing electrolytic copper plating while supplying power to the base layer 20, a copper layer 31 is deposited only on the portion forming the conductor pattern (D in FIG. 3 ). The thickness of the copper layer 31 is, for example, about 1 μm to 30 μm.

[0073] After forming the copper layer 31, the plating resist is removed, resulting in a substrate (FIG. 3E, FIG. 1) with the base layer 20 exposed between the patterned copper layer 31 (in areas 5 where the copper layer 31 is not formed). This substrate is then treated sequentially with the first and second etchants of the etching solution set to etch away the base layer 20 in areas 5, resulting in a printed wiring board (PCB) having a conductor pattern 3 formed on an insulating substrate 10, comprising the patterned copper layer 31 and the base layer 21, as shown in FIG. 2 .

[0074] The above-described process forms a conductive pattern using a so-called semi-additive method, but a subtractive method can also be used. In the subtractive method, after forming a base layer 20 on an insulating substrate 10, an electrolytic copper plating layer is formed on the base layer, and the portion of the copper layer that constitutes the conductive pattern is covered with an etch resist. Using a copper etchant, the copper layer in the areas not covered by the etch resist is etched, and then the resist is stripped off, resulting in a substrate with the base layer 20 exposed between the patterned copper layers 31. This substrate is then sequentially treated with the first and second etchants of the etchant set to etch away the base layer 20 in area 5, resulting in a printed wiring board having a conductive pattern 3 formed on the insulating substrate 10, comprising the patterned copper layer 31 and the base layer 21, as shown in FIG2 .

[0075] In both the semi-additive and subtractive methods, by sequentially contacting the first and second liquids with the substrate being processed, copper etching is suppressed while selectively removing the base layer in areas where the copper layer is not formed. This ensures insulation between the conductor patterns while maintaining minimal change in the shape of the copper layer forming the conductor patterns.

[0076] The method of the present invention, which uses a first liquid containing hydrochloric acid and a thio compound and a second liquid containing hydrochloric acid and a nitrous acid source, exhibits minimal fluctuation in liquid composition even when processing multiple substrates continuously. Furthermore, even if the copper ion concentration in the liquid increases due to continuous use, the copper etching rate is unlikely to increase, requiring less frequent liquid replacement, resulting in excellent operability.

[0077] The aforementioned etching solution set also exhibits excellent etching properties against Pd. While Pd is used as a catalyst for electroless copper plating in the manufacture of printed circuit boards, residual Pd catalyst remaining on the surface of the insulating substrate during etching away the electroless copper plating can reduce electrical insulation between patterns. Furthermore, residual Pd catalyst can cause metal deposition in unwanted areas during the subsequent gold plating process. Using the aforementioned etching solution set allows for selective removal of Pd remaining on the surface of the insulating substrate while suppressing etching of the copper layer that constitutes the conductive pattern. [Example]

[0078] The present invention is described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0079] [Preparation of etching solution] <First Liquid> Hydrochloric acid and a thio compound were mixed to achieve the concentrations (weight %) shown in Table 1 to prepare a first solution. The remainder of Table 1 is water (the same applies to the second solution). The abbreviations for the thio compounds are as follows. In Comparative Example 3, propionic acid (PA) was 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: Ethylene thiourea (molecular weight: 102.16) PA: Propionic acid

[0080] <Second Liquid> Hydrochloric acid and nitrite (sodium nitrite or calcium nitrite) were prepared as the second liquid so as to have the concentrations (wt%) shown in Table 1. In Comparative Example 4 and Comparative Example 6, nitrite was not prepared, but nitric acid and sulfuric acid were prepared. In addition, sulfuric acid was also prepared in Examples 2 to 4 and Comparative Example 2. In Comparative Example 2, 0.5 wt% of β-mercaptopropionic acid was prepared as the sulfur compound. Immediately before using the etching solution, the nitrite and nitric acid were prepared so as to have the concentrations shown in Table 1. In addition, the nitrite concentration (mM) in Table 1 is the molar concentration of the nitrite source. For the example of using calcium nitrite as the nitrite, it represents a value twice the molar concentration of calcium nitrite.

