For via structures landed on aluminum lines, a significant increase of via resistance has been observed if the titanium (Ti) via liner is introduced by the ionized metal plasma (IMP) vapor deposition method instead of the standard physical vapor deposition method. To understand the underlying mechanism of this phenomenon, the reaction between the IMP deposited Ti and the aluminum under-layer has been studied. The experimental results indicate that during IMP-Ti deposition, energetic titanium ions react with the aluminum under-layer, forming a resistive titanium aluminide (TiAlx) layer. This reaction can be further enhanced by accelerating the titanium ions with a more negative substrate bias. The existence of this TiAlx layer at the via interface contributes to the elevated via resistance that has been observed at subsequent electrical parametric testing. (C) 2007 Elsevier B.V. All rights reserved.