Vacuum deposition

Vacuum deposition , also known as vacuum coating or thin-film 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 based on the vapor source; physical vapor deposition uses a liquid or solid source and chemical vapor deposition uses a chemical vapor. This method protects the substrate from extraneous variables that might cause wear and lower its overall efficiency. Vacuum coatings are distinguished by their thinness, which generally ranges from 0.25 to 10 microns (0.01 to 0.4 thousandths of an inch). The vacuum environment may serve one or more purposes: reducing the particle density so that the mean free path for collision is long reducing the particle density of undesirable atoms and molecules (contaminants) providing a low pressure plasma environment providing a means for controlling gas and vapor composition providing a means for mass flow control into the processing chamber. Condensing particles can be generated in various ways: thermal evaporation sputtering cathodic arc vaporization laser ablation decomposition of a chemical vapor precursor, chemical vapor deposition 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).