Copper electroplating solution, copper electroplating solution additive and preparation method thereof

Abstract

The present invention relates to a copper electroplating solution, a copper electroplating solution additive, and a preparation method thereof. The solution comprises an accelerator, an inhibitor, and a leveler. The accelerator is sodium polydipropylene glycol sulfonate, the inhibitor is polyethylene glycol-6000, and the leveler is an azoaromatic benzyl quaternary ammonium salt compound. The additive is used as a leveler in the copper electroplating solution. The leveler is pyridinium benzyl ammonium chloride, having the structural formula: #imgabs0#. The additive is synthesized from pyridine and benzyl chloride. Compared with the prior art, the present invention can effectively shorten the electroplating time and achieve super filling without voids or gaps even in blind vias with higher aspect ratios.

Description

Technical Field

[0001] The invention belongs to the technical field of electroplating and relates to a copper electroplating solution, a copper electroplating solution additive and a preparation method thereof. Background Art

[0002] The recent rapid development of electronic products has placed higher demands on the production of printed circuit boards (PCBs). The need for lightweight and compact products has driven the evolution of PCBs from single-board to double-sided, multi-layer boards, and then to high-density interconnect (HDI) boards, featuring increasingly smaller blind via diameters and deeper depths. This type of PCB presents greater challenges for high-density, intensive production. Copper, due to its low resistivity and excellent conductivity, is widely used as an interconnect material for filling blind vias in PCBs. Currently, copper filling of PCB blind vias is achieved through wet electroplating. To ensure that the blind vias are completely and flawlessly filled with copper, copper needs to be gradually grown upwards from the bottom of the via during the electrodeposition process. This process is achieved through the interaction of several different types of additives. At present, there are mainly inhibitors represented by macromolecular polyether compounds, such as polyethylene glycol (PEG) and polypropylene glycol (PPG); accelerators represented by propane sulfonate derivatives, such as sodium 3-mercapto-2-propane sulfonate (MPS) and sodium polydisulfide propane sulfonate (SPS); and levelers represented by heterocyclic or alkyl compounds, such as Janus green (JGB), diazine black (DB), and Alcian blue (ABPV).

[0003] Levelers in copper electrodeposition are typically nitrogen-containing heterocyclic compounds or quaternary ammonium compounds. Generally, levelers are positively charged and adsorb in areas of high current density, thereby inhibiting copper electrodeposition. This is crucial for achieving seamless, void-free super-filling. Organic dye-based levelers such as Janus Green, Diazine Black, Methylene Blue, and Alcian Blue have been developed. While these can achieve good filling effects under certain conditions, they suffer from the disadvantages of being unable to withstand high temperatures, leading to decomposition and environmental pollution. The most reported non-dye leveler molecules are nitrogen-containing aromatic heterocyclic compounds, such as the commercial nitrogen-containing aromatic heterocyclic compounds 2-mercaptopyridine (2-MP), 4,6-dimethyl-2-mercaptopyrimidine (DPT), benzotriazole, and small molecule tetrazole derivatives, which can achieve super-conformal filling of micro blind holes. There are also new leveler molecules synthesized independently. Xu Jie et al. (Xu J, Chen B, Lv J, et al. Aryl modification of diketopyrrolopyrrole-based quaternary ammonium salts and their applications in copper electrodeposition [J]. Dyes and Pigments, 2019, 170, 107559) designed and synthesized a series of diketopyrrolopyrrole (DPP) quaternary ammonium salts with different aromatic substituents as levelers in copper electroplating solutions; Luo Jiye et al. (Luo J, Li Z, Tan B, et al. Communication—triphenylmethane-based leveler for microvia filling in copper In the study of super-conformal electroplating [J]. Journal of The Electrochemical Society, 2019, 166(13): D603-D605), a leveler (TPM-1) with three pyrrolidine rings connected by a triphenylmethane (TPM) skeleton was studied, which showed excellent micropore filling performance in a relatively wide concentration range. However, there are few reports on the independent synthesis of new leveler molecules. The modification of nitrogen-containing aromatic heterocyclic molecules to further improve their hole-filling electroplating performance is worthy of in-depth study, so it is particularly important to continue to develop and design the synthesis of new high-efficiency levelers.

