Study on temperature-dependent growth characteristics of germanium oxide film by plasma-enhanced atomic layer deposition

Abstract

Germanium oxide (GeOx) films were grown by plasma-enhanced atomic layer deposition (PE-ALD) at 70, 130, 190 and 250 °C, using tetrakis (dimethylamino)-germanium as a precursor and O2 plasma as a reactant. For GeOx film grown at 250 °C, a relatively low growth-per-cycle (GPC) of 0.55 Å/cycle and high refractive index of 1.73 was observed as compared to the GPC and refractive index for the films grown at 70, 130, and 190 °C.Meanwhile, the areal portion of the germanium monoxide (GeO) peak to germanium dioxide (GeO2) in the Ge 3d core-level spectra of X-ray photoelectron spectroscopy increased proportional to the refractive index of the film. When estimating the mean molar mass of the GeOx films from the Lorentz-Lorenz equation, low molar mass was obtained from the GeOx film grown at 250 °C indicating germanium monoxide bond formation in the film.As the PE-ALD grown GeOx films exhibited high densities of about 3.5 g/cm3 almost close to the typical density value (3.6 ∼ 3.7 g/cm3) of germanium oxide film, low water-etch rates of 5 ∼ 10 nm/s were achieved for the PE-ALD grown GeOx films, compared to the reported etch rates of 60 ∼ 100 nm/s for germanium dioxide films. In summary, PE-ALD process for growing GeOx films has the advantage of obtaining high film density with controllable water-etch rate.