Etching solution for copper thin film and method for manufacturing semiconductor substrate

Abstract

One embodiment of the present invention provides an etching solution for a copper thin film, the etching solution comprising, on the basis of the total mass of the etching solution, (A) 0.01-20 mass% of an oxidizing agent, (B) 1-20 mass% of a sulfoxide having a carboxy group, (C) 0.0001-2 mass% of an oxo acid of phosphorus, (D) 0.00001-0.1 mass% of a copper corrosion inhibitor, and (E) water, wherein the etching solution is substantially free of halide ions, and the copper corrosion inhibitor is a nitrogen-containing heterocyclic compound, a cationic surfactant containing a quaternary ammonium salt in the structure thereof, or a combination thereof.

Description

Etching solution for copper thin films and method for manufacturing semiconductor substrates

[0001] This invention relates to an etching solution for copper thin films and a method for manufacturing semiconductor substrates.

[0002] In response to the increasing functionality and miniaturization of semiconductor devices, flip-chip mounting has been widely adopted. This method involves forming numerous electrodes (bumps) on a copper seed layer on a substrate, and connecting the semiconductor device to the substrate via these electrodes.

[0003] Patent Document 1 discloses an etching solution used for etching a workpiece in which a substrate, a copper thin film, and a copper plated object are stacked in this order in the thickness direction of the substrate, comprising an oxidizing substance and water, wherein the oxidizing substance comprises a combination of an oxoacid and a peroxide, or a peracid, and the oxidizing substance comprises at least one of acetic acid as an oxoacid and peracetic acid as a peracid.

[0004] Patent Document 2 discloses an etching agent for copper, which is an aqueous solution containing hydrogen peroxide, an acid, an amino acid, and a nitrogen-containing heterocyclic compound, wherein the acid is nitric acid, sulfuric acid, hydrochloric acid, etc., the amino acid has a molecular weight of 300 or less, and the nitrogen-containing heterocyclic compound is 5-aminotetrazole, 3-aminopyridine, etc.

[0005] Patent Document 3 discloses an etching solution that contains hydrogen peroxide and sulfuric acid, wherein the sulfuric acid content is 0.1 to 500 g / L, the hydrogen peroxide content is 0.1 to 1 g / L, and the ratio of hydrogen peroxide to sulfuric acid is 1:2.5 or more in g / L units, which is used to etch the surface of copper or copper alloy to the order of nanometers, thereby creating a surface to which DFR, solder resist, interlayer insulating resin, or coverlay can be firmly adhered.

[0006] Patent Document 4 discloses a copper etching solution for laminates of copper or a copper alloy and nickel or a nickel alloy, comprising hydrogen peroxide, nitric acid, and water, wherein the concentration of hydrogen peroxide is 1 to 10 wt%, the concentration of nitric acid is 0.01 to 10 wt%, and the ratio of the hydrogen peroxide concentration to the nitric acid concentration is 0.5 or more.

[0007] Japanese Patent Application Laid-Open No. 2022-181453, Japanese Patent Application Laid-Open No. 2021-195572, Japanese Patent No. 6164861, Japanese Patent Application Laid-Open No. 2004-43895

[0008] In the manufacturing process of a semiconductor substrate, a copper structure (for example, a Cu pillar bump structure in which a copper pillar, a nickel layer, and a tin-silver layer are laminated in this order) serving as an electrode is formed. When forming the copper structure on the insulating layer of the substrate, a copper thin film (for example, a copper seed layer) is formed on the insulating layer, and the copper structure is formed thereon. After the formation of the copper structure, the unnecessary copper thin film is removed using an etching solution. In the removal of the copper thin film by the etching solution, not only the copper thin film but also the copper structure is etched by the etching solution, and the copper structure may be damaged.

[0009] Therefore, an object of the present invention is to provide an etching solution for removing a copper thin film while reducing damage to a copper structure on the copper thin film for use in the manufacturing process of a semiconductor substrate.

