Copper sulfate plating solution

Abstract

The present invention provides a highly versatile copper sulfate plating solution for circuit formation, with which it is possible to perform both a smoothing plating treatment and a recess-filling plating treatment using the same plating solution. The present invention is a copper sulfate plating solution that is composed of copper sulfate, sulfuric acid, and chlorine, and contains a brightener, a polymer, a leveler A, and a leveler B as additives, said copper sulfate plating solution being characterized by the addition of a mixture of: the leveler A, which is an amine compound obtained by reacting epichlorohydrin with a nitrogen compound selected from among ammonia, alkyl amines, aliphatic amines, and aromatic amines; and the leveler B, which is a methyldiallylamine such as a N-methyldiallylamine hydrobromide / sulfur dioxide copolymer.

Description

Copper sulfate plating solution

[0001] The present invention relates to a copper plating technology for semiconductor wafers, package substrates, printed wiring boards, etc., and more particularly to a copper sulfate plating solution that can be used to fill recesses such as trenches, vias, and through-holes with copper and also to a copper sulfate plating solution that can be used to perform smooth plating for the formation of rewiring circuits and fine-line circuits. Furthermore, the copper-plated film produced using the copper sulfate plating solution of the present invention can control the twin ratio in the deposited copper crystals, which may improve electromigration resistance without significantly changing the volume resistivity.

[0002] Copper plating has traditionally been used to ensure electrical continuity in electronic materials such as semiconductor wafers, package substrates, and printed wiring boards. This copper plating process is used to form conductive circuits on printed wiring boards and to fill recesses such as trenches, vias, and through-holes with copper. Recently, copper plating has also been used to form rewiring circuits, known as rewiring layers, in fan-out packages for smartphones and other devices.

[0003] In such copper plating processes, copper sulfate plating solutions containing various additives such as polymers, brighteners, and levelers in addition to the basic components of copper sulfate, sulfuric acid, and hydrochloric acid are known. By adding these additives, the electrodeposition properties of copper plating can be controlled, and copper plating processes tailored to each situation can be realized.

[0004] Recently, electronic materials have been formed with fine wiring patterns having gaps with high aspect ratios, and copper plating is often performed on plating surfaces having such gaps. In this case, the copper plating process is required to completely fill the gaps with copper.

[0005] For example, Patent Document 1 proposes a method for filling copper into non-through holes in a conductively treated substrate, using an acidic copper plating bath containing a filling additive consisting of a water-soluble copper salt, sulfuric acid, and a polymer having both brightener and leveler functions. Patent Document 2 also proposes a technology for filling copper into conductively treated non-through holes in a substrate with an aspect ratio (depth / opening diameter) of 5 or more by performing a copper plating process with periodic current reversal using an acidic copper plating bath containing a copolymer of diallylamine and sulfur dioxide.

[0006] Patent No. 5578697 Patent No. 5568250

[0007] Although the copper plating processing techniques proposed in the above-mentioned prior art documents can fill high-aspect-ratio blind holes with copper, the following problems remain of concern. Patent Document 1 uses a sulfur dioxide copolymer as a brightener, which reduces the surface gloss of the copper plating film. Furthermore, when performing via filling processing for microvias, bis-3-sulfopropyl disulfide disodium (hereinafter sometimes simply referred to as SPS) is generally used as a brightener. However, if SPS is not used, there is no bipolar potential effect due to the Cu thiolate produced by the reaction, which could result in the formation of defects such as voids inside the vias and trenches during via filling, and it is also thought that the surface roughness of the copper plating film may tend to increase.

[0008] In Patent Document 2, a copper plating process is performed using an acidic copper plating bath different from that of Patent Document 1, and current control is performed using a PR (Periodic-Reveres)-pulse method. However, when the pattern size of the plating surface changes, it is necessary to appropriately determine the current control conditions. Furthermore, because the current is periodically reversed, insoluble anodes such as iridium oxide are prone to copper deposition on the anode surface when reverse electrolysis is applied, making the process more complicated. Furthermore, with phosphorus-containing copper, which is commonly used as a soluble anode, problems such as the detachment of the black film formed on the anode surface tend to occur, making it difficult to perform a rapid copper plating process. Furthermore, the power source used in the PR-pulse method is industrially expensive, which is a disadvantage in terms of production costs.

