Method for electrolessly depositing a metal layer on a substrate

Abstract

The present invention relates to a method for electrolessly depositing a metal layer on a substrate, the method comprising the chronological steps of: a) treating the substrate surface to be plated with an etching solution; b) treating the substrate surface to be plated with a polyelectrolyte or organosilane compound; c) treating the surface to be plated with a solution containing metal particles; and d) treating the surface to be plated with a solution containing at least one metal salt to be deposited on the substrate.

Description

[Technical Field]

[0001] The present invention relates to a method for electrolessly depositing a metal layer on a substrate to provide an economical method for depositing very thin metal layers on a substrate without the use of a vacuum. [Background technology]

[0002] The prior art knows many methods for providing a substrate with a metal layer, in which electroless methods and methods using electroplating offer economical solutions, while other methods, such as those that work in a vacuum or with steam, are often significantly more expensive.

[0003] In the well-known wet chemical methods, the surface to be plated is usually first subjected to a cleaning pretreatment. The surface to be plated is then activated, often with tin or palladium particles. Palladium-based activation has been used in industry since the 1950s. After activation, the surface is treated in a well-known manner with a metal salt solution, which is reduced on the surface. If a thicker metal layer is desired, galvanic plating techniques are used. In contrast, electroless plating techniques are used, particularly in the field of semiconductor technology, to obtain very thin metal layers with significantly less effort.

[0004] One of the challenges of the above methods has been, and still is, providing sufficient adhesion of the so-called metal seed layer. The most common method used to achieve this is to perform an etching process on the surface. This is done, especially for glass surfaces, to achieve mechanical interconnection of the activated reagents on the substrate surface. However, roughening the glass surface by an etching process is not ideal, especially for high-frequency applications. Before metallization, polymers are often also subjected to swelling and etching processes, because these processes are usually used for repassivation and redistribution. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a method for the electroless deposition of a metal layer on a substrate, which allows for the deposition of an extremely thin and smooth metal layer on the substrate at the lowest possible cost, and which is intended to adhere the metal layer to the substrate as firmly as possible. [Means for solving the problem]

[0006] According to the invention, this object is achieved by a method having the features of claim 1. After treating the substrate surface to be plated with an etching solution, the substrate surface to be plated is first treated with a polyelectrolyte or an organosilane compound. The substrate surface is then activated by treatment with metal particles, particularly gold, silver, copper, and / or platinum particles. These metal particles are fixed to the substrate by the previously applied polyelectrolyte and / or organosilane compound. This significantly improves the adhesion of the activated metal particles to the substrate surface. The surface to be plated is then treated with a solution containing a salt of the metal to be deposited on the substrate, thereby allowing for the cost-effective deposition of an extremely thin and smooth metal layer on the substrate, with a thickness of 50 nm to 1,000 nm. Typically, the solution in step d) contains copper ions, such as copper sulfate. It has been found that the method according to the present invention allows for the deposition of particularly thin and smooth copper layers on substrates.

[0007] In step b), the substrate surface to be plated is treated with a polyelectrolyte, preferably selected from the group consisting of polydiallyldimethylammonium (PDDA), polyethyleneimine (PEI), polyacrylic acid (PAA), polystyrene sulfonic acid (PSS), polyethylene oxide (PEO), and polylysine, which have been found to be particularly effective for immobilizing metal particles, in particular gold, silver, copper, and / or platinum particles.

[0008] In a particularly preferred variant of the method according to the invention, the solution in step d) contains at least one polysaccharide, preferably at a concentration of 0.05% or less. It has been found that polysaccharides in the plating solution can modulate the ionic interactions and the size of the deposited particles, thereby improving the adhesion of the deposited metal layer. It has also been observed that polysaccharides can achieve more uniform layer growth during electroless deposition of metal layers. It has also been found that polysaccharides act as stabilizers for the plating solution. It is believed that polysaccharides reduce the particle size of the deposited metal, particularly copper particles. The use of polysaccharides in the plating solution also reduced etching of the glass substrate. The polysaccharide source can be, for example, agar.

[0009] Advantageously, the gold, silver, copper, and / or platinum particles in step c) are present as gold, silver, copper, and / or platinum nanoparticles, preferably having a diameter of about 5 nm to 100 nm and preferably carrying charged functional groups. The charged functional groups result in particularly favorable electrostatic ionic interactions between the nanoparticles and the previously deposited polyelectrolyte and / or previously deposited organosilane compound, thereby providing particularly stable immobilization of the nanoparticles on the surface of the substrate to be plated. Advantageously, step c) contains gold nanoparticles, particularly nanoparticles comprising gold chloride and citric acid, and at least one surfactant, preferably Triton-X®. Triton-X® is a polyethylene glycol-based surfactant. In particular, this type of surfactant reduces the tendency of the particles to aggregate by a factor of two. Steric hindrance stabilizes the nanoparticles, and polyethylene glycol further improves wetting. Optionally, sodium citrate can be added to enhance stability.

