Abstract: A functional load lock apparatus having two or more load lock chambers mounted on a central chamber which can be mounted on a single opening in a vacuum chamber such as a substrate processing platform for making integrated circuits on silicon wafers. Each load lock chamber preferably has a semi-cylindrical valve which remains sealed when the load lock chamber is open to atmospheric pressure. A wafer cassette holder positioned within each load lock chamber can be loaded and unloaded while the semi-cylindcical valves seal the vacuum chamber from atmospheric pressure. The semi-cylindrical valve pivots to an open position when the load lock chamber is under vacuum and the entire wafer cassette moves from the load lock chamber to the central chamber.