Consistent control of drying rates of solution thin films on wafer-sized substrates by dynamic air-knife drying with optimal trajectories

Rapid and consistent drying of thin solution films is a key enabler for high-throughput fabrication of emerging semiconductor materials. This work has the objective of achieving consistent drying rates of a solution film deposited on a 20 cm-wide substrate ( ≈ silicon-wafer size) that is dried dynamically with a narrow air flow ejected by a slot nozzle (or ”air knife”). The methodology is based on evaluating drying dynamics at multiple positions and investigating the impact of the relative movement trajectory between the air knife and the substrate on the resulting drying rates. It is assumed that the Biot number is sufficiently small and that the drying rate at the critical stage determines the quality of the deposited film. The main result is a novel optimization strategy overcoming the trade-off between homogeneity and drying speed: The dynamic movement of the air knife is tailored to the wet film thickness distribution following the ”drying front”. If the film thickness does not decrease along the movement direction of the air knife, there is a consistent solution of the optimization. This is showcased both for idealized and experimental thickness distributions. Generally, wet films cannot always be dried fully consistently by optimizing the air knife trajectory alone, but optimization improves drying results significantly in all investigated scenarios. Such trajectory optimization could yield substantial improvements in consistency and speed of thin film drying, potentially increasing throughput by an order of magnitude while maintaining drying rate control.