What is Thermal Evaporation?

A Complete Guide to Resistive Boat Evaporation for Thin Film Deposition

Thermal evaporation, sometimes called resistive or boat evaporation, is one of the simplest and most established physical vapour deposition (PVD) techniques. It is widely used in research and teaching labs for depositing thin metal films, thanks to its low cost, simplicity and reliability.

How Does Thermal Evaporation Work?

In thermal evaporation, the source material is placed in a container, such as a filament, boat or crucible, made from a refractory metal like tungsten, tantalum or molybdenum. Inside a vacuum chamber, a high electrical current is passed through this container, causing it to heat up resistively. As the temperature rises, the source material melts and evaporates (or sublimes), and the resulting vapour travels in straight lines – a line-of-sight process – until it reaches and condenses on the substrate, forming a thin film.

Types of Thermal Evaporation Sources

Source Design

Characteristics & Target Materials

Filaments

Simple wire or foil configurations, ideally used for vaporizing small quantities of material such as wire-fed metals.

Boats

Dimple or basket-shaped containers that securely hold granules, pellets, or wire pieces, offering an optimal balance of charge capacity and ease of use.

Crucibles (with resistive elements)

Utilized for advanced materials that must be strictly contained, protecting against larger volume charges or target materials prone to spitting.

Advantages & Limitations of Thermal Evaporation

Advantages

  • Simple, robust and cost-effective compared with other PVD techniques.
  • Fast deposition rates for many common metals, such as gold, silver, aluminium and copper.
  • Lower equipment complexity and capital cost than electron beam evaporation.
  • Well suited to routine, repeatable processes and academic teaching environments.

Limitations

  • Not suitable for high melting point or refractory materials, which cannot be reached by resistive heating alone.
  • Risk of material contamination from the boat or crucible structure itself at elevated processing temperatures.
  • Less precise deposition rate control compared to electron beam evaporation systems.
  • Features a narrower compatible material range overall when contrasted with sputtering or e-beam evaporation.

Common Applications

  • Metal contact pads and electrodes for micro-device fabrication.
  • High-reflection mirror and industrial optical reflective coatings.
  • Standard lift-off metallisation processes.
  • Academic training environments due to its safe operation, low running costs, and underlying simplicity.

For sensitive organic materials or low-melting-point metals such as lithium, a dedicated low-temperature evaporation source such as ORCA is often a better fit, as it allows precise control between 50 and 600°C. (Internal Links: /organic-thermal-evaporation/)

Thermal Evaporation vs Sputtering vs E-Beam Evaporation

Process Feature

Thermal Evaporation

E-Beam Evaporation

Magnetron Sputtering

Cost & Complexity

Lowest entry cost; highly simple setup and operation.

Higher cost and mechanical profile; precise automated controls.

Moderate-to-high system complexity depending on scale.

Material Capacity

Routine metal deposition (gold, silver, copper, aluminum).

Extends temperature reach to refractory metals & dielectrics.

Broadest library; exceptional for alloys, compounds, oxides & nitrides.

Film Quality

High purity but lower density; directional line-of-sight.

Ultra-high purity with sub-monolayer depth control; line-of-sight.

Superior step coverage and film adhesion; high-density packing.

Many labs choose a system that offers more than one of these sources, so the right technique can be selected for each material and application.

Thermal Evaporation Sources from Korvus Technology

The TES thermal boat evaporation source integrates a range of thermal boats for depositing standard metals. It offers an extremely cost-effective, robust and reliable evaporation option for the HEX Series, ideal for labs that want straightforward, repeatable thermal evaporation alongside other deposition techniques. See TES – Thermal Boat Evaporation.

For low temperature evaporation requirements, Korvus offer the ORCA – Low temperature evaporator.

Frequently Asked Questions

Thermal evaporation works well for metals with relatively low to moderate melting points, such as gold, silver, aluminium, chromium and copper. Materials with very high melting points, such as tungsten or tantalum, are better suited to electron beam evaporation.

Read more about thin film deposition

Thermal evaporation is one specific technique within the broader family of physical vapour deposition (PVD) processes, which also includes sputtering and electron beam evaporation.

Thermal evaporation is simpler and less expensive, and can offer very high deposition rates and purity for suitable metals. Sputtering is generally preferred when better adhesion, denser films, or deposition of alloys and compounds is required.