[0010] Advantageously, the metal salt in step d) is in the form of fine particles, in particular with a diameter of about 100 nm to 1,000 nm. In this way, a transition layer of polyelectrolytes, nanoparticles and microparticles can be produced, with the help of which a very thin and very smooth metal layer can finally be produced.

[0011] The substrate may be made of polymer or silicon-based. However, the substrate is preferably made of glass, and the substrate is preferably an interposer with through-holes. Glass interposers are particularly used in the semiconductor field. In this case, the glass interposer allows for direct matching of the thermal expansion coefficient with the silicon chip. Furthermore, interposers made of glass offer better electrical properties compared to silicon. In addition, this type of interposer is available in panel size and offers high interconnect density. A metal seed layer on the glass interposer also provides a promising solution for high transmittance and memory bandwidth applications.

[0012] As a rule, the substrate in step a) is treated with an acid. Preferably, before step b), the plastic substrate is treated with dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) at about 25°C to 60°C, followed by treatment with a swelling agent such as DMSO, a polyethylene glycol surfactant such as Triton-X®, ammonium hydroxide and / or sodium hydroxide, and an alcohol such as methanol, isopropanol, or ethanol. In principle, the glass substrate is treated with at least one acid such as nitric acid, sulfuric acid, piranha solution, hydrochloric acid, or aqua regia, or with potassium hydrogen fluoride, sodium hydrogen fluoride, and / or ammonium hydrogen fluoride.

[0013] In a further development of the method according to the invention, the plated substrate surface is galvanically plated after step d). This combination of electroless plating and galvanic plating allows filling of the through holes of the interposer. This combination allows layer thicknesses of more than 1 μm to be achieved.

[0014] Conveniently, the substrate is rinsed with water, in particular distilled water, before and after every step, and preferably the substrate is treated with water and acid after step d).

[0015] In a preferred variant of the method according to the invention, the solution of step d) further contains a reducing agent, in particular formaldehyde, hydrazine and / or glyoxylic acid, which reduces the metal cations of the metal salts of step d) to elemental metal, resulting in an extremely thin metal layer with a thickness of 50 nm to 1,000 nm.

[0016] If an organosilane compound is used as immobilization reagent in step b), it is preferably selected from the group consisting of alkenylsilanes, chloropropylsilanes, aminopropylsilanes, thiopropylsilanes and / or cyanoethylsilanes and / or ethersilanes, estersilanes and / or epoxy-substituted alkylsilanes.

[0017] As a rule, the solution of step d) has a pH value of about 10-12. Advantageously, the solution of step d) contains at least one complexing agent, such as EDTA, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (Quadrol) or sodium potassium tartrate.

[0018] As a rule, step b) is carried out at a temperature between 25°C and 90°C. The method of the present invention, which allows the formation of metal layers on surfaces provided with noble metal particles, is also suitable for surface plasmon resonance (SPR) applications as well as thermal photonic and optoelectronic applications. The size of the nanoparticles used, the plating rate, the pH value, and the nanoparticle density influence the morphological and mechanical properties of the resulting metal layer. Example 1

[0019] Glass substrates were cleaned with acetone and piranha solution for 1 hour and then incubated in a 10%–20% PDDA solution for 2 hours. The samples were then rinsed with distilled water and placed in a solution containing gold nanoparticles prepared according to the Turkevich method, with particle sizes <100 nm. The solution contained 1% gold chloride, 0.01% Triton-X®, and 0.3 g / L trisodium citrate. After the nanoparticles were immobilized on the substrate for at least 2 hours, the samples were rinsed again and placed in a plating bath containing 0.05% agar, 3.2 g / L copper sulfate pentahydrate, 11.3 g / L potassium sodium tartrate, 5 g sodium hydroxide (pH 10–12), and 32 ml / L formaldehyde. In this case, agar was used as the polysaccharide source. Seed layers with thicknesses of 30 μm–150 μm were obtained by varying the plating time from 2 to 20 minutes at room temperature. The ASTM tape test gave a grade of 5B, indicating strong adhesion. Example 2

[0020] Example 2 was carried out in the same manner as Example 1, except that PDDA was replaced with 1 g / l of branched polyethylene (molecular weight 25,000-750,000, PEI). Example 3

[0021] Example 3 was carried out in the same manner as Example 1, except that PDDA was replaced with 0.946 g / l of (3-aminopropyl)triethoxysilane or APTES. Example 4

[0022] Example 4 was carried out in the same manner as Example 1, except that the glass substrate was replaced with a photoreactive cured polyimide or dry layer epoxy substrate deposited on a silicon or glass substrate. An additional swelling or etching treatment was incorporated into this method as part of the pretreatment before incubation in PDDA / APTES. Swelling in an aprotic solvent such as dimethyl sulfoxide (DMSO) was performed for 1 minute at 25°C to 60°C. Microetching was then carried out for 20 minutes to 1 hour in a solution containing 0.5% to 1% of a water-soluble swelling agent such as DMSO, 0.5% to 1% of a polyethylene glycol surfactant such as Triton-X®, 1% to 3% of an ammonium hydroxide compound and / or a sodium hydroxide compound, and 10% to 30% of an alcohol compound such as methanol, isopropanol, or ethanol. The substrate was then treated with 10% sulfuric acid, rinsed, and immersed in a polyelectrolyte solution.

