TAU | E-Beam Evaporation System

Learn more about the TAU e-beam source

The TAU E-Beam Evaporation Source

The TAU E-Beam evaporation source is a ‘mini’ source, meaning that it doesn’t use the beam-bending magnets found in other, larger electron beam evaporation sources. The TAU produces a high voltage at the target material while using the low voltage at the tungsten emission filament to produce a direct heating and evaporative effect.

One of the most significant concerns with the e-beam evaporation process is the heat generated during the vaporisation stage. The TAU uses an enclosed head that reduces the thermal load in the vacuum chamber, allowing for coating at relatively low substrate temperatures. This reduced thermal energy makes the TAU a useful tool in lift-off processes and the coating of sensitive substrates.

TAU e-beam evaporation system

Technical Specification

TAU E-Beam features TAU-S TAU-4
Pockets
1
4
Maximum Power
250W (500 optional)
250W (500 optional)
Flux Monitoring
Yes
Yes
Materials
Rods (max 4mm dia), Crucibles
Rods (max 4mm dia), Crucibles
Co-Evaporation
No
Yes
Cooling
Water (min 0.5l/min)
Water (min 0.5l/min)

Electron Deposition Technique

One of the significant drawbacks of traditional thermal evaporation is that it uses radiative heating, limiting the maximum evaporation temperature. Certain metals, such as tungsten, ruthenium, and niobium, have high melting points, low vapour pressures, and large bond energies between atoms, making them difficult to vaporise in a traditional thermal evaporation process.

Electron-beam evaporation alleviates this issue by using a direct, high-energy electron beam that heats the target material directly, without the need for a heating element. Not only does this allow for high material utilisation efficiency, but it also allows for a broader range of source materials.

Electron Beam Evaporation FAQs

Electron beam coating is a thermal evaporation physical vapour deposition (PVD) method that uses a high-energy electron beam to vaporise a source material that coats a particular substrate. Other thermal evaporation methods use reactive evaporation, which relies on the direct transfer of heat. However, it may not produce sufficient energy to vaporise metals with high melting temperatures and produce the required thin film.

The main benefit is that it allows for the use of materials with high melting points in a PVD process. It also produces a high material utilisation efficiency in materials with lower melting points. Common applications of e-beam evaporation include the production of thin films to protect surfaces on solar panels, laser optics, and even architectural glass.

Traditional e-beam evaporation systems use two magnetic coils to direct a high-energy electron beam evenly across the source material holder (known as a pocket or crucible). The high kinetic energy of the e-beam induces high temperatures in the target material, which, when combined with a high vacuum, forces the material into its gaseous phase. 

The most common e-beam evaporation strategy is the anodic arc method. In this method, the electron beam travels from the negatively charged tungsten filament to the target material into a vacuum chamber where the substrate acts as the positively charged diode, guiding the vaporised atoms into the deposition chamber where they hit the substrate and coat it evenly.

Electron beam evaporation systems use one of the three main ways to hold the evaporation material:

  • Single pocket: A system with a single truncated cone that holds the target material in place
  • Rotary pocket: A system with multiple pockets in a linear configuration. Each pocket holds different evaporation materials, allowing for multiple coats on a single target substrate.
  • Linear pocket: A system with multiple pockets, where the pockets are placed in a linear configuration rather than a rotary one

The systems also come in three main configurations that affect target heating, including:

  • Electromagnetic alignment and electromagnetic focusing: The configuration magnetically curves the e-beam and uses magnetic fields to focus or diffuse the electron beam before heating the source material in a crucible.
  • Pendant drop configuration: This configuration also uses a magnetic field during the deposition process but requires that the target material be present as a rod instead of an ingot.

As the e-beam sweeps through the target material, it releases high-energy electrons that heat the source material until it evaporates. The evaporated atoms follow a straight line, known as the mean free path, until they hit another atom, which alters their course and starts the formation of a vapour cloud. This charged cloud moves towards the substrate, forming a thin film.

Some materials may undergo changes in tensile stress during the deposition phase when subjected to EBPVD. Solutions such as ion-beam-assisted deposition help alleviate these concerns, increase thin film density, and even change its molecular structure.

The largest drawback of e-beam evaporation is that it requires line-of-sight to the substrate at low pressures, making coating interiors of complex objects with an even thin film challenging.

Filament degradation can also result in a non-uniform evaporation rate, which reduces the utilisation rate of the target material.

While e-beam evaporation is a reliable method for high-melting-point metals, some materials or applications benefit from other techniques, such as glancing angle deposition or magnetron sputtering.

Please contact us at Korvus Technology for more information on our electron-beam evaporation system and its industrial applications.