[0009] Furthermore, currently available commercially available copper sulfate plating solutions include those containing various additives for copper plugging plating of trenches, through-silicon vias, and vias in semiconductor wafers, package substrates, and printed circuit boards, as well as those for forming circuits such as rewiring on semiconductor wafers and printed wiring boards. Thus, copper sulfate plating solutions exist for each application. In other words, it is generally known that the compositions of copper sulfate plating solutions used for forming wiring by copper smooth plating and copper plugging plating differ. Therefore, when manufacturing a single electronic material, it is necessary to prepare copper sulfate plating solutions with different compositions to suit the application when performing smooth plating and plugging plating. For these reasons, there is currently a demand for a copper sulfate plating solution with the same composition that can be used for both copper plugging plating and copper smooth plating.

[0010] The present invention has been made in light of the above circumstances, and provides a versatile copper sulfate plating solution that is capable of smooth plating for forming rewiring circuits and fine-line circuits, as well as plugging recesses such as trenches, vias, and through-holes with copper.

[0011] To solve this problem, the inventors conducted detailed studies on levelers in copper sulfate plating solutions and found that by adding a mixture of two types of levelers, it is possible to simultaneously perform smooth plating and hole-filling plating using a copper sulfate plating solution of the same composition. Furthermore, they also found that a copper plating film formed using a copper sulfate plating solution containing a mixture of two types of levelers contains twin grain boundaries in the deposited copper crystals, which are said to be effective in suppressing electromigration, but does not significantly change the volume resistivity of the copper plating film, leading to the present invention.

[0012] The present invention relates to a copper sulfate plating solution that is composed of copper sulfate, sulfuric acid, and chlorine, and that contains, as additives, a brightener, a polymer, and two types of levelers A and B. The brightener is SPS (bis-3-sulfopropyl disulfide disodium), the polymer is one or more of polyethylene glycol dimethyl ether (molecular weight 2000 to 4000), polyethylene glycol monomethyl ether (molecular weight 2000 to 4000), polyethylene glycol monomethyl ether methacrylate (molecular weight 2000 to 4000), polyethylene glycol methyl ether tosylate (molecular weight 2000 to 4000), and polyethylene glycol (molecular weight 2000 to 6000), and the leveler A is ammonia, alkylamines, aliphatic amines, or the like. and the leveler B is an amine compound obtained by reacting a nitrogen compound selected from the group consisting of aromatic amines and aromatic amines with epichlorohydrin, and the leveler B is at least one selected from the group consisting of N-methyldiallylamine hydrobromide-sulfur dioxide copolymer, N-ethyldiallylamine hydrobromide-sulfur dioxide copolymer, N-propyldiallylamine hydrobromide-sulfur dioxide copolymer, N-methyldiallylamine hydroiodide-sulfur dioxide copolymer, N-ethyldiallylamine hydroiodide-sulfur dioxide copolymer, N-propyldiallylamine hydroiodide-sulfur dioxide copolymer, N-methyldiallylamine hydrochloride-sulfur dioxide copolymer, N-ethyldiallylamine hydrochloride-sulfur dioxide copolymer, and N-propyldiallylamine hydrochloride-sulfur dioxide copolymer. The copper sulfate plating solution of the present invention contains four additives: a brightener, a polymer, two types of leveler A, and a leveler B. By adjusting and mixing the amounts of two of the levelers, it is possible to create a copper sulfate plating solution that preferentially performs circuit formation by smooth plating, or a copper sulfate plating solution that preferentially performs hole-filling plating. According to the present invention, smooth plating and hole-filling plating can be performed simultaneously by adjusting the blending ratio of the two types of levelers. Furthermore, by mixing two types of levelers, it is possible to achieve a copper plating film in which the proportion of twin grain boundaries in the deposited copper crystals is controlled without significantly changing the volume resistivity of the copper plating film.

[0013] The brightener added to the copper sulfate plating solution of the present invention promotes the electrodeposition reaction, reduces the size of copper deposit particles, and produces a glossy, dense copper plating film. Specifically, SPS (bis-3-sulfopropyl disulfide disodium) is used as the brightener.

[0014] The polymer added to the copper sulfate plating solution of the present invention interacts with chloride ions to form a monomolecular film at the cathode interface, thereby broadly suppressing copper deposition and improving copper throwing power. Specifically, the polymer may be any one of polyethylene glycol dimethyl ether (molecular weight 2000 to 4000), polyethylene glycol monomethyl ether (molecular weight 2000 to 4000), polyethylene glycol monomethyl ether methacrylate (molecular weight 2000 to 4000), polyethylene glycol methyl ether tosylate (molecular weight 2000 to 4000), and polyethylene glycol (molecular weight 2000 to 6000), or a combination thereof.

