Copper electrodeposition is used in the damascene process for the fabrication of interconnections of ultralarge-scale integrated semiconductor devices. Copper electroless plating is one of the most promising processes for the formation of a seed layer for electroplating. In this article, the effect of additives of mercapto alkyl carboxylic acid (MACA) such as 3-mercaptopropionic acid, 11-mercaptoundecanoic acid, and 16-mercaptohexadecanoic acid on bottom-up filling of electroless copper in deep submicrometer via holes was investigated. The inhibition of copper plating deposition on the plane surface was observed with an addition of MACAs, and bottom-up fill was confirmed for MACAs with alkyl chain numbers of 3, 11, and 16. The bottom-up fill tendency was enhanced with increasing alkyl chain number. This result strongly suggests that the diffusion coefficient of inhibitor molecule plays an important role for bottom-up fill mechanisms, because MACA with longer alkyl chain has smaller diffusion coefficient than that with shorter alkyl chain. (c) 2006 American Vacuum Society.