[0081] [Evaluation] <Etchability of Ni-Cr alloy> A Ni-Cr alloy film (atomic ratio of Ni:Cr = 88:12) with a thickness of 20 nm was formed on one side of a polyimide film with a thickness of 50 μm by sputtering. The sample was cut into a square of 40 mm × 40 mm, immersed in the first liquid (50 °C) for 30 seconds, and then immersed in the second liquid (50 °C) for 30 seconds to dissolve the Ni-Cr alloy film. After washing and drying the sample with water, it was observed at 50 times magnification using a digital microscope ("VHX-5000" manufactured by Keyence) to confirm the presence or absence of etching residues of the Ni-Cr alloy film. The sample with no residues observed had good etchability (〇), and the sample with residues observed had poor etchability (×).

[0082] <Etch rate of copper> A double-sided copper-clad laminate (40 × 40 mm, board thickness 0.2 mm, copper thickness 35 μm) manufactured by Lichang Industry was immersed in the first liquid (50 °C) for 30 seconds, and then immersed in the second liquid (50 °C) for 30 seconds. After that, the double-sided copper-clad laminate was washed and dried with water, and the etch rate of copper was calculated from the weight change (etch amount of copper).

[0083] <Etchability in the presence of copper ions> The double-sided copper-clad laminate was immersed in the second liquid (50 °C), and copper was dissolved until the copper concentration in the liquid became 0.05 g / L, 0.2 g / L, 0.35 g / L, 1.0 g / L, or 2.0 g / L. After that, the nitrite source in the liquid was quantified by the Griess method (described later). When the concentration of the nitrite source decreased, nitrite was added so that the concentration of the nitrite source became the same as the formulation composition (immediately after preparation) in Table 1. In Comparative Example 4 and Comparative Example 6, since nitrite was not used, quantification of the nitrite source and addition of nitrite were not carried out.

[0084] As the second liquid, a solution prepared by the above-described method to a predetermined copper concentration was used (a model liquid in which the copper of the substrate being processed is dissolved in the second liquid along with the use of an etching solution, reproducing the state of a nitrous acid source being supplied). The etching properties of the Ni-Cr alloy and the copper etching rate were evaluated in the same manner as above.

[0085] Table 1 shows the formulations of the first and second solutions for the Examples and Comparative Examples, as well as the evaluation results for Ni-Cr alloy etching properties and copper etching rates. In Table 1, the copper concentration of the second solution is 0, indicating the evaluation results when the first and second solutions were used immediately after preparation.

[0086] [Table 1] Liquid preparation Ni-Cr removal Copper etching rate (μm / min) First liquid Second liquid Second solution copper concentration (g / L) Second solution copper concentration (g / L) hydrochloric acid Thio compounds hydrochloric acid nitrite sulfuric acid Nitric acid Thio compounds 0 0.05 0.20 0.35 1.0 2.0 0 0.05 0.20 0.35 1.0 2.0 type wt% type wt% mM Example 1 14.0 ATG 2.25 14.0 Na 0.006 0.87 - - - ○ ○ ○ ○ ○ ○ 0.02 0.02 0.05 0.05 0.05 0.11 Example 2 14.0 ATG 2.25 13.8 Na 0.006 0.87 1 - - ○ ○ ○ ○ ○ ○ 0.02 0.02 0.05 0.05 0.06 0.11 Example 3 14.0 ATG 2.25 13.2 Na 0.006 0.87 4 - - ○ ○ ○ ○ ○ ○ 0.03 0.03 0.06 0.06 0.07 0.13 Example 4 14.0 TGA 1.90 14.0 Na 0.006 0.87 1 - - ○ ○ ○ ○ ○ ○ 0.03 0.03 0.05 0.05 0.06 0.11 Example 5 18.0 TG 3.24 18.0 Ca 0.05 7.57 - - - ○ ○ ○ ○ ○ ○ 0.09 0.12 0.15 0.17 0.20 0.24 Example 6 10.0 TU 0.80 20.0 Ca 0.01 1.51 - - - ○ ○ ○ ○ ○ ○ 0.03 0.04 0.08 0.12 0.17 0.20 Example 7 7.0 RCoM 15.0 10.0 Na 0.15 21.7 - - - ○ ○ ○ ○ ○ ○ 0.23 0.23 0.24 0.26 0.29 0.33 Example 8 5.0 MPA 1.00 12.0 Na 0.10 14.5 - - - ○ ○ ○ ○ ○ ○ 0.17 0.18 0.19 0.21 0.25 0.28 Example 9 20.0 TGA 9.00 25.0 Ca 0.002 0.30 - - - ○ ○ ○ ○ ○ ○ 0.05 0.06 0.07 0.09 0.12 0.15 Example 10 25.0 DETU 0.50 16.0 Na 0.07 10.1 - - - ○ ○ ○ ○ ○ ○ 0.11 0.14 0.17 0.20 0.23 0.27 Example 11 15.0 ETU 1.25 18.0 Ca 0.12 18.2 - - - ○ ○ ○ ○ ○ ○ 0.22 0.23 0.23 0.25 0.28 0.30 Comparative Example 1 14.0 Ca 0.006 0.91 - - - × × 0.03 0.05 Comparative Example 2 14.0 Na 0.05 7.25 20 - MPA 0.5 ○ ○ ○ ○ × × 0.02 0.02 0.03 0.03 0.35 0.48 Comparative Example 3 14 PA 0.15 14.0 Na 0.10 14.5 - - - × × 0.26 0.37 Comparative Example 4 14 ATG 0.15 14.0 - 12.5 0.7 - × ○ × × ○ ○ 0.01 0.02 0.06 0.09 0.20 0.39 Comparative Example 5 14 ATG 0.15 14.0 Na 0.006 0.87 - - - ○ ○ ○ ○ ○ × 0.02 0.02 0.05 0.05 0.09 0.17 Comparative Example 6 14 ATG 2.25 14.0 - 12.5 0.7 - × ○ × × ○ ○ 0.01 0.02 0.05 0.06 0.17 0.38 Comparative Example 7 14 TGA 1.90 14.0 Ca 0.0005 0.08 - - - × × 0.01 0.02 Comparative Example 8 10 ETU 0.50 10.0 Na 0.30 43.5 - - - ○ ○ 0.41 0.49

