Growth of Self-Aligned Crystalline Cobalt Silicide Nanostructures from Co Nanoparticles

Abstract

We have developed a new method with which we can for the first time produce self-aligned cobalt silicide (CoSi 2 ) nanostructures from Co nanoparticles. These nanostructures are formed by reacting Co nanoparticles with Si substrates at 900°C. Their dimensions are normally 3 to 10 nm wide and up to a few micrometers long. The orientations of these nanostructures are controlled by the crystalline substrate, as they are orthogonally and hexagonally aligned on Si(100) and Si(111), respectively. Because these self-aligned nanostructures (SAN) are thermally stable up to 1000°C in air and chemically inert to prolonged treatment with strong acids, and because their sizes are uniform and much smaller than those made from lithography, they can be ideal materials for making components such as electric contacts, interconnects, and gates for future nanoelectronics.One dimensional crystalline materials such as carbon nanotubes and nanowires made of ZnO, GaN, InP, and Si have been the focus of many studies in the past decade. 1-3 Challenges to the applications of these materials arise not only from making them but also from manipulating them to form devices. It is thus advantageous if one can directly produce desired nanostructures on suitable substrates for device fabrication. Such methods are usually called a bottom-up approach, and the starting materials are often monolayers or sub-monolayers of atoms. 4-7 Lithography, on the other hand, is a top-down method. It relies on the making and breaking of large, uniform materials such as thin films. Thus, if crystalline films are available, lithography can also be used to make microstructures. 8-10 For example, using this top-down method, submicrometer cobalt silicide structures have been made. 10-15 These structures can be used as contacts, gates, and interconnects in microelectronics because cobalt silicides are an excellent conductor and are thermally and chemically stable. However, the dimensions of the structures so fabricated using the top-down approach are much larger than those of the nanotubes and nanowires mentioned above.We report here a new method to directly synthesize as small as sub-5 nm and uniform CoSi 2 self-aligned nanostructures (SAN) with the bottom-up approach. Instead of using layers of atoms, our method uses nanoparticles (NP) of different sizes. The products are silicide crystalline nanostructures aligned on Si wafers. Co nanoparticles were made by following the reported procedure. 16 In brief, 0.54 g of Co 2 (CO) 8 was dissolved in 3-mL of oxygen-free, anhydrous dichlorobenzene in a drybox. The solution was then injected into a mixture of oleic acid, trioctylphosphine oxide, and trioctylamine at a temperature slightly above the boiling point of dichlorobenzene under Ar. After several minutes, portions of the solution were withdrawn from the reaction flask and placed in Ar-filled vials. Depending on the ratios of the surfactants, different sized Co nanoparticles were made, and their sizes were verified by transmission electron microscopy (TEM). Figure 1a sh...

Self-assembled epitaxial NiSi2 nanowires on Si(001) by reactive deposition epitaxy

“…A large number of self-assembled epitaxial silicide NWs were investigated in recent years [8][9][10][11][12][13][14][15][16]. The main focus on the study of these NWs has been on the rare-earth/Si and Ti/Si systems, based on the formation mechanism of strain-driven ''shape transition'', as represented by the Tersoff and Tromp and Jesson et al models [17,18].…”

Metal silicides: An integral part of microelectronics

“…A large number of self-assembled epitaxial silicide nanowires were investigated in the past. [36][37][38][39][40][41][42][43][44] Many RE silicide nanowires were grown on silicon substrates. These RE nanowires are commensurate with nearly perfect lattice match in their long direction and are limited in their ability to grow coherently 20 nm Figure 7.…”

Magnetic properties of Co–Si alloy clusters

“…In particular, cobalt silicide (CoSi 2 ) nanoclusters are applied as contacts, gates, and interconnects in nanoelectronics because cobalt silicide is thermally and chemically stable material as well as an excellent conductor [3].…”

“…In recent experiments, the Co-Si alloy clusters have been obtained from Co-Si mixture in a rapid thermal annealing process using CO 2 laser radiation [3,6]. Carter et al developed a new method with bottom-up approach and synthesized self-aligned CoSi 2 nanoclusters from Co nanoparticles on Si substrates, where their sizes are uniform and much smaller than those made from lithography [3].…”

“…Carter et al developed a new method with bottom-up approach and synthesized self-aligned CoSi 2 nanoclusters from Co nanoparticles on Si substrates, where their sizes are uniform and much smaller than those made from lithography [3]. The CoSi 2 , CoSi, and CoSi 2 phases exist and the CoSi phase converts to the CoSi 2 phase at 900 1C.…”