A cyclodextrin derivative-based cyanide-free gold plating solution and its application

Abstract

This invention pertains to cyanide-free gold plating solutions, specifically a cyclodextrin derivative-based cyanide-free gold plating solution and its applications. It comprises a gold sulfite salt, a primary complexing agent, an auxiliary complexing agent, and a cyclodextrin derivative. The primary complexing agent is a sulfite or a bisulfite salt, and the auxiliary complexing agent is ethylenediamine. This invention, by introducing a cyclodextrin derivative, utilizes supramolecular host-guest recognition technology to achieve a dynamic balance of "reservoir-release" of free ethylenediamine in the plating solution, enabling reversible control of its concentration. This ensures long-term stability of the plating solution while simultaneously protecting the photoresist and improving the plating surface leveling performance. Through a dual mechanism of free ethylenediamine concentration control and interface shielding, it effectively inhibits photoresist swelling and diffusion, making it suitable for fine-pitch micro-bump electroplating.

Description

Technical Field

[0001] This invention pertains to cyanide-free gold plating solutions, specifically relating to a cyclodextrin derivative-based cyanide-free gold plating solution and its applications. Background Technology

[0002] Gold plating, with its excellent conductivity and high corrosion resistance, has become a key protective layer in semiconductor bump manufacturing and chip interconnection. Sulfite-based cyanide-free gold plating systems are gradually replacing traditional cyanide systems due to their environmental friendliness and coating quality advantages. This system often adds ethylenediamine (EDA) as an auxiliary complexing agent to maintain plating solution stability; however, the strong polarity and alkalinity of EDA can interact with photoresist, causing it to swell, soften, and even detach, resulting in "bleed-through" defects that severely limit its application in fine-pitch packaging.

[0003] Therefore, it is necessary to capture and consume excess free ethylenediamine to reduce its erosion of the photoresist. However, this approach has an inherent limitation: because the ethylenediamine is permanently consumed, the concentration of ethylenediamine in the plating bath shows a unidirectional decreasing trend. In continuous electroplating production, ethylenediamine needs to be frequently replenished to maintain the stability of the plating bath, which increases the complexity of process control and operating costs. Summary of the Invention

[0004] This invention provides a cyclodextrin derivative-based cyanide-free gold plating solution and its application, to solve the technical problem that free ethylenediamine in current gold plating solutions will corrode photoresist.

[0005] To solve the above-mentioned technical problems, the present invention provides a cyclodextrin derivative-type cyanide-free gold plating solution, which includes a gold sulfite salt, a main complexing agent, an auxiliary complexing agent and a cyclodextrin derivative, wherein the main complexing agent is a sulfite or a bisulfite salt, and the auxiliary complexing agent is ethylenediamine.

[0006] Cyclodextrin derivatives protect photoresist through two pathways: First, thanks to their unique cavity supramolecular structure (externally hydrophilic and internally hydrophobic), cyclodextrin derivatives can form host-guest inclusion complexes with ethylenediamine through hydrophobic interactions and hydrogen bonds, establishing the following dynamic equilibrium: the ethylenediamine inclusion complex of cyclodextrin is converted into cyclodextrin and free ethylenediamine. This equilibrium endows the plating bath with dual regulatory functions: a reserve function: when the concentration of free ethylenediamine is too high, cyclodextrin includes and stores it, reducing the risk of erosion to the photoresist; a release function: when ethylenediamine is consumed by complex alloy ions, the equilibrium shifts to the left, and the ethylenediamine in the inclusion complex is automatically released to replenish it, maintaining the stability of the plating bath. Second, the hydroxyl groups in the cyclodextrin derivative molecules form a hydrophilic shielding layer on the photoresist surface, blocking the penetration of ethylenediamine. Simultaneously, the differentiated adsorption of cyclodextrin derivatives on the metal surface can generate a cathodic polarization regulation effect, achieving microscopic leveling of the coating.

[0007] The cyclodextrin derivatives refer to natural cyclodextrin and modified cyclodextrin.

[0008] Optionally, the cyclodextrin derivative is β-cyclodextrin or modified β-cyclodextrin.

[0009] Optionally, the cyclodextrin derivative is selected from one or more of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, methyl-β-cyclodextrin, and sulfobutyl ether-β-cyclodextrin, preferably hydroxypropyl-β-cyclodextrin or sulfobutyl ether-β-cyclodextrin.

[0010] Optionally, the gold sulfite is selected from one or more of sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite, and the main complexing agent is selected from one or more of sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, and potassium bisulfite.

[0011] Optionally, the mass concentration ratio of the auxiliary complexing agent to the cyclodextrin derivative is 2:1-100:1, preferably 4:1-20:1.

[0012] Optionally, the concentrations of each component in the plating solution are as follows: gold sulfite, based on the mass of gold ions: 5-20 g / L; main complexing agent: 20-100 g / L; auxiliary complexing agent: 10-60 g / L; cyclodextrin derivative: 0.5-10 g / L.

