Particle transport in a parallel-plate semiconductor reactor: Chamber modification and design criterion for enhanced process cleanliness

Convective, diffusive, and thermophoretic particle transport in a parallel- plate semiconductor reactor is investigated. Measurements that illustrate p article transport in the reactor are presented and a Eulerian continuum par ticle transport formulation is used to quantitatively explain the measureme nts. Experimental and numerical results show that particles formed in the p arallel-plate region are confined in a thin sheath (similar to 2 cm) betwee n the "hot" water and "cold" showerhead inlet. This sheath is located at th e point where downward convective transport balances upward transport by th ermophoresis. The particle sheath location is independent of particle size but is dependent on gas flow rates and temperature of the wafer and showerh ead inlet. In addition, experimental and numerical results show that as par ticles exit the parallel-plate region, the radial thermophoretic particle t ransport can produce "ring-like'' contaminant deposits on the outer wall of the reactor under certain flow conditions. We propose a simple reactor des ign modification and an analytic design criterion to avoid particle deposit ion on the chamber walls. (C) 2000 American Vacuum Society.