Abstract: A wafer processing apparatus includes a common path, extending in a Y-axis direction, in which one wafer or a plurality of wafers are conveyed, a plurality of process units stacked on both sides of the common path to constitute multi-stage structures, a main handler moved in the common path in the Y-axis direction and rotated about a Z axis at an angle .theta.

Abstract: A wafer processing apparatus includes a common path, extending in a Y-axis direction, in which one wafer or a plurality of wafers are conveyed, a plurality of process units stacked on both sides of the common path to constitute multi-stage structures, a main handler moved in the common path in the Y-axis direction and rotated about a Z axis at an angle &thgr; to load/unload the wafer into/from the process units, an arm section arranged to move in the main handler in the Z-axis direction, a plurality of holding arms arranged in the arm section to constitute a multi-stage structure so as to respectively hold the wafers, each holding arm being advanced and retreated on an X-Y plane from the arm section, an optical sensor, arranged in the arm section, for detecting a holding state of the wafer in each of the plurality of holding arms, and a controller for controlling an operation of the main handler, an operation of the arm section, and operations of the plurality of holding arms on the basis of a detection resul