[0087] The etching solution set of the example exhibits excellent Ni-Cr removal performance in its initial formulation (copper concentration of 0), low copper etching rates, and excellent etching selectivity. Furthermore, when the copper concentration in the solution is increased to 2.0 g / L, Ni-Cr removal performance is maintained, and the copper etching rate does not reach 0.35 μm / min, maintaining excellent etching selectivity.

[0088] It can be seen that the etching solution set of the embodiment can maintain a low copper etching rate without compromising Ni-Cr removal even when the copper concentration in the solution increases due to continuous processing of the substrate to be processed, and has excellent operability.

[0089] In Comparative Example 1, which was treated with the second solution containing hydrochloric acid and nitrite instead of the first solution, Ni-Cr residue was observed after 30 seconds of immersion, indicating poor etching properties for the treated metal. Similarly, in Comparative Example 3, which was treated with the first solution containing no thiolate compound and then the second solution, similarly to Comparative Example 1, poor Ni-Cr etching properties were observed.

[0090] These results suggest that the etching solution set of the examples exhibits the following effects: the thio compound in the first solution is carried into the second solution, enhancing the etching performance of Ni-Cr in the second solution and suppressing the etching of copper. In contrast, in Comparative Examples 1 and 3, the thio compound is not introduced into the second solution, resulting in lower Ni-Cr etching performance. Furthermore, Comparative Example 3 exhibits a higher copper etching rate than Comparative Example 1. In Comparative Example 3, the increased copper etching rate is believed to be due to the high concentration of the nitrous acid source in the second solution, in addition to the absence of a thio compound.

[0091] Comparative Example 5, in which the first solution has a low sulfide compound concentration, exhibits excellent Ni-Cr removal in the initial formulation (copper concentration of 0), low copper etching rates, and excellent etching selectivity. Even at high copper concentrations, increases in copper etching rates are suppressed. However, when the copper concentration reaches 2.0 g / L, Ni-Cr etching performance decreases. In Comparative Example 5, it is believed that the sulfide compound concentration in the first solution decreases with continued use of the etching solution. When etching is continued until the copper concentration in the second solution reaches 2.0 g / L, the sulfide compound concentration required for Ni-Cr etching cannot be maintained, resulting in a decrease in Ni-Cr etching performance. (For details on the residual sulfide compound rate and etching characteristics, refer to Examples 12 to 14, Comparative Examples 10, and Comparative Examples 11, described later.)

[0092] Comparative Example 2, which did not undergo treatment with the first solution but instead treated with a second solution containing a thio compound, supplemented with hydrochloric acid and nitrite, showed excellent Ni-Cr removal, a low copper etching rate, and excellent etching selectivity in the initial formulation (copper concentration of 0). However, above a copper concentration of 1.0 g / L, Ni-Cr removal decreased, and the copper etching rate also increased significantly. In Comparative Example 2, it is believed that the thio compound in the second solution was consumed as copper dissolved, and the first solution could no longer supply the thio compound. This decrease in thio compound concentration reduced Ni-Cr removal, lost copper etching inhibition, and increased copper etching rate. Furthermore, while the second solution in Comparative Example 2 had a sufficiently high thio compound concentration in the initial formulation, the coexistence of the thio compound and the nitrite source in the second solution facilitated the decomposition of the thio compound. This, combined with the consumption of the thio compound as copper dissolved, led to a decrease in the thio compound concentration due to decomposition, contributing to the decreased Ni-Cr removal and increased copper etching rate.