[0004] Patent CN114959810A discloses a novel copper electroplating additive and its application. The novel copper electroplating additive is benzethonium chloride, which acts as a leveling agent in the copper electroplating process. The copper electroplating process comprises: preparing a copper sulfate pentahydrate aqueous solution, adding sulfuric acid, chloride ions, SPS, PEG-6000, and benzethonium chloride to obtain an electroplating solution; pretreating a test board containing blind vias with ethanol and then a dilute sulfuric acid solution to obtain a pretreated test board; and electroplating is completed in the electroplating solution using the pretreated test board as the cathode and a phosphorus-containing copper plate as the anode. However, this patent requires a long electroplating time and is only suitable for filling blind vias with low aspect ratios. Summary of the Invention

[0005] The object of the present invention is to provide a copper electroplating solution, a copper electroplating solution additive and a preparation method thereof in order to overcome at least one of the defects of the above-mentioned prior art. The present invention can effectively shorten the electroplating time and obtain super filling without voids and gaps in blind holes with higher aspect ratios.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a copper electroplating solution, which includes an accelerator, an inhibitor and a leveler, wherein the accelerator is sodium polydisulfide dipropylene sulfonate, the inhibitor is polyethylene glycol-6000, and the leveler is an azoaromatic benzyl quaternary ammonium salt compound.

[0008] Furthermore, the proportion of the accelerator is 1-10 ppm, the proportion of the inhibitor is 150-300 ppm, and the proportion of the leveler is 1-10 ppm.

[0009] One of the technical solutions of the present invention is to provide an electroplating copper solution additive, which is used as a leveling agent in the electroplating copper solution. The leveling agent is pyridinium benzyl ammonium chloride, and its structural formula is:

[0010]

[0011] One of the technical solutions of the present invention is to provide a method for preparing an additive for electroplating copper solution, wherein the additive is synthesized from pyridine and benzyl chloride.

[0012] The structural formula of pyridine is:

[0013]

[0014] The structural formula of benzyl chloride is:

[0015]

[0016] Furthermore, the molar ratio of pyridine to benzyl chloride is (0.5-1.5):1.

[0017] Furthermore, the preparation method comprises the following steps:

[0018] Step S1: Add pyridine to a three-necked flask, heat and stir, and add benzyl chloride dropwise using a constant pressure dropping funnel;

[0019] Step S2, heating the mixture to reflux for reaction, transferring the product to a round beaker, and cooling to obtain a slightly light brown viscous liquid;

[0020] Step S3: recrystallize the product with a solvent and filter to obtain a white solid, which is the electroplating copper solution additive pyridinium benzyl ammonium chloride.

[0021] Furthermore, in step S1, the heating temperature is 30-70° C., the stirring speed is 200-600 rpm, and the time is 0.5-3.0 h.

[0022] Furthermore, in step S2, the heating temperature is 40-60° C., and the reflux reaction time is 2-4 h.

[0023] Furthermore, in step S3, the solvent is petroleum ether, acetone or chloroform.

[0024] Furthermore, in step S3, the ratio of the solvent to benzyl chloride is (300-500 mL):1 mol.

[0025] The nitrogen heteroaromatic benzyl quaternary ammonium salt synthesized in the present invention is synthesized on the basis of an existing commercial nitrogen-containing aromatic heterocyclic compound. The quaternary ammonium salt structure enables the compound to be fully dissolved in an electroplating solution, and the nitrogen-containing aromatic heterocyclic ring is more likely to undergo an electrophilic reaction, so that the compound is easily adsorbed on the cathode surface, thereby inhibiting the copper electrodeposition process.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The pyridinium benzyl ammonium chloride synthesized by the present invention is used as a leveling agent in the copper electroplating process. Compared with the patent CN114959810A, it can effectively shorten the electroplating time in blind hole filling with an aspect ratio of 0.625;

[0028] (2) The pyridinium benzyl ammonium chloride synthesized by the present invention is used as a leveling agent in the copper electroplating process. The nitrogen-containing aromatic heterocycle is more likely to undergo electrophilic reaction, making the compound easy to adsorb on the cathode surface, and super filling without voids and gaps can be obtained in blind holes with an aspect ratio of 0.625 and an aspect ratio of 1.25. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a lowest unoccupied molecular orbital (LUMO) diagram of the copper electroplating solution additive in Example 1 of the present invention;

[0030] Figure 2 is the highest occupied molecular orbital (HOMO) diagram of the copper electroplating solution additive in Example 1 of the present invention;

[0031] Figure 3 This is a metallographic image of a blind hole of an electroplated PCB test board in Example 1 of the present invention;

