DMAB Oxidation for Electroless Deposition from Alkaline Solutions

Abstract

Dimethylamine borane (DMAB) has been used as a reducing agent in electroless baths for many years. There has been an increased interest in DMAB-based electroless baths recently for applications in microelectronics such as barrier/capping layers for copper IC interconnect. To optimise the plating baths a thorough understanding of the role of each of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for DMAB and the simpler ammonia borane (AB) to assist in the analysis of borane oxidation in alkaline solutions. Both DMAB and AB are shown to oxidise in two steady state mass transport- controlled oxidation waves for specific concentration ranges. The potential range for oxidation, the optimum concentration and a suggested mechanism for oxidation are shown.

Electroless Plating Cycle Process for High-Conductivity Flexible Printed Circuits

“…DMAB [(CH 3 ) 2 NH-BH 3 ] has only three active hydrogens connected to the boron atom and theoretically should reduce three Cu 2+ for each DMAB molar consumed . However, in addition to the reduction reaction, DMAB can be consumed by its hydrolysis. − In the acid environment, DMAB has the acid hydrolysis that (CH 3 ) 2 NH-BH 3 + H – + 3H 2 O → (CH 3 ) 2 NH 2 + + H 3 BO 3 + 3H 2 . In the alkaline environment, DMAB has the hydrolysis that (CH 3 ) 2 NH-BH 3 + OH – + H 2 O → (CH 3 ) 2 NH + BO 2 – + 3H 2 .…”