Cyanide-free gold plating solution and electroplating method for gold plating of micro blind holes

Abstract

The present application provides a cyanide-free gold plating solution and electroplating method for gold plating of micro blind holes. The cyanide-free gold plating solution includes the following components: cyanide-free water-soluble gold ions, a main complexing agent, an auxiliary complexing agent, a brightener, a penetrant, a leveler and a stabilizer, and the solvent is water; the penetrant is a betaine derivative, and contains at least one long carbon chain alkyl or long carbon chain amide structure. The present application can significantly reduce the surface tension of the gold plating solution by adding a betaine derivative as a penetrant, and can better wet the micro blind hole during the electroplating process. The gold plating solution can smoothly enter the bottom of the micro blind hole for electrochemical reaction, and the bottom and the top are gold-plated simultaneously to form a complete and tightly fitted solid gold plating layer on the micro blind hole, which has good stability and high reliability in subsequent assembly and processing, thereby improving the quality of semiconductor devices.

Description

Technical Field

[0001] The present application relates to the technical field of electroplating, and in particular to a cyanide-free gold plating solution and an electroplating method for gold plating of micro blind holes. Background Art

[0002] Gold has the advantages of good conductivity, stable chemical properties, low hardness, easy wire bonding, and easy sintering, and is one of the most commonly used metals in the semiconductor manufacturing process. As semiconductors develop towards miniaturization and intelligence, the metal wiring layers of chips are becoming more and more complex, the dielectric layers between different wiring layers are gradually becoming thicker, and the depth-to-width ratio of interconnected holes is also increasing, forming smaller micro blind holes.

[0003] Traditional gold plating liquid and electroplating process easily lead to the growth rate of gold plating near the top of the micro blind hole opening being higher than that at the bottom, gradually forming a "self-masking" phenomenon. The "self-masking" at the top further makes it more difficult to exchange the gold plating liquid at the bottom of the hole. When the gold plating at the top of the micro blind hole grows to a certain extent, it becomes closed. The bottom of the micro blind hole is completely unable to exchange gold plating liquid with the outside world and stops growing the gold plating. Therefore, a cavity or gap closed from the top will be formed. In addition, the gold-plated micro blind hole will be subject to stress from the installation operation in subsequent further processing. Due to the presence of cavities and slits at the bottom, the gold plating at the top will be separated from the hole wall of the micro blind hole due to external stress, forming a larger gap, which greatly affects the final performance of the semiconductor device. In the future, the gold plating layer will become loose or even fall off directly, causing reliability problems.

[0004] On the other hand, mature gold plating processes at home and abroad mainly use cyanide gold salts for gold plating, which has good chemical stability, bright coating, good dispersion ability and depth ability, but cyanide gold plating solution is very toxic and has a great destructive effect on humans and the environment. Cyanide-free electroplating process can reduce environmental pollution, but the stability of cyanide-free gold plating solution is poor and the service life of the plating solution is short, which affects the actual promotion and application.

[0005] In view of the above shortcomings, the inventors have actively explored a cyanide-free gold plating solution for gold plating of micro blind holes, which can meet the needs of not using cyanide preparations while improving the quality of gold plating of micro blind holes. Summary of the invention

[0006] Based on this, the present application provides a cyanide-free gold plating solution and an electroplating method for gold plating of micro blind holes. The cyanide-free gold plating solution for gold plating of micro blind holes adds a betaine derivative as a penetrant to reduce the surface tension of the gold plating solution. For micro blind holes with a relatively large depth-to-width ratio, the electroplated gold coating can completely fill the space inside the micro blind holes, thereby achieving void-free and gap-free gold plating of the micro blind holes, thereby meeting the performance requirements of subsequent processing of semiconductor devices.

[0007] The specific technical solution of this application is:

[0008] In the first aspect, the present application provides a cyanide-free gold plating solution for gold plating of micro blind holes, wherein the cyanide-free gold plating solution for gold plating of micro blind holes comprises the following components: cyanide-free water-soluble gold ions, a main complexing agent, an auxiliary complexing agent, a brightener, a penetrant, a leveling agent, and a stabilizer; the solvent is water; the penetrant is a betaine derivative, and the nitrogen atom in the quaternary ammonium base structure of the betaine derivative is connected to at least one long carbon chain alkyl structure or an amide structure containing a long carbon chain alkyl, and the amide structure containing a long carbon chain alkyl is: -RN-CO-R', wherein R is an alkyl group containing 1-3 carbon atoms, and R' is a long carbon chain alkyl group.

