In Situ Visualization via X‐Ray Diffraction of Phase Transformations During Flash Lamp Annealing

Flash lamp annealing (FLA) enables sub‐millisecond thermal processing with low thermal budgets, but the extreme heating and cooling rates have so far prevented direct, time‐resolved temperature metrology and observation of structural transformations in nanometer‐scale thin films. We present a custom FLA system, integrated with halogen lamp annealing, for time‐resolved synchrotron grazing‐incidence X‐ray diffraction (GIXRD), achieving 200 µs temporal resolution to directly track reversible and irreversible structural evolution during FLA. We achieve simultaneous real‐time surface temperature measurement and visualization of structural transformation in ultra‐thin hafnia‐based ferroelectric layers of intensive interest for future non‐volatile memory applications. The measurements reveal two distinct characteristic timescales: rapid post‐flash thermal relaxation of the metal–ferroelectric–metal stack and a slower phase evolution within the ferroelectric layer. By correlating transient thermal profiles with diffraction signatures, we quantify the thermal budget required to induce the desired ferroelectric phase and show that it is several orders of magnitude lower than conventional annealing, while still achieving a large remanent polarization of 36 µC/cm 2 . This method enables direct, time‐resolved observation of ultrafast crystallization and phase transformation processes in nanometer‐scale thin films and provides a general experimental framework for studying pulsed thermal processing of nanoscale materials for a wide range of advanced technologies.