[0015] The two types of leveler A and leveler B added to the copper sulfate plating solution of the present invention basically adsorb in greater amounts to the convex portions of the plated surface and in smaller amounts to the concave portions, thereby suppressing the electrodeposition reaction on the convex portions and imparting smoothness to the copper plating film. Leveler A uses an amine compound obtained by reacting a nitrogen compound selected from ammonia, alkylamines, aliphatic amines, and aromatic amines with epichlorohydrin. Furthermore, as Leveler B, any one of N-methyldiallylamine hydrobromide / sulfur dioxide copolymer, N-ethyldiallylamine hydrobromide / sulfur dioxide copolymer, N-propyldiallylamine hydrobromide / sulfur dioxide copolymer, N-methyldiallylamine hydroiodide / sulfur dioxide copolymer, N-ethyldiallylamine hydroiodide / sulfur dioxide copolymer, N-propyldiallylamine hydroiodide / sulfur dioxide copolymer, N-methyldiallylamine hydrochloride / sulfur dioxide copolymer, N-ethyldiallylamine hydrochloride / sulfur dioxide copolymer, and N-propyldiallylamine hydrochloride / sulfur dioxide copolymer, or a combination thereof, can be used. When electrochemical measurements were performed using a rotating disk electrode with a potentio-galvanostat device to compare Leveler A and Leveler B, it was confirmed that Leveler A had a smaller overvoltage and a weaker leveling effect than Leveler B. Furthermore, it was confirmed that Leveler B had a larger overvoltage and a stronger leveling effect. When Leveler A is mixed with Leveler B and added to a copper sulfate plating solution, Leveler A tends to improve copper throwing power, while Leveler B is effective for hole-filling plating. By adjusting the amounts of these two types of Leveler A and Leveler B added, a copper sulfate plating solution with the same composition can be realized, enabling both smooth plating and hole-filling plating. Furthermore, copper plating films formed using a copper sulfate plating solution containing a mixture of two types of levelers, as in the present invention, exhibit a twin grain boundary ratio of 40% or more in the deposited copper crystals after 30 days at room temperature without significant changes in volume resistivity. As shown in the reference document (Patent No. 3741938), the formation of more than half of twins in the crystals of copper wiring is expected to reduce electromigration rates.

[0016] A stabilizer can also be added to suppress the production of 3-mercaptopropane-1-sulfonic acid (hereinafter simply referred to as "MPS") due to a side reaction of SPS (bis-3-sulfopropyl disulfide disodium), the brightener added to the copper sulfate plating solution of the present invention. This is because the presence of more than a certain amount of MPS in the copper sulfate plating solution makes it impossible to form a copper plating film with the desired plating properties. In particular, when performing hole-filling plating, if the amount of MPS in the copper sulfate plating solution is high, recesses tend to be insufficiently filled with copper plating. Therefore, polyethylene glycol (molecular weight 1000) can be used as the stabilizer.

[0017] The copper sulfate plating solution of the present invention preferably contains 100 to 250 g / L of copper sulfate (as copper sulfate pentahydrate), 30 to 200 g / L of sulfuric acid, and 10 to 90 mg / L of chlorine. If the copper sulfate pentahydrate concentration is less than 100 g / L, copper replenishment tends to be difficult. If the concentration exceeds 250 g / L, copper sulfate crystals tend to form in the plating solution due to a drop in temperature. If the sulfuric acid concentration is less than 30 g / L, electrical conductivity tends to deteriorate, and overall throwing power tends to decrease. Furthermore, if the concentration exceeds 200 g / L, electrical conductivity improves, but seed layers of semiconductor wafers, package substrates, and printed wiring boards tend to be eluted when immersed in the plating solution. If the chlorine concentration is less than 10 mg / L, the surface roughness of the copper plating film tends to increase, and as the chlorine concentration increases, the copper plating deposition suppression effect increases, which has the effect of improving uniformity and filling properties, but if the chlorine concentration exceeds 90 mg / L, it tends to have an adverse effect on workability, such as the generation of mist.

