An apparatus with a processing chamber subjects a substrate to atomic layer deposition and deposits a film layer. The processing chamber includes at least a first gas switching port. A gas switching manifold is coupled to the processing chamber and configured to mix reactants with a neutral carrier gas and provide gas switching functionality for ALD processes. An upstream gas source and pressure setting apparatus is coupled to the gas switching manifold. The upstream gas source and pressure setting apparatus includes at least a first reactant source, a second reactant source and a neutral gas source. Additionally, the upstream gas source and pressure setting apparatus is configured to provide a cascade of continuing, decreasing pressures.