[0013] Optionally, the concentrations of each component in the plating solution are as follows: gold sulfite, based on the mass of gold ions: 8-15 g / L; main complexing agent: 30-60 g / L; auxiliary complexing agent: 20-40 g / L; cyclodextrin derivative: 1-8 g / L.

[0014] A method for preparing wafer microbumps in semiconductor packaging, which uses the above-mentioned cyclodextrin derivative type cyanide-free gold plating solution for electroplating.

[0015] Optionally, the spacing between the micro-bumps is less than 20 micrometers.

[0016] Optionally, the electroplating current density is 0.1-2.0 ASD and the temperature is 40-60℃; negative photoresist is used in the encapsulation.

[0017] This invention introduces cyclodextrin derivatives and utilizes supramolecular host-guest recognition technology to achieve a dynamic balance of "reservoir-release" of free ethylenediamine in the plating solution, enabling reversible control of its concentration. This ensures the long-term stability of the plating solution while also protecting the photoresist and improving the plating surface leveling performance. Through the dual mechanisms of free ethylenediamine concentration control and interface shielding, it effectively inhibits photoresist swelling and diffusion, making it suitable for fine-pitch micro-bump electroplating. Attached Figure Description

[0018] Figure 1 This is a photograph of the photoresist before it swells in Example 1;

[0019] Figure 2This is a photograph of the photoresist film swelling and cracking in Comparative Example 1;

[0020] Figure 3 This is a photo of the stability test results of the plating solution in Comparative Example 2. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Example 1

[0023] A cyclodextrin derivative-based cyanide-free gold plating solution, comprising the following components:

[0024] Sodium gold sulfite (based on gold ion mass): 10 g / L

[0025] Sodium sulfite: 40 g / L

[0026] Ethylenediamine: 25 g / L

[0027] Hydroxypropyl-β-cyclodextrin 4 g / L

[0028] Adjust the pH to 8.5 with sodium hydroxide and bring the volume to a final volume.

[0029] Preparation method: At room temperature, dissolve sodium sulfite in deionized water, add sodium gold sulfite and stir until transparent, slowly add ethylenediamine salt solution and stir for 10 min, add hydroxypropyl-β-cyclodextrin and stir for 20 min, adjust pH to 8.5 with sodium hydroxide, and bring the volume to 1 L.

[0030] Application method: Using a silicon wafer patterned with photoresist (SU-8 photoresist) as the cathode and a platinum mesh as the anode, electroplating is performed for 15 minutes at a current density of 1 ASD, a temperature of 50°C, and a stirring rate of 60 r / min. The silicon wafer is then removed, rinsed thoroughly with deionized water, and air-dried. This yields wafer microbumps with a spacing of 15 micrometers for semiconductor packaging.

[0031] Photoresist state as Figure 1 As shown.

[0032] Example 2

[0033] A cyclodextrin derivative-based cyanide-free gold plating solution, comprising the following components:

[0034] Potassium gold sulfite (based on gold ion mass): 8 g / L

[0035] Potassium sulfite: 32 g / L

[0036] Ethylenediamine: 20 g / L

[0037] Sulfobutyl ether-β-cyclodextrin: 2 g / L

[0038] Adjust the pH to 8 with sodium hydroxide and bring the volume to a final volume.

[0039] The preparation and application methods are the same as in Example 1.

[0040] Example 3

[0041] A cyanide-free gold plating solution based on sulfurous acid, comprising:

[0042] Sodium gold sulfite (based on gold ion mass): 15 g / L

[0043] Sodium sulfite: 60 g / L

[0044] Ethylenediamine: 40 g / L

[0045] 10 g / L methyl-β-cyclodextrin

[0046] Adjust the pH to 9.5 with potassium hydroxide and bring the volume to a final volume.

[0047] The preparation and application methods are the same as in Example 1.

[0048] Example 4

[0049] The difference from Example 1 is the addition of 5 g / L α-cyclodextrin.

[0050] Application Method: Using a silicon wafer patterned with photoresist (SU-8 photoresist) as the cathode and a platinum mesh as the anode, electroplating was performed for 10 minutes at a current density of 1 ASD, a temperature of 50℃, and a stirring rate of 60 r / min. The silicon wafer was then removed, rinsed thoroughly with deionized water, and air-dried. No photoresist swelling or peeling was observed; after removing the photoresist, the gold pattern edges were neat and there was no plating seepage.

[0051] However, after electroplating for 15 minutes under the same conditions, the silicon wafer was removed, rinsed with deionized water, dried, and the gold plating showed slight seepage at the edges after removing the adhesive.

[0052] In other words, α-cyclodextrin and ethylenediamine have an unstable inclusion complex, which has limited protective effect on the photoresist. As the electroplating time increases, the photoresist film will still swell.

[0053] Plating solution stability: After being placed at 25℃ for 30 days, no sediment was found in the plating solution.

[0054] Example 5

[0055] The difference from Example 1 is that the electroplating time was 1 hour. After removing the silicon wafer, it was rinsed with deionized water and dried. No swelling morphology was observed in the film. In this example, the electroplated layer is thick gold, which is not used in the micro-bump process. Therefore, the roughness and resistivity of the plating layer are not tested; the purpose is only to verify the film's durability.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that no cyclodextrin derivative is added.