[0018] The copper sulfate plating solution according to the present invention preferably contains 1 to 20 ppm of brightener, 50 to 150 ppm of polymer, 0.05 to 100 ppm of leveler A, and 0.05 to 5 ppm of leveler B. If the brightener content is less than 1 ppm, the brightener will not last during plating, resulting in a narrower gloss range. If the brightener content exceeds 20 ppm, the difference in film thickness between copper-plated circuits will increase, the rectangular portions above the copper-plated circuits will become rounded, and the surface roughness of the copper-plated film will tend to increase. If the polymer content is less than 50 ppm, the plating-suppressing effect will be weaker, and the copper-plated portions on the circuit surface will also tend to thicken when vias, trenches, and other holes are filled with plating. If the polymer content exceeds 150 ppm, deep dimples will tend to form inside the filled holes. Since the adsorption of the leveler is governed by diffusion, if the leveler A is less than 0.05 ppm, shallow depressions tend to form on the upper surface of the copper-plated circuit formed due to stirring during the copper plating process, and if it exceeds 100 ppm, the surface roughness of the copper-plated film tends to increase. If the leveler B is less than 0.05 ppm, the leveler is not adsorbed to the cathode surface due to stirring of the copper sulfate plating solution, and the plating deposition suppression effect is not obtained, so it tends to be difficult to fill holes in vias and trenches in the circuit. If it exceeds 5 ppm, the copper plating deposition rate drops drastically when the plating solution is stirred, so the copper plating process takes a long time and workability tends to decrease.

[0019] In the copper sulfate plating solution according to the present invention, when copper plating is performed with priority given to smooth plating, it is preferable to add Leveler A in an amount of 0.05 to 100 ppm and Leveler B in an amount of 0.05 to 1 ppm. More preferably, the amount of Leveler A is 20 to 50 ppm and the amount of Leveler B is 0.25 to 0.5 ppm. When the amount of Leveler B is in the range of more than 1 ppm but not more than 5 ppm, the copper sulfate plating solution is effective for plugging through holes with a high aspect ratio, for example, for plugging through-silicon vias (TSVs) with a high aspect ratio.

[0020] The leveler A and leveler B used in the copper sulfate plating solution of the present invention can also be applied to copper plating solutions used in producing general electrolytic copper foils used as manufacturing materials for printed wiring boards and the like, and copper foils for negative electrode current collectors for Li-ion batteries.

[0021] As explained above, according to the present invention, by increasing the overvoltage during deposition using a copper sulfate plating solution of the same composition to which Leveler A and Leveler B are added, it is possible to perform smooth plating for forming rewiring circuits and fine-line circuits, as well as copper filling plating for recesses such as trenches, vias, and through-holes. The volume resistivity of the resulting copper plating film remains unchanged even after 30 days at room temperature, and by increasing the twin ratio of the grain boundaries to 40% or more, electromigration can be suppressed.

[0022] Graph showing overpotential in electrochemical measurement of Levelers A0 and B0. Cross-sectional observation photograph in the case of a copper sulfate plating solution containing Leveler A0. Cross-sectional observation photograph in the case of a copper sulfate plating solution containing Leveler B0. Measurement diagram showing the shapes of wiring circuits with wiring widths of 30 μm and 5 μm. Surface observation photograph in a Hull cell test of a copper sulfate plating solution containing a polymer. Modes for carrying out the invention

[0023] An embodiment of the present invention will be described below. First, the results of electrochemically measuring the overpotential of Leveler A and Leveler B will be described. The electrochemical measurement conditions are as follows. The equipment used was a potentio-galvanostat HZ7000 (manufactured by Meiden Hokuto Co., Ltd.) and a rotating disk electrode measuring device HR-501 (manufactured by Meiden Hokuto Co., Ltd.) at 0 rpm, 100 rpm, and 1000 rpm. The reference electrode used was Ag / AgCl, Leveler A0: dimethylamine ammonium epichlorohydrin, and Leveler B0: N-methyldiallylamine hydrobromide sulfur dioxide copolymer.

[0024] The measurement results at each rotation speed are shown in Figure 1. The graph shows the overvoltage measurement results at rotation speeds of 0 rpm (a), 100 rpm (b), and 1000 rpm (c). The vertical axis of each measurement shows the current density (A cm －２), the horizontal axis is E / V vs. Ag / AgCl, and the overpotential increases as you move left on the horizontal axis. As shown in Figure 1, when comparing Leveler A0 (dotted line) and Leveler B0 (solid line), Leveler A0 had a smaller overpotential than Leveler B0 at all rotation speeds, suggesting that its leveling effect was weaker than that of Leveler B0. On the other hand, Leveler B0 had a larger overpotential and a stronger leveling effect.

