Patent ID: 7280225

Claim:
A stage apparatus comprising: a stage movable in a first direction and a second direction, different from the first direction, the first and second directions being a horizontal direction; first and second measurement systems each having a laser interferometer and a mirror system including a first reflecting mirror elongated in the first direction and a second reflecting mirror elongated in the second direction, and measuring a position of the stage with respect to a vertical direction based on measurement of a length of a laser beam light path formed by the mirror system; a switching unit configured to transfer a measurement value from the first measurement system in use to the second measurement system and to switch the measurement system in use from the first measurement system to the second measurement system within an overlapping zone in which said first and second measurement system simultaneously measure the position of the stage; and a first correcting unit configured to correct the measurement value transferred by the switching unit, based on a difference in the length of the light path due to shapes of surfaces of the first and second reflecting mirrors of the first and second measurement systems.