A highly stable chemical palladium plating solution for semiconductor surface pattern metallization

Abstract

The invention discloses a highly stable chemical palladium plating solution for semiconductor surface pattern metallization, comprising the following components in concentration: 0.5-3.5 g / L of ammoniacal palladium salt, 5-20 g / L of a main complexing agent, 0.1-20 g / L of an auxiliary complexing agent, 1-8 g / L of a reducing agent, 5-50 g / L of a composite stabilizer, and 10-100 mg / L of a uniforming agent. The chemical palladium plating solution of the invention has good stability, can normally deposit a thick palladium film layer for compound semiconductor photosensitive fine patterns, has a high product yield, is easy to use, and has a low maintenance cost.

Description

Technical Field

[0001] The invention relates to a semiconductor advanced packaging surface metallization wet process material, a highly stable chemical palladium plating solution used for semiconductor surface pattern metallization. Background Art

[0002] The introduction of palladium in the chemical nickel-palladium-gold process, on the one hand, meets many new packaging applications, and its corrosion resistance and solder joint reliability have been greatly improved compared with immersion tin, immersion silver, organic solder, etc. On the other hand, compared with the nickel-gold process, it reduces nickel corrosion and the amount of gold used. It has obvious advantages in packaging applications and has become the mainstream process for surface metallization of compound semiconductors.

[0003] However, the plating rate obtained in many published technical documents is often faster in the initial stage, but as the use period of the plating solution increases, the deposition rate continues to decrease, and even falls below the lower limit level, resulting in the end of the life of the palladium plating solution. The rate reduction can usually be resisted by increasing the plating solution temperature and increasing the palladium metal concentration or the reducing agent concentration, but this approach also increases the risk of instability of the plating solution.

[0004] Patent CN 103898490 A discloses a high-reliability chemical palladium plating solution using palladium chloride, which can meet the nickel-palladium-gold process on workpieces such as PCBs. However, the palladium layer is deposited by displacement palladium plating, and the palladium thickness of the given embodiment is less than 0.05μm, which cannot meet the production requirements of thick palladium (>0.2μm).

[0005] Patent CN 107002242 B discloses a method for obtaining a higher palladium plating rate. The rate shown is significantly higher than the normal value of commercially available chemically reduced palladium. The patent does not show specific indicators of plating solution stability, and the reliability of the plating solution life is unknown.

[0006] Patent CN 117926235 A discloses a halogen-free, highly stable chemical palladium plating bath. The obtained coating is a pure palladium coating. Under vigorous stirring, palladium films can still be normally deposited on tiny BGA points and hole rings, but the application effect on semiconductor microstructures and photosensitive structures is not described. According to the applicant's practice, for chemical palladium deposition on compound semiconductor photosensitive microstructures, the pure palladium system can be deposited normally in the initial stage, but as the use cycle increases, the activity decreases, and poor plating easily occurs. It is necessary to deviate from normal parameters to improve the activity, but at this time, the plating solution decomposes and precipitates, which greatly increases the cost. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a highly stable chemical palladium plating solution for semiconductor surface pattern metallization, which has good stability and can normally deposit thick palladium film layers on compound semiconductor photosensitive fine patterns. The product yield is high, the plating solution is easy to use, and the maintenance cost is low.

[0008] The technical solution of the present invention is: a highly stable chemical palladium plating solution for semiconductor surface pattern metallization, comprising the following components in concentration: 0.5-3.5 g / L of ammonia palladium salt, 5-20 g / L of a main complexing agent, 0.1-20 g / L of an auxiliary complexing agent, 1-8 g / L of a reducing agent, 5-50 g / L of a composite stabilizer and 10-100 mg / L of a uniforming agent.

[0009] Furthermore, the ammonia-containing palladium salt is tetraamminepalladium dichloride or tetraamminepalladium sulfate.

[0010] Furthermore, the main complexing agent is ethylenediamine.

[0011] Furthermore, the auxiliary complexing agent is a phosphonate complexing agent, which is one of inositol hexaphosphate, tris(2-carboxyethyl)phosphine hydrochloride, aminotrimethylenephosphonic acid, sodium dihexenetriaminepentamethylenephosphonate, tris(2-cyanoethyl)phosphine and sodium ethylenediaminetetramethylenephosphate.

