Fundamentals of ion-beam-assisted deposition. I. Model of process and reproducibility of film composition

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Abstract
An ion-beam-assisted-deposition (IBAD) system is under development to fabricate Si1−x Nx films for optical devices. Reproducible film composition requires characterization of the relationship between the incorporated nitrogen atom fraction x and the real time experimental measurable quantities. In this paper a simple model is presented which relates the film composition x to the measured beam current density JF , the vapor impingement rate Q, and the chamber pressure p. Effects included in the model are reflection of energetic particles, sputtering from the film surface, and charge exchange neutralization of the ions. Each term in the model is examined as a potential source of both systematic and random deviations of the data from the model. Data on film composition as a function of the nitrogen ion current to deposition rate ratio are presented for several sets of ion source voltages and chamber pressures. It is shown that by modifying the deposition system so as to minimize the identified sources of error, variation in composition can be reduced below 3 at. % nitrogen. Both the model and the discussion of the experimental sources of error are applicable to other IBAD systems.

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