Electron Beam Evaporation Applications and How They Work

Written by Matt Clancy

Published on March 30, 2022

The deposition of a thin-film is a critical manufacturing step involving creating and applying a coating onto a substrate material. The coating can be a compound, metal, or oxide. 

Each coating has a unique set of characteristics to enhance the substrate and ensure that it is suitable for its application. For example, a coating can protect the substrate against extreme temperatures, scratches, or infrared radiation. A coating can also be transparent or change the conductivity of the substrate. 

Various methods exist to apply thin films to substrates, and the suitable method depends on the source material, substrate, and application. This guide looks at electron beam evaporation applications, one of the most effective forms of physical vapour deposition, and what this thin-film deposition method entails. 

To learn more about the equipment necessary for e-beam evaporation, sputtering, and thermal evaporation, read more about the HEX Series from Korvus Technology. 

Physical Vapor Deposition: What Is E-Beam Evaporation?

Various industries use high-vacuum chamber systems for the thin-film deposition of materials, such as insulators or metals, to substrates. The processes for producing these films include physical vapour deposition (PVD) and chemical vapour deposition (CVD). Physical vapour deposition processes are ideal for creating a rigid thin film resistant to extreme temperatures and corrosion.

The three primary physical vapour deposition (PVD) methods for thin films include:

• Sputtering
• Thermal evaporation
• Electron-beam evaporation (e-beam evaporation)

Sputtering involves plasma generation under high voltage between the source material and the substrate. These methods include ion beam-assisted deposition, reactive sputtering, and magnetron sputtering. 

Electron-beam and thermal evaporation use an evaporation coating process. An electric current heats the target material during the thermal evaporation process, melting it and evaporating it to a gaseous phase. The vapour cloud travels upwards in the deposition chamber and precipitates against the substrate that requires the coating, forming a thin film.

The e-beam evaporation process is similar to thermal evaporation in that it uses evaporation deposition. However, an e-beam evaporation system doesn’t heat the evaporation material using electric resistance. Instead, a charged tungsten filament aims a beam of high-energy electrons at the source material or a crucible containing the target material.

The high kinetic energy of the focused electron beam transfers to the target material, which evaporates and deposits onto the substrate. The e-beam has a high electricity density, allowing for the efficient evaporation of high-melting-point materials that don’t sublimate during thermal evaporation. These materials include deposit metals and materials that transition to a vapour phase at high temperatures, including gold, platinum, and silicon dioxide.

Electron-Beam Deposition: An Overview of the Thin-Film Deposition Process

An electron beam system has two components – the electron gun, containing a filament, and the crucibles, containing the evaporation materials for coating the substrate. The substrate is above the crucible in the vacuum chamber.

Heating the tungsten filament [1] is necessary to generate the electron beam. Sending a current of up to 10 kV through the electron gun heats the filament and generates an electron beam via thermionic emission. E-beam generation can also occur via the field-electron emission or anodic-arc method.

Depending on the electron-beam configuration, a set of magnets direct the electron beam towards the evaporation materials in the crucibles. When the electron beam hits this source material, the high energy of the electrons converts into heat, evaporating the material. 

The evaporated material is a vapour stream that traverses the vacuum environment without colliding or reacting with other atoms. When the vapour hits the substrate, it clings to the surface as a thin film. 

Electron-Beam Evaporation Configurations

Three electron-beam evaporation configurations exist:

• Electromagnetic focusing

• Electromagnetic alignment

• Pendant drop configuration

E-beam evaporation systems with electromagnetic focusing and alignment configurations bend and guide electron beams towards the source material using a magnetic field. With magnetic field e-beam guidance, direct heat transfer occurs instead of indirect heating via the container. [2]

In e-beam evaporation systems with a pendant drop configuration, the evaporation material is in the form of a wire or a rod in the centre of a cathode loop. As the rod’s tip melts, the material evaporates to coat the substrate.

Reactive Evaporation vs Co-Evaporation

A reactive gas, such as oxygen or acetylene, reacts with the target material vapours near the substrate to form the thin film during reactive electron-beam evaporation. The co-evaporation process involves simultaneously heating a metal and carbon ingot to form a metal carbide film on the substrate. 

Electron Beam Evaporation Applications in Modern Times

The Advantages of E-Beam Evaporation

Electron-beam evaporation is a thin-film deposition method with a wide application range. The direct heat transfer between the e-beam and the target material is the most significant advantage of e-beam evaporation over thermal evaporation. Electron-beam evaporation allows for very high deposition rates and high melting temperatures, including:

• Refractory metals, such as tantalum, tungsten, and graphite

• Metals with high melting temperatures, such as silicon dioxide and gold

With a deposition rate ranging from 0.1 to 100 nanometers (nm) per minute at low substrate temperatures, e-beam evaporation is ideal for achieving a high-density thin film and optimal substrate adhesion. The ability to control the coatings’ reflection of specific wavelength bands is valuable in producing laser optics and architectural glass products.

