Vacuum bearing structure and a method of supporting a movable member

摘要

A vacuum bearing structure comprises a combination of a planar gas bearing with a differentially-pumped vacuum seal. The bearing surface and the vacuum seal surfaces are formed of a porous material 112 divided into a first outer region 120 through which bearing gas can percolate to provide support and an inner second region 121 providing the vacuum seal. An exhaust groove 97 separates the two regions so that bearing gas can flow to atmosphere. The resulting structure can operate at a lower fly height d to reduce loading on the differentially-pumped vacuum seal. The structure is particularly useful for motion feedthroughs into vacuum processes such as ion implantation. The porous material may be graphite and the surface layer 123 may be impregnated to control the porosity.