<scp>CFD</scp> modeling and sensitivity‐guided design of silicon filament <scp>CVD</scp> reactors

Abstract Filament‐based chemical vapor deposition (CVD) for silicon (Si) coatings is often treated as an adaptation of planar deposition. But this overlooks fundamental shifts in transport phenomena and reaction kinetics. In filament CVD, the filament acts as a substrate, heat source, and flow disruptor simultaneously. In this work, we ask: What really governs Si film growth on filaments? Using a three‐dimensional computational fluid dynamics model, validated against three independent experimental studies, we show that filament geometry, thermal gradients, and buoyancy define the very regimes of deposition. We show that reducing filament diameter can triple growth rates, but only in carefully tuned temperature regimes. Similarly, multi‐filament setups reshape flow and thermal fields, affecting film uniformity. To bridge physical understanding with design actionability, we apply global sensitivity analysis via polynomial chaos expansion and Sobol’ indices, revealing control shifts between growth regimes. In this way, our model lays the foundation for knowledge‐based design strategies.