Metallic Nanostructure Formation Limited by the Surface Hydrogen on Silicon

Abstract

Constant miniaturization of electronic devices and interfaces needed to make them functional requires an understanding of the initial stages of metal growth at the molecular level. The use of metal-organic precursors for metal deposition allows for some control of the deposition process, but the ligands of these precursor molecules often pose substantial contamination problems. One of the ways to alleviate the contamination problem with common copper deposition precursors, such as copper(I) (hexafluoroacetylacetonato) vinyltrimethylsilane, Cu(hfac)VTMS, is a gas-phase reduction with molecular hydrogen. Here we present an alternative method to copper film and nanostructure growth using the well-defined silicon surface. Nearly ideal hydrogen termination of silicon single-crystalline substrates achievable by modern surface modification methods provides a limited supply of a reducing agent at the surface during the initial stages of metal deposition. Spectroscopic evidence shows that the Cu(hfac) fragment is present upon room-temperature adsorption and reacts with H-terminated Si(100) and Si(111) surfaces to deposit metallic copper. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to follow the initial stages of copper nucleation and the formation of copper nanoparticles, and X-ray energy dispersive spectroscopy (XEDS) confirms the presence of hfac fragments on the surfaces of nanoparticles. As the surface hydrogen is consumed, copper nanoparticles are formed; however, this growth stops as the accessible hydrogen is reacted away at room temperature. This reaction sets a reference for using other solid substrates that can act as reducing agents in nanoparticle growth and metal deposition.

Controlling the Formation of Metallic Nanoparticles on Functionalized Silicon Surfaces

“…This analysis suggests that the majority of the copper deposited on the functionalized Si(100) surfaces is metallic, as contrasted with the copper standards and copper oxide samples. 28,52 It should again be emphasized that the presence of CuO as a majority species could be ruled out based on the XPS spectra alone. The diagram presented in Figure 3 helps to rule out Cu 1+ species as a majority as well.…”

“…The reaction of Cu(hfac)VTMS with the H-terminated silicon surfaces have been suggested previously to initiate at surface defects. 28 It is also known from detailed spectroscopic and microscopic studies 27,54−56 that the H−Si(100) surface prepared by a modified RCA procedure is atomically rough, leaving many surface defects available for reaction; thus, following the reaction of this surface with Cu(hfac)VTMS, nanoparticles with a narrow size distribution are formed, as shown in Figure 5. The H−Si(111) surface, when etched with ammonium fluoride, is atomically flat, with a minimum of surface defects; The copper nanostructures produced on the other functionalized surfaces in Figure 5 are compared to understand the copper nanoparticle growth on these surfaces.…”

“…Similarly to the previous studies, we assume that the copper particles have to nucleate on a surface reactive site, such as a N-or O-containing functional group or a defect (for example, an unoccupied dangling bond). 28 Thus, the surface with the largest number of reactive sites per unit area should result in the fastest initial deposition rate. At the same time, particle nucleation competes with the growth process, governed both by the chemistry of the deposition and by the surface diffusion processes, making the analysis of the overall process on the functionalized surface complicated.…”

Chemical Vapor Deposition of Copper: Use of a Molecular Inhibitor to Afford Uniform Nanoislands or Smooth Films

“…27,[44][45][46] The effect of the VTMS inhibitor on copper growth is very distinct from that of NH 3 on growth of HfB 2 on SiO 2 from Hf(BH 4 ) 4 , in which the density of nuclei increased continuously with time. 18 Evidently, in the latter system, nucleation is not directed by surface defects.…”

Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

“…For example, Cu(hfac)VTMS (copper(i) hexafluoroacetylacetonate vinyl trimethylsilane) and Cu(hfac) 2 (copper(ii) hexafluoroacetylacetonate) are common precursors for ALD or CVD methods and are used to produce either coppercontaining nanoparticles or continuous thin films. [18][19][20][21][22] Due to the structural differences of the two precursors, different reactivities and therefore surface morphologies of the structures produced are expected, as has been observed on surfaces such as ZnO, 22 silica, and silicon. 18,20,21 In addition, since the VTMS moiety from Cu(hfac)VTMS is expected to desorb from the substrate immediately upon adsorption, as was observed on several substrates even at room temperature, [20][21][22][23][24][25][26][27] Cu(hfac) is actually expected to be the reactive adsorbate (Figure 1(a)) that will interact with the surface for deposition based on this precursor.…”