[0012] Furthermore, the reducing agent is sodium hypophosphite.

[0013] Furthermore, the composite stabilizer is a mixture of an unsaturated carboxylic acid and an ammonium-containing compound; the concentration ratio of the unsaturated carboxylic acid to the ammonium-containing compound is (1:3-3:1).

[0014] Furthermore, the unsaturated carboxylic acid is one of acrylic acid, methacrylic acid, crotonic acid, 2-methyl-3-butenoic acid, maleic acid, 3-pentenoic acid and 4-pentenoic acid.

[0015] Furthermore, the ammonium radical-containing compound is one of ammonium hydride, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium phosphate and diammonium hydrogen phosphate.

[0016] Furthermore, the uniformizing agent is dodecyl dimethyl betaine.

[0017] The beneficial effects of the present invention are: 1) The palladium salt of the present invention is an ammonia-containing palladium salt, and compared with the palladium salt not containing ammonia, the metal ion source itself is more stable.

[0018] 2) In addition to ethylenediamine, which has a better palladium complexing effect, the complexing agent is supplemented with a phosphonate complexing agent. This type of substance has a strong chelating ability for metal ions and can further complex and stabilize free palladium ions, reducing the chance of their unstable precipitation.

[0019] 3) The unsaturated carboxylic acid in the composite stabilizer has unsaturated -C=C-bonds and -C=O-bonds. Its conjugated system can form a strong coordination with palladium, affecting its catalytic activity and preventing the reaction from getting out of control. Ammonium-containing compounds contain a large amount of NH4+ ions, which can form palladium-ammine complexes with palladium ions, thereby stabilizing palladium ions. The two substances in the composite stabilizer work together to further ensure the stability of the plating solution.

[0020] 4) The uniformizing agent is acid-base resistant dodecyl dimethyl betaine which is easily soluble in water. Its betaine group also has good wettability and permeability, which can better ensure the uniformity of palladium deposition between different patterns.

[0021] 5) The working condition of this patented plating solution can be an acidic environment, pH = 4.0-7.0. Under this condition, the reducibility of the reducing agent is maintained at a high level, and the palladium layer can be deposited normally for photosensitive semiconductors with fine patterns, avoiding the leakage plating abnormality that occurs after chemical plating of palladium plating solutions in other systems. In addition, by using auxiliary complexing agents and composite stabilizers, the plating solution using sodium hypophosphite as a reducing agent can also have excellent stability under this condition. Compared with the traditional system that only works under neutral or weakly alkaline conditions, it can adapt to the processing requirements of more compound semiconductors, especially products whose photoresists are intolerant to alkaline solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] Figure 1 This is a 500-fold microscope image of the photosensitive semiconductor A in Example 1 after nickel-palladium-gold treatment.

[0024] Figure 2 This is a 250x microscope image of the photosensitive semiconductor B in Example 2 after nickel-palladium-gold treatment.

[0025] Figure 3 This is the verification of Example 3, the photosensitive semiconductor C is plated with nickel-palladium-gold and then gold wire is punched.

[0026] Figure 4 This is a 1000x microscope image of the photosensitive semiconductor A in comparative example 1 after nickel-palladium-gold plating.

[0027] Figure 5 This is a 1000x microscope image of the photosensitive semiconductor B of comparative example 2 after nickel-palladium-gold treatment.

[0028] Figure 6 This is a 250x microscope image of the photosensitive semiconductor B of comparative example 3 after nickel-palladium-gold treatment.

[0029] Figure 7 This is a 1000x microscope image of the comparative example 4 photosensitive semiconductor B after nickel-palladium-gold treatment. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below through specific implementation methods.

[0031] The invention discloses a highly stable chemical palladium plating solution for semiconductor surface pattern metallization, comprising the following components in concentration: an ammoniacal palladium salt, a main complexing agent, an auxiliary complexing agent, a reducing agent, a composite stabilizer and a homogenizing agent.

