Vacuum deposition

Aluminising vacuum chamber at Mont Mégantic Observatory used for re-coating telescope mirrors

Vacuum deposition is a group of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmospheric pressure (i.e., vacuum). The deposited layers can range from a thickness of one atom up to millimeters, forming freestanding structures. Multiple layers of different materials can be used, for example to form optical coatings. The process can be qualified by the vapor source; physical vapor deposition uses a liquid or solid source and chemical vapor deposition uses a chemical vapor.

The formation of snow occurs by vapor depostion, but not in a vacuum. Individual water molecules leave the gas phase (humid air) and deposit, one by one, on the surface of a snow flake (solid water), which causes the snow flake to grow. Snow flakes have a delicate structure because they are formed one molecule at a time. If gaseous water (vapor) condensed into liquid water first, you would have chunks of ice rather than delicate snow flakes.

Description

The vacuum environment may serve one or more purposes:

Condensing particles can be generated in various ways:

In reactive deposition, the depositing material reacts either with a component of the gaseous environment (Ti + N → TiN) or with a co-depositing species (Ti + C → TiC). A plasma environment aids in activating gaseous species (N2 → 2N) and in decomposition of chemical vapor precursors (SiH4 → Si + 4H). The plasma may also be used to provide ions for vaporization by sputtering or for bombardment of the substrate for sputter cleaning and for bombardment of the depositing material to densify the structure and tailor properties (ion plating).

Types

When the vapor source is a liquid or solid, the process is called physical vapor deposition (PVD), which is used in semiconductor devices, thin-film solar panels, and glass coatings. When the source is a chemical vapor precursor, the process is called chemical vapor deposition (CVD). The latter has several variants: low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), and plasma-assisted CVD (PACVD). Often a combination of PVD and CVD processes are used in the same or connected processing chambers.

Applications

A thickness of less than one micrometre is generally called a thin film, while a thickness greater than one micrometre is called a coating.

See also

References

  1. ↑ "Daily events and images of the installation of the BBSO New Solar Telescope". Big Bear Solar Observatory. Retrieved 6 January 2020.
  2. ↑ Quintino, Luisa (2014). "Overview of coating technologies". Surface Modification by Solid State Processing. pp. 1–24. doi:10.1533/9780857094698.1. ISBN 9780857094681.
  3. ↑ Christensen, Thomas (2022). "Chapter 9 : Physical Vapor Deposition". Understanding Surface and Thin Film Science (1st ed.). CRC Press. ISBN 9780429194542.
  4. ↑ Green, Julissa. "Table Comparison: Physical Vapor Deposition Vs. Chemical Vapor Deposition". Stanford Advanced Materials. Retrieved Oct 23, 2024.

Bibliography