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 copper electroplating solution additive is a Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol, and the structural formula of the Schiff base compound is: #imgabs0# The copper electroplating solution additive is synthesized from 5-amino-1,3,4-thiadiazole-2-thiol and 2-naphthaldehyde; the copper electroplating 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 the copper electroplating solution additive. Compared with the prior art, the present invention can obtain blind hole copper plating filling without gaps and voids, and the surface of the plated layer is bright and smooth. The thickness of the copper layer obtained by electroplating is reduced from 36.2 μm when 5-amino-1,3,4-thiadiazole-2-thiol is used as the additive to 23.9 μm. The Schiff base compound can be used as an effective leveler for copper electroplating.

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] In recent years, with the rapid development of multifunctional microelectronic devices, the demand for high-density interconnects in printed circuit boards (PCBs) and integrated circuits (ICs) has increased dramatically. Copper electrodeposition is a key process for manufacturing high-density interconnect metals in microelectronic devices, and blind and through-hole filling with copper electrodeposition are two primary technologies for PCB electrical interconnects. Void-free filling of blind and through-hole vias generally indicates high-quality microvias, which means high stability and reliability of microelectronic devices. However, achieving uniform filling while achieving level copper deposition is a significant challenge.

[0003] Because uneven current density distribution exacerbates the difficulty of achieving uniform deposited layers, using only a basic electroplating solution is not sufficient. Therefore, organic additives are added to achieve bottom-up micropore filling. Three typical types of organic additives include accelerators, inhibitors, and levelers. Accelerators, such as sodium polydisulfide (SPS), inhibitors, such as polyethylene glycol (PEG), and levelers play a crucial role in the accelerator-inhibitor-leveler system to achieve uniform copper deposition.

[0004] Among all additives, levelers play a key role in void-free filling of microvias. This filling is based on convection-related adsorption behavior, such as its dependence on pore location. Currently, a significant amount of research is focusing on novel non-dye levelers. While there are a wide variety of non-dye leveler molecules, the most reported are nitrogen-containing aromatic heterocyclic compounds, such as low-molecular-weight tetrahydrothiazolidinethiones, small-molecule tetrazole derivatives, and benzotriazoles, as well as high-molecular-weight quaternary ammonium salts of polyethyleneimine alkyl compounds. To obtain even higher-performance hole-filling electroplating leveler molecules, some researchers have begun to design and synthesize novel leveler molecules. For example, Chen Biao et al. (Chen B., Xu J., Wang L., et al. Synthesis of Quaternary Ammonium Salts Based on Diketopyrrolopyrroles Skeletons and Their Applications in Copper Electroplating [J]. ACS Appl Mater Interfaces, 2017, 9 (8): 7793-7803) designed and synthesized four quaternary ammonium salts based on diketopyrrolopyrrole skeletons with different alkyl chain lengths and studied their effects in the electrodeposition process. The results showed that these four diketopyrrolopyrrole (DPP) derivatives all had an inhibitory effect on copper electrodeposition, and their inhibitory effect was closely related to the length of the alkyl chain contained in the DPP derivatives. 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 five diketopyrrolopyrrole-based quaternary ammonium salts with different aryl substituents (H - 、CI - 、CH 3- Br - and CF 3- ) of DPP derivatives, which have 100% water solubility and different surface activities. 3--DPP levelers have great advantages in inhibiting copper deposition. Wang Kang et al. (Wang K., Feng J., Xu J., et al. Engineering aromatic heterocycle strategy: Improving copper electrodeposition performance via tuning the bandgap of diketopyrrolopyrrole-based leveler [J]. Tetrahedron, 2020, 76 (5), 130882) synthesized four DPP-based quaternary ammonium salts and replaced the aromatic groups of traditional DPP with various heterocycles to obtain a smaller band gap to improve copper electrodeposition performance. However, there are not many reports on the independent synthesis of new leveler molecules, and it is particularly important to continue to develop and design the synthesis of new high-efficiency levelers.

