DE10052449B4 - Process for the metallization of polymer surfaces - Google Patents

Abstract

Process for the metallization of polymers, in which a uniformly thin layer of metal nuclei is wet-chemically deposited for activation on the polymeric surface, and subsequently a metallic coating is carried out by wet-chemical means,
characterized in that
In a first step for the formation of a layer of metal nuclei in the polymer reductive acting molecules are stored,
- subsequently the polymeric surface is rinsed,
In a second step, the polymeric surface is treated with a substance reactive with the molecules,
Wherein reductive molecules emerging from the polymer react with the applied substance to form a layer of metal nuclei,
- And the wet chemical metal deposition takes place on the metal seed layer thus formed.

Description

The The invention relates to a process for the metallization of polymer surfaces the preamble of claim 1.

such Procedures are z. B. from Kunststoffgalvanisierung Leutze Verlag 1973 known.

For activation is used in a commonly performed procedure the surface with acid stannous chloride solutions pretreated: after a rinsing step with hydrolysis of the adsorbed Zinnchlorids the reduction takes place of palladium ions from an acidic palladium salt solution. When The problem with this process is the rinsing process. In the flush may precipitate the hydrolysis to tin hydroxide particles (pebbles, star dust) on the surfaces to lead, whose size is the structure size on a wafer surface far beyond. In addition, can during the rinsing process Desorb a portion of the adsorbed palladium ions.

A similar one Activation process consists of a treatment of the surface with a colloidal palladium solution, made of stannous chloride and palladium chloride. The resulting Palladium colloids (the size is a few Nanometers) are with a shell stabilized from tin dioxide. Also stick with this method the Particles, palladium colloids, with low surface power and can but by flushing a too smooth surface again be washed off. this leads to to a non-uniform coating a smooth surface.

to higher Process safety, these methods are applied to rough surfaces or ABS plastics applied. Otherwise, there are usually problems with adhesive strength on. In ABS graft polymers, caverns can form from the polymer surface etched which increase the liability after activation.

In addition there there ways Palladium on the surface ionic or over to bind an organic complex. After reduction become moderately adhesive and only submono layers obtained.

An example of this may be the treatment of a silane-modified surface (with amino or mercapto groups) with HAuCl ₄ or CuSO ₄ solution (1 Elect. Chem. Soc., 144 (1997) L151). The surface atoms can then be reduced and provide submonolayers. This process is problematic because of the intermediate rinsing processes, especially with smooth microstructured surfaces.

From the DE 689 16 523 T2 For example, a method of pretreating certain organic polymeric materials to deposit a metallic layer thereon in an electroless plating bath is known. The process should result in improved adhesion between the metal and the polymeric material. An essential feature of the method is that the surface of the organic polymer is brought into contact with a chemical reducing agent, wherein the chemical reducing agent does not remain on the polymer material. Since the method has a reducing effect on the surface of the polymer, only those polymers can be used which can be themselves reduced. This excludes from the outset the vast majority of polymers for the application of this method.

In DE 689 523 T2 During the treatment of the polymer, an exchange of electrons takes place on the surface of the polymer. That is, the actual charge transfer takes place at the beginning of the treatment of the surface. The process requires at least a low intrinsic conductivity, which is fulfilled only by very few polymers. In contrast, the polymer must have ionic conductivity to ensure exchange of the organic anions of the reducing agent with the cations of the metal. Very few polymers possess this ionic conductivity.

Light can also be used to activate polymer surfaces such as polyimide (J. of the Electrochem., Soc., 142 (1995) 3, 944). However, this process will be eliminated in structured surfaces because in structures the walls, the floor and the surface outside the structures are irradiated with very different light intensities. In the method according to US 4,775,556 a metal ion) is incorporated into the surface. Overall, this method appears much less suitable because small nonpolar molecules can be stored much more easily in a polymer than metals or metal ions. In addition, the process is considerably more complicated, by the necessary avoidance of oxygen or air, the reaction according to the invention must be carried out in a glove.

Furthermore, it is known in the so-called damascene process before a copper deposition structures, as in 1 listed to produce.

So far is used as a dielectric silicon dioxide or silicon nitride. For the Future, however, alternatives, such as Silk (non-polar polymer by Dow Chemical), which is characterized by a lower dielectric constant distinguished.

When Barrier becomes tantalum, tantalum nitride, tungsten titanium (PVD processes approx. 50nm) and so on. In the following process becomes the barrier coated with copper (PVD, approx. 100nm).