[0025] Next, we will explain the results of investigating the leveling effect of Leveler A and Leveler B in hole-filling plating processes. A copper sulfate plating solution was prepared by adding 30 ppm of Leveler A0 (dimethylamine-ammonium-epichlorohydrin) and 1 ppm of Leveler B0 (N-methyldiallylamine hydrobromide-sulfur dioxide copolymer) to the copper plating solution composition shown below. Copper plating was performed on the copper seed layer of a semiconductor wafer with vias measuring 5 μm in diameter and 10 μm deep. The cross section was then observed to examine the state of the leveling effect. The basic composition of the copper plating solution was 195 g / L of copper sulfate pentahydrate, 100 g / L of sulfuric acid, 50 mg / L of chlorine, 7.5 ppm of brightener (SPS), and 100 ppm of polymer (polyethylene glycol monomethyl ether (PEG-MME) molecular weight 2000). The plating conditions were a solution temperature of 25±5° C., a current density of 0.5 ASD, a plating time of 20 minutes, and puddle stirring of the solution. Cross-sectional observation was performed using an FIB-SEM (manufactured by JEOL Ltd.).

[0026] Cross-sectional observation photographs (6500x magnification) are shown in Figure 2 (copper sulfate plating solution with Leveler A0 added) and Figure 3 (copper sulfate plating solution with Leveler B0 added). It was confirmed that copper plating within vias was possible using both Leveler A0 and Leveler B0 copper sulfate plating solutions. Measurement of the thickness of the copper plating film on the upper side of the vias revealed that Leveler A0 produced copper plating that was nearly twice as thick as Leveler B0 under the same plating conditions. Considering the overpotential survey results of the electrochemical measurements described above, Leveler B0 exhibited a large overpotential, confirming its strong leveling effect. This indicates that Leveler B0 prioritizes filling vias with plating, while its strong leveling effect inhibits plating deposition on exposed plating surfaces other than the vias. In contrast, since Leveler A0 has a weaker leveling effect than Leveler B0, it was confirmed that the weak leveling effect allows a copper plating film to be formed on exposed plating surfaces other than vias without suppressing plating deposition.

[0027] Next, we will explain the results of copper plating using copper sulfate plating solutions containing Leveler A0 and Leveler B0 at different mixing ratios. The mixing ratios when Leveler A0 and Leveler B0 were added were adjusted to the concentrations shown in Table 1. The basic composition of the copper sulfate plating solution was 170 g / L of copper sulfate pentahydrate, 130 g / L of sulfuric acid, 40 mg / L of chlorine, 4 ppm of brightener (SPS), and 100 ppm of polymer (polyethylene glycol monomethyl ether, molecular weight 2000). The plating conditions were a solution temperature of 25±5°C, a current density of 1 ASD, and a plating time of 30 minutes, with puddle stirring. The substrate to be plated was an 8-inch Si wafer with a 50 nm Ti barrier layer and a 300 nm Cu seed layer. This substrate was provided with a resist thickness of 5 μm, an aperture ratio of 50%, and a rewiring pattern shape (wiring widths of 30 μm, 15 μm, 5 μm, and 3.5 μm), and copper plating was performed on the evaluation plating substrate.

[0028]

[0029] First, wiring circuits were formed from copper plating films obtained by adding Leveler A0 and Leveler B0 at different mixing ratios to the copper sulfate plating solution of the present invention, and the shapes of the wiring circuits were measured using a hybrid laser microscope, OPTELICS (manufactured by Lasertec). The results are described below.

[0030] The measurement was performed using a hybrid laser microscope, OPTELICS, for wiring widths of 30 μm, 15 μm, 5 μm, and 3.5 μm, and the wiring circuit shapes were examined. For comparison, the wiring circuit shapes were also measured when copper plating was performed using a copper sulfate plating solution containing no leveler. Figure 4 shows the results of examining the wiring circuit shapes for representative wiring widths of 30 μm and 5 μm.

[0031] In Figure 4, the top row shows the results of measuring the wiring circuit shape when no leveler was added, and the rows below show the results when a mixture of levelers A0 and B0 was added (the second row corresponds to Example 2, the third row corresponds to Example 3, and the bottom row corresponds to Example 4). When no leveler was added at all in the top row of Figure 4, the circuit height varied for 5 μm wiring widths, and a depression was observed at the top of the circuit for 30 μm wiring widths. For the case where leveler A0 and leveler B0 were mixed, the narrow 5 μm wiring width was surrounded by resist during copper plating, resulting in a slightly rounded tip due to the influence of the solution flow in the plating equipment used, but the copper plating thickness was found to be consistent. For the 30 μm wiring width, the circuit top surface was flat, the copper plating thickness was consistent for each leveler mixture, and the edge of the circuit top surface was also rectangular. It was found that the mixed addition of leveler A0 and leveler B0 resulted in good circuit formation.