The crucible holding the target material typically has a copper or tungsten construction. [3] Crucibles holding high-temperature materials can also be ceramic. The focused electron beam only heats a small area of the target material, which means there is enough room for multiple crucibles in the high-vacuum chamber.

An e-beam evaporation configuration with a four-pocket hearth can contain up to four source materials. This configuration allows for the sequential deposition of four material layers without needing to break the vacuum.

During some e-beam evaporation techniques, water cooling the crucible prevents it from heating through thermal energy. Directly heating the source materials also eliminates the risk of heat damage to the substrate.

The electron beam only heats the target materials and not the crucible. Keeping the crucible cool throughout e-beam evaporation prevents target material contamination and maximizes material use efficiency, reducing costs.

In others, the crucible is the part targeted by the electrons and so is the part of the source being heated, this is turn, indirectly heats and vaporises the material within the crucible.

Electron-Beam Evaporation Applications

The automotive and aerospace industries typically use e-beam evaporation when constructing components that should have high wear resistance. This process creates rigid chemical barriers resistant to extreme temperatures and corrosive environments, making it ideal for manufacturing cutting tools, machinery components, and marine fittings.

Optical Thin Films

Multi-layer electron-beam evaporation allows for the production of optical films with unique reflective and transmissive properties. It is possible to achieve specific film properties by layering multiple optical coatings—for example, cold filters that block infrared radiation on a glass substrate.

Optical and oxide thin films have multiple uses. Applications requiring optical coatings include the production of architectural glass, laser optics, solar panels, semiconductors, and eyeglasses.

Metallic Films

With the e-beam evaporation of low-resistance metals, manufacturers can produce various metallic films, including wiring films, decorative films, electromagnetic shielding films, and reflective films.

The products requiring metallic film e-beam evaporation during production include:

• Power packs

• Organic and inorganic electroluminescent (EL) diode displays

• Surface acoustic wave (SAW) filters

Some components of watches and lithium-ion batteries also have metallic films.

Electron-Beam Evaporation Limitations

Like thermal evaporation, e-beam evaporation is a line-of-sight deposition method and is unsuitable for coating the inner surfaces of complex geometries. Secondary electron emission and X-ray production can cause incident electron energy loss. During e-beam evaporation, filament degradation can also cause an inconsistent evaporation rate by the e-beam. 

E-Beam Evaporation System: How Does It Work?

 

Electron beam evaporation involves the acceleration of electrons as a targeted beam to a source material within a crucible. Quartz crystal monitors [4] regulate the thickness of the developing film during deposition.

The HEX Series by Korvus Technology includes compact thin-film deposition systems. These high-end systems are suitable for a wide range of research and development applications with sufficient energy for several deposition methods, including:

• Sputtering

• Thermal evaporation
• Electron-beam evaporation

• Organic physical vapour deposition (PVD)

• Pulsed laser

The Korvus’ thin film deposition systems feature a modular design with a six-sided vacuum chamber that is lightweight but rigid. The systems offer six modular panels that include:

• A blank panel

• A viewport panel

• A deposition source panel

• A QCM panel for evaporation speed monitoring

• A pulsed laser deposition (PLD) instrument panel for controlling mass flow and film thickness

The HEX deposition systems are highly versatile with standard fittings, including Hamlet gas and water connections. The base HEX system features a multi-sample hearth and supports electron microscopy (EM) sample preparation, new film research, magnetron sputtering deposition optimization, and other methodologies. 

Final Words

E-beam evaporation is among the most effective methods for the deposition of dielectrics and metals with high melting points. Generally speaking, this process offers a higher deposition rate than resistive thermal evaporation or sputtering. Electron beam evaporation also offers exceptional directionality, allowing multiple crucibles and optimal target material heating. 

The high uniformity and purity levels translate to a high material use efficiency and low costs. These systems are also compatible with ion-assist sources. To learn more about the benefits of other deposition methods, read these articles on thermal evaporation, sputtering, and PVD coating. 

References

[1] Bishop, Charles. (2007) “Electron Beam (E-Beam) Evaporation,” Chapter 15 in Vacuum Deposition onto Webs, Films, and Foils, 239-250. Elsevier Press. DOI:10.1016/B978-081551535-7.50013-6

[2] Wang, Zhongping, and Zengming Zhang. (2016) “Electron Beam Evaporation Deposition.” In Advanced Nano Deposition Methods, 33–58. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. http://dx.doi.org/10.1002/9783527696406.ch2.

[3] Madou, M. J., Fundamentals of Microfabrication: The Science of Miniaturization, 2nd Edition. CRC Press (2002), 135–136.

[4] Varineau, Pierre T., and Buttry, Daniel. (1987) “Applications of the Quartz Crystal Microbalance to Electrochemistry.” J. Phys. Chem. 1987, 91, 6, 1292–1295. https://doi.org/10.1021/j100290a003