A load port receives a wafer carrier. An equipment front end module (EFEM) transfers semiconductor wafers to and from the wafer carrier via an access opening of a housing of the EFEM, and also transfers wafers to and from a semiconductor processing or characterization tool. A gas flow device disposed inside the housing of the EFEM is connected to receive a low humidity gas having relative humidity of 10% or less, and is positioned to flow the received low humidity gas across the access opening. A saturated pressure layer of the gas flow device has a permeability for the low humidity gas that increases with increasing distance from a gas inlet edge of the saturated pressure layer, for example due to holes of varying diameter and/or density passing through the saturated pressure layer. A filter layer of the gas flow device uniformizes the gas exiting the saturated pressure layer.