[0010] The present invention includes the following embodiments. [1] An etching solution for a copper thin film, based on the total mass of the etching solution, (A) an oxidizing agent of 0.01 to 20% by mass, (B) a sulfoxide having a carboxyl group of 1 to 20% by mass, (C) an oxo acid of phosphorus of 0.0001 to 2% by mass, (D) a corrosion inhibitor of copper of 0.00001 to 0.1% by mass, and (E) water, the etching solution substantially does not contain halide ions, and the corrosion inhibitor of copper is a nitrogen-containing heterocyclic compound, a cationic surfactant having a quaternary ammonium salt in its structure, or a combination thereof. [2] The etching solution according to [1] above, wherein (B) the sulfoxide having a carboxyl group is a compound of formula (I). In the formula, R １ is H, CH ３ NH ２ or COOH, and R ２ is C ｎ H ２ｎ (n is an integer of 1 to 10), and R ３ is C ｍ H ２ｍ＋１(m = integer from 1 to 10). [3] R １ NH ２ And R ２ is C ｎ H ２ｎ (n = integers from 1 to 4) and R ３ CH ３The etching solution described in [2] above. [4] The etching solution described in any one of [1] to [3] above, wherein (C) the oxoacid of phosphorus is phosphoric acid, phosphonic acid, or a combination thereof. [5] The etching solution described in any one of [1] to [4] above, wherein the nitrogen-containing heterocyclic compound is 1,2,3-benzotriazole, 1,2,4-triazole, imidazole, 5-amino-1H-tetrazole, purine, or a combination thereof, and / or the surfactant containing the quaternary ammonium salt in its structure is benzethonium chloride. [6] The etching solution according to any one of the above [1] to [5], wherein (A) the oxidizing agent is hydrogen peroxide, (B) the sulfoxide having a carboxyl group is methionine sulfoxide, S-methyl-L-cysteine ​​sulfoxide, or a combination thereof, (C) the phosphorus oxoacid is phosphoric acid, phosphonic acid, or a combination thereof, (D) the nitrogen-containing heterocyclic compound is 1,2,3-benzotriazole, 1,2,4-triazole, imidazole, 5-amino-1H-tetrazole, purine, or a combination thereof, and / or the surfactant containing the quaternary ammonium salt in its structure is benzethonium chloride. [7] The etching solution according to any one of the above items [1] to [6], wherein the etching solution comprises (A) 0.08 to 10% by mass of the oxidizing agent, (B) 1 to 12% by mass of the sulfoxide having a carboxyl group, (C) 0.0008 to 1.2% by mass of the phosphorus oxoacid, and (D) 0.00008 to 0.02% by mass of the copper corrosion inhibitor. [8] The etching solution according to any one of the above items [1] to [7], for etching a copper thin film from a semiconductor substrate comprising a copper thin film formed by a method other than plating and a copper structure formed on the copper thin film by plating. [9] A method for manufacturing a semiconductor substrate, comprising the steps of: forming a copper thin film on a substrate by a method other than plating; forming a copper structure on the copper thin film by plating; and etching the copper thin film using the etching solution according to any one of the above items [1] to [7].

[0011] The etching solution of the present invention is used in the manufacturing process of semiconductor substrates and can remove copper thin films while reducing damage to copper structures on the copper thin films.

[0012] This is a schematic diagram of an evaluation substrate used in one embodiment of the present invention.

[0013] 1. Etching solution for copper thin films The etching solution for copper thin films of the present invention comprises, based on the total mass of the etching solution, (A) 0.01 to 20% by mass of an oxidizing agent, (B) 1 to 20% by mass of a sulfoxide having a carboxyl group, (C) 0.0001 to 2% by mass of a phosphorus oxoacid, (D) 0.00001 to 0.1% by mass of a copper corrosion inhibitor, and (E) water, but substantially free of halide ions. The copper corrosion inhibitor is a nitrogen-containing heterocyclic compound, a cationic surfactant containing a quaternary ammonium salt in its structure, or a combination thereof.