[0032] Next, copper plating was performed using a copper sulfate plating solution containing Leveler A0 and Leveler B0 added in the mixing ratios shown in Table 1, and the results of evaluation tests were conducted to determine the uniformity and surface roughness of the resulting copper plating film.

[0033] The uniformity of the copper plating film was evaluated by plating a copper substrate for evaluation with each copper sulfate plating solution, observing the cross section of the wiring for each circuit width after removing the resist, measuring the average height of the cross section of three wirings for each circuit width, and determining the total average height of the wiring from the average height values ​​for all circuit widths. The surface roughness of the copper plating film and the wiring height (plating thickness) of the cross section of the wiring for each circuit width were measured with a laser microscope, such as an OPTELICS hybrid laser microscope (manufactured by Lasertec), after removing the resist.

[0034] In addition, analytical evaluation samples of copper plating films were prepared using each copper sulfate plating solution under the same plating conditions as the above evaluation test. The analytical evaluation samples used for this crystalline structure analysis were left at room temperature for 30 days after copper plating film formation. Surface diffraction of the copper plating surface films of the analytical evaluation samples was performed using XRD (X-ray diffraction). Crystal structure analysis was performed by preparing cross sections of the copper plating films using the FIB method and using EBSD (manufactured by TSL) at an acceleration voltage of 15 kV, a sample tilt angle of 70°, a measurement area of ​​12 μm × 200 μm, and a measurement step of 0.2 μm. Regarding the average crystal grain size and the proportion of twin grain boundaries, locations with a certain or greater orientation difference between adjacent measurement points in EBSD (electron backscatter diffraction) were defined as grain boundaries, and each crystal grain was colored in an arbitrary color to create and measure the crystal grain map. The volume resistivity was measured (four-terminal method) using a MILLIOHMMETER 4328A (manufactured by Agilent Technologies) with a pin-type probe 16006A (manufactured by the same company) with a sample size of 10 mm x 15 mm, a measurement temperature of 22°C (humidity 60%), and three measurements were taken on the same sample and the average was calculated. The results are shown in Table 2.

[0035]

[0036] The average wiring height in Table 2 is the total average wiring height calculated from the average wiring heights obtained for four circuit widths: 3.5 μm, 5 μm, 15 μm, and 30 μm. Surface roughness (Ra) was also measured. The crystallite size in Table 2 is the average crystallite size of each crystal plane calculated using the Scherrer formula from the diffraction peaks obtained by XRD.

[0037] The results in Table 2 show that when only one type of leveler was added, as in Comparative Examples 1 and 2, the thickness of the copper plating film plated between 5 μm thick resists, i.e., the average wiring height, tended to decrease. Furthermore, in Comparative Example 1, in which only Leveler A0 was added, the surface roughness tended to increase. In contrast, as shown in Examples 1 to 5, when Leveler A0 was added at 0.05 to 100 ppm and Leveler B0 at 0.05 to 1 ppm, the thickness of the copper plating film plated between 5 μm thick resists, i.e., the average wiring height, was at the same level as the resist thickness. Furthermore, as shown in Examples 6 and 7, the average wiring height tended to decrease as the ratio of Leveler B0 to Leveler A0 increased. The surface roughness of Examples 1 to 7 exhibited consistently small values. This demonstrates that by adjusting and mixing Leveler A0 and Leveler B0, it is possible to control the smooth plating process and the hole-filling plating process using a copper sulfate plating solution of the same composition.

[0038] The results of the crystal structure analysis in Table 2 revealed the following. It was found that the volume resistivities of the copper plating films obtained using the copper sulfate plating solutions of each Example and Comparative Example were approximately the same. The proportion of twin grain boundaries was found to be in the range of 40 to 75% for the copper plating films of Examples 1 to 7. Given the result that the proportion of twin grain boundaries was greater than 70% when only Leveler B0 was added in Comparative Example 2, it is believed that the addition of Leveler B0 further increases the proportion of twin grain boundaries in the crystals of the deposited copper in the copper plating film. It was also found that the proportion of twin grain boundaries could be controlled to 40 to 75% by adding a mixture of Leveler A0 and Leveler B0. Furthermore, twin grain boundaries, like crystal grain boundaries, are known to hinder the movement of dislocations and therefore improve their strength. It was thought that they would affect the movement of electrons and change the volume resistivity. However, the volume resistivities of Examples 1 to 7 were in the range of 0.9 to 1.10 μΩ·cm, and no significant change was observed. Furthermore, the following reference document reports that twins in copper crystals impart electromigration resistance. Based on this, the copper plating films obtained using the copper sulfate plating solutions of Examples 1 to 7 can be expected to reduce the electromigration rate, since the volume resistivity can be controlled within the range of 0.9 to 1.10 μΩ cm and the proportion of twin grain boundaries can be controlled to 40 to 75%. Reference: Japanese Patent No. 3741938