[0093] Comparative Example 7, in which the second solution had a low nitrite source concentration, exhibited poor Ni-Cr removal. Comparative Example 8, in which the second solution had a high nitrite source concentration, exhibited a high copper etching rate even in the initial formulation with a copper concentration of 0, indicating poor etching selectivity for the metal being treated.

[0094] In Comparative Examples 4 and 6, the second solution contained nitric acid instead of a nitrous acid source. While the initial Ni-Cr etching performance was poor, it improved at a copper concentration of 0.05 g / L. Furthermore, at higher copper concentrations, the Ni-Cr etching performance decreased again. At a copper concentration of 2.0 g / L, the Ni-Cr etching performance increased again, but the copper etching rate also increased.

[0095] Comparative Examples 4 and 6 are believed to have poor Ni-Cr etching performance due to the lack of a nitrous acid source in the initial second solution, resulting in the absence of copper ions, making it difficult to generate nitrous acid from nitric acid. When the copper concentration in the second solution is 0.05 g / L, it is believed that the copper ions in the second solution act as a catalyst, converting nitric acid into nitrous acid, thereby improving Ni-Cr etching performance. However, as the copper concentration increases, the copper etching rate increases, and most of the nitrous acid generated from the nitric acid is consumed by etching copper, resulting in a decrease in Ni-Cr etching performance. Furthermore, at higher copper concentrations, Ni-Cr etching performance further increases, presumably because the amount of nitrous acid generated from the nitric acid exceeds the amount consumed by etching, or because the etching power of the copper ions increases, resulting in a further increase in Ni-Cr etching performance.

[0096] When nitric acid is used as the second liquid, as in Comparative Examples 4 and 6, the amount of nitrous acid generated or consumed changes significantly due to changes in the composition of the liquid with continued use, which in turn changes the etching characteristics, resulting in a lack of stability and operability issues.

[0097] [Exploring the influence of the concentration of thio compounds in the first solution] <Residual Rate of Sulfur Compounds> The first and second solutions were prepared in the same manner as in Example 1, except that the type and amount of the thio compound were changed as shown in Table 2. Copper (II) oxide was added to the first solution to a concentration of 0.025 wt% (copper concentration of 0.2 g / L), and copper (II) oxide was added to the second solution to a concentration of 0.25 wt% (copper concentration of 2 g / L). After the copper (II) oxide was added, the first and second solutions were stirred at room temperature for 5 hours. After the copper (II) oxide was added and stirred for 5 hours, the concentration of the thio compound in the first solution was quantified by iodine titration, and the residual rate relative to the initial concentration was calculated.

[0098] <Copper Etching Rate> The copper etching rate was measured using the same method as above using a first solution containing copper (II) oxide and a second solution (a model solution that reproduces the state in which copper on a substrate being processed is dissolved in the second solution) mixed and stirred.

[0099] Table 2 shows the preparation of the first and second solutions for Examples 1, 12 to 14, and Comparative Examples 10 and 11, the copper etching rates of the first and second solutions after stirring for 5 hours using copper oxide, and the residual rate of the thio compound in the first solution.

[0100] [Table 2] Etching solution preparation (wt%) After 5 hours of copper oxide preparation First liquid (Copper(II) oxide 0.025wt%) Second liquid (Copper(II) oxide 0.25wt%) Thio compounds Residual rate (%) Copper etching rate (μm / min) hydrochloric acid Thio compounds hydrochloric acid Sodium nitrite Example 1 14.0 ATG 2.25 14.0 0.006 100 0.11 Example 12 TG 2.00 96.7 0.18 Example 13 TG 1.00 85.0 0.18 Example 14 TG 0.50 72.2 0.18 Comparative Example 10 TG 0.10 9.0 0.32 Comparative Example 11 ATG 0.05 23.8 0.28

[0101] 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. This also indicates that the copper etching rate tends to decrease when the copper is added to the second solution after treatment with the first solution. When the thio compound concentration is less than 0.5% by weight, the residual rate of the thio compound decreases significantly, and the copper etching rate increases significantly.

