Native oxide removal from Ge surfaces by hydrogen plasma

The mechanisms to remove the native oxide layer on Ge(001) surfaces by an in situ hydrogen plasma inside an atomic layer deposition (ALD) reactor has been studied. A strong dependence of the reaction mechanism in the temperature range commonly employed by ALD has been identified through the combined analysis of atomic force microscopy, x-ray photoelectron and Raman spectroscopy. At low temperatures (e.g., 110 °C), the hydrogen plasma removed both Ge and O species from the native GeO₂ layer, but also induced surface damage to Ge substrate. At high temperatures (e.g., 330 °C), only O species were removed from the native oxide leaving a nanocrystalline Ge overlayer behind. The thermodynamically unstable nature of hydrogen passivation on Ge resulted in a Ge surface with a high density of dangling bonds. The transition temperature between the two reaction mechanisms was determined to be about 270 °C, allowing to compromise between removing a native oxide layer entirely and hydrogenating the underlying Ge surface without surface damage.