[0009] In some embodiments, the opening diameter of the micro blind hole is ≤2 μm and the aspect ratio is ≥2:1, and the penetrant comprises at least the structural formula: (R1R2R3N + )-R4-(O x AO - ), at least one of R1, R2 and R3 is the long carbon chain alkyl structure or the amide structure containing a long carbon chain alkyl, the long carbon chain alkyl is a straight chain alkyl having more than or equal to ten carbon atoms, R4 is a carbon chain having 1 to 3 carbon atoms, and in the structural formula (O x AO - ) is connected to the R4 carbon chain, the A atom can be selected from carbon, sulfur or phosphorus, x is 1 or 2, and the A atom is connected to at least one of the x oxygen atoms by a double bond.

[0010] In some embodiments, the added concentration of the osmotic agent is: 10-90 mg / L, and the osmotic agent is one or more of myristyl betaine, lauroyl propyl betaine, cocamidopropyl betaine, dodecyl dimethyl betaine, 3-sulfopropyl hexadecyl dimethyl betaine, 3-sulfopropyl tetradecyl dimethyl betaine, 3-sulfopropyl dodecyl dimethyl betaine, phosphate betaine, coconut oil phosphate betaine, dodecyl hydroxypropyl phosphate betaine, tetradecyl hydroxypropyl phosphate betaine, hexadecyl hydroxypropyl phosphate betaine and octadecyl hydroxypropyl phosphate betaine.

[0011] In some embodiments, the cyanide-free water-soluble gold ions satisfy the following conditions simultaneously: a: the source of the cyanide-free water-soluble gold ions is one or more gold-containing compounds selected from gold sulfite, gold thiosulfate, tetrachloroauric acid and tetrachloroauric acid salts; b: the amount of the gold-containing compound added is measured based on the added concentration of the cyanide-free water-soluble gold ions, and the added concentration of the cyanide-free water-soluble gold ions is 10-15 g / L.

[0012] In some embodiments, the cyanide-free gold plating solution satisfies the following conditions at the same time: c: the main complexing agent is sulfite; d: the added concentration of the main complexing agent is 20-150 g / L; e: the auxiliary complexing agent is one or two of 2-[(2-carboxyethyl)thio]nicotinic acid and 2-mercapto-3-pyridinecarboxylic acid. When the auxiliary complexing agent contains both the 2-[(2-carboxyethyl)thio]nicotinic acid and the 2-mercapto-3-pyridinecarboxylic acid, the mass ratio of the 2-[(2-carboxyethyl)thio]nicotinic acid to the 2-mercapto-3-pyridinecarboxylic acid is: (1-10):1; f: the added concentration of the auxiliary complexing agent is 5-20 g / L.

[0013] In some embodiments, the brightener satisfies the following conditions simultaneously: g: the brightener is polydimethyldiallylammonium chloride; h: the added concentration of the brightener is 5-35 mg / L.

[0014] In some embodiments, the leveler also satisfies the following conditions: i: the leveler is 6-nitrocoumarin; j: the added concentration of the leveler is 1-25 mg / L.

[0015] In some embodiments, the stabilizer also satisfies the following conditions: k: the stabilizer is a nitrogen-containing heterocyclic compound; m: the added concentration of the stabilizer is 30-150 mg / L.

[0016] In some embodiments, the stabilizer is ethyl N-benzyl-3-oxopiperidine-4-carboxylate hydrochloride.

[0017] In some embodiments, the cyanide-free gold plating solution includes the following components in mass concentration: potassium gold sulfite 25-37.5 g / L, potassium sulfite 20-150 g / L, 2-[(2-carboxyethyl)thio]nicotinic acid 5-20 g / L, polydimethyldiallylammonium chloride 5-35 mg / L, 6-nitrocoumarin 1-25 mg / L, 3-sulfopropyl hexadecyl dimethyl betaine 10-90 mg / L, N-benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 30-150 mg / L, and the solvent is pure water. The gold ion concentration corresponding to the 25-37.5 g / L potassium gold sulfite is 10-15 g / L.

