DE4111558C1 - Formaldehyde-free bath for electroless deposition of copper - contains copper salt complexing agent, and formic acid (salts) or addn. prods. as reducing agent - Google Patents

Abstract

A bath for the electroless deposition of Cu contains (A) as known a Cu salt a complex former (mixt) and (B) HCOOH, its salts, derivs or its addn. prods. as reducting agent. The salt is pref. Cu formate. The reducing agent is a 1,2 or 3 main gp. salt of HCOOH, NH4COOH, activated HCOOH. The complex former is e.g. a carboxylic acid (salt), phosphonic acid (salt), a polyamine, polyethyleneimine, esp in amounts of 0.05-100g/D. The bath also contains additives, e.g. maleic acid, a fluoride, diphosphate. Deposition is carried out at 25-100 deg.C. ADVANTAGE - The bath is free from HCOH and toxic substances; environmetally acceptable reducing agents are used; a better quality Cu deposit than previously is obtd.

Description

The invention relates to a formaldehyde-free bath for electroless deposition of Copper and procedures using this bath.

From the prior art are a variety of reductive copper baths for electroless deposition known (for example, from Electroplating 80, 406 (1989) and US Pat. No. 4,695,505). It is usual that from a strongly alkaline copper solution the copper is reduced by means of formaldehyde to metallic copper. The Basic composition of such formaldehyde-containing baths has been around Not significantly changed in 1960. The baths contain in addition to the reducing agent Formaldehyde Copper ions in free or complexed form, besides usually another stabilizer.

The operation of these formaldehyde-containing baths is extremely expensive because a large monitoring effort is required. Sometimes you need up to four Regenerating solutions are used to maintain the setpoints of bath ingredients to arrive at a satisfactory copper deposition. Furthermore can be the reducing properties of the highly toxic formaldehyde exploit only in baths with high alkalinity at elevated temperature what the Applications for alkali-sensitive coating materials essential limited. The previously known baths can therefore only conditionally Copper deposition on thin plastic films in the resist technique within the Conductor technology can be used.

Also, the addition of phosphinic acid or its salts with the usual complexing agents does not lead to a significant improvement of chemical copper deposition, because of the Passivwerden the copper coatings only one layer thickness by Max. 0.4 microns is deposited and these coatings also still by Copper (I) hydride and copper (I) oxide are contaminated.

It can be determined that from the prior art for the previously known Copper baths for electroless plating have the following disadvantages:

• a) formaldehyde-containing baths,
• b) strongly alkaline baths,
• c) quality of the copper coatings to be improved,
• d) Use of toxic substances.

The present invention has the object, a formaldehyde-free bath for electroless Deposition of copper using a more environmentally friendly reducing agent, operating in the acidic range.

This object is achieved by the subject invention, according to the claims, solved.

The most important point of the present invention is that the reducing agent Methanoic acid can be used.

The methanoic acid is a cheap chemical product and is used for example in the Food technology used for preserving.

This is to be considered as the simplest carboxylic acid as aldehyde and has in the Tat pronounced reductive features. Thus, the methanoic acid is able to and to reduce mercury ions in aqueous solution to metals.

In this context, there has been no lack of considerations and attempts to use these also very specifically for copper reduction.

E. B. Saubrestre describes, for example, in Proc. Amer. Electoplaters Soc. (1959) Pp. 267-276 corresponding experiments with methanoic acid. As a result of this work it is reported that the reduction of copper II succeeds only up to the copper I stage and the addition of formate to the formalin tape deteriorates the quality of the copper overcoat becomes.

Further by U. Gehringer and coworkers in the magazine for Galvanotechnik 80 (1989) p. 406 that an autocatalytic deposition of Copper is not possible in the presence of the reducing agent methanoic acid.

Surprisingly, it has now been shown that addition of the complexing agents according to claim 7 an autocatalytic reduction of copper (II) - Ion with methanoic acid and this process for technical separation of copper can be used.

