Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/38—Coating with copper
  • C23C18/40—Coating with copper using reducing agents
  • C23C18/405—Formaldehyde

Definitions

• the present invention relates to autocatalytic plating of metal, and more particularly, to improved autocatalytic metal plating solutions having an enhanced rate of deposition.
• SUMMARY Autocatalytic copper solutions which are capable of depositing copper continuously over long periods of time without the use of electricity, i.e., electrolessly, are now well known in the art.
• Such solutions ordinarily comprise a water soluble copper salt, a complexing agent for cupric ion, a reducing ion for cupric ion, and a pH adjustor.
• the rate of deposition and bath stability are important parameters from a commercial standpoint. Generally speaking, it can be said that slowing the rate of deposition will tend to increase the stability of the solution. Conversely, increasing the rate of deposition will tend to decrease stability.
• An object of the present invention is to enhance the rate of deposition from autocatalytic copper solutions without adversely affecting stability.
• the osmium is preferably in the form of osmium containing compounds.
• the osmium or osmium compound should be maintained in the solution in small amounts effective to control the plating rate.
• the amount of these materials will generally vary so as to maintain between about 0.001 milligram per liter and milligrams per liter of osmiurn in the solution. It should be emphasized that the osmium content of the bath will vary with the nature and activity of the osmium compounds used, and with the particular results desired.
• the selection of the water soluble copper salts for the electroless copper solutions of this invention is chiefiy a matter of economics. Copper sulfate is preferred for economic reasons, but the halides, nitrates, acetates and other organic and inorganic acid salts of copper may also be used.
• Rochelle salts the sodium (mono-, di-, triand tetrasodium) salts of ethylenediaminetetraacetic acid, nitrilotriacetic acid and its alkali salts, gluconic acid, gluconates, and triethanolamine are preferred as copper ion complexing agents, but commercially available g'lucono- 6-lactone and modified ethylenediamineacetates are also useful, and in certain instances give even better results than the pure sodium ethylenediaminetetraacetates.
• Preferred reducing agents for cupric ion which have been used in alkaline electroless metal baths include formaldehyde, and formaldehyde precursors or derivatives, such as paraformaldehyde, trioxane, l-hydroxymethyl 5,5-dimethyl hydantoin, glyoxal, and the like.
• borohydrides such as alkali metal borohydrides, e.g., sodium and potassium borohydride, as well as substituted borohydrides, e.g., sodium trimethoxy borohydride.
• borohydrides such as alkali metal borohydrides, e.g., sodium and potassium borohydride
• substituted borohydrides e.g., sodium trimethoxy borohydride.
• reducing agents in such baths may also be used boranes, such as amine borane, e.g., isopropylamine borane, morpholine borane, and the like.
• hypophosphites such as sodium and potassium hypophosphite, and the like.
• the pH adjustor or regulator may consist of any acid or base.
• the pH adjustor 0n the alkaline side is preferably potassium or sodium hydroxide, with particularly good results being obtained by the use of potassium hydroxide.
• pH will usually be adjusted with an acid having a common anion with-the copper salt. Since the preferred copper salt is the sulfate, the preferred pH adjustor on the acid side is sulfuric acid.
• the copper salt serves as a source of cupric ions
• the reducing agent reduces the cupric ions to metallic form.
• reducing agents of the type described above are oxidized to provide electrons for the reduction of the cupric ions, hydrogen is released at the site of deposition.
• the complexing agent serves to complex the cupric ion, and at the same time makes the cupric ion available as needed to the reducing action of the reducing agent.
• the pH adjustor serves chiefly to regulate the internal plating potential of the bath.
• a typical electroless metal deposition bath made according to the present invention will comprise:
• Preferred embodiments of highly active electroless copper solutions comprise:
• a soluble cupric salt preferably cupric sulfate-0.002 to 0.60 gram mole Alkali metal hydroxide, preferably sodium or potassium hydroxide, to give-pH of 10-14 Reducing agent, preferably formaldehyde-0.03 to 1.3
• surfactants in an amount of less than about 5 grams per liter may be added to the baths.
• suitable surfactants are organic phosphate esters and oxyethylated sodium salts, which may be obtained under the trade names Gafac RE 610 and Triton QS-lS, respectively.
• the potassium salts in general are preferred over the corresponding sodium salts in preparing the solutions of this invention.
• the osmium compounds of this invention may be used alone, or in combination with other activation ions, such as phosphorus, sulfur, or cyanide ions, or ions containing phosphorus, sulfur or cyanide.
• alkali cyanides such as sodium and potassium cyanide
• nitriles such as ehloroacetonitrile and alpha hydroxynitriles, e.g., glyconitrile and lactonitrile, and dinitriles, e.g., succinonitrile, iminodiacetonitrile and 3,3'-iminodipropionitrile.
• the source of sulfur may be used any sulfur compound, preferably one containing divalent sulfur, capable of forming a stable but dissociable chelate with cuprous ion.