[0018] In a second aspect, the present application provides a method for electroplating gold for micro blind holes, wherein the electroplating method adopts any of the aforementioned cyanide-free gold plating solutions, and the electroplating method satisfies the following conditions at the same time: n: the electroplating temperature is 50-65°C; o: the pH of the gold plating solution is 7.5-9.5; p: the current density is 0.05-0.8A / dm 2 ;q: The electroplating method is spraying.

[0019] Compared with the prior art, this application has the following advantages:

[0020] (1) This application uses cyanide-free water-soluble gold ions in combination with corresponding main complexing agents, auxiliary complexing agents and stabilizers to form a cyanide-free gold plating solution with good stability, which prolongs the service life, is suitable for industrial-scale production, and is safe and environmentally friendly.

[0021] (2) The present application adds betaine derivatives as penetrants, which can significantly reduce the surface tension of the gold plating solution and better wet the micro blind holes during the electroplating process, especially the solid micro blind holes with an opening diameter of ≤2μm and a depth-to-width ratio of ≥2:1 that are difficult to electroplate. The gold plating solution can smoothly enter the bottom of the micro blind hole for electrochemical reaction, and the bottom and the top are gold plated simultaneously, forming a complete and tightly fitted solid gold plating layer on the micro blind hole, which has good stability and high reliability in subsequent assembly processing, thereby improving the quality of semiconductor devices.

[0022] (3) The cyanide-free gold plating solution for gold plating of micro blind holes of the present application reduces the overall roughness by selecting a suitable brightener and a leveling agent, effectively preventing the formation of large particle protrusions that increase the difficulty of subsequent other processes. The surface of the gold plating layer is smoother and brighter, thereby improving the texture and appearance of the semiconductor device.

[0023] (4) The present application is a method for electroplating gold in micro blind holes, which adopts a spray plating method instead of a traditional vertical hanging plating method, and sets the main flow direction of the gold plating solution to be parallel to the axial direction of the micro blind hole, so that the gold plating solution can enter the interior of the micro blind hole more smoothly, thereby ensuring the gold ion concentration in the micro blind hole. Under the condition of a higher current density, the gold deposition rate near the bottom of the hole can also be ensured, thereby ensuring the continuity of the gold plating layer and preventing the occurrence of undesirable phenomena such as voids or slits in the hole in the gold plating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the description of the present application will be briefly introduced below.

[0025] Figure 1 This is an electron microscope image of a longitudinal section of a gold-plated blind micro-hole in Example 1, magnified 5,000 times;

[0026] Figure 2 This is an electron microscope image of a longitudinal section of the gold-plated micro blind hole in Example 2, magnified 5,000 times.

[0027] Figure 3 The 3D microscopic morphology of the surface of the gold-plated micro blind hole in Example 3 after magnification 20,000 times.

[0028] Figure 4 This is an electron microscope image of a longitudinal section of the gold-plated blind micro-hole in Comparative Example 1, magnified 5,000 times.

[0029] Figure 5 This is an electron microscope image of a longitudinal section of the gold-plated blind micro-hole in Comparative Example 2, magnified 5,000 times. DETAILED DESCRIPTION

[0030] Examples of the present embodiment are described in detail below. The examples are only used to explain the present embodiment and are not to be construed as limiting the present embodiment.

[0031] In the description of the present application embodiment, it should be noted that all ranges disclosed in the present application will be understood as covering any and all sub-ranges included therein. For example, the stated range "10 to 15g / L" should be deemed to include any and all following sub-ranges: it starts with a minimum value of 10g / L or greater, and ends with a maximum value of 15g / L or less, for example, 10 to 12g / L or 11 to 13g / L or 12 to 14g / L. At the same time, all ranges disclosed in the present application are also deemed to include the endpoints of the scope, unless otherwise explicitly stated. For example, the range "between 7.5 and 9.5" or "7.5 to 9.5" or "7.5-9.5" should generally be deemed to include endpoints 7.5 and 9.5.

[0032] Herein, unless otherwise specified, ratio refers to mass ratio and percentage refers to mass percentage.