[0058] Photoresist condition: such as Figure 2 As shown, the photoresist edges are clearly curled, swollen, and partially detached; after removing the photoresist, there is obvious plating penetration at the edges of the gold plating layer.

[0059] Coating appearance: The coating is reddish with edge effect; Ra=0.45 μm; resistivity 2.4×10⁻⁶ -8 Ω·m.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that the concentration of hydroxypropyl-β-cyclodextrin is 15 g / L.

[0062] Photoresist condition: The photoresist shows no swelling or peeling; after removing the photoresist, there is no obvious plating at the edge of the coating.

[0063] Plating solution stability: After being placed at 25℃ for 30 days, a pink precipitate appeared on the bottom surface of the plating solution. Figure 3 .

[0064] Coating appearance: The coating brightness decreased, and SEM showed that the C and O elements on the coating surface were too high.

[0065] The above embodiments and comparative examples underwent the following performance tests:

[0066] Evaluation of photoresist protection effect: After electroplating, the macroscopic morphology of the photoresist pattern is first observed under an optical microscope (50x), recording whether there are any visible curling, peeling, or flaking. Subsequently, the photoresist is removed, and the morphology of the gold plating layer on the substrate is observed. If irregular metal "tails" or an additional thin layer of gold deposition at the bottom (i.e., "bleed-through") appears after photoresist removal, it is determined that the photoresist has swelled during the electroplating process, and the interfacial adhesion has been damaged. (See figure) Figure 1 The condition is defined as follows: the photoresist shows no swelling or peeling; the gold pattern edges are neat and there is no plating seepage after the photoresist is removed.

[0067] 1. Plating solution stability:

[0068] 2.1 Room temperature test: The plating solution is sealed and left to stand at a constant temperature of 25℃ for a maximum of 90 days. The time when precipitation, yellowing or turbidity occurs is observed and recorded.

[0069] 2.2 Accelerated test: Place at a constant temperature of 60℃ for 72 hours and observe for any precipitation.

[0070] 2. Coating performance: The surface roughness (Ra) of the coating was tested using an atomic force microscope; the gloss and levelness of the coating were observed using an optical microscope; and the resistivity of the coating was tested using a four-probe tester.

[0071] The test results are shown in Table 1.

[0072] Table 1

[0073]

[0074] Performance tests revealed that the addition of cyclodextrin derivatives can effectively inhibit photoresist swelling and diffusion, and has a leveling effect on the coating. However, if the amount added is too large, the plating solution will become unstable, the appearance and roughness of the coating will deteriorate, and the resistivity of the coating will increase, among other adverse effects.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cyclodextrin derivative-based cyanide-free gold plating solution, characterized in that, It includes a gold sulfite salt, a primary complexing agent, a secondary complexing agent, and a cyclodextrin derivative, wherein the primary complexing agent is a sulfite or a bisulfite salt, and the secondary complexing agent is ethylenediamine.

2. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 1, characterized in that, The cyclodextrin derivative is β-cyclodextrin or modified β-cyclodextrin.

3. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 2, characterized in that, The cyclodextrin derivative is selected from one or more of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, methyl-β-cyclodextrin and sulfobutyl ether-β-cyclodextrin, preferably hydroxypropyl-β-cyclodextrin or sulfobutyl ether-β-cyclodextrin.

4. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 1, characterized in that, The gold sulfite salt is selected from one or more of sodium gold sulfite, potassium gold sulfite, and ammonium gold sulfite, and the main complexing agent is selected from one or more of sodium sulfite, potassium sulfite, ammonium sulfite, sodium bisulfite, and potassium bisulfite.

5. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 1, characterized in that, The mass concentration ratio of the auxiliary complexing agent to the cyclodextrin derivative is 2:1-100:1, preferably 4:1-20:

1.

6. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 1, characterized in that, The concentrations of each component in the plating solution are as follows: gold sulfite, based on the mass of gold ions: 5-20 g / L; main complexing agent: 20-100 g / L; auxiliary complexing agent: 10-60 g / L; cyclodextrin derivative: 0.5-10 g / L.

7. The cyclodextrin derivative-type cyanide-free gold plating solution according to claim 6, characterized in that, The concentrations of each component in the plating solution are as follows: gold sulfite, based on the mass of gold ions: 8-15 g / L; main complexing agent: 30-60 g / L; auxiliary complexing agent: 20-40 g / L; cyclodextrin derivative: 1-8 g / L.

8. A method for fabricating wafer microbumps in semiconductor packaging, characterized in that, Electroplating is performed using the cyclodextrin derivative-type cyanide-free gold plating solution described in any one of claims 1-7.

9. The method for preparing wafer microbumps in semiconductor packaging according to claim 8, characterized in that, The spacing between the micro-bumps is less than 20 micrometers.

10. The method for preparing wafer microbumps in semiconductor packaging according to claim 8, characterized in that, The electroplating current density is 0.1-2.0 ASD, and the temperature is 40-60℃; the encapsulation uses negative photoresist.

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