Abstract: An electrostatic cassette assembly comprising, a cassette body having a central opening for receiving a wafer to be processed in a particle beam lithographic system, a charge plate with a top surface having a coating of dielectric (nonconductive) material or a plurality of nonconductive means, or both, on which the wafer is supported, means for forcing said charge plate and wafer into contact with stop means to hold the wafer rigidly in said cassette assembly, and means for applying a potential difference between the wafer and the charge plate to flatten said wafer by Coulombic force so that the wafer is held both mechanically and electrostatically in said cassette assembly. Means are also provided for insuring a good electrical contact with the wafer and for aligning the wafer in the cassette assembly.