SIZE-CONTROLLED COLLOIDAL PD(II) CATALYSTS FOR ELECTROLESS NI DEPOSITION IN NANOLITHOGRAPHY APPLICATIONS

A new Pd(II) electroless metal deposition catalyst dispersion, PD2, pr epared by quenching a PdCl42- solution with HCl and excess NaCl follow ing rapid hydrolysis at pH similar to 7 and similar to 0.8 mM NaCl is described. The precursors to the catalytic Pd(0) species are shown to be chloride-rich Pd(IT) colloidal particles having negative surface ch arge by x-ray photoelectron spectroscopy, W-visible spectroscopy, cent rifugation, and chemical tests. The particles bind selectively and cov alently at ligand-modified surfaces with complete surface coverage occ urring for treatment times greater than or equal to 2 min. Atomic forc e microscopy indicates that the average and maximum sizes of the bound particles are 9 +/- 3 and 18 nm, respectively. A cor respondingly nar row distribution (15 to 33 nm) of Ni particles of average size 21 +/- 5 nm is obtained following metallization of catalyzed surfaces. The ab ility to control Ni particle morphology using PD2 is successfully expl oited in the selective metallization of similar to 15 nm features patt erned by scanning tunneling microscopy. Metallization occurs with mini mal 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 e vents and dispersion medium chemistry during colloid formation determi ne particle surface binding, stability, size, and dispersity.