Suitable reducing agents are not only the methanoic acid, but also their Salts or their derivatives or their addition compounds. As salts of Methanoic acid are, for example, those containing elements of first, second or third main group, in particular lithium, sodium, potassium,  Magnesium, calcium, boron and aluminum. In addition, ammonium and Copper formate also usable. Also suitable are salts of methanoic acid, containing nitrogen-containing cations, for example quaternary Ammonium compounds. As derivatives of methanoic acid can be esters of methanoic acid and / or Methansäureamide use. Particularly noteworthy are the Methyl, ethyl and propyl esters.

According to claim 7, the copper complexing listed there Compounds are used. Suitable complexing agents are carboxylic acids or their salts, hydroxycarboxylic acids or their salts, alcohols or Alcoholates, phosphonic acids or their salts, primary, secondary or tertiary Amines or polyamines, amino acids or their derivatives, polyethylenimines or their substitution products. Particularly suitable are polyalkyleneimines, such as these be described in DE-OS 37 43 744.

It is possible, a complexing agent or a mixture of different To use complexing agent in the baths according to the invention.

It is advantageous, as indicated in the examples, a copper complex mixture to use, consisting of biologically well degradable complexing agents with functional OH and COOH groups exists. Complex these complexing agents predominantly copper. The compounds specified in claim 7 can in be added from a quantity of 50 mg / liter.

The copper plating solutions are relatively simple and absolutely stable. Copper instantly becomes a shiny salmon red color on the corresponding pretreated substrates deposited without causing an initial dark dirty copper deposit comes. Because no stabilizers needed and no decay products of methanoic acid adversely affect the metal deposition influence, it comes to a very pure copper deposition.

If very pure copper layers at low temperature (room temperature up to 50 ° C), it is advantageous to use only nitrogen-containing complexing agents and here, especially about an economic process perform the bath regeneration with a copper formate solution.

The according to claim 12 claimed according to the invention pH range between 3.5 and 11.0 has its optimum range of 4.0-10.0. To be pH correction  Methane or alkali metal hydroxides used to prevent foreign ions additionally enter the bathroom.

The deposition temperature is in the range of 25 ° C to 100 ° C, preferably at 70 ° C.

The copper metallization can also be carried out in an autoclave, the deposition temperature is thus above the boiling point of the water.

In accordance with claim 11, in support of the copper deposition at appropriate Contacting possibilities an electrical potential applied or a Alternating voltage to be superimposed. The required potential level is empirical Value and depends on the bath composition and the bath geometry.

The regeneration of the bath systems described in the patent is extremely easy.

The addition of copper can be carried out as a copper salt solution, wherein the metered addition automatically via a photometer.

The pH correction can be done via a measuring electrode and is treated with methanoic acid performed, which also acts as a reducing agent. Stabilizers are in the Normally not necessary, since these are stable deposition systems.

Leave with the formalin-free acidic copper bath described in the invention pure ductile copper exhaust after a very economical and environmentally friendly Produce process.

The following examples are intended to illustrate the invention:

example 1 Copper sulphate pentahydrate | 19.65 g / l ethylenediamine 10.40 g / l Polymin P35 15.00 g / l sodium 10.00 g / l

pH adjustment to pH 4.5 with methanoic acid; 50 ° C

Example 2 Copper hydrate pentahydrate | 11.80 g / l diethylenetriamine 11.00 g / l sodium 10.00 g / l

pH adjustment to pH 6.0 with methanoic acid; 70 ° C

Example 3 Copper sulphate pentahydrate | 19.65 g / l ethylenediamine 10.30 g / l 1-hydroxyethane-1,1-diphosphonic acid 1.90 g / l Sodium phosphate Dodekanhydrat 10.00 g / l sodium 15.00 g / l

pH adjustment to pH 6.0; 60 ° C

Example 4 Copper sulphate pentahydrate | 19.65 g / l boric acid 20.00 g / l tartaric acid 15.50 g / l copper formate 0.01 g / l sodium 10.00 g / l

pH adjustment to pH 7.0; 60 ° C

Example 5 Copper sulphate pentahydrate | 19.65 g / l ethylenediamine 10.00 g / l Succinic acid 20.25 g / l boric acid 10.00 g / l sodium 10.00 g / l

pH adjustment to pH 5.0; 50 ° C

Example 6 Copper sulfate pentahydrate | 11.80 g / l Succinic acid 12.50 g / l Quadrol 10.00 g / l Phosphate dodecahydrate 5.00 g / l sodium 15.00 g / l