[0014] Here, "substantially free of halide ions" means that the etching solution does not contain halide ions, or that the concentration (content) of halide ions in the etching solution is less than 0.02% by mass, less than 0.001% by mass, or less than 0.0002% by mass, based on the total mass of the etching solution.

[0015] [Component (A) Oxidizing Agent] Component (A) oxidizing agent in the etching solution is a component for oxidizing copper. The oxidizing agent (A) does not contain sulfoxides having a carboxyl group, oxoacids of phosphorus, or acids containing halogen elements such as hydrogen halides. The oxidizing agent (A) is preferably hydrogen peroxide. There are no particular restrictions on the hydrogen peroxide used, and various grades such as industrial and electronics grades can be used.

[0016] The concentration (content) of (A) the oxidizing agent in the etching solution is 0.01 to 20% by mass, 0.01 to 16% by mass, 0.01 to 12% by mass, 0.01 to 10% by mass, 0.01 to 8% by mass, 0.08 to 20% by mass, 0.08 to 16% by mass, 0.08 to 12% by mass, 0.08 to 10% by mass, 0.08 to 8% by mass, 0.1 to 8% by mass, or 0.1 to 7% by mass, based on the total mass of the etching solution.

[0017] [Component (B) Sulfoxide having a carboxyl group] Component (B) sulfoxide having a carboxyl group in the etching solution is preferably a compound of formula (I). In the formula, R １ H, CH ３ NH ２ , or COOH, R ２ C ｎ H ２ｎ (n = integers from 1 to 10), R ３ C ｍ H ２ｍ＋１ (m = an integer from 1 to 10).

[0018] More preferably, (B) the sulfoxide having a carboxyl group is a compound of formula (I), where R １ NH ２ And R ２ is C ｎ H ２ｎ (n = integers from 1 to 4) and R ３ CH ３ The compound is such that (B) the sulfoxide having a carboxyl group is methionine sulfoxide, S-methyl-L-cysteine ​​sulfoxide, or a combination thereof.

[0019] The concentration (content) of (B) carboxyl group-containing sulfoxide in the etching solution is 1 to 20% by mass, 1 to 16% by mass, 1 to 12% by mass, 1 to 10% by mass, 2 to 20% by mass, 2 to 16% by mass, 2 to 12% by mass, 2 to 10% by mass, or 2.5 to 10% by mass, based on the total mass of the etching solution.

[0020] [Oxoacid of component (C) phosphorus] The oxoacid of component (C) phosphorus in the etching solution is phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphate, triphosphate, metatriphosphate, or a combination thereof, preferably phosphoric acid, phosphonic acid, or a combination thereof. More preferably, the oxoacid of (C) phosphorus is phosphoric acid.

[0021] The concentration (content) of (C) phosphorus oxoacid in the etching solution is 0.0001 to 2% by mass, 0.0001 to 1.6% by mass, 0.0001 to 1.2% by mass, 0.0004 to 2% by mass, 0.0004 to 1.6% by mass, 0.0004 to 1.2% by mass, 0.0008 to 2% by mass, 0.0008 to 1.6% by mass, 0.0008 to 1.2% by mass, or 0.001 to 1% by mass, based on the total mass of the etching solution.

[0022] [Component (D) Copper Corrosion Inhibitor] The component (D) copper corrosion inhibitor in the etching solution is a nitrogen-containing heterocyclic compound, a cationic surfactant containing a quaternary ammonium salt in its structure, or a combination thereof. The nitrogen-containing heterocyclic compounds are 1,2,3-benzotriazole, 1,2,4-triazole, imidazole, 5-amino-1H-tetrazole, purine, or a combination thereof. The surfactant containing a quaternary ammonium salt in its structure is benzethonium chloride.

[0023] The concentration (content) of (D) copper corrosion inhibitor in the etching solution is 0.00001 to 0.1 mass%, 0.00001 to 0.06 mass%, 0.00001 to 0.02 mass%, 0.00001 to 0.01 mass%, 0.00008 to 0.1 mass%, 0.00008 to 0.06 mass%, 0.00008 to 0.02 mass%, 0.00008 to 0.01 mass%, or 0.0001 to 0.01 mass%, based on the total mass of the etching solution.

