(A) study on the kinetic model the thin film growth in ALD

Abstract

Atomic layer deposition (ALD) has received considerable interest in depositing thin films because of its digital controllability for film thickness. Moreover, the films grown by ALD have shown superb step coverage due to the surface limited reaction. In ALD, some works have reported that more than one monolayer (ML) was deposited during one deposition cycle. However, so far there has been few works to explain these and to model the kinetic growth. In this paper, a kinetic model of film growth rate in ALD has been studied introducing the concept of readsorption for explaining the film growth of over one ML/cycle and furthermore designing the optimum deposition cycle for maximum throughput. On the other hand, this model is derived separately in a transient region and a converged region, and finally it combines the film growth kinetics in both regions. During the initial stage of ALD, i.e. in the transient region, the outer-most surface is converted gradually from the substrate into the film as the film deposition proceeds. Therefore, the digital characteristics in controlling film thickness by the number of deposition cycles in ALD are lost in the transient region. Hence, it is necessary to consider the transient region in combination with the converged region in order to predict the accurate film thickness, especially when the film thickness is less than 10 nm. Moreover, by utilizing the physical parameters which are extracted from the fitting of the proposed model to the experimental data of deposited film thickness versus pulse time of each reactant gas, an optimum deposition cycle for the maximum throughput can be designed. In order to evaluate the combined kinetic model, it has been applied to TiN-ALD performed on $SiO_2$ substrate using tetrakis (dimethylamido) titanium (TDMAT) and $NH_3$. The adsorption rate constant and size factor related the number of available sites, were extracted through the fitting this model to experimental data. The existence of t...