In this TLP, thin films will be defined as solid films formed from a vapour source:
Built up as a thin layer on a solid support (substrate) by controlled condensation of individual atomic, molecular, or ionic species.
This can lead to structures which are far from equilibrium so understanding how different deposition techniques can lead to different growth mechanisms and structures is essential in being able to control the properties of the film.
The applications of these films can vary depending on the thickness, among other properties:
- Optical interference effects
- Electron tunnelling
- High resistivity
- High surface to volume ratio
- Gas absorption
- Catalytic activity
- Microstructural control
- High hardness
- Optical absorption
- Corrosion protection
Because of their many controllable aspects, thin films play a major role in microelectronics, communications, protective coatings, optics and the medical industry.
There is always continued pressure for advances in size reduction, uniformity, purity, reproducibility and manufacturing speed.
One of the main methods for forming these films is through Physical Vapour Deposition (PVD). In PVD a vapour is generated from a source and travels to a substrate, where there is nucleation and growth of the solid film materials. The two main ways of forming this vapour flux are through Evaporation and Sputtering. A common, general set up for this process is shown schematically below:
Simple deposition will lead to amorphous film material unless the depositing atoms have enough energy to rearrange themselves into a more thermodynamically stable crystalline structure. If the film growth is epitaxial then it is forming on a lattice-matched crystalline substrate and so will be crystalline from the start.
This is a multidisciplinary subject which includes vacuum engineering, fluid dynamics, plasma physics and molecular simulations.