Holder driving unit

摘要

A holder driving device has: a holder holding a substrate, a shaft supporting the holder, a driver for driving the shaft reciprocatingly and linearly in the direction along the shaft, a bearing unit having mechanical linear motion bearings for supporting the shaft thereon and having one or more stages of exhaust chambers surrounding the shaft; a vacuum pump for vacuum-pumping the exhaust chambers of the bearing unit; and a gas replacement mechanism for supplying dry gas, the humidity of which is lower than that of at least the surrounding atmosphere and the pressure of which is positive, from the outside of the bearing unit to at least the neighborhood of an atmosphere-side entrance portion of a gap between an end portion of the bearing unit one the side opposite to the vacuum vessel and the shaft passing the end portion, so as to replace the atmosphere near the entrance portion by the dry gas.