Thermal evaporation method as PVD coating method

What are evaporation materials?

Most optical components such as lenses and prisms are coated with thin films-some with a single layer and others with multiple layers. These thin films "control" light by modifying the transmission, reflection, and/or absorption of specific frequencies on the surfaces of the coated components. This optical "functionalization" is exploited in a wide range of products-digital cameras, projectors, reflectors, CD players, and Blu-ray disc players-and, in fact, in most electro-optical devices available today.

Our evaporation materials are intended for used in the production such thin film coatings. Of course, the type of evaporation material chosen will depend on the characteristics you require, e.g., transmittance range, refractive index, chemical stability, anti-corrosion, etc., and most optical thin films are deposited using a combination of two or more evaporation materials. However, unlike the raw materials we provide, our evaporation materials are specially designed for producing thin films by physical vapor deposition (PVD).

What is the difference between the granule- and the pellet-type products?

Granules can be refilled into the gaps left inside the crucible and then fusedagain; this is a very cost-effective option. But to obtain a perfectly flat evaporation surface inside the crucible, you will have to heat the surface of the granule material and fuse it again each time you refill the crucible. So it will take a bit longer to "precondition" the material.

Pellets, on the other hand, can be easily placed inside the crucible and do not need to be fused before deposition. This will reduce the preconditioning time and improve your production efficiency, albeit at a slightly higher cost per piece. Moreover, you must also consider the fact that granules and pellets may behave differently during the deposition process.

Overall, the best choice for you will depend on your priorities, coating methods, and deposition conditions, as well as on the physical properties and behaviors of the materials that you are going to evaporate.

What is the difference between "sintered" and "fused"?

Sintered materials are called ceramics, and tend to have very porous structures, whereas fused materials are crystalline and are made from crystal ingots. The merits and demerits of these two types are highly dependent on the kinds of materials you choose. Although the chemical structures are the same, sintered and fused materials behave differently when depositing a thin film.

For example, MgF2, a material with one of lowest refractive indexes in practical use (commonly used in AR coatings), is often used in the form of fused granules, which is often the cheapest and most cost-effective option. But using fused granules can often cause severe outgassing and spitting. One option for reducing these phenomena is to use sintered pellets, which will reduce spitting even at high deposition rates. But again, the best choice for you will depend on the physical and chemical properties of the materials you wish to use.

What is outgassing?

Outgassing is an unwanted phenomenon that can occur inside the coating chamber. It literally means the release of gasses inside the vacuum chamber; these gasses can originate from various sources: Any remnant oil or water inside the chamber will turn into a gas during deposition. And gasses adsorbed on the evaporation material are another source of outgassing.

Moreover, when the material is heated inside the chamber, the dissociation of oxides can produce oxygen and the dissociation of fluorides, fluorine. Although the main source for outgassing is often the evaporation material, there are still several other sources that must be considered. We employ specially designed sintered structures that reduce the outgassing from the evaporation materials.

Will the pellets crack? Won't the beam simply drill holes through the pellets?

Cracking and hole-drilling are phenomena that must be avoided.

There are several causes for cracking: A common cause is the use of pellet or tablets that are is too dense. And of course, an excessively high deposition rate can also crack the tablet.

"Heat cracking" occurs because of the temperature differential across the pellet: one side heated by the e-beam and the opposite side, under the crucible, cooled with water. Our solution is to create an "escapeway" for heat inside the pellet, itself. While higher deposition rates will increase your production efficiency, they also tend to heat the material very fast. We recommend our escapeway solution if you need to achieve higher deposition rates without suffering from heat cracking.

What is the difference between evaporation materials and raw materials?

Evaporation material for physical vapor deposition coatings are made from raw materials and often have purity levels between 3N (99.9%) and 4N (99.99%); the two are very different products. But since they have the same chemical compositions and appearances, we sometimes receive questions regarding the huge price difference.

To produce evaporation materials, which are best suited to thin film production, the raw materials must go through a very long process, largely involving granulation, forming, and sintering. All evaporation materials, unlike raw materials, can be directly used to form thin films; in other words, the manufacturer must know exactly how these materials will behave when irradiated by an e-beam or when heated inside the coating chamber, as well as how the materials turn into thin films.

Our years of dedicated research have allowed us to develop evaporation materials that reduce the occurrence of outgassing and spitting during the deposition process. We strongly recommend our evaporation materials even for small-scale use in laboratories, as they will afford dependable results.

Difference between the sputtering target and the evaporation material

Our evaporation materials are intended for use in thin film production process employing physical vapor deposition (PVD), and especially thermal evaporation deposition using an e-beam or resistive heating. They are also suitable for use in ion-assisted deposition and plasma-assisted deposition.

Our sputtering targets, however, are intended for use in sputtering, which is also categorized as PVD but generally uses a different type of evaporation source. Sputtering targets comprise the evaporation material and a backing plate that is bonded to the material.

Granules are produced by crushing pellets or tablets?

Our sintered granules and pellets are produced using different production process. The sintered structure of each product is the outcome of years of development, and the pellets and granules are, therefore, very different products. Though some of our products can be used in this manner, we recommend that you purchase our granule-type product if that is what you need.