Optimized Surface Pre-treatments for Cu Electroless Plating in ULSI Device Interconnection

Abstract

We investigated the effects of under layer pretreatments on Cu electroless deposition to optimize the resistivity and morphology of the Cu. The pretreatments used in the Cu electroless plating process consisted of the removal of the titanium oxide layer on the barrier metal, TiN, and the deposition of Pd to activate the TiN diffusion barrier layer. Surface pretreatment using a 1%HF solution to remove the native Ti oxide formed on a TiN diffusion barrier layer showed a remarkable surface conditioning effect for the catalytic metal activation stage in Cu electroless plating, even in the absence of a wetting agent. Microcavities generated during Ti oxide etching are believed to be the key factor for the improved uniformity of the deposited catalytic metal on the pretreated TiN layer. Electroless plated Cu layers on non-uniform or rough Pd layers exhibited high resistivity and RMS roughness.