Sticking probabilities of H ₂ O and Al(CH ₃ ) ₃ during atomic layer deposition of Al ₂ O ₃ extracted from their impact on film conformality

The conformality of a film grown by atomic layer deposition (ALD) is strongly affected by the reactivities of the precursor and coreactant, which can be expressed in terms of their sticking probabilities toward the surface. We show that the leading front of the thickness profile in high-aspect-ratio structures gives direct information on the sticking probabilities of the reactants under most conditions. The slope of the front has been used to determine the sticking probabilities of Al(CH ₃ ) ₃ and H ₂ O during ALD of Al ₂ O ₃ . The determined values are (0.5-2) × 10 ^-3 for Al(CH ₃ ) ₃ and (0.8-2) × 10 ^-4 for H ₂ O at a set-point temperature of 275 °C, corresponding to an estimated substrate temperature of ∼220 °C. Additionally, the thickness profiles reveal soft-saturation behavior during the H ₂ O step, most dominantly at reduced temperatures, which can limit the conformality of Al ₂ O ₃ grown by ALD. This work thus provides insights regarding quantitative information on sticking probabilities and conformality during ALD, which is valuable for gaining a deeper understanding of ALD kinetics.