[0032] Figure 4 This is a metallographic image of the blind holes of the electroplated PCB test board in Comparative Example 1 of the present invention;

[0033] Figure 5 This is a metallographic image of a blind hole of an electroplated PCB test board in Example 2 of the present invention;

[0034] Figure 6 This is a metallographic image of the blind holes of the electroplated PCB test board in Comparative Example 2 of the present invention;

[0035] Figure 7 This is a field emission scanning electron microscope (FE-SEM) topography image of copper deposited on the surface of the electroplated PCB test board in Example 1 of the present invention;

[0036] Figure 8 This is a FE-SEM morphology image of copper deposited on the surface of the electroplated PCB test board in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0039] Example 1:

[0040] A copper electroplating solution additive and a preparation method thereof, the preparation method comprising the following steps:

[0041] Add 0.1 mol of pyridine to a 100 mL three-necked flask, heat to 50°C, stir at 400 rpm for 0.5 h, and add 0.1 mol of benzyl chloride dropwise using a constant pressure dropping funnel; heat to 50°C, reflux for 3 h, transfer the product to a round beaker, and cool to obtain a slightly light brown viscous liquid; recrystallize with 40 mL of petroleum ether, and filter to obtain a white solid, which is the electroplating copper solution additive benzyl ammonium pyridinium chloride.

[0042] like Figure 1As shown in the figure, the lowest unoccupied molecular orbital (LUMO) electron cloud density of pyridinium benzyl ammonium chloride is mainly concentrated on the six-membered nitrogen-containing heterocyclic ring. This region is the preferred site for nucleophilic attack. The compound can be strongly adsorbed on the copper surface by donating the lone pair electrons in the heteroatom to the unoccupied orbital of copper. Figure 2 As shown, the highest occupied molecular orbital (HOMO) electron cloud density of pyridinium benzyl ammonium chloride is mainly distributed on the benzene ring, which means that this area is susceptible to electrophilic attack.

[0043] According to frontier molecular orbital theory, E HOMO and E LUMO They are related to the electron donating and electron accepting abilities of the molecule, respectively. HOMO A high value of means that the molecule has a higher tendency to donate electrons to the acceptor, while E LUMO The lower the value of E, the higher the tendency of the molecule to accept electrons from the donor. HOMO The increase and E LUMO The energy gap value (ΔE) is also an important parameter to characterize the adsorption ability of organic molecules on metal surfaces. The ΔE value is given by the formula ΔE=E LUMO -E HOMO The calculated ΔE values ​​indicate that the additive itself has a stronger adsorption capacity on the metal surface and has a greater inhibitory effect on the electroreduction of copper ions. The quantum chemical calculation results of pyridinium benzyl ammonium chloride are listed in Table 1.

[0044] Table 1 Quantum chemical calculation results of pyridinium benzyl ammonium chloride

[0045]

[0046] As shown in Table 1, the energy gap ΔE=2.618. The calculation results show that pyridinium benzyl ammonium chloride has strong adsorption on the copper surface and also has a strong inhibitory effect on the electroreduction of copper ions.

[0047] An application of a copper electroplating solution additive in a copper electroplating process comprises the following steps:

[0048] (1) Preparation of microporous copper electroplating solution: sulfuric acid, chloride ions, accelerator sodium polydisulfide bis(propane disulfide) sodium salt (SPS), inhibitor polyethylene glycol (PEG)-6000 and leveler nitrogen-aromatic benzyl quaternary ammonium salt copper electroplating solution additives are added to the prepared copper sulfate pentahydrate aqueous solution. The specific process is as follows:

[0049] 220 g of copper sulfate pentahydrate was dissolved in 1 L of deionized water, 29.9 ml of sulfuric acid was slowly added, and then 60 ppm of chloride ions, 1 ppm of SPS, 200 ppm of PEG-6000, and 3 ppm of pyridinium benzyl ammonium chloride were added to obtain an electroplating solution;

[0050] (2) Pre-treatment of the test board with a blind hole depth-to-diameter ratio of 0.625. The specific process is as follows:

[0051] The test board was immersed in ethanol for 3 minutes to remove contaminants on the surface of the test board, and then rinsed with deionized water. The test board was then placed in a 1 mol / L dilute sulfuric acid solution and shaken evenly for 3 minutes to remove oxides on the surface of the copper layer, thereby obtaining a pretreated test board.

