Environment-friendly copper etching solution

Abstract

This invention belongs to the field of chemical etching technology, specifically a copper etching solution. Its components are: 0.1-10% hydrogen peroxide as an oxidant, 0.1-5% ammonium oxalate as a main compounding agent, 0.1-5% hydroxyethylidene diphosphonic acid, 0.001-0.5% surfactant, and the balance being deionized water. This invention is highly environmentally friendly: the system does not contain harmful components such as chlorine and fluorine; the decomposition product of hydrogen peroxide is water, achieving clean production; it has high stability, greatly improving the service life of the etching solution; it produces excellent etching quality; and the wastewater treatment process is simple.

Description

Technical Field

[0001] This invention belongs to the field of chemical etching technology, and specifically relates to a copper etching solution. Background Technology

[0002] In PCB manufacturing, copper etching is a crucial step in forming circuit patterns. Currently, mainstream etching solutions such as acidic copper chloride and alkaline ammonia etching solutions present problems such as environmental pollution (containing chlorine and ammonia), strong equipment corrosion, and severe side etching. Hydrogen peroxide (H2O2), as a green oxidant, decomposes into water, making it an ideal environmentally friendly oxidant. However, the simple hydrogen peroxide-acid system for etching copper has the following drawbacks: poor stability: hydrogen peroxide reacts with metal ions (such as Cu...) 2+ It decomposes rapidly under catalysis, leading to oxidant failure and unstable etching rate. Its cohesive ability is weak: under acidic conditions, it is difficult for a few anions (such as sulfate) to effectively cohede the Cu generated by oxidation. 2+ This leads to Cu 2+ Accumulation of hydrogen peroxide can contribute to its decomposition and potentially form a passivation film on the copper surface, affecting etching uniformity. Poor lateral etching control: Traditional hydrogen peroxide systems have limited control over lateral etching, making them unsuitable for high-precision circuitry. Summary of the Invention

[0003] The purpose of this invention is to provide an environmentally friendly copper etching solution that can stabilize hydrogen peroxide, has strong compatibility, and excellent side etching control.

[0004] The environmentally friendly copper etching solution provided by this invention comprises the following components:

[0005] Oxidizing agent hydrogen peroxide (H2O2): 0.1-10%, preferably 0.4-0.5%, more preferably 0.48%;

[0006] The main complexing agent, ammonium oxalate ((NH4)2C2O4), is 0.1-5%, preferably 2.5-3.5%, and more preferably 3%.

[0007] Auxiliary complexing agents, stabilizers, and grain boundary corrosion inhibitors HEDP (hydroxyethylidene diphosphonic acid): 0.1-5%; preferably 1.5-2%, more preferably 2%;

[0008] Surfactant: 0.001-0.5%, preferably 0.05-0.15%, more preferably 0.1%;

[0009] Deionized water, balance.

[0010] in:

[0011] Hydrogen peroxide (H2O2) is used as the main oxidizing agent to oxidize Cu0 to Cu. 2+Cu + H₂O₂ + 2H₂O + -> Cu 2+ +2H2O;

[0012] The main synergist, ammonium oxalate ((NH4)2C2O4), plays a synergistic role: oxalate ions react with Cu... 2+ It forms a stable, soluble [Cu(C2O4)2] 2- Alternatively, a CuC₂O₄ complex can drive the chemical reaction to the right. It provides ammonium ions (NH₄⁺). + Ammonium ions have a certain pH buffering effect and can slightly promote etching.

[0013] The auxiliary complexing agent and stabilizer HEDP can form an extremely thin protective film on the copper surface, playing a powerful complexing and stabilizing role: HEDP is a powerful organophosphonic acid complexing agent, and its phosphonic acid groups are effective against Cu... 2+ Its chelating ability is extremely strong, which can more firmly "lock in" Cu. 2+ This is key to stabilizing hydrogen peroxide; it effectively blocks Cu. 2+ -> Cu + -> Cu 2+ catalytic cycle.

[0014] The auxiliary agents and stabilizers are grain boundary corrosion inhibitors, specifically HEDP, which is used to suppress excessive corrosion of active sites such as grain boundaries, thus helping to obtain a uniform and smooth etched surface.

[0015] The surfactant can be polyoxyethylene dodecyl ether or other similar surfactants.

[0016] In this invention's environmentally friendly copper etching solution, the synergistic effect of the oxidant hydrogen peroxide (H2O2), the main complexing agent ammonium oxalate ((NH4)2C2O4), the auxiliary complexing agent and stabilizer, and the grain boundary corrosion inhibitor HEDP is as follows: hydrogen peroxide is responsible for oxidation, while ammonium oxalate and HEDP act like two pliers, "grabbing" and dissolving the generated Cu from different angles. 2+ The three work together to achieve a stable, efficient, and high-quality etching process.

