Size-controlled colloidal Pd(II) catalysts for electroless Ni deposition in nanolithography applications

A new Pd(II) electroless metal deposition catalyst dispersion, PD2, prepared by quenching a PdCl sub 4 exp 2- solution with HCl and excess NaCl following rapid hydrolysis at pH approx =7 and approx =0.8 mM NaCl is described. The precursors to the catalytic Pd(0) species are shown to be chloride-rich Pd(II) colloidal particles having negative surface charge by x-ray photoelectron spectroscopy, UV-visible spectroscopy, centrifugation, and chemical tests. The particles bind selectively and covalently at ligand-modified surfaces with complete surface coverage occurring for treatment times > =2 min. Atomic force microscopy indicates that the average and maximum sizes of the bound particles are 9plus/minus3 and 18 nm, respectively. A correspondingly narrow distribution (15 to 33 nm) of Ni particles of average size 21plus /minus5 nm is obtained following metallization of catalyzed surfaces. The ability to control Ni particle morphology using PD2 is successfully exploited in the selective metallization of approx =15 nm features patterned by scanning tunneling microscopy. Metallization occurs with minimal distortion of feature geometries and no pattern degradation due to Ni overgrowth or bridging of adjacent features. Catalyst behavior is well described by a model in which domination of particle nucleation events and dispersion medium chemistry during colloid formation determine particle surface binding, stability, size, and dispersity.