Infrared spectroscopy study of a poly-silicon film for optimizing the boron-implanting dose

Mikko Tuohiniemi, Martti Blomberg, Feng Gao

    Research output: Contribution to journalArticleScientificpeer-review

    3 Citations (Scopus)


    An experiment was carried out for recording the infrared transmission between 3 and 16 μm for a free-standing poly-silicon (Si) thin film as a function of the boron-ion implanting. The optical constants were extracted in order to optimize the postdeposition implanting of the membranes in a surface micromachined Fabry-Perot interferometer for the thermal infrared. The free-carrier concentration must not degrade the refractive index n significantly since a high and constant value over the application wavelength range is desired. Moreover, an increase in the extinction coefficient k is detrimental for the interferometer performance. On the other hand, poly-Si electrical conductivity must be doped high enough to avoid static charging and to prevent any layout-dependent distribution of the applied control voltage. We applied the variable-angle transmission spectrometry for recording the data of suspended poly-Si membranes, doped with different levels of implanting dose. The Drude model dispersion formula was exploited for extracting the optical constants n(λ) and k(λ). The optical constants are presented as a function of the dopant concentration and the electrical resistivity.
    Original languageEnglish
    Pages (from-to)1207-1212
    JournalJournal of Microelectromechanical Systems
    Issue number5
    Publication statusPublished - 2013
    MoE publication typeA1 Journal article-refereed


    • boron
    • implanting
    • optical constants
    • polysilicon


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