[0033] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0034] The present application targets micro blind holes with a pore size of ≤2μm and a depth-to-width ratio of ≥2:1, which are difficult to solidly gold plate. A specific betaine derivative is selected as a penetrant, which can effectively reduce the surface tension of the gold plating solution, thereby making it easier to infiltrate the bottom of the micro blind hole with a single-side opening, a small pore size and a long depth, thereby achieving simultaneous gold plating on the top and bottom of the micro blind hole and improving the quality of the plating layer. At the same time, a cyanide-free raw material is selected to produce water-soluble gold ions, and a main complexing agent and an auxiliary complexing agent are compounded to complex the water-soluble gold ions to increase the solubility and stability of the metal ions in the solution. In addition, a stabilizer is added to prevent the uncomplexed free gold ions from being reduced to cause the precipitation of elemental gold, thereby improving the overall stability of the gold plating solution system, thereby extending the service life and improving the utilization rate of raw materials.

[0035] In general, the inventors of this case selected a cyanide-free gold plating liquid system, which is environmentally friendly and harmless, and also optimized the formula, added a variety of chelating agents and compounded stabilizers to ensure the stability of the gold plating liquid system; on the other hand, for micro blind holes with a relatively large depth and width, betaine derivatives were innovatively added to effectively reduce the surface tension of the gold plating liquid, thereby smoothly infiltrating the bottom of the micro blind hole and achieving uniform growth of gold crystals on the inner wall of the micro blind hole, forming a high-quality gold plating layer with no voids or slits inside and tightly fitting the wall of the micro blind hole on the outside.

[0036] In some embodiments, the source of the cyanide-free water-soluble gold ions is one or more gold-containing compounds selected from the group consisting of gold sulfite, gold thiosulfate, tetrachloroauric acid and tetrachloroauric acid salts. Furthermore, the amount of the gold-containing compounds added is measured based on the added concentration of gold ions of 10-15 g / L.

[0037] Furthermore, the source of the cyanide-free water-soluble gold ions is gold sulfite. Specifically, the gold sulfite can be selected from one of potassium gold sulfite, sodium gold sulfite and ammonium gold sulfite.

[0038] In some embodiments, the main complexing agent is a sulfite, and the added concentration is 20-150 g / L, for example, 70-100 g / L, which is used to ionize and produce sulfite in the gold plating solution, capture and complex free gold ions, and the sulfite is preferably potassium sulfite; the auxiliary complexing agent is one or two of 2-[(2-carboxyethyl)thio]nicotinic acid and 2-mercapto-3-pyridinecarboxylic acid. When 2-[(2-carboxyethyl)thio]nicotinic acid and the 2-mercapto-3-pyridinecarboxylic acid are included at the same time, the mass ratio of the 2-[(2-carboxyethyl)thio]nicotinic acid to the 2-mercapto-3-pyridinecarboxylic acid is: (1-10):1, and the total added concentration of the auxiliary complexing agent is 5-20 g / L, for example, 15-20 g / L, the auxiliary complexing agent works synergistically with the main complexing agent potassium sulfite in the gold plating solution to complex free gold ions, reduce the probability of inactivation of cyanide-free gold salt, and further stabilize the gold plating solution system.

[0039] In some embodiments, a nitrogen-containing heterocyclic compound is used as a stabilizer, such as N-benzyl-3-oxopiperidin-4-carboxylic acid ethyl ester hydrochloride. The nitrogen heterocyclic compound in the nitrogen-containing heterocyclic compound can, on the one hand, complex free gold ions and carry gold ions to migrate and adsorb on the surface of fine metal particles, hindering the explosive self-catalytic deposition of gold crystals on fine particles; on the other hand, it contains unsaturated double bonds, which can effectively passivate the active sites in the reducing agent, stabilize its reduction activity at a controllable level, and avoid gold ions being reduced to a single substance and precipitating and inactivating, and finally achieve the overall stability of the gold plating solution. Further, the addition concentration of the nitrogen-containing heterocyclic compound is 30-150 mg / L, for example, 55-120 mg / L of N-benzyl-3-oxopiperidin-4-carboxylic acid ethyl ester hydrochloride.

[0040] In some embodiments, the osmotic agent comprises at least the structural formula: (R1R2R3N + )-R4-(O x AO - ), at least one of R1, R2 and R3 is a long carbon chain alkyl structure or an amide structure containing a long carbon chain alkyl, wherein the long carbon chain alkyl is a straight chain alkyl having more than or equal to ten carbon atoms, and R4 is a carbon chain having 1 to 3 carbon atoms. In the structural formula, (O x AO - ) is connected to the R4 carbon chain, the A atom can be selected from carbon, sulfur or phosphorus, x is 1 or 2, and the A atom is connected to at least one of the x oxygen atoms by a double bond.

