TABLE OF CONTENTS Several publications have presented a detailed review of thin-film deposition processes;[1] thus only brief descriptions of the thin-film growth and deposition processes are presented in this chapter.
Any thin-film deposition process involves three main steps:
Production of the appropriate atomic, molecular, or ionic species.
Transport of these species to the substrate through a medium.
Condensation on the substrate, either directly or via a chemical and/or electrochemical reaction, to form a solid deposit.
Formation of a thin film takes place via nucleation and growth processes. The general picture of the step-by-step growth process emerging from the various experimental and theoretical studies can be presented as follows:
The unit species, on impacting the substrate, lose their velocity component normal to the substrate (provided the incident energy is not too high) and are physically adsorbed on the substrate surface.
The adsorbed species are not in thermal equilibrium with the substrate initially and move over the substrate surface. In this process they interact among themselves, forming bigger clusters.
The clusters or the nuclei, as they are called, are thermo-dynamically unstable and may tend to desorb in time, depending on the deposition parameters. If the deposition parameters are such that a cluster collides with other adsorbed species before getting desorbed, it starts growing in size. After reaching a certain critical size, the cluster becomes thermodynamically stable and the nucleation barrier is said to have been overcome. This step involving the formation of stable, chemisorbed, critical-sized nuclei is called...