[0024] [Component (E) Water] Component (E) water in the etching solution is obtained by removing metal ions, organic impurities, particles, etc., through distillation, ion exchange treatment, filtration treatment, various adsorption treatments, etc., and is preferably pure water, and more preferably ultrapure water. The concentration (content) of (E) water in the etching solution is the remainder after removing components (A) to (D). If the etching solution contains the following other components, the concentration (content) of (E) water in the etching solution will be the remainder after removing components (A) to (D) and the other components.

[0025] [Other Components] As long as the effects of the etching solution of the present invention are not impaired, the etching solution may contain various additives commonly used in etching solutions as other components. For example, the etching solution may contain known hydrogen peroxide stabilizers such as alcohols, phenylurea, organic carboxylic acids, organic amine compounds, etc., and an etching rate adjuster, etc. Further, the etching solution is preferably a solution and does not contain solid particles such as polishing particles.

[0026] [Preparation of Etching Solution] The etching solution for a copper thin film of the present invention can be prepared by uniformly stirring components (A) to (E) (and other components if necessary) at room temperature and atmospheric pressure. The stirring method is not particularly limited, and a stirring method commonly used in the preparation of etching solutions can be adopted.

[0027] [Use of Etching Solution] The etching solution for a copper thin film of the present invention is used to remove a copper thin film formed to form a copper structure serving as an electrode in the manufacturing process of a semiconductor substrate. Preferably, the etching solution is used to etch a copper thin film from a semiconductor substrate including a copper thin film formed by a method other than plating and a copper structure formed by plating on the copper thin film. More specifically, in the manufacturing process of a semiconductor substrate, the etching solution for a copper thin film is used to sequentially form a metal seed layer other than copper such as titanium and a copper seed layer (copper thin film) on a substrate by a method other than plating such as the PVD method (physical vapor deposition method), and after forming a copper pillar (copper structure) containing copper by plating on the copper seed layer, it is used to remove the copper seed layer by etching.

[0028] The thickness of the copper thin film to be etched is not particularly limited, but is 0.01 to 100 μm, 0.01 to 10 μm, 0.01 to 1 μm, or 0.1 to 1 μm. The etching rate of the copper thin film by the etching solution is also not particularly limited, but at a liquid temperature of 25 °C, it is 0.01 to 10 μm / min, 0.01 to 1 μm / min, 0.1 to 10 μm / min, or 0.1 to 1 μm / min.

[0029] There is no particular limitation on the use temperature of the etching solution, but it is 10 to 50 °C, 20 to 45 °C, or 25 to 40 °C. If the temperature of the etching solution is 10 °C or higher, the etching rate will be good and the production efficiency will be improved. Also, if the temperature of the etching solution is 50 °C or lower, the change in the liquid composition can be suppressed and the etching conditions can be kept constant. By increasing the temperature of the etching solution, the etching rate will increase, but an appropriate optimum treatment temperature should be determined in consideration of suppressing small changes in the composition of the etching solution (decomposition of hydrogen peroxide), etc.

[0030] There is no particular limitation on the etching treatment time of the copper thin film with the etching solution, but it is, for example, 20 to 240 seconds, 30 to 120 seconds, or 30 to 90 seconds. The etching treatment time may be appropriately selected according to various conditions such as the surface state and thickness of the copper thin film, the concentration and temperature of the etching solution, etc.

[0031] The method of bringing the etching solution into contact with the object to be etched is not particularly limited. For example, a method of bringing the etching solution into contact with the object to be etched by means of dropping (single-wafer spin processing) or spraying of the etching solution, or a wet (wet) etching method such as a method of immersing the object to be etched in the etching solution can be adopted.

