Why In Situ, Real-Time Characterization of Thin-Film Growth Processes?

Extract

It is anticipated that a new generation of advanced electronic and optical devices will involve the synthesis of diverse materials in single or multielement thin-film form, or in layered heterostructures. These devices will most likely involve diverse materials such as high-temperature superconductors, ferroelectric, electrooptic, and optical materials; diamond; nitrides; semiconductors; insulators; and metals in the form of ultra-thin layers with sharp interfaces in which the layer thickness may reach atomic dimensions. Therefore, it becomes increasingly important to be able to monitor the deposition process in situ and in real time, particularly for complex multicomponent oxides or nitrides, in which the production of the desired phase is a highly sensitive function of the growth conditions, often requiring relatively high-pressure oxygen or nitrogen environments up to several hundred mTorr, and in some cases, several Torr. Consequently, the growth environment for many of these materials is incompatible with conventional surface-analytic methods, which are typically restricted to high-or ultrahigh-vacuum conditions. New deposition and analytical methods, or adaptation of those already established, will be required.

Since thin-film growth occurs at the surface, the analytical methods should be highly surface-specific, although sub-surface diffusion and chemical processes also affect film properties. Sampling depth and ambient-gas compatibility are key factors which must be considered when choosing in situ probes of thin-film growth phenomena. In most cases, the sampling depth depends on the mean range of the exit species (ion, photon, or electron) in the sample.