Physical vapor deposition

The term physical vapor deposition ( english physical vapor deposition, PVD short ), rarely physical vapor deposition refers to a group of vacuum-based coating method and thin film technologies. Unlike methods of chemical vapor deposition, the starting material is converted into the gas phase by physical methods. The gaseous material is then led to the substrate to be coated, where it condenses and forms the target layer.

Method

The group of methods of physical vapor deposition include the topics listed below, as well as reactive variants of these processes.

• Evaporation method (Also called sputtering ), thermal evaporation
• Electron beam ( electron beam evaporation engl. )
• Laserstrahlverdampfen (English pulsed laser deposition, pulsed laser ablation ): atoms and ions are vaporized by a short intense laser pulse.
• Arc evaporation (English arc evaporation, Arc- PVD): atoms and ions by a strong current flowing in an electrical discharge between two electrodes ( similar to lightning ), extracted from the starting material and converted into the gas phase.
• Molecular beam epitaxy (English molecular beam epitaxy )

• Ion beam assisted deposition ( engl. ion beam assisted deposition, IBAD )

General Process Description

All these methods have in common is that the deposited material is in solid form in the mostly evacuated coating chamber. By bombarding with laser beams, magnetically deflected ions or electrons as well as by arc discharge, the material which is referred to as the target, is evaporated. What is the proportion of atoms, ions or larger clusters in the vapor varies from procedure to procedure. The vaporized material moves either ballistic or guided by electric fields through the chamber and impinges on the parts to be coated, where it comes to layering.

Thus, the vapor particles reach the components also, and are not lost by scattering at the gas particles, must be used in the vacuum. Typical operating pressures are in the range of 10-4 Pa to about 10 Pa. Since the vapor particles propagate in a straight line, are areas that are seen from the steam source is not visible, coated with a lower deposition rate. If all surfaces are homogeneously coated, the parts must be moved during the coating in an appropriate manner. This is usually done by rotation of the substrate.

Meet the vapor particles now on the substrate, they begin to deposit by condensation on the surface. The particles do not remain in place, where they meet on the substrate, but move, depending on how high their energy is, along the surface ( surface diffusion ) to find an energetically more favorable place. These are sites on the crystal surface with as many neighbors ( higher binding energy).

In order to increase the deposition rate and layer uniformity, the plants will vary slightly depending on the coating process and the material to be deposited. Thus, a negative voltage ( bias voltage) is applied, for example, in thermal evaporation of the parts to be coated. This accelerates the positively charged vapor particles or metal ions (see relevant article).

Since the method for physical vapor deposition coatings are vacuum, they ( batch mode) are in production usually operated in batch mode: charging (filling ) of the vacuum chamber, evacuating, coating, venting, opening and removal of the coated parts. For certain applications ( coating sheet, fibers or wires, and architectural glass ), there is, however, continuous flow systems where the vacuum is achieved via a lock system and to be coated is continuously supplied.

With some PVD ( magnetron sputtering, Laserstrahlverdampfen, thermal evaporation, etc.) very low process temperatures can be realized. Thus it is possible, even to coat the low-melting plastics. The once feared in the coating of plastics " eggshell " effect, that is cracking and peeling of the layer due to the large flexibility of the substrate under rigorous conditions, also was similar to that of through targeted influence on the layer construction with multi -layer coatings with biomimetic structure shells are minimized.

Layer

With the various PVD variants almost all metals and also carbon in a very pure form, can be deposited. Performs to the process reactive gases such as oxygen, nitrogen or hydrocarbons, also oxides, nitrides or carbides can be deposited.

A method for physical vapor deposition are primarily used for the deposition of thin layers of a few nanometers to a few micrometers. With the layer thickness so do the internal stresses within the layers, which can lead to detachment from the substrate ( delamination ). This is one of the reasons that can not be with PVD process producing layers of arbitrary thickness.

Applications

Layers of the physical vapor deposition are used in many areas of industry. Tools are now largely used in coated cutting tool materials, especially in the area of machining. As coatings today are primarily hard coatings based on titanium nitride ( TiN), titanium carbonitride ( TiCN ), or titanium aluminum nitride ( TiAlN ) is used. In the early 1990s, were investigated by various research institutions further applications in the field of tool coatings for die casting of aluminum and magnesium. In these applications, especially chrome -based layer systems such as chromium nitride (CrN ), Chromvanadiumnitrid ( CRVN ) and Chromaluminiumnitrid ( CrAlN ) are used. Of CrN coatings are widely in use corrosion protection. Furthermore, PVD - layers used in microelectronics for producing, inter alia, metal, or ( organic ) semiconductor layers. Also, architectural glasses or displays are coated with protective layers in the PVD process. Polyethylene films in the food industry (eg, potato chip bags ) obtained from inside a thin PVD layer as a vapor barrier. In many other applications of plastics ( like. eg for wear protection, optical and decorative purposes ) find PVD coating process at low temperatures ( room temperature) increased use. In fuel cells, in particular solid oxide fuel cells, the electrolyte may be formed by PVD so as to obtain thin as possible electrolytes, which increase the electrical capacity of a cell. In the field of consumer electronics media such as hard drives, CDs and DVDs with PVD process are coated.