[0039] Furthermore, the polymers used in the copper sulfate plating solution of the present invention were subjected to Hull cell tests to examine their gloss. This gloss evaluation was conducted under more than 50 conditions. Here, the gloss evaluation results are shown for five types of polymers: (a) polyethylene glycol dimethyl ether (molecular weight 2000), (b) polyethylene glycol monomethyl ether (molecular weight 2000), (c) polyethylene glycol monomethyl ether methacrylate (molecular weight 2000), (d) polyethylene glycol methyl ether tosylate (molecular weight 2000), and (e) polyethylene glycol (molecular weight 1000). The Hull cell tests were conducted using a high-throw copper sulfate plating solution containing 140 g / L of copper sulfate pentahydrate, 180 g / L of sulfuric acid, 50 mg / L of chlorine, 2 ppm of brightener (SPS), 1 ppm of leveler A0 (dimethylamine ammonium epichlorohydrin), and 100 ppm of polymer. The surface observation results of the Hull cell tests for the copper sulfate plating solutions containing each polymer are shown in Figure 5.

[0040] As shown in Figure 5, the areas surrounded by white lines in each observation photograph are glossy areas, and although the area in which (E) polyethylene glycol exhibits gloss is slightly smaller, it was confirmed that the polymers (A) to (D) exhibited the same level of gloss.

[0041] Next, a copper sulfate plating solution using an additive with a different composition from the two types of Leveler A0 (dimethylamine-ammonium-epichlorohydrin) and Leveler B0 (N-methyldiallylamine hydrobromide-sulfur dioxide copolymer) described above will be described.

[0042] First, copper plating was performed using copper sulfate plating solutions containing N-ethyldiallylamine hydrobromide / sulfur dioxide copolymer as Leveler B1 and Leveler A0 (dimethylamine / ammonium / epichlorohydrin) at various mixing ratios. The mixing ratios for Leveler A0 and Leveler B1 were adjusted to the concentrations shown in Table 3. The basic composition of the copper sulfate plating solution was 170 g / L copper sulfate pentahydrate, 130 g / L sulfuric acid, 40 mg / L chlorine, 4 ppm brightener (SPS), and 100 ppm polymer (polyethylene glycol monomethyl ether, molecular weight 2000). The plating conditions were a solution temperature of 25±5°C, a current density of 1 ASD, and a plating time of 30 minutes, with puddle stirring. Analytical evaluation samples of copper plating films were then prepared using each copper sulfate plating solution.

[0043]

[0044] Table 3 shows the proportion of twin grain boundaries obtained by performing a crystal structure analysis on the copper plating film of the prepared analysis and evaluation sample. The analysis and evaluation sample used for this crystal structure analysis was one that had been left at room temperature for 30 days after the formation of the copper plating film. The crystal structure analysis method was the same as in Example 1 above.

[0045] In Examples 8 to 14 shown in Table 3, it was confirmed that the proportion of twin boundaries was 40% or more. Judging from the result of Comparative Example 4, in which the proportion of twin boundaries was greater than 60% when only Leveler B1 was added, it is believed that the addition of Leveler B1 tends to increase the proportion of twin boundaries in the crystals of deposited copper in the copper plating film. It was also found that the proportion of twin boundaries could be controlled to 40% or more by adding a mixture of Leveler A and Leveler B.

[0046] Next, we will explain the case of a copper sulfate plating solution containing a mixture of Leveler A1 (a reaction product of dimethylamine, ethylenediamine, and epichlorohydrin), Leveler A2 (a reaction product of propylamine and epichlorohydrin), and Leveler A3 (a reaction product of diethanol and epichlorohydrin) and Leveler B0 (an N-methyldiallylamine hydrobromide-sulfur dioxide copolymer). Table 4 shows the mixing ratios of the levelers. The other plating solution compositions are the same as in Example 8. Furthermore, analytical evaluation samples were prepared under the same plating conditions as in Example 8, and crystal structure analysis was performed. Table 4 shows the proportions of twin grain boundaries in the copper plating films of the analytical evaluation samples prepared.

