Cyanide-free monovalent copper electroplating solutions

Abstract

A substantially cyanide-free plating solution for depositing copper from the monovalent ionic state, which includes monovalent copper ion, a reducing agent capable of reducing divalent copper ions to monovalent copper ions, an alkali material in an amount sufficient to maintain the pH of the solution in the range of about 7 to about 10, and a complexing agent of an imide, such as succinimide, 3-methyl-3-ethyl succinimide, 3-methyl succinimide, 3-ethyl succinimide, 3,3,4,4-tetramethyl succinimide, or 3,3,4-trimethyl succinimide, or a hydantoin, such as dimethyl hydantoin. The substantially cyanide-free plating solutions may also include at least one of a conductivity salt, an additive to promote brightness, or an alloying metal. The reducing agent may be an alkali sulfite, alkali bisulfite, hydroxylamine, or hydrazine. The copper is typically provided in the form of CuCl, CuCl.sub.2, CuSO.sub.4, or Cu.sub.2 O in an amount sufficient to provide a monovalent copper concentration of from about 2 to about 30 grams per liter of solution, and the complexing agent is present in an amount sufficient to provide a molar ratio of copper to complexing agent of from about 1:1 to about 1:5, preferably about 1:4. The alkali material is typically NaOH, KOH, NH.sub.4 OH, or Na.sub.2 CO.sub.3, and the conductivity salt is typically NaCl, KCl, Na.sub.2 SO.sub.4, K.sub.4 P.sub.2 O.sub.7, Na.sub.3 PO.sub.4, C.sub.6 H.sub.5 Na.sub.3 O.sub.7, C.sub.6 H.sub.11 NaO.sub.7, NH.sub.4 Cl, or KNaC.sub.4 H.sub.4 O.sub.6. Useful additives include organic amines or oxyalkyl polyamines, such as triethylene tetramine, tetraethylene pentamine, and polyoxypropyl-triamine. Methods for preparing such a solution for plating copper onto a substrate, and of plating copper onto a substrate with such a solution are also disclosed.