A system and method for introducing a substrate into a process chamber is provided. A presence or absence of a substrate on a stage in an apparatus for manufacturing a semiconductor or a flat panel display may be determined by lift pins used for loading and unloading a substrate, the introduction of another substrate may be prevented and a broken state or the erroneously loaded state of the substrate may be detected. An opening or closing of a gate valve may also be determined, and the introduction of a substrate into the process chamber may be prevented while the gate valve is closed.