A thin film evaporator is a machine used to create thin film. By evaporating or sublimating various elements, a thin film evaporator can deposit extremely thin layers of atoms or molecules onto a substrate material. The machine consists of a vacuum chamber, a heating element and an apparatus that holds and moves a substrate while a thin film is deposited onto it.
There are two primary types of evaporation that can be used to create a thin film. These are resistive evaporation and electron beam evaporation. In both of these techniques, a target material is heated in a thin film evaporator until it either evaporates or sublimates. As a gas, the target material moves through a vacuum chamber until it lands on a substrate and forms a thin film. Both of these techniques require that the target materials are as stable as a gas.
In resistive evaporation, an electrical current is passed through a target material, which becomes hot as it is energized. With enough heat, the target material evaporates or sublimates. Gold and aluminum are common target materials that can be evaporated in the form of metal wires, called filaments. Target materials in the form of filaments are difficult to load onto an evaporator and can only be worked in small quantities. A thin film evaporator can also use thin sheets of a target material, which often are easier to work with and yield more matter when evaporated.
Some target materials are unsuitable for resistive evaporation because they can shed large sections of solid matter during the process. If these solids collide with the thin film forming on the substrate, they can ruin it. Evaporating these materials requires the use of an enclosed heating source that allows the gaseous form of the material to escape through small holes while trapping sections of solid matter within the heating chamber.
Electron beam evaporation heats the target material by directing a beam of high energy electrons at it. In this type of thin film evaporator, the target material is kept in a cooled hearth while it is bombarded with electrons and heated. This process is useful for target materials with a very high evaporation temperature because the focused beam of energy can heat the target material without heating the entire apparatus. The container holding the target material is not exposed to extreme heat, so it doesn't melt or evaporate during the process. This type of thin film evaporation requires specific equipment and can be quite costly.