Effect of a Trap Zone in Reducing Nanoparticle Contamination of Wafers and Photomasks in Parallel Airflowp

Particle contamination control is important for increasing the yield in semiconductor manufacturing. In this paper, a trap zone was suggested to reduce the level of particulate contamination of wafers and photomasks during transport in horizontal direction. Trap zone efficiency was numerically and theoretically analyzed by calculating local deposition velocity onto a critical surface representing a wafer or a photomask. The effects of diffusion, gravitational settling, convection, and thermophoresis on particle behavior were considered. The deposition velocity onto the critical surface was found to be effectively reduced with the use of the trap zone, especially for nanoparticles of large diffusivity. As the trap zone became longer, the degree of critical surface contamination by nanoparticles was estimated to be more reduced. An equation was suggested to estimate the reduction of particulate contamination of the critical surface as a function of the trap zone length. It is anticipated that the results of this paper are very helpful for designing wafer/photomask transport systems with a reduced level of contamination by nanoparticles.