Modeling the Conformality of Atomic Layer Deposition: The Effect of Sticking Probability

The key advantage of atomic layer deposition (ALD) is undoubtedly the excellent step coverage, which allows for conformal deposition of thin films in high-aspect-ratio structures. In this paper, a model is proposed to predict the deposited film thickness as a function of depth inside a hole. The main model parameters are the gas pressure, the deposition temperature, and the initial sticking probability of the precursor molecules. Earlier work by Gordon assumed a sticking probability of 0/100% for molecules hitting a covered/uncovered section of the wall of the hole, thus resulting in a stepwise film-thickness profile. In this work, the sticking probability is related to the surface coverage theta by Langmuir's equation s(theta)=s(0)(1-theta), whereby the initial sticking probability s(0) is now an adjustable model parameter. For s(0)congruent to 100%, the model predicts a steplike profile, in agreement with Gordon , while for smaller values of s(0), a gradual decreasing coverage profile is predicted. Furthermore, experiments were performed to quantify the conformality for the trimethylaluminum (TMA)/H(2)O ALD process using macroscopic test structures. It is shown that the experimental data and the simulation results follow the same trends.