Immersion Deposition of Metal Films on Silicon and Germanium Substrates in Supercritical Carbon Dioxide

Abstract

A low-temperature CO2-based technology, supercritical fluid immersion deposition (SFID), has been developed for producing Pd, Cu, Ag, or other metal films on Si-based substrates in supercritical CO2 solutions. The reaction is most likely initiated by oxidation of elemental silicon to SiF4 or H2SiF6 with HF, causing the reduction of a metal chelate precursor to the metallic form on silicon surface in CO2. Using this method, only the substrate surfaces exposed to CO2 solutions are coated with metals, and the metal films (Pd, Cu, and Ag) exhibit good coverage, smooth and dense texture, and high purity. Preliminary experiment indicates that palladium films deposited on silicon by SFID can be converted to palladium silicide by annealing treatment. Metal films can also be deposited onto germanium substrates using SFID. The gaslike properties and high pressure of the supercritical fluids, combined with the low reaction temperature, make this SFID method potentially useful for fabricating thin films of metal or metal silicide in small features, which is difficult to accomplish by conventional metal deposition methods.

Equilibrium of dissolving species in aqueous H2SiF6 solution during the liquid phase deposition reaction

“…A part of the reason is because the aqueous reaction system including F -ion is very complicated. Intermediate species in the equilibrium reaction of SiF6 2-anion and oxides have been studied for gaseous reaction using plasma, 11) and surface finishing of Si wafer and its related materials 12) using various kinds of spectroscopic measurements. However, there are few studies for the equilibrium reaction of SiF6 2-complex anion species in the oxide deposition in liquid phase, whereas the equilibrium condition and reaction constant have been studied in detail.…”

Nanoparticle film deposition using a simple and fast centrifuge sedimentation method

“…This process requires an ultra-high vacuum or presence of a background gas (Aziz 2008). The supercritical CO 2 deposition method enables filling nanostructures of substrates with nanoparticles (Smetana et al 2008;Wang et al 2010;Ye et al 2003) but involves operations at high pressure with specialized equipment and knowledge.…”

Palladium nanostructures from galvanic displacement as hydrogen peroxide sensor

“…Metal deposition on silicon via galvanic displacement methods has been extensively reported for a wide range of metals [13], such as nickel [14], platinum [15], copper [16], silver [17], or gold [18]. In contrast, there exist few reports detailing palladium deposition, and they rely on the use of complex methodologies such as supercritical CO 2 fluid deposition [19], or they are based on less standard substrates such as germanium [20], or cobalt deposited on glassy carbon electrodes [21]. The electroless method presented here, and monitored by AFM, KPFM, SEM and XPS techniques, allows for the first time the synthesis of Si-nanoPd substrates as an effective way of plating silicon with Pd films and particles, while providing electrical conductivity all along the surface for implementation in electrochemical measurements.…”