METHOD FOR ELECTROLESSLY DEPOSITING A METAL LAYER ONTO A SUBSTRATE

Abstract

A method for electrolessly depositing a metal layer onto a substrate, including the following chronological steps: a) treating the substrate surface to be plated with an etching solution; b) treating the substrate surface to be plated with a polyelectrolyte or 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 salt of the metal to be deposited onto the substrate.

Claims

1. A method for electrolessly depositing a metal layer onto a substrate, the method comprising the following chronological steps: a) treating the substrate surface to be plated with an etching solution; b) treating the substrate surface to be plated with a polyelectrolyte or 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 salt of the metal to be deposited onto the substrate.

2. The method according to claim 1, wherein the solution from step c) contains gold, silver, copper and/or platinum particles, in particular colloidal gold.

3. The method according to claim 1, wherein the solution from step d) contains copper ions, such as copper sulfate.

4. The method according to claim 1, wherein the substrate surface to be plated is treated with a polyelectrolyte selected from the group consisting of polydiallyldimethylammonium (PDDA), polyethyleneimine (PEI), polyacrylic acid (PAA), polystyrene sulfonate (PSS), polyethylene oxide (PEO) and polylysine, in step b).

5. The method according to claim 1, wherein the solution from step d) contains at least one polysaccharide, preferably at a concentration of 0.05 % or less.

6. The method according to claim 2, wherein the gold, silver, copper and/or platinum particles from step c) are present as gold, silver, copper and/or platinum nanoparticles, the nanoparticles preferably having a diameter of approximately 5 nm to 100 nm and preferably having charged functional groups.

7. The method according to claim 1, wherein the solution from step c) contains gold nanoparticles, in particular nanoparticles having gold chloride and citric acid, and preferably at least one surfactant, such as Triton-X®.

8. The method according to claim 1, wherein the metal salt from step d) is present in the form of microparticles, in particular having a diameter of approximately 100 nm to 1,000 nm.

9. The method according to claim 1, wherein the substrate is made of glass, polymer or based on silicon, the substrate preferably being an interposer having through-holes.

10. The method according to claim 1, wherein the substrate from step a) is treated with acid.

11. The method according to claim 1, wherein prior to step b), a plastic substrate is treated with dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) at approximately 25° C. to 60° C. and is subsequently treated with a swelling agent, such as DMSO, a surfactant based on polyethylene glycol, such as Triton-X®, ammonium hydroxide and/or sodium hydroxide and an alcohol, such as methanol, isopropanol or ethanol; or a 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 bifluoride salts, sodium bifluoride salts and/or ammonium bifluoride salts.

12. The method according to claim 1, wherein the plated substrate surface is galvanically plated after step d).

13. The method according to claim 1, wherein the substrate is treated with water, in particular distilled water, before and after every step, the substrate preferably being treated with water and acid after step d).

14. The method according to claim 1, wherein the solution from step d) further contains a reducing agent, in particular formaldehyde, hydrazine and/or glyoxylic acid.

15. The method according to claim 1, wherein alkenyl silanes, chloropropyl silanes, aminopropyl silanes, thiopropyl silanes and/or cyanoethyl silanes and/or ether silanes, ester silanes and/or epoxy-substituted alkyl silanes are used as an organosilane compound.

16. The method according to claim 1, wherein the solution from step d) has a pH value of approximately 10 to 12.

17. The method according to claim 1, wherein the solution from step d) contains at least one complexing agent, such as EDTA, N, N, N′, N′-tetrakis(2-hydroxypropyl) ethylendiamine (quadrol) or potassium sodium tartrate.

18. The method according to claim 1, wherein step b) is carried out at a temperature of 25° C. to 90° C.

Description

EXAMPLES

Example 1

[0024] Glass substrates were cleaned using acetone and piranha solution for one hour and then incubated in 10 % to 20 % PDDA solution for two hours. Subsequently, the samples were rinsed with distilled water and placed in a solution with gold nanoparticles which was produced according to the Turkevich method, wherein the particle size was < 100 nm. The solution contained 1 % of gold chloride, 0.01 % of Triton-X® and 0.3 g/l trisodium citrate. After the nanoparticles had been immobilized on the substrate for at least two hours, the samples were rinsed once more and placed in a plating bath having 0.05 % of agar agar, 3.2 g/l copper sulfate pentahydrate, 11.3 g/l potassium sodium tartrate, 5 g sodium hydroxide (pH value 10 to 12) and 32 ml/l formaldehyde. In this case, the agar agar was used as a polysaccharide source. By varying the plating times from 2 minutes to 20 minutes at room temperature, seed layers having a thickness of 30 .Math.m to 150 .Math.m were obtained. A tape test according to ASTM showed a 5B grade, indicating a strong adhesion.

Example 2

[0025] Example 2 was carried out analogous to Example 1, with the exception that PDDA was replaced by 1 g/l branched polyethylene (molecular weight 25,000 to 750,000, PEI).

Example 3

[0026] Example 3 was carried out analogous to Example 1, with the exception that PDDA was replaced by 0.946 g/l (3-aminopropyl)triethoxysilane or APTES.

Example 4

[0027] Example 4 was carried out analogous to Example 1, with the exception that the glass substrates were replaced by photoreactive, cured polyimide or dry-layer epoxy substrates, which were deposited on a silicon or glass substrate. Additional swelling or etching treatments were integrated into the method as a part of the pre-treatment, before an incubation in PDDA/APTES was carried out. Swelling in an aprotic solvent, such as dimethyl sulfoxide (DMSO), was carried out at 25° C. to 60° C. for one minute. Subsequently, micro-etching took place in a solution containing 0.5 % to 1 % of a water-soluble swelling agent, such as DMSO, 0.5 % to 1 % of surfactants based on polyethylene glycol, such as Triton-X®, 1 % to 3 % of ammonium hydroxide compounds and/or sodium hydroxide compounds and 10 % to 30 % of alcoholic compounds, such as methanol, isopropanol or ethanol for 20 minutes to 1 hour. Subsequently, the substrates were treated with 10 % sulfuric acid before being rinsed and immersed in a polyelectrolyte solution.