These Both PVD processes are relative to wet-chemical processes expensive, on the other hand arise increasingly difficulties in coating of small structures. The layer thickness on the wall of the structures is only a fraction of the nominal layer thickness.

A continuously wet chemical Coating separates so far, as for a high activation Germ density is required.

The The object of the invention is a process for wet chemical Activation of polymer surfaces for subsequent adherent wet chemical Deposition of a uniform thin, in particular indicate structured metal layer.

The The object is in connection with in the preamble of the claim 1 mentioned characteristics solved by the formation of the Layer of metal nuclei embedded in the polymer initially reductive molecules be, the polymeric surface with one with the molecules reacting substance, leaving the polymer exiting reductive molecules react with the applied substance, and so a layer of Metal nuclei is formed.

In a first step according to the invention by immersion in a solution (hydrazine, Boranate-containing, alkylaminoborane or formic acid-containing), which is a small non-polar reductive molecule (eg Hydrazine, boric acid, formic acid or hydrogen) in the Polymer can give off the surface layer loaded reductively.

At the subsequent rinsing process become only the adsorptively bound reductive components washed away in the surface embedded molecules stay preserved.

In A second step is by dipping in a precious metal-containing Solution, in particular a solution with palladium ions and partially modified (mostly opposite the first step) increased Temperature, the reductive molecules are outsourced from the surface and reacted with the palladium ions.

Preferably be on the polymer surface Deposited palladium bacteria. The deposition of the metal can even be performed partly directly on these reductively pretreated surfaces.

Further advantageous variants of the method are mentioned in the subclaims.

Of the Advantage of the invention is that the deposition of palladium nuclei preferred in the "molecular Sinks "of the total (microscopic) smooth polymer surface occurs. At the following Metallization is significantly less water trapped. Both leads to a significant increase the adhesion between the metal and the polymer layer over conventional Method. When activated can be significantly more than a monolayer be deposited.

The Further advantages of the invention are that for storage a small reductive molecule in the surface layer a polymer's process of activation largely independent of the adsorption or desorption of palladium complexes / ions or of the reducing agent. This offers advantages in uniform coating very smooth but textured surfaces (eg feature size 200 nm, Surface roughness of the Substrate about 1 nm) as in the field of application of semiconductor technology. The process depends on the removal of the reductive molecule from the surface layer of the polymer. Accordingly, the deposition on the surface can be enforced be, and it can small germs are formed. The formation of metal nuclei in the solution (this would be lead to particle contamination of the solution) can be prevented.

The Invention will be explained in more detail with reference to 3 embodiments. In show the drawings:

1 a damascene structure according to the prior art, which is coated with a metal layer (diffusion barrier or direct copper),

2 a representation to illustrate the reaction kinetics

3 a SEM image

The in the 1 Damascene structure shown is attributable to the prior art and has been previously explained.

When carrying out the process, a polymer is to be loaded in a first step with a molecule having a reductive action. For this purpose, about 10% of the polymer volume is available [(News from Chemie 48 (2/2000)).]. For determination of this polymer volume, the polymer can be immersed in a hot iodine / potassium iodide solution after the second step. The amount of iodine consumed can be determined by titration and provides the amount of stored reducing agent. It can be shown that after heating a pretreated after the first step of epoxy resin workpiece about 10% of the volume of the workpiece can be dispensed as a reducing agent to the solution again.

in the second step is the polymeric surface with one reacting with the molecules Treated substance and released the reductive molecules again. to Speeding up the swaging can increase the temperature during the second step opposite the first step in the solution elevated be. With insufficient surface-active precious metal solutions can the temperature of this second solution be lowered.

To a successful implementation of the procedure the following main reactions and their reaction rates get noticed.

The Embedding of the reducing agent in the polymer is such Main reaction. This reaction is characterized by the diffusion rate, which depends is of the diffusion coefficient. The diffusion coefficients of such small molecules in polymers are usually smaller by 1 to 2 orders of magnitude than the Diffusion coefficients in aqueous Solutions. The stored amount can be determined as described above and is temperature dependent.

• a) Auslagerung des Reduktionsmittels aus dem Polymer
• b) Antransport der Palladiumionen
• c) Reaktion zwischen dem Reduktionsmittel und dem Palladiumadsorbat
• d) Nebenreaktion und Abdiffusion des Reduktionsmittels

dargestellt.In the 2 is the reaction scheme of the running in the second step partial reactions

• a) removal of the reducing agent from the polymer
• b) Transport of the palladium ions
• c) Reaction between the reducing agent and the palladium adsorbate
• d) side reaction and diffusion of the reducing agent

shown.

