Orthogonal Self-Aligned Electroless Metallization by Molecular Self-Assembly

A strategy for achieving orthogonal electroless metallization (i.e., formation of a metal pattern not overlapping and self-aligned with a first metal pattern) is described. The approach comprises molecular passivation of a first gold pattern with 1-hexadecanethiol (HDT), followed by priming of the SiO2 substrate with (3-aminopropyl)triethoxysilane (APS) and activation with Pd(II) complexation to spatially direct electroless nickel metallization. Scanning electron microscopy indicates that the nickel nucleates on the gold sidewall and grows laterally over the dielectric but not over the gold surface. This confirms successful deactivation of the intrinsic catalytic activity of gold. Using this two-step orthogonal self-assembly of the molecular resist and primer, a lateral nickel metal pattern orthogonal and self-aligned to the first gold pattern with line width down to 10 μm has been demonstrated. The process can also be applied to curved and flexible substrates.