• organic sulfur compounds may be mentioned the following: aliphatic sulfunnitrogen compounds, such as thiocarbamates, e.g., thiourea; S-membered heterocyclics containing S-N in the 5-membered ring, such as thiazoles and iso-thiazoles, e.g., 2-mercapto benzol thiazole and the like; dithiols, e.g., 1,2-ethanedithiol and the like; G-membered heterocyclics containing S--N in the ring, such as thiazines, e.g., 1,2-benzisothiazine, benzothiazine, and the like; thioamino acids, such as methionine, cystine, cysteine, and the like; thio derivatives of alkyl glycols, such as 2,2'-thiodiethanol, dithiodiglycol and thioglycollic acid; and the like.
• alkali metal sulfides e.g., sodium sulfide, potassium sulfide, sodium polysulfide, potassium polysulfide
• alkali metal thiocyanates such as sodium and potassium thiocyanates
• alkali metal dithionates such as sodium and potassium dithionate.
• sulfur compounds are merely typical of sulfur compounds which are capable of stabilizing autocatalytic copper baths as taught herein.
• the organic and inorganic phosphorus containing salts, acids and bases such as the water soluble phosphate, tetrapyrophosphate and hexametaphosphate acids and salts, including alkali and alkaline earth metals.
• the amount of sulfur compound required is a small effective amount and will vary, depending upon the particular compound used, from a trace to about 300 parts per million (ppm) or more. For most sulfur compounds 1 p.p.m. will be the upper limit and about 0.001 m. the lower limit. A good working limit for most sulfur compounds is between about 0.01 and 0.02 p.p.m.
• the amount of the cyanide compound to be added to the bath is between about 0.00001 to 0.06 mole per liter, preferably between about 0.00005 to 0.01 mole per liter. In Examples 1-2 below a bath formulation, designated A, was employed. It had the following composition:
• steel test strips (approximate area of 10 square centimeters) were immersed in the solution which was maintained at 60 C. for the time specified.
• the electroless copper solutions described herein are particularly suitable for metallizing insulating substrata on surfaces which have been suitably treated to make them sensitive to the reception of electroless metal deposition.
• Such sensitization techniques include the well known treatment with an acidic aqueous solution of stannous chloride (SnCl followed by treatment with a dilute aqueous acidic solution of pal adium chloride (PdCl Alternatively, sensitization may be achieved by treating the insulating substrata with an acidic solution containing a mixture of stannous chloride and precious metal chloride, such as palladium chloride, the stannous chloride being present in stoichiometric excess, based on the amount of precious metal chloride.
• metal surface is to be plated, it should be degreased, and then treated with an acid, such as hydrochloric or phosphoric acid, to free the surface of oxides.
• an acid such as hydrochloric or phosphoric acid
• the surface to be plated is immersed in autocatalytic metal baths, and permitted to remain in the bath until a metal deposit of the desired thickness has built up.
• portions of the surface of an insulating substratum in the form of a desired circuit pattern may be sensitized for the reception of electroless metal.
• the substratum is immersed in the electroless metal solution of the type described and permitted to remain therein until a metal deposit of the desired thickness has been built up.
• the circuit may be formed on one or more surfaces of the substratum. If desired, interconnections between the surfaces may be provided by drilling or punching holes and sensitizing the lateral walls thereof prior to exposure of the substratrum to the electroless metal solution.
• electroless metal builds up on the circuit pattern, as well as on the walls surrounding the holes to form interconnections.
• a bath for the electroless plating of copper which comprises a water soluble copper salt, a complexing agent for cupric ion, a pH adjustor and a reducing agent for cupric ion; the improvement which comprises in combination therewith a soluble osmium compound in an amount, calculated as osmium, sufiicient to enhance the rate of deposition of electroless copper.
• osmium is present in the form of a compound selected from the group consisting of osmium tetroxide and potassium osmiate.
• cyanide compound is a member selected from the group consisting of inorganic cyanides and organic nitriles.
• the sulfur compound is a member selected from the group consisting of thio derivative of alkyl glycols; a aliphatic S-N compounds; 5- members heterocyclics containing SN in the 5- membered ring; dithiols; G-membered heterocyclics containing S-N in the ring; thioamino acids; alkali metal sulfides; alkali metal polysulfide; alkali metal thiocyanate; alkali metal dithionates; and mixtures of the foregoing.
• the water soluble copper salt is present in an amount from about 0.002 to 1.0 mole per liter; the complexing agent for cupric ion is present in an amount between 0.7 to times the moles of copper salt; the pH adjustor is an alkali metal hydroxide which is present in an amount sufficient to maintain a pH of from about 10.0 to 14.0; and the reducing agent is formaldehyde and is present in an amount between 0.005 to 4.0 moles per liter.
• a process of electroless copper plating which comprises immersing a receptive surface to be plated in the electroless copper solution of claim 1.

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Cited By (6)

Citations (1)

• 1967
  • 1967-12-28 US US694086A patent/US3515563A/en not_active Expired - Lifetime
• 1968
  • 1968-12-19 GB GB60309/68A patent/GB1218850A/en not_active Expired
  • 1968-12-23 FR FR1599408D patent/FR1599408A/fr not_active Expired
  • 1968-12-24 NL NL6818581.A patent/NL157661B/xx not_active IP Right Cessation
  • 1968-12-28 DE DE19681817355 patent/DE1817355B2/de not_active Withdrawn

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