Claims

1. 1. A method for electrolessly depositing a metal layer on a substrate, the method comprising, in time sequence: a) treating the substrate surface to be plated with an etching solution; b) treating the substrate surface to be plated with an organosilane compound; c) treating the surface to be plated with a solution containing metal particles; d) treating the surface to be plated with a solution containing at least one metal salt to be deposited on the substrate; The method of claim 1, wherein the metal particles of step c) are present as nanoparticles, the nanoparticles having a diameter of between 5 nm and 100 nm.

2. 2. The method of claim 1, wherein the solution of step c) contains gold, silver, copper and / or platinum particles.

3. 3. The method of claim 2, wherein the solution in step c) contains colloidal gold.

4. 4. The method according to claim 1, wherein the solution of step d) contains copper ions.

5. 5. The method of claim 4, wherein the solution of step d) contains copper sulfate.

6. 6. The method according to any one of claims 1 to 5, characterized in that the solution of step d) contains at least one polysaccharide.

7. 7. The method of claim 6, wherein the concentration of the at least one polysaccharide is 0.05% or less.

8. 8. The method according to any one of claims 2 to 7, characterized in that the gold, silver, copper and / or platinum particles of step c) are present as gold, silver, copper and / or platinum nanoparticles.

9. The method of any one of claims 1 to 8, wherein the nanoparticles have charged functional groups.

10. 10. The method according to any one of claims 1 to 9, characterized in that the solution of step c) contains gold nanoparticles.

11. 11. The method of claim 10, wherein the solution of step c) contains nanoparticles with gold chloride and citric acid.

12. 12. The method of claim 10 or 11, wherein the solution of step c) contains at least one surfactant.

13. 13. The method of claim 12, wherein the at least one surfactant is a polyethylene glycol-based surfactant.

14. 14. The method according to any one of claims 1 to 13, characterized in that the metal salt of step d) is present in the form of fine particles.

15. 15. The method of claim 14, wherein the metal salt of step d) has a diameter of 100 nm to 1,000 nm.

16. The method according to any one of claims 1 to 15, wherein the substrate is made of glass, or made of a polymer, or is silicon-based.

17. The method of claim 16 , wherein the substrate is an interposer with through holes.

18. The method according to any one of the preceding claims, characterized in that in step a) the substrate is treated with an acid.

19. 19. The method according to any one of claims 1 to 18, characterized in that after step a) and before step b), the plastic substrate is treated with dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) at about 25°C to 60°C, and then treated with a swelling agent, a polyethylene glycol surfactant, ammonium hydroxide and / or sodium hydroxide, and an alcohol.

20. 20. The method of claim 19, wherein the swelling agent is dimethyl sulfoxide.

21. 21. The method of claim 19 or 20, wherein the alcohol is methanol, isopropanol or ethanol.

22. 19. The method according to any one of claims 1 to 18, characterized in that step a) comprises treating the glass substrate with at least one acid or with potassium, sodium and / or ammonium hydrogen fluoride salts.

23. 23. The method of claim 22, wherein the at least one acid is nitric acid, sulfuric acid, piranha solution, hydrochloric acid, or aqua regia.

24. A method according to any one of the preceding claims, characterized in that the plated substrate surface is galvanically plated after step d).

25. The method according to any one of claims 1 to 24, characterized in that the substrate is treated with water before and after every step.

26. 26. The method of claim 25, wherein the substrate is treated with distilled water before and after every step.

27. 27. The method of claim 25 or 26, wherein the substrate is treated with water and acid after step d).

28. The method according to any one of claims 1 to 27, characterized in that the solution of step d) further contains a reducing agent.

29. 29. The method of claim 28, wherein the reducing agent is formaldehyde, hydrazine and / or glyoxylic acid.

30. 30. The method according to any one of the preceding claims, characterized in that the solution of step d) has a pH value of 10 to 12.

31. 31. The method according to any one of claims 1 to 30, characterized in that the solution of step d) contains at least one complexing agent.

32. 32. The method of claim 31, wherein the at least one complexing agent is EDTA, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (Quadrol), or sodium potassium tartrate.

33. 33. The method according to any one of claims 1 to 32, characterized in that step b) is carried out at a temperature between 25°C and 90°C.

34. The method according to any one of claims 1 to 33, wherein in step b) alkenylsilane, chloropropylsilane, aminopropylsilane, thiopropylsilane and / or cyanoethylsilane and / or ether silane, ester silane and / or epoxy-substituted alkylsilane is used as organosilane compound.