Paper SS2-MoM6
Chemical Vapor Deposition of Boron Carbo-nitride as a Passivation Film for Ge Surfaces

Monday, October 15, 2007, 9:40 am, Room 611

As electronic device dimensions are scaled down Ge is receiving considerable attention as an alternative to Si. The primary motivation is the higher charge carrier mobility in Ge compared to Si. However, the Ge/GeO_x interface is chemically and electrically unstable. This work investigates the ability of boron carbo-nitride (BCN) films to passivate single crystal Ge surfaces and Ge nanowires. The BCN films are deposited by thermal chemical vapor deposition (CVD) using dimethylamine borane with NH₃ and C₂H₄ coreactants. Adjustments to the gas composition during CVD make it possible to tune the BCN stoichiometric composition, constituent bonding, and dielectric constant. Ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) were used to determine the minimum thickness of BCN resulting in a continuous film on Si(100) and Ge(100) substrates. Si(100) was chosen to develop the experimental protocol because of its well-documented surface chemistry. To determine film continuity using ISS, the ratio of the post-BCN substrate signal (either Si or Ge) to the predeposition bare substrate signal was plotted as a function of BCN thickness (determined by XPS peak attenuation for Si and spectroscopic ellipsometry for Ge). Due to the high surface sensitivity of ISS, a continuous BCN film should result in complete attenuation of the substrate signal. BCN becomes continuous at ~2.5nm when grown on Si(100) and ~3.5nm when grown on Ge(100). Differences in the BCN/Si and BCN/Ge interface were examined by depth profiling to understand how interface reactions affect film nucleation. A series of ISS scans gradually sputters the BCN, and XPS scans following each ISS scan track the atomic composition of BCN until the Si or Ge substrate is reached. In both cases the film composition at the substrate interface drastically differs from the bulk composition (BC_0.7N_0.1), with N dominating the B and C contributions at the interface. Nitrogen accumulation is much more pronounced on Si. The BCN film at the BCN/Si interface is comprised of ~70% N whereas the film at the BCN/Ge interface is only ~40% N. XPS was used to determine BCN-coated Ge's ability to withstand oxidation by monitoring changes in the Ge 2p and Ge 3d oxidation states with increasing ambient exposure time. A discontinuous 2.0nm BCN film slows, but does not prevent, Ge oxidation. A continuous 3.5nm BCN film shows no oxidation of Ge following 2 weeks ambient exposure.