[0032] 2. Method for manufacturing a semiconductor substrate The method for manufacturing a semiconductor substrate of the present invention includes a step of forming a copper thin film on a substrate including a wafer such as silicon, quartz, glass, SiC, GaN, etc. by a method other than plating, a step of forming a copper structure by plating on the copper thin film, and a step of etching the copper thin film using the above etching solution.

[0033] The substrate may further include an additional layer such as a passivation layer formed on a wafer such as silicon. Also, before forming the copper thin film, a metal seed layer or metal alloy seed layer other than copper such as titanium may be formed on the substrate by a method other than plating, and the copper thin film may be formed thereon. As a method other than plating, a PVD method such as a vacuum evaporation method, a sputtering method, or an ion plating method, or a chemical vapor deposition method (CVD method) can be used.

[0034] The copper structure includes copper pillars formed by plating. The copper structure may further include bumps on the copper pillars, each bump comprising a first metal layer formed by plating, which includes one or more selected from the group consisting of nickel and nickel alloys, and a second metal layer, which includes one or more selected from the group consisting of tin, tin alloys, gold, and gold alloys.

[0035] The present invention will be specifically described below with reference to examples, but the embodiments can be modified as appropriate insofar as the effects of the present invention are achieved.

[0036] [Examples 1-19] In a 30 mL glass beaker, the following components were added: (A) an oxidizing agent (hydrogen peroxide), (B) a sulfoxide containing a carboxyl group, (C) a phosphorus oxoacid, (D) a copper corrosion inhibitor (nitrogen-containing heterocyclic compound), and (E) pure water. The mixture was then stirred to a homogeneous state to prepare an etching solution. All preparations for the examples and comparative examples were carried out at room temperature (approximately 25°C) and atmospheric pressure.

[0037]

[0038] As indicated by the blank space for "Halogen component" in Table 1, the etching solutions of Examples 1 to 19 do not contain any additional halogen components other than components (A) to (D) and (E) pure water. The units of the values ​​in Table 1 and Table 2 below represent the mass percentage of each component relative to the total mass of the etching solution. Furthermore, the concentration (content) of (E) pure water in the etching solution is the remainder after excluding components (A) to (D).

[0039] [Comparative Examples 1-18] Etching solutions were prepared in the same manner as in the above examples, except that the compositional components listed in Table 2 were used. Blank spaces in Table 2 indicate that the component was not included.

[0040]

[0041] [Evaluation Substrate] A semiconductor substrate having the structure shown in Figure 1 was used as the evaluation substrate. Figure 1 schematically shows the cross-sections of the two copper structure portions of the evaluation substrate. The evaluation substrate is an 8-inch Si substrate on which a SiN passivation layer 101 was deposited on a Si wafer 100. A Ti seed layer 102 with a thickness of 100 nm and a Cu seed layer 103 with a thickness of 150 nm were deposited by PVD (Physical Vapor Deposition), and numerous Cu pillars 104 with a diameter of 10 μm and a height of 10 μm were formed on top of these by plating (100 μm ２ Each Cu pillar consists of one Cu pillar, and a 3 μm thick Ni plating layer 105 and a 2 μm thick SnAg plating layer 106 are laminated on each Cu pillar 104. The distance between adjacent Cu pillars is 10 μm.

[0042] [Method for evaluating etching solutions using evaluation substrates] 10 g of each of the prepared etching solutions for the examples and comparative examples, along with a stirring bar, were placed in a 30 mL polypropylene container. The container was placed in a constant temperature water bath set to 25.9°C and left to stand for at least 10 minutes until the etching solution reached 25°C (under atmospheric pressure). Then, with the stirring bar rotating at 600 rpm, evaluation substrates cut into 1 cm squares were immersed in the etching solution with the Cu pillar structure facing upwards. While the evaluation substrates were immersed in the etching solution, the removal time of the Cu seed layer was measured, and the evaluation substrates were removed from the container after a predetermined time (equivalent to 1.5 times the removal time of the Cu seed layer) from the start of immersion. The removed evaluation substrates were rinsed for 10 seconds in a 100 mL glass beaker filled with pure water, and then rinsed again for 10 seconds in another 100 mL glass beaker filled with pure water. After rinsing, the evaluation substrates were dried with nitrogen gas to prepare the dried evaluation substrates.