The Removal of the reducing agent after partial reaction a) follows the same physical laws as the storage in the first process step and is characterized by the diffusion coefficient, the temperature difference and the occupied volume.

Of the Transport of the palladium complexes by partial reaction b) is characterized by the diffusion coefficients and the concentration of the reaction involved particles and is usually a fast-running process.

The surface reaction of the reducing agent with the palladium complexes after partial reaction c) can be accelerated by the use of surfactants Palladium solutions so solutions, those on nonpolar surfaces achieve a high occupancy with palladium ions / palladium salts.

The Side reactions d) (essentially Abdiffusion of the reducing agent and Abreaktion of the reducing agent with z. B. water) can together here to be viewed as.

For the successful coating in the second step, the reaction rates RG of the reactions b) - e) should behave as follows:
RG (d) «RG (c), RG (a)« RG (b)

The Partial reaction a) and its reaction rate can usually through temperature control very well on the other reaction rates be matched. If RG (c) <RG (d) turns out to be an optimization (nucleation in the solution, too much enlargement of the Germs on the surface etc,) is the palladium salt solution not sufficiently surface-active.

to Reducing the germ size is also the surface diffusion of the reducing agent and the palladium nuclei formed, which is not shown in the reaction scheme shown.

There these individual reaction rates are very specific to that used plastic (a polymer is particularly characterized by its degree of crosslinking, accordingly by the diffusion coefficients the stored reducing agent, the temperature dependence the usable polymer volume and the surface diffusion of palladium atoms) depend, is the optimization for to perform any plastic according to the above scheme. To shorten the Coating time can the temperatures of the individual solutions are increased

example 1

• 1) 15 min Tauchen in eine wässrige Lösung (80 g/l DMAB) bei 70°C
• 2) 1 min Spülen mit Wasser oder leicht angesäuerten Lösung (z. B. 0,5 g/l KH₂PO₄) bei RT
• 3) 15 min Tauchen in eine palladiumhaltige Lösung bei 50°C z. B. 5 g/l PdCl₂ 11 g/l HCl (konz.) 50 g/l KH₂PO₄
• 4) 15 min Tauchen in eine palladiumhaltige Lösung bei 70°C z. B. 5 g/l PdCl₂ 11 g/l HCl (konz.) 50 g/l KH₂PO₄
• 5) 15 s Spülen in Wasser
• 6) Tauchen in Lösung 1) zur Verhinderung von Wildwuchs in dem folgenden stromlosen Metallisierungsbad
• 7) 2 min Spülen in Wasser zur Reinigung der Oberfläche von Ionen

The activation of BCB (benzocyclobutadiene) surfaces (eg 500 nm layer thickness) was carried out as follows:

• 1) immersion in an aqueous solution (80 g / l DMAB) at 70 ° C for 15 min
• 2) Rinse with water or slightly acidified solution (eg 0.5 g / l KH ₂ PO ₄ ) for 1 min at RT
• 3) 15 min immersion in a palladium-containing solution at 50 ° C z. B. 5 g / l PdCl ₂ 11 g / l HCl (conc.) 50 g / l KH ₂ PO ₄
• 4) 15 min immersion in a palladium-containing solution at 70 ° C z. B. 5 g / l PdCl ₂ 11 g / l HCl (conc.) 50 g / l KH ₂ PO ₄
• 5) Rinse in water for 15 seconds
• 6) Dipping in solution 1) to prevent sprouting in the following electroless plating bath
• 7) 2 min rinsing in water to clean the surface of ions

Example 2

• 1) 20 min Tauchen in eine wässrige Lösung (80 g/l DMAB) bei 70°C
• 2) 2 min Spülen mit Wasser oder leicht angesäuerten Lösung (z. B. 0,5 g/l KH₂PO₄) bei RT
• 3) 20 min Tauchen in eine palladiumhaltige Lösung bei 30°C z. B. in 20 g/l PdCl₂ 25 g/l HCl (konz.) 100 g/l KH₂PO₄
• 4) 30 min Tauchen in eine palladiumhaltige Lösung bei 50°C z. B. in 20 g/l PdCl₂ 25 g/l HCl (konz.) 100 g/l KH₂PO₄
• 5) 30 s spülen in Wasser
• 6) Tauchen in Lösung 1)