[0041] It should be further explained that the amide structure containing a long carbon chain alkyl group has a corresponding general formula: -R-NH-CO-R', wherein R is an alkyl group containing 1 to 3 carbon atoms, R' is a long carbon chain alkyl group, and the amide structure is connected to the nitrogen atom in the quaternary ammonium base structure at one end of the R group. The long carbon chain alkyl structure and the long carbon chain alkyl in the amide structure extend spatially away from one end of the inner salt structure of the betaine derivative, forming the lipophilic end of the betaine derivative, while the inner salt structure serves as the hydrophilic end, thereby realizing the physical and chemical properties of the amphoteric surface activity of the penetrant.

[0042] In the present application, the penetrant contains a characteristic inner salt structure of a betaine-type substance, and the characteristics of the amphoteric surfactant can effectively reduce the surface tension of the gold plating solution system and improve the wettability and dispersibility of the gold plating solution; the charged groups at both ends of the inner salt structure can improve the conductivity of the gold plating solution system, which helps to form a coating with good uniformity and good bonding with the substrate, thereby improving the electroplating efficiency and coating quality; it can also adapt to the hardness changes of the gold plating solution system during the electroplating process and improve the stability of the gold plating solution system.

[0043] In some embodiments, the betaine derivative is one or more of myristyl betaine, lauroyl amidopropyl betaine, cocamidopropyl betaine, dodecyl dimethyl betaine, 3-sulfopropyl hexadecyl dimethyl betaine, 3-sulfopropyl tetradecyl dimethyl betaine, 3-sulfopropyl dodecyl dimethyl betaine, phosphate betaine, coconut oil phosphate betaine, dodecyl hydroxypropyl phosphate betaine, tetradecyl hydroxypropyl phosphate betaine, hexadecyl hydroxypropyl phosphate betaine, and octadecyl hydroxypropyl phosphate betaine.

[0044] In a further embodiment, the osmotic agent is added at a concentration of 10-90 mg / L, such as 45-60 mg / L.

[0045] In some embodiments, polydimethyldiallylammonium chloride is used as the brightener and 6-nitrocoumarin is used as a leveler and added to the gold plating solution. Both of them can refine the grains and inhibit the growth of oversized grains, thus greatly reducing the surface roughness of the gold plating layer and improving the surface gloss. To a certain extent, they also ensure the effective area of ​​the surface of the micro-blind hole gold plating layer for packaging connection, thereby reducing the difficulty of subsequent process technology.

[0046] In a further embodiment, the concentration of the brightener is 5-35 mg / L, such as 10-15 mg / L, and further such as 10 mg / L or 15 mg / L; the added concentration of the leveler is 1-25 mg / L, such as 15-25 mg / L, and further such as 15 mg / L, 20 mg / L or 25 mg / L.

[0047] On the other hand, the present application also provides an electroplating method for gold plating of micro blind holes, wherein a gold plating solution is prepared according to any of the cyanide-free gold plating solution formulas described above, injected into an electroplating device, and a semiconductor device pre-drilled with the micro blind hole is placed in the electroplating device, powered on, and an electroplating operation is performed.

[0048] In some embodiments, the micro blind holes are gold-plated by spraying. Specifically, during the electroplating process, at least a portion of the gold plating solution needs to be injected into a corresponding device with a liquid spraying function, and the device is aimed at the opening of the micro blind hole to inject the gold plating solution inward, thereby enhancing the exchange of the gold plating solution in the micro blind hole, ensuring the gold ion concentration in the micro blind hole, and ensuring the gold deposition rate near the bottom of the hole under a higher current density condition, thereby ensuring the continuity of the gold plating layer and preventing the gold plating layer from having undesirable phenomena such as voids or slits in the hole.

[0049] In some embodiments, the electroplating temperature is controlled to be 50-65°C, preferably 55-60°C.

[0050] In some embodiments, the pH of the gold plating solution is controlled to be 7.5-9.5, preferably 7.8-8.5.

