Nanoseeding via dual surface modification of alkyl monolayer for site-controlled electroless metallization

In this work, an attempt to fabricate nanostructured metallization patterns on SiO(2) dielectric layers is made by using plasma-patterned self-assembled monolayers (SAMs), in conjunction with a novel aqueous seeding and electroless process. Taking octadecyltrichlorosilane (OTS) as a test material, the authors demonstrate that optimizing the N(2)-H(2) plasma conditions leads to the successive conversion of the topmost aliphatic chains of alkyl SAMs to carboxyl (COOH) and hydroxyl (C-OH) functional groups, which was previously found in alkyl SAMs only by exposure to "oxygen-based" plasma. Further modifying the plasma-exposed (either COOH or C-OH terminated) regions with an aqueous solution (SC-1) creates surface functionalities that are viable for site-controlled metallic seeding (e.g., Co or Ni) with an adsorption selectivity of greater than 1000:1. Neither the combination of costly PdCl(2) and complex additives nor the demerits of the associated aqueous chemistry (e.g., seed agglomeration and seed sparseness) are involved. Therefore, the seed particles are only 3 nm in size. Simultaneously, there are sufficient particle densities previously unattainable for electroless deposition to trigger highly resolved Cu metallization patterns with a film thickness of less than 10 nm. The formation of the seed-adsorbing sites is discussed, based on a plasma-dissociated, water-mediated chemical oxidation route.