Behavior of Particles Reflected by Turbo Molecular Pump in Plasma Etching Apparatus

The behavior of particles that are reflected in a turbo molecular pump is investigated by measuring particle trajectories and the number of particles that fall on a wafer in a plasma etching apparatus. Some scattered particles collide with the wafer at high velocity, which damage fine patterns of the photoresist on the wafer. Particle contamination can be reduced by supplying carrier gas to form a down-flow when the etching plasma is not discharged. During plasma discharge, the number of particles that fall on the wafer decreases because particles are trapped near the plasma-sheath boundary. The down-flow gas reduces particle contamination by 90% through the etching sequence, including wafer transfer.