Abstract: A novel automatic vertical-slide door assembly for a supply chamber, and a substrate-processing apparatus incorporating such a door assembly for sealing engagement in the presence of either negative or positive pressure, such as atmospheric pressure, within the supply chambers or load locks and the central transfer station. The present door assemblies are relatively thin and vertically movable to fully cover and uncover the access port or opening to the load lock chamber, and a section thereof is also horizontally-movable a slight distance into compression against the face surface of the load lock to seal the load lock against leakage of either positive or negative pressure, while avoiding any frictional sliding contact with the face surface of the load lock or with the sealing gasket surrounding the access port or opening thereto during vertical operation thereof.