Passive sputtering (PVD method)
Atomise to recreate
PVD technology (Physical Vapour Deposition) is used to apply thin films measuring just micrometres to materials of various qualities. To do so, a block of material, consisting of the film material to be applied, is evaporated in a vacuum. This creates a gas mixture of atomic particles, which precipitate onto the substrate. In plasma-assisted PVD processes, a cathode is evaporated by being bombarded with ions. This sputter or evaporation process can take place at room temperature. It is divided into three stages: Sputtering, diffusion, and film growth.
A vacuum reaction chamber contains the non-reactive noble gas argon. In this chamber, a suitable direct current, medium, or radio frequency voltage is applied. Thus, a low-temperature plasma ignites above the cathode (target), which consists of the film material. Positively charged argon ions are accelerated in the electrical field towards the cathode. On impact, these argon ions chip off particles from the cathode material. Eventually the cathode will be almost completely sputtered.
The atoms chipped off the target are distributed like gas. If the cathode and the substrate are properly arranged, the film particles will move towards the substrate.
A certain percentage of the sputtered atoms hits the substrate and precipitates there. As a rule, crystalline films should be created, and in some cases, also amorphous films. Several conditions must be met at the same time for ultra-pure crystalline films to grow. These conditions include the correct substrate temperature and the correct kinetic energy of the impacting particles. In addition, the film atoms require time to arrange themselves in regular crystal lattices. To achieve even film growth over the entire surface, the substrates move past the cathode in a planar manner at a speed of metres per minute. For a film that is to be coated on three sides, for example, the substrate rotates in front of the cathode to allow the film to be deposited on all sides.