EFFECT OF WAFER ORIENTATION ON THE PARTICLE DEPOSITION IN SUBATMOSPHERIC PRESSURES

The significance of gravity, electrostatic force, and turbulence on particle deposition on wafers in subatmospheric pressure chambers was investigated by conducting experiments with wafers placed in various orientations in an e-beam evaporator chamber used in the fab line at the Microelectronics Center of North Carolina (MCNC). These experiments carried out with naturally occurring particles generated by the operation of the equipment indicated that gravity usually dominated deposition. However, particle contamination on wafers in the vertical and upside down orientations suggested that electrostatic forces and turbulence within the chamber during venting and pumpdown also contributed to wafer contamination. In order to study particle deposition characteristics with known particles at subatmospheric pressures, a new particle generating method using a modified vibrating orifice aerosol generator (VOAG) was developed for the production of monodisperse particles at low pressures with controllable charge and concentration.