[0005] Patent CN113502512A discloses a copper electroplating solution additive, a copper electroplating solution, and an electroplating method. The copper electroplating solution additive includes 1-10 parts of an accelerator, 150-300 parts of an inhibitor, and 1-20 parts of a leveler. The accelerator is sodium polydisulfide dipropane sulfonate, the inhibitor is any one or a combination of polyethylene glycol-6000, polyethylene glycol-8000, and polyethylene glycol-10000, and the leveler is 5-amino-1,3,4-thiadiazole-2-thiol. However, the copper layer obtained by electroplating with the electroplating solution disclosed in this patent is still relatively thick and needs to be further thinned. Summary of the Invention

[0006] The purpose 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 the defects of the above-mentioned prior art. The Schiff base compound of the present invention is used as a leveling agent in the copper electroplating process to obtain blind hole copper plating filling without gaps and voids, and the surface of the plated layer is bright and flat. The thickness of the copper layer obtained by electroplating is reduced from 36.2μm to 23.9μm.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide an electroplating copper solution additive, which is a derivative of 5-amino-1,3,4-thiadiazole-2-thiol, namely a Schiff base compound, and the structural formula of the Schiff base compound is:

[0009]

[0010] 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 5-amino-1,3,4-thiadiazole-2-thiol and 2-naphthaldehyde.

[0011] The structural formula of 5-amino-1,3,4-thiadiazole-2-thiol is:

[0012]

[0013] The structural formula of 2-naphthaldehyde is:

[0014]

[0015] Furthermore, the molar ratio of the 5-amino-1,3,4-thiadiazole-2-thiol to 2-naphthaldehyde is (0.5-1.5):1.

[0016] Furthermore, the preparation method comprises the following steps:

[0017] Step S1, 5-amino-1,3,4-thiadiazole-2-thiol, 2-naphthaldehyde and a solvent are added and mixed in a three-necked flask;

[0018] Step S2, heating the mixture to reflux for reaction, and transferring the compound after the reaction is completed to a round-bottom flask;

[0019] Step S3: using a rotary evaporator to remove most of the solvent by distillation under reduced pressure, solid matter is precipitated, and a dark yellow solid additive is obtained by filtration.

[0020] Furthermore, the solvent in step S1 is anhydrous ethanol.

[0021] Furthermore, in step S1, the usage ratio of the solvent to 2-naphthaldehyde is (2.5-7.5L):1mol.

[0022] Furthermore, in step S2, the temperature of the heating reflux reaction is 40-60° C. and the time is 3-6 hours.

[0023] Furthermore, in step S3, the pressure of the reduced pressure distillation is 0.07-0.09 MPa, the temperature is 40-50° C., and the time is 2-6 h.

[0024] 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 polydipropylene glycol sulfonate, the inhibitor is polyethylene glycol-6000, and the leveler is the copper electroplating solution additive prepared by the preparation method.

[0025] 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 1-15 ppm.

[0026] The material synthesized by the present invention has the following advantages:

[0027] (1) The aromatic ring can undergo electrophilic reactions, making the derivatives easily adsorbed on the cathode surface;

[0028] (2) The planar structure of the molecule will help the derivative molecules to adsorb on the cathode surface, preventing copper ions in the solution from reaching the cathode surface and inhibiting copper electrodeposition.

[0029] Therefore, the present invention designs and synthesizes the substance for use in the copper electroplating process, which can obtain blind hole copper electroplating filling without gaps and voids, and the surface of the plated layer is bright and smooth.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) The Schiff base compound of the present invention is used as a leveling agent in the copper electroplating process, and synergistically acts with an accelerator and an inhibitor to obtain blind hole copper plating filling without gaps and voids, and the surface of the plated layer is bright and smooth;

[0032] (2) The Schiff base compound of the present invention is used as a leveler in the copper electroplating process. The aromatic ring and planar structure of the molecule help the derivative molecule to adsorb on the cathode surface, preventing copper ions in the solution from reaching the cathode surface, inhibiting copper electrodeposition, and reducing the thickness of the copper layer obtained by electroplating from 36.2 μm to 23.9 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a lowest unoccupied molecular orbital (LUMO) diagram of the copper electroplating solution additive in Example 1 of the present invention;

[0034] Figure 2 is the highest occupied molecular orbital (HOMO) diagram of the copper electroplating solution additive in Example 1 of the present invention;

[0035] Figure 3 This is a metallographic image of a blind hole of an electroplated PCB test board in Example 1 of the present invention;

[0036] Figure 4 This is a metallographic image of a blind hole of an electroplated PCB test board in Example 2 of the present invention;

[0037] Figure 5 This is a metallographic image of a blind hole of an electroplated PCB test board in Example 3 of the present invention;

[0038] Figure 6 This is a metallographic image of a blind hole in an electroplated PCB test board in a comparative example of the present invention;

