The above-described deposition apparatus enables deposition of an oxide semiconductor whose hydrogen concentration measured by SIMS is lower than or equal to 2×1020 atoms/cm3, preferably lower than or equal to 5×1019 atoms/cm3, further preferably lower than or equal to 1×1019 atoms/cm3, still further preferably lower than or equal to 5×1018 atoms/cm3.
Furthermore, an oxide semiconductor whose nitrogen concentration measured by SIMS is lower than 5×1019 atoms/cm3, preferably lower than or equal to 1×1019 atoms/cm3, further preferably lower than or equal to 5×1018 atoms/cm3, still further preferably lower than or equal to 1×1018 atoms/cm3 can be deposited.
Moreover, an oxide semiconductor whose carbon concentration measured by SIMS is lower than 5×1019 atoms/cm3, preferably lower than or equal to 5×1018 atoms/cm3, further preferably lower than or equal to 1×1018 atoms/cm3, still further preferably lower than or equal to 5×1017 atoms/cm3 can be deposited.
Furthermore, an oxide semiconductor can be deposited of which the released amount of each of the following gas molecules (atoms) measured by TDS is less than or equal to 1×1019/cm3, preferably less than or equal to 1×1018/cm3: a gas molecule (atom) having a mass-to-charge ratio (m/z) of 2 (e.g., a hydrogen molecule), a gas molecule (atom) having a mass-to-charge ratio (m/z) of 18, a gas molecule (atom) having a mass-to-charge ratio (m/z) of 28, and a gas molecule (atom) having a mass-to-charge ratio (m/z) of 44.