Dose- and exposure-controlled stop-flow atomic layer deposition of TiO2 in deep macroporous silicon: Quantifying infiltration by energy-dispersive x-ray line profiling

Atomic layer deposition (ALD) enables conformal coatings on complex three-dimensional substrates, but precursor transport in deep porous systems remains strongly constrained by diffusion and surface consumption. Here, TiO2 ALD is investigated in branched macroporous silicon with pore depths of 15–30 μm and average diameters of 100 nm, corresponding to aspect ratios up to 300. Continuous-flow ALD, single-injection stop-flow ALD, and double-injection stop-flow ALD are compared in order to distinguish the respective roles of precursor dose, exposure time, and injection strategy. Cross-sectional SEM and energy-dispersive x-ray spectroscopy (EDX) line profiling show that continuous-flow ALD yields a Ti signal limited to only a few micrometers, whereas optimized stop-flow conditions extend the Ti-containing distribution down to approximately 22 μm without evidence of pore entrance clogging. Penetration-depth metrics derived from normalized Ti EDX profiles reveal that increasing precursor dose strongly improves infiltration, while increasing exposure time is beneficial only up to an optimum. Excessively long dwell times lead to reduced Ti signal near the pore bottom, consistent with transport limitations within the progressively coated porous network. These results establish macroporous silicon as a stringent benchmark for evaluating ALD infiltration in realistic porous semiconductors and demonstrate that EDX line profiling provides a practical process-qualification route to compare oxide infiltration in complex high-aspect-ratio architectures.