[0043] [Removal time of Cu seed layer] The time required for the Cu seed layer 103 to be completely removed by visual inspection while the evaluation substrate was immersed in the etching solution was measured. Since a short Cu seed layer removal time is desirable in the semiconductor manufacturing process, a time of less than 300 seconds was considered acceptable.

[0044] [Maximum Etching Amount] After drying, the evaluation substrate was examined using a Hitachi High-Tech scanning electron microscope "SU-9000" at an observation magnification of 8000x (acceleration voltage 2.0kV, emission current 5μA) to determine the maximum lateral etching amount of the Cu pillar 104.

[0045] The maximum etching amount in the lateral direction was calculated for each of the three Cu pillars 104 using the formula: (Etching amount in the lateral direction (μm)) = {(Diameter of Cu pillar 104 before etching solution treatment (μm)) - (Diameter of Cu pillar 104 after etching solution treatment (μm)} / 2. The maximum value among these was taken as the maximum etching amount. A larger etching amount is undesirable because it makes the Cu pillar thinner and reduces its volume as an electrode. Therefore, a maximum etching amount of 0.5 μm or less was considered acceptable.

[0046] [Etching Selectivity Ratio] The etching rate (μm / min) of the Cu seed layer was calculated from the film thickness of the Cu seed layer 103 and the removal time of the Cu seed layer. The etching rate (μm / min) of the Cu pillar was calculated from the maximum etching amount of the Cu pillar 104 and the etching solution treatment time at that time (i.e., a time equivalent to 1.5 times the removal time of the Cu seed layer). Based on these, the etching selectivity ratio was calculated using the formula: (Etching selectivity ratio) = (Etching rate of Cu seed layer) / (Etching rate of Cu pillar). A higher etching selectivity ratio means that the Cu seed layer can be removed faster while keeping the etching amount on the Cu pillar low. Therefore, an etching selectivity ratio of 0.8 or higher was considered acceptable.

[0047] [Cu / Ni Galvanic Corrosion] After drying, the evaluation substrate was examined using a Hitachi High-Tech scanning electron microscope "SU-9000" at an observation magnification of 8000x (acceleration voltage 2.0kV, emission current 5μA) to check for corrosion at the boundary between the Cu pillar 104 and the Ni plating layer 105. The degree of corrosion was evaluated according to the following criteria, with a rating of 0 or 1 being considered a pass. 0: No corrosion 1: Slight corrosion of about 0.1μm in the diametrical direction is observed. 2: Etching (corrosion) of less than half the radius of the Cu pillar is observed. 3: Etching of more than half the radius of the Cu pillar but less than the radius is observed. 4: Etching equal to the radius of the Cu pillar is present, and the upper Ni and SnAg layers are separated and disappear.

[0048] [Damage to Ni and SnAg Layers] After drying, the evaluation substrate was examined using a Hitachi High-Tech scanning electron microscope "SU-9000" at an observation magnification of 8000x (acceleration voltage 2.0kV, emission current 5μA) to check for corrosion in the Ni plating layer 105 and the SnAg plating layer 106. The degree of corrosion was evaluated according to the following criteria, with a rating of 0 or 1 being considered a pass. 0: No corrosion 1: Slight corrosion of about 0.1μm in the diametrical direction is observed. 2: Corrosion of less than half the radius of the Cu pillar is observed. 3: Corrosion of more than half the radius of the Cu pillar but less than the radius is observed. 4: Corrosion equal to the radius of the Cu pillar is present, and the upper Ni and SnAg layers are gone.