[0032] Ammoniacal palladium salt: tetraamminepalladium dichloride or tetraamminepalladium sulfate, 0.5-3.5g / L; Main complexing agent: ethylenediamine, 5-20g / L; Auxiliary complexing agent: phosphonate complexing agent: inositol hexaphosphate, tris (2-carboxyethyl) phosphine hydrochloride, amino trimethylene phosphonic acid, dihexene triamine pentamethylene phosphonic acid sodium, tris (2-cyanoethyl) phosphine, ethylenediamine tetramethylene phosphate sodium, 0.1-20g / L; Reducing agent: sodium hypophosphite, 1-8g / L; Composite stabilizer: unsaturated carboxylic acid + ammonium radical compound mixture (1:3-3:1), unsaturated carboxylic acids include acrylic acid, methacrylic acid, butenoic acid, 2-methyl-3-butenoic acid, maleic acid, 3-pentenoic acid, 4-pentenoic acid, etc., 5-50g / L; ammonium radical compounds include ammonium hydride, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium phosphate, diammonium hydrogen phosphate, etc., 5-50g / L; Uniform dose: dodecyl dimethyl betaine, 10-100 mg / L.

[0033] The present invention has good stability, can also normally deposit a thick palladium film layer on compound semiconductor photosensitive fine patterns, has a high product yield, is easy to use the plating solution, and has a low maintenance cost. Example 1

[0034] The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.5g / L Ethylenediamine: 10g / L Aminotrimethylenephosphonic acid: 5g / L Sodium hypophosphite: 3g / L 2-Methyl-3-butenoic acid: 20g / L Ammonium phosphate: 30g / L Dodecyl dimethyl betaine: 100 mg / L Balance: pure water.

[0035] pH=5.5, T=50℃, t=20min, cycle: 8STO, shaking: 10 times / min. Example 2

[0036] The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.0g / L Ethylenediamine: 15g / L Inositol hexaphosphate: 5g / L Sodium hypophosphite: 5g / L Acrylic acid: 30g / L Ammonium sulfate: 30g / L Dodecyl dimethyl betaine: 50 mg / L Balance: pure water.

[0037] pH=5.0, T=45℃, t=20min, cycle: 5STO, shaking: 20 times / min. Example 3

[0038] The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Tetraamminepalladium sulfate: 1.0g / L Ethylenediamine: 15g / L Sodium dihexyltriamine penta methylenephosphonate: 15g / L Sodium hypophosphite: 5g / L Butenoic acid: 40g / L Ammonium sulfate: 30g / L Dodecyl dimethyl betaine: 50 mg / L Balance: pure water.

[0039] pH=6.0, T=50℃, t=20min, cycle: 5STO, shaking: 20 times / min.

[0040] Comparative Example 1 The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.5g / L Ethylenediamine: 10g / L Aminotrimethylenephosphonic acid: 5g / L Sodium hypophosphite: 3g / L 2-Methyl-3-butenoic acid: 20g / L Ammonium phosphate: 30g / L Dodecyl dimethyl betaine: 100 mg / L Balance: pure water.

[0041] pH=7.5, T=50℃, t=20min, cycle: 8STO, shaking: 10 times / min.

[0042] The composition of the plating solution is the same as that of Example 1, except that NaOH is used to increase the solution pH to 7.5, and other parameters are the same.

[0043] Comparative Example 2 The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.0g / L Ethylenediamine: 15g / L Inositol hexaphosphate: 5g / L Sodium formate: 50g / L Acrylic acid: 30g / L Ammonium sulfate: 30g / L Dodecyl dimethyl betaine: 50 mg / L Balance: pure water.

[0044] pH=5.0, T=45℃, t=20min, cycle: 5STO, shaking: 20 times / min.

[0045] The difference between the plating solution composition of Example 2 and that of Example 2 is that the reducing agent uses sodium formate commonly used in pure palladium systems, and the amount used is a known conventional larger value, and the other parameters are the same.

[0046] Comparative Example 3 The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.0g / L Ethylenediamine: 15g / L Inositol hexaphosphate: 5g / L Sodium hypophosphite: 5g / L Dodecyl dimethyl betaine: 50 mg / L Balance: pure water.

[0047] pH=5.0, T=45℃, t=20min, cycle: 5STO, shaking: 20 times / min.

[0048] The difference between the plating solution composition of Example 2 is that there is no composite stabilizer in the plating solution, and other parameters are the same.

[0049] Comparative Example 4 The following materials were stirred and dissolved in sequence to prepare a 20L chemical palladium solution to complete the deposition of the palladium metal layer: Dichlorotetraamminepalladium: 1.0g / L Ethylenediamine: 15g / L Inositol hexaphosphate: 5g / L Sodium hypophosphite: 5g / L Acrylic acid: 30g / L Ammonium sulfate: 30g / L Balance: pure water.

