Bottom-up copper fill with addition of mercapto alkyl carboxylic acid in electroless plating

We investigated bottom-up electroless copper plating with addition of mercapto alkyl carboxylic acid (MACA) such as 3-mercapto-propionic acid (3-MPA), 11-mercapto-undecanoic acid (11-MUA), and 16-mercapto-hexadecanoic acid (16-MHA). 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 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.