Influence of ALD temperature on thin film conformality: Investigation with microscopic lateral high-aspect-ratio structures

Unparallelled conformality is driving the interest to use coatings made by atomic layer deposition (ALD) in a growing number of applications from microelectronics to catalysis to biomedical devices and beyond. Despite the fundamental importance of conformality, dedicated conformality studies of ALD processes have been scarcely reported, as available, easy-to-use conformality test structures have been missing. In earlier work, we have developed silicon-based lateral high-aspect-ratio (LHAR) test structures [J. Vac. Sci. Technol. A, 33, 010601 (2015)], which are used in this work to analyse the influence of ALD temperature on the conformality of aluminium oxide, titanium dioxide and their nanolaminates. With the LHAR structures of a gap height of 500 nm and aspect ratios (AR) up to 10 000:1, films grown at 110 to 300 degrees Celsius are observed enter typically up to an aspect ratio of 100:1 to 200:1. The temperature trend of conformality differs for aluminium oxide and titanium dioxide ALD processes: aluminium oxide penetrates deeper in the 3D structures at lower temperatures, while titanium dioxide has a maximum penetration depth at 200 degrees Celsius. An inverse correlation was seen between a decreasing ALD growth per cycle (GPC) and an increasing conformality. Metal reactant consumption along the trench is proposed to explain the correlation. Microscopic LHAR structures expose a new parameter space conformality analysis and are likely to enable novel experimental and theoretical conformality studies in the future in ALD and related fields.