[0051] In some embodiments, the current density is controlled to be 0.05-0.8 A / dm 2 , preferably 0.3-0.7 A / dm 2 .

[0052] The present application is further explained below with reference to embodiments.

[0053] The reagents and raw materials used in the examples and comparative examples of the present application are all commercially available.

[0054] Example 1

[0055] Embodiment 1 of the present application provides a cyanide-free gold plating solution for gold plating of micro blind holes.

[0056] S1. Prepare a cyanide-free gold plating solution for gold plating of micro blind holes, including the following components:

[0057] Gold ions from potassium gold sulfite 12g / L Potassium sulfite 70g / L 2-((2-Carboxyethyl)thio)nicotinic acid 15g / L Polydimethyldiallylammonium chloride 15mg / L 3-Sulfopropylhexadecyl dimethyl betaine 45mg / L 6-Nitrocoumarin 10mg / L N-Benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 55mg / L DI pure water margin

[0058] S2. Adjust the working temperature of the gold plating solution to 55°C, pH value to 7.8, and current density to 0.5 A / dm 2 , electroplating is carried out using spraying equipment;

[0059] S3. Power on the spraying equipment and continue electroplating for 15 minutes. After completion, inspect and observe.

[0060] Example 2

[0061] Embodiment 2 of the present application provides a cyanide-free gold plating solution for gold plating of micro blind holes.

[0062] S1. Prepare a cyanide-free gold plating solution for gold plating of micro blind holes, including the following components:

[0063] Gold ions from potassium gold sulfite 15g / L Potassium sulfite 80g / L 2-((2-Carboxyethyl)thio)nicotinic acid 20g / L Polydimethyldiallylammonium chloride 25mg / L 3-Sulfopropylhexadecyl dimethyl betaine 60mg / L 6-Nitrocoumarin 10mg / L N-Benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 70mg / L DI pure water margin

[0064] S2. Adjust the working temperature of the gold plating solution to 60°C, pH value to 8.5, and current density to 0.7A / dm 2 , electroplating is carried out using spraying equipment;

[0065] S3. Power on the spraying equipment and continue electroplating the sample with micro blind holes for 12 minutes. After completion, inspect and observe.

[0066] Example 3

[0067] Embodiment 3 of the present application provides a cyanide-free gold plating solution for gold plating of micro blind holes.

[0068] S1. Prepare a cyanide-free gold plating solution for gold plating of micro blind holes, including the following components:

[0069] Gold ions from potassium gold sulfite 10g / L Potassium sulfite 100g / L 2-Mercapto-3-pyridinecarboxylic acid 20g / L Polydimethyldiallylammonium chloride 20mg / L Myristyl Betaine 45mg / L 6-Nitrocoumarin 15mg / L N-Benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 120mg / L DI pure water margin

[0070] S2. Adjust the working temperature of the gold plating solution to 55°C, pH value to 8.2, and current density to 0.3 A / dm 2 , electroplating is carried out using spraying equipment;

[0071] S3. Power on the spraying equipment and continue electroplating the sample with micro blind holes for 25 minutes. After completion, inspect and observe.

[0072] Comparative Example 1

[0073] Comparative Example 1 provides a cyanide-free gold plating solution for gold plating of micro blind holes, comprising the following components:

[0074] Gold ions from potassium gold sulfite 12g / L Potassium sulfite 70g / L 2-((2-Carboxyethyl)thio)nicotinic acid 15g / L Polydimethyldiallylammonium chloride 15mg / L Sodium Lauryl Sulfate 45mg / L 6-Nitrocoumarin 10mg / L N-Benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 55mg / L DI pure water margin

[0075] The electroplating conditions were the same as those in Example 1.

[0076] The difference between this embodiment and Example 1 is that the penetrant in the gold plating solution formula is a conventional non-betaine surfactant: sodium dodecyl sulfate.

[0077] Comparative Example 2

[0078] Comparative Example 2 provides a cyanide-free gold plating solution for gold plating of micro blind holes, comprising the following components:

[0079] Gold ions from potassium gold sulfite 12g / L Potassium sulfite 70g / L 2-((2-Carboxyethyl)thio)nicotinic acid 15g / L Polydimethyldiallylammonium chloride 15mg / L 3-Sulfopropylhexadecyl dimethyl betaine 45mg / L 6-Nitrocoumarin 10mg / L N-Benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride 55mg / L DI pure water margin

[0080] The electroplating conditions are: working temperature is 55℃, pH value is adjusted to 7.8, and ordinary rack plating is used at 0.5 A / dm 2 The sample with micro blind holes was electroplated under the conditions for 15 min.

[0081] The difference between this embodiment and Example 1 is that the conventional rack plating method is used at 0.5 A / dm 2 Electroplating was carried out for 15 min at a current density of .

[0082] Performance Evaluation

[0083] Test 1: Cyanide-free gold plating solution stability test

[0084] The cyanide-free gold plating solutions prepared in the above-mentioned Examples 1-3 and Comparative Examples 1-2 were placed in a water bath at 80° C. and the time when gold particles began to precipitate on the side wall or bottom of the beaker was recorded.

[0085] Test 2: Gold plating appearance observation test

[0086] The electroplated samples of the above-mentioned Examples 1-3 and Comparative Examples 1-2 were taken and placed under a VH-Z250R 3D microscope to capture 3D microscopic images of their surfaces, and the surface flatness and color were compared and observed.

[0087] Test 3: Gold plating surface roughness test

[0088] The electroplated samples of the above-mentioned Examples 1-3 and Comparative Examples 1-2 were placed in a DektakXT step profiler to measure the surface roughness.

[0089] Test 4: Observation test of gold filling in micro blind holes

[0090] The electroplated samples of the above-mentioned Examples 1-3 and Comparative Examples 1-2 were taken, and longitudinal sections of the micro blind holes were obtained using an IM4000 CP slicer, and the cross-sectional structures were observed under a SEM electron microscope.

[0091] Test 5: Gold plating liquid life test

[0092] The gold plating solution prepared in the above-mentioned embodiments 1-3 and comparative examples 1-2 is continuously electroplated using dummy sheets to consume gold ions, and gold ions and corresponding additives are replenished in proportion. Each replenishment of one cylinder of gold ions is recorded as 1.0 MTO. When the gold-plated surface shows color difference, blackening, or voids / cracks appear in the gold filling in the hole, the plating solution is determined to be failed.

[0093] The test results are shown in Table 1:

[0094] Table 1

[0095] serial number 80℃ empty burning stability / h Coating appearance Surface roughness / nm Gold filling in the hole Gold plating solution life / MTO Example 1 ＞130 Golden and smooth 72 No voids, no cracks ≥3.0 Example 2 ＞150 Golden and smooth 56 No voids, no cracks ≥3.5 Example 3 ＞140 Golden and smooth 62 No voids, no cracks ≥3.2 Comparative Example 1 ＞130 Golden and smooth 79 There are holes and cracks / Comparative Example 2 ＞130 Golden and smooth 86 There are holes, no cracks /

[0096] Among them, voids refer to the presence of voids in the gold plating layer which is not completely solid; cracks refer to the poor bonding between the gold plating layer and the hole wall of the micro blind hole, which is not completely fitted, resulting in the presence of cracks.

[0097] It can be seen from the above test results that Examples 1-3 use the gold plating solution and electroplating method composed of all the components and concentrations required by the present invention, and all performance indicators meet the requirements and have a long service life; Figure 1-Figure 3 As shown, the gold plating of Examples 1-3 has a normal appearance and color, a surface roughness of <80nm, the gold plating in the micro blind hole is tightly filled without voids, there is no crack between the hole wall, the bonding strength is good, and no separation marks appear. In the gold plating solution formula of Comparative Example 1, sodium dodecyl sulfate is used as a penetrant. Figure 4 It can be seen that there are poor cavities in the gold plating layer in the micro blind holes, and there are gaps between the gold plating layer and the hole wall in some holes, which proves that when using a non-betaine derivative penetrant, the wetting performance of the gold plating solution is limited. When the gold plating solution enters the micro blind hole, it is still affected by the surface tension and it is difficult to uniformly wet the hole wall and bottom wall of the micro blind hole, resulting in poor quality of the plating layer, which cannot meet the strength requirements of the gold plating layer of the micro blind hole in the subsequent process. Figure 5 It can be seen that compared with the spraying method, when the hanging plating method is used, under the conditions of the same current density and electroplating time, voids and poor gaps appear in the micro blind holes, indicating that the hanging plating method will lead to poor exchange capacity of the gold plating liquid at the bottom of the micro blind hole, and the gold ions are not replenished in time during electroplating deposition, resulting in abnormal deposition in the hole, which cannot meet the strength requirements of the gold plating layer of the micro blind hole in the subsequent process.

[0098] Although examples of the present embodiment have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present embodiment, and the scope of the present embodiment is defined by the claims and their equivalents.

Claims

1. A cyanide-free gold plating solution for gold plating of micro blind holes, characterized in that: The opening diameter of the micro blind hole is ≤2μm and the aspect ratio is ≥2:

1. The surface roughness of the gold plating layer obtained by electroplating the micro blind hole with the cyanide-free gold plating solution in a spraying electroplating manner is less than 80nm. The cyanide-free gold plating solution comprises the following components: 10-15g / L cyanide-free water-soluble gold ions, 20-150g / L main complexing agent, 5-20g / L auxiliary complexing agent, 5-35mg / L brightener, 10-90mg / L penetrant, 1-25mg / L leveler and 30-150mg / L stabilizer. L, the solvent is water; the source of the cyanide-free water-soluble gold ion is potassium sulfite gold, the main complexing agent is potassium sulfite, the auxiliary complexing agent is 2-[(2-carboxyethyl)thio]nicotinic acid or 2-mercapto-3-pyridinecarboxylic acid, the brightener is polydimethyldiallylammonium chloride, the leveling agent is 6-nitrocoumarin, the stabilizer is N-benzyl-3-oxopiperidine-4-carboxylic acid ethyl ester hydrochloride, and the penetrant is a betaine derivative, and the betaine derivative at least comprises the structural formula: (R1R2R3N + )-R4-(O x AO - ), at least one of R1, R2 and R3 is a long carbon chain alkyl structure or an amide structure containing the long carbon chain alkyl, the long carbon chain alkyl is a straight chain alkyl with more than or equal to ten carbon atoms, the amide structure is: -R-NH-CO-R', wherein R is an alkyl containing 1 to 3 carbon atoms, R' is the long carbon chain alkyl, and R4 is a carbon chain with 1 to 3 carbon atoms. In the structural formula, (O x AO - ) is connected to the R4 carbon chain, the A atom can be selected from carbon element or sulfur element, x is 1 or 2, and the A atom is connected to at least one of the x oxygen atoms by a double bond.

2. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The added concentration of the penetrant is 45-60 mg / L, and the penetrant is one or more of myristyl betaine, lauryl amidopropyl betaine, cocamidopropyl betaine, dodecyl dimethyl betaine, 3-sulfopropyl hexadecyl dimethyl betaine, 3-sulfopropyl tetradecyl dimethyl betaine and 3-sulfopropyl dodecyl dimethyl betaine.

3. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The added concentration of the cyanide-free water-soluble gold ions is 12-15 g / L.

4. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The addition concentration of the main complexing agent is 70-100 g / L, and the addition concentration of the auxiliary complexing agent is 15-20 g / L.

5. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The added concentration of the brightener is 10-15 mg / L.

6. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The added concentration of the leveling agent is 15-25 mg / L.

7. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The stabilizer is added at a concentration of 55-120 mg / L.

8. The cyanide-free gold plating solution for gold plating of micro blind holes according to claim 1, characterized in that: The cyanide-free gold plating solution comprises the following components in mass concentrations: 25-37.5 g / L of potassium gold sulfite, 20-150 g / L of potassium sulfite, 5-20 g / L of 2-[(2-carboxyethyl)thio]nicotinic acid, 5-35 mg / L of polydimethyldiallylammonium chloride, 1-25 mg / L of 6-nitrocoumarin, 10-90 mg / L of 3-sulfopropyl hexadecyl dimethyl betaine, and 30-150 mg / L of ethyl N-benzyl-3-oxopiperidine-4-carboxylate hydrochloride, and the solvent is pure water.

9. A method for electroplating gold for micro blind vias, characterized in that: The electroplating method adopts the cyanide-free gold plating solution according to any one of claims 1 to 8, and the electroplating method satisfies the following conditions at the same time: n: The electroplating temperature is 50-65℃; o: The pH of the gold plating solution is 7.5-9.5; p: Current density is 0.05-0.8A / dm 2 ; q: The electroplating method is spraying.

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