Grounded and Suspended Polysilicon Nanowires fabricated by Top Down approach
Résumé
Owing to their physical and electrical properties, silicon nanowires (SiNWs) represent a promising material with strong potential for a large variety of applications. In this study, polycrystalline silicon nanowires (poly-SiNWs) are synthesized using a classical fabrication method commonly used in microelectronic industry: the sidewall spacer formation technique. Assets of this technological process rest on low cost lithographic tools use, classical silicon planar technology compatibility and the possibility to get by direct patterning numerous parallel nanowires with precise location on the substrate. Sidewall spacer formation technique consists in depositing a polysilicon layer by Low Pressure Chemical Vapour Deposition method on a wall patterned by conventional UV lithography technique. Polysilicon film is then etched by anisotropic Reactive Ion Etching (RIE). Accurate control of the etching rate leads to the formation of nanometric size spacers along the vertical sidewall. These spacers are used as polysilicon nanowires. Such synthesis method is performed in three different ways: i) the wall is kept throughout the technological process, so poly-SiNWs are anchored to this wall. ii) the wall is a SiO2 layer deposited by Atmospheric Pressure CVD technique and is removed after nanowires formation. These two configurations lead to the formation of grounded poly-SiNWs. iii) the nanowires underlying sacrificial layer is removed after nanowires synthesis leading to suspended poly-SiNWs. Poly-SiNWs with a curvature radius as low as 50 nm are integrated into the fabrication of resistors and electrical properties are studied in function of N and P type in-situ doping levels over a large range, from 2.1016 at.cm-3 to 2.1020 at.cm-3. Current-temperature measurements performed in the range 200 K - 530 K show that poly-SiNWs dark conductivity is thermally activated following the Mott's theory related to the nanowires size dependent structural quality. Field effect transistors with grounded nanowires as channel region are fabricated and results show potential use of these nanowires for electronic applications. Moreover, from process i) to iii), poly-SiNWs present an increasing surface with environment making them interesting for charged chemical species detection.