[0039] 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;

[0040] Figure 8 This is a FE-SEM morphology image of copper deposited on the surface of the electroplated PCB test board in Example 2 of the present invention;

[0041] Figure 9 This is a FE-SEM morphology image of copper deposited on the surface of the electroplated PCB test board in Example 3 of the present invention;

[0042] Figure 10 This is a FE-SEM morphology image of copper deposited on the surface of the electroplated PCB test board in the comparative example of the present invention. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] Example 1:

[0046] A copper electroplating solution additive and a preparation method thereof, the preparation method comprising the following steps:

[0047] In a 100 mL three-necked flask, 0.01 mol of 5-amino-1,3,4-thiadiazole-2-thiol and 0.01 mol of 2-naphthaldehyde were added, respectively, with 50 mL of anhydrous ethanol as the solvent; the reaction was heated under reflux at 50°C for 4 hours, and the compound after the reaction was completed was transferred to a round-bottom flask; the pressure was reduced to 0.08 MPa using a rotary evaporator, and the solvent was removed by distillation at 45°C for 3 hours. Solid matter precipitated and was filtered to obtain a dark yellow solid, which was a Schiff base compound derivative of 5-amino-1,3,4-thiadiazole-2-thiol, an additive for electroplating copper solutions.

[0048] like Figure 1 As shown in Figure 2, the electron cloud density is mainly distributed on the N=C double bond and the benzene ring, indicating that these groups are active sites for copper ion attack. Figure 2As shown in the figure, the electron cloud density is mainly concentrated on the SH bond and the five-membered heterocyclic nitrogen, which indicates that the Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol can strongly adsorb on the copper surface by donating the lone pair electrons in these heteroatoms to the unoccupied orbitals of copper.

[0049] According to frontier molecular orbital theory, the energy of HOMO and LUMO is often related to the electron donating ability and electron accepting ability, E HOMO The larger the value, the stronger the ability of the leveler to provide electrons. LUMO The smaller the value of , the stronger the ability of the leveler to accept electrons. HOMO and E LUMO The value of ΔE only reflects the tendency of electrons to donate or withdraw, but does not fully reflect the adsorption stability of a molecule during electroplating on a metal surface. ΔE is often used to characterize the stability of the adsorption layer of metal surface levelers. The quantum chemical calculation results for the Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol are listed in Table 1.

[0050] Table 1 Quantum chemical calculation results of Schiff base compounds of 5-amino-1,3,4-thiadiazole-2-thiol

[0051]

[0052] As shown in Table 1, the energy gap ΔE = 3.4483. The calculation results show that the Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol has a strong adsorption ability on the copper surface as a leveling agent, and can effectively inhibit copper deposition.

[0053] An application of a copper electroplating solution additive in a copper electroplating process comprises the following steps:

[0054] (1) preparing a copper sulfate pentahydrate aqueous solution, adding sulfuric acid, adding chloride ions, an accelerator SPS, an inhibitor PEG-6000 and a leveling agent electroplating copper solution additive to obtain an electroplating solution, and the specific process is as follows:

[0055] 220 g of copper sulfate pentahydrate was dissolved in 1 L of deionized water, 29.9 ml of sulfuric acid was slowly added, and chloride ions, SPS, PEG-6000, and a copper electroplating solution additive were added to obtain a plating solution with a chloride ion concentration of 50 ppm, an SPS concentration of 1 ppm, a PEG-6000 concentration of 200 ppm, and a copper electroplating solution additive concentration of 0.5 ppm.

[0056] (2) Test board pre-treatment, the specific process is:

[0057] Soak the test board in ethanol for 3 minutes to remove contaminants on the test board surface, and rinse it with deionized water. Then, place the test board in a 1 mol / L dilute sulfuric acid solution and shake it evenly for 3 minutes to remove oxides on the copper layer surface and ensure that the copper surface undergoes relevant reactions during the electroplating process.

[0058] (3) Place the pretreated test plate as the cathode and the phosphorus-containing copper plate as the anode in the electroplating solution, turn on the air pump, and pass 0.25L / min of air flow through the electroplating tank for stable stirring. Pass direct current to the cathode and anode with a current density of 1.5A / dm 2 , electroplating is completed after 75 minutes of power on.

[0059] Example 2:

[0060] An application of the copper electroplating solution additive prepared by the preparation method described in Example 1 in a copper electroplating process, except that the concentration of the copper electroplating solution additive is 1 ppm.

