Thin-Film Conformality Analysis, Reliability and Modeling using All-Silicon Lateral High Aspect Ratio Structures

Device downscaling in semiconductor and microelectromechanical device industry brings new challenges from the process perspective as increased three-dimensionality sets demands towards higher aspect ratio structures which have to be filled conformably. Atomic layer deposition (ALD), based on the use of repeated, self-terminating reactions of typically at least two compatible reactants on a solid substrate, is a promising technique especially from the conformality point of view. Traditionally thin film conformality has been analysed with cross sectional specimens. Our approach is to turn the analysis to horizontal plane with all-silicon lateral high aspect ratio structures (LHAR) and reflectometry line-scans.
This work continues on earlier work on conformality analysis [1–6]. The LHAR structures consist of a lateral gap of typically 500 nm in height while the gap length varies from 1 to 5000 μm, giving aspect ratios of 2:1 to 10 000:1. LHAR chips were coated with ALD Al2O3 and TiO2 films, the effects of pulse and purge times were inspected from conformality point of view, and the measurement reliability was characterized with atomic force microscopy and QuickVision optical coordinate measuring tool. Diffusion model [6] was used to study the propagation of the ALD growth in the narrow channel. According to reflectometry measurements longer pulse time increased the penetration depth of the film to the narrow channel. The diffusion model was well in agreement with the experimental results. Measurement reliability and uncertainty components of the measurement were studied systematically. Therefore realistic uncertainty estimates can be given for the results. The LHAR structures presented here with thin film analysis and theoretical diffusion model accelerate the process up-scaling from small to large industrial scale.