A study on the step coverage modeling of thin films in atomic layer deposition

Abstract

Atomic layer deposition (ALD) is one of the most promising thin film deposition techniques to enable the nano-scale device fabrication, due to its advantages over other conventional deposition techniques such as physical vapor deposition and chemical vapor deposition. The advantages include the ability to control the film thickness at atomic dimensions, the ability to produce highly conformal thin films, and wide area uniformity, as a result of surface-limited reactions between alternately dosed precursor and reactant gases. Among these, the production of highly conformal thin films on micro-features with high aspect ratios has been considered as one of the greatest advantages, especially for capacitors in semiconductor memories. However, even in ALD, as aspect ratios severely increase, it is not trivial to obtain conformal thin films on micro-features. To support this task, it is necessary to theoretically investigate the film deposition inside a micro-feature in ALD and predict the process time required to achieve reasonable film step coverage. In general, ALD of binary compound systems is performed by supplying precursor and reactant gases onto the outermost surface sequentially, with purges of an inert gas between precursor and reactant gases. The non-overlapping alternate dosing of precursor and reactant gases prohibits reactions in the gas-phase and thus leads to the film deposition that highly depends on the adsorption and surface reaction kinetics. Among these steps in one ALD cycle, the film step coverage is greatly influenced by the precursor injection step because much more reactant is supplied to the reactor than precursor. A film growth model on micro-features was proposed to evaluate the film step coverage depending on the precursor injection time in ALD. The proposed model is based on that the chemisorption rate of precursors at a certain position along the depth of a micro-feature is determined by the total flux of precursors and the sticking ...