Using a Heavy Inert Diffusion Additive for Superconformal Atomic Layer Deposition

Abstract

The shrinking of device nodes increases the demand for deposition processes to seamlessly fill nanometer-scale features. Despite the precision of atomic layer deposition (ALD), it cannot deposit in a V-shaped fashion, which is characteristic of superconformal thin-film deposition. We propose a strategy for superconformal ALD by adding a heavy inert gas as a diffusion additive. We show that the step coverage in an 18:1 aspect ratio feature increased from 1 to 1.6 with the addition of Kr in an ALD process for AlN from Al(CH₃)₃ and NH₃. We speculate that the heavier Kr (84 amu) promotes diffusion of the lighter NH₃ (17 amu) down the trenches. Consequently, NH₃ molecules are pushed to the trench bottom, resulting in a lower growth per cycle at the trench openings. Further studies are needed to understand the effect of Kr, but we foresee that this approach to superconformal ALD is applicable to many ALD processes.