The Difference Between Systems for Thermal Evaporation and Sputtering

Ever wondered how manufacturers put such thin metal coatings on things like solar cells, and OLED lights? The answer is physical vapour deposition.

Physical vapour deposition (PVD) is a method by which a source material (metals like aluminum, silver, nickel, and chrome) is turned into a vapour and deposited onto another surface (known as the substrate), where it turns forms a thin coating.

Over the years, companies have developed many different techniques for PVD, including thermal evaporation (or resistive evaporation) and sputtering. There are pros and cons of both techniques, depending on your application.

What is Thermal Evaporation?

Thermal evaporation is a simple PVD technique manufacturers use to deposit a metallic contact layer on thin film devices like OLEDs, solar cells, and thin-film transistors. Systems for thermal evaporation create a metal coating in three steps:

  1. The system uses electrical energy to heat the source material to its evaporation pointmagnetron sputtering
  2. Vaporized molecules travel from the source to the substrate
  3. The source molecules nucleate together on the substrate surface, creating a thin-film coating

Importance of High Pressure in Thermal Evaporation

One of the important distinctions about thermal evaporation systems is that they employ a high-vacuum environment and low gas pressure (below 10-5 Torr). This is important for two reasons.

First, thermal evaporation is used when you don’t want the source molecules to collide with gas molecules and change direction. Using a high-pressure environment means the molecules can travel from the source to the substrate without colliding with gas molecules.

Second, it ensures the film coating is pure by preventing gas molecules from becoming incorporated into the deposition.

What is Sputtering?

Like thermal evaporation, sputtering is a PVD technique used to create a metal coating on an object. However, whereas systems for thermal evaporation are designed to prevent source molecules and gas molecules from colliding, sputtering encourages this behaviour.

Sputtering techniques, like Angstrom’s sputtering system, use a strong magnetic field to pull source molecules to a designated area close to the source target. There, the molecules will collide with neutral gas molecules and create more source ions that collide with the target and eject material. This results in a denser rate of deposition.