[0017] The copper etching solution of the present invention has the following significant advantages:

[0018] Highly environmentally friendly: The system does not contain harmful components such as chlorine and fluorine, and the decomposition products of hydrogen peroxide are water, achieving clean production.

[0019] Excellent stability: Through the synergistic effect of HEDP and ammonium oxalate, Cu in the solution is effectively chelated. 2+ Eliminate Cu 2+ The catalytic decomposition effect on hydrogen peroxide greatly improves the service life of the bath solution.

[0020] Excellent etching quality:

[0021] Low lateral corrosion: Ammonium oxalate and HEDP can react with newly formed Cu 2+ The rapid formation of soluble complexes prevents surface passivation and ensures uniform etching progress, thereby obtaining fine lines with good sidewall verticality.

[0022] Smooth surface: The etched copper surface is clean, without residue or corrosion spots.

[0023] Synergistic effect: Oxalate ion (C2O4) 2- ) and HEDP molecules against Cu 2+ Both have strong compatibility; their combination forms a multi-component complex system that can efficiently process the Cu produced in the reaction. 2+ Removed from the copper surface, maintaining a high etching rate.

[0024] Easy to treat wastewater: Copper in wastewater can be easily recovered through complexation precipitation, and the treatment process is simple. Attached Figure Description

[0025] Figure 1 The images show metallographic microscope photographs and actual photographs of the copper sheet after etching at -25℃ with a formulation of 3% ammonium oxalate + 2% HEDP + 0.48% H2O. (a) is a metallographic microscope image (5X), (b) is a metallographic microscope image (50X), and (c) is an actual photograph of the etched copper sheet.

[0026] Figure 2 The images show metallographic micrographs and photographs of the copper sheet after etching with a formulation of 3% ammonium oxalate + 0.48% H2O at -25℃. Among them, (a) is a metallographic micrograph at 5X, (b) is a metallographic micrograph at 50X, and (c) is a photograph of the copper sheet after etching.

[0027] Figure 3 The images show metallographic micrographs and photographs of the copper sheet after etching at -25℃ with a formulation of 3% ammonium oxalate + % HEDP + 0.48% H2O. (a) is a 5X metallographic micrograph, (b) is a 50X metallographic micrograph, and (c) is a photograph of the etched copper sheet.

[0028] Figure 4 The formulation is 3% HEDP + 0.48% H2O, 25℃, pH adjusted to around 6. Metallographic microscope images and actual photographs are shown after etching. (a) is a 5X metallographic microscope image, (b) is a 50X metallographic microscope image, and (c) is an actual photograph of the etched copper sheet.

[0029] Figure 5The images show metallographic micrographs and photographs of the copper sheet after etching with a formulation of 0.1% glycine + 0.1% H2O2 at -25℃. (a) is a 5X metallographic micrograph, (b) is a 50X metallographic micrograph, and (c) is a photograph of the etched copper sheet.

[0030] Figure 6 The images show metallographic micrographs and photographs of the copper sheet after etching with a formulation of % glycine + 0.48% H2O at -25℃. (a) is a 5X metallographic micrograph, (b) is a 50X metallographic micrograph, and (c) is a photograph of the etched copper sheet.

[0031] Figure 7 Metallurgical microscope images and actual photographs of the copper sheet after etching with 3% phosphoric acid + 0.48% H2O at -25℃ and pH adjusted to around 6 are shown. Among them, (a) is a 5X metallurgical microscope image, (b) is a 50X metallurgical microscope image, and (c) is an actual photograph of the etched copper sheet.

[0032] Figure 8 The images show metallographic microscope photographs and actual photographs of the copper sheet after etching with a formulation of 3% DTPMPA + 0.48% H2O at -25℃ and pH adjusted to around 6. (a) is a 5X metallographic microscope image, (b) is a 50X metallographic microscope image, and (c) is an actual photograph of the etched copper sheet. Detailed Implementation

[0033] The copper etching solution formulation of this invention

[0034] 1. The organophosphonic acid is hydroxyethylidene diphosphonic acid (HEDP), 2-hydroxyphosphonoacetic acid (HPAA), diethylenetriaminepentamethylidene phosphonate (DTPMPA), aminotrimethylenephosphonic acid (ATMP), and phosphoric acid, with the following structural formulas in sequence:

[0035] ;

[0036] The copper sheet used in this experiment was 1cm*2cm*0.1mm.

