This invention is directed to precision positioning devices which are well suited
to manufacturing and inspection of semiconductor devices. A pair of coil assembles
are attached to a base plate. The base plate forms a static portion of a gas bearing
assembly. A carriage assembly, forming a movable portion of the gas bearing assembly,
is capable of in-plane motion over the coil assembly. The carriage assembly contains
permanent magnets and a soft magnetic bridge. A metrology component, such as a
mirror, is attached to the carriage kinematically. Three in-plane constraints consist
of substantially straight line connections between the metrology component and
the carriage in a plane substantially parallel to the plane of motion of the gas
bearings. Three out-of-plane constraints on the metrology component comprise substantially
straight line connections between it and the gas bearings. The positioning device
is operable in vacuum by directing the flow of gas out of the bearings to a vacuum
pump. The positioning device is further capable of creating an area of low stray
magnetic fields through the use of moving magnetic shielding material.
