An electrostatic chuck comprises a sample stage 9 provided with electrodes 1, 2 and 3 for applying n-phase alternating voltage wherein n is equal to or greater than 2, and a circuit for applying the n-phase alternating voltage. The roadway is an intelligent system, having an access control computer limiting access of the roadways to the appropriate vehicles. The top plate 550 comprises a plurality of top discharge vents and a front discharge plate cover 545 comprises a plurality of side discharge vents 546.