Evaluation of a passive trap structure for mitigating wafer surface contamination induced by natural convection in a FOUP

After high-temperature processes, wafers are stored inside a Front Opening Unified Pod (FOUP), where natural convection generated by heated wafers can transport friction-origin particles and induce wafer surface contamination. Previous studies have mainly focused on suppressing external particle inflow, analyzing particle generation mechanisms, and characterizing particle transport and contamination. However, structural approaches for directly capturing particles generated inside the FOUP have remained limited. Therefore, in this study, a passive trap structure for the preemptive capture of internally generated particles under natural convection conditions in an enclosed FOUP environment was proposed, and the particle transport characteristics and contamination reduction performance were evaluated through numerical simulations and experiments. Particle transport and deposition on the wafer surfaces induced by natural convection around the heated wafer were confirmed through numerical simulations, and similar contamination distribution trends were qualitatively observed in the FOUP-mimicking chamber experiments using fluorescent aerosols. The trap structure obtained through geometric optimization exhibited a particle capture efficiency of 54.55% for 0.1 μm particles under a three-wafer condition in which the top wafer was continuously heated. Based on these results, a passive trap structure optimized using a design of experiments (DOE) methodology was demonstrated to mitigate wafer contamination induced by natural-convection-driven particle transport under the conditions considered in the present study. However, the present study was limited to the sparsely loaded, top-heated FOUP condition, and the natural-convection flow structure and particle transport characteristics may differ under fully loaded conditions owing to the different inter-wafer spacing.