[0102] When the sulfide compound concentration in the first solution is low, it's thought that the sulfide compound is easily consumed in the presence of copper ions, resulting in a smaller amount of sulfide compound carried from the first solution to the second solution, leading to a higher copper etching rate due to the second solution. These results indicate that the copper etching rate is less likely to increase as the sulfide compound concentration in the first solution increases and the concentration decreases, leading to superior etching stability and operability.

[0103] [Study on the concentration of sulfuric acid in the second solution] <Residual rate of nitrite source> In the preparation of the second solution for Examples 1 to 4, sodium nitrite was added to a concentration of 0.006% by weight (nitrite source concentration of 0.87 mM) after heating at 50°C. 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 one hour, and the residual nitrite source rate was calculated. For Comparative Examples 12 to 14 shown in Table 3, the residual nitrite source rate after standing at 50°C for one hour was also determined using the same method as for Examples 1 to 4.

[0104] The residual amount of nitrite source is quantified using the Griess method. Griess reagent (containing sulfonamide and o-(1-naphthyl)ethylenediamine) is added to the sample and allowed to stand at room temperature for 30 minutes. The sample's absorbance at 520 nm to 550 nm is then measured using a spectrophotometer. The nitrite source concentration is calculated from the sample's absorbance using a calibration curve created using standard samples of known nitrite ion concentrations.

[0105] Furthermore, adding Griess reagent to a sample containing a nitrite source produces a reddish-purple color that deepens over time, with the absorbance between 520 nm and 550 nm increasing. After adding the Griess reagent, the absorbance remains constant for 30 minutes to several hours, after which the color fades and the absorbance decreases.

[0106] <Etching Properties> As the second solution, a solution that had been adjusted and left at 50°C for one hour (a model solution that reproduces the state in which the nitrous acid source concentration decreases with the use of the etching solution) was used to evaluate Ni-Cr removal and measure the copper etching rate using the same methods as above.

[0107] Table 3 shows the preparation of the first and second liquids of Examples 1 to 4 and Comparative Examples 12 to 14, the residual rate of the nitrite source in the second liquid one hour after the nitrite was prepared in the second liquid, and the etching properties (Ni-Cr removal properties and copper etching rate) when using the second liquid.

[0108] [Table 3] Etching solution preparation (wt%) 1 hour after nitrite preparation First liquid Second liquid (Na nitrite 0.006wt%) Nitrite source Residual rate (%) Ni-Cr Removal Copper etching rate (μm / min) hydrochloric acid Thio compounds hydrochloric acid sulfuric acid Example 1 14.0 ATG 2.25 14.0 - 43.3 ○ 0.02 Example 2 ATG 2.25 13.8 1 42.3 ○ 0.02 Example 3 ATG 2.25 13.2 4 42.2 ○ 0.03 Example 4 TGA 1.90 14.0 1 47.4 ○ 0.03 Comparative Example 12 ATG 2.25 13.0 5 37.0 × 0.03 Comparative Example 13 ATG 2.25 12.0 10 35.0 × 0.03 Comparative Example 14 TGA 1.90 14.0 5 32.6 × 0.04

[0109] A trend was observed where the residual rate of the nitrous acid source decreased after one hour as the sulfuric acid concentration in the second liquid increased. In Comparative Examples 12 and 14, where the sulfuric acid concentration was 5% by weight or greater, the residual rate of the nitrous acid source after one hour was less than 40%. Using this as the second liquid resulted in poor Ni-Cr removal.

[0110] When the sulfuric acid concentration of the second solution is high, good etching performance can be achieved by simply using the second solution immediately after preparation. However, the rapid decrease in the nitrous acid source will tend to reduce the Ni-Cr removal performance (etching rate), necessitating frequent addition of the nitrous acid source to maintain etching performance.

[0111] These results demonstrate that a low sulfuric acid concentration in the second liquid is preferred to suppress the decrease in the concentration of the nitrite source in the second liquid and reduce the frequency of nitrite source addition or liquid replacement required by the replenishing liquid. Furthermore, the results of the aforementioned Examples and Comparative Examples demonstrate that etching solutions containing a nitrite source in the second liquid exhibit excellent etching characteristics and operability even when sulfuric acid is absent.

[0112] 3: Conductor pattern 5: Region 10: Insulating substrate 20,21: basal layer 31: Copper layer 40: electroplating resist layer 41: Resist pattern

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