system, the drive unit comprising a stationary part which is fastened to a machine frame
of the lithographic device, while the measuring system comprises a stationary part and a
movable part which is fastened to the substrate table for cooperation with the stationary
part of the measuring system, characterized in that the stationary part of the measuring
system is fastened to a reference frame of the lithographic device which is dynamically
isolated from the machine frame.
6. A lithographic device as claimed in claim 5, characterized in that the substrate table is
displaceable over a guide which extends perpendicularly to the main axis and is fastened
to the reference frame.
7. A lithographic device as claimed in claim 6, characterized in that the lithographic
device is provided with a force actuator system which is controlled by an electric control
unit and which exerts a compensation force on the reference frame during operation,
which compensation force has a mechanical moment about a reference point of the
reference frame having a value equal to a value of a mechanical moment of a force of
gravity acting on the substrate table about said reference point, and a direction which is
opposed to a direction of the mechanical moment of said force of gravity.
Van Engelen claim 10 depends on claim 9, which depends on claim 8, which depends on
claim 5. Van Engelen claims 8-10 are as follows:
8. A lithographic device as claimed in claim 5, characterized in that the lithographic
device comprises a further drive unit for displacing the mask table relative to the
projection system in a scanning direction perpendicular to the main axis, the further drive
unit comprising a stationary part which is fastened to the machine frame, while the
substrate table is displaceable relative to the projection system parallel to at least the
scanning direction, the measuring system comprising a further stationary part which is
fastened to the reference frame and a further movable part which is fastened to the mask
table for cooperation with the further stationary part of the measuring system for
measuring a position of the mask table relative to the projection system or for measuring
a position of the mask table relative to the substrate table.
9. A lithographic device as claimed in claim 8, characterized in that the mask table is
displaceable over a first guide extending parallel to the scanning direction and the
substrate table is displaceable over a second guide extending perpendicularly to the main
axis, the first guide and the second guide being fastened to the reference frame.
10. A lithographic device as claimed in claim 9, characterized in that the lithographic
device is provided with a force actuator system which is controlled by an electric control
unit and which exerts a compensation force on the reference frame during operation,
which compensation force has a mechanical moment about a reference point of the
reference frame of a value which is equal to a value of a sum of a mechanical moment of
a force of gravity acting on the substrate table about said reference point and a mechanical
moment of a force of gravity acting on the mask table about said reference point, and a
direction which is opposed to a direction of said sum of mechanical moments.
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