[0049] [Surface Morphology] After drying, the evaluation substrate was observed near the center using a Hitachi High-Tech scanning electron microscope "SU-9000" at an observation magnification of 8000x (acceleration voltage 2.0kV, emission current 5μA) to check for significant irregularities or deposition on the surfaces of the Cu pillar 104, Ni plating layer 105, and SnAg plating layer 106. Significant irregularities refer to irregularities of ±0.5μm or more relative to the initial (pre-etching) surface of the Cu pillar. Depositions are thought to be due to copper oxide, etc., and refer to those with a diameter of 0.5μm or more. The following criteria were used for evaluation, and a score of 0 or 1 was considered a pass. 0: No irregularities or precipitation. 1: Significant irregularities or precipitation are observed on the surface of less than 1 out of 50 Cu pillars. 2: Significant irregularities or precipitation are observed on the surface of 1 or more out of 50 Cu pillars, and less than 1 out of 20. 3: Significant irregularities or precipitation are observed on the surface of 1 or more out of 20 Cu pillars, and less than 1 out of 5. 4: Significant irregularities or precipitation are observed on the surface of 1 or more out of 5 Cu pillars.

[0050]

[0051]

[0052] As shown in Table 3, the etching solutions of Examples 1 to 19 were all able to remove the Cu seed layer in a sufficiently short time (less than 300 seconds), the amount of etching on the Cu pillars was not large (maximum etching amount of 0.5 μm or less), Cu / Ni galvanic corrosion was suppressed, there was no damage to the Ni layer and SnAg layer, and no significant changes were observed in the surface morphology.

[0053] Conventional technology has suggested that acetic acid improves the etching selectivity ratio between the Cu seed layer and the plated Cu pillar, thereby reducing the etching amount of the Cu pillar while removing the Cu seed layer (Patent Document 1). However, as shown in Table 4, in the etching solution of Comparative Example 2, which had acetic acid added, the etching amount (maximum etching amount) of the Cu pillar decreased compared to Comparative Example 1, but the effect was not sufficient, and neither reached an acceptable level (0.5 μm or less). Furthermore, although the etching selectivity ratio of the etching solution of Comparative Example 3 improved slightly, Cu / Ni galvanic corrosion was observed, and the etching amount (maximum etching amount) also did not reach an acceptable level.

[0054] In recent years, the distance between Cu pillar bumps has decreased, and consequently, the diameter of the Cu pillar bumps has also decreased. The smaller diameter increases the opportunities for the etching solution to contact the Cu pillars, thus increasing the etching rate of the Cu pillars. On the other hand, the shorter distance between Cu pillar bumps makes it more difficult for the solution to penetrate between the Cu pillars, resulting in a tendency for the removal rate of the Cu seed layer to decrease. With the decrease in both the distance between Cu pillar bumps and the bump diameter, a higher etching selectivity ratio is required than before. Under these circumstances, it is considered that the conventional etching solutions shown in Comparative Examples 1 to 3 did not meet the acceptance criteria.

[0055] The etching solutions of Comparative Examples 4 and 5 (Patent Document 2), which are based on the prior art known as Cu etching solutions, did not meet the standards for Cu / Ni galvanic corrosion and surface morphology. Furthermore, the etching solutions of Comparative Examples 6 and 7 (Patent Documents 3 and 4), which are based on the prior art, both had high etching amounts and extremely low etching selectivity ratios, and therefore did not meet the acceptable standards.

[0056] In Comparative Examples 8-13 and 17, the etching solutions that used carboxylic acids or amino acids instead of sulfoxides containing carboxyl groups failed to meet the passing standard in one or more items. In Comparative Examples 14-16, which used other inorganic acids instead of phosphorus oxoacids, one or more items failed to meet the passing standard.

[0057] In Comparative Example 18, the etching solution to which halogen (HCl) was added showed a significant increase in the maximum etching amount, a drastic decrease in the etching selectivity ratio, and deterioration of the surface morphology. As a result, all three items failed to meet the acceptable standards. From the results of Comparative Example 18, it is preferable for the etching solution to substantially contain no halide ions.

