Deposition Mechanism of Oxide Thin Films Manufactured by a Focused Energetic Beam Process
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Deposition Mechanism of Oxide Thin Films Manufactured by a Focused Energetic Beam Process H.D. Wanzenboeck, S. Harasek, H. Langfischer, E. Bertagnolli Vienna University of Technology Institute for Solid State Electronics Floragasse 7 / E362; Vienna, AUSTRIA ABSTRACT Chemical vapor deposition (CVD) is a versatile deposition technique for both dielectrics and metals. CVD is based upon the adsorption of a volatile species from the gas phase and the decomposition of the adsorbed molecules on the sample surface resulting in the deposition of solid material. In contrast to thermal CVD or plasma assisted CVD used for large area coatings this work focuses on a method for locally confined deposition. A focused energetic beam is used to provide the necessary activation energy for CVD. With a focused beam material could be deposited locally within a strictly confined area down to the nanometer range. The deposition of silicon oxide microstructures utilizing two precursor gases - siloxane and oxygen - was performed by direct-write nanolithography. For initiating the CVD process energy is introduced by local ion exposure utilizing a scanning focused ion beam (FIB). The influence of the different ion fluxes and the effect of the mixture ratio of precursors were studied. Deliberate changes in the process parameters allowed adjusting the physical properties and the chemical composition of the solid silicon oxide. Process control allows tailoring of material properties according to requirements of the application. INTRODUCTION Thin layers prepared by chemical vapor deposition (CVD) have a broad technological application range [1]. With CVD volatile precursor compounds are first adsorbed on a surface and then react with additional energy to form a solid film [2]. Metalorganic CVD (MOCVD) utilizes metalorganic precursor substances to deposit metal films. Using a mixture of precursor gases also alloys, oxides or nitrides can be deposited. In microelectronic applications oxide layers are frequently used as dielectric layer. The composition of the gas phase determines the properties of the deposited material. Structures with a feature size in the sub-µm range are required for semiconductor devices. The typical fabrication method utilizing optical lithography requires the deposition of a homogeneous thin film over the entire sample. In the second step the film is patterned using lithographic methods. As alternative method direct-write nanolithography has been established during the last decade. This new technology is particularly useful for chip prototyping and circuit modification. With direct-write lithography the material can be deposited only in a spatially confined area. Without a photomask fine structures can be deposited within a single process step. Direct-write nanolithography utilizes a chemical vapor deposition process. The particularity is that the energy for activating the CVD process is provided by a focused energy beam such as laser, ion beam or electron beam. The CVD process is restricted to a spatially confined a
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