For the coating of tetrafluoroethylene, the procedure was as follows:

• 1) immersion in an aqueous solution (80 g / l DMAB) at 70 ° C. for 20 minutes
• 2) Rinse with water or slightly acidified solution (eg 0.5 g / l KH ₂ PO ₄ ) for 2 min at RT
• 3) 20 min immersion in a palladium-containing solution at 30 ° C z. In 20 g / l PdCl ₂ 25 g / l HCl (conc.) 100 g / l KH ₂ PO ₄
• 4) 30 min immersion in a palladium-containing solution at 50 ° C z. In 20 g / l PdCl ₂ 25 g / l HCl (conc.) 100 g / l KH ₂ PO ₄
• 5) Rinse in water for 30 seconds
• 6) Dipping in solution 1)

to increase the amount of the incorporated reducing agent, the polymer and previously heated (eg at 150 ° C), the exposure times elevated or it may be the coating in bath 1) at elevated temperature (80 ° C).

Example 3

• 1) 5 min Tauchen in eine wässrige Lösung (8 % DMAB 5 g/l H₃PO₄) bei 60°C
• 2) 30 s Spülen mit Wasser oder leicht angesäuerten Lösung (z. B. 0,5 g/l KH₂PO₄) bei RT
• 3) 5 min Tauchen in eine palladiumhaltige Lösung bei Raumtemperatur z. B. 5 g/l PdCl₂ 11 g/l HCl (konz.) 50 g/l KH₂PO₄
• 4) 30 s spülen in Wasser
• 5) Tauchen in Lösung 1)

For the coating of epoxy resin, the procedure was as follows:

• 1) immersed in an aqueous solution (8% DMAB 5 g / l H ₃ PO ₄ ) at 60 ° C. for 5 min
• 2) Rinse with water or slightly acidified solution (eg 0.5 g / l KH ₂ PO ₄ ) for 30 sec at RT
• 3) 5 min immersion in a palladium-containing solution at room temperature z. B. 5 g / l PdCl ₂ 11 g / l HCl (conc.) 50 g / l KH ₂ PO ₄
• 4) Rinse in water for 30 seconds
• 5) dipping in solution 1)

To thorough do the washing up (eg 10 min) with water, the metal coating (de-energized) the activated polymer surface respectively.

To increase the stability of the palladium-containing bath, hydrogen peroxide can be added (concentration of hydrogen peroxide (30%) in the noble metal-containing bath to 0.2 g / l at 5 g / l PdCl ₂ )

Claims (10)

Process for the metallization of polymers, in which a uniformly thin layer of metal nuclei is wet-chemically deposited for activation on the polymeric surface, followed by a metallic coating by wet-chemical means, characterized in that - in a first step to form a layer of metal nuclei in the polymer reductive acting molecules are incorporated, - in the following the polymeric surface is rinsed, - treated in a second step, the polymeric surface with a substance reactive with the molecules, - reacting emerging from the polymer reductive molecules with the applied substance, and a layer of metal nuclei is formed, and the wet-chemical metal deposition takes place on the metal seed layer thus formed. Method according to claim 1, characterized in that that for the incorporation of reductive acting molecules the Polymer treated with a hydrazine-containing, borane-containing or alkylaminoboranhaltigen solution becomes. Method according to claim 2, characterized in that that to increase the activity the alkyl amino borane solutions, especially dimethylaminoborane or diethylaminoborane, slightly acidified. Method according to claim 3, characterized that the solution is acidified to a pH above 3. Method according to claim 2, characterized in that that hydrazine as 5% - 50 % aqueous solutions used becomes. Method according to claim 2, characterized in that that ionic boronates are used directly. A method according to claim 1 to 6, characterized in that the polymeric surface after the first step in water or in a slightly acidified solution, in particular about 1 g / l KH ₂ PO ₄ or in a 0.01% hydrogen peroxide-containing solution 15 s - Rinsed for 10 min. A method according to claim 1 to 7, characterized in that the polymer after rinsing in a second step with a noble metal-containing solution, in particular 5 g / l PdCl ₂ 11 g / l HCl (conc.) Treated 50 g / l KH ₂ PO ₄ becomes. Method according to claim 8, characterized that the precious metal-containing solution is stabilized by addition of about 0.005% hydrogen peroxide. Method according to claims 1, 2, 7 and 8, characterized that foreshortening the coating time the temperature is increased.