Application of remote hydrogen plasma to selective processing for Ge-based devices: Crystallization, etching, and metallization

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We demonstrated a novel technique for crystallizing ∼80-nm-thick hydrogenated amorphous Ge films (a-Ge:H) covered with Pt patterns with ∼2-nm-thick SiO<inf>2</inf>interlayers on quartz substrates by exposing them to remote H<inf>2</inf>plasma (H<inf>2</inf>-RP) without any external heating. After the samples were exposed to the H<inf>2</inf>-RP for 5 min, the crystallization of the whole film was confirmed in Raman scattering spectra, which implies that the exothermic recombination of hydrogen radicals generated in H<inf>2</inf>plasma on a Pt film surface plays an important role in improving the crystallinity caused by energy transfer through the SiO<inf>2</inf>interlayer. In the case without Pt coating and a SiO<inf>2</inf>interlayer, the a-Ge:H film was completely removed at an etching rate as high as ∼56 nm/min. We also studied the impact of H<inf>2</inf>-RP exposure of a-Ge:H directly covered with Pt on the germanidation reaction without any external heating. Raman scattering signals attributable to the Pt–Ge phase were observable within the first 1 min of H<inf>2</inf>-RP exposure. After exposure for 20 min, full germanidation of ∼80-nm-thick a-Ge:H was achieved, and its resultant sheet resistance was as low as ∼4.5 Ω/sq. The driving force of such a germanidation reaction is attributed to heat transfer caused by the efficient recombination of atomic hydrogen on the Pt surface.
2014-09-30