An apparatus (10) for depositing a thin film on each surface (116) of a plurality of substrates, such as wafers (114). The apparatus comprises a liner tube (50) having a first end (54), a second end (56) and an interior (68) capable of accommodating the substrates between the first and second ends. The apparatus includes a gas supply system (140) for providing a reactive gas to the liner tube interior at or near its first end, and a gas exhaust system (160) to exhaust the gas emerging from the second end. A gas flow restrictor (120) is arranged at the second end and is designed so as to restrict the flow of the gas at the second end such that the gas flow velocity at the first end is substantially the same as the gas flow velocity at the second end. This uniformizes the gas flow between the substrates within the liner tube, which results in the thin film being deposited more uniformly on each wafer surface.