Infrared Laser Specroscopy of Radicals: A Diagnostic for Etching/Deposition Plasmas

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This RUI project is in the general area of analytical and surface chemistry and in the subfield of plasma diagnostics. Radio frequency and direct current plasmas in silane and halogenated gases are used extensively for etching and depositing thin films on semiconductors. The understanding, control, and optimization of these processes requires non-intrusive in situ diagnostic probes. In this research activity, infrared absorption spectroscopy will be used to provide complementary information to more commonly used diagnostic techniques such as laser induced fluorescence and optical emission spectroscopy for the characterization of transient polyatomic radical species typically present in these technologically important plasmas. The energies of the infrared absorptions will be used to identify the species present and the corresponding intensities of the absorptions will be used to determine their concentrations. Data obtained from these experiments will be used to model chemical events within the plasmas that are of importance to surface etching and deposition processes as well as to combustion chemistry. To achieve the goals of this research, a tunable infrared laser will be used to measure the high resolution spectra of significant plasma-generated radicals such as SiF3, SiCl2, SiH2, HSiF, and Si2H4. Initially the radicals will be generated in a radio frequency or direct current plasma contained in a multipass cell. Frequency, Zeeman, and concentration modulation will be employed to improve the minimum detectability and to differentiate the radical spectra from those of stable molecules. Following analysis of the spectra, a plasma reactor that simulates the conditions encountered in the manufacture of semiconductor devices will be built and the radical concentrations, spatial distributions, and rotational, vibrational, and translational temperatures will be measured as functions of external plasma parameters. These measurements should then enable the development of a model for the chemical reactions that take place in these plasmas and should also establish infrared absorption spectroscopy as a powerful plasma diagnostic.