The Dynamic Nature of Hydridosilsesquioxane Clusters on Gold Surfaces

Abstract

The chemisorption of the hydridosilsesquioxane clusters H8Si8O12 and H10Si10O15 onto a freshly evaporated gold surface has been observed by X-ray photoemission and reflection-absorption infrared spectroscopies. On the basis of these analytical techniques and supporting nonlocal density functional calculations, a single Si-Au bond at a cluster vertex is created through a surprising gold-mediated Si-H bond activation. The chemisorbed clusters are stable in a vacuum and when exposed to oxygen or water. Coverage-dependent peak frequency and infrared intensity shifts, characteristic of a chemically dynamic interface, are detected as a function of cluster overpressure. An equilibrium between the clusters and the gold surface is proposed, evidenced by a fairly constant rate of adsorption to gold for several coverage regimes. IntroductionProgress in the areas of microelectronic device packing density, speed, and functionality generally requires smaller device dimensions. 1 The ensuing problems associated with smaller line dimensions such as propagation delay, crosstalk noise, and power dissipation must be addressed. As a solution to these problems, new, low dielectric constant (k < 3) materials as well as alternative architectures have been proposed to replace the current Al(Cu) and SiO 2 interconnect technology. However, the replacement of SiO 2 as the insulator of choice is frequently complicated by the occurrence of undesired chemical reactions at the interface between the new low-k material and the metal lines. As dimensions approach the atomic scale, characteristics of microelectronic devices can become dominated by the chemical structure and dynamics of the interfaces.Hydridosilsesquioxane (HSQ) resin (k ) 2.9) is a siloxane-based polymer consisting primarily of O 3 SiH entities with an overall stoichiometry of (HSiO 1.5 ) n . High thermal stability, excellent gap fill capability, low electrical leakage, and relatively low outgassing properties are some of the desirable attributes of this polymer. 2 However, device failure results when the polymer is used in direct contact with metal lines. To avoid this problem, the first step used during device fabrication involves the formation of a very thin layer of SiO 2 directly on the metal lines. The HSQ resin is then spun cast onto the SiO 2 followed by curing and testing. 2 This procedure is problematic because it adds additional steps to the process and adds nonnegligible amounts of SiO 2 (k ∼ 4) to the dielectric layer. Ideally, a low-k dielectric could be applied directly without the formation of the SiO 2 barrier layer. In this paper, the reactions that HSQ resin may undergo when in direct contact with metal surfaces are explored.The interface of metal-insulator metal (MIM) devices is also of substantial interest. MIM devices show interest-

Formation of Mixed Layers Derived from Functional Silicon Oxide Clusters on Gold

“…A diffusion barrier may exist that is dependent upon the contours of the atomically rough gold surface. The chemisorption and displacement behavior of a monosubstituted cluster, C 6 9 The XPS spectrum reveals two Si 2p 3/2 core-level features with binding energies (BEs) of -101.2 and -102.5 eV, which have full-widths at half-maximum (fwhm) of 0.57 and 1.14 eV, respectively. These two features comprise the three nominal types of silicon atoms on the surface, H-SiO 3 , C-SiO 3 , and Au-SiO 3 can be assigned as Au-SiO 3 .…”

“…Since the frequency position of the ν as (Si-O-Si) is coverage dependent, this affords yet another piece of evidence for the cluster desorption. 9 These observations are reversible by simply reintroducing clusters to the vacuum chamber.…”

“…on freshly evaporated gold surfaces in ultrahigh vacuum (UHV) has been previously characterized by soft X-ray photoelectron (XPS) and reflection-absorption infrared spectroscopies (RAIRS). 8,9 These adsorbates, commonly known as hydridosilsesquioxane clusters, are a volatile, well-defined chemical species that are easily synthesized and can be separated into several sizes of the formula (HSiO 1.5 ) n (n ) 8, 10, 12, remains intact including Cl 8 Si 8 O 12 and (CH 3 ) 8 Si 8 O 12 have also been reported in the literature. 17 Some of the dynamic properties of the silicon oxide cluster monolayer have also been previously discussed.…”

“…18 D 8 Si 8 O 12 has been observed to undergo displacement reactions with H 8 Si 8 O 12 on gold surfaces(Figure 2). Note the appearance of the feature at 1662 cm -1 assigned to ν(Si-D) 9. The intensity of the ν(Si-H) at 2271 cm -1 and the δ(Si-H) at 888 cm -1 has also decreased considerably(Figure 2b).…”

The gas-phase structure of the decasilsesquioxane Si10O15H10

“…9 The vibrational spectra of Si 10 O 15 H 10 have been studied in detail for solutions, 12,13 the solid phase 12,14, 15 and when deposited onto a surface. 13,16 Binding energies for Si 10 O 15 H 10 on surfaces have also been determined by photoemission spectroscopy. 16, 17 The potential of Si 10 O 15 H 10 as a CVD precursor to high-quality SiO 2 films has been demonstrated, 18 as has its use as a component in a photosensitive resist film.…”