Solid Bridging during Pattern Collapse (Stiction) Studied on Silicon Nanoparticles
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Solid Bridging during Pattern Collapse (Stiction) Studied on Silicon Nanoparticles Daniel Peter1, Michael Dalmer1, Andriy Lotnyk2, Lorenz Kienle2, Alfred Lechner3, and Wolfgang Bensch4 1
Lam Research Corporation, SEZ Str. 1, 9500 Villach, Austria Institute for Material Science, Christian-Albrechts-Universität Kiel, Kaiserstr. 2, 24143 Kiel, Germany 3 Microsystems Engineering, University of Applied Sciences Regensburg, Seybothstr. 2, 93049 Regensburg, Germany 4 Inorganic Chemistry, Christian-Albrechts-Universität, Max-Eyth-Str. 2, 24118 Kiel, Germany 2
ABSTRACT The high surface to volume ratio of nanoparticles allows a detailed experimental study of the surface phenomena associated with solid bridging. Besides bulk analyses, the local view on the structure and composition via HRTEM is particularly essential. 50 nm core shell particles consisting of a silicon (Si) core and a SiO2 shell were used as model system to understand surface phenomena appearing for Si-based nanostructures. Evaporative drying from de-ionized water shows the most significant bridging effect based on SiO2. There is only a localized deposition of oxides between the particles during the drying process and no overall oxidation. For the deposition material, silicates are the most likely candidates. INTRODUCTION The surface preparation of semiconductor wafers is an important part of the production process. One essential requirement for wet surface preparation (i.e., etching and cleaning) is to avoid any damage of the structured wafer surface. The most vulnerable patterns are high aspect ratio structures, which are typically capacitor over bitline, shallow trench insulator (STI), or future FinFET structures. The largest mechanical forces in a wet clean process are generally attributed to physical force assisted cleaning steps (e.g., megasonics, spray systems) [1] and the surface tension forces in the drying step [2]. The distinctive damage from surface tension forces is the connection of the former free ends of the structures after drying (Figure 1). The fixed end can either be ruptured or elastically bent . The latter case is important for micro-electromechanical systems (MEMS) [3], which differ from microelectronic structures mainly by the higher aspect ratios and the larger size of micrometers versus nanometers. For a permanent damage, a sufficiently large sticking force [3] has to keep the structures in place against the restoring elastic moment after the liquid, and therefore the surface tension force, is removed. On MEMS devices, the main adhesive force for hydrophilic surfaces is hydrogen bonding, and for hydrophobic surfaces, van der Waals forces (vdW) [4]. Additionally, after the collapse, residues (e.g., silica) can accumulate around the contact site and form a solid bond which is called solid bridging [4-7]. Corresponding adhesive energies are expected to be larger than hydrogen bonding and vdW forces; however, the determination of the characteristic energies is complicated by the inhomogenous deposition of the silica residues. The aspect
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