[0052] (3) Place the pretreated test plate as the cathode and the phosphorus-containing copper plate as the anode in the electroplating solution, connect the power supply to complete the electroplating. The specific process is as follows:

[0053] Pour the prepared electroplating solution into the electroplating tank, use the pretreated test board as the cathode, and place the phosphorus-containing copper plate as the anode in the electrolytic tank. Connect the positive electrode of the DC power supply to the phosphorus-containing copper plate, and the negative electrode to the test board. Turn on the air pump to continuously pass 0.25L / min of air flow for stable stirring. The current density is 1.5A / dm 2 , electroplating is completed after 45 minutes of power on.

[0054] Example 2:

[0055] An application of the copper electroplating solution additive prepared by the preparation method described in Example 1 in a copper electroplating process, wherein the blind hole on the test board serving as the cathode has an aspect ratio of 1.25, the concentration of pyridinium benzyl ammonium chloride is 5 ppm, and the electroplating time is 120 min.

[0056] Depend on Figure 3 、 5 As shown in Figure 7, when using benzyl pyridinium chloride for electroplating copper blind hole filling, no matter the aspect ratio is 0.625 or 1.25, by adding additives of appropriate concentration and electroplating for a certain time, the blind hole can be super filled without holes and gaps, and the copper layer on the plating surface is flat and uniform.

[0057] Comparative Example 1:

[0058] The application of an electroplating copper solution additive in the electroplating copper process is basically similar to that of Example 1, except that the leveling agent benzyl pyridinium chloride is not added to the microporous electroplating copper solution.

[0059] Comparative Example 2:

[0060] The application of an electroplating copper solution additive in the electroplating copper process is basically similar to that of Example 2, except that the leveling agent pyridinium benzyl ammonium chloride is not added to the microporous electroplating copper solution.

[0061] like Figure 4 、 6As shown in Figure 8, for the test board electroplated in the plating solution without the addition of the leveling agent pyridinium benzyl ammonium chloride, the blind hole filling effect is not good regardless of whether the aspect ratio is 0.625 or 1.25, and the surface copper layer is rough and uneven, and the copper grains are coarse. Figure 3 、 5 Compared with Figure 7, it can be seen that the addition of the leveling agent pyridinium benzyl ammonium chloride can fill the blind vias with seamless voids, and the grain size of the copper deposit becomes smaller. In other words, adding the leveling agent pyridinium benzyl ammonium chloride to the electroplating solution can improve the surface morphology of the copper coating and achieve super filling of the blind vias. It can be used to manufacture high-reliability and conductive substrates for semiconductor electronic devices, and plays an important role in the defect-free filling of blind vias through the electrodeposition process.

[0062] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A copper electroplating solution, characterized in that The solution includes an accelerator, an inhibitor and a leveler, wherein the accelerator is sodium polydisulfide dipropane sulfonate, the inhibitor is polyethylene glycol-6000, and the leveler is pyridinium benzyl ammonium chloride, and the structural formula is: ； The proportion of the accelerator is 1-10 ppm, the proportion of the inhibitor is 150-300 ppm, and the proportion of the leveler is 1-10 ppm.

2. The copper electroplating solution according to claim 1, wherein The leveling agent is synthesized from pyridine and benzyl chloride. The structural formula of pyridine is: ， The structural formula of benzyl chloride is: 。 3. The copper electroplating solution according to claim 2, wherein The molar ratio of pyridine to benzyl chloride is (0.5-1.5):

1.

4. The copper electroplating solution according to claim 2, wherein The preparation method of the leveling agent comprises the following steps: Step S1, heating and stirring pyridine, and adding benzyl chloride dropwise; Step S2, heating the mixture to reflux for reaction, and cooling; Step S3: recrystallize the product with a solvent and filter to obtain benzyl pyridinium chloride, an additive for the copper electroplating solution.

5. The copper electroplating solution according to claim 4, characterized in that: In step S1, the heating temperature is 30-70° C., the stirring speed is 200-600 rpm, and the time is 0.5-3.0 h.

6. The copper electroplating solution according to claim 4, characterized in that: In step S2, the heating temperature is 40-60° C., and the reflux reaction time is 2-4 h.

7. The copper electroplating solution according to claim 4, characterized in that: In step S3, the solvent is petroleum ether, acetone or chloroform.

8. The copper electroplating solution according to claim 4, characterized in that: In step S3, the ratio of the solvent to benzyl chloride is (300-500 mL):1 mol.

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