[0058] The above embodiment demonstrates that, in etching a Cu seed layer (thin copper film) on which Cu pillar bumps (copper structures) are formed, the etching solution of the present invention can remove the Cu seed layer while suppressing etching of the Cu pillar bumps, and also reduce Cu / Ni galvanic corrosion and damage to the Ni and SnAg layers.

[0059] Furthermore, for example, copper wiring used as a redistribution layer in semiconductor resin package substrates, glass substrates, and resin interposers is formed from plated copper, similar to Cu pillar bumps, and it is believed that the same chemical etching reaction proceeds. Therefore, it is thought that the etching solution of the present invention can similarly remove the Cu seed layer while suppressing etching of the copper redistribution of plated copper, even in the process of removing the Cu seed layer during the manufacturing of the redistribution layer.

[0060] 100 Si wafer 101 SiN passivation layer 102 Ti seed layer 103 Cu seed layer 104 Cu pillar 105 Ni plating layer 106 SnAg plating layer

Claims

1. An etching solution for copper thin films, comprising, based on the total mass of the etching solution: (A) 0.01 to 20% by mass of an oxidizing agent, (B) 1 to 20% by mass of a sulfoxide having a carboxyl group, (C) 0.0001 to 2% by mass of a phosphorus oxoacid, (D) 0.00001 to 0.1% by mass of a copper corrosion inhibitor, and (E) water, wherein the etching solution is substantially free of halide ions, and the copper corrosion inhibitor is a nitrogen-containing heterocyclic compound, a cationic surfactant containing a quaternary ammonium salt in its structure, or a combination thereof.

2. (B) The etching solution according to claim 1, wherein the sulfoxide having a carboxyl group is a compound of formula (I). In the formula, R １ is H, CH ３ , NH ２ , or COOH, and R ２ is C ｎ H ２ｎ (where n is an integer from 1 to 10), and R ３ is C ｍ H ２ｍ＋１ (where m is an integer from 1 to 10).

3. R １ NH ２ And R ２ is C ｎ H ２ｎ (n = integers from 1 to 4) and R ３ CH ３ The etching solution according to claim 2.

4. (C) The etching solution according to claim 1, wherein the phosphorus oxoacid is phosphoric acid, phosphonic acid, or a combination thereof.

5. The etching solution according to claim 1, wherein the nitrogen-containing heterocyclic compound is 1,2,3-benzotriazole, 1,2,4-triazole, imidazole, 5-amino-1H-tetrazole, purine, or a combination thereof, and / or the surfactant containing the quaternary ammonium salt in its structure is benzethonium chloride.

6. The etching solution according to claim 1, wherein (A) the oxidizing agent is hydrogen peroxide, (B) the sulfoxide having a carboxyl group is methionine sulfoxide, S-methyl-L-cysteine ​​sulfoxide, or a combination thereof, (C) the phosphorus oxoacid is phosphoric acid, phosphonic acid, or a combination thereof, (D) the nitrogen-containing heterocyclic compound is 1,2,3-benzotriazole, 1,2,4-triazole, imidazole, 5-amino-1H-tetrazole, purine, or a combination thereof, and / or the surfactant containing the quaternary ammonium salt in its structure is benzethonium chloride.

7. The etching solution according to any one of claims 1 to 6, wherein the etching solution comprises (A) 0.08 to 10% by mass of the oxidizing agent, (B) 1 to 12% by mass of the sulfoxide having a carboxyl group, (C) 0.0008 to 1.2% by mass of the phosphorus oxoacid, and (D) 0.00008 to 0.02% by mass of the copper corrosion inhibitor.

8. An etching solution according to any one of claims 1 to 6 for etching a copper thin film from a semiconductor substrate comprising a copper thin film formed by a method other than plating and a copper structure formed on the copper thin film by plating.

9. A method for manufacturing a semiconductor substrate, comprising the steps of: forming a copper thin film on a substrate by a method other than plating; forming a copper structure on the copper thin film by plating; and etching the copper thin film using an etching solution according to any one of claims 1 to 6.

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