Method of consistently producing a copper deposit on a substrate by electroless deposition which deposit is essentially free of fissures

A method of formulating an electroless copper deposition solution capable of electrolessly depositing copper on a substrate the method comprising the steps of:

• a. forming a stable electroless copper deposition solution comprised of the following constituents:
• copper, one or more ligands to solubilize the copper, formaldehyde, an alkali metal hydroxide and one or more additives selected from accelerators, ductility promoters and surfactants;
• b. measuring the intrinsic anodic reaction rate of said deposition solution;
• c. measuring the intrinsic cathodic reaction rate of said deposition solution;
• d. whenever the ratio of the intrinsic anodic reaction rate to the intrinsic cathodic reaction rate is greater than or equal to 1.1, adjusting said ratio so that it is less than about 1.1;
• e. repeating steps b and c to determine whether said ratio is less than about 1.1;
• and
• f. repeating step d and then steps b and c until the measured ratio is less than about 1.1.

A method of adjusting an electroless copper deposition solution to ensure that it will deposit copper on a substrate such that the copper electrolessly deposited is free of fissures, the deposition solution comprising copper, one or more ligands, formaldehyde, an alkali metal hydroxide, and one or more additives, said method comprising the step of:

• a. measuring the intrinsic anodic reaction rate of said deposition solution;
• b. measuring the intrinsic cathodic reaction rate of said deposition solution;
• c. comparing the measured rates to determine whether the ratio of said intrinsic anodic reaction rate to said cathodic plating rate;
• is less than about 1.1.
• d. adjusting the intrinsic anodic reaction rate so that said ratio is less than about 1.1.

A method of operating an electroless copper deposition solution comprising copper, one or more ligands, formaldehyde, an alkali metal hydroxide, and one or more additives, said method comprising the steps of:

• a. measuring the intrinsic anodic reaction rate of said deposition solution;
• b. measuring the intrinsic cathodic reaction rate of said deposition solution;
• c. comparing the measured rates to determine whether the ratio of said intrinsic anodic reaction rate to said cathodic reaction rate is less than about 1.1;
• and
• d. adjusting the concentration of the constituents of the solution so that said ratio is less than about 1.1.

A method of controlling the commercial operation of an electroless copper deposition solution comprising copper, one or more ligands, formaldehyde, an alkali metal hydroxide, and one or more additives, the method comprising the steps of:

• a. measuring the intrinsic anodic reaction rate of said deposition solution;
• b. measuring the intrinsic cathodic reaction rate of said deposition solution;
• c. comparing the measured rates to determine whether the ratio of measured intrinsic cathodic reaction rate to the measured intrinsic anodic reaction rate is less than about 1.1;
• d. discontinuing commercial use of said deposition solution unless said ratio is less than about 1.1.

A method of adjusting an electroless copper deposition solution which has become contaminated causing reduction in deposition rate, quality of the copper deposit, or local passivation, to ensure that the solution will deposit copper on a substrate such that the copper electrolessly deposited is free of fissures, the deposition solution comprising copper, one or more ligands, formaldehyde, an alkali metal hydroxide, and one or more additives, said method comprising the steps of:

• a. increasing pH and/or formaldehyde concentration of the solution to increase the plating current produced by the anodic reaction;
• b. measuring the intrinsic anodic reaction rate of the solution;
• c. measuring the intrinsic cathodic reaction rate of said deposition solution;
• d. comparing the measured rates to determine whether the ratio of said intrinsic anodic reaction rate to said cathodic plating rate is returned to the ratio of the solution before contamination, or is less than 1.1.
• e. increasing the copper concentration of the solution;
• and
• f. adjusting the intrinsic cathodic rate so that said ratio is returned to the ratio before contamination or less than 1.1.

In a solution useful for electrolessly plating copper, said solution including copper ions, a complexing ligand to solubilize the copper ions, a pH adjuster in a concentration sufficient to adjacent the pH, a stabilizer or ductility promoter and a formaldehyde reducing agent, the improvement comprising:

• the concentration of the pH adjustor being sufficient to adjust the pH (as measured at 25.degree. C.) to at least 11.9;
• an accelerator containing a delocalized pi bond, the accelerator being selected from among
• (i) heterocyclic aromatic nitrogen and sulfur compounds,
• (ii) non-aromatic nitrogen compounds having at least one delocalized pi bond, and
• (iii) aromatic amines and mixtures of the foregoing;
• the mole concentration of the formaldehyde reducing agent being no greater than 1.2 times the mole concentration of the copper ion, and
• the stabilizer or ductility promoter being present in an amount sufficient to prevent extraneous copper plating or spontaneous decomposition of the solution at said pH and formaldehyde concentration and substantially less than the amount that would stop the plating reaction at said pH and formaldehyde concentration.

A method of forming a copper deposit on a substrate, said copper deposit being substantially free of fissures, the method comprising:

• a. providing an electroless copper deposition solution which comprises copper ions, a complexing ligand to solubilize the copper ions, a stabilizer or ductility promoter in an amount sufficient to prevent extraneous copper plating or spontaneous decomposition of the solution and substantially less than the amount which would stop the electroless copper deposition reaction, a formaldehyde reducing agent wherein the mole concentration of the formaldehyde reducing agent is no greater than 1.2 times the mole concentration of the copper ions, the solution having a pH of at least 11.9 when measured at 25.degree. C.;
• b. contacting the substrate with the solution for a time sufficient to form a deposit having a preselected deposit thickness;
• c. substantially maintaining the formaldehyde reducing agent concentration no greater than 1.2 times the concentration of copper ions during the time or deposition, and
• d. electrolessly depositing copper on the substrate.