[0061] Example 3:

[0062] An application of the copper electroplating solution additive prepared by the preparation method described in Example 1 in a copper electroplating process, except that the concentration of the copper electroplating solution additive is 3 ppm.

[0063] Depend on Figure 3 、 4 , 5, 7, 8 and 9 show that the Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol is used for electroplating copper blind hole filling. It can be seen that the blind hole is deposited from the bottom up, without voids and pores, and the surface of the coating is bright and smooth, which can effectively prevent the disadvantage of unstable transmission due to blind hole voids and has better stability and reliability.

[0064] like Figure 3 and 7 As shown in FIG, when 0.5 ppm of the electroplating copper additive of the present invention is added, copper is preferentially deposited at the bottom of the micropores. Although the filling from bottom to top is relatively uniform, the blind hole filling performance is poor, and there are still tiny particles on the surface of the copper layer. Figure 4 and 8 As shown in Figure 2, as the concentration increases to 1ppm, the blind hole filling performance becomes better and better, the copper layer surface becomes smoother, and the particle size becomes smaller. Figure 5 and 9 As shown in the figure, when the concentration is 3ppm, the filling efficiency is the best, the blind hole is completely filled from bottom to top, and the copper surface is the smoothest and flattest.

[0065] Comparative Example:

[0066] The use of an electroplating copper solution additive in the electroplating copper process is basically similar to that of Example 3, except that the leveler is 3 ppm 5-amino-1,3,4-thiadiazole-2-thiol.

[0067] like Figure 5 、 6 As shown in Figures 9 and 10, the Schiff base compound synthesized on the basis of 5-amino-1,3,4-thiadiazole-2-thiol in the present invention can obtain blind hole electroplating copper filling without gaps and voids, and the surface of the plated layer is bright and flat. The thickness of the copper layer obtained by electroplating is reduced from 36.2μm to 23.9μm. The Schiff base compound can be used as an effective leveling agent for electroplated copper.

[0068] 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 additive, characterized in that The additive is a Schiff base compound of 5-amino-1,3,4-thiadiazole-2-thiol, and the structural formula of the Schiff base compound is:

2. A method for preparing the copper electroplating solution additive according to claim 1, characterized in that: The additive is synthesized from 5-amino-1,3,4-thiadiazole-2-thiol and 2-naphthaldehyde. The structural formula of 5-amino-1,3,4-thiadiazole-2-thiol is: The structural formula of 2-naphthaldehyde is:

3. The method for preparing a copper electroplating solution additive according to claim 2, wherein: The molar ratio of the 5-amino-1,3,4-thiadiazole-2-thiol and 2-naphthaldehyde is (0.5-1.5):

1.

4. The method for preparing a copper electroplating solution additive according to claim 2 or 3, characterized in that: The preparation method comprises the following steps: Step S1, mixing 5-amino-1,3,4-thiadiazole-2-thiol, 2-naphthaldehyde and a solvent; Step S2, heating the mixture to reflux for reaction; Step S3, removing the solvent by distillation under reduced pressure, precipitating the solid matter, and filtering to obtain the additive.

5. The method for preparing a copper electroplating solution additive according to claim 4, characterized in that: The solvent in step S1 is ethanol.

6. The method for preparing a copper electroplating solution additive according to claim 4, characterized in that: In step S1, the usage ratio of the solvent and 2-naphthaldehyde is (2.5-7.5L):1mol.

7. The method for preparing a copper electroplating solution additive according to claim 4, characterized in that: The temperature of the heating reflux reaction in step S2 is 40-60° C. and the time is 3-6 hours.

8. The method for preparing a copper electroplating solution additive according to claim 4, characterized in that: The pressure of the reduced pressure distillation in step S3 is 0.07-0.09 MPa, the temperature is 40-50° C., and the time is 2-6 h.

9. A copper electroplating solution, characterized in that The solution comprises copper sulfate, sulfuric acid, an accelerator, an inhibitor and a leveler, wherein the accelerator is sodium polydipropylene glycol sulfonate, the inhibitor is polyethylene glycol-6000, and the leveler is a copper electroplating solution additive prepared by the preparation method according to any one of claims 2 to 8, and the concentration of the leveler is 1 to 15 ppm.

10. The copper electroplating solution according to claim 9, characterized in that: The concentration of the accelerator is 1-10 ppm, and the concentration of the inhibitor is 150-300 ppm.

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