[0037] 2. The effect of HEDP concentration changes on experimental results

[0038] After verification, the HEDP concentration of 1.5-2.5% showed good etching rate and surface quality for copper; the etching rate and surface quality were optimal at around 2% HEDP concentration. Without HEDP, the etching rate was approximately 493 Å / min, and needle-like blue deposits appeared on the surface. Lower concentrations resulted in blue spots on the surface, while higher concentrations led to white deposits. The experimental results are shown in Table 1 below.

[0039] Table 1

[0040] .

[0041] See details Figure 1 , Figure 2 , Figure 3 As shown.

[0042] 3. Comparison of experimental results for organophosphonic acids

[0043] This invention also validated different formulations with individual additions of phosphoric acid or organic phosphoric acid. The etching rates were generally low and / or the surface quality was poor. The experimental results are shown in Table 2 below:

[0044] Table 2

[0045] .

[0046] See Figure 4 As shown.

[0047] 4. Comparison of experimental results with other patents US7951653 / CN101098989A

[0048] The experimental results are shown in Table 3 below:

[0049] Table 3

[0050] .

[0051] This invention verifies the formulations provided in two patents, US7951653 and CN101098989A. Verification shows that both have relatively slow etching rates for copper, and some formulations have a significant impact on the copper surface. Gold or blue deposits cannot be used in chemical etching solutions for copper wiring formation processes in semiconductor devices or printed circuit boards (PCBs). See also... Figure 5 , Figure 6 .

[0052] 5. Comparative experimental results of other organophosphates combined with ammonium oxalate

[0053] This invention verifies different formulations of phosphoric acid or organic phosphoric acid combined with 3% ammonium oxalate. The etching rate is still relatively low and / or the surface quality is poor. The experimental results are shown in Table 4 below:

[0054] Table 4

[0055] .

[0056] 6. Effects of different pH values ​​on etching rate and surface quality

[0057] This invention uses different phosphoric acids or organic phosphoric acids added individually to the formulation and adjusts the pH to around 6 with KOH to conduct comparative experiments to verify the effect of pH on this experiment. It proves that the change of pH value has different effects on the etching rate of copper by different phosphoric acids or organic phosphonic acids. The experimental results are shown in Table 5 below. Conclusion: The surface and corrosion rate of copper are affected differently without the addition of the complexing agent ammonium oxalate, but the surface effect and corrosion rate are not as good as the formulation with the addition of the complexing agent ammonium oxalate.

[0058] Table 5

[0059] .

[0060] See Figure 7 , Figure 8 As shown.

[0061] 7. Effects of different temperatures on etching rate and surface quality

[0062] This invention also verifies the etching rate of copper under increased temperature conditions, confirming that appropriately increasing the etching temperature can improve the etching rate of copper. The experimental results are shown in Table 6 below:

[0063] Table 6

[0064] .

[0065] 8. Testing the corrosion rate of other metals such as Ti and Al.

[0066] This invention also verified the selectivity of the formulation for different metals. Besides having a relatively high corrosion rate for copper, this formulation showed good selectivity for other metals such as titanium, aluminum, and copper wafers. The experimental results are shown in Table 7 below:

[0067] Table 7

[0068] .

[0069] 9. Life test:

[0070] This invention also conducted a lifespan experiment on the formulation, verifying corrosion after 1 day, 3 days, and 8 days. The results showed that the formulation had little impact on the corrosion rate after prolonged storage. The experimental results are shown in Table 8 below:

[0071] Table 8

[0072] .

[0073] 10. Increased hydrogen peroxide concentration

[0074] This invention also verified the effect of increasing hydrogen peroxide concentration. Experiments showed that increasing the hydrogen peroxide concentration had little impact on the corrosion rate of this formulation system. The experimental results are shown in Table 9 below:

[0075] Table 9

[0076] .

Claims

1. An environmentally friendly copper etching solution, characterized in that, Its components, by weight percentage, are: The oxidizing agent, hydrogen peroxide, is 0.1-10%. The main compounding agent, ammonium oxalate, is 0.1-5%. Hydroxyethylidene diphosphonic acid: 0.1-5%; The surfactant content is 0.001-0.5%; Deionized water, balance.

2. The environmentally friendly copper etching solution according to claim 1, characterized in that, Its components, by weight percentage, are: The oxidizing agent, hydrogen peroxide, is at a concentration of 0.4-0.5%. The main compounding agent, ammonium oxalate, is 2.5-3.5%. Hydroxyethylidene diphosphonic acid: 1.5-2%; The surfactant content is 0.05-0.15%; Deionized water, balance.

3. The environmentally friendly copper etching solution according to claim 1 or 2, characterized in that, The surfactant is polyoxyethylene dodecyl ether, or a similar surfactant.

Images