[0047]

[0048] It was found that in Examples 15 to 17 shown in Table 4, the proportion of twin grain boundaries was 40% or more.

[0049] The results of Examples 1 to 17 and Comparative Examples 1 to 4 described above can be summarized as follows. Copper plating within vias is possible using copper sulfate plating solutions containing either Leveler A or Leveler B. Furthermore, Leveler A tends to produce copper plating that is nearly twice as thick as Leveler B under the same plating conditions. Considering the results of the overpotential investigations using electrochemical measurements, Leveler B exhibits a large overpotential and therefore has a strong leveling effect. It was found that Leveler B has the effect of prioritizing hole-filling plating within vias, and that its strong leveling effect has the effect of suppressing plating deposition on exposed plating surfaces other than vias. In contrast, Leveler A has a weaker leveling effect than Leveler B, and therefore is able to form a copper plating film on exposed plating surfaces other than vias without suppressing plating deposition due to its weak leveling effect. Based on these findings, we determined that a copper sulfate plating solution containing a predetermined amount of brightener and polymer, with a leveler A concentration of 0.05 to 100 ppm and a leveler B concentration of 0.05 to 1 ppm, can be used for smooth plating to form rewiring circuits and fine-line circuits, as well as for plugging recesses such as trenches, vias, and through-holes with copper. Furthermore, we found that adding leveler B in an amount exceeding 1 ppm and not exceeding 5 ppm is effective for plugging high-aspect-ratio through-silicon-vias (TSVs). Furthermore, we found that a copper sulfate plating solution containing such a mixture ratio of leveler A and leveler B can produce copper plating films with no significant change in volume resistivity and with a grain boundary twin ratio of 40% or more after 30 days at room temperature. Even when only Leveler B is added, the proportion of twin grain boundaries can be increased to 40% or more, but the strong leveling action of Leveler B tends to make it difficult to smooth the upper copper surface when copper is plated to fill holes.

Claims

1. A copper sulfate plating solution is composed of copper sulfate, sulfuric acid, and chlorine, and contains as additives a brightener, a polymer, and two types of leveler A and leveler B. The brightener is bis-3-sulfopropyl disulfide disodium, the polymer is one or more of polyethylene glycol dimethyl ether (molecular weight 2000-4000), polyethylene glycol monomethyl ether (molecular weight 2000-4000), polyethylene glycol monomethyl ether methacrylate (molecular weight 2000-4000), polyethylene glycol methyl ether tosylate (molecular weight 2000-4000), and polyethylene glycol (molecular weight 2000-6000), and the leveler A is an amine compound obtained by reacting a nitrogen compound selected from ammonia, alkylamines, aliphatic amines, and aromatic amines with epichlorohydrin, a copper sulfate plating solution characterized in that leveler B is at least one selected from the group consisting of N-methyldiallylamine hydrobromide-sulfur dioxide copolymer, N-ethyldiallylamine hydrobromide-sulfur dioxide copolymer, N-propyldiallylamine hydrobromide-sulfur dioxide copolymer, N-methyldiallylamine hydroiodide-sulfur dioxide copolymer, N-ethyldiallylamine hydroiodide-sulfur dioxide copolymer, N-propyldiallylamine hydroiodide-sulfur dioxide copolymer, N-methyldiallylamine hydrochloride-sulfur dioxide copolymer, N-ethyldiallylamine hydrochloride-sulfur dioxide copolymer, and N-propyldiallylamine hydrochloride-sulfur dioxide copolymer.

2. The copper sulfate plating solution according to claim 1, wherein the copper sulfate is 100 to 250 g / L as copper sulfate pentahydrate, the sulfuric acid is 30 to 200 g / L, the chlorine is 10 to 90 mg / L, the brightener is 1 to 20 ppm, the polymer is 50 to 150 ppm, the leveler A is 0.05 to 100 ppm, and the leveler B is 0.05 to 5 ppm.

3. The copper sulfate plating solution according to claim 1 or 2, further comprising polyethylene glycol (molecular weight 1000) as a stabilizer.

4. A copper plating method using a copper sulfate plating solution containing two types of levelers as described in claim 1 or claim 2, which forms a copper plating film in which the proportion of twin grain boundaries in the copper plating film is 40% or more after being left at room temperature for 30 days.

5. A semiconductor wafer, a package substrate, a printed wiring board, or an electrolytic copper foil produced by using the copper plating method according to claim 4.

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