The present invention provides a positioning mechanism and an exposure
apparatus that can be used in a vacuum ambience and has a damping
function with small degassing and small dust creation. A positioning
mechanism according to the present invention, when used with first and
second members, serve to position the second member with respect to the
first member, wherein the positioning mechanism include a positioning
portion capable of relatively positioning the second member relative to
the first member, and an attenuating material provided at least at a
portion of a periphery of the positioning portion.