[0050] pH=5.0, T=45℃, t=20min, cycle: 5STO, shaking: 20 times / min.

[0051] The difference between the plating solution composition of Example 2 is that there is no uniformity agent in the plating solution, and other parameters are the same.

[0052] Table 1 Statistics of results after chemical palladium plating in different implementation schemes Implementation Sinking speed Appearance Missing plating ratio Homogeneity Binding force Bath stability Embodiment 1 0.025μm / min Bright silver white 0% 7.6% OK ≥25d Embodiment 2 0.020μm / min Bright silver white 0% 5.3% OK ≥30d Embodiment 3 0.019μm / min Bright silver white 0% 6.5% OK ≥30d Comparative Example 1 0.007μm / min Bright silver-white, the unplated part is gray and dark 65% / OK ≥35d Comparative Example 2 0.023μm / min Bright silver-white, the unplated part is gray and dark 85% / OK ≥45d Comparative Example 3 0.072μm / min The whole surface is rough and dull 0% / NG ≤2d Comparative Example 4 0.021μm / min Partial fogging, color difference, rough particles 0% 26.8% OK ≥30d Result detection method: 1. Sedimentation speed & uniformity: Use an X-ray thickness gauge to measure the film thickness data corresponding to the graphics at 13 points evenly distributed on the entire wafer. According to: uniformity value = (maximum value - minimum value) / 2 times the average value × 100%, calculate the thickness uniformity. The smaller the value, the better the uniformity. According to: sedimentation speed = thickness average value / time, calculate the corresponding sedimentation speed. The larger the value, the faster the sedimentation speed.

[0053] 2. Appearance: Use a 3D microscope to directly observe the appearance after electroless plating under different magnifications.

[0054] 3. Leakage plating ratio: select a certain area to measure the film thickness and observe the appearance, count the ratio of abnormal film thickness / abnormal appearance graphics to all graphics in the area, and calculate the leakage plating ratio. The smaller the value, the better.

[0055] 4. Adhesion: Use the 100-grid method to test, and observe the peeling of the coating after tearing the 3M tape. If there is peeling, the adhesion is NG.

[0056] 5. Stability of plating solution: Place the prepared plating solution in a 50℃ water bath and heat it in an empty space. Record the time when obvious metal ion precipitation appears. The longer the time, the better the stability.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A highly stable chemical palladium plating solution for semiconductor surface pattern metallization, characterized in that: The composition comprises the following components in concentration: 0.5-3.5 g / L of ammonia palladium salt, 5-20 g / L of a main complexing agent, 0.1-20 g / L of an auxiliary complexing agent, 1-8 g / L of a reducing agent, 5-50 g / L of a composite stabilizer and 10-100 mg / L of a uniforming agent.

2. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The ammoniacal palladium salt is tetraamminepalladium dichloride or tetraamminepalladium sulfate.

3. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The main complexing agent is ethylenediamine.

4. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The auxiliary complexing agent is a phosphonate complexing agent, which is one of inositol hexaphosphate, tris(2-carboxyethyl)phosphine hydrochloride, aminotrimethylenephosphonic acid, sodium dihexenetriaminepentamethylenephosphonate, tris(2-cyanoethyl)phosphine and sodium ethylenediaminetetramethylenephosphate.

5. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The reducing agent is sodium hypophosphite.

6. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The composite stabilizer is a mixture of unsaturated carboxylic acid and ammonium-containing compound; the concentration ratio of the unsaturated carboxylic acid and the ammonium-containing compound is (1:3-3:1).

7. A highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 6, characterized in that: The unsaturated carboxylic acid is one of acrylic acid, methacrylic acid, crotonic acid, 2-methyl-3-butenoic acid, maleic acid, 3-pentenoic acid and 4-pentenoic acid.

8. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 6, characterized in that: The ammonium radical-containing compound is one of ammonium hydride, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium phosphate and diammonium hydrogen phosphate.

9. The highly stable chemical palladium plating solution for semiconductor surface pattern metallization according to claim 1, characterized in that: The uniformizing agent is dodecyl dimethyl betaine.

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