Reducing contamination by particles reflected in turbo molecular pump

The behavior of particles that are reflected in a turbo molecular pump was investigated by measuring particle trajectories and number of particles that fell on the wafer. Some scattered particles collide with a wafer at a high velocity, which damage fine patterns of the photoresist on a wafer. Particle contamination can be reduced by supplying carrier gas to form down-flow, when 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. We found that down-flow particle control reduces particle contamination by 90% through etching including wafer transfer.