pH adjustment to pH 5.0; 70 ° C

Example 7 Copper sulphate pentahydrate | 19.65 g / l D-fructose 31.00 g / l citric acid 36.00 g / l Phosphate dodecahydrate 15.00 g / l sodium 10.00 g / l

pH adjustment to pH 7.0; 70 ° C

Example 8 Copper sulphate pentahydrate | 19.65 g / l Natriumglucomat 37.00 g / l Polymin P 5.00 g / l Sodium phosphate pentahydrate 15.00 g / l Phosphate dodecahydrate 15.00 g / l sodium 15.00 g / l

pH adjustment to pH 5.00; room temperature

Example 9 Copper sulphate pentahydrate | 19.65 g / l Sodium trihydrate 42.00 g / l Natriumdiphospat pentahydrate 35.00 g / l sodium 20.00 g / l

pH adjustment to pH 7.50; 50 ° C

Example 10 Copper sulphate pentahydrate | 19.65 g / l glycerin 15.80 g / l Sodium diphosphate pentahydrate 34.00 g / l sodium 20.00 g / l

pH adjustment to pH 6.00; 70 ° C

Example 11 Copper sulphate pentahydrate | 19.65 g / l glycerin 23.40 g / l Decahydrate 20.00 g / l Sodium phosphate dodecahydrate 25.00 g / l sodium 15.00 g / l

pH adjustment to pH 6.00; 80 ° C

Example 12 Copper sulphate pentahydrate | 19.65 g / l iminodiacetic 41.50 g / l Sodium phosphate dodecahydrate 5.00 g / l sodium 20.00 g / l

pH adjustment to pH 6.00; 80 ° C

Example 13 Copper sulphate pentahydrate | 19.65 g / l ethylenediamine 18.70 g / l

pH adjustment to pH 5 with methanoic acid; 90 ° C

Claims (15)

1. formaldehyde-free bath for the electroless deposition of copper with a copper salt, a complexing agent or a mixture of a plurality of complexing agents and a reducing agent, characterized in that it contains as a reducing agent or mixture of reducing agents of methanoic acid or its salts or their derivatives or their addition compounds. 2. Bath according to claim 1, characterized in that it copper formate and a complexing agent or a mixture of several complexing agents and optionally contains additives. 3. Bath according to claim 1, characterized in that it is used as salts of methanoic acid, those of the elements of the 1st, 2nd or 3rd main group of the periodic table contains the elements. 4. Bath according to claim 1, characterized in that it salts of the methanoic acid containing nitrogen-containing cations such as ammonium formate. 5. Bath according to claim 1, characterized in that it is used as addition compound the methanoic acid activated formic acid contains. 6. Bath according to claim 1, characterized in that it as a reducing agent Contains methanoic or methanoic acid amides. 7. Bath according to claim 1 or 2, characterized in that it as Complexing agent carboxylic acids or their salts, hydroxycarboxylic acids or their salts, alcohols or alcoholates, phosphonic acids or their salts, primary, secondary or tertiary amines or polyamines, amino acids or their derivatives, polyethyleneimines or their substitution products. 8. Bath according to claim 7, characterized in that the zuzusetzenden Complexing agents in a concentration of 0.05-100.00 g / l in the bath are present.   9. Bath according to claim 2, characterized in that it as additives Maleic acid, succinimide, phosphates, fluorides, chlorides, bromides or diphosphates contains. 10. Process for copper deposition using the baths after at least one of claims 1-9, characterized in that for support the autocatalytic deposition of a laser beam is used. 11. A process for copper deposition using the baths after at least one of claims 1-9, characterized in that for copper deposition an electrical potential is applied or an AC voltage is superimposed. 12. The method according to claim 10, characterized in that the copper deposit in the pH range of 3.5-11.0. 13. The method according to claim 10, characterized in that the deposition temperature is maintained in the range of 25 ° C to 100 ° C. 14. The method according to claim 10, characterized in that the copper deposit at a deposition temperature greater than 100 ° C in one Autoclave is performed. 15. The method according to claim 10, characterized in that for copper regeneration in the bath, copper is dissolved anodically via a diaphragm system.