A six-free-degree displacement measurement method of an
exposure zone on a
wafer stage is applied in six-free-degree displacement measurement of the
exposure zone on the
wafer stage. The
wafer stage comprises a
coil array and a movement bench. A planar optical
grating is fixed below a magnetic steel array of the movement bench, so that a reading head is fixed in the gap of the
coil array, wherein a
central line of the reading head is coincided with a
central line of a lens. A measurement zone is formed by an incident measurement
light beam from the reading head on the planar optical
grating, wherein the centers of the measurement zone and the
exposure zone are positioned at the same vertical line. One part, which is covered by the exposure zone, of the movement bench is approximately considered as a
rigid body, when the movement bench is deformed due to movement or vibration, the six-free-degree displacement of the exposure zone is obtained by means of calculation of the six-free-degree displacement, which is measured by the reading head, of the measurement zone, thereby achieving six-free-degree displacement measurement of the exposure zone at any time during movement of the wafer stage. The method can reduce measurement complexity and increase
measurement precision, and especially can accurately measure the six-free-degree displacement of the exposure zone at any time even the movement bench his high in flexibility.