Electrochimica Acta 70 (2012) 69–75 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Investigation of additives for electroless plating of nanowires Elliott J. Bird 1 , Kyle A. Nelson, John N. Harb, Dean R. Wheeler ∗ Department of Chemical Engineering Brigham Young University, Provo, UT 84602, United States a r t i c l e i n f o Article history: Received 1 March 2012 Accepted 4 March 2012 Available online 12 March 2012 Keywords: Palladium deposition Nanowire metallization Electroless plating additive a b s t r a c t The goal of this work is to deposit nanoscale metal features on a nonconductive substrate in a specific and controlled manner in order to make nanoscale devices. To this end we studied the effects of several plat- ing additives on electroless plating of nanoscale-thin layers in a model system, namely palladium metal on plain and chemically modified silicon oxide substrates. We selected and tested a series of candidate additives including sulfur- and sulfonate-containing molecules such as 3-mercapto-1-propanesulfonate (MPS) and propane disulfonate (PDS). Comparative growth rates, surface composition, morphology, and surface electrical conductivity on homogeneous surfaces were used as a proxy for determining the speci- ficity and quality of deposits on a heterogeneous substrate. MPS and PDS showed the greatest effect on the electroless seeding and plating of palladium on the surface. This work shows that the use of partic- ular additives under electroless plating conditions can lead to nanoscale-thin, selective, and conductive deposits of palladium metal. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction While electroless metallization is a well-developed industrial field, nanoscale metallization is still not fully developed or under- stood, though there has been growing interest in using it to create templated nanowires [1–9]. In order for electroless plating to be a viable solution to creating nanowires needed for nanocircuits and other nanodevices, the method must be able to produce pat- terned features on a nanoscale that are selective (bound to the substrate only in desired locations) and conductive. Conductivity on the nanoscale demands that the method produce metal crystal- lites with close packing and even distribution within the deposit region and with low metal–metal junction resistance. This work attempts to achieve these objectives by adjusting process additives for the seeding and plating steps. Additives are used to both accelerate and inhibit plating of metal on surfaces [10,11] by controlling the energetic barriers to crystallite nucleation and growth [12,13]. Additives used in the copper damascene process allow for trench filling and uniformity of the deposit [14]. Our use of additives in an electroless plat- ing environment is with the intention of enhancing metallization and conductivity in templated locations and decreasing metalliza- tion in other locations. However, in most industrial applications of electroless plating, rapid metallization and uniform coverage of all exposed surfaces is the desired outcome. Thus the plating baths ∗ Corresponding author. Tel.: +1 801 422 4126. E-mail address: dean wheeler@byu.edu (D.R. Wheeler). 1 Current address: U.S. Military Academy, West Point, NY, United States. used by industry for electroless plating are generally too aggressive to function in our application. This paper and a companion paper [15] investigate the possi- ble advantages of using organic additives for plating of nanoscale conductive regions on an insulating substrate. Here we examine the effects of seven particular additives for nanoscale electro- less deposition of palladium metal on a silicon oxide substrate. Aminosilane-coated and non-coated substrates were used. Com- parative growth rates, surface composition, morphology, and surface electrical conductivity were determined. MPS and PDS showed the greatest positive effect on the electroless seeding and plating of palladium on the surface. 2. Experimental design 2.1. Additives Table 1 contains a list of additives, generated from suggestions in the literature, which we tested for a possible positive effect on plat- ing [12,16–19]. In preliminary tests four of the additives showed a qualitative effect on palladium plating, compared to samples that were not treated with additive, and became the focus of this work (indicated with ‘Y’ in Table 1). The additives selected for further study have either thiol or a sulfonate functionality that is commonly associated with electroplating additives. The effect of the additives on electroless plating was assessed at the seeding and plating steps. In this context the term pretreat- ment means application of the additive to the substrate prior to the seeding step. Treatment means application of the additive to the substrate after the seeding step and prior to the plating step. For 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2012.03.013