Cyanide-free monovalent copper eletroplating solutions

Abstract

A substantially cyanide-free plating solution for depositing copper from the monovalent ionic state, which includes a source of copper ions, 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 CuC1, CuC12, CuSO4, or Cu20 in an amount sufficient to provide a copper ion 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 ions to complexing agent of from about 1:1 to about 1:5, preferably about 1:4. The alkali material is typically NaOH, KOH, NH4OH, or Na2CO3, and the conductivity salt is typically NaC1, KC1, Na2SO4, K4P2O7, Na3PO4, C6H5Na3O7, C6H11NaO7, NH4C1, or KNaC4H4O6. 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.

Description

[0001] The invention relates to a monovalent copper cyanide-free electroplating solution for electroplating copper on a substrate. Background technique [0002] Various plating solutions using cyanide as a complexing agent have been successfully used for copper plating for many years. In this type of plating solution, copper exists in the form of complexes of monovalent copper and cyanide. This type of plating solution can also contain free or uncomplexed alkali metal cyanide, alkali metal hydroxide and complexing agents such as alkali metal tartrate to facilitate the dissolution of copper anodes. Although such baths have been used successfully, the industry continues to seek alternatives to the highly toxic cyanide ion. [0003] The plating solutions used to deposit monovalent copper are quite different from those used to deposit monovalent silver. Under normal circumstances, monovalent silver is very stable in the plating solution. However, if there...

AI Technical Summary

Problems solved by technology

Although this method has achieved some industrial success, it has been reported that the plating solution is occasionally unstable.