Effect of reactant dosing on selectivity during area-selective deposition of TiO_2 via integrated atomic layer deposition and atomic layer etching

摘要

A key hallmark of atomic layer deposition (ALD) is that it proceeds via self-limiting reactions. For a good ALD process, long reactant exposure times beyond that required for saturation on planar substrates can be useful, for example, to achieve conformal growth on high aspect ratio nanoscale trenches, while maintaining consistent deposition across large-area surfaces. Area-selective deposition (ASD) is becoming an enabling process for nanoscale pattern modification on advanced nanoelectronic devices. Herein, we demonstrate that during area-selective ALD, achieved by direct coupling of ALD and thermal atomic layer etching (ALE), excess reactant exposure can have a substantially detrimental influence on the extent of selectivity. As an example system, we study ASD of TiO_2 on hydroxylated SiO_2 (Si-OH) vs hydrogen-terminated (100) Si (Si-H) using TiCl_4/H_2O for ALD and WF_6/BCl_3 for ALE. Using in situ spectroscopic ellipsometry and ex situ x-ray photoelectron spectroscopy, we show that unwanted nucleation can be minimized by limiting the water exposure during the ALD steps. Longer exposures markedly increased the rate of nucleation and growth on the desired non-growth region, thereby degrading selectivity. Specifically, transmission electron microscopy analysis demonstrated that near-saturated H_2O doses enabled 32.7 nm thick TiO_2 patterns at selectivity threshold S > 0.9 on patterned Si/SiO_2 substrates. The correlation between selectivity and reactant exposure serves to increase fundamental insights into the effects of sub-saturated self-limiting surface reactions on the quality and effectiveness of ASD processes and methods.