A thin transition film formed by plasma exposure contributes to the germanium surface hydrophilicity

Plasma treatment and 10% NH₄OH solution rinsing were performed on a germanium (Ge) surface. It was found that the Ge surface hydrophilicity after O₂ and Ar plasma exposure was stronger than that of samples subjected to N₂ plasma exposure. This is because the thin GeO_x film formed on Ge by O₂ or Ar plasma is more hydrophilic than GeO_xN_yformed by N₂ plasma treatment. A flat (RMS < 0:5 nm) Ge surface with high hydrophilicity (contact angle smaller than 3°) was achieved by O₂ plasma treatment, showing its promising application in Ge low-temperature direct wafer bonding. (paper)