Ja-Yong Kim

Film growth model of atomic layer deposition for multicomponent thin films

Atomic layer deposition (ALD) has become an essential technique for fabricating nano-scale thin films in the microelectronics industry, and its applications have been extended to multicomponent thin films, as well as to single metal oxide and nitride films. A mathematical film growth model for ALD is proposed to predict the deposition characteristics of multicomponent thin films grown mainly in the transient regime, where the film thickness varies nonlinearly with the number of cycles. The nonlinear behavior of the growth rate and the composition of multicomponent thin films deposited by ALD depend on the precursor used and adsorbing surface. Hence, the equations to describe the change of surface coverage with precursor adsorption and the surface reaction are derived. The area reduction ratio is introduced as a parameter related to the number of adsorbed precursor molecules per unit area. The proposed model was applied to the deposition of Sr–Ti–O thin films to confirm its validity. SrO and TiO2 films wer...

Step coverage modeling of thin films in atomic layer deposition

A film growth model on microfeatures is proposed to evaluate step coverage depending on precursor injection time in atomic layer deposition. The proposed model is based on that the chemisorption rate of precursors at a certain position along the depth of a microfeature is determined by the total flux of precursors and the sticking probability. The total flux includes the flux coming from the entrance of a microfeature and the flux reflected from other positions inside a microfeature, and the sticking probability depends on the surface coverage of chemisorbed precursor, which is a function of precursor injection time. The proposed model was applied to the deposition of Al2O3 films on 0.3μm diameter holes with an aspect ratio of 10. It was confirmed that the experimental data for step coverage depending on precursor injection time follow the trend predicted by the proposed model.

Applicability of Step-Coverage Modeling to TiO2 Thin Films in Atomic Layer Deposition

The applicability of a step-coverage model in atomic layer deposition was extended to the deposition of TiO 2 films, focusing on the effect of a precursor partial pressure and a deposition temperature, as well as the number of cycles in step coverage. Using the extracted model parameters, step coverage depending on the number of cycles was predicted, which shows a nonlinear dependence of film thickness inside a hole on the number of cycles because the area of a hole entrance decreases as the deposition proceeds. The experimental data agreed well with the model predictions. To confirm the validity of the step-coverage model, the effect of a precursor partial pressure and a deposition temperature on step coverage was also investigated. The flux of precursors that strikes the flat surface is the model parameter related to a precursor partial pressure, and the initial sticking probability and the adsorption order are the model parameters related to a deposition temperature. For different experimental conditions, by obtaining the model parameters related to changed experimental conditions from the experimental data at the flat surface, film thickness per cycle at the bottom inside a hole depending on precursor injection time could be predicted within reasonable accuracy.

Increment of dielectric properties of SrTiO3 thin films by SrO interlayer on Ru bottom electrodes

SrTiO3 thin films were deposited on Ru using plasma-enhanced atomic layer deposition with and without a SrO interlayer. When the SrTiO3 films were deposited on Ru directly, the dielectric constants of the films decreased abruptly from 65 to 16 as the thickness fell below 20nm. This change was related to film crystallinity. Conversely, when a seed layer was prepared by depositing 2.7nm SrO and postannealing before SrTiO3 deposition, the crystallinity of the SrTiO3 films was enhanced and the thickness dependency of the dielectric constant was reduced. As a result, the dielectric constant of 10nm SrTiO3 films was improved from 16 to 50.

Effect of crystallinity and nonstoichiometric region on dielectric properties of SrTiO3 films formed on Ru

The dielectric constant depending on the film thickness for SrTiO3 films formed on Ru was investigated after an annealing step at 600°C, which shows that the dielectric constant increased abruptly with the film thickness up to 20nm and then increased slightly, remaining relatively constant at a value of about 65. The abrupt increase was due to the crystallinity of SrTiO3 films. On the other hand, the slight increase was related to the existence of nonstoichiometric region near the interface of SrTiO3 film and Ru, which was intermixed with SrTiO3 and Ti–O phases having an equivalent oxide thickness over 0.32nm.