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

Germanium oxide (GeO_x) 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 GeO_x 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 GeO_x films from the Lorentz-Lorenz equation, low molar mass was obtained from the GeO_x film grown at 250 °C indicating germanium monoxide bond formation in the film. As the PE-ALD grown GeO_x 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 GeO_x films, compared to the reported etch rates of 60 ∼ 100 nm/s for germanium dioxide films. In summary, PE-ALD process for